 Okay, let's start. Very good, so welcome to all of you. Thank you for joining us. I would like to particularly welcome the new students who just arrived from the new diploma students. We have more than 40 new faces here. So it's great to have you here. And we have a proper welcome ceremony, but the best way to introduce you to ICDB is to have a great colloquium and we have a great colloquium speaker today. So as we are looking forward to the talk. So as you know, this is the year of the periodic table. So at some point we discuss with our colleagues on the server to see if we can have an active colloquium just on the origin of elements from the astrophysicist point of view. And we got a very good advice from Paolo Volara who is here and Paolo Kriminelli also held. And we found a great speaker who is here. He is Timothy Beers. So let me just try to embarrass him a little bit to read his CV. So Timothy is the greatest roughly professor of physics at the University of Notre Dame. And he's a co-PI in the Physics Frontier Center which is called Joint Institute for Neucarastrophysics Center for the Evolution of the Elements. That is funded by the United States National Science Foundation and he's a former director of the U.S. Kid Peak National Observatory. I spent 25 years working as a professor of physics and astronomy in Michigan State University. Timothy is interested in the origin of evolution of the elements in the universe and the assembly of large spiral galaxies such as the Milky Way. A field now referred to as galactic archeology. For decades, Professor Beers has designed and executed large scale surveys of stars in the Milky Way, efficiently sifting through literally millions of individual stars in order to find those objects that have recorded the chemical history of the universe in their atmospheres. His work has led to the identification of a subset of the so-called carbon-enhanced metal pool, C E M P, stars that exhibit a characteristic like element signature enhance C N O N A S I M G. Now recognized to be due to nucleosynthesis processes associated with the very first stars born in the universe. Presently he is conducting a survey of so-called R process enhanced stars which are metal pool stars that exhibit over abundances of elements produced by the rapid neutron capture process and place strong constraints on the origin of over half of the elements that are in the region iron in the project table. So please join me to welcome Timothy. Okay, very good. Well, certainly I'm pleased to be here. I have a long experience with Trieste. Turns out my first visit was almost 25 years ago, something like that. And work with many Italians here and throughout Italy on what you hear about today. So PR table is near and dear to certainly astronomers' hearts and I suspect to condense matter physicists at some point have had to interact with that and I know there's a work on C M here and other places. Let me just tell you what I know about the periodic table. Well, for one thing we have questions. How did this come about? For most of us, we just walked into a chemistry physics class in junior high and saw it on the wall. That was it. Turns out it had an origin. And nowadays astronomers try to tell a story of how those elements got to be there in the first place. And I'll be concentrating on a few examples, not the whole thing. And try and convey what we're doing now about this problem. But in fact, what I like about the story of PR table is that like many examples, you reach back into history and you see a story of science in action. It's not like you get it right the first time. In fact, people were discovering elements at the same time that they were trying to classify them. So it's not like you have the whole picture. It comes in on timescales of decades or many decades and you try to make sense of it. So it's the usual confusion, observation, theory, experiment, breakthroughs, prediction, et cetera, et cetera, et cetera, all built into one. And eventually, the purpose of this is to reach understanding. It's good, it's appropriate that the young people are in the audience today just starting a scientific career, because you have to understand, you're going to spend a lot of your time in the confused and observation and trying to work your way through to understanding. And it's not a linear path. It can be frustrating sometimes. So keep in mind, that's what science is, period. Doesn't matter how smart you are. So anyway, here are the elements in nature as most people probably saw them introduced from a young age. And I found that instead of just listening to my voice describe it, I found a couple of nice YouTube videos that summarized in pictures more quickly than I could some of the aspects of where the PR table came from. So I want to show those to you now. And hopefully, this will just go. Yes, part two is very nice. Matter can exist in the form of elements, compounds, and mixtures. When elements were discovered, a proper classification was required for the easier and better understanding. Many scientists adopted different ways to classify them. They tried to find out some pattern or regularity in the properties of elements. The first among them was Johann Wolfgang Dauberreiner, a German scientist who in 1829 found some groups of three elements which showed similar properties. These groups are called as Dauberreiner triads. Here, if we have a look at triad table, we can see that the atomic mass of the middle element is approximately the mean of the atomic masses of the other two elements. As this classification was a primitive step, Dauberreiner could identify only some triads from the elements known. Other triads did not obey the rule. Hence, the system of triads was not useful. After the failure of Dauberreiner's triads, the next attempt to classify elements was done by British chemist Newlands. By this time, 56 elements were discovered. He arranged all these elements in an increasing order of the atomic