Pulsars, Magnetars, Black Holes (Oh My!): The Wickedly Cool Stellar Undead

this video was produced by good evening welcome to her last public science talk of the year my writing the director of the donkey weld planetarium shoe box Easter here and a faculty I'm the department physics and astronomy I want to thank the Department of physics and astronomy supporting for supporting our public signs talking the second year running though we've done it and without their help we could not have made this happen so I'm really grateful for that and then I have of course the distinct honor and privilege of introducing our speaker tonight dr. Scott ransom he's one of the world's foremost authorities on neutron stars see the fantastic Department technical talk earlier this afternoon and he talked about how using these neutron stars which we'll talk about more generally tonight how they're doing some fantastic basic physics with it was just incredible so they are background on Scott he's a tenured astronomer with the National Radio Astronomy Observatory in Charlottesville he's the faculty member of the Department of astronomy at the University of Virginia worked a lot of graduates doing his main focus is on searching for exotic pulsar system so these are stellar end points such as millisecond pulsars and baris once these pulsars are identified he uses them as tools to probe a variety of basic physics including sets of general relativity and the emission of gravitational waves and the physics of matters supranuclear densities much of his time is spent working on the state-of-the-art signal signal processing information and high-performance computing software required to analyze the data he's getting my cabbages from the Green Bank telescope which well we'll talk about a little brief leak which just over the mountain Wesley here Scott I ran into him when he was a graduate student at Harvard he was yeah just finished being the lead Teaching Fellow for epochal astronomy class and there are 12 students that had to work as tf's teaching fellows and he had already developed almost a sophisticated computer code for all the TAS real leather they're great overwhelmed about one and horses continued since then let me give you a brief CV it was awarded at Hertz Foundation fellowship for a PhD Lions last year as a cadet at West Point he completed a master's degree in astronomy at Harvard and then an entered active duty in the US Army as a field artillery officer after almost six years of service he returned to Harvard to fit his PhD thesis on the new search techniques for binary pulsars in 2001 after he graduated he went to McGill University in Montreal as a Thomasson postdoctoral fellow and then in 2004 he's moved ten reo that's a radio genre where he's been ever since in 2006 he won the barkbox prize which is awarded for a distinguished research by a Harvard astronomy PhD recipient under the age of 35 and just four years ago he was awarded the American Astronomical Society held in the mortar prize for significant contribution to observation observational or theoretical astronomy through the last five years of the award he has authored co-authored over 150 publications including 15 in Nature signs are most virginities prestigious science magazine for basic research so it's my honor to welcome Scott round center stage well thanks now that now that I I know I'm bored from that introduction so you guys must be so hopefully we'll talk about something that's a lot cooler which is the the cool stuff that stars turn into after they die and that's mostly what my talk is going to be about is what do stars do when they die there's a lot that people talk about about the births of stars but stars are kind of the engines of our universe and they're certainly what we see when we go outside and look up in the sky but a lot of people don't know what happens to them after you know long amounts of time millions or billions or even trillions of years so that's most mostly what my talk is going to be about and one of the reasons what I'm going to talk about that is because the thing that I study most is is neutron stars but particularly in the form of pulsars which are one of in my opinion at least the most interesting things that stars become when they die so let's start off with with a picture of this this is our home this is the Milky Way galaxy this is an actual picture of it because it's taken from here on earth of the plane of the Milky Way we live embedded in it it's the it's a galaxy that's that's a disk it has spiral arms and stuff we think we've never actually seen that because we can't go outside of the galaxy to look down in but what we can see are stars and obviously our eyes are well adapted to see starlight evolution made them that way so that we can see the yellow light from our Sun because that's where stars emit most of their energy so everything you see here all of the light at least is is stars and there are hundreds of billions of stars in our galaxy most of them are our puny little things that we can't even see in this in this in this picture right here and most of the stars that we can see are actually quite special and I'll show you this during the talk these are the stars that are the most luminous the biggest the most massive or there at a certain stage of their lifetime that they become big and bloated and therefore we can see them but most of the stars in our galaxy we can't even see and the other thing that you'll notice is that there's all these dark patches through here that's dust and the dust is what gives us the it's actually gives us a problem to look at stars in our galaxy because the dust blocks the light of the optical light so we can't see through our galaxy and a lot of the work I'm gonna be talking about today is done in the radio waves because radio waves can penetrate that dust and the dust is basically transparent to the radio waves and so we're able to see stars these dead stars the stellar Undead that are buried deep in the in the plane of the Milky Way galaxy so let's actually look at a little at a zoo min a bit and look at a star field and what I want to point out about a field like this if you look towards the plane of our galaxy fields of stars like this are very very common because there's hundreds of billions of stars in our galaxy but one thing you'll notice even by looking at a picture like this is that there are differences even though we see stars as points of light there are differences that you can even pick out just just you know from your seats right there and one of the biggest differences obviously are the brightness of stars some stars are brighter than others and you can see that when you go outside even if you're in a city where there's a lot of light pollution the brightest stars are still visible to your eyes but beyond that there's a more subtle difference and that is the color of stars and the color of stars plays a really important role in astronomy and it's taught astronomers a lot about the way stars work and you can see these two bright stars right here this is obviously much bluer than that star there which is much redder and the color of stars basically tells us it's temperature and that temperature can give us a lot more information about what that star is going to do how it's going to live its life let's zoom in a little bit more and look at C you can see how there's these bunches of stars stars often especially the most massive stars which I'm going to focus on they the most massive stars tend to form in clusters like this like I'm showing you here on the screen and these clusters of brilliant jewel like stars they're blue white in color these are massive stars much more massive than our Sun they burn very very hot that's why they're blue white in color and it's these stars that are gonna turn into a lot of these weird stellar undead thing that I'm gonna focus on on today but this variety of stars that especially that the fact that they're differences in in brightness their luminosity and their differences in color there should be some way that we can we can you know kind of systematize that well you know we can figure something out make a plot you know make a diagram that may well maybe tell us something about the stars and one of the most famous diagrams and all of astronomy is called the hertzsprung-russell diagram and this is it right here this diagram basically tells you an incredible amount of in my opinion really fascinating information about stars these these balls of gas that are out there in our galaxy and what this diagram shows you it's basically temperature on this axis and it's a little bit strange this is this weird historical convention that astronomers have hot are over here normally you think of diagrams like this starting low and going high but it's exactly the opposite here and that hot stars are over here and cool stars are over here and by cool stars I'm not talking you know like room temperature I'm talking still 3,000 degrees but that's still about half the temperature that our Sun is but then this axis this is a special kind of axis this is a logarithmic axis and a lot of astronomy whenever you show any kind of diagrams you'll see logarithmic plots and it's an important concept it's it allows you to show ranges of values they it's tough for your mind otherwise to comprehend so every time you go between two different marks in this plot right here the brightness in this case in terms of Suns if we talk about this you know you talk about a ball a light bulb as being like a hundred watt bulb how many hundred watt bulbs or how many candles does this represent here we're talking about how many Suns does the brightness represent if you go between two marks the brightness increases by a factor of 10 so a star that's at this level is 10 times fainter than one at this level and notice that there's stars on this diagram over 1 2 3 4 5 6 7 8 9 10 11 what we call orders of magnitude that means 10 to the 11 power or a hundred billion times is the difference in brightness from the most massive I'm sorry from the most bright to the least bright stars so stars can vary a huge amount in how bright they are and some of the biggest things that affect that brightness there's three big things the mass the temperature and the size and what you can see is that stars that are living their normal lives are along this band and this is called the main-sequence our Sun sits right here in the very center of this band it's a yellow star temperature of about 5000 Kelvin there's a bunch of stars matter of fact most of the stars in our galaxy down here the puny stars they're much cooler the stars that are more massive live up here and they're thousands or even tens or hundreds of thousands of times brighter than our Sun we tend to think of our Sun as being incredibly bright but it's not it's a pretty much garden-variety normal star out in the middle of our galaxy so this is where the main healthy normal stars live but at the beginning and ends of their life stars are not on this main sequence they're basically off of the main sequence and so most of my talk today is gonna be spent about what happens when the stars leave this and when they leave it at first they go up with what's called a giant branch here and then they'll turn and deduce and do other other things so stars will actually move on this diagram as they live their lives so to speak the other stars I'm going to point out are these guys up