Public Lecture | Brown Dwarfs: Failed Stars or Overachieving Planets?

thank you thank you Greg for the introduction and thank you everyone for coming out here to hear a little bit about brown dwarfs the unfortunate middle child of astronomy they usually get lost in all the attention paid to stars and to planets but hopefully I can talk to you a little bit about why they're actually interesting in their own right as well as Greg mentioned I'm Erik Nielsen I'm a research scientist here at Stanford I work down on campus my main research interests are direct detection of extra planets of brown dwarfs of actually studying them and trying to understand where they came from and hopefully I can share a little bit of what we've learned recently with you all today okay just to sort of set the stage this is a movie from the recons team looking at the solar neighborhood looking at stars within a few light-years of the Sun and basically what's gonna happen is the movies just gonna zoom out from the solar system it's pulling out now for the Oort cloud just pulling out further and further away from the Sun and seeing what systems pop up as we move further and further away once we get out to about four light-years we hit the the first star other than our Sun which is the Alpha Centauri system and then as we pull out further and further away more and more stars appear and so you know the average distance between stars is a couple of light years and we see that the solar neighborhood is actually you know pretty packed with lots and lots of different stars the one one trend you may notice that a lot of them are red they'll come back to that a little bit and so pulling out to about 33 light-years we see the results of a census of pretty much every star within that radius just wait for it to finish there right now okay so again the the the group that put this together is called recons the research consortium on nearby stars they did a census of all stars within about ten parsecs thirty-three light-years you know well time for the census that we're in the US are going to do in about a year and literally just counting up every single store every single brown dwarf every single stellar remnant within that radius and what they found by doing this this full-on census was about 20 stars that look like the Sun about half as many that are more mass the Sun and then over 300 that are less mass than the Sun so this is the first thing I sort of jumped out of you immediately we do not or we don't orbit ordinary star most stars are lower mass than our own Sun so you add the lull together you get about 350 stars also in that 10 parsec radius 50 brown dwarfs so there's a lot of brown dwarfs out there there's about in the Milky Way galaxy as a whole there's about 200 billion stars and so that works out to about 20 billion brown dwarfs in our galaxy alone so there's there really are a lot of brown dwarfs they've been if we've only really been able to study them a detail for the past 20 or 30 years and hopefully I can tell you a little bit about what we've learned in that time okay so first of all definitions what do we mean when we say brown dwarf it's a purely mass definition so let's go through mass a little bit here so if you think about planets and just rank them according to mass here from low mass at the bottom to high mass at the top go from the low the the lower mass planets like rocky planets like the earth here higher mass planets ice giants up to gas giants like Jupiter and Saturn all the way up to about 13 Jupiter masses a relatively arbitrary boundary that we call the upper limit of planets anything lower than 13 Jupiter masses we call a planet at the high end we have the stars so the Czar's like the sun start more high mass stars and more low mass stars and then we have another boundary here at 75 Jupiter masses at 75 times the mass of Jupiter anything above that becomes a star and this is this is a slightly more physical limits this is the mass you need to actually fuse hydrogen into helium so inside inside of a any star deep in the core temperatures and pressures are so high that the hydrogen fuses into helium and this is the energy source for stars this is what causes them to shine this was stopped them from collapsing most stars when most their lives just you know day by day by day fusing hydrogen into helium which provides them with their energy but you can only do that if you have enough gravity to keep the core hot enough and that limit about 75 G per two masses and so we have these these two boundaries here everything below 13 super masses of planets everything above 75 Jupiter masses is a star and that blank space in between is the brown dwarfs and so the the named brown dwarf is a purely mass definition anything that falls in this mass range anything bigger than 13 times the mass of Jupiter smaller than 75 meant the mass of Jupiter recall a brown dwarf and this is also why they come about that they're sometimes called failed stars they just didn't get enough mass to ignite nuclear fusion in their core and they're there you know somewhere below and so I'm gonna try and talk a little bit about how they fit into this range how are they like stars how are like planets what's really going on with them okay so start out a little bit just run talked a little bit about how we talk how we think about stars how we classify them and for astronomers the the main way we classify stars is by temperature specifically temperature at the surface but the the outer envelope of the star the part we can actually see what's the temperature at the surface and the temperature range is a quite a bit about an order of magnitude here and we use these special letters called spectral types to basically encode what the temperature of the surface of the star is so all the way from the hottest star type star coolest star the M star and the great thing about stars is so long as they're currently burning hydrogen and helium they all look pretty much the same and so temperature for stars that are burning hydrogen and helium that are fusing hydrogen and helium of temperature tracks mass trax radius so the the hottest stars are also the most massive stars are also the physically largest stars similarly these smallest stars in terms of mass or the small stars in terms of radius and also the coolest stars and so if you tell me a star's a G star I know it's this about the same size of the Sun say mass of the Sun same temperature as the Sun so long as it's currently fusing hydrogen into helium the reason that these letters are in this very nonsensical order is a bit of a historical accident if you ever want to remember the order OB AF g/km my suggestion is only bad astronomers feel good knowing them on okay in terms of numbers this is a little pie chart here just shows a how many of each spectral type we have in the galaxy the vast majority are M stars so again most stars are less mass than the Sun so full 3/4 of all stars are these low mass M stars the coolest of all stars another significant chunk the case stars and then the the stars like the Sun the G stars are again relatively rare with even fewer stars more massive than that so again most stars less passion than the Sun the one of the reasons we like to use temperature is temperature really encodes the the light that we see from these stars it tells us about the light that we see how much energy we get and what sort of energy that that comes out as and just give some you know everyday examples here this is an incandescent light bulb for younger people in the audience you can consult a nearby museum as to what an incandescent light bulb is but back in the day we would heat a filament of tungsten to about 3000 Kelvin and it would glow in the visible part of the spectrum so basically you get visible lights by heating something up to up to this high temperature essentially what's happening is atoms will give give off light depending on what their temperature is the higher the temperature the the shorter wavelength of light they will emit so at 3000 Kelvin you'll get some visible lights if you heat up a element on your stove up to its maximum and we could hit a temperature as high as about 500 Kelvin and most of the light will come off in the infrared but there'll be a significant chunk of energy coming out and be red as well and you'll see the the the the stove actually start to turn red just because of how hot that element actually is one more thing one more item around the house human beings an off-the-shelf human the being runs around 300 Kelvin it gives off mostly energy in in the infrared the deep and the thermal and Fred so if you have a special infrared camera you can actually see the energy being given off just by a human being at the you know everyday body temperature this is actually a self-portrait of me trying to prove that a Mac seen infrared astronomer okay alright so this is true for you no items here on earth it's true for stars as well the the hottest stars end up becoming blue so that they're there so the surfaces are so hot that most energy is in the actually ultraviolet part of the spectrum and they look blue to the naked eye similarly the the coolest stars Energy Star most energy is coming out in the infrared and they look red to the naked eye with sort of a whitish yellow in the middle here and so the temperature of the star controls what what sort of light