masses and found that every eighth element had properties similar to that of the first. He compared this to the octaves found in music. And therefore, this classification was known as Newlands octaves. However, this classification had its own share of shortcomings, the main points being that Newland could arrange elements only up to the calcium out of the total 56 elements known, after which the elements did not show similar properties. Also later, several new elements which did not feature in Newlands classification were discovered. After the failure of Newlands octaves, Dmitri Ivanovich Mendeleev, a Russian chemist, put forward a periodic table that was called Mendeleev periodic table. Mendeleev examined the relationship between the atomic masses of the elements and the physical and chemical properties. He believed that atomic mass of element was the most fundamental property in classifying the elements. He arranged the known elements in the increasing order of the atomic masses and their properties, and thus created the first periodic table containing 63 elements, till then known as Mendeleev's periodic table. Mendeleev's law states that the physical and chemical properties of elements are a periodic function of the atomic masses. In the Mendeleev's periodic table, the horizontal rows in the periodic table are called periods. There are in total seven periods. The vertical columns in the periodic table are called groups. There are eight groups numbered from one to eight. Mendeleev kept some blank spaces in this periodic table. The vacant spaces were for elements that were yet to be discovered. He named them Ekka boron, Ekka alumina, and Ekka silicon, and also predicted the properties which later were found to be correct. When noble gases were discovered, they were placed in Mendeleev's table without disturbing the position of other elements. The Mendeleev's periodic table, however, had its own demerits. Firstly, no fixed position could be given to hydrogen in the table as it resembled alkali metals as well as halogens. At certain places, an element of higher atomic mass has been placed before an element of lower mass. For example, Kubot, whose atomic mass is 58.93, is placed before Nikol, whose atomic mass is 58.71. Also, some elements placed in the same subgroup had different properties. For example, Banganese, M.N., is placed with halogens, which totally differ in properties. Due to these irregularities, the need for a new classification thus emerged. In 1913, Henry Mosley, an English physicist, discovered that atomic number is the most fundamental property of an element and not its atomic mass. This discovery changed the whole perspective of elements and their properties. Accordingly, Mendeleev's periodic law was modified into modern periodic law, which states that the chemical and physical properties of elements are a periodic function of the atomic number. The periodic table based on modern periodic law is called modern periodic table. Many versions of this periodic table are in use, but the one which is most commonly used is long. OK, I have one more short clip. But before we move off of this, a few things. Clearly, Mosley is the final word on the subject, not Mendeleev, but Mendeleev made the greatest significant leap. And he relied on the measurable property of atomic mass. That's something you could measure in the mid-1800s through chemical and physical techniques. Mosley, you noticed, did his published work in 1913. What happened between the mid-1800s and 1913? We developed a model of the nucleus and a model of the electrons surrounding the nucleus. So we had the notion that something else was involved, not just total numbers of particles in the center. And that's what gave Mosley the intuition to try assigning by atomic number, i.e. protons, instead of the total mass. And so another lesson of science is that it often progresses erratically, as I mentioned, but also close but not quite. This happens so often in what we do. It's very rare that ideas, new ideas are totally wrong. They hopefully advance the field to the point where the next person will see where the problems still remain. So don't defend your ideas till you die about being right. There is no right and wrong. We're all wrong. Your sole goal is to be slightly less wrong than the last guy. That's called a success. So let me close out with another short one. I want to show you a view of the periodic table that most people have never seen unless you happen to be chemist history buff. The periodic table has seven horizontal rows. What about these rows down below called the lanthanides and actinides? Well, they really belong to rows six and seven and should slot into these spaces. The lanthanides are elements 57 to 71 and the actinides are elements 89 to 103. To slot them in, we have to make the periodic table wider. This full table is more accurate and some versions are printed this way. This layout also makes it easier to see how many elements are in each row. Two in the first row, eight in the second, eight in the third, 18 in the fourth, 18 also in the fifth, 32 in the sixth, 32 in the seventh. All together there are 118 elements. So what you see there is that a view of the periodic table that most people have never seen. Now it makes sense because you notice that there are elements above in the long version. There are elements above the lanthanides and the actinides which are not in their group. They do not share common properties with those. And similarly, the layout when it's shown in the long form ties directly to the electronic model because those numbers two, eight, eight, 18, 32, 32, those are the numbers of valence electrons that are available for the chemical reactions to take place. And they stack up one at a time to match the protons to keep the overall atom neutral. And that's just not at all evident in the nice printable hang on the school version. You have to do some real mental gymnastics to get your 32 in the