Science of SLAC | A Deep Look for Dark Energy: Science and Discovery with the LSST

good afternoon everybody welcome to the next year the science of slack lecture series thank you all for coming our first speaker this year Zarin roodman professor here at slack is going to be talking to us about the large synoptic survey telescope and all the awesome science we'll be doing with that so Aaron started his career over desk-bound south from here at Caltech as a PhD student before moving to the University of Chicago where he's working on the CDF experiments and also looking at the matter/antimatter asymmetry in the k-on system and around 1998 Aaron came to join us here at slack working on the Bob our experiment again looking at the difference between matter and antimatter I'm experimental II so after about 20 years of trying to understand why the universe is made of matter and not antimatter Aaron switched his research focus to looking at cosmology and trying to understand why there's so little matter in the universe in the first place and trying to understand something about the nature of the dark energy in the dark matter that we think makes up the majority of the contents of our universe today and to that end he's been heavily involved in the dark energy survey and the large synoptic survey telescope they were involved in here at Chi PAC and it's a LSST the large synoptic survey telescope that Aaron's going to be telling us about today thanks can people hear me yes so the title for the talk is a deep look for dark energy and as we go I'll try to explain what that means so this is the engineering drawing of the large synoptic survey telescope this is the instrument that we have begun to build and that we're very excited about and it's what I'll tell you today now the mantra in some sense of the LSST is is wide wide because we will take images with our telescope of the entire sky this is a a map of the sky just like a map of the globe but this is a map of the whole sky north-south equator and the colors are meant to show how much of the sky we'll be able to observe with the LSST as you can see it's it's virtually everything that you can see from a mountaintop in Chile it's fast it's fast because we will take these images rapidly enough to be able to observe every part of the sky well every part of the sky visible from a mountaintop in Chile at that time of the year in 3 to 4 nights so that every point on the sky will be observed many many times over 10 years and to do that you have to be fast and it will also be deep and oh and the other one the the the colored region is observed less a little less frequently this is the galaxy this is how the galaxy shows up the pole is all is is a a touch less interesting and a little bit harder to get to and this region is the ecliptic so this is where solar system objects will lie so that's why we go above the equator here but not everywhere but the we look at the galaxy but because it's it's such a dense region that we don't look at it quite the same that is the northern hemisphere can't see it at all ok the last part of the mantra is deep we that the the telescope is big enough the field of view of Y is wide enough we take so many images that we can observe galaxies that are extremely dim and the technical literally the technical word for that and the external community is that's deep observing you're seeing things very dim things far away this is actually a simulated image this is what the images from the LSST should look like there's false-color in this image so it's a combination of first of all a combination of many many individual images and then a combination of images taken with different optical filters and they're put together with false color this isn't this is similar to what it would look like if you could see this with your naked eye of course to see with your naked eye you would have to have a very big eye so this so that the the technical definition of deep is in a funny astronomical unit called magnitudes it's a logarithmic unit that is actually designed to match what the ancient Greeks how the ancient Greeks classified stars so it actually is a a good object lesson and being careful about defining your units because if you do it you might be stuck with them for 2,500 years so the these images go to about 26 and a half magnitude and the bigger the number the the deeper you go the dimmer the object so with your naked eye you can see about four maybe here if you look over the valley maybe it's three and a half but in a dark spot it could be five so that's the mantra of LSST wide fast and deep let me tell you a little bit more so let me let me move now to talk about first some of the scientific goals especially our aim to learn more about dark energy so a little bit about what dark energy is and how LSST will be capable of learning more I'll talk a little bit about the instrument the telescope and especially the camera which will be building here at SLAC and then lastly talk about some of the other science that will able to do with the LSST but first just one retrospective to talk about dark energy it's worth saying something about the expansion of the universe and that was discovered around a hundred years ago with much of the key work done by Edwin Hubble with this telescope this is the hundred inch telescope at Mount Wilson in the hills in the mountains above Los Angeles and in some ways things haven't changed this telescope you know is very recognizably similar to the LSST in certain ways but in certain ways of course we've gone far past it in particular the instruments that they're working on here you know having the end photographic film and of course today we digitize everything we have electronic detectors and in our case we have this spectacular camera that Elsa Steve will use so Hubble discovered that the universe was expanding and in the time since then if you go back say 20 years we thought there were one of three possibilities for the expansion of the universe and actually up until about twenty years ago we did we did not know which one was correct what are the three possibilities possibility one that the universe would expand forever and that's what would happen if the density