we actually see from it so what is this mean for the brown dwarfs well brown dwarfs are going to be cooler than the coolest star they don't undergo fusion they can't keep themselves warm and so in general they're going to be even cooler than these M stars here and so if we want to look for brown dwarfs we shouldn't look in the ultraviolet we shouldn't look in the visible we should probably look in the infrared the infrared is probably going to be the best our best shot at actually imaging these things so this is a shot of the Pleiades and the visible this is from the digitized Sky Survey the PD is named for the Seven Sisters a Greek mythology so named because there are seven stars visible to the naked eye and you know in the visible that those seven stars really really dominate the image if you look in the exact same field but you look in the infrared and said you know those seven stars are still there but they're not quite so dominant you started to pick up a lot more the the other the fainter stars and in particular you start picking up a lot of the M stars that were a lot harder seeing the visible that become a lot more prominent in the infrared okay so step one look in the infrared there are other tricks as well to pick up these brown dwarfs and I actually wanted to go through one really nice trick that's been used just in the last few years to identify the the very closest brown dwarfs of the Sun ones that basically have only been identified in the past ten years or so that were there hiding all along but we're only able to actually identify them starting in 2012 and so we use a technique called proper motion and the idea here is pretty straightforward you take images year after year after year a field of stars and look for the one that's moving and you know hopefully you spotted that one there that's quite obviously not not not like the rest of them and what's happening here is all the nearby stars are orbiting the center of the galaxy you know in their own specific orbits and moving relative to each other any stars that's really really close to us is gonna appear to move at a much faster rate the analogy I have is imagine Jerrod an airport watching a plane taking off it's going to go across your field of view in a couple of seconds similarly if you're sending out in the field somewhere and watching a plane pass overhead it'll take several minutes to go across your field of view just because when the plane is you know physically closer to you it appears to be moving much faster and that's the same idea here any star that's tough quite close to the Sun will appear to just be zipping across the sky compared to be much more distant stars in the background and so this star here is Proxima Centauri this is the the closest star to the Sun and it's just you know 10 years of motion from image after image after image so the the brown dwarf that was discovered in this way is something we call lumen 16 and again this is a very recent discovery just twenty twelve about seven years ago when this was identified using this proper motion method actually explain what's going on here these are four different images from four completely different sky surveys using different telescopes different wavelengths which is why the stars appear to get bigger and smaller from image to image to image the size of a star on the image depends on the the size of your telescope the way think you're looking at and so ignore the fact that stars are you know changing all the time but you do see this one object that's moving across the field there and that's new 116 ice not just a brown dwarf it's actually a pair of brown dwarfs it's - brown dwarfs in this very very close binary configuration here this is the actual data we have here's a you know nice little artist conception so I'm sort of two objects that are if you know Jupiter ish with the Sun in the background of the image there so you know brand-new close close binary the closest brown dwarfs to the Sun lumen 16 one more found in this this way object with a very long confusing serial number for a name here found by the wise telescope and the very long confusing coordinate system you know where the object was also found using this proper motion method by stringing together years and years of data you see it moving across the sky compared to the background stars so this after lumen 16 this is the next closest brown dwarf to the Sun okay so so let's put that all together so what are the closest neighbors to the Sun we talked about the the 33 light year sample this is the even closer sample just the the handful of stars that are closest to us here so for all the stars all the brown dwarfs close to us the very closest one should not be a surprise he's our friend the Sun next up the Alpha Centauri system this is a triple system with an F with a G star a K star and an M star possibly a couple of planets as well orbiting some of those members number three another M star called Barnard's star which was also identified as being very nearby almost a hundred years ago by this proper motion method as well next up lumen 16 so number four on the list already is a couple of brown dwarfs our friend wise o 8:55 is next and finally Wolf 359 ask a Star Trek fan why that name sound familiar to you but yeah so you know of all the stuff of the sick of the six systems that are closest to us there there's two G stars a K star three M stars and three brown dwarfs so not only are there a lot of brown dwarfs out there there lot closer than you think they are all right so the the sunny brown dwarfs has been you know a pretty recent thing it really required the advent of you know wide wide area surveys as well as infrared detectors to really be able to detect these of these objects for the first time and really starting in about 1995 1996 was when it's Tron you know Brown door signs you know really started to take off and the the the reason it sort of took to that point was the Serrano's really need to convince themselves that they were actually looking at brown dwarfs and not just looking at low mass stars and the thing that I don't know convincing astronomers is lithium so if you haven't consulted your periodic table recently hydrogen helium number three is lithium so the the third element on the periodic table the Big Bang produces hydrogen produces helium it produces you know trace amounts of lithium something of order one lithium atom for every billion hydrogen atoms and that you know those trace amounts basically become part of you know anything that forms in compared entire stars that come about part of brown dwarfs quarter planets and so you know any star or brown dwarf that is formed it has a little bit of lithium built into it so you can think of it as a gift from the early universe what a stars do with this gift will they squander its star stars fuse that lifts them away as quickly as they can and essentially what happens is it's really easy to fuse lithium plus a plus a proton into two helium atoms it's so easy in fact it happens at a much lower temperature than you need to fuse hydrogen into helium and so if if a star's is the core is hot enough to fuse hydrogen and helium it can really easily fuse that lithium away and so any lithium that finds its way into the core of a star it's gone it's very quickly destroyed converted into helium and you know so how does looking find its way into the core well stars are you know largely convective there's large convective zones where material just constantly being dredged around the star so for star like the Sun between about you know half and 1.5 solar masses there's a convective outer layer here and a non-conductive zone in the center but for the lower mass stars that anything lower than about half the mass of the Sun the entire star is conductive so any lithium on the surface they're going to find its way into the core get destroyed by fusion and never find its way back up and so low mass stars very quickly destroy their entire supply of lithium quite early on in their lifetime and so you know if we're looking for evidence for this we the way that we astronomers look for to try to understand the composition of objects is we take spectra we look at the light from an object split it up by wavelength and look for signs of molecules of atoms and fuels in the atmosphere based on the lines we see in that spectrum so again this is wavelength here 6700 angstroms is about the red part of the spectrum here amount of flux here on the y axis and anytime you see an absorption line this this little dip down that's the sign of an atom in the atmosphere of the star thus absorbing light at that specific wavelength and so all four of these stars they have calcium and so you see this a lot this line here precisely where calcium has a transition there's also iron lines they all have iron and some of them have lithium absorption and one doesn't and essentially what what you're seeing here is a difference between young stars and old stars young stars have not gonna had a chance to destroy their lithium they're trying very hard they're gonna get there one day but but they still have a little bit that primordial lithium left the old star has completely destroyed its lithium supplies and so there's no lithium left and so this is a neat trick to use to tell the difference between old stars and young stars based on how much the lithium they have left