last two rows. But that's what it is. So that's why I like that. Okay, so back to the astronomy. All right, here we go. I think that's good, yes. Why do I have that thing still there? So here's the question we want to ask. How did the universe begin? It turns out, as you'll see shortly, astronomers pretty early on had an idea that the universe might have begun with a very large explosion and in the process might have been able to form the very light elements, hydrogen, helium and lithium. But still that leaves a lot of periodic table left to explain over the history of the universe. And so in the early years of trying to attack this problem, there were basically two approaches to answering the question, what is the origin of the elements? Now, in 1948, a triplet of famous physicists by the name of Alpha, Beta and Gamoff. Actually, I liked that. That was so clever in their title. And they said, okay, well, there was a creation event they hypothesized because that had been worked out by Gamoff some time before then. And conditions were so extreme that it's possible through a variety of proton and neutron captures to just make the whole thing, make the whole periodic table. And if you're curious, you can see in 1948 how they explained that that could be done. But look, just a few years later, 1957, a group of people known as Burbage, Burbage, Fowler, and Hoyle, or B-square FH to astronomers. And at the same time, Al Cameron, there's a picture of Al in the next slide, which I'll show, we're doing similar work. And they said, no, no, no, no. We think something else is responsible. That's something else's stars. What happened? That's less than 10 years. What happened? One observation of one star. Okay? So here's where we were. Hygiene, helium, lithium. So the rest of them, where did they come from? And you see that arrow pointing to the white element? That element's called technetium. That's a funny-sounding name for an element. Doesn't sound like a Swedish village somewhere, right? Okay. That's to remind you that technetium is not a natural element. It's man-made. The point is that, at least on the earth, because it has no stable isotopes. And that provided the clue. So it turns out that once we, and you don't have to worry about trying to read ancient spectra, I'll just tell you the answer. If you look at the bottom here, what you see are lines on some photographic spectra, little white lines. It's the reverse of a negative when you take spectra the old way. And those correspond to technetium. Not all stars show technetium. Only a particular star happens to be a star at the very end of its lifetime. What we today call an asymptotic giant branch star. These are stars which have run out of hydrogen in their core. And they've actually even run out of helium in their core. And they're climbing the giant branch for the very last time before they eject their envelope and become a white dwarf. During that period, they are capable of undergoing stages of evolution which free up neutrons. And those neutrons can be captured and form elements beyond iron. And that's what happens in this case. So the point is the longest live to isotope of technetium is four million years. And Paul Merrow in 1952, you see comfortably between the 48 and 57, pointed his telescope at a particular star. He didn't know that that was gonna leap out that night. But there were lines of technetium. Stars are much older than four million years. And we knew that. But the point is you couldn't have made that elsewhere like in the Big Bang 13 billion years prior and have it be found in that star today. It was made in that star. That's one of the joys I think of astronomy. One star, one observation, answer a puzzle that's been around for what? Forever. People didn't have an answer to that question. Okay, so they knew what they were doing. So ultimately, and I'll try to skip some of the more technical things, we have goals and we'd like to understand how the abundances in our solar system and how they differ from one star to the next look to make the discussion tractable. We divide that discussion into lighter elements, carbon, nitrogen, oxygen, iron group elements, calcium, magnesium, titanium. Actually, those are sort of alpha elements. The iron group is iron and nickel, chromium up to here. Some of you probably are already aware that interesting things happen once you reach iron. Typically that produces, you get to iron by way of alpha capture charged particle collisions that have to overcome Coulombic repulsion. But that repulsion gets so strong that past iron, it doesn't work. So everything past iron has to be made in some kind of particle capture, usually involving neutrons, which are uncharged. So these are where the neutron capture elements come in. Okay, so basically the B square of H wrote this paper in 57. Al Cameron, that's one of the last pictures. I took that at a party he was at before he passed away. And it's amazing, they were just doing very similar work, didn't know of each other's work. It was all theoretical. Coming up with a plausible set of stories as to how this all occurred. And they were amazingly good stories with a few holes left in them. We're trying to fill those holes right now. So basically astronomers, especially the theoretical astronomers, give them a chart and tell them here's some processes and they'll start making up stories. Here's how this happens, here's how this happens, here's how this happens. And we have a pretty good story for most of the elements. I don't have time to go to every one, but I wanted to highlight two of them in particular. And I'd like to talk about the lighter elements, which include carbon, nitrogen, and oxygen, and also the heaviest elements, the ones down here. In the lanthanides and actinides, okay? They sort of set the bookends of this story. So in a single slide, here's what astronomers think of when they say chemical evolution. We begin with the Big Bang, and here's the three elements