of matter in the universe was too low and because the expansion is potentially modified by the gravitational interaction of the universe on itself if there wasn't that much matter in the universe if the density was low then what would happen is that the universe would just continue to expand forever that's possibility one possibility too was if the density of matter was too high above some or above some critical amount the universe would expand and eventually it would stop expanding and then it would contract ending in the corollary to the Big Bang sometimes called for fun the Big Crunch perhaps another Big Bang that's what would happen if the density was too high and of course there's a there's a case right in the middle the the Ox situation if the density of matter was just right the universe would still continue to expand but as it expanded it would it would do so more and more slowly and sort of asymptotically continue to kind of zero expanse we're never quite getting there so those are the three possibilities and it all depended on how much matter was in the universe so we discovered around not quite twenty years ago but actually all three of those possible futures all three of those histories for expansion were wrong and the reality is somewhat different so I'll just tell you just a little bit about that the key in doing that was finding a certain class of objects certain class of supernovae exploding stars for which we could measure both their velocity from their redshift and their distance from their brightness so the redshift if you don't know what that is is akin to a Doppler shift right a Doppler shift is the thing that makes a train the pitch of a trains whistle changed as it goes past you changes the wavelength of light depending on whether an object is moving towards you or away from you the redshift is it's similar to that very similar not quite the same actually but it enables us to make a measurement let's call it if the velocity of a distant galaxy but then how to measure the distance measuring distances is actually not easy when you don't know the intrinsic brightness or the intrinsic size of the thing you're looking at but a certain kind of supernova gave us a way around that so called type 1a supernovas all have the same well let's say similar intrinsic brightness we know how bright they are were we to be nearby to them but if there are billions of light-years away we can look at how bright they appear and infer a distance so that's what was done in the late 90s actually by two competing groups reporting their world results almost at the same time and this is the this is the the summary plot from those two those two teams the color is the two teams it's a plot of the red shift so here's red shift this is red shift of one that's nearly ten billion light years away if I remember right and then on this axis is kind of a funny unit that I'll call it the logarithm of the distance so this is things getting much further away and well it's hard to see what's going on here so let's compare these points to the different lines to this line in particular which is one one of the possibilities that I just mentioned and that's actually the a density to low the density to low case so here on the bottom is the data so the points minus our picture our model of how the universe expands and you can see that the points lie they certainly lie above this line which is the density being just right and they actually lie above this line the straight line which is the density to low and they're consistent with something else entirely and the something else entirely turns out to be a universe that has a density that's just right in some sense but a composition that isn't all matter a composition that is 30% matter and 70% something else and that combination gives you a different history for how the universe is expanded and in turn that history controls how bright or in this case how dim these distant supernovae appear and that is the discovery of dark energy so the Nobel Prize in 2011 was given to these three gentlemen for this discovery and really what that means is if we step back so by looking at how the universe expanded we're able to determine that we don't understand what the universe is made of we know how much stuff how much matter and energy is in the universe partly well combining these measurements with other measurements of the Cosmic Microwave Background that's the glow from the Big Bang we know how much stuff is in the universe but 70% of it is something we'll call it dark energy to give it a name it's the thing that's making the universe's expansion accelerates making these objects appear dimmer just by a little than they would be otherwise but we don't know what it is and that is that is the challenge for the future it's the the one of the biggest pieces of scientific discovery that Ellis's t aims to make to discover what dark energy is and try to understand that part of the universe better now actually along the way or as part and parcel of this we've also found out that we know how much matter is in the universe universe is 30% matter but if you look at how much of the universe is made up of atoms right regular matter that we know and love the things that are in the periodic table that only makes up a portion of it that's 5% of the total so 25% of the total is some other kind of matter dark matter and I should say that if you're if if you're if you just pay attention to the names you can be confused easily right they both have dark in their name right there's dark matter this dark energy there's no there's no evidence that they're related that would be awfully interesting and if they were but certainly now we have no evidence that they're related the only common the only commonality between them is that they don't shine neither of them emits light or interacts that much with regular matter if at all and so they're dark in that sense and it's also true they're also dark in the sense that they're unknown we don't really understand either okay so in this talk we're just we're really going to focus on dark energy dark matter will play its role in the old deals as you'll see but mostly we're interested in dark energy so we