How fast does the Sun orbit the Milky Way? | Brian May's Astrophysics Thesis on Solar System Dust

oh that is a hefty hefty thesis and yep I read it and I really wish at this point I could say please welcome special guest a Brian May but I can't because he's Brian May and I'm just here in my state bedroom talking to myself again some of those that don't know Brian May is actually a doctor of astrophysics he started his PhD in 1971 Imperial College London in the same year he also started a band he played their first gig with the lineup of Brian May Freddie Mercury John Deacon and Roger Taylor which we all now know as Queen so he continued his research for his PhD through 72 and 73 but in 73 they signed a record deal and they had huge success with their first album and again in 74 with the second album and that's when Brian May abandoned his thesis [Music] in order to go tour the world with Queen by the next year in 1975 Bohemian Rhapsody had come out and essentially catapulted them to start him so after Queens incredible success worldwide throughout the back of the 20th century in 2006 Brian decided that it was about time he went back to Imperial College London and actually finished off his PhD picked up where he left off wrote his thesis all 215 pages of it how long my thesis is hang on 189 damn it well regardless of thesis length finishing something like this which is such a large part of your life in such a massive piece of work after only three or four years is an incredible feeling what Brian had to do was come back to it after 35 years away science changes so much in that time fields move on we get new results things are looked at differently but thankfully the field that Prime was in actually his research was still relevant because minimal amount of time have been spent looking into this before because what Brian was researching was dust and this is why I'm surprised they publish this to the public is a book that you could just go into a bookstore and buy because it is so incredibly technical astrophysics thesis by definition it has to be technical so it's so dry and in-depth on something that like even I am like sometimes like oh either a bit over my head or just puts me to sleep because I don't really care about dust I think most of Shonna Mo's would say that as well we actually care about the stuff behind the dose we care about the stars and the galaxies and the black holes and the dust is just stuff that gets in the way and stops you from looking at what you actually want to look at there's not something that you necessarily want to study but the thing is you kinda have to study it because if you don't understand the dust which blocks light from behind it then you're never going to understand the light that you're getting from the object you actually care about so it affects everything the highest cited paper of all time in astronomy is a paper about how much you correct your observations by because of dust what actually is dust it's question I get asked a long time which I got dust in space interstellar dust but what is it actually made of well it's essentially anything heavier than hydrogen and it's particles that are either ranging in size from a few molecules across to a fraction of a millimeter across and essentially it comes from stars it's the waste product you get when a star dies so when it stars happily living its life it's just fusing hydrogen into helium and that's what gives them energy to shine and give us heat the way the Sun does but when that runs out of hydrogen to burn it then starts to fuse helium together to make the heavier elements like oxygen carbon nitrogen all the way up to iron so that when the star finally dies and goes supernova it throws out all those elements into interstellar space disperses them around that you end up with this really diffuse dust and so we think the Sun and the solar system formed in an area where a star had lived and died otherwise where would we have got those elements from to form the earth and you and me out of carbon oxygen and nitrogen so wherever there are more stars like in the center of the galaxy you're gonna get more dust and the thing is those dust particles are opaque so they effectively block the light from the center of the galaxy so the way that it does that is because the wavelength of light that comes in like optical light is very similar to the size of the particles in the dust cloud and so what happens is that light gets bounced and scattered around and so never makes it out the other side if you have a longer wavelength of light like infrared light that kind of to just go around all those dust particles and can make it through so the way we see to the center of our galaxy is using infrared light you look probably notice if you've ever been to the southern hemisphere and look towards the center of our galaxy in the sky and seen a load of dark dust fans blocking a load of stars it's also responsible for things like the coalsack canopy in the southern hemisphere sky as well but wherever you've had planets form around a star you're also gonna have dust and so there's a lot of dust in the solar system and this is the dust that Brian May was interested in because this dust we're so close to it and the light that it will be blocking from getting out the solar system is the sun's light but it means that on earth what we ended up seeing is all the light that scattered around and back to us this dust appears to glow in our sky and we call it the zodiacal white zodiacal because we find this glow along the constellations of the zodiac in the sky ie the route that the Sun Moon planets all take through the sky which when you think about it well that's just the plane of the solar system so if you've got dust in the plane of the solar system that's where you're gonna see the glow from that dust in the sky so you might have heard this called the false dawn before because it's really easy to see right before sunrise and right after sunset as well especially when the zodiac is making a really steep angle to the horizon so I'm talking about like spring and autumn times and the nearer to the tropics you are the better as well the thing is though you know any bright moon and any light pollution completely swamp this light it's actually brighter than the Milky Way in the sky so you should be able to spot it relatively easily but you need a dark sky to do it so next time maybe you're on holiday or camping or something somewhere where the night sky is dark so it still begs the question why would anybody want to study dust in the solar system when they can study things like black holes instead