Cosmology's Observational Journey: From Slipher to Supernovae

[00:00:13]that was a joke another astronomers get a student extraordinary drastically always so what I'm going to talk about her lobbies don't give you in the art of about being an observer but also being part of discovery of accelerating expansion of usuals and point of view which is but I start out with this is very interesting both from book by Vera has an important philosophical assumption later which is manifest from the outside inside the universe and must be accessible so where you started process well I like to start in this particular slide to slide that most people have never seen before this is one of this is a copy of one of the plates that Vesto Slipher took in in 1912 it's if you look at the very top it says September 17th Andromeda nebula this is one of his plates where he measured the velocity of the Andromeda nebula you can see the c3 they're three Specter in the middle there the upper and the lower ones that's the pipe that's the iron arc in the middle of it is the the spectrum event all this out like this you may be able to see the HMK right over here so what's amazing about this is that the velocity the came out was extraordinary just three three hundred kilometers a second actually coming towards us now stars have been measured their velocities have been measured for many years and there were some velocities that were rather large but there is nothing like this this score is a revelation to astronomy at that time there was something that was moving this fast as a matter of fact if you go and read you read Einstein's planting the paper on general Nativity he on the small motions of the stars as part of the justification for the observational justification of what he was talking about in the paper he was not talking about the loskis this large this opened up universe who applies a to strange things that were happening so one of the the papers that slifer published back then which many of you probably seen is this paper where he talks about the popular velocities in the spiral nebulae and as you can see almost all the velocities are positive there only a few that are negative and so the few cosmologists that were working on the early 1920s they all knew this they only that most of the nebulae were moving away from from us which was also a strange result there are these huge velocities much much larger than stars and most of them are moving away from us the editor didn't catch it so I don't know so most of you have also probably seen the plate that's on the right so that's the famous of our plate that probably discovered the the Cepheid and m31 that refers to plate a CH 3 through 5 H that's the hooker 100-inch telescope the 335th plate that was taken on it and the final H stands for Edwin Hubble that was taken in October October 6 1923 the Hubble took a bunch of plates at the end of 1983 ostensibly trying to find no B which worthy work for the subject de jour at that time we marked some some movi with his his pan here and you can see he marked them and here also I don't think he actually was the one that linked these plates I think someone else did but doesn't matter the things that he was looking for were no B and of course you know the story instead of he also discovered something now most of you I'm probably none of you have ever seen this before so on the right is a plate that I have it on loan from the Carnegie Institution I was a Carnegie fella for quite a number of years and I sent you this plate for other reasons and I'd like to point out that so here are the novi you can see how bright they are the star that Hubble discovered the Cepheid number one that he discovered which set the scale of universe is that being star right there you see that he was not good an observer that he was looking over this plane for very very faint objects he noticed an object that was appearing and disappearing right at the clayton limit he was an outstanding observer I I just marvel over the fact that his eye caught this as he blinked the plates pop back and forth this object appeared in disappear because as an observer when you take plates like this the seeing changes and so the objects the very platelet appear and disappear over time seeing something regularly appear and disappear upon plates such as this for me is a remarkable achievement so I'm going to skip over Lemaitre for a little while and I'm going to jump to the next sort of milepost in an observational astronomy that piece was important to me his wiki is shown here on the left I hate the photograph where he's going like this it makes him I didn't know Zwicky at all but he looks like a clown going like this he was of course a really serious grilling an astronomer here he's standing in front of the 48-inch telescope but not Wilson that's me in a Palomar Observatory but he wrote this book which was is a classic and observational astronomy we don't teach much out of it anymore but it really is a very interesting book it's actually used probably more in philosophy classes than it then in astronomy because what morphological astronomy it's very dense book 3 but if you distill what what it's talking about is that if you have no idea what it is you're looking at and don't understand it the way you begin to do science is you create morphological boxes and you classify something you put something in one box and another box in another box and after you've classified a whole bunch of objects you count up the number of objects in each box and you publish an app J letter and then over time you hope that those boxes begin to end up having physical significance but the idea is you always start out with morphological boxes but the thing about