that are made in the Big Bang in any quantity. And at some point, the first stars have to form. Forming the first stars is very hard. And the reason is, in order to make a hot thing like a star, you have to cool the gas. And cooling gas is very hard in the early universe because there are not many cooling channels. There's no easy way to get that cooling to happen. So that's a major hurdle that has to be overcome. But as a result, it takes a little bit of time for the universe to get around to the first stars. But after that happens, then it's possible for them to live their very short lives, explode, create other elements, including elements such as carbon. And once you have carbon magnesium produced, those open up other cooling channels. So it's hard at first, and then the damn bursts and stars can form because they can cool and become much smaller due to the readily available cooling channels. And then other things happen in this fans of the other lifetime of the universe, making other kinds of elements such as we find here on the earth today. And the picture at the bottom is meant to remind you that this is an era of time that only runs one direction. So it's always getting messier. It's always getting more polluted. The universe that led to us in the solar system and made our sun was already eight and a half billion years of chemical evolution through by the time it made the solar system. So when we look at our sun, we're looking at a bucket into which eight and a half billion years of chemical evolution has been thrown. And yet that used to be the only tool we had. And so astronomers realized decades ago that there's great advantage in finding objects which are born back here at a time when the overall pollution level is low. So you're looking at differentials, not integrals. That's the idea. And so that's what we're talking about today. Okay, so I have a long story for this slide. I'll cut to the chase. Basically, what we're looking for when we look for metal core stars, I'm talking about this right down here, is a characteristic set of elemental abundances that are only found at the lowest metalicity. We find different patterns for stars that appear to be less and less polluted. That's what we mean by the metalicity, basically. As we go to lower and lower metalicity, we find less and less abundances of elements. If we get to the lowest metalicity stars, we're looking at patterns to emerge that we never see, not in the sun, not in anything even close to the sun. Only those patterns are, if they're only found at the lowest, most pure state of matter, we can make the assumption that they came from the first stars. That's what we're trying to do, okay? I can tell you that story more if you like. But anyway, the examples I had in mind are what I call the elements of life, carbonation, oxygen, and the heaviest elements, including the jewelry store elements, gold, silver, platinum, and also the ones that can kill you, thorium and uranium, the universe makes it all. So it turns out that I had to include a slide here because I'm in Italy, and many of you maybe have know this story if you've lived here your whole life. There was a father, Angelo Secchi, who worked in Rome in the 1800s, late 1800s, and it turns out that he was a Jesuit and he carried out observations. One time he got left behind, didn't go on a solar exhibition, a solar eclipse, he was pretty irritated. He wrote about it. But he went observing that night and something good happened. It turned out that he describes it in detail here, but he noticed an extraordinary star and he wasn't just looking at stars. This is something that sometimes people haven't understood. Father Secchi was actually a very clever guy. It turns out that he invented and perfected a handheld spectroscope that he could put up to the eyepiece of his telescope and disperse the light. So he wasn't just looking at a white point of light. He was looking at the dispersed optical spectrum, star by star. So he got to know details long before we understood how to put labels on what he was observing. We didn't understand how all the elements interacted with light for the same reason that Mendeleev didn't have full understanding, but he was able to classify. And I liked one little bit of his summary here because I'm an observer. He says, although I have not examined the whole sky, I believe that you will have very few of these stars and they will be found among the red and variable stars. Here's to our best of our ability, here's what he saw. That's the star he wrote about. So you can imagine he was looking at many different stars and this one came out. The reason that star is so red is because if you look on the bottom here, those are, what you see in black are molecular bands. And basically they're absorbing the blue light. Those molecular bands by and large are carbon. So he had found carbon stars without knowing that it was carbon responsible and with his little portable spectrograph he was able to put that story together. So I always appreciated that. I'm gonna skip this one. So fast forward to this century and I'm doing a postdoc in 1983 and about eight or nine years into it, we were looking, had low metallicity stars. This one, this carbon enhanced metal pour star, that's the name that'll come up. The way we recognize a low metallicity star, I have to get centered on this a little bit better, is these two lines here, those are lines of ionized calcium. If there are any chemists, you might refer to them as calcium H and K, okay? Named after Frone Huffer, Frone Huffers, because he labeled from red to blue. But in any case, the calcium K line turns out to be the most convenient. What you can see is as you go from the top, all the way down, it gets weaker and weaker and weaker. Can you see that? Same thing applies over here, it's a little more obvious. There's a calcium K line and here it's gradually disappearing. It turns out that that particular line is what's called a