here on the top these are the super Giants these are the brightest stars in our galaxy the ones that we can see basically throughout the whole galaxy if we're on one side we can see as we can see a supergiant star even on the other side of our galaxy there are very very bright objects and they're very bright because they're incredibly massive and they do some pretty spectacular things at the end of their lifetime so another thing so besides the fact that color corresponds to temperature which is a really important thing so the blue-white stars are over here and the red stars are over here and by the way that that color is exactly the same thing is if you turn on an electric burner on your stove and how the stove gets gets a orange red hot that's that's the same type of radiation that the stars give off if you were to make that burner get hotter and hotter it would turn yellow and then it would turn a yellow white and then finally a blue white in color it's the same exact temperature scale that the stars are so it really does correspond to heat the other thing that's important about these stars is their size and these stars you can see these letters here this is a famous nomenclature that astronomers have used to describe the basically the masses of the stars where you go from the lowest mass stars down here the M stars up to the Giants these huge saw stars here called the O stars and there's a very famous mnemonic that many of you might have heard of that starts on this to this side who here knows what I'm going to say here what's the what's the onic does anyone know how do you remember these letters Oba does anyone know okay so that it's not really politically correct anymore but I'm gonna say it anyway and it's Oh be a fine girl kiss me is the way you can remember these stars and that goes from the most massive stars down to the least massive stars and actually astronomers in the last ten years have found more stars that actually go on the lower end but the important thing that I'm going to show here is that the colors are very different from red to blue the sizes are very different and that also corresponds to mass because these stars are all giant balls of hydrogen gas and if you put a whole bunch of gas together that's this size compared to that size this thing has got to be a lot more massive the other thing is is the numbers of the stars and most of the stars in our galaxy are those little puny M stars here's our Sun and only a handful of stars a very small percentage are these really big guys but they all live their lives by doing the same thing they all convert hydrogen into heavier elements by the process of fusion in order to make energy and that energy comes off as star light okay now our Sun is evolving and is in it's burning hydrogen into helium and making its fusion and it has a life cycle this our Sun is about five billion years old had it went through a birth and a some kind of stellar nursery a big molecular clouds gas clouds and then it joined the main sequence of stars and it's been burning hydrogen gently quietly in its core for the last four and a half billion years okay so this is where we are right now but the Sun is evolving its burning fuel in it and like any any type of machine that burns fuel the fuel gets used up and the Machine changes and ages and the Sun does the same thing so gradually over the next few billion years so don't worry this isn't happening today on any kind of basis that we can see this is not what's causing global warming this is a whole different thing this is Billy of years we're talking about here the Sun will gradually get slightly bigger gradually increase the rate at which it's burning fuel in its center and then at about five billion years from now it goes through a pretty nasty stage called the red giant stage where it gets dramatically bigger matter of fact that will get so big that it will probably we don't know for sure but probably engulf the earth the outer parts of the Sun will certainly engulf Mercury will definitely engulf Venus and might come out and actually engulf the earth as well this will not be a good time to live on earth but luckily we have five billion years to figure out a way to get off this planet what happens after that though is where things get interesting and this is where the stellar and dead undead come into it because at the end of its life we go through the stage from a red giant the outer parts of the star get ejected and what's left over is a thing called a white dwarf and that's the core of the star the core of our Sun after you get rid of all the other hydrogen is this highly compressed core of core of the star that weighs a lot probably about four tenths of the mass of the Sun so a lot of the mass of the Sun has been burned down into that core but when you eject off everything else out what you're left over with is something that's about the same size as the earth and given that the earth is hundreds many many hundreds of times smaller than the Sun this is a tiny tiny fraction of the size of the Sun but yet it has a huge amount of the mass that means that this is has a huge amount of gravity and it's a very dense interesting object matter of fact quantum mechanics helps to rule helps to hold up this star there's no more fusion going on there what's holding it up is quantum mechanics in a very special way so this is a very interesting weird process but this is what's going to happen to almost every single star in the galaxy the thing is that the stars burn their fuel at very very different rates and you there's a famous saying you know a candle that burns twice as bright burns half as long well the stars in our galaxy the bigger the star the brighter they burn they get that they can burn thousands of times brighter than the Sun they will live thousands of times shorter than our Sun so instead of living 10 billion years the more massive stars might only live millions of years and even though there's only a one letter difference between those two words that's a factor of thousands so millions to billions is a very very big difference in time on the other side the really really puny stars the stars that are less massive than our Sun say 1/2 of the mass of our Sun they will live trillions of years once again we'll only a one or two-letter difference but that's a thousand times longer than what our Sun will live but eventually all of those stars are going to go through this stage and turn into a white dwarf and as I said unfortunately during this stage the Earth's going to kind of get in the way for when this happens we want to make sure that we're not around it will be beautiful though as can be shown by these objects right here these are the so-called planetary nebulae these are stars that are in the process of throwing out those outer parts of their stars as they're dying and in the Centers you can see these very bright glowing things those are the white dwarfs in the very very center so those are the hot cores of the stars that remain and meanwhile the gas that is ejected and gradually floats away and it spreads elements like carbon and oxygen and other dust throughout our galaxy those are the elements that then help make new stars and new planets and new life we're made of a stuff that's ejected from stars just like this so this is where this is what what's gonna happen to our star our Sun in about five billion years so that's pretty cool but what I want to show you now is what happens to the bigger stars because the bigger stars at the end of their lives they get even that they do a lot more interesting things so what happens inside a very massive star and by very massive here I'm talking a star that's maybe 20 30 40 times the mass of our Sun so you take a 20 or 30 or 40 times the amount of hydrogen put it all into the same volume and compress it to get gravity going gravity pulls it in gravity has this big balance in terms the gravity's pushing inward and fusion is converting high helium etc making pressure outwards so the fusion balances gravity and every time you start converting more and more hydrogen into helium for instance the star gets a little bit hotter and eventually you get enough heat that you can start converting helium into carbon and eventually it compresses and gets even hotter you can convert carbon into oxygen gets compresses and gets a little bit hotter and this happens all over the space of only a few million years you you it voraciously burns all of its fuel in the center of the star until finally you make more than a solar mass more than the total mass of our Sun of iron in the center of these stars and what happens when you get iron the problem with fusion with nuclear fusion is that you can't extract any extra energy out of nuclei when you fuse beyond iron so if you if you turn hydrogen into helium you get tons of energy and that's why fusion is one of the big goals of scientists of energy scientists here on earth because it would be basically an inexhaustible energy supply for us but once you get to to iron you can't get energy you have to give energy and so there's no way to get that pressure then and so gravity is relentless gravity continues to pull very very strongly on the center of this star but once there's iron there's nothing holding it up and so what happens is that core collapses after a few million years and when that star collapses because the fuel supply doesn't exist anymore the most massive stars turn into black holes that Center iron core gets so massive that nothing that there's not enough pressure that those nuclei can hold themselves apart and Italy falls inward nothing can stop it it's there's too much mass that quantum mechanics even can't hold it up like it will a white dwarf and the this object then it falls completely through and at the center of the star turns into a black hole we're not exactly sure what the outer what the outer star does but part of it is going to go into the black hole part of the rest of it is gone almost certainly from some kind of shockwave going to get it going to get ejected we may have seen this happen in our universe but we're not exactly sure because black holes it's kind of hidden on the inside and we don't think that there's a super huge explosion when this happens but we do know that it happens because we do see black holes and just a couple words on black holes so this is how they get formed the small ones at least these are called stellar-mass black holes and really they are black their light cannot escape their gravitational pull but you can look at them they don't suck you in there not cosmic vacuum cleaners they're not gonna come hunt you down and eat you if our Sun today turned into a black hole we would not even know until the light went out eight minutes from now because that's how long it takes light to travel from the Sun to us and then the earth would still be going around the Sun and we gradually freeze to death but we would not be sucked into the black hole it's still not a very pleasant way to die but at least we wouldn't be sucked into the black hole and here all you're seeing is the bending of light because of Einstein's relativity of the Stars behind because the the gravitation is so strong it bends light so these really are truly exotic objects Einstein's relativity discusses them in great detail and we don't know what's going on inside of this black region it's it's completely unknown and it's beyond our current physics so these also are