morphological boxes is if they don't disappear over time chances are the astronomers that are working in the field don't quite understand what it is they're looking at still which is very true of type 1a supernovae where we have ten different subclasses at least of type 1a soup it gets to be absurd mr. odden either they're variable stars there's a variable star class called RV tari stars and for while the I you was arguing over whether the star RV tari was a member of the RV tari class of variable stars it now is but for a while it was kicked out of the out of the morphological classification okay let's jump to the next astronomer this is a remarkable paper by Allan Sandage on remarkable observer maybe some of us considering perhaps one of the greatest observers in the 20th to 20th century he wrote a paper on the ability that 200-inch telescope discriminate between selected world models and this paper he started talking about measuring these two numbers H naught and Q naught here to not being a deceleration parameter what's amazing about this paper is that in this paper he tells you exactly how he's going to measure Q naught now many astronomers are not going to publish papers on their best ideas saying I'm going to work on the subject no by the way this is exactly how I'm going to do it but Sandage was able to do this for one particular reason he had access to the 200-inch telescope and you didn't so it didn't make any difference he was giving you giving it giving up all of his ideas because he didn't have any competition at that point well I went to after Lick Observatory went to Mount Wilson and the lost Campanas Observatory ostensibly to work with Allan Sandage and that's a whole other story of itself how work with unsanded but when I was working within that I was there because I was working on oral Argost I was not on cosmology he told me that there are only two none two important numbers to measure H naught and Q naught but at the same time there's lots of interesting astronomy to do along the way so I kind of drummed into my mind that that really what I should be doing as an observe a tional astronomers yes study RL Aries but in the context of doing cosmology well sanded and collaborators at this interesting idea of how to use type 1a supernovae which we now know is the explosion of carbon-oxygen of white dwarfs to measure distances into the universe and it's we we now know a lot about them they're still extremely difficult objects to to study because they have no hydrogen in them and therefore the opacity of the material is very low per unit gram and so the these things are horribly in a non non local thermodynamic equilibrium but if you think very very generally of what a type way type 1a supernova is you have a star which somehow white dwarf which is approaching the Chandrasekhar mask somehow it decides to explode and it it goes through to almost statistical equilibrium and produces two oh two elements nickel-56 and cobalt adhesives now if nickel-56 and cobalt 50 cent energy was deposited completely in the supernova you would end up with this red curve over here because this is the exponential decay nickel-56 and this is cobalt 56 but because the gamma rays leak out the actual light curve the supernova looks like this thing and that the maximum is given by something called Arnett's law which relates the maximum of type 1a supernova the amount of nickel-56 that is produced so this is all becoming evident at the time that these three astronomers Alan Gustav and Gustav student green at lymangood began the Las Campanas supernova survey now for me although there was a previous Hubble diagram by Charlie Cowell at Palomar back in the 60s this really was the beginning the pioneers of supernova cosmology because Sandage and Tom on with the help of Brunel I bethought who did this for his thesis tried to find supernovae photographic plates and then tried to measure do photometry in the supernovae afterwards they completely failed and it wasn't their fault that they failed was because the plates at that time that you buy from Kodak had lots of plate flaws on them and you're trying to find supernovae by blinking plates back and forth if you have plate flaws it drives you crazy and so they ended up not being able to find many super novae because of the large number of plate flaws well in 1986 I moved to Sarah to Lolo and having been sort of a student of Sandidge so to speak Sandage urged me to pick up this project but to also do it using CC DS and so we had the first CCD in the southern hemisphere at Cerullo in the formular telescope and in 1987 mark phillips i published this paper which is not reference very much but it actually I think is a very interesting paper because in this we compared to supernovae which were 86 G and whatever the other one is and the we notice that the light curves were different not only were they different they appeared to rise and fall at different speeds and the one that seemed to fall more quickly turns out to be the fainter one and that's all in the paper but this is 1987 this is well before the discovery was made however there was already a paper in the literature by a Russian astronomer soft speed who also saw this in some much much poorer data but much more much larger amount of data from photographic place so although we found this in our data had already been pre discovered by someone else we started the CTO bright supernova survey in 1986 and we produce all sorts of light curves library with Mark Phillips Mario Hanoi no see Jose Moss in the next slide Mark Phillips in 1993 took my photometry and came up with these relationships which relate the brightness of the supernovae we're supernovae you're bright over here