resonance line and it's very sensitive to the overall abundance of heavy metals. And so what was surprising to many of us, myself included, is that when we got down here of the lowest metallicities, these are more than 1,000 times less than the sun in the scale that we measure, okay? About 3,000 times. We can still, of course, see those lines, that's how we get the numbers, but focus on this feature over here. That feature over here is a carbon molecule, CH. Also has a Frone Huffer name, the G band. And it turns out that most expected that that line would get weaker as the metallicity decreased. Because we imagine without knowing that there was some process that raised the overall abundance of all metals or of all elements in stars. But the carbon stays nice and strong as you go down. That was a surprise. We didn't understand that and astronomers didn't have a good story as to how that could be. That's another clue for people just starting their scientific career. When you don't understand something and your advisor doesn't understand it and his friends don't understand it, that's an excellent thing to publish. And basically say, here's something new, we don't understand it. Because that's the slide you'll be showing 20 or 30 years from now and say, now we understand this finally. But if you never published it, then you have nothing to say. Anyway, so I'm gonna skip some details here. But basically once we saw that there were a lot of theoretical activities which for the purpose of this lecture I don't have to go into. But astronomers started to recognize there may be more than one way to make a carbon star. The one that astronomers already thought about is something we call mass transfer binaries. I have a picture I'll show you in a second. But we realized this signature that was emerging at the lowest metallicity, that might come from the very first stars. That was something else. Okay, so I'm gonna skip some of this again. In pictures, it's easier in pictures. Here's how the carbon comes to be for many stars of moderately low metallicity. You start with a star anywhere from one to four times the mass of the sun. And at a particular point in its lifetime, it evolves to the place where it can produce carbon and also other heavy elements. And then it transfers that material to a binary companion. This star is now dead. It's turned into a white dwarf. Remember that's the end of the stage. But the receiving star lives on. That's what we observe. But it turns out that there are more exotic examples and this is another example of mass transfer just a slightly higher mass star which creates a certain kind of carbon enhancement which I won't go into. And then there's a really complex set which I'll just skip to the chase. Basically, we believe that there are kinds of stars which at the end of their lifetimes do not explode and expel all that they have made. But in fact, in certain mass ranges, the star which has built up heavier elements in its interior, including all the way up to iron before it explodes, finds a way to start forming a neutron star in a black hole before that final explosion occurs. So it actually eats up a lot of the heavy metals. And the only stuff that gets out are the light elements, carbon dioxide and oxygen. So the iron gets eaten up. You don't make the iron, but you make lots of light elements. So that's how you stay metal poor and get that carbon signature. Now that would have been a creative story we would have told back in 1992, but there were no models for that, so that wouldn't have made it. But that's what we think is going on. Okay, so I like to look at original spectra, discovery spectra, here is one. These are medium resolution spectra, just taking a smaller telescope, a star that's almost 10,000 times more metal poor than the sun. When I say more metal poor, that sounds double negative, right? Basically, what that means is for every 10,000 atoms of iron in the sun, there's one in this star. That's how pure it is, okay? And so there's that line of calcium down over here, very weak, but what, oh, sorry, over here. That's the calcium line right there, calcium K. But what's this? You know, it looks like a shark took a bite out of the spectrum right there. That turns out to be the G band, the CH feature, the molten molecular carbon. It's huge. And it turns out we started finding that in other stars. So in fact, when we looked at the relative abundances of carbon nitrogen, we couldn't measure oxygen for this star. They were way high, factors of 100, this is logarithmic, 100 or so, higher than other stars of similar metallicity. So maybe those were like those first, what was made by first stars and preserved in the next generation, that's the idea. Okay, and here is another example. You'll notice at the top, this is a logarithmic scale that runs backwards like any good astronomy. So now we're down below minus five. So minus 5.5 is 300,000 times lower than the sun. When I started, when Paulo Malaro started, the party line was you will never find individual stars lower than the lowest metallicity globular cluster, which is minus 2.5, 300 times. Lower than the sun. Everybody knew that. I had difficulty getting my first papers published, actually until some of the Italians, including Paulo and his PhD offspring, made the measurements that proved it to be true. So in any case, we're now down in this star to 300,000 times, so many orders of magnitude wrong, but the same deal exists. And so in fact, when we plot the now more complete measurements of these ratios, you see it's the same pattern. And I claim, and at least our current understanding suggests that that pattern is what the first stars make. So now it goes back to the theoreticians. They have to make their predictions and so on and so forth. So it's an interesting time. Oh, I forgot this one thing, I'll mention it quickly. March, 2014, one of the worst titles in nature history, except possibly for the guys who do the biomedical