welcome to the science for the public lecture series science for the public is an organization committed to bringing science information and issues to the general public this is our website for our program robertson coa soci a professor of physics at m i t and a research fellow this year at radcliffe institute for advanced research dr simcoe specializes in observational astrophysics with particular emphasis on the chemistry of galaxies in the inner lactic matter of the early universe a crucial and very challenging area of investigation for astronomy dr simcoe received his ph d in astronomy from california institute of technology in two thousand and three he joined the mit physics faculty in two thousand and six and he served as the p i n projects scientist for an innovative infrared spectrometer for the magellan telescopes tonight he'll tell us about the effort to penetrate the early pop of the universe when the first stars were forming and why that era is so important for understanding the evolution of the universe will also understand how infrared spectroscopy reveals the features of that period and how dr simple as work has vastly improved this essential technology we are very experiments because these objects are so far away and so we're in a situation where we're looking at these very distant objects in the only way we can infer about their properties is to deal with the light that comes to us whether we think of it as particles which we call photons or waves you can think about it equally either way if you like to think about it as waves they have different frequencies associated with them and even though radio we can't see it with our eyes but it's still a form of light it's just li us so to speak for our eyes to see and so we need antennas to capture that kind of radiation so the that deals with the lowest frequencies or the longest wavelengths of light what i do is optical astronomy and infrared astronomy and those focus on things that our eyes can see and those there are several advantages to working with optical light and one of those is that most stars in the universe actually emit a substantial fraction of the radiation at these wavelengths that our eyes can see in fact our eyes not all fast forwarded that's purpose specifically and there are other reasons that that optical wavelengths are advantageous as well there are certain atomic properties that we're interested in studying in how stars interact with their surroundings when starlight leaks out and then it illuminates gas clouds around it often times it can bounce electrons around in their constituent atoms and then we can see these prophecies based on line radiation that's emitted from those clouds and that tends to come out of optical wavelengths for example in atomic hydrogen you can take an electron from one energy level to another and then have it come back down and it emits a little bit of light a particle of light that you can see at optical wavelengths so there is really very distinct for that you can see things with this with  are particularly good for looking at stars yeah for the same reasons that our eyes are there's another advantage too which is this gets to something that i hope we'll talk about later it's a technical advantage which is that we have detectors that operate essentially perfectly at optical wavelengths because we're piggybacking on a lot of the technology that's developed for the remote sensing industry for what's in your digital cameras and just industrial and military technologies and that drastic they reduced the cost for us to build wonderful hardware that we can put on the back end of our telescopes we're a small field and so we can't afford to develop all those technologies from scratch in ground zero and so we'd like to take what we can from other field hard to get our heads around this distance this time and this distance how far you are looking back and how is it possible help and light pass through there fi shined the flashlight outside i can see it go a distance but then it disappears right how does it work well i'm stunned was one of the folks who first realized that the light provides the ultimate speed limit for the universe  and it moves at roughly three hundred thousand kilometers per second or hundred eighty six thousand miles per second and so that's very fast but it's not infinitely fast it takes a certain amount of time if i shine that flashlight the energy that goes from it will move out at that speed and so if i want to detect if i shine that flashlight in just flick it on and off a person who is one hundred eighty six thousand miles away it'll take one second for that person to realize what i've done in the same way it's kind of interesting that we can use the distance to objects in the universe almost like a time machine because we see them not as they are at the present time but as they were at the time when they emitted their radiation in so that's why we often talk about distances in light years so for an object this one light year away we are seeing it today as it was one year ago and for a an object that's ten light years away we're seeing it today as it was ten years ago and if we want to see what it's like right now we would have to wait for ten years in the objects that i'm looking at in the early universe are something like thirteen billion light years away and that's a distance that's hard to do is for sure because you have to take that you know hundred eighty six thousand miles per second and then multiply that by the fact that a year has roughly times ten million seconds and that is a very large number sure and so we like to think of it in terms of time because if if we're looking at something that's thirteen million light years away we're seeing as it was thirteen million years ago which is about ninety five percent of the way back to the big bang right sort of the frontier but we can see exactly and that's a good take it by the way that that's fairly recent to be able to go back that distance oh yes yes i would say that  point where you could look at things that were substantial fraction across the history of the