and faint over here verse is how fast the supernova is all the way from maximum light so this is called the phillips relationship or as mark phillips likes to call it the sasuke Filippis relationship we then step into trying to do the work that Sandidge and turn on and live in good Rubik we're trying to do and we did this with the help of Jose masa was a professor at University of Chile where we took photographic plates we discovered supernovae and then we followed them up with CCDs and this is the calibration that we came up with but what was amazing was this is the Hubble diagram that we came up with and so here is redshift over here here is luminosity over here this relationship here was so much tighter than any of the bubble diagram that ever been made for us it was revolutionary over here when we correctly correct it to dispersion of a little bit more than a tenth of the magnitude which is about point zero five about five percent in distance that is we could measure distances to objects way across the universe to five percent using this technique well Mari Hanoi went up to Harvard and showed this particular diagram in 1993 we had been I had been collaborating with Brian Schmidt giving Brian some of her data on core-collapse supernova Brian saw that the diagram and got all excited now the clong tolola Survey was created it for us to calibrate type 1a supernovae to measure H naught and kuna that was what we set out with in 1989 and so by 1993 we had begun to work on trying to measure Q not I built a CCD camera and put it the prime focus of the Schmidt camera at Sarah Palolo in 1994 Brian over here peach Alice and myself started talking about how we could also do this on a four meter telescope now we knew Saul parametres group was we doing this but we also knew that we had the calibration on how to measure distance as the Saul didn't so we figured that we could catch up if we work really hard and so we put together a group and I actually was the one that put together the rules of the group and we had two rules in our group the first one was that we would all as a group would work for six months and give all of the analysis of the data to any into a particular group at a university and so we had different universities our Observatory Sarah Tolo ESO Australian National University University Washington Harvard Berkeley etc and and six months by six months we marched down this list piling on more and more data and the other one was that whoever was the intellectual leader of the paper would be first author and I'm really proud of the fact that the Heisey supernova team which were one of the two teams that won the Nobel Prize all the papers be published except for one first author was either postdoc or a graduate student it was not any of a senior astronomers okay so we've now seen seen this it's very nice to have both three Nobel laureates Bob Kirchner and Alex Filippenko to always give the talks on dark energy because they have to explain all that stuff and I get to talk in the stuff that I really like to talk about so I'm not going to go over what Alex talked about but what I want to do stick but I do want to show here is that the room this is so these are the two discovery papers redshift versus distance modulus notice that the high Z supernovae mustered up over here they're about as many of them as at the low Z supernovae and this has now become a problem because the low Z supernovae now have this the larger errors than all the high Z stability so you've already seen this this diagram from the Thule at all and it's a very very beautiful Hubble diagram notice that the low Z supernovae over here do not have remarkably smaller errors that one's high redshift which really says that it low Regin high redshift were being our errors are being caused by something else as a matter of fact we now have no fuel low redshift supernovae that we have higher redshift supernovae so the whole anchor of this whole process is now being driven by the statistics over here and not driven by the statistics over here it's the low redshift sample that is limiting our cosmology at this point with Type Ia supernovae okay the reality of photometry I hate doing photometry I've been doing it 40 years I still can't stand it if you have to worry that the sky is cloudy you have to worry about all sorts of things whereas the spectroscopy is all you have to do is start the exposure wait an hour and start another exposure topology are always worried but it's very important in order to do the cosmology so here are some rough estimates for how good you have to be at doing photometry so if you want to measure the range in the Hubble constant relative the Hubble constant in terms of magnitudes well converting from distance to magnitudes is just the 1 over d squared factor so if you want a 10% if you have a 10% range in the hub accounts that that is 73 versus 67 plug that into this formula and you find that the range that you have to be dealing with is two tenths of magnitude that's easy to do photometry two tenths of magnitude however the equation of state parameter which is what everyone wants to know right now is much more difficult the error in W / W is point for tightness so theorists are asking us to go to one percent errors here if we have one percent errors here that means that I have to do photometry to 0.4 milli magnitudes the original LSST bowl was 20 millimetres magnitudes now this number has gone down because we have to do precision redshifts but no one is doing this level of photometry right now it's impossible for us to do this so we have a bowl of really trying to improve the value of the equation of state parameter but it is much much harder harder than it is to do the Hubble