like I do but there are a lot of reasons that we need to do this the first one is that any observation of oh say a galaxy or a star that you're trying to make that happens to be along the zodiac you're gonna need to understand the light that you'll also be collecting from the zodiacal light the second reason was really big in the 70s when Brian started his thesis and that was because it was during the space race and people were worried about the effect of these tiny micro particles if they were traveling at really high speed if there would be a danger to spacecraft number three is that when we look out and find exoplanets around of the stars we see them forming in these dusty discs so perhaps by studying the dust in our own solar system we'll be able to understand how planets are forming around other stars as well so in particular what people do is that they look at the zodiacal light and they try and work out its composition and also its motion in the sky as well to try and understand how the solar system formed so this is particularly what Brian May was interested in he was trying to probe the speed or a velocity at which particle were actually moving at Invista Scot and that should hopefully give clues as to how the solar system as a whole had formed so the title of his thesis is a survey of radial velocities in the zodiacal dust cloud so if you do want to go out and buy this great but it's also available online and I'll link it in the description below but what's really cool is that there's a lot of images in this thesis slow which is not really typical of a normal thesis but what he does is he put in images that he's actually taken himself when he's gone to the observatories in tenerife up in the mountain of the night sky and the glow of the dust cloud and then also of the mountains and of him working up there as well which is pretty cool and there's a forward from his professor and from him as well about his PhD and why he went back to it and it's a really really nice read actually so 10 out of 10 would recommend so chapter one of Brian's thesis is actually a really nice introduction to the zodiacal light especially sort of the history of its observations as well and its historical significance in various different cultures which is a really nice read there's also a discussion on whether it's variable as well apparently Cassini was convinced that it disappeared like in the latter half of like the 1600s which is a really interesting read as well and it's definitely the easiest chapter to read as someone who isn't an expert in the field like I would recommend if you're gonna read anything of his thesis read this section it does get a little bit scientific and mathematical halfway through but if you remember sort of like geometry in high school you probably able to follow it quite easily so chapter two is the typical science paper this was my experiment and my setup and the observations that I did the first half of it is really nice it talks about his trips to Tenerife and there's a particularly awesome photo of him up the mountain with the instrument that they use to try and this which I absolutely love God 70s was just the decade of hairography wasn't it it's amazing in particular as well there's a diagram showing the map of the sky that they were trying to probe and there's just this one big area over here that's like bit that was obscured by hut it's just like so unscientific but yet so true at the same time we couldn't fit it fit because with the building in the way the rest of the description is a very specific description of the instrument on the telescope they were using it how it works which I do not understand but I like to exploit the fact that somebody else does so I can do my own research that I care about so that chapter 3 is then all about how you reduce the data when I say that I mean how do you go from the raw image you get off the telescope and remove all the sources of noise and bias in your instrument and stuff in the sky as well how do you remove cosmic rays and trails from satellites and this chapter I can really empathize with because this is what I spend you know maybe a quarter of my time doing is grappling with data and trying to get it into a usable format so it is painstaking to actually do this but it's so necessary to document it so that people understand the steps that you took to get your final images that you then publish what I love is that the code that he used to do this is actually printed in the back of his thesis as well and it's in Fortran which is this really sort of like retro code and everyone used to program in capital letters as well so it looks like it's just like yelling at you like yelling at the computer like do this if this which is not something we do anymore like put code in the back of the thesis because I mean we literally use code to do everything the data reduction making the plots writing the actual paper itself so what we tend to do instead now is actually publish the code online in a repository a special website called github for those who know it where you publish your code so that people can see it people can download it actually use it you know for this if you wanted to use this code you would have to like type it all back out again rather than just downloading it so it shows I guess how times have changed a little bit since 70s and even in since the last decade as well so chapter 4 is actually all about the results that he got from his research was really interesting it talks about how the data that he has supports the idea of what's called a heliocentric dust model ie a dust cloud that is centered on the Sun and it is orbiting around it as well he talks a bit about how there's some evidence for seasonal variation because seeded observations in April and they--but observations in the September as well and so that could suggest that maybe the dust cloud isn't homogeneous it's kind of like lumpy and different in certain areas perhaps due to the fact that we have comets that come in on these huge elongated orbits that orbit around the Sun and they bring more dust particles with them as well because the Sun heats the icy exterior of the comment and it throws off that huge sort of dust and gas trail that we're so used to seeing in the sky as a comment then there was also an unexpected resort as well and this was the result that he hadn't actually managed to publish before he went off to tour the world with Queen so he published two papers describing his research and showing that you know the results were consistent with this heliocentric dust cloud model of the solar system and there