universe and what actually has enabled us to go back to the very earliest times it's not just the raw telescopes in detector technology but also our ability to sift through pictures of the whole sky and find those sources that are sort of speaking to us from the very distant very early universe how do we see them in the context of all the stuff that's in between yeah  stay right now when we in the strada merce see these images from nasa and so on and they say oh well this ancient galaxy or something from way back but what we see is one dimensional you know and a smear of things and you have to be told you have to take on faith that's really old you know how do you know how can you you you penetrate back there say thirteen billion years thirteen billion light years rather and then how do you distinguish this is really ancient when you're looking at this field oh sure that's an excellent question and this is actually the thing that  hubble's claim to fame is that he had discovered the property of the sort of rosetta stone that unlocks this because of what i said before that the things that are old are the things that are distant and it's easy to see on the sky we see a projected view of the universe  n until about one hundred years ago as i said people had no idea how to determine the distances to objects other than the ones that were very close like stars that were nearby us but galaxies that were far away there were there was no way  what his come to our rescue is the fact that the universe is expanding in the aftermath of the big bang and we can measure the distances to objects based on how fast they're moving away from us in this spectroscopy where we take the light that comes into our large telescopes and then we split it up into what we would call a spectrum by shining the light onto special optical elements that are placed in the path of the telescope at the back end and actually i can show you one of these here i've brought up an example of one such object this is something that we call a diffraction grating and it's just a small piece of glass and if i hold it at this angle you can see this little square inscribed region but now if i actually shine the studio lights off this towards a camera you'll see some colors flash by ok and the reason for that is that instead of this just being a regular piece of glass it's actually been etched with lots and lots of funny fine tiny little lines by a diamond so that there's twelve hundred lines per inch and what that does is it actually acts sort of like a prism but it actually splits the light into its colors and i can take this light in by tilting this grating it different angles yes i can change the color of light that comes through from blue to red and back and forth and so this is all the light that's coming from a single source in your studio which is like by us but we do the same thing and i could actually tell you what the chemical composition of your studio lights are by looking at the relative distributions of colors maybe some people would have done  something with like halogen street lamps or sometimes they'll sell in the back of magazines or comics or a glasses but really all you're seeing is one of these now we can do the same thing with objects all the way across the universe it's just that we have to shine the light from the telescope we focus it on to this and then a bounces off of this and onto a camera exactly like your studio yes so if we look at this i've talked about how these kind of optical elements will split light into its colors but the color of course as we said before represents a frequency or a wavelength ok and so the colors on the red end of the rainbow have longer wavelengths of light in the colors that are on the blue end of the rainbow have shorter wavelengths of light and we measure it in units of of that light or its wavelength and here we go so if you go from blue to red you're going from towards higher and higher wavelengths but then if you have different kinds of astronomical sources they might not have the same distribution of light intensity as relative to different colors and you can show that two different ways if you were to actually look at this in one of our instruments you would see as you go from purple towards blue towards red and then sometimes you would see a bright spike  your spectrum here and if you were to take a cross section just imagine taking a slice through this yes and then you can plot this line that you see above you see that the intensity of a spike and then it comes back down and then you see that there's another spike here again if it's smaller and that corresponds to this one here i am ok and this is actually a spectrum of real object in the universe and based on the location of the spike i can tell that this is an object that has hydrogen in the spot on  the thing that's interesting is we never see objects like this we only see them as they've been modulating by that are there the light travels through the entire universe and so it gets modulating so if you watch this so you can imagine going through a representative slice of the universe ok where you start with an object whose intrinsic spectrum looks like this and then i'm going to have it traversed through a simulated volume of the universe ok so this is a computer simulation not a real image of the universe but you have to imagine that it's filled with structures and galaxies and gas and as that light travels through by the time it reaches us on the other side we observe something that's somewhat different and you can notice that there are black lines in the spectrum here in the black lines are coming from the fact that trip on the journey it intercepts these structures in the universe that have gas in them and the locations of at the locations of that gas there some of the light from that background object is absorbed by the gas and then i think in a way from what we see yes ok so let me zoom in so you can see a little more closely so this is that object that i saw before and you see here is the spike that you see from hydrogen in that the object itself and it is in the object itself