stuff. You can't even read the titles, but this is pretty bad. A single low-energy iron-pore supernova is a source of metals in the star and then they just give the coordinates. Nature Magazine owns the title and the first paragraph. So you can't blame the authors. There are a lot of friends of ours, including one Nobel Prize winner, Brian Schmidt. I like to point that out because that shows that even Nobel Prize winners like metal-pore stars, all right? Then I realized that that might be a little bit broad. So just the smart ones, they're the ones who like metal-pore stars. But in any case, they announced a star where they couldn't even measure any metals. It was below minus seven. That's 10 million times lower than the sun. That's getting interesting. I have a conversation with Brian Schmidt at a meeting during the period that they were taking that data. He said, Tim, we found the most amazing star. And he described what they had found so far. And I said, let me tell you, I don't want you, don't tell me no more. It's gonna have carbon. It's gonna have a little bit of calcium because that's where you can see the resonant line and perhaps some lithium. You know, and that's about it. That's all you're gonna see. And he looks at me like, did you talk to the observer? I said, no, let me see. That's cause it's one of these CMP no stars. Those are the, that's the name we give to that particular signature. Okay, that's what it is. Do you see the carbon there? Right there. We couldn't measure at the time. In oxygen, we have a measurement for now. Have some magnesium and there's some calcium and lithium is measured. Everything else is an upper limit. You can't see it at all. Looks like a continuum. So we think that this pattern, which we established some years ago is what the very first star has made. Okay, so I'm gonna skip some of this so I can talk about one other area. I realize I had too much here for this discussion, that's okay. Oh, one thing that's interesting. I'm an observer. So I love sort of the sociology of this. So a lot of times, once you get a great idea and you have at least a modicum of data to support it, that's when the pit bulls jump in. That's when the theoreticians attack. And this is 2007, 2008 classification of extremely metal pores, simplifying, that's a terrible name. Simplifying, they're referring to carbon-enhanced metal pore stars being responsible to the progenitors of them for the re-ionization of the universe. I mean, you know, this just comes out of sitting around having coffee. Yeah, and if this happens, then this happens. Let's write a paper. I mean, this is all in this span of like 12 months. And so it's sort of fun. And some story buried in there is probably a piece of what the correct story is, but we won't know for a while. Not all those ideas are true. Okay, so since time is limited, I want to spend at least 10 minutes or so talking about the other thing, which is neutron capture processes. Some of you may be familiar with the terms slow and rapid neutron capture. That's very simple. It just means that under certain circumstances, a nucleus can be bombarded by neutrons. That's at such a rate that there's plenty of time, in the case of the slow neutron capture process, plenty of time to have the beta decay occur before the next neutron comes along. That's what we call the slow capture. The rapid capture is just the opposite. You bombard a seed nucleus so rapidly with neutrons that before they have a chance to decay. And what is a neutron decay into? A proton and an electron. You're making elements, remember? And so before that has a chance to happen, the next neutron comes. That allows much heavier elements to be formed than you'd get with the slow, the slow neutron capture. Well, some of you may be aware that in the last couple of years, people have gotten real interested in the R process. And I'll touch on that once again because of a little something called a neutron star, neutron star merger. But here's the essence of this process. This is the chart of the isotopes. Just like the periodic table is a chart of our knowledge, the chart of the isotopes is a chart of our ignorance. It's basically the only thing we actually know details about are what you see in the middle of it in black. That's in the so-called Valley of Stability. People are building billion-dollar instruments today, one of them on the campus of the university I used to work with, work at, Michigan State, in order to learn more about what's on the outside. This is a simulation of the R process, and I just wanna say it without spending, whoop, sorry, gotta go backwards, here we are. I wanna start the video without too much commentary on it. Here we go. It happens pretty fast. Here's a clock. You see the clock ticking away? It takes a while to even get up to a second. Now we're at a second. These are all isotopes that were formed basically in the first second after an explosion. That's why it's called rapid. And look how far up it goes. These are the high neutron. These are high protons up here. Everything after that first second is decay. You see that? And then just decay. Turns out that's really, really important, as nature just did that. And we were watching. That's what makes this exciting. Oh, and just so you don't have to do the mental gymnastics, the process is basically terminated at 80,000 seconds. That's 10 days. That's it. That is you can, if you have a source that's gonna make the R process, 10 days it's over. Not thousands of years, et cetera. 