a very interesting end state of massive stars what we do know about these and we see them in our galaxy we can't see them by themselves like this and we and there certainly are black holes that are zipping through our galaxy all by themselves but we can't see them the ones we do see have a companion star like this if there's a big giant star companion that's near another star that already collapsed and turned itself into a black hole that star Wilkin that some of its material go into a disk around that star and that makes a very very energetic system called an x-ray binary and tons of x-rays including some jets and all sorts of light and energy can come out of these systems and we see these systems in our galaxy matter of fact this one is an artist impression of one a very famous one called Cygnus x1 which some of you may have heard of for the rush aficionados in the audience like myself there was a song from the early 70s written about this object by Rush and it's it is the first what most people thought was the first black hole that was conclusively identified in our galaxy so it's a pretty historic object but we see tons of x-rays that's what the X stands for they're coming off these objects so these do exist we see them in our galaxy and they're very interesting objects for people to study these so-called x-ray binaries now that's the most massive stars what I'm going to now do is go a little bit a little bit less massive to the stars that are maybe eight or ten or twelve times the mass of our Sun so not as massive as the ones that made a black hole these are ones that still do this same burning of hydrogen into helium helium to carbon up to iron but they don't have enough to burn as much and make as much iron in the core so if there's not quite as much iron when finally the pressure when gravitation overcomes the pressure it collapses but there's not too much iron that it goes directly to a black hole quantum mechanics saves the day yet again and creates what's called a neutron star and these are the things that I study and when this happens we know and we've seen these objects because when when you create a neutron star that actually has a surface unlike a black hole so when the core of the star collapses it instantly makes a neutron star the rest of the star bounces off of that creates a massive shockwave which rips apart at the top of the star and that's a supernova we see supernovae all throughout the universe we've seen thousands and thousands of them now they're some of the most bright up objects in the universe they last for days well the initial collapse to a neutron star only lasts a second or two but we see the fireball explosion lasting for days and there's all sorts of great articles and and images and movies and stuff on how supernovae work that you can view on the web but the important thing for me in my research is how the supernova produces yet another stellar undead and that is the Pulsar that's the magnetar these are the neutron stars that result from these stars okay and these objects can be quite interesting here's just a picture of what a supernova looks like here's a beautiful galaxy this is a relatively nearby galaxy and a supernova went off in the edges of it one of these stars blew up and the total amount of light coming from this one star exploding is more than the total amount of light integrated up if you if you add up all this light there's more light there than there is from the whole galaxy yet there's hundreds of billions of stars here that tells you how bright a supernova is these really are extraordinary events and what they show is that is the conversion of a live healthy star into the it's dead stellar remnant a neutron star so this is a pretty famous field of stars I haven't shown the whole thing but I bet some people in the audience can recognize there's a famous part of a constellation here does anyone know let's just yell it out Orion yeah so here's the belt of Orion one two three here's Orion's this is a sword this is the Ryan Nebula here's a big star here's a big star this is the other part of his shoulder there's some nebulosity and you can see all the stars in the background okay the reason I'm showing this is because one of these stars is going to go supernova quite soon and that's this star that's Betelgeuse so Betelgeuse is a red supergiant it's an extraordinarily massive star it's near the end of its lifetime the red supergiant phase we know that's near when when this thing is going to explode this is a gargantuan star if we put that in our solar system it would engulf beyond earth clear out past Mars I close to even to Jupiter I think it's a gargantuan huge star and someday soon probably not this week it's gonna go supernova now that could be a million years from now but astrophysically speaking a million years is like tomorrow right but it's going to go supernova quite soon but it actually it could be whatever we just don't know we could get the Galactic lottery and have it go off very soon astronomers would love that if it goes off its it's not too far away in our galaxy we would get a spectacular light show it would be visible during the daytime easily and the amount of scientific data on how supernovas work would be spectacular but that star will turn into a pulsar quite soon and I'd be very excited to see that we do have objects that did go supernova within the last thousand years that we can see in our galaxy we know that this happens okay here is a very famous object called the Crab Nebula this this object is one of the most studied objects in the sky there's perhaps more papers on this one object that have been written by astronomers than almost any other object because this was from a supernova that went off in 1054 ad so almost a thousand years ago and we know that date exactly we know the exact date that it went off because it was observed by Chinese astrologers and they and I noted I used the word astrologers not astronomers they were trying to tell the horoscope for the the Chinese emperors they were not doing astronomy but they were watching the heavens and they made some good astronomical measurements it was also observed by a lot of other cultures here's a famous painting by the Anasazi Indians a cave pictogram in New Mexico where you see there's a star a bright star that's the supernovae here's a crescent moon and that's that's exactly where we expected to see the supernovae with respect to the moon at the date that this went off and here is the artists signature right above it the handprint what is amazing is that this is this object we can still see this object expanding today when you wait when you wait over the course of like 10 years you can measure how this is still expanding from the star exploding this is the explosion is we can see it happening most of the time we're not used to seeing things change in the sky but this one is still changing and you can see it's glowing hugely in the center that's because it's being powered by an extremely energetic object still to this day in the center and that's that neutron star right in the center there is a glowing blue white star that's the core of that star that's the neutron star it's a pulsar this is from one of the discovery observations the which happened about almost 40 years ago over 40 years ago and what they found out astonishingly and I have to go over here to make this work was that this neutron star is rotating 30 times per second that's pretty astonishing and we can actually record the signals you see if I give this to work alright this should work so this is this is what 30 times a second sense is going to sound like if this is recorded signals with one of the biggest telescopes the Arecibo telescope on the crab pulsar [Music] all right so that's pretty annoying but it's also really cool because to me that blows my mind because this is something that weighs more than the Sun and all of the planets and the asteroids and the Comets and all the dust everything in our in our solar system it's been compressed down to the size of a city and it's rotating 30 times a second that's ridiculous but yet it's right there and we can see it we can measure it we can use x-ray telescopes and gamma-ray telescopes and radio telescopes and optical telescopes and yes if you have really sensitive eyes and use a big optical telescope and you look through an eyepiece your eye can actually see the flickering at 30 at 30 Hertz if you have really sensitive eyes so probably the kids and the audience can probably do it the grown-ups pride not so much but this is an astonishing object the whole nebula is being powered by this blue dot right here in the center and it's visible throughout the whole electromagnetic spectrum from the lowest frequency radio waves clear through the infrared to optical to x-rays and the most energetic gamma rays this object is giving those off and it's powering this whole nebula these pulsars are incredibly energetic objects there it is right there you can see the blue here is from x-rays there's all these rings and wisps and over a course of 10 years we can see these winds changing in this nebula because it's the energy being given off by the rotation the rotation from this neutron star there's no fusion no chemical reactions it's purely this energies coming from the rotation of a neutron star and the crab is not the only one we see this throughout the sky that we see these are beautiful x-ray images from the Chandra x-ray satellite of supernova remnants supernova remnants glow beautifully in x-rays so Chandra takes really nice pictures of them and at the Centers of every one there there and there those energetic young pulsars that are keeping these things alive and glowing so that they will keep these these supernova remnants glowing for tens of thousands of years powering them by their rotational energy so that's what's inside these pulsars but so where did these pulsars come from well there is a fascinating story and I can't I don't have time to go into it tonight but I highly encourage you if you're at all interested in in kind of the sociology of science especially to dig into the to Google on the internet and read about the discovery of pulsars because it's a fascinating story there was a professor Anthony Hewish at Cambridge University he had a graduate student named Jocelyn Bell they built her radio telescope it looks almost like a fence because it's almost what it was it's basically a fence post with a bunch of wires strung together and her PhD thesis was to build this telescope and make very very tiresome manual observations before computers of radio signals in the sky and she found this is the original trace where they found it she found this little blip blip blip blip blip everyone point some-odd seconds of an object that they had no clue what it was in the beginning they kept an incredibly secret over the course of the next two months they found two more they were blipping on it from different parts of the skies at slightly different rates and at first they thought that this was that these were extraterrestrial civilizations and the first object this object they called LGM zero zero one for little green men one and LGM 0 0 2 for the second one and then then finally after they found three of them from different parts they set out there's probably not three of them all trying to contact us at the same time and they realize there had to be something different but these observations