and if you put this all together this becomes a beautiful test for whether or not an object is a brown dwarf so let me go through it so a brown dwarf like a star is gonna be entirely conductive so any lithium on the surface is going to make it down to the core of the brown dwarf and back up for a star any material that makes it down to the core will be destroyed because the core of the star is hot enough to fuse hydrogen and helium and therefore it's hot enough to fuse lithium as well the brown dwarf will have a cooler core and the the lithium can go to the core and come back without being fused away so you can find an object that's old enough that word a star it should have destroyed just looking by now but but you know still has some lithium left over that's a sign that you're looking at a brown dwarf and this was the thing that convinced astronomers in 1996 that we were actually looking at you know actual brown dwarfs we weren't just for air so by looking at very low mass stars a series of brown dwarf Kennedy's in the Pleiades all with the deep yellow lithium absorption lines and so you know lithium was was the so-called smoking gun to really show that you know we were actually looking at real brown dwarfs based on the fact that you know the stars should have destroyed that lithium by now these brown dwarfs still had it's okay so that's a little historical aside once you have actual detection actual discoveries the the process in science is you immediately write and press release and to go along with your press release you write you contact an artist to make beautiful images for you and so we got these beautiful images then you know of the new Brown Dorf discovery is here and these are actually you know probably pretty close to what's going on this the planet in the foreground is completely fictional but other than that everything looks pretty good in this image here so you know the brown dwarfs that look you know that are quite hot that look a lot like low mass stars brown dwarfs that are cooler looks sort of like a you know slightly brighter Jupiter and so there's a pretty big range in depending on the temperature of the brown dwarf and what they probably actually look like okay so what are they actually you know what are their actual physical properties and if you have sister numbers there's always one question they want to answer first when they want to understand an object and that's basically how does it stand up to gravity that you know grab anytime you have a massive object gravity's didn't try and make it collapse what stops that collapse for objects like the earth here what what on what top side collapse is basically pressure from liquids and solids they push back against compression and they hold the plateau they hold the planet up and so that works for you know low-mass planets like the earth it holds up for you know for asteroids for for comments and things like that does not hold for giant planets on the high mass M stars nuclear fusion hole pushes back against gravity the energy produced by nuclear fusion pushes back as the star tries to collapse so what are all in between what about for brown dwarfs what about for giant planets they're both the of both sets are too big for solid or liquid pressure to push back against gravity but too small to ignite nuclear fusion why don't they collapse what what do they do to hold back against gravity okay so I'm gonna assume that you all consulted your quantum mechanics textbooks before you came here and it reminded me yourself a little bit about the Pauli exclusion principle and the Pauli exclusion principle is actually what's behind the giant planets and the brown dwarfs being Alda to hold themself up against gravity this thing we call electron degeneracy pressure and the the the Sigma Pauli exclusion principle is that two fermions cannot occupy the same quantum the same quantum state at the same time electrons are fermions protons refer me on neutrons refer beyonds and this metaphor here cards are fermions as well so and imagine a imagine a parking lot if the parking lot has lots and lots of open spaces and you try to compress a bunch of cars trying to push a lot a bunch of cars in the same location things are okay there's a lot of spaces where you can put those extra cars and everything behaves the way you would expect as those spaces get to be filled up there actually ends up being this pressure that it's something that stops you from being able to continue to push more cars in the same location simply because there's physically no space to put them anymore there's something similar is happening for the electrons as well as you try to compress material if there's plenty of quantum state now quantum states available for those electrons to go into you you can keep pushing that material closer and closer together but eventually you'll hit a limit where all the all the quantum states are filled up and you just physically can't compress the material any further because there's no place for the electrons to go and so this is what I was actually holding up both giant planets like Jupiter as well as brown dwarfs this electron degeneracy pressure is the thing that's pushing back against gravity and that is a couple sort of you know you know fun consequences one of them is that across a broad range of masses things are exactly the same size so all the way up from Jupiter you know at one Jupiter mass all the way up to a 90 drooping mass star all these objects are about the same size there's a factor of 90 difference in mass sizes are all about the same there's even a little bit of weird counterintuitive that thing going on which is actually larger objects or more massive objects are smaller than less massive object you know this is you know think of a snowball you add more snow to a snowball the snowball gets bigger the opposite happens for brown dwarfs you add more mass to a brown dwarf it becomes smaller all a result of a degeneracy pressure okay so that's one way that both brown dwarfs and giant planets are different than stars they're not held by fusion they're held by this degeneracy pressure one more way they're different is because they're not few hydrogen to helium because they have no internal energy source they cool down over time and so unlike stars or we can just talk about okay a star of this mass will have this temperature song as its fusing hydrogen is this nice table thing that's not the case for brown dwarfs for planets that cool over time they start out just being born very very hot hotter than some stars in many cases then they cool down cooler and cooler and cooler over time and so you know you can't really talk about you know what's the temperature of this brown dwarf with the temperature in this planet you have to tell me the age as well because it just keeps it cooling and cooling over time okay so here's here's a fun a theoretical plot of just how how these objects are cooling how they're getting fainter over time so on the x-axis here is age from 1 million years after the object forms all the way up to 10 billion years after the object forms brightness on the y-axis from faint too bright here and in the blue is what is how stars evolve green is the brown dwarfs and red is the planets so stars start out hot just as they form they cool down they contracts over time meanwhile the core is getting hotter and hotter as more material comes into it and eventually the core gets hot enough to ignite nuclear fusion at which point nuclear fusion stops the contraction stops the cooling and the the brightness of stars just levels out as it happily burns a hydrogen as long as it has hydrogen - Burton so there's an iced ability given by you know sustained nuclear fusion brown dwarfs they initially follow the the same path they're cooling and attracting over time there's a glimmer of false hope that they gets because there's just like there's a little bit of lithium left over from the Big Bang there's a little bit of deuterium left over from the Big Bang deuterium is a heavier isotope of hydrogen just so you know little trace amounts left from the Big Bang and it's actually even easier to fuse deuterium than is to fuse lithium and so these brown dwarfs will fuse to Tyrion in their core which will temporarily push back against gravity but there's not a lot of deuterium and they have no way of making more once they finished using it and so there's this little blip where things you know start to smooth out and then they started you know dropping again they started dropping in brightness they talked for a start dropping in temperature as well once they once they finished fusing their deuterium all hope is lost there there's nothing else for them to do to stop this cooling to stop this contraction that they're gonna stop contracting when they hit the energy limit but they'll just keep cooling and cooling as time goes on planets will never actually never get hot enough to even fuse deuterium and so this is the arbitrary line that we divide we used to divide planet giant planets and brown dwarfs at 13 Jupiter masses above that you're hot enough to fuse deuterium below that you're not and so this is again somewhat arbitrary boundary where we say brown dwarfs and and planets begin thirteen times the mass of Jupiter based on your ability to fuse deuterium very early on in your life okay so what sort of temperatures are the surfaces