this is from other elements that are in the object itself this is ok carbon ok so in the same way that you would do spectroscopy you know so you're looking at a gas sample in the airport or somebody is trying to you know there's a crime lab that's interesting analyzing chemical composition they shine some light on it and they look at the chemical composition that's just what we do each chemical element has its own fingerprint and lines where we expect them to occur and we can look for those patterns to find different elements in different properties of objects in the universe what well that's what you find in the early so we mentioned carbon for instance would that be an indication that that is a later object or a very early object so in the early universe in the immediate aftermath of the big bang essentially the entire universe is made up of hydrogen and helium a little bit of lithium really in but it's really negligible and there's nothing else the universe was only hot enough for a few minutes to fuse latest elements on what you're going to table and so everything else that we know of all of the heavier elements on the periodic table oxygen carbon nitrogen everything all the way down was manufactured in stars either is they're burning nuclear fuel in their cores or there's some that's manufactured towards the end of their lives and well right there's sort of two different ways but the main point is that it all comes from stars and so most of the universe still is composed of hydrogen helium  everything else is only about two percent by mass but at the very early universe there's zero percent of everything else by mass and so when you look out you'll see that most of what you see in absorption so that as i said before this what you see is from hydrogen in the object itself in all of these lines that you see are coming from hydrogen between us and the object and then these lines you see that there's less there's less of this absorption that occurs to the right of the hydrogen peak get but there is some you see some individual lines right and those are coming from other elements ok so those are coming from in the early universe were mostly looking for carbon oxygen ok but you also see silicon and iron in maggie's ok there's the whole but closer to us to us now you would see much more of the heavy heavier elements yes that's what so the concentration of heavy elements those are rather universe gets old ok all right so is is my point was  when you're going is one of the indications that you are where you're headed there in the very early that the of the nature of those gases that you're able to pick up at that time that's a good indication yes so so we sort of got on this topic from talking about how we determine distance objects and i'll get back to that but let me just say that one of the driving questions behind a lot of this research is trying to figure out where and when the first stars of the universe ye warms in one of the ways that we look for that is to look for evidence of when this we called pollution of the universe by these elements produced in star started to turn on ok and we sort of because we're looking it backwards in time if you go to more distant objects we often almost think backwards in terms of the pollution of the universe that is we go progressively further back in time logic dictates that the chemical concentration of these other things should get lower and lower and then at the time when the very first stars formed it should go to zero ok so there should be no carbon for example example for the first star trek i just wondered if that was an indicator for you yeah absolutely that's one of the things that we're looking for i would say we're not quite there yet but we're say from nasa and they all say oh absolutely yeah the first stars and galaxies most certainly the first galaxies and of course a galaxy is just a collection of stars yeah that that's one way to think about it's a gravitationally bound collection of stars  in those very first galaxies were much smaller than things that we're used to because the universe hadn't had enough time to grow big big objects but also the way they formed stars is somewhat different  that's quite different sure without getting into too much detail i think one way to think about it is that in the modern day universe if you want to form a star the way you do it is by taking a large  gas and then letting it collapse under its own gravitational influence and when you take something and try to squeeze it into a smaller volume a parcel of gas it wants to heat up in the same way that the algae i often like to use is if you to spray paint can or something like this and you spray it and then you feel it feel as if you're cold and that's the opposite of what you're trying to do if you imagine taking the spray paint that you something smaller and smaller and smaller till it gets the point where it's hot enough and dense enough that it can start a nuclear fusion in the way that we do it in the modern universe is that you dump that excess heat through heavy elements where heavy means things like carbon and especially oxygen is very important that kind of stuff in the clouds yes so nowadays you have to seed a cloud with heavy elements in order to make a star like the kite like a sun like star i see the problem is there is there's a chicken and egg thing going on in the early universe because these heavy elements don't exist how would you make the first star in we don't actually know we have an existence proof that it must have happened because you're finding that well well actually no we haven't found any of these very first first generation stars this is one of the holy grails in the field but what we know is that they must have existed because we have stars now only have heavy elements so at some point this process started but that very first generation we still haven't seen we think that the way they cooled is just through their own hydrogen which is very inefficient and it would lead to stars that are much much bigger than the sun maybe fifty two hundred times bigger than the sun and they would