they discovered the first time neutron stars and about a year later after they published this that's when they discovered you know once people realize that pulsars were there then people looked in the Crab Nebula and found that xxx that pulsar rotating 30 times a second in the Crab Nebula the amazing thing is that Jocelyn did almost all the work well a huge amount of the work I got to give Hewish some credit but Hewish won the Nobel Prize and Jocelyn Bell did not and this has been a big source of contention in the scientific community ever since and there was there's a little follow-up story that happened at pulsars ended up winning another Nobel Prize later on with a faculty member and a student and during that Nobel Prize the student and the faculty member both got the Nobel Prize so that's probably not gonna happen again but this was a kind of an amazing thing given that it was a woman graduate student who was kind of snubbed by the Nobel Committee and I should say she's still fantastic scientist she's won every other prize in the book in science since then and she's always been incredibly gracious about it whenever it's brought up but still I think a lot of other people think that she should have a Nobel Prize on her wall but a fascinating story so this is what our cartoon picture of a pulsar looks like we have a neutron star it's rotating about this red line right here and it has a strong magnetic field so as I mentioned this thing is a neutron star one to two solar masses of material all compressed down into something that's the size of a city these are incredibly exotic objects they're so hot the surfaces are about a million degrees so they give off copious x-rays okay their densities are several times what the nucleus of an atom is matter of fact these are our gigantic nuclei they're made almost exclusively of neutrons so they're gigantic city size nuclei they have their gravity because they're so dense and so compressed gravity is so strong it's a hundred billion times stronger than the surface of the earth if you were to come anywhere close to a neutron star the tidal force is alone and a tidal force by the way is just the fact that at the top of my head gravity is less than it is at my feet so if I were to come anywhere near a neutron star its gravity so strong it would rip apart my body by tidal forces and you know stretch me into spaghetti thin spaghetti thinness just because of its tidal forces ten billion times stronger than the Earth's gravity they can spin up to over 700 times per second I told you 30 times a second was a lot but the one that graduate student and I we found 10 years ago is the record holder seven and 16 times per second that's faster than a kitchen blender spins that's faster than a racecar engine rotates that's faster than a drill spins yet this is the size of a city and more massive than a star that's I studied this stuff every day and this blows my mind okay they have these magnetic fields don't worry about these weird units these units that astronomers use called Gauss but they have an extraordinarily strong magnetic fields and what I want you to know is just look at these numbers these tend to the large numbers you can get an idea of the size of a magnetic field you know if you hold a compass in your hand a compass can you can detect the Earth's magnetic field with a compass very easily you know a pocket compass the Earth's magnetic field is one Gauss those the weakest magnetic fields are a billion times the Earth's magnetic fields that's the weakest ones the magnet ours which I'll talk a little about later can be a hundred or can be a thousand trillion times the the magnetic field of the earth I mean truly exotic objects we don't understand exactly how the emission comes off it comes off of them but the emission the radio emission that we see and sometimes x-rays and gamma-rays comes off in these out of the magnetic poles and because there this thing is turning and the magnetic axis is not on the rotation axis as it rotates just like a lighthouse whenever my arm sweeps by you you see a pulsation that's why we call them pulsars they're not actually flashing they're just rotating like a lighthouse and so that beam causes something that looks like flashing light and this also blows my mind the most energetic ones like the crab pulsar itself there's so much energy coming off these that they can give off more than a 10,000 times the energy that our Sun gives off and it's only coming from rotation once again there's no fusion there's no chemical reactions this is purely rotation of the star being turned in to gamma rays and x-rays and radio waves and particles I mean that's extraordinary if you can't tell these are truly exotic objects okay really really amazing and one things that I do in my science I mean this stuff blows me away but one of the whole keys of my science is to forget about all that and and just think of them as perfect clocks because what happens if we have a lighthouse out spinning in the middle of space and it's giving off if it's rotating perfectly like a this is exactly like a perfect gyroscope or a perfect flywheel every time it passes we see a perfect flash of light it's like a tick of a clock and we can use those clock ticks to make really beautiful measurements of other other objects that are out there in space so this diagram I got explained a little bit this is the Pulsar person's version of the hertzsprung-russell diagram and number that's the star diagram that shows you how the lives of stars well the pulsars do the same thing we measure two things how fast the Pulsar spinning this is also logarithmic so this is a millisecond 10 milliseconds a tenth of a second one second 10 seconds and this is the spin down rate I said that it's turning rotation energy and giving off rotation energy so that has to be slowing down that shows you how fast the Pulsar slowing down so the ones up here at the top are are slowing down rapidly the ones at the bottom are slowing down they're staying almost the exact same rate okay they're barely slowing down at all and we can see most of the pulsars are here in this diagram and there's a few outliers and so I'm going to talk a little bit about each of these the neat thing is we can turn these two numbers how fast they're spinning and how fast that that spin rates changing into physical parameters we can use it to estimate the ages of the objects we can use it to estimate how strong the magnetic field is because by the way the stronger the magnetic field it's it's moving a magnetic field that causes particles to be given off so the stronger the magnetic field you give off more particles that means you slow it down faster so the faster it's slowing down the stronger the magnetic field is and B is what physicists call magnetic field so stars up here have really strong magnetic fields stars down here have really low magnetic fields stars over here are young pulsars down here are old and we can figure this out just by these two parameters and a few basic physics equations which I won't show you so young pulsars like the crab re showed you sits right there on this diagram and there's all those other ones that are in supernova remnants sit up here as they give off energy remember they're trading rotational energy they're giving it off that means they're slowing down with time that means they move this way on the diagram and their magnetic fields we don't think change so they move down this way and so sure enough we see the young pulsars here and eventually they end up with all their other companions out in the galaxy in this big blob so they move down and right just like on the hertzsprung-russell diagram how stars move up that red giant branch and then down to the white dwarfs well eventually they spin so slow so this is where they end up with normal pulsar is eventually they keep on moving and they Pat they end up passing this line where they're spinning too slow so that the Matt if you move a magnetic field you can't get enough electric field to accelerate particles and one there when they're rotating too slowly then that means they shut off as radio pulsars we call that going into the graveyard okay so now in our galaxy there are millions and millions of neutron stars that have gone this way and are piled up here that we can't even see because there's no way to see them they've cooled that they're too cool to see by their x-rays they're too far away to see by any kind of other light they're not giving off radio waves because the the emission mechanism has turned off and basically pulsars live between ten to a hundred million years and given that our galaxy is five billion years old this is short compared to the lifetime of our Sun or our galaxy so there's tons there's a whole ton of neutron stars that are here that week just it's impossible for us to see but not all supernovae make pulsars and here's a very famous supernova remnant this little rings here it's and it's in the nearest galaxies next to us it's a supernova that went off in 1987 we know that a neutron star was created because we can see these there was a burst of particles called neutrinos that are given off when every time you turn a proton into a neutron and to make a neutron star you have to turn a lot of protons in the neutrons there was a burst of these neutrinos that was measured when this thing exploded but people have searched and searched and searched with x-rays and gamma rays and radio waves including using the biggest telescopes in the world and the most sophisticated instruments in software and we have not found the pulsar that we think must be there so there are other neutron stars that don't turn into pulsars here's another beautiful example this beautiful supernova remnant that dominates the northern sky in almost every other wavelength except for optical light here's optical you need the Hubble Space Telescope to make this very dim picture but in radio and x-rays it's booming bright this is one of the brightest objects in the sky at both of those frequencies and it shows up incredibly well at the center of this beautifully spherical nebula you might see something there here's that here's a composite image of infrared x-rays and I think radio waves and right there in the center that is a neutron star we know that's a neutron star it has every property in the x-rays of being a young neutron star but there are no pulsations we've looked in gamma rays x-rays radio waves every way we've used the biggest and best telescopes in the world and we see quite a few of these objects we call them compact central objects it sounds really boring given that they're actually pretty interesting but we don't know why these things don't have pulsations is there something wrong with their magnetic fields don't they have big enough magnetic fields are they somehow spinning too slowly to cause any kind of pulsations is there something weird about their surface that doesn't let x-ray light out and the way that we expect it to what we really don't understand these are these are kind of enigmas and we see about a half a dozen of these in supernova remnants in our galaxy there's another object fascinating objects here's a supernova remnant a bright x-ray source in the very center this is a so-called magnetar these are objects that are very much related to pulsars they're neutron stars and they probably at least sometimes give off radio pulsations the thing is their magnetic fields are