could ask what do we know what positive things do we know about dark energy we know a few things one I already said it's not rape it's certainly not regular matter and it's not regular energy regular energy would be heat energy or photons light energy it's not that the other thing we know is how much there is in the universe we actually know that reasonably accurately at this point so if we if we look at the energy density so that's the energy equivalent in a certain volume of the universe we find that there is 3.7 proton masses so you can convert the mass into energy if you like in a cubic meter so cubic meter something like this 3.7 proton masses not much so it's extremely diffuse what else do we know well here's the here's that the next two are really interesting okay because they indicate how strange dark energy is the energy density stays constant as the universe expands so regular matter if you have some volume you know could be a cubic meter it could be a cubic Lightyear it doesn't matter which you've got a certain amount of matter in case they're as the universe expands that volume grows but the amount of matter doesn't change so that it City goes down dark energy does not work that way as the universe expands the energy density stays constant growing with the volume so as the volume increases the energy density the energy increases such that the density stays constant so it's an energy that's really associated in some deep way with space so that's also not the normal way that matter behaves not the normal way that energy behaves lastly if we look at its pressure now pressure here is kind of an abstraction because it doesn't interact with regular matter so it's not the kind of pressure you have in a bottle of nitrogen gas where the air molecules are bouncing off the sides and that gives you the pressure right there's no bad but you can think about a pressure as being associated with dark energy as a fluid so I'm sort of abstract fluid but here too it's odd because the pressure is negative and the closest analogy you can come to that is a rubber band right where as you as you pull more in the rubber band it's the the restoring force grows and it's that sense it's got a negative pressure analogy is not the greatest frankly and really there's no I think there's really no solid analogy for its behavior okay so again it acts fundamentally differently than the kinds of things we understand well around us the kind of things we expect from regular energy regular matter now what can we learn about it how can we what can we determine amount dark energy actually here two is only a few limited things we can determine how much there is in the universe we can measure the pressure compared to the energy density and we can try to look at how the pressures changed over cosmic times is the pressure the same today as it was a you know a billion years ago or three billion years ago those are the things we can measure we assume as as a sign light will say I will say we assume that it's uniform in the universe and maybe that's a maybe that's a fourth thing we can measure we can test that assumption now it turns out that this pressure the actual details of the negative pressure determine the fate of the universe so what's gonna happen to our universe 10 or 20 or 50 billion years into the future it's kind of given by this graph here's time zero is today this is some distance where one means it can be in the distance to some distant galaxy pick your galaxy call that distance today one OK just normalize it to one if you go back into the distant past it goes the distance goes to zero that's the Big Bang what happens into the future well here are the two cases I said are not correct dark energy tells us it's probably one of these but the amount of pressure this ratio pressure over energy density tells us what happens into the future and the most interesting case is if W is smaller than minus 1 in this case the future may be that space-time itself will be ripped apart so it's not just you know the future if it were minus 1 exactly is also kind of grim eventually you would not be able to observe other galaxies other galaxies would have moved would have accelerated so far away that you could no longer see them eventually perhaps the galaxy itself would be pulled apart but if it's if this quantity is less than minus 1 actually space-time itself is doomed a long time into the future ok the Sun is gone by then the solar system is not not the same place but that's actually what that's the conclusion we would draw so in some sense we're with LSST today we are trying to learn about what's gonna happen tens of billions of years into the future now what could dark energy be let's go one level deeper what is it there are a few possibilities that people people think about one is it's Einsteins cosmological constant I won't go into that history today but it's a very interesting history if you're if you're interested in the history of science and the history of ideas that's one possibility another is that it's a quantum field actually in certain ways similar to the Higgs field the higgs field that gives particle masses that's associated with the Higgs boson field could be a little bit like that if it were though there are serious conceptual problems because the amount of dark energy in the universe seems you know phenomenally smaller than you might have expected otherwise were dark energy to be a quantum field the last possibility is it's a modification of the laws of general relativity of themselves and that of course would be fantastic so we're trying to learn if we can if we can figure out whether dark energy is one of these things or perhaps something else entirely now how are we going to go about learning more about dark energy it's and and maybe you can see it because dark energy it doesn't interact with any normal matter it's very diffuse in the universe so we cannot detect it directly it binds very nature its interact so the first step in in our study of it is to look at how matter is distributed in the universe so this is a simulation you can see it in 3d upstairs in the compact biz lab along with other interesting simulations of this sort it's a simulation of