constant just from simple facts of doing photometry most photometry at best get down to 1% there are a lot of other problems with doing supernova cosmology these to me are the really big three big ones and I'm sorry it's a little bit complicated because these are all astronomer minutes but the first one is reddening so in astronomer units this is the color axis this is the the total to selective extinction ratio but let me just say that this number here range is somewhere between 1.8 and 3 we really don't know what the value is it may actually range between those two and we really can't measure this dot this value more than it then to a few hundreds of the magnitude so just right here the errors on the reddening are a few hundreds of a magnitude which already overwhelms the ability to measure the equation of state now we can reduce that by by going to root n statistics but still we do not understand the reddening law in particular we don't understand what it is that's causing the reddening but the size of the grains are we have these crazy reddening laws which are very steep which look like brains which we see nowhere else except around type 1a supernova and type 2 supernova so we are trying to use an object we're not quite sure what is it exploding we're not quite sure what the dust is around it because we've never seen this dust before except in one line of sight towards our galactic center and we're going to try to do precision cosmology with it we're working on it but it's a tough problem the other thing that few people know is the fundamental calibration in order for us to measure something in the sky the brightness of the star we have to measure it relative to another star and you would think that by now we would know the relative brightness of the star to a few percent that is what's the flux of sirius afforded nanometers what is it at one like on we actually don't know that better than 1% and as a matter of fact we probably don't know it even though it's a 2% so I can't do quick Corrections better than that right now until we actually launch a satellite that does fundamental calibrations in the stars in the sky and Gaia will help us with that but we really need a dedicated satellite this right now is the largest limiting factor and our ability to do precision cosmology we don't know the relative flux of any object in the sky except the sound of the Sun is too damn bright and it's also out in the daytime and observing at night so this is a real problem for us and finally this is something that we have been working on really hard and we haven't been able to break this nut but we have this crazy correction in doing supernova cosmology where we say ok this supernova looks a little bit redder than this other one we don't know why it's red it could be for two reasons one is that well maybe there's some dust and it's causing reddening but also could be as cooler supernova so those are two very different parameters one's dust and one's the the temperature of the suit of photosphere and yet we assume that both of those have the precisely same color relationship we love them together into a single parameter so we're lobbying together the temperature of the supernova which is relative to supernovae and the dust properties which may not even be associated with the supernova could be interstellar reddening and we're putting that into a single parameter because so far we can't separate out those two something is red or because it's either cooler or because there's dust and since we don't know what's blowing up intrinsically we have not been able to separate those two that was really a scary assumption that we're still making okay but those those things we all know about in super cosmic in supernova cosmology the stuff that we argue about I'm really going to fortunately show you one particular diagram because this is real ugly stuff is this so I don't really want you to understand it very well I just want you to to accept the fact that this is a real scatter plot and yet we're trying to pull some numbers out of this plot we have here this is from Andy Howell by the way we have here a galaxy host from the supernova we basically have here the Hubble residual is the supernova to brighter to faint and so we take the Hubble flow we we calculate Delta magnitude whether it's too bright or to paint faint and applaud it versus the galaxy s we're plotting galaxy mass versus a supernova luminosity so do you see a polar ation correlation there well it's really hard to say but right now in doing supernova cosmology we are assuming that there is a discontinuity roughly at this stellar mass in the galaxy such that we apply this value which is about 0.04 magnitudes for the low mass galaxies where the supernovae develop in them and we apply this value for the high mass and we have no idea what's causing this so-called mass step but these are the sorts of things that we are putting into our data to pull out precision supernova cosmology well as I said we're one of the real problems is that we don't have enough type 1 type 1a supernova at low redshift we are we've been working in the last 10 years we just finished our 10-year program for the part of the supernova project when we're recalibrating type 1a supernovae using extremely well calibrated filters and photometric systems and we're now getting down to about a point one magnitude range out in the near infrared we're reddening is not much of a problem and because the temperatures of type 1a supernovae are roughly 5000 degrees we're also really genes part of the blackbody curve this is not a blackbody of course but on a blackbody curve where a small changes in temperature really don't affect the colors very much so we can