of these objects and again remember this depends on how old the brown dwarf is because they're going to cool down over time so the very youngest objects you know going to be pretty much as hot as the lowest mass stars you know thousands and thousands of degrees as they get older that they'll start to cool down more and more eventually you know 100 Celsius you know the temperature of boiling water something getting you know very very cold you know a good winter in Fargo North Dakota a sort of cold so you know you know actually relatively chilly uh surfaces so this is some of the most recently found brown dwarfs have these you know very very cold surface temperatures okay so go back to our little diagram stars here remember we classify stars by their surface temperature add with these little coating here oba FG km to denote what the temp of surface temperature of these stars is as we introduce brown dwarfs we're gonna need to introduce new spectral types as well and so we introduce these three brand new spectral types L T and Y to get these even colder temperatures you need to describe both brown dwarfs and giant planets remember giant planets also play this game of starting out very hot and then cooling over time and of course we have to update the mnemonic only bad astronomers feel good know we know - like this you know it's got the Scott was gotten me through many a tests and so we can you know update this temperature chart not just with temperatures but with the spectral types of these objects as well so again hottest objects that they're actually you know the same spectral type as the low mass star they have their an M dwarfs spectral type even though they're a brown dwarf go down to the ELLs the T's and finally the Y dwarfs as well the the the very coolest of these objects and again remember you know the the fact that something is an old Wharf it doesn't tell me that it's a brown dwarf or a planet it could be either I need to know the age before I can tell you what the mass that object is because all these things cool over time so in fact you actually are probably already familiar with an example of the white dwarf class Jupiter Jupiter's temperature puts it in the in the Y dwarf cat category as well you know Jupiter started out life as a probably just an Emer and L dwarf cool down to a tee and then finally cool down to a lie beside it the whole time but it went through these different spectral classes as the surface got colder and colder is it contracted with time okay so what do these temperatures actually mean for what's going on in the atmosphere well once again I'm gonna take a quick step back two stars to remind ourselves how this all works so on the surface of a star like the Sun the atmosphere is actually relatively boring it's just a lot of ionized gas hydrogen helium trace amounts of everything else iron oxygen carbon you know not a lot of really exciting stuff going on in terms of chemistry on the surface of the Sun for small stars things get a little bit more interesting the surface is cooled enough that you're not gonna get molecules on the surface of these stars it's things like titanium oxide indium oxide carbon monoxide are you know things that we can see in the spectra that is actually taking existing on the surfaces of these stars I think it's even better for the brown dwarfs because not only we got these molecules you actually hard to get clouds forming in the atmospheres of these objects and so when you go from M to L you start getting a calcium oxide TM oxide clouds you move you cool down from the ML transition to L dwarfs you still have these calcium by clouds but they're lower in the atmosphere now near the surface yeah so you turn to have silicon clouds and my personal favorites liquid iron clouds starting to form on these things so a Chance of liquid iron rain and as you go from an elder to a tea dwarf again you get the same set of clouds further down in the atmosphere and you add on top sulfides and and potassium chloride clouds along with the advent of methane in the atmosphere and even more interesting you started to get gaps in these clouds you sort of get patchy clouds and so instead of just being you know a single cloud layer covering covering the object you start to you know be able to do see differences in the clouds as you go further down and so again you push from the t dwarfs to the wide dwarfs I'm gonna use the you know best example of a wide where if I have which is Jupiter and you see like you know really interesting cloud structures going on there and so you have ammonia clouds water clouds on Jupiter's you know different layers patchiness you can you know see down the different layers but any whether you're looking at the other cloud cloud deck or looking at the gaps between clouds deeper down and just to sort of drive this point home this is what Jupiter looks like in the visible this is what Jupiter looks like in the infrared and so again the the amount of light you see from Jupiter depends on what the cloud structure is doing in a particular if there are gaps between clouds that those appear as very very bright spots if there's a gap but between the clouds you can look quite deep into the atmosphere of Jupiter you can see the much hotter late layers down there which then allows which then you know gives off a lot more light than the cooler layers on top and so the gaps between the clouds provide this little extra bit of brightness so it's pretty easy for an object like Jupiter Jupiter is quite close by we can hang to take this beautiful resolved image of the surface but we have really no chance of you know taking these beautiful images for any brown dwarf or planet outside our own solar system they're just you know no but building a telescope big enough to take out that level of resolution but we can cheat we can we can try to reproduce what these things look like through some clever observations so imagine this little toy model here we have a planet that's rotating and has a green splotch a red splotch and a blue swatch on it as it rotates you know different amounts of green blue and red I rotate into and out of your field of view and if you just plot the amount of red light versus time blue light versus time green light versus time you can sort of reconstruct what's happening on the surface of this object based on how much you see as the object just rotates you know over the course of however long it's rotation period is so here's an example that you know in for an actual brown dwarf this is about six days of data here on four separate nights you know the span here is about four hours for the third night here and this is brightness versus time and so you see this variability where about a couple percent variability it goes from your relatively bright to get any fainter brighter again fainter brighter and what you're looking at is the brown dwarf rotating it's about a three three hour rotation period and it rotates there are some gaps in the cloud that retired towards us and then rotate out of the field of view and then back again and you see this variability this this change in the brightness due to the fact that this object is rotating and has these gaps of the cloud so you can trace out not just the the rotational period the the amount of patches to the clouds and in fact you notice the variability is not constant it doesn't come back to the exact same shape over and over again the clouds are evolving as we watch they're there they're going away in some places and coming back in others sort of the best example of this is you know again closest Brown door to the Sun alumina 16 a particularly the lower mast member of the binary lumen 16 B in a cross field used the very large telescope in Chile to put together this map of the surface and here's a clever trick which was not to just monitor brightness over time but also to monitor the spectra at the same time and therefore core the Doppler shifts of the material and so here's able to tell you know not just that you know that they're you know bright splotches and dark splotches coming in but could actually figure out where on the planet I in in latitude those that those bright and dark regions were jacked and as a result of putting it all together he create a surface map of what the clouds actually looked like for this object and so this is you know an actual you know map of this of the surface of the cloud layer of this brown dwarf that's just a couple you know a few light years away and as an aside ian has a great website here that will allow you to cut out this little model of Luna 16 and get either a cube shaped or sphere shaped depending on how good you are with scissors and folding for four lumen 16 so just just Google in across field and in 16 and these great patterns you can download and print outs okay alright so I promise in the title that the question of where did brown dwarfs actually fit in you know should we think of them more as failed stars should we think of them as overachieving planets you know on this continuum of mass from the stars down to the giant planets where should we think of brown dwarfs are they're more like they're you know planetary Matt they're their planetary little brothers or more like they're their star older siblings and so think about that I'm going to take a little bit of a detour out of astronomy and back into humans and I'm going to I'm