actually dark matter so the the the lumps here the bright spots are hunks of dark matter and as you can see as time goes on it's being pulled together and this little piece of the universe is becoming clumpy ER if you will as the gravity from from the largest the largest collections of dark matter pull in more and more matter let's watch it again let's watch it again so you start out with actually a fairly uniform universe and it's time goes on you start to develop clumps and filaments and then as time continues these come together further and the universe becomes yet more in homogeneous and so what we think is that for many of these bright spots which are really hunks of dark matter these are places where galaxies would form and the key is that how this happens in the universe depends on how the universe has expanded very simply if the universe is expanded more rapidly then the gravitational interaction I will watch it one more time on then the gravitational interaction between matter has less of a chance to operate because the universe is expanding faster so the universe ends up less clumpy alternatively if the universe expands more slowly different lumps of dark matter will be closer to each other will stay in the vicinity longer the force of gravity will have more of a chance to interact and the universe will become clumpy ER and so it turns out that by measuring how matter is distributed in the universe is it is it clumpy ER or less clumpy we can tell how the universe expanded and this is a very very powerful tool to understand both the expansion and to understand the details of dark energy and we can do this study at different periods in cosmic time as we look deep into the past and how do we look deep into the past well we need a telescope like LSST that has capabilities to see very deeply into the universe a little bit more along this line so how do you tell how matter is distributed in the universe the problem is most of the matter is dark matter it's not in stars it's not in galaxies it does not shine so how can you tell how much there is and how its distributed in the universe well you use the only the only method you have which is the force of gravity because dark matter still feels the force of gravity so you need some way of seeing gravitational interactions and that is that we can do directly by something called gravitational lensing and that's the bending of light by matter this is a terrific example here this is a picture this is a Hubble Space Telescope picture of a very large galaxy cluster so that's a collection of in this case you know a thousand galaxies that are all have been pulled together by their mutual gravitational interaction into some fairly small volume well fairly small you know a million or several million light year aside but okay for this in this context that's small and one thing you notice is that there are these fantastic streaks all over this image what are those those are more distant galaxies than this galaxy cluster each of these things you see here is actually a galaxy almost everything you see here is a galaxy but these are other galaxies that are behind that are further away than this galaxy cluster and their light is being bent and it's being bent into these arcs and so by studying phenomena like this you can detect matter and how lumpy matter is in the universe without seeing it directly and in fact what we'll do is we'll study we'll study effects like this this is called strong lensing strong gravitational lensing will also go far out from the center of this galaxy cluster and we'll look at galaxies on the outside and those won't be bent into these fantastic arcs those will just be distorted a little bit their shapes will change a little bit kind of like this but in a much more subtle way the importance of that is that these sort of galaxy clusters are relatively rare well LSST we'll see you know a couple hundred thousand of them but relatively they're you know relatively speaking they are rare and we want to look at the distribution of matter everywhere across the entire wide field of the sky that LSST will look at and in that case the effects are more subtle matter is not uniform it's it's distributed in lumps but not so dramatically is this and likewise the effect of gravitational lensing won't be as dramatic as this either but we still need to detect it so then we come back to this image which is of well you know somewhat more typical region of the universe and everything so the thing to point out is almost everything you see here is a galaxy or most of what you see is the galaxy only a few stars these are stars all of these big fuzz balls you see are galaxies and then of the little ones perhaps some are stars and some are galaxies it's hard to tell here's here's one of the challenges we face then because we need to find many galaxies to study how light has the light from those distant galaxies to us has been bent by gravitational forces by gravity so that we can measure how lumpy matter is how manners distributed in the universe so we can see how the universe is expanded it expands a little faster or a little slower so that we can learn about well we learn about the expansion then we can learn about dark energy and dark matter in the universe well to do all that we need to get a sample of galaxies all talking a little bit about how big that sample is but maybe it's worth just showing you what a typical galaxy that LSST will detect will look like that's and you see it in the back that's this little fuzzball and then to study those you want to have stars stars are great as a calibration source because they're you know stars are in our own galaxy by and large these stars are and but they're so far away that they should appear as a point source to us well they don't for various reasons they appear as a little blob that would be a typical star so we have to understand those typical stars to help us understand the typical galaxies to do the science we want to do but it's worth mentioning that they're not the spectacular spiral armed things that you see in pictures well you know if you are I mean some of these some of these look pretty impressive you know this is a elliptical galaxy so it