do supernovae photometry using these filters so let me let me leave with the following few slides the first is there are going to be future techniques for measuring H not Alex Filippenko didn't have time to talk about this but this is a technique that his team is going to use we're instead of using Cepheid x' they're going to be using myra variables and so similar to the Levitt diagram here is a period versus magnitude the blue points are my wrists that are oxygen-rich and the red tie the red points are carbon-rich and we can separate out these things easily using photometry what's amazing about this and this was discovered by a graduate student Lyme University just as dependent as thesis last week is that this relationship has a dispersion of 0.12 magnitudes that's as good as the set feels so Mira's may be able to be used like Sophia's but the good thing about IRAs is they don't just appear in early and young galaxies they also appear late type they're in both late type and early type galaxies so now you can go out to ellipticals and instead of using exceptions you can use Myra's both in ellipticals and in spirals this will greatly increase the number of calibrators for the local distance scale so let me leave with some really stupid questions this is the obvious part first question I have is what defines the big bang these days I have no idea is it the end of inflation or is the beginning of inflation there I've seen papers written about this in both directions and it's not particularly important but I think it's important that we decide once and for all what we decide is the beginning of the big bang second going back to Lemaitre what defines the universe do we admit to operational ISM a word that Eddington coin which is a concept believed by Lemaitre which states that physics actually never achieves reality now there's a great word from Christian theology pantego G which means the spirit behind reality there are four different levels of knowledge and an ago G is the hook is the final form of knowledge it's also the same as the Platonic theory of forms it states that there is a Universal truth beyond everything that we can see in reality and the question is are we getting to the point where we're creating creating cosmologies which really are anagon geez because they are beyond the reality of what we can measure but they're important parts of our theory they're essentially a truth that is required for us to do our theories I think that Mike Michael Turner pointed out many years ago was why is lambda Omega lambda roughly equal to Omega and what's causing this coincidence the second coincidence is even weirder the more we measure W naught the closer it's getting to minus 1 plus or minus epsilon epsilon is now about 8% but some people claim 5% but as epsilon goes to 0 and this stays close to minus 1 likelihood the W a that the time rate of change of W is anything else but 0 gets to be very small because if there really is an oscillation and W going like this what's the chance that we happen to be living right at the epoch where it's crossing through it minus 1 it's really easy to measure W it's really hard to measure this and then finally now it finally I'll show one more slide after this another thing that is something some ways we're confusing words it's not necessarily important for us to figure this out but I just want to put it out here as an observer I talk about when I talk about the universe I talk about the observable universe but that has changed in time we now talk about a meta universe universe that's outside of our abilities to measure things which I hope it never catches on but I'm going to call it the AMA Gajic well universe the truth beyond what we out beyond the physics that reality the reality of physics can measure and then finally there's another universe that we're talking about which is the one which i think is prior to the Big Bang which would we call inflation or something before that and again I hope this doesn't catch on but the word you would use would be you universe or is is the Babylonian City it means primitive time via three universes the one we observe the one that is beyond reality as we see it and the other one is the primitive universe this is my final slide the first photograph I showed you those photographs were sent to me by a collector who somehow got ahold of Owen Wilson's slides from 1958 and so he was up at Castel Gandolfo and he was visiting with with these three astronomers father Montana Parthi other daniel o'connell and father four-bar - I knew McCarthy I didn't know the other - I certainly need this dialogue because he is kind of the father of measuring light pollution he wrote the first papers on the problems of light pollution for observatories he was very much a polyglot he was a theorist he was an observer amazing man but what I want to leave you with is that for me as an American citizen right now it's kind of embarrassing to say that I'm from the United States considering the strange politics that's going on and the more it goes on the more there is a wedge being driven through science and religion religion is used more and more in in politics in the United States what I'd like to say here is that I would like to thank the Vatican Observatory the astronomers here in the Society of Jesus for giving us a platform where we can talk about both science and if we want to religion and theology in an environment where we're all very comfortable with it because right now in my country in the United States it's extremely uncomfortable to talk about these things but I really appreciate the chance that I have to come here and to be in this very humanistic environment for us to talk about these particular issues