so strong they're about a thousand times stronger than a normal pulsars magnetic field that they spin down very rapidly so they don't live long they basically die very very quickly as radio pulsars but if you catch them early enough when you can still see their supernova you can you can often see some interesting things happening with them and this particular object here it's got an incredibly strong magnetic field as I said thousand times stronger their normal pulsar and when you put that much magnetic energy together you get a bunch of crazy things that happen when you pack that much magnetic energy together you can actually cause even that dense neutron star surface you can actually kind of rip it apart and cause it to to stress and flex because there's so much energy in the magnetic field to give you an idea how much energy if you took a cubic centimeter that's about the size of a sugar cube of the magnetic field if you're able to somehow cut out a cubic say sugar cubes worth of magnetic field in that cubic centimeter is more power than the human race has ever produced period out of all of our nuclear reactors all of our atomic bombs everything together and that's what's stored in the magnetic field that's not even talking about all the gravitational energy and everything else in these objects totally crazy so these things live way up here on that diagram and you can see there's a handful of them there's we know about 20 of these now and they're purely powered not by rotation like normal pulsars these have so much energy in their magnetic field that they're powered by the magnetic field so crazy magnetic objects and they can do crazy things with this object in 1998 this magnet are this it's called soft game or a repeater bla bla bla these give off gamma rays it's magnetic field kind of twists it a bit just like the Sun does it the sun's atmosphere the 99 fields twists and we get solar storms this thing you twist them at this magnetic field and it ripped like kind of it caused a crack in the neutron star's crust which sent a massive pulse of gamma rays through our galaxy this thing is thousands of light years away thousands of light years away yet this this is the ionosphere on earth this is the measure of how ionize the top of the Earth's atmosphere is and a gamma-ray pulse hit this is the gamma rays when the gamma rays hit the satellite that was measuring it the Earth's ionosphere became much more ionized it ionized a chunk of our atmosphere and then it took minutes for the ionosphere to recover because there's so many more gamma rays coming these are the pulsations of the neutron star as it slowly rained down this is only over a course of a couple minutes but these gamma-ray bursts if this thing were to happen very very close to us it would fry our atmosphere and do really be really bad for us the good thing is there are no magnet ours that live close to us we know that because they show up brightly in x-rays and we know that there are no magnet ours within a few hundred light years probably not even less than about a thousand light years from Earth and so even if another one of these goes off it'll fry our atmosphere a little bit but not enough to hurt us but still crazy but these things can do so the last things I want that I want objects these are the ones that are most dear to my heart are these guys which I didn't talk about I told you about how the young pulsars moved down here and then they died over here and making this big graveyard but how did these guys get down here okay these are the so-called millisecond pulsars these are the ones that we use for basic physics tests and they have almost no magnetic field magnetic fields they're still very strong for earth but compared to pulsars there's almost nothing so these were discovered by this guy one of my mentors Don Becker who unfortunately passed away a few years ago a fantastic discovery the first one pulsar the first millisecond pulsar spins at one point five five eight milliseconds that's 640 times per second it's 21 times faster than the crab pulsar spins and this for about almost 30 years 25 years was the record holder for the fastest spinning neutron star until the 716 Hertz one I mentioned a little bit ago was found this is no I'll play it for you but this it's spinning so fast it makes a tone it's not like hearing a machine gun but like the crab pulsar it's actually a tone he's even get this to work [Music] really annoying I use that as my alarm but that you know it's above concert a on the piano keyboard okay that's a star spinning that's not some that's a star spinning that's just ridiculous these things because they have the low magnetic fields even though they spin that fast they're still giving off tons of energy but they will spin that rapidly for a huge amount of time so how do we get these things well the millisecond pulsars are like this you the way you get them is by having a companion star so if you make a pulsar in a supernova and there's a sun-like star in orbit around it that's the key part you have to have a sun-like star that stays there eventually what happens is this pulsar just like all the other pulses I mentioned will give off energy and slow down and after 10 or 100 million years will die okay it just becomes a dead neutron star but a star I already told you those last billions of years so this pulsar is long and dead but say after one or two or five billion years this thing decides to do what the sun's gonna do and it turns into a red giant as it turns into a red giant it expands in its dumps material into a disk around the new dead neutron star that's in the center and we see this stage this is an x-ray binary just like Cygnus x1 we see these objects doing this we see them in the x-rays we see them dumping material this happens we know this happens we we observe it and all throughout the galaxy it's rare but we still see dozens of these systems eventually this evolution ends and the the outer parts get ejected this becomes a white dwarf just like our Sun is going to be and what you're left over with once this disk goes away you have a white dwarf and this thing turns on as a millisecond pulsar because when it dumped this material it just like a basketball player hitting a basketball making a spin faster this material falling onto the surface makes that neutron stars spin much much much faster it also buries a lot of that magnetic field that was there it buries it underneath the material and so this process that this other star revitalizes this pulsar okay we call it recycling it takes something from the graveyard and puts it back to life I mean this really is the stellar undead that's these are like stars a'm beats right they came back to life by the recycling process so the other star gave it new life and now that it's back to life it's gonna last for billions of years because these things are perfect clocks so how perfect clocks are they okay so at 7:30 oops I missed a buy half hour so a half hour ago today this particular pulsar which is very well studied spins exactly at this rate in milliseconds and like any good scientists we have to have an error bar on our measurements so there's the error bar in that last digit okay we know that number how fast it spins very very precisely but remember it's giving off energy as its rotation is is turned into the stuff that we can see so that means that it's slowing down well how fast is it slowing down well the last digit changes by about one every half hour so right now this would you know I since I'm wrong by half hour this would be 245 as opposed opposed to 244 but that means that this is kind of like a cosmic odometer on your car you can see this thing ticking out going slower and slower but if the last digits changed my once every hour that means that that digit changes only every 500 years that means the first six digits are the same for a thousand years that's how pure and beautiful of a tone these things are and because of that we can use these perfect celestial clocks as tools to do basic physics and we do it by this magical thing called pulsar timing which I'll only very briefly explain that the important thing is is we unambiguously count every single rotation of a pulsar over the timescale of years so without missing a cont and we do it like this time is going this direction and where we're rotating with the Pulsar so we're stacking pulses on top of one another when we do that that's an observation we make these measurements of when the pulses arrive we stack the pulses on top of each other we can then make a model and predict forward I can go back with my telescope again and I can predict where I'm going to see my pulsar and on my next observation if my models correct the pulses line exactly upward where my model is okay and then I can come back another another day or two later to my telescope make another model measurement and I find my little bit off then I have exaggerated in this case usually we don't make it we don't we don't make us over that far off but if we're a tiny tiny bit off then I tweak my model a little bit I make my model a little bit better that tells me a little bit more about the Pulsar where it is in space what it's binary orbital parameters are how its spinning down and we get a much better model for how the Pulsar behaves and we know exactly how many pulses are between these observations down to the exact number and when we do it correctly we get data that looks like this this is two years where we take the measurement minus the model all we're doing is taking what we measured minus our prediction and we're plotting how far off from zero we are and in this case you can see this is in microsecond so this is millionths of a second here's the day at the telescope there's a whole bunch of measurements they're all within a microsecond and over two years our measurements are perfect so that we can predict any individual pulse to 200 nanoseconds a nanosecond is a billionth of a second I can tell you where every individual pulse from that millisecond pulsar arrives and if you do this properly so you don't miss count you get unbelievably precise measurements here's an example of a paper that shows that what we call a timing solution for a millisecond pulsar here's that long number that I showed you that's that's the spin period of the Pulsar about I don't know eight or nine years ago here's the position on the sky this is like a micro arc second that's something like the width of your hair on the moon from here I mean it's some absurd precision is as the the angle here's the the parameters of the orbit - many many decimal points there's six or ten decimal points of precision and all these measurements of the orbit its position how fast it spins down we can use these things as truly precise measuring devices and here's a really nice party trick example millisecond pulsars are get created in circular orbits here's the eccentricity the eccentricity tells you how circular the orbit is if this eccentricity is zero it's perfectly circular but Kepler showed us that all things orbit with ellipses okay so nothing is a perfect circle in space it's always gonna have some eccentricity and this has got zero point zero zero zero zero one nine one eight six that's its eccentricity so it's really close to zero but it's not exactly zero but I can't really think in terms of eccentricity I don't know how circular that is right well the next line above it tells us how why how big