going to show you this this graph is with very little context this is a graph showing fat mass index versus fat free mass index these two measurements that they're basically a derivative of the body mass index which is your weight divided by your height but it's broken up into how much of your how much of that mass is your fat and how much that mass due to everything else particularly muscle and so if I ask you you know does it look like the the the people represented by these purple dots are the same populations that people represented by this these red dots hopefully you would say no these look like two different populations again I'm giving you no no context I haven't told you you know what's going on with these two objects but you'd probably say to yourself something is different there's something different for the for the purple set of points compared to the red set of points something different in formation or or development over time something is fundamentally different about these two populations and sure enough the purple population represents men who have not undergone any particular training and the red represents secretory class sumo wrestlers the highest-ranked of sumo wrestlers and so without knowing anything about you know sumo wrestling sumo wrestlers dietary requirements or their training regimen we're able to tell that there's you know two different populations that work here just by looking at the demographics and I highly recommend this paper hierarchical differences of body composition to professional sumo wrestlers when I pulled this plot from but you know it's a great example of how you know with demographics you can learn a lot about formation about development just by being very clever about what measurements you make and how you consider objects of different types okay so our goal is to something similar for it for brown dwarfs and planets if we can find the right set of variables the equivalent of fat free mass index and fat mass index can we make a plot where the brown dwarfs are clearly separate from the planets or do we make plots where there's a same distribution and that's what we really ain't aiming to do now so this burger you know the the project I'm currently working on which is called the generate planet imager exoplanet survey or G pies that the goal of which is to discover planets and brown dwarfs to characterise them and really to push on the fundamental nature and how they formed and evolved over time and really to answer these key questions our plants can brown dwarfs you know really the same population or are we looking at you know two different sets of objects that form differently the technique we use to discover these brown dwarfs is something called direct imaging and the idea is you know straightforward enough you take a picture of a star and you see if there's a planet or a brown dwarf orbiting that star it's a straightforward technique was actually quite challenging technically and the example we always give is imagine that you're staring directly into the beam of a lighthouse and you're trying to spot a firefly that's sitting on the lighthouse beam but the sort of the order of magnitude we're looking at the you know planets tend to be about a million times fainter than their parent star and so you need a way of just digging out underneath the glare of the star to see the planets at the brown dwarf that's hiding on behind it but remember we know the trick if we go for young objects we have a better chance young planets young brown dwarfs they're hotter they're brighter than their older counterparts so if we can limit ourselves to young stars we have a better chance of seeing the planets that brown dwarfs that are that are orbiting them we have to do one more trick as well you know I know we all love the atmosphere it allows life and things like that but it's really awful for astronomy the atmosphere does just horrible things to the light from stars as it passes through through the air and so we have to use adaptive optics to correct for the things the atmosphere is doing and to you know restore the the light to what it was before hit our atmosphere and just as an example here's an astronomical object image with one of the largest most sensitive telescopes in the world I'll give you a minute to try to guess what object that is if you guessed the planet Neptune you're correct so you know this is this is you know the same telescope state I was looking at the same planet you know without adaptive optics and with adaptive optics so you you know this is you know a really nice to a set of technologies that allows you to that's allowing us to you know get correction what the atmosphere is doing and in the case of looking for planets and brown dwarfs to really get behind the glare of the star and see what's going on and so um as an example of what you can do with this this is this is the HR 8799 system this is a system of four giant planets orbiting a nearby star the stars the center has been blocked out by by the instrument and we see this movie that runs about you know eight years long showing these four giant planets between about five and eight times the mass of Jupiter orbiting that star over this eight year period and they obey Kepler's laws like they should the inner one the most the outer one moves quite slowly but you know this is an example of what you can do with direct imaging you can you know you can detect these planets you can study them you can watch them go about their orbits and the whole goal of the G PI survey is to find more of these objects just to study the ones we already know about to add more to the list and to really get a you know handle on you know where they came from and and what we can learn about them so this is a little slide here I'm just showing the the g'bye he was about a hundred of us scientists and engineers all working together to try to you know make this project a success we're based at the the tell us the instrument is based a telescope called gem-knight South in the Chile and the chili here it is a top Serapis on the the summit of the mountain there this this is the Gemini South dome inside is an 8 meter mirror so about 24 feet edge to edge there beautiful primary mirror allowing us to get you know really good resolution on the objects we image and just before you know we observe we all you know go to visit G PI here hanging off the back of the telescope so again this is the mirror up here pointing upwards and this blue box here is G PI hanging off the bottom of the telescope so you know it's a mountain so some nights are not so good and try to control console yourself with a long exposure camera and a flashlight and making small you know frowny faces to draw attention to the unfortunate number of clouds there in the sky and some nights it's quite good it's you know just you know beautiful sky up there you know relatively far from city lights ignore those city lights the in the background there but you know it's just you know nice you know a beautiful night sky they're allowing us to go and look for planets as an aside this is being to pick it has a plan they were opening itself alright okay one of our big discoveries with G PI's was the discovery of a planet called 51 Eridani B this was a relatively early on in the campaign we discovered this planet's a beautiful artist conception here it's about two and a half times the mass of Jupiter orbiting got about 30 day use so the equivalent of a little bit beyond the the orbit of Saturn in your own solar system and it's you know a t dwarf type planet orbiting a relatively young star this is what the actual data coming off of G PI looks like G PI takes data in such a way that we can produce an image at a series of wavelength slices and stacking them about on each other and so this movie is running through wavelength showing the spectrum of the object as we go and each individual object each individual image shows the the data we have at that particular wavelength and so right here you see the planet pop up and then fade into the noise and the reason it's the spectrum is changing so much is just because of how these T dwarfs Factory actually look there's there's a lot of methane absorption here on the right a lot of water absorption here on the left and flux can really only escape between those two absorption bands and so you get this peak of emission between the two molecular bands on either side zooming out a bit to the the full spectrum this is sort of almost a classic T dwarf spectrum a lot of these you know peaky emission peak emission features in between you know really deep absorption bands from molecules and so from the spectrum we all do plot the temperature we're able to pull out the amount of you know patchiness of the clouds on the surface and a lot of the you know just the fundamental properties the atmosphere based on this you know really exquisite spectra we get from this planets and so again though this is a plant in about a hundred light years away that we're able to you know really get you know just exquisite detail on thanks to the high fidelity of the of the GPI instrument okay so in addition to 51 airy we also discovered a brown dwarf hd25 62 that's the brown dwarf there the the trick in direct imaging is you always look for the little arrow and that tells you where the the planet of the brown dwarf is so yeah so you know we have a