10 days. Well, it turns out that about 30, not quite 30, 25 years ago, we actually found a single star that had lines that correspond to the R process in the star. Remember the story of Paul Merrill and the Technician? Well, this is not quite as exciting, but second. Because elements, and these are metal poor stars, a thousand times lower than the sun. Elements like Europium, Lanthanum, Serium, Neodymium, Disprosium are not expected to be seen in the spectra of very chemically pure stars. But there they are in this one. That means that this star formed out of gas that the R process polluted. And it's so chemically pure that before any of the mixing could take place, this star actually formed and recorded it. So we've been looking for these kinds of stars to help us tell the story of how these came to be. And here's another sort of interesting thing. Same star, we go to large telescopes and we measure high dispersion spectra, similar to work that Paolo's done in the past. And we go with Hubble Space Telescope and look at the ultraviolet spectrum, which we can't see from the Earth's surface. And when we take that, we can measure the abundances of the what's so-called second R process peak. And what you see here is not a fit. That blue line is not a fit. Because first thing people say is, oh, your air bars are too small for that fit. No, it's not a fit. That's the solar pattern brought down by a factor of a thousand. So that's what we see in the sun in a star which was born 12 and a half billion years ago. The sun was born four and a half billion years ago. That says that the same R process that made the lower half of the periodic table in our sun was active at the very beginning. That's a big clue. So we can understand the nature of the R process if we find more of these stars. And so I'll skip some of this. This is what we've been doing. And part of the story has to do with the details of the models, but basically for years we knew we had to, if we're gonna make the R process, we had to have something explode because the energy involved. So many people said, well, we know core collapse supernovae happen. Turns out that there are problems with that model. So people tried to look at neutron star mergers in a theoretical way even before we knew they happened. And there are variations on the theme that people have made. The problem comes even now after we've observed a neutron star merger to occur is we have to now say, does the sums work? Does the chemistry that we observe and the stuff that's predicted and we can measure in these stars, does that all add up to something that is a coherent story of how the elements were made? That's the stage we're at right now. And in the interest of time, I'm gonna skip some of these slides and just bring it to the punchline here. Some of you might have seen this. It's a very nice cover of the neutron star merger that happened in August of 2017. Just so happened, I was down in Chile in August of 2017, not observing, sitting there on a visiting arrangement that Notre Dame had with one of the universities. But I have sent my two students. This is a student story. I had sent my two graduate students to go observing at Los Companas Observatory in Chile. Trying to find more of these R process enhanced stars. And on the night that the neutron star merger occurred, or the signal reached Earth to be more precise, they were sitting at the telescope. So you know what happened? The powers that be called them up and said, oh, by the way, we're relieving you of your time on this telescope. We are now taking it over for a far more important thing. And of course, that far more important thing was understanding the nature of the R process. And they said, anyway, that's what we're doing. I said, look, they were second year students at the time. I said, second year graduate student. I said, first things first, grouse a little bit. Don't just give it up. I mean, they own the telescope, they can do what they want, but let them know you're not exactly pleased. Because maybe they'll give you some time back. This is how it works. And so they grouse and they call me back the next day and say, yeah, we got some time back and that's good. And then I thought, wow, that was easy. I said, grouse a little bit more. And then go make yourself useful. Go around and observe at some of the other telescopes on Las Campanas the next couple of nights, because that's when all the action is happening. Maybe we can get you on the paper. Hmm. All right, so they did that, called me back. They said, Professor Beers, guess what? Good news, we're on the paper. Okay, good, it's one of the papers in this volume. And then I thought about it a little bit more and I said, wait a minute, this is my project. I'm paying my money, my grand money, to send those students down there. So maybe I better grouse a little bit. So I called up the first author. And actually she was very understanding. She said, well, they had already decided that anybody who got kicked off the telescope, PI plus who was physically there, they're on the paper. So there's a paper in this thing, which basically is the only one which actually says neutron star mergers are processed nuclear synthesis. So historically that will be, I think, an important paper. But here's, and I'll probably close out here because I want to leave time for questions. I hope this, well the lights make it a killer. I don't know, do we have, can you turn off the front lights a little bit? Is that possible? These? Yeah, is it possible? I'm trying to bring out a color, that's the problem. So what you're looking at is before and after. You see this thing pretty easily. This is what I'm trying to make sure you can see. Okay, because the color is important. Can you make it as good? You can turn them all off, it's only for a second. Oh, perfect. Okay, that's good. Okay, so August 17th, 2017. This is a distant galaxy, not inside our own. This is when the neutron, the gravitational wave signature was captured by Virgo and Ligo. So they could triangulate and very quickly it was found to be in this direction. You see that bright and blue? You know what that is? Actonites. They're the big, they're not even the actonites. There are those isotopes that you saw in that simulation, beginning to cascade. That high energy cascade is what gave that blue color during the explosion. And then here you are four days later. It's fainter and it's what? Red. You