the orbit is this is in terms of seconds it's how long light takes to travel it's called a light second so this orbit is three point three light seconds across well in terms of units that we can think better the Sun the sun's radius is about one one point four or four times the sun's radius is that is this same distance okay it's about 10 to the 11 centimeters okay so that's the size of the sort of the circle we're talking about it's about one and a half one point four times the radius of the Sun and it's got some eccentricity that's really close to zero well but if we know this is an ellipse I can say hmm ellipses have a short side and a long side right what's the difference in length between the long side and the short side that's something we can easily think about that's I can tell I can tell what that is so if I measure the difference between the long side and the short side of the ellipse it's eighteen point five nine plus or minus 0.01 centimeters it's that much yeah this is the size of the Sun and we can measure how perfectly that circuit circle is by timing a pulsar by measuring when pulses arrive this is how we do the really precise work measure masses and do general relativity tests using millisecond pulsars and two of the best telescopes in the world for this are owned by the US the National Science Foundation funds these the Arecibo telescope it's the biggest in the world in Puerto Rico 300 meters across it's astounding if you ever get to Puerto Rico I highly recommend you go visit it there's a beautiful visitor center there and then this in your own backyard the Green Bank telescope run by the National Radio Astronomy Observatory in Green Bank West Virginia a hundred meters in diameter these are basically the size of semi tractor-trailer trucks here this is this is huge okay that's really big and we need big because pulsars are faint objects okay the other thing I'll say about this is that these things are making spectacular measurements of pulsars but they're both in financial trouble the NSF wants to cut funding on both of these and it would be a total travesty not only just to my career but it's the the amount of excellent science of but especially pulsar science that comes from these telescopes is amazing and they only cost about five million between five and eight million dollars per year to run each of them I mean it's piddly anyways the u.s. it has really great stuff last couple things I'm going to talk about here's one of the very famous objects this one was the first binary pulsar discovered 59 millisecond spin period in an eight-hour orbit and it's a pulsar orbiting a neutron star this was the first binary system ever found and it's two neutron stars orbiting each other in a highly eccentric crazy relativistic orbit and it has so much relativity in it that it's easily to measure they measured it beautifully these are curves that show that this is a really amazing thing here this are the myse are the measurements of how the orbit changed from 1975 to 2004 --is-- these are the measurements that curve is not a fit that's the prediction of how the orbit would behave due to general relativity Einstein's relativity so you need find signs general relativity to predict the system Newton's gravity which explains everything in our solar system basically cannot do it okay really amazing stuff and we can easily make these measurements and this is the system where the graduate student and the adviser got the Nobel Prize back in 93 we're still doing this kind of stuff this is beautiful work from the Green Bank telescope another neutron star system this one has two pulsars a pulsar orbiting a pulsar and we can measure one two three four five six six different relativistic effects well I'm going to the details all those relativistic effects cross at this one point that's a way of doing an extraordinary test of general relativity of Einstein's theory of relativity down to about 0.01 percent this is the kind of stuff you can do by Counting pulses a big project that I and a bunch of other people are involved in right now is we're using an array of millisecond pulsars a whole bunch of millisecond pulses around the sky and we're using those arrays to try to measure ripples in space-time or right now this room our galaxies everything is being pushed and pulled apart at tiny levels by gravitational waves ripples in space-time that are being created by supermassive black holes and other galaxies that are orbiting each other and as they orbit each other they change the distance between you guys where your my pulsars and me the telescope and as the gravitational waves pull me away from you all of your signals would be a little bit late when the gravitational waves make me go back towards you all of your signals will be a little bit early but the pulsars back there will be a little bit late it makes a very specific pattern on the sky that we can measure and we're now doing this really what we need really excellent pulsars and we need really fantastic timing precision of about 100 nanoseconds for a long time and in the u.s. we're called nano grav and we're using the G BT in Greenbank and Arecibo to do this and we're hoping to have a detection within just a few years this is another beautiful measurement this is a pulsar when the pulses go around the companion star near the companion star grab that the space-time is bent by that star according to Einstein's theory of relativity and as the pulses from the Pulsar go go past it we see a delay in the pulses this is a this shows you the delay as the Pulsar moves behind the companion star and it's of a few microseconds we build our new instrument at Green Bank and we measured this spectacular relativistic delay as the Pulsar went behind its white dwarf companion this lets us measure the mass of the Pulsar too extreme so it's a really beautiful precision and it kind of tests general relativity at the same time if we pretend that general relativity doesn't exist this is the best we can do to fit our data and you can see there's still this big pointy thing there which is not good it's a beautiful pointy thing but it's not supposed to be there if you simply turn on general relativity it all goes away and general relativity beautifully predicts these high-precision pulsar data and this signal is only a few microseconds we're measuring pulses to just you know a microsecond and precision the last thing is this guy that I want to mention this is a fantastic system that the Green Bank telescope found two years ago here's the Pulsar in the center it's a millisecond pulsar it's being orbited every 1.6 days by a white dwarf but there's that guy in the background that guy is another white dwarf that's orbiting this every 327 days it's a triple system the first time we've ever seen a triple system a millisecond pulsar being orbited by two white dwarfs there's three stellar Undead in the same system all orbiting totally beautifully there's the outer one going around and you can see the inner one is tracing its orbit this is a fantastic system we just published it we're gonna be doing a spectacular test of general relativity with it within this year that no one has ever done before it's a test that you can't do it's a way of testing the so-called equivalence principle and this this one pulsar will do it way better than any kind of system measurement you can do here on earth and this is what it looks like here's the center here's the little orbit we know the mass is everything is completely well known because the beautiful the pulsar timing it's a white dwarf we can see it the-the-the this is the hot white dwarf we can measure it and this is the orbit this is pretty cool this shows you the delay as the Pulsar is going in the orbit it goes around the star so it goes away from you so there's a delay then it's coming in an orbit towards you so it gets advanced this shows you that delay so this is how far the pulses are delayed by seventy seventy seconds on the backside and it comes 70 seconds early on this side and this is over 327 days but if you zoom in right here that's this and here's the 1.6 day orbit and all these are measurements in our measurements there's thousands of data points and every one of these little colored blob blobs there we have error bars on those measurements the the air bars are a million times too small to see on this plot that's how precise we've measured these orbits these these things are really exquisite tools so what about the future well right now we only know of about 2000 pulsars in our galaxy and we think that they're somewhere between 30,000 and 50,000 pulsars in our galaxy that we could detect we're only seeing the ones in our neighborhood okay there's a unbelievable riches out there still to find okay and some of them are gonna be really amazing pulsars that spin faster than a millisecond we think those should exist Paul stars that orbit black holes that would be amazing test of general relativity we could see things there that we've never been able to see before a millisecond pulsar orbiting a millisecond pulsar to have to ultra precise clocks it could be exquisite and we think these things exist out there in our galaxy and the neat thing is a bunch of huge new telescopes are being built right now meerkat is this amazing new telescope which will have the same sensitivity as the GBT but in the far southern hemisphere so we can see a different part of the sky and then here is that the Chinese are building like the Chinese tend to do a ridiculously huge thing it's 500 meters in diameter so it's twice as big as Arecibo twice the sensitivity of Arecibo they had to remove a village out of this hole in order to build this thing and it's in construction right now both these telescopes will be operational by about 2018 and they're going to be fantastic for pulsars and then in the next decade is a telescope that's about at least five times the the collecting area of this called the Square Kilometre Array that's going to be built in the southern hemisphere right now the u.s. is not part of it but I'm hoping that we get our butts in gear to fund science and especially astronomy and it will join that project for the next decade because it'll be spectacular for pulsars so just to finish up I think you'll you'll you can see that I'm probably like these things a lot these these things are really amazing and I do work on this stuff every day and I love it thanks [Applause] so do we want our move so we move this down in case the people I'm talking [Music] yeah any questions either shout him out or come to the microphone don't be shy I'm happy to answer some questions or if you want to leave feel free I'll go have a beer yeah what makes a pulsar rotate so that's a good question so when you have a star the center of the star stars rotate but they rotate very slowly they're very big like our Sun rotates about once a month okay but that's still rotating if you shrink the star by a factor of a thousand or so and the core of the star is shrinks by about a factor of a thousand and when it goes from the size of the earth to the size of a city when you shrink like that just like a figure skater spinning and bringing her arms in that makes that slow spin turn into a really fast spin it's conservation of angular momentum that that's exactly what it is what makes like the Sun spin ah that's a deeper question so what makes that spin is that everything and it's all goes back to conservation of