doesn't have spiral arms but some of these are you know could be more spiral and these are pretty far away so they don't appear that large but many of them will appear a little bit more like this they're so far away they're really just a tiny fuzzball okay so actually maybe I'll come back I'm gonna come back to this line I'm gonna come back to this line so that's an introduction to some of the dark energy science we want to do we want to understand how matter is arranged in the universe and to do it we can measure galaxies so it's very indirect measure dark energy directly now let me let me change change directions just a little and talk about the instrument talk about LSST as a project but before doing that maybe it's worth defining one word which you may or may not have been familiar with before synoptic if you look it up in the dictionary well and you combine a couple of the definitions that you might find you could you could arrive at this definition furnishing a general view over a large area at a point in time that's pretty close to what we're gonna do with the addendum that we're gonna do it at many points in time okay but that's that defines us now what is LSST LSST actually is there are three major legs to LSST one is the telescope the observatory facility all the infrastructure that will be on our mountaintop in Chile here's a here's a picture of the primary mirror being being constructed that's one component that's funded by the National Science Foundation another big component is the one were most concerned with here at SLAC that's the camera this is this is the project that slack is the the leader of and I'll talk a little bit more about it but there are quite a few of us working to start building this this beast and we're very excited about it the the third big leg of LSST is the data management and that's the group of people that is going to write all the software algorithms to corral the fantastic data set that we'll have and of course there's going to be a lot of computing hardware to do all that to do all that work as well actually that is a distributed effort and one aspect of the data handling is here at slack too so there's our group developing XO scale sized databases is here at slack as part of the overall data management okay so some superlatives so so it's really how you know how wide how fast how deep is LSST we're that mirror I showed you is almost eight and a half meters diameter it's not the largest telescope mirror in the world right now the biggest maybe is 11 meters equivalent but it's pretty close and it's certainly enormous it's coupled though with a system that has a 10 square degree field of view so that's three and a half degrees across when the moon is half a degree across so this is much bigger than the full moon there are some small telescopes that have a giant field of view like this but it's the combination that's actually totally unique the big telescopes have tiny fields of view telescopes with big fields of view are pretty small but we have the combination and that's the thing that enables us to see so much of the sky so fast and to look so far away now the camera that you need to do that is also enormous it's the input camera lens so we go back here the first thing that the camera has is actually a pair of giant lenses is 1.6 metres across that is pretty close it's the same size as the biggest refractive telescope ever built actually it's somewhat it's somewhat bigger and it's I don't know that it's the biggest lens ever built but I have a feeling that bigger lenses may be kind of on the secret side of what happens in our country or others it's certainly quite large but the next superlative is the camera the camera has an array of CCDs charge couple devices that is 3.2 gigapixels so now when this was being designed about a decade ago or designed really in detail decade ago that seemed totally enormous you know 3.2 gigapixels actually today when you can buy a phone with a 40 megapixel camera it doesn't seem quite as large but what's really impressive is that the size of it to get good quality images you can't do it with a small device it has to be a large device and so the focal plane is about 64 centimeters across and so the total area of the CCDs is really enormous by far the biggest area camera of any astronomical camera and if you compare it to what's in your iPhone se it's a in size at least the sensor size is about 20,000 iPhones equivalent so it's fairly large that way and then the last thing that's impressive is actually its readout extremely quickly so only two seconds to read out all 3.2 gigapixels doing that with the the low noise requirements that we have and the other conditions that were under that's extremely fast so the electronics have to be equal to that task more superlatives well I said I said this before we see the entire sky in three or four days that's 15 to 20 terabytes a night and we'll take images nearly every night for 10 years and we'll see every spot in the southern sky around not maybe not quite a thousand but very close to a thousand times so it's it's it's a way of looking at the sky that's different than any other telescope has really used before and I'll talk more about that closer to the end of the talk some final superlatives will observe twenty billion galaxies that's an appreciable fraction of the total number of galaxies that we would ever conceivably be able to observe based on the age of the universe and the speed of light we'll also see 17 billion stars so those are stars in our own galaxy we'll see objects in our own solar system six million solar system objects and every night we'll get 10 million alerts the computing system will spin out a message that says something has changed in the guy and I'll come back to this one a little bit more and the last thing that's really actually I think is going to be quite is going to be fantastic is that all of our data is public ok so public to the entire scientific community at least in the US France and Chile and perhaps in the whole world but it'll be public not just a scientists but also to interested interested citizens citizen scientists and that has not been done in any in any way like this before either