have only lived for a very short while few million years and then they would have exploded but when they explode then they see their surroundings with these heavy elements and then the that surrounding partial can begin forming normal stars because it has these sort of seeds that it needs to do that in so there's sort of a qualitative difference in that first generation of stars from the subsequent generations that we think must have happened but we don't right even know it's good to know earliest stars began and the universe had become transparent at that time or is this does this even while it's ok oh is it so that's another interesting question so you would ask about different ways that we can determine that the arab is being illuminated by those first stars and we're looking back in time yes which means that we're looking towards ever more distant objects  using our r spectra and there's another way that you can determine that the universe is being illuminated by those first stars and this is also something that derives from our spectra so let me actually go back in show you the signature that we're looking for i think ok so here i'm actually showing the spectra of three different objects of the same class ok so here one of the things that's interesting that we've found in again this is what claim to fame was is that things in the universe that are more distant from us are racing away from us in ever higher speeds and how do we detect that when we detect it looking for what we call the red shift and here is a an actual example of three of the same class of objects three different redshifts in you can see that this one is registered by a factor of three point one that means that the many of us are familiar with the concept of the doppler shift like when a car may help to show this so if there's something that's a middling radiation as waves and this is a distant source those waves come out as fears but then as it starts to move to the right which source is actually catching up on the right side of it the waves are sort of compressed by the end of the source on the left side the waves are stretched yes because of the fact that the source is moving away and when waves are stretched in the real universe what that does is it makes the object look redder because red wavelengths are more stretched and so what this means when you look at these three objects you see that the bottom one is the closest one to us it well it's moving away from us at the slowest speed because it's the least red but you can see that the one in the middle looks the same but it's sort of shifted to the right it's yet redder yes that means this one is moving away from faster and then you look at the one of the top and this one's shifted even further to right and that means it's moving away the fastest ok and then what edwin hubble says is that things that are moving away from us faster are further away and what that means is that the bottom one is closest which means we're seeing it more recently the middle one is next up in the latter distance and the one that's on the top is the most distant object and therefore it's giving us the oldest view of the universe so when you're looking at a verse you can get this th simply look at right things right and one of the things that you can see here is that that top one to the left of this peak here it actually you see that the radiation more or less blacks out you can see a couple areas where there are prior to that time the universe it least immediately prior to that all of the surrounding gas was made up of hydrogen he said and that hydrogen had its electrons bounds to protons it was what we call neutral and neutral hydrogen is opaque to overbuy that radiation and the is the stars turned on the energy that comes out from the stars actually strips the electrons away ok from the hydrogen atoms and once that happens it becomes transparent the universe becomes transparent again this is a phenomenon we call rianna zation and we call it that because the universe when it was in its very early stages was electrons were all free from each other bouncing around it was only after it got cooler that they combined and then when the stars turned on again they were split apart again and one of the things that we notice here is that this spectrum here which is all black is you go towards these very distant very early objects the blackness in that spectrum is thought to relate to the fact is that the universe is becoming more opaque as you go back in early in the early period that it was opaque and astronomers are not able to view it in that period yet but it's when it becomes transparent that you can see and that's what hell far back is that when it becomes transparent well that's an interesting question we we have a sense of when the when the universe was starting to become when this veil was sort of lifted we don't know when when that process first began when the in the very first star the first photon we can only see the sort of late stages when it's almost all the way transparent again and one of the things that we're interested in is looking back and trying to peer further back into that  physics in and then we just let it go in one of the physical processes that light will leak out from galaxies so in the simulation they're galaxies forming and they start to shine and as they start to shine then the they start to evacuate little cavities  from being opaque to being transparent until eventually they start to overlap so let me let this run and will describe it as it's going to turn it on and don't be confused about the fact that we're kind of rotating around the cube and that's just for visual effects so you can see the three dimensional nature of this so the black parts of the simulation are the opaque areas where the hydrogen is neutral and what you can see are these sort of translucent areas that are growing and that's because there's radiation leaking out from these galaxies in the simulation and evacuating little bubbles around themselves which then start to overlap in as they overlap then you can actually start to peer in and see those galaxies