angular momentum when you have a big cloud of gas and which makes the Stars okay as the big cloud of gas starts to collapse under gravity to make stars even if you if you try as hard as you can not to make something have a tiny bit of spin in space it always has a tiny tiny bit and especially as you contract it it always starts spinning faster because the conservation of angular momentum so every time you make a disk and that disk turns into a star and makes planets it always turns into a disk and there's always a little bit of rotation conservation of angular momentum other questions yeah came out or Steve Mobbs was talking about that may or may not yeah so this is um this is an a point of quite controversy and active research right now we don't know as I said when I showed the black hole slide we don't know the physics that goes on inside a black hole and as a matter of fact the what we call the edge of the black hole there's not even in there's no physical edge you can't go touch a black hole that's called an event horizon and all the event horizon is is it's the distance from the black hole at which light can't escape that's the definition of the black of the event horizon so if you start light out if you start if you take a bit of light and say go run away light and you're just outside of the event horizon it'll escape but if you're just inside the event horizon it won't escape that's that's the definition of the event horizon so there's probably nothing physical there but it does define what we call the event horizon and but what goes on inside of that is beyond physics so general relativity does not describe what goes on inside there and a bunch of very famous physicists have had some bets as to whether we'll ever be able to figure out by using clever techniques to figure out what's going on inside the event horizon and I and I'm not actually sure what's the result of their bets right now who is 1 and whose loss or whether it's still in contention but a lot of people are still thinking about that other questions yeah how come there's two event horizons okay so a spinning black hole yeah this is getting into the details of some of the math of general relativity which can be very complex but if you if you have a spinning black hole what basically happens just like if you spin a sphere or if you spin the earth or a ball really you know how the earth that things become like oblong or oblate because the the spin kind of poops out that the the bottom the same type of thing happens to space-time space-time has weird stuff that goes on near a black hole when it's spinning very rapidly space-time gets dragged around okay that's frame dragging but it also you get something that's kind of like an event horizon it's not actually a separate event horizon but there's parts of space-time where you can't orbit you can't you can't make an orbit that goes in is stable for instance within a certain radius that the orbit will always go closer and closer and eventually go in the black hole even though light could escape so there's there's a couple extra weird zones it's like the what does it call the ergodic zone or something can you remember what it's called right now but some weird zones that when you add spin because space-time gets dragged along that extra stuff happens but that's called the Kerr black holes what is what that's called yeah you have a question yeah what you got which which star I don't know why don't you tell me I don't know which star that one is so if it's if it's a really really big supergiant it's gonna probably have some kind of thing that's like a supernova and it will probably become a black hole in the center but what's going to happen to the outer parts I'm not exactly sure there's a few stars in our galaxy these very very special stars that we think have almost a hundred times the mass of our Sun there's a star called the pistil star and there's a star called a to Carina have you heard of those two they're very famous big stars and they're so they're so huge and have so much going on that they're causing these big eruptions one of them called a to Carina was bright it was one of the brightest stars in the sky in the 1800s and it's now really dim because I went through this big eruption and there's a famous Hubble Space Telescope picture of it but they're all gonna do something like a supernova within the next million years that's crazy big yeah that Betelgeuse is like that - Betelgeuse ism is is huge also that's huge that's amazing you should give this talk yeah ah yes that's a good question so when things yeah there's no as you can probably guess there's not like a line where it's a it's a bright pulsar and all of a sudden it just turns off it's there's kind of a region where it's going slowly and a start sputtering and flickering and we see a lot of pulsars that are spinning slowly that are sputtering the flickering there we don't see pulses from them for minutes or hours or even days at a time and also milk they'll sputter back with a couple pulses and then they'll go they'll go away again and something weird is going on in their magneto spheres and we don't we do not understand the process that's happening there but we think that beyond the group beyond that death line in the graveyard occasionally very rarely we could see sputtering in the atmospheres of these stars and see flashes in a matter of fact there's a type of star called a rat a rotating radio transient that we think might be regular pulsars that have gone beyond the graveyard but most of them will not do this because they're too slow to even do that and they're just dead neutron stars that we'll never see magnetic haha another good question and one that we don't really know the answer to so there's a lot of things about pulsars which I will wave my hands a lot because we have a general rough idea why they are but we don't know the details and this is one of them and it has some it has something to do with the supernova mechanism so when that massive star explodes the core of the star collapses that's a very chaotic process and it's not perfectly symmetric because there's rotation there's these big convection cells on the top of the star and that causes causes it not to be perfectly spherical and so you get all sorts of turbulence and all sorts of basically chaotic mechanic mess that causes the conservation of angular momentum to be slightly off from everything else the other thing is is that everything in the center of a star is ionized it's all ionized hydrogen and because it's so hot in the center of the star whenever you move ionized gas for those of you who are physics students if you make a current what do you generate a magnetic field every time you generate a current you generate a magnetic field so if you have rotation of ionized material you're making a generator in you're generating magnetic field so you use you're somehow making magnetic field along with the rotation and if because of all the chaoticness when that locks in sometimes it's not quite lined up with a rotation but once again that's a very hand wavy explanation but our physics simulations that people do about supernovae seem to show that that's very much the case anything else yes what percent of your sale I got a lot of cool stuff going on without without gambling on Beetlejuice but I would I give 5% of my salary I guess one year one year of 5% of my salary the magnetic field so well that's it's very different answer depend on which fields I mean talking about gravitational field magnetic fields so magnetic fields in space in general almost everywhere through the universe even between galaxies there are magnetic fields very very faint and once again this all goes back to the fact that whenever you move charged particles you create magnetic fields and whenever you have stars that are bright they ionize hydrogen so you have ionized gas everywhere and because of gravity gas is moving so you always have in the universe moving charged particles therefore you always have induced magnetic fields and so once you start moving those magnetic fields and then moving the charged particles it basically they're always there's always this interplay between the two and you end up locking them together if you if you bring the ionized gas together you make the magnetic field stronger if you move the magnetic field lines together you move the charged particles together and so it's this movement of charged particles that's always causing the net magnetic fields to be there everywhere we look but they're very very different strengths yes so Stephen Hawking the very famous physicist there's a thing called Hawking radiation and this goes along with the the question over there about what happens at the event horizon when you move when you put together quantum mechanics and general relativity so quantum mechanics is the physics that describes the very very small atoms nuclei stuff like that it's how the reason computers work is because of quantum mechanics we know quantum mechanics works it's real you know it's in your pockets when our cell phone good general relativity it works I've showed you the data right jump these are both work the problem is that general relativity and quantum mechanics don't mesh together when we really think they should there should be a theory of gravity that meshes well with quantum mechanics so sometime we think there's gonna be a problem in probably general relativity when we get to a certain energy scale or certain density some problem characteristic will show up and this is one of the reasons why we keep testing general relativity's to try to find when general relativity breaks but because there's this kind of disconnect between the two at the boundary of the black hole at the event horizon quantum mechanics can take a charged particle and in quantum mechanics you can make particles appear out of nothingness and they'll make a positive charged particle and a negative charged particle and together they cancel each other out they there's no if they're both going in the other direction there's no net energy there's no net angular momentum but quantum mechanics says you can actually make particles like that appear if you did that right at the event horizon you can cause one charged particle to go in the black hole and one to leave it that's a big problem because you effectively lose information then if you're outside of space in in regular space I said there's no net energy gain or loss but if you put anything in a black hole it's gone you've lost it so there's all these quantum mechanic issues with the the edge of a black hole and what Hawking radiation is is that basically it's a way that quantum mechanics can be used to cause an a black hole because of this this process of chunking one particle out and keeping one in you can cause a black hole to evaporate by quantum mechanics can chuck particles out but that takes a ridiculously long time for a normal black hole that I showed I don't even remember the number I don't know do you know the number it's ten to that yes way way longer than the age of the universe I mean like billions of times or I don't even know a lot longer than the age of the universe not nearly yeah so and that's the size of an asteroid the so these ones the ones that are much much bigger they take way longer to it to evaporate so it's this is this is kind of it so it's a it's kind of a mental idea of what happens when quantum mechanics and and general