know what that is? Lantonites. Because it turns out that the lanthanites have very tightly packed electronic levels. Right, they're big, complex elements and very closely packed electronic levels. And it turns out that in the particular energies that four days later the decay has reached, only the lanthanites are capable of providing significant absorption. So that red color comes from absorbing the blue color that came from the decaying isotopes. But the take home bit is clear. What we're looking at is the birth of those lower two rows and some of that other half of the PRI table that night. So in fact, that's the kind of power you have when you understand these details. Okay, so I think I'll just leave that slide up here and attend to some questions if people have, let me do that. Thank you very much for the opportunity for a very nice presentation. Any questions? Sorry, you said that there are probably many sources of our processes and do they get different signatures or they just contribute to this? Yeah, so the question is, there may be more than one source or family of sources for the R process. It may all be neutron star mergers. My personal guess is that's probably not the entire story because the part of this lecture I didn't get to tell you about is we're building up an inventory of many more R process enhanced stars like that first one that we saw that had the detectable Europium and other lines. And when we study those patterns, we see the variations which are small but we also can see what kinds of signatures that are expected in different models and how those translate into the observational plane. But by building a big enough sample, that's when it really gets interesting. In 25 years, since we first ran into that star I pointed to earlier, we've only found about 2012. The community has found 25 more. So that's one star per year. That's a pretty slow discovery rate. And so some years ago, five years ago, I decided to do a survey to find more of these fast. So I'll spare you the details, but I figured out a way with the right people and the right telescopes, we could do it pretty fast. So we've already found about 40 new ones in the last couple of years. We wanna get the sample up to 100 or more. Then you can actually see is that distribution of the amounts of material that you see is the Europium coming up and the right amount to have been formed in a single burst of neutron star mergers early on was distributed over the history of the galaxy. There are many options and these are the data that we think we'll sort it out. And you're gonna need to know that no matter how many gravitational wave detections that people find, you're still gonna need to know does the chemistry work? And that's how we think we'll do it. More questions? Yes. Hi, Tim. And just a curiosity about the Merrill, Merrill star in 1952, how did you know the lines of technetium actually at that time? Since was not stabilized, that popped up to my mind right now. Yeah, yeah, that was 1952. Technetium by that time had actually been observed in the lab. Okay. In the Manhattan. That was done by, I think the people at Berkeley and some of the early cyclotrons, they had done a lot of like bombardment of various elements just to sort of see what would happen. And technician was one of the things that came off. Thanks. Yeah, but that's exactly right. So as a follow up myself, what happened historically? Did people get convinced immediately after this? You know, just about the origins of the elements coming from the stars after the folder and the paper? Yeah, well, I mean, the simple, I mean, what was great was you were using physics arguments. So the physicists had no basis to complain, okay? Because basically you're looking at a half-life, which is so short, that there is no mechanism that would be plausible to transport that material to that star. It had to be made in that star. And if you could make that kind of heavy element, it stands to reason that many of the other elements could be made. That's happened to be S process. So that doesn't account for everything. But it says, you don't have to do it all in the Big Bang. Right, but I mean, this is 52 and then it took five years for the folder and the paper. Yeah, well, people, I think, even though the original Alpha, you know, Beta and Gamoff suggestion was initially taken seriously. Very quickly people were able to demonstrate that if the universe expanded anywhere near the rate that it probably was. This is an inflation expansion. This is a later expansion. The universe gets too cool too fast. And so you can't, the density isn't there for the interactions to form heavier nuclides. So basically once you get beyond Helium and Lithium is just one beyond Helium, there's just no way you can support it. Yeah. Well, I'm not expert in this field, so I can ask a very simple question. I assume that the observation you've made is in different galaxies and stars at different places in the universe. So that means at different times in the history of the universe. Okay, well, let me clarify that. Already, that's wrong, because your assumption is flawed. Okay. Every star that I showed today, with the exception of the one that died in a neutron star merger, is in the Milky Way galaxy, our galaxy. All right, so that was a different question. There are people you will hear talks from in this venue who will try to convince you that the only way to understand the first billion years of the history of the universe is to build a bigger and far more expensive telescope to look to the edge of what is possible. You've probably heard talks like that before, either from space or from the ground. Turns out that that's not true. It turns out that if we believe the axioms of physics that the laws are basically or exactly physical laws in this universe are the same everywhere and every when, then the stars around us in the Milky Way saw the early history of the universe just as much as the most distant