series of planets 51 area new discovery recovered previously known planets that we're known before this area began also pulled out some previously known brown dwarfs as well and end up with you know a pretty good yield of planets and brown dwarfs there's some the hundreds of stars we looked at and so I like to condense this all into a single plot that I like to call the tongue plot and there's a lot going on here so I'm gonna try to walk you through it through it a little bit slowly here so on the x-axis here we have seven major axis national McLeod's this is the distance from the star so lives that 1au from the sun saturn lives 10 au from the sun and so moving out getting further and further away from the star masses on the y-axis here from one jupiter-mass up to 13 Jupiter masses the line between planets and brown dwarfs up to about 75 Jupiter masses the line between between brown dwarfs and between stars the red dots are the detection z' these are the six planets and three brown dwarfs that we found from the GPI survey of the first 300 stars so three hundred stars nine detection z' here and finally the colors and the contours show the sensitivity of the survey the number of stars where we could have seen a planetary brown dwarf of the given mass and center major axis and so for example these brown dwarfs there are 160 stars we could have seen a brown dwarf like these things and something give us the rough frequency of these objects by knowing how many stars we could have seen them seen them around and how many we actually saw is roughly three out of 160 is the current rated brown dwarfs as you move down to the the tip of my tongue as I like to say down to these two objects here on the 16 star contour we're much less sensitive to giant planets and that implies a much higher occurrence rate given that we were barely sensitive to play us down here and yet we picked up two and so everything in the survey is encoded in this one very busy plot what we actually saw and what our sensitivity was and by careful analysis of this we can try to work out what the underlying distribution was actually like and so for example one of the tricks we can play is to break things up by stellar mass break things up by the mass of the host star so I'm just gonna move everything that's above one-and-a-half solar masses anything bigger than 1.5 times the mass of the Sun we move all the stars all the objects around them to the right and everything below that line below one-half solar masses to the left and what you see is all the planets they're orbiting the higher mass stars this is surprising for a couple reasons one there's fewer high mass stars in our sample and two were less sensitive to planets around these higher mass stars and so one of the really big results from the gpio survey is this you know really clear statistical evidence that planets that these giant planets these wide separations are just you know inherently more common around higher mass stars as some that we had hints of for a while but you know really nailed down things to our you know really large sample size and our high sensitivity okay but yeah the the question we really want to answer is planets vs. brown dwarfs what what what does the results the g5 survey tell us about that and to get to that question I'm gonna take a quick step back here talk a little bit about how stars and planets actually formed so stars form in what are called molecular clouds clouds of gas and dust that are collapsing and getting colder collapsing down and forming a star at the center so this is the the Eagle Nebula these little Tufts there are molecular clouds that are collapsing with with young stars forming in the middle there inside one of those molecular clouds that there'll be a little region that's a little bit more dense than the rest it'll start collapsing and a star will form in the center and as that star forms material will form a disk around that star a flat sort of a you know flat disc and material orbiting that star and in this case you know if you're forming a binary star you have two to little clumps in the cloud that are collapsing down next to each other and it will eventually form a binary orbiting each other so this is the way that stars form they're they're they're clumps in the cloud that that collapse gravity pulls them together and you get this disc around them planets will in turn will then form inside that disc so that disc that's currently forming the star planets are going to form through that disc by pulling material down onto them by gravity and certain and getting bigger and bigger as they pull in material from that disc and you've seen this beautiful hardest conception here these big rings open up here with these gaps as the planets eat up more and more material so a beautiful artists conception this one looks like in real life this is a wonderful image from the Atacama Large millimeter Array or Alma of the young star HL tau where you see something very similar you see these these concentric rings around the star stars in the center there with with gaps between them that could easily be caused by planets forming inside of this disk okay so how do the planets actually form inside the disk well we have two competing theories for the way you can get a planet to show up in this disk one of them is this bottom-up process called core accretion and the idea here is that you have solid material in the disk you have Isis and rocks that will come together by gravity they'll collide they'll you know build up to a larger and larger solid core and eventually create gas onto itself and so it's essentially a two-step process so if you want to form a planet like Jupiter first you need to build about ten Earth masses of solid material into a core so again the the gas they the ices and the and the rocks and the in the disk need to form about you know 10 masses of solids and once you go to 10 earth masses your gravity is now strong enough that you can pull a down gas from the rest of the disk you can you can pull on about 300 Earth masses of gas on to your tenure of mass core so you start out with a you know small amount of solids and you have becoming a giant planet just by the amount of gas you're able to pull up pull down from your ear gravity I like to think of this a little bit like compound interest it's you you put it a little bit at a time a little bit at a time and eventually it pays off big if you're if you're able to wait long enough for the for the dividends to really come in and this is very much a race against time because this gaseous disk here it only lasts for about five or ten million years before she's blown away by the young star and so it's it's it's a race that you have to that the planet has to build up the core fast enough so that there's still enough gas left over for it to make a giant planet before the gas is gone forever so if this is a little bit like compound interest the other method is a bit like learning you have a long-lost uncle who's left you a ten million dollar inheritance it's it's called gravitational instability this is where materials based just thrown onto the planet very very quickly instead of taking millions and millions of years in this simulation takes about four hundred years it's you know much much faster and what's happening here is you have a disc that it's it's not a you know perfectly smooth disc there's areas that are a little bit more dense than others as the material in the disc orbits around the stars those dense regions start get to more dense the the gravity of over density pulls in more material to it and you very quickly form giant planets just just by the material but just by the self gravity of the material in the disk if anything it's almost too efficient it's just so easy using this method to form you know very large planets all throughout the disk so we have these two competing methods of two competing theories of how you'll actually form giant planets in the disk and we can ask the question then what do they predict what do they predict that jeep I should have seen from three hundred stars we looked at if either one of those is true start with quark reaching so core accretion is a much more efficient around higher mass stars so you'd expect to have more objects around higher mass stars of core accretion holds similarly core cretians is this race against time you have to form your object very very fast before the gas disc goes away and so you start to see more low mass plants than high mass planets it's harder to get more gas onto the planet if the gas disc is going right away in just a few million years and finally the preferred location for these objects to actually form under the core accretion scenario very close to what's called the snow line where where water and other material can fall can freeze and ices and so you expect plans to be closer in compared to further out and you get very different predictions from the other method from the gravitational instability method it doesn't actually care what about the star is it is sort of the efficiency is independent of the mass of the star you tend to get more high mass companions than low mass companions it's just such an efficient method that it's really easy to just keep adding mass and to get planets to get more than brown dwarfs to get you know very high mass companions through this method and I'm like ground unlike