relativity get together but no one has ever seen a black hole give off Hawking radiation or evaporate nor do I think we actually ever will yep so I that's the question that I can't actually give you a good answer and I'm not sure how many people can we I don't think we know why there's a preponderance of matter as opposed to antimatter does anyone know I don't know the answer to that and I think it's I think it's actually quite a big mystery yeah yes yes absolutely and we actually don't know how the supermassive ones in the Centers of galaxies form so there's a couple ideas one of the ideas is that the very earliest stars the very very first generation of stars that formed in general stars need gas besides hydrogen to form because the the carbon the oxygen the stuff that stars that supernovae and stars make that become us right we're all made of star stuff that famous thing that Carl Sagan says it's really true every atom in your body made in the star the all that stuff where was I going with this we asked about so so yeah the very very first generation of stars it was only hydrogen then basically there's a little bit of helium but the hydrogen is what is what collapse and so is what collapse to make the first stars and it's thought that those stars burnt we're actually huge stars maybe even a thousand times the mass of our Sun and they burnt very very rapidly through their fuel and quickly collapsed into big relatively big black holes like maybe even a hundred solar masses it's also thought that they possibly formed in these very dense clusters so if you make a whole bunch of these very massive stars then all these 100 solar mass black holes can then coalesce together and then very quickly then you have a thousand or a couple thousand solar mass black hole and when you have that that's enough of a seed that by just by gathering gas over the rest of the billions of the age of the universe you can grow it to be billions of solar masses because once it makes it to the center of the galaxy gas is always funneled to the center of the galaxy just because of basically friction and then it keeps feeding the black hole but that's once again that's a hand-wavy idea right now that's an that's an area of very active research yeah yes aha now we're burgeoning on the realm of science fiction so first off we don't know if white holes even exist what the idea of a white hole potentially possibly is that you know I said we don't know what the physics is inside of a black hole right so there is an idea in it it is possible to work it into general relativity that inside a black hole is a wormhole and that basically it's a connection of two different distinct points in space-time and the idea of a black hole is if a black hole nothing can escape everything's being dumped in this side if there's a wormhole then the stuffs got to get squirted out someplace else okay the problem is we don't see anything like white holes anyplace in the universe right now but if you as a thought process according to general relativity that type of thing is possible in general relativity but does it actually occur in real life I don't know but I doubt it has anything to do with antimatter because it's probably it would be the exit of a wormhole rather than an antimatter version of a black hole it's a help cool anything else yeah say again turns in five yeah so turns and five is one of my favorite objects in the sky so turns in five is a glob I have a beautiful movie which I'd have to dig it out of my laptop but it's in the very center of our galaxy it's very close to the sent the the supermassive black hole only well galactically speaking it's like a few neighbors down you know down the street from the black hole at the center of our galaxy but right through all the dusts towards the center and it's a massive cluster of stars it's a globular cluster there are these stars that are there they're billions of years old about 12 billion years old these stars they all four at the same time there's about a million of them in terms a and five and they're all in the area the size of the volume between us and our nearest star so the nearest star to us is Alpha Centauri it's actually actually Proxima Centauri but that's four light-years away if you took that distance and stuffed a million stars in it that's what turns a and five would be like and they're all orbiting each other and these these objects the reason why I love them is that because if you create a pulsar there long ago twelve billion years ago if you created a pulsar when the stars went supernova because all those stars are long dead but then because the stars are so dense they can interact stars in our galaxy are so far away that our stars never interact with each other but in a globular cluster you can get a star that interacts and if you have a binary for instance that's orbiting and another star comes by you can have a little triple dance and you can fling out one of the partners you can have partner swapping and all sorts of crazy 70s stuff going on there and what you're left with is a you can take that old dead neutron star that's past the graveyard and put a normal star in orbit around it and then that star can turn into a red giant and recycle the Pulsar so globular clusters are factories for millisecond pulsars and one of the big things that I did in my postdoc was I found me and my collaborators not just myself we found 33 now 35 I think there's a total number of pulsars in one cluster in this tiny little part of the sky by using the G BT the Green Bank telescope to put towards the center of the galaxy and they're very interesting exotic pulsars including these eccentric binaries and sorts of crazy stuff so really fun exotic pulsars can be found if you look in the right places over here before it starts to defy the laws of physics well that's a tricky question given that we don't understand the laws of physics inside a black hole but I'll give you an example so the biggest at the center of basically every galaxy we think there are supermassive black holes and by supermassive I mean at least a million solar masses so like Cygnus x1 that I showed you is about ten solar masses so at the center of the galaxies we're talking a million solar masses that are galaxies in the middle of our galaxy Sagittarius a star that's the black hole's name is about four million solar masses that's a kind of a puny though on galactic scales there are galaxies that have billions or maybe even ten billion solar mass black holes and the crazy thing about those black holes this is really bizarre the black holes get bigger the more mass you put in but bigger in that the event horizon gets bigger but remember what I said the event horizon is not really a thing you can touch if you take a multi billion solar mass black hole the event horizon is almost the size of our solar system and when you have a black hole that big the tidal forces that I mentioned for like a neutron star are puny so unlike a neutron star where you can't get anywhere closer you'd be rip rip to shred or Cygnus x1 the tidal forces would rip you to shreds if you got next to a ten billion solar mass black hole you can walk right through the event horizon the trouble is you couldn't turn around and walk back out so you'd be walking right to the center because gravity even though you walked right through you there'd be no feeling it wouldn't feel different at all but you would just be like sliding you know gravity will be pulling you towards the center so it's a very bizarre thing it's it's so counterintuitive to the way that we deal with with with regular life but still that would still we think obey all the laws of general relativity it just wouldn't obey the loss of your mind yeah other questions yeah like one of the particles went into a black hole I'm not even going to touch this one because this this is like related to these bets that people like Stephen Hawking or having and if they can't agree I know I certainly have no chance of being able to tell the answer to that but once again that's this weird boundary layer between quantum mechanics and general relativity where people do not understand what's going on we really do not that's the forefront of theoretical physics knowledge yeah so this is a interesting question I've actually thought about this neck and that been a little bit of work on this so the very first exoplanets that were found were found around a millisecond pulsar it was like the fourth millisecond pulsar we ever discovered I showed you Don backer my mentor who found the first one only about three or four years later a professor at Penn State named alex Vulcan found a millisecond pulse for their first looked like an isolated millisecond pulsar he didn't have a binary companion it was all normal he started that really magical process of pulsar timing and things weren't quite adding up turned out that he had found a system of three planets and the planets are all earth mass or below there's like an earth-mass planet a Mars mass planet and a moon mass planet and pulsar timing was so precise that he was able to map out and measure the masses of all those planets beautifully and even now if you look at the best the most cutting-edge planetary results now using optical techniques which is what all the new techniques are using we're just now getting being able to find things that which are close to optical or earth masses but this was done with pulsar timing a completely new technique but here's the bizarre thing he found this planetary system which has been confirmed it's definitely there with the fourth millisecond pulsar we now know of about 300 millisecond pulsars and there's only one other system that has a planet and it's a weirdo it's in one of these globular clusters so it almost certainly this an exchange encounter thing and probably a planet from someplace else got caught around a millisecond pulsar probably we don't know for sure but probably so out of those other 300 millisecond pulsars why don't they have planets we know they don't because pulsar timing is so precise that we would have seen them like that I've already showed you know I showed you the Pulsar data there's no extra wiggles and the Wiggles would be huge for these planets that's how precise our signals are so that's a bit of a bizarre thing when you find a weirdo system the fourth one you ever find you find something totally weird about it planets and then 300 more and not another planet basically that's bizarre but yet astronomies filled with stuff like that and to me that makes it one of the really fun scientists to study because we find weird and exotic and crazy stuff all the time and it makes it great to go into work I love it thanks you

Channel: jmu planetarium

Views: 165,517

Rating: 4.6367307 out of 5

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Id: rKpFFTGbaDc

Length: 94min 46sec (5686 seconds)

Published: Fri Apr 25 2014

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Dr. Scott Ransom, National Radio Astronomy Observatory (NRAO)

The biggest stars burn the fastest and brightest, and when they die, they do so spectacularly, exploding as supernovae and leaving behind some of the most fantastic objects in the universe: neutron stars and black holes. In this talk, Dr. Ransom will discuss how these crazy objects are created, some of their amazing properties and why we (probably!) don’t need to worry about them too much here in our cozy homes on Earth.