as they're forming stars and eventually all of the bubbles will completely overlap now you see that's getting close and then the dots that are left are going to be the galaxies where the actual stars are forming and here you see it's almost complete now it's stopped i know all of this you can see back into how long did that take for do you have a rough idea for it to that's one of the big questions so we know roughly when it ended we think that this process ended when the universe was around a billion years old now not just for context the universe is about thirteen point eight billion years old so this was the first sort of five to ten percent of the history of not perhaps the big bang right ok the we don't know when it started but we think that it probably lasted five to seven hundred million years but the we can construct models that fit and you know they're bounded on one side yes because we know that the universe is transparent which means that contributed a lot in terms of the development of the instruments for looking back this distance so you know it's a very exciting thing but could you tell us about that you are the instrument that you have i guess that you're best known for but it looks like just a little thing kid if you could tell us why this has been so important oh sure and i'd be happy to this is a big part of my research there is a subculture within a strong i mean astrophysics of people who build their own instruments because they're all one off you know we have custom made telescopes that are very large so i being it  have a few percent efficiency and they don't have spectrographs attached to them if we want to do this kind of spectroscopy because when you're looking at physics we always say that you know pictures worth a thousand words in a spectrum is worth ten thousand pictures because you get ten thousand color yes and the reason for that is simple it's because when you're looking at this early time in history the universe the red shifts are extreme right we've talked about red shifts and things are moving away from us it the speed that looks  it looks like it's seventy eight times faster than the speed of light in fact it's these things are not moving away faster than the speed of light but it's sort of parallel that which means things that would normally be too blue for our head see have already shifted all the way through the optical there in the infrared  clean in there and so these are major undertakings this is an instrument like this takes about four years to build an additional two to plant and the reasons are numerous but one of the big challenges for infrared is that normally we think of infrared as night vision or heat vision but we're looking at very faint signals from the sky that are much much much fainter than trust real foregrounds and so the way that we have to control the instruments is we actually have to cool the instruments we've basically put it into a deep freeze liquid nitrogen temperatures so that it's so cold that it's even colder than the sky so that otherwise when we look at it it would be like trying to observe a faint astronomical object in this room with all the lights turned on because there's a radiation coming there's heat coming from everywhere and that's what infrared yes now that creates challenges so if you want to operate this thing it minus two hundred celsius then you put you know glass optics into metal fixtures and as everything cools down if you don't design it right the metal fixture will will crack the glass because everything shrinks it's the case that if the bit but i think it's fair to say that we're not always completely lucid and so we design these things and it's a major effort and then they want to design and they stay on the telescope for years but this is just a few the inside of one of these instruments and at the lower right you can actually see one of the sensors and one of the interesting things about these is you know we make use of sensors that are also used by civilian industry in the military one of the challenges with these is that these are called dual use technologies and since they're used for military applications to there's export regulations and we have to go through a lot of hoops to remember that i was about the size of this red thing yes so this gives you a sense of scale for the entire apparatus have no idea what this thing is doing when you just look at that nice box right there and it's good to know the back story there of how long it takes to put a piece of equipment like that together then to keep it operating like this for the observatory doesn't want to slow job yeah and that is where we wait for photons to come thirteen and a half billion across the universe yet and make it into the dome you know bounce off three mirrors and then into our instrument get recorded on the detector so these are ancient photons from the early user that isn't that amazing to see because i don't imagine are you able to sit here at mit and look at the data is that transmitted so because i'm asking because telescope time i've heard is really dear and a lot of demand for it and so and you need to have a kind of constant already or whatever viewing time or whatever it are you able to look at it hear the data it is technically possible in for that and it's often called the water heater effect which is that if you want to if there telescope time is that precious and you only get a few nights per year in and you are observing from your office in cambridge and you get a call from home that says that the water heater just exploded then it's going to be very hard not to go and pay attention to those that whereas if you're in chile too bad you better so i'm here i'm doing what i'm doing but it's never gets old as part of the job in the sky down there is magnificent that's so we hear that it's super clear and that i hope it lasts forever these wonderful wonderful telescopes i'm afraid that we are out of time i would love to go on and on because this is so very interesting you've given us a wonderful information and i really appreciate your sharing your knowledge with the public