all right let me let me I'll show some pictures so LSST is going to be on a mountaintop called Sarah pizon it's in the Chilean mountains here's so this is these are engineering drawings of what the observatory and the dome you can see the telescope inside the dome would look like this is a picture I took myself a couple years ago at that point the mountaintop had been cleared but no more construction had been done and this is a picture taken more recently showing sort of the start of construction so at least there are there are trucks there are trucks and workers there things are getting going the camera let me just say a little bit more about the camera so this is the piece we're doing here at SLAC I know some of the engineers working on the camera are here steve khan here is the has been the leader of the camera project for 10 years perhaps and now he's also the leader of the the entire observatory as well so here's the camera that we're going to build it's well you call it a camera but this is you know this is 1.6 metres across it's almost 4 meters long so it's kind of as large a thing as you could ever call a camera but it has lenses there are three lenses it has a shutter one of these things here is actually a shutter that will close and open to let light in or not there's a filter exchanger so we have giant filters that admit only one sort of narrow band of light at a time and we have we have six filters total we can only fit five of them in here when they're not used we actually slide them off to the side kind of along the side so they don't stick out outside of this cylinder and there's actually quite an impressive mechanical device to get them from here to here reliably the green is the cryostat so that's the vacuum vessel used to keep the CCDs cold and then in the front of that you can kind of see it drawn schematically these squares are the SI cds 189 C CDs and then in the back there's equipment to cool the crime stats there's refrigeration equipment as well as electronics and other control control equipment and then this entire camera assembly bolts on to the right spot in the observatory kind of at this at this plate back here so we are just starting construction now we're still the the design phase is mostly over not entirely over but mostly over and we're really seeing into actual construction so just a few pictures and I should say you know sonken's were mostly activity is but as as these things work we have a collaboration including Livermore Brookhaven a couple laboratories in France and a couple other universities in the US to help us build this this camera so the center picture is I r2 so if you've never been over there that's where the Babar experiment ran now that Babar has been removed we're making use of part of that space sharing it with the LZ Dark Matter experiment to build this giant cleanroom and we'll do the camera assembly and testing in that cleanroom so here you can see it taking shape here are some CCD some sort of first article type CCDs on on a plate so each plate holds nine ccd is here at three here is the the crate we call it that holds the electronics for the CCDs and one of the several innovative things we're doing is that the there's so many channels for this camera that instead of taking out analog signals out of the that we're digitizing inside the cryostat and that really there's maybe one other camera that's done that but by and large that has not been the practice so here's the electronics board prototype the atronics board that will read out the camera here's other work going on at SLAC this is the refrigeration testbed this is testing the somewhat novel joule-thompson style refrigeration unit that we're going to use to cool the camera refrigeration is is easier if your objects stay still but since it's a telescope and you're moving across the sky and actually we're moving across the sky quite rapidly that places a whole set of interesting demands on your refrigerator and this last this is just an engineering drawing still where we already have we have a contract now for the two giant lenses and so those will be made by Ball Aerospace so things are happening so with the with the remaining time actually I wanna I want to come to my third topic so we talked about dark energy we talked about how to make measurements of dark energy we talked about the capabilities of the the instrument and how those are matched to studying dark energy because we're so deep because we will see objects galaxies so far away but there's there's a whole other aspect there many other aspects so the science will do with LSST besides dark energy and I'll just talk about one of them is in in general today and that's the alerts the ability to see changes in the sky and this is enabled by the fact that we look at the same part of the sky many many times we this is the fast part of the LSST mantra and so an alert is any object observe to change in the sky and well I said already well we'll get 10 million per night and those will be detected transmitted the the promise is within a single minute of their observation so really real time as images are being taken the data is sent to processing farms and it's analyzed really instantly to look for anything it's changed in the sky what would those changes be well one our new objects things that just didn't exist before supernovae are a great example so will detect literally thousands and thousands of different kinds of supernovae another thing are objects that are there but they change variable stars are a good example there's no lack of variable stars in our own galaxy or in nearby galaxies that are interesting to study will also look at objects that move in the sky things in our own solar system by and large Kuiper belt objects so the Kuiper belt is those are objects past the past orbit of Neptune that are interesting to study and as well as asteroids so we will look for killer asteroids and lastly is the thing that I can't list because it's unexpected and I think here so in addition to making discoveries about what dark energy is my personal feeling is that this is the place where LSST is really poised to discover something new because we're looking at the sky in a much different