were some seasonal variations and he talks about in the beginning of his thesis how he was really miffed that he didn't get chance to publish it because someone actually picked him to the post in 2004 which was just after the u.s. sees probe had flown past Jupiter and it started to register these high velocity impacts of dust particles but they weren't coming from the direction of the Sun they were coming from the other direction they were going from outer space and so it was the first evidence that we were actually getting interstellar dust particles transiting through our solar system the thing is Brian May found evidence of that in like 1973 so he shows this in these bigger 4.6 and he shows the velocities of the particles that they've measured throughout the night in September and then in the April observing that they did as well and what they've done is shaded green the areas of the plot where if you have a model of a heliocentric dust cloud those are the skis that they would have and you can see that the speeds they measured were way outside that and they do this by measuring what we call wavelength shift because of the speed that the particles are traveling at so it's what we call a Doppler shift because the particles are either moving away or towards us they will get shifted to longer wavelengths or to shorter wavelengths and the way they probe that is by looking at the spectrum of light that you get out finding one of the absorption features that you get from heavier elements in this case magnesium where magnesium is going to be absorbing a specific wavelength of light from the Sun so that when you get that reflective light back you have this feature where there's a dip in the light and that wavelength but you can see if that's been shifted relative to the wavelength we know that the magnesium absorbs that at least on earth in the lab is stationary and so you can see whether it's moving away or towards you by that shift in that absorption feature and so the wavelength shifts they were getting were just too high to be part of dust clouds orbiting the Sun and so they realize these particles must be interstellar dust particles coming from space transiting through the solar system at least we say they're transiting through the solar system but really what's happening is that the Sun is orbiting around the Milky Way but then actually what you're going to be doing is that the solar system is transiting through these interstellar dust clouds and that's the motion we're detecting so if you can measure the wavelength shift in this zodiacal light you can actually probe the speed that the Sun is orbiting around the Milky Way and that's really easy to do it's a nice simple equation the fractional wavelength shift is actually just the same as the speed that they're going relative to the speed of light [Music] and so if you put in the maximum wavelength shift that they actually measured which was about point seven angstroms and you put it into that equation then what you get out is about forty kilometers a second which sounds fast but in reality from other measurements we've done to probe this we actually know that the Sun is going around the Milky Way over 200 kilometers a second but Brian also goes into this as well and it's because you have to take into account lots of different effects you've also got the earth going around the Sun about thirty kilometres a second you've got two separate wavelength or Doppler shifts that you've got to account for which is the the sun's movement and then hitting the dust particle which is moving and then obviously then that goes towards the earth and that's moving in that direction if the dust particle isn't moving directly towards Earth you're not actually probing its full motion you're only probing the the motion in the angle that you're viewing as well and so when you take all of that into account you actually show that the model that you come up with actually fits pretty well to your data I mean it's a little bit noisy but you know this was the 70s they weren't working with the most advanced kit back then that we would associate with 21st century science and so yeah we'll take that it shows that by actually measuring these particles in the zodiacal light and the speeds they're going out you can probe the speed that the Sun is orbiting the Milky Way which in my book is pretty cool so then chapter 5 is a really nice summary of his whole thesis he also goes on to talk about the plans for future work to study the zodiacal light more with the group at Imperial College London that are still working on this which i think is really nice but also what he did was he actually drew some really nice diagrams some images of how the understanding of zodiac will I had changed from the 1970s when he started his thesis all the way through to 2006 based on the extra work that was done by himself and then other colleagues as well in those intervening years shows you that you know in the 1970s the picture was you know just a generic homogeneous dust cloud orbiting the Sun but that now we kind of know that it's made up of these different components and so you can see the sort of yeah there's still this heliocentric model but actually it's a lot more complicated than we first thought until this whole diagram allows us to really study everything else in the universe because we now know what we're looking through which in my book is a fantastic accomplishment and just as rock and roll as anything he accomplished with Queen so in 1974 Brian essentially abandoned seem to be calling him Brian like he's my best friend or something like yeah ala Brian Oh hot in here today I'm sure Brian maybe I'm writing a thesis didn't really think it would ever be used as a fan but it's coming in very useful right now sorry Bri the offending hook just chips and nail changing the battery on the camera and I'm really nicked another one bites the dust another one bites the dust oh my universe this thing is so me like an arm workout trying to read this thing oh I hadn't seen this oh there's a really cool picture of him with a guitar up a mountain in the back wish that I thought some might look that cool on top of a mountain

Channel: Dr. Becky

Views: 421,802

Keywords: astronomy, space, astrophysics, dust, universe, brian may, queen, thesis, astrophysics thesis, imperial college london, interstellar dust, zodiacal light, false dawn, solar system dust, radial velocities, doppler shift, orbital speed of sun, milky way, dr becky, dr becky smethurst, rebecca smethurst, becky smethurst

Id: noT8kkdl8hE

Length: 19min 34sec (1174 seconds)

Published: Wed Jul 03 2019