core accretion it will form objects anywhere in the disk there's no preferred location to put a planet that they should appear throughout the disk okay so we have these two different predictions for where we should find objects which of them actually matches observations well core accretion actually matches the planets that we saw with G pi and gravitational instability matches the brown dwarfs and so for the first time we're actually you know seeing some you know tentative evidence that we actually have different formation mechanisms for the planets and for the brown dwarfs at least of these wire separations were GPI sensitive and so again this is you know small numbers we you know we only have less than a dozen objects but but there were you know early results are you know pretty interesting and pointing us to this you know really interesting direction that we're seeing a difference in formation for the planets for the brown dwarfs and that these aren't just that you know the same set of objects all form the same way but there's a you know different formation and so there's a different underlying history behind the true sense of objects okay so again early results what we're still looking at the the remaining stars in the survey we've mostly finished up our survey German myself we have plans for the future now to go Gemini has two observatories one in the South one in the north this is again G PI here with friendly on the court on lookers in the back and we have a going plan to upgrade G PI to make it even more sensitive to be open they pull out you know even fainter planets from the data and move it to Gemini north and so the hope is you know you go to the northern hemisphere there's there's more stars that are accessible to you and we can you know continue the survey and hopefully you just you know make these results even more robust one more way we're gonna learn about brown dwarfs going forward is there's a Space Telescope called Gaia and Gaia is has been up for about two or three years now it's observing every single star in the sky and very precisely measuring their position over time and so it doesn't go quite faint enough to see many brown dwarfs by itself but guy is going to see these stars with brown dwarfs orbiting them you know of showing the reflex motion the star is going to move slightly on the sky in response to the gravity of the brown dwarf orbiting it and we could actually pull a lot more brown dwarfs indirectly through Gaia and actually get their masses through the through the guy orbits which is pretty exciting and finally a connection to hear it's a here at SLAC LSST is going to help a lot the large synoptic survey telescope the camera for which is being built here at SLAC elseís Hughes actually on the same Alton is Gemini south just a little bit off to the right here outside this the field of view here as Jim myself and here else s T it was gonna be an 8 near telescope it's going to survey the entire sky every couple of nights it's gonna be you know really sensitive to brown dwarfs and hopefully pull out you know a lot more so again you know we've in the past 30 years we found about 2,000 brown dwarfs going from 0 to 2000 in just about 30 years again we have a long way to go there's about 40 billion in the Milky Way galaxy but you start somewhere okay and so I think I'll stop there and just take any questions thank you we will take number of questions but the way the system works you those of you have visited here before already know that you have to raise your hand in which case if I recognize you you have to push a little button and the light goes on on the microphone and then you can start speaking to the microphone so we don't have to have microphone runners here okay so if there are any questions so let's let's start with you yes you talked about using hydrogen and choosing two terrarium which happens in brown dwarfs other a class of stars that feels lithium even though they're not hot enough to fuse hydrogen so so yeah so all stars to diffuse lithium they're gonna most stars will run through their entire primary oh Bosch of lithium quite quickly some stars and you can't get it to here but but some of the higher mass stars there convert to convective envelope is actually a quite shallow as think actually preserve their lithium for much longer because the lithium at the surface never makes it down to the core but every star's gonna try and get rid of all of this lithium but as such a trace amount remember for every one lithium atom you have a billion hydrogen atoms so most of the energy of the stars and they come from hydrogen but but the the lithium is just sort of this extra a little bit of additional abuse so I mean the star with less than 75 Jupiter masses it would not fuse lithium so as always the stronger the answer is tricky for the low mass brown dwarfs about down about below about 50 Jupiter masses they never fuse their lithium it turns out actually that the higher batch brown dwarfs actually do fuse their lithium a little bit at a time so the higher mass brown dwarfs the core will actually get hot enough for a brief period of time where will fuse some of that lithium away so there's actually a differentiation of brown dwarfs between those that fuse lithium in those that don't thank you so you're you're getting light curves off of there your iron look liquid iron clouds and so forth how are you filtering if how do we filter that in transit data for smaller stars like M Class stars and and below we're trying to find planets using transit data so so yeah so there's a neat trick he used with transient planets as well which is what we call phase curves and what happens is if you have a planet that's close enough to it to a star it actually gets totally locked just just like the moon shows the same face to us as it orbits these planets show the same face of their star as they go around because they're so close to their star they feel these an immense tidal forces and what that means is there's a hot spot that's always you know that that's basically bathed in the perpetual sunlight and a dark spot that's always in night time and so there's a huge temperature difference between the the front of the planet and the back of the planet and so there's actually really cool observations using the spitzer space telescope and others that as the planet goes around you see the combined light of the star plus planet get a little bit brighter and a little bit fainter as the bright spot of the planet points towards us and then points away from us and so you could actually map out the temperature structure of these transiting planets based on these phase curve measurements looking at the bright side and the dark side of the planets so you mentioned during the lecture that the stars surrounding the Sun are more red or there's more red stars why is that yeah so basically just comes down to the way that stars form there's a huge preference for making lower mass stars there's for making the higher mass stars it's just the fundamental physics of you know how these a little over densities in the clouds form most of the over entities that form tend to be on the on the lower mass end and so lower mass stars are red and so most of the stars you know near the Sun are actually quite red so you know again it's almost ten to one you know most of the stars are these lower mass stars and then just a tiny fracture the ones like the like the Sun are bigger than us thank you so you talked quite a bit about brown dwarfs that are orbiting stars do you believe there are large populations of brown dwarfs that are not orbiting stars that are in between stars oh yeah absolutely so you've seen my bias where I look for faint things next to bright things so I spent most of the talk discussing the brown dwarfs orbiting stars but there's been incredible work seeing isolated brown dwarfs so either brown dwarf boundary of binaries or just isolated brown dwarfs and with the advent of you know large-scale surveys that survey the entire sky especially in the infrared we've detected you know really thousands of these objects and so you know there are quite a few it's more difficult for them because we if there's a brown dwarf orbiting a star we know what the age of the system is but you so knowing how old the star is if there's a brown dwarf by itself so a little bit more difficult to piece together what's going on there but we still have you know these really large samples of just isolated brown dwarfs all over the sky so you've said you know the cooler stars the smaller stars are far more populous do we have any reason to or what do we believe the population of brown dwarfs is say relative to M stars yes so the numbers we have from the smaller neighborhood is that for every 350 star there's about 50 brown dwarfs so it's about 7 to 1 and as to how whether there are more high-mass brown dwarfs than low-mass brown dwarf that's actually in ad area to sell you right now and I'm actually hoping to be able to get some more data shortly it's an answer that's you have to push the button on yeah that's it does it doesn't kenny brown dwarf have small planet like objects if so have you found one that has it if not is it not possible yes that's actually a great question in fact the the first planetary mass object found outside the solar system via direct imaging was orbiting a brown dwarf as it's a brown