way than has been before repeatedly to great death if we're looking at distant or just very dim objects depth can be both distant objects or dim objects that are nearby and we'll be doing it over and over and so I am I am quite confident that we will discover new things along these lines now there are challenges well one you know there are opportunities the data is public anyone could look at this stream this fantastic stream of alerts and look for something new in it or study phenomena that they already know about they're interested in but it really does present a challenge because how can you follow 10 million alerts per night in any kind of reasonable way that is that is a phenomenal challenge let me let me talk a little bit in the remaining time about about the alerts about changing objects in the sky so one thing just to make make it a little more concrete how LSST observes one of our colleagues made this kind of stimulated view so again this is the whole sky you know north south you know one end of the celestial globe to the other this line is the night sky so this is what's visible at night from chile this is pointing this is where you point straight up here's the moon here's where the planets go and then this is the galaxy over here and so each one of these little hexagons is one LSST image and this is a simulation of how you would observe over time so this is night as well start from zero so this is the first night and you can see we're tiling the sky kind of back and forth the colors actually mean something it's purple is one of the cult of the filters this was called Y band and that's that was used because the moon is up here's the next night we're observing in a different filter and we stay for a while at this spot and we haven't given up then there are actually certain spots on the sky that we look at even more frequently than every four nights and those are special places where we look the where we really want to see supernovae but we might see other interesting phenomena as well and so here's the the third night and you can see at this point we have we have really tiled quite a bit of the of the available sky and this will actually all be done under computer control there's no way you could have someone sitting figuring out where to take the next image every 15 seconds you can't do that for for an hour much less for multiple nights so yeah here's the night three so it's the fourth night and now you can see we have really weave tile just to mount the whole available sky in that period and we've done it in different filter bands and some we've seen twice and maybe there's some reasons we haven't quite seen once but it averages out to seeing the whole available sky over three or four nights well this continues for a long time we won't we won't continue to watch it but that's what will be capable of doing so what will we see then when we look at the sky repeatedly here's one example this is an example from another project I'm working on the dark energy survey dark energy survey is kind of a junior version of LSST maybe between fifty and a hundred times less capable pretty interesting right now much bigger than anything that's happened to date and we certainly hope to learn we will learn a lot that will inform LSST here's a supernova here's the before you can see it's a there's a fuzzball there but after it's actually a bigger fuzzball and if you take the difference of these two being very careful to take into account the different conditions the sky had a different brightness the images had a different quality you know observing on earth is not so easy things are not that static but if you do things right you see the difference you get this little dot and that is a supernova it's actually not a normal supernova it's a superluminous supernova it doesn't decay away very fast actually people are people are confused about exactly what those objects are all right and I think that you know here's an example we've detected lots of supernovas but LSST is gonna see so many I would be surprised if we don't find different sorts of supernovae from Ellen sisty here's another type of object so here our solar system objects these are quite four belt objects and so if you look at I think these are two different ones but this little dot you can see is moving across the sky the stars are sort of set up to be fixed in the image but you can see the moving object this is how the planets you know well I was about to say Pluto it's not a planet anymore but it was discovered this way with photographic plates using our fantastic camera will see a you know remarkable numbers of these another way to see another way that Kuiper belt objects will appear shown by this kind of visualization put together by my colleague Dave Gerdes from data from the dark energy survey these regions are the dark energy survey focal plane their CCD set and the dots are where Kuiper belt objects appear and the color scale here is is overtime from 2012 to 2014 and these orbits are the apparent orbits of the Kuiper belt objects now mostly what you're seeing actually is the Earth's rotation these things are so far away they take you know hundreds and hundreds of years to go around the Sun so in one or two years they don't move very far really but they do move a little but mostly they appear to move because we're moving we're going around the Sun and our vantage of them changes but you can use that to your advantage to find them to link together different images taken and and and prove yourself that that's the same object from one image to the next and they trace out these interesting orbits dave has found a handful in this in this region of the dark energy survey they'll they'll find plenty more LSSC will find a spectacular number and so the Six Million number I mentioned a solar system object is you know some good fraction of that or will be these Kuiper belt objects so people studying the solar system will really go to town one last thing in alerts that these are the things we know about asteroids or in particular killer asteroids so it this is a plot of this is diameter this is the number of objects the red is sort of an estimate of what's been discovered as a function of size so we think and the blue is is different models of how many asteroids there are in near-earth orbits so we think we found all of them that are bigger than a kilometer that could ever hit us so those are the ones which you know really cause damage here's the here's the the size of the asteroid that I guess maybe the dinosaurs go extinct here's the the Russian asteroid that hit in the early 20th century I am told that that our government has a law or a demand that some project find all asteroids bigger than 140 meters diameter so that's around here and that's a interesting point because at that size they don't burn up in the atmosphere and if they hit the ocean they'll cause a tsunami and they could cause a pretty damaging tsunami so it's a level at which you really have to worry here well they could do some damage that's of a different character but here they're real there are real problems and the red curve is how many we've discovered and the blue is how many we think there might be and you can see that depending on where this is you know we've only found one in 10,000 one in a thousand or one in 10,000 so there are lots and lots of them and LSST we think we'll find about 90% of those so it will find you know not all but almost all and well that'll be interesting to study as well although you may you may find you know more frequent messages in the in the news media about some object that may or may not hit the earth so but at least it's better to know than not now okay so one last comment and and it's really related to the fact that the data will be public and all these alerts will be public and so science recently has has taken on different efforts to get science into the public's hands more directly not just telling people about what we're doing but finding ways for them to do it too citizen science one of the most interesting one of the originators really of this is the so called Galaxy Zoo and actually any of these you can just go online and look up if you're interested Galaxy Zoo which supplied little pictures of galaxies found in the Sloan Sky Survey to the public and said trying to classify these galaxies for us use your eyeballs in your brain which are still much more powerful than computer algorithms for certain kinds of problems why don't you use those for us and classify what these galaxies look like another case is space warps developed by phil marshall here here at a chi pac to look for gravitational lensing these little arcs are similar to the arcs in the galaxy cluster i showed earlier and those are not easy to detect in objects like this but your eyes your brain are still quite good at doing it that was this team may have so many of these that you know putting these before the public and harnessing the power of thousands of people to look at them may be a you know may be a good way to go maybe the only way to go and then last lvl SST project has an iPhone app called transient events which will supply events to you from a smaller survey that's going on now that's the Catalina Sky Survey but when elseis t starts you know this kind of product will produce this fantastic flow ten million events a night and i think there's a lot of potential for us and for our partners in the community to do more some final thoughts so we have a schedule as any kind of project like Alice's T does we have a schedule that schedule shows us delivering the camera Chile in 2020 I can't wait for that at the observatory I think the first light the first time we put the full camera and take an image of the sky like will be later that year in 2020 there's some time to tune things up to Commission the entire facility but our ten-year survey will start in 2022 you know I talked about dark energy I talked about transients or alerts there's much more science that you'll be able to do the people will be able to do with Alice St and discoveries await so with that I thank you oh I'd be happy to entertain questions greg has one in the front mm-hmm I have I have two questions the first one is probably a nitpicking question but I didn't understand how this would work you said that by pointing to this podium here that in the universe on average there was three point seven protons per cubic meter proton equivalents the equivalence energy so in dark energy if you if you want to sum up how much energy is there it's the energy that you know whatever that number is three point seven protons have okay so when the energy equivalent not protons know but then if the energy if the universe grows then for the energy to stay constant the energy must be increasing yes okay good the second thing is you gave a phenomenal description of this instrument but can you just remind us again and you're gonna discover a zoo a mega zoo okay but how does that discovery of the mega Zoo resolve the question of what dark energy is unless you have some kind of model so it's it's really the indirect sequence of steps I mentioned right we'll we'll observe billions of galaxies not all of them will be usable for gravitational lensing of the twenty billion but maybe four or five billion will be usable so we'll study those four or five billion galaxies in particular will measure their shape will measure their brightness will measure a crude version of their redshift from the different filters we have and from those things will then infer how matter and it's mostly dark matter is distributed around the universe I mean the technical thing we'll do is we'll measure the power spectrum of dark matter so that means you know how much how is the matter distributed is it smoother or is it clumpy ER in space and that will tell us how the universe expanded and that will tell us about dark energy it's really this whole line of inferences that you need to do it because there's just no way to see it directly okay

Channel: SLAC National Accelerator Laboratory

Views: 18,059

Rating: 4.6811595 out of 5

Keywords: SLAC National Accelerator Laboratory (Department), Large Synoptic Survey Telescope (Structure), Dark Energy, Science (TV Genre), Astrophysics (Field Of Study), Kavli Institute for Particle Astrophysics & Cosmology

Id: 41XRLKK3aRI

Length: 59min 58sec (3598 seconds)

Published: Mon Mar 02 2015