dwarf with the creative name to mass 1207 was about a 27 g per mass brown dwarf orbited by about of five jupiter-mass planetary mass objects and i keep saying the words planetary mass object for fun i international astronomy union rules a player is a thing that orbits the star and therefore because it was overlaying a brown dwarf i am legally not allowed to call the planet guards will rush in and tackle me if I try but but you know you can easily get you know planetary mass objects that orbit these brown dwarfs and so you know how those form and when they that's different from normal planet formation that's actually a really interesting question that we're trying to look into what's the brown doors name so the this is a sad part about being an action plan astronomer that that all of our objects have very very boring sort of serial number type names the the shorthand we use is to mass 1207 from the the to mass survey and 1207 is a shortening of a 15 digit number which I can never remember but it's basically based on where in the sky it is and so there's actually been a nice recent movement recently by the International strata me Union to actually give names some of these planets and every year a year or two they actually have a public contest to actually suggest names for some of these objects and so you know hopefully some of these you know crazy or serial numbers get replaced or something that's a little bit more you know friendly to years what is the planet like objects name it's even more boring than you would think so in in astronomy when we find a binary star we attach a B to the name of that's a capital B to the name of the companion so for example HRT's have been so Alpha Centauri becomes Alpha Centauri a and Alpha Centauri B when we find a planet we attach a lowercase B to the Stars name to show to show that say you know a planet not a star and then as we add find more objects they become so a charged seven nine nine has a charge ten nine lowercase B lowercase C lowercase D and lowercase e and I feel very ashamed having to you know it admit the way we do things as astronomers questions yes of the head is a mass the size of Jupiter is there a certain amount of the heat generated from the gravitational contraction yes yeah so I sort of left out you know where all this heat comes from why they're cooling over time and a lot of it comes from the gravitational contraction of formation they start out slightly larger so I said that all planets of ground are about the same size that's mostly that's only half a lie they'll come down to about one Jupiter radius they start out somewhere around two or one-and-a-half Jupiter radius and they slowly contract over time and so the the the temperature the the the brightness we see is them converting that gravitation potential energy into heat and therefore in into brightness and so Jupiter for example right now the the the total amount of energy admitted by Jupiter is about half and half half reflected light from the Sun half residual gravitational energy from the last a little bit of collapse so most of most of the energy from the Sun is coming out visible the the subway see most of the gravitational collapse is coming out in the Indian ffred do you have confidence that you've found pretty much all the brown dwarfs dwarfs and our 10 parsec neighborhood very little confidence so you know the you know these brown dwarfs get you know incredibly incredibly cold and so that this this Y dwarf category I mentioned for you know most most astronomy Jupiter was the really the only example we had I think it was only about eight years ago that this that the second Y dwarf was founded the first one outside of our solar system and so again these things could be you know and just incredibly faint you know the surface temperature of minus 20 C so it takes you know really dedicated surveys it takes you know do you need to go really far into the infrared to chase their flocks and so I think there's probably quite a few more in the solar neighborhood so I say twenty billion if there's probably a lower limit on how many are in the galaxy there's a question of my daughter why are brown dwarfs called brown dwarfs oh I actually skipped the most important parts yeah so where does the name come from again more dumb astronomy names for things we basically classify stars into two types that the big ones we call giants the small ones we call dwarfs were very unimaginative lots and then if you think of the M stars these are the reddest stars that we have and we and Brown were first theorized about the 1950s about 30 years before the first one was seen but we already have sort of a rough idea of what they should look like based on what we knew about stars and so the the if you imagine a red star a brown one has been cooler than that has to be even redder than red what's redder than red brown brown sort of the next thing that comes up when you think about something that's you know even cooler even redder than the reddest star and so it's not a giant it's small their forces dwarf its rather than red therefore it's brown and we in a in a moment of just you know beautiful naming we call them brown dwarfs for the brown dwarfs that are not orbiting a star do you believe they formed differently uniquely in themselves or they were they flung out of a system what it what is the mindset there there are beautiful theories that for both those things there's a you know some of the pictures are you have molecular clouds you have two forming stars orbiting each other and then one gets flung out before it can it create enough mass become a star so it's necessarily the accretion theory of how brown dwarfs come from the other is just sort of that no they're just the low mass end of star formation that that's you form you know a very small number of big objects some number of small objects and some number of them release us small ones and I'm not actually sure you know where theory has come down on today but there's a couple of competing theories as to you know how you formed these isolated objects question at this point because I think we're running a bit short of time but please go ahead one of my colleagues that ever asked me to ask you this could you talk a little about Planet X and how that got discredited or not so yeah maybe for some people you might need to define it so I will freely admit that it's well beyond my my field of study and I've I don't know the the final answer on you know how is thought of the the back story was based on the distribution of Kuiper belt objects these sort of no comment like objects you know beyond the orbit of beyond the orbit of Neptune so things like Pluto and the other large objects that there seem to be signals in there we assign and how they were disputed on the sky that seemed to indicate there was a higher mass object orbiting at the wide wider edge of the solar system and I I will unfortunately admit that I don't know the latest research as to how things stand now but some of my colleagues are here you can come up and ask afterwards and hopefully they have a better answer for you taking questions here but if there are any pressing questions few of us Eric possibly Leah myself and maybe Bruce will stand outside here and please don't hesitate to ask us and Eric again and once again I look forward to see you here in two months thank you [Music] you you

Channel: SLAC National Accelerator Laboratory

Views: 68,112

Rating: 4.723485 out of 5

Keywords: SLAC, SLAC National Accelerator Laboratory, Stanford University, Science, Planets, Space, Spectroscopy, cosmos, brown dwarfs, stars, cosmology

Id: 6yaFU6HyTY4

Length: 72min 54sec (4374 seconds)

Published: Wed Jul 31 2019

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Giant planets can be up to 13 times the mass of Jupiter, while the least massive stars are about 80 times the mass of Jupiter. In between are objects called "brown dwarfs" – too massive to be called planets, but not massive enough to burn hydrogen and shine like stars. Since 1994, a few thousand brown dwarfs have been observed close to us in the galaxy. But, what are they? Are they more like half-pint cousins of stars, or more like overgrown planets? This lecture explains how we observe and study brown dwarfs and what we have learned about them. It describes clues to their nature from their composition and their evolution over time, and the insights they give us into how stars and planets are born.

About the Speaker:

Eric Nielsen is a research scientist in the Kavli Institute of Particle Astrophysics and Cosmology at Stanford University. He obtained his PhD in astronomy at the University of Arizona, and was a postdoctoral researcher at the University of Hawaii at Manoa and the SETI Institute. His research interests include searches for exoplanets, brown dwarfs, and the demographics of giant planets. He has collaborated in a number of planet-hunting surveys, trying to directly image giant planets around young nearby stars, including the ongoing Gemini Planet Imager Exoplanet Survey (GPIES) using the Gemini-South Telescope in Chile. This work includes the discovery of 51 Eridani b, a planet two-and-a-half times more massive than Jupiter. Nielsen is working to apply lessons learned from these ground-based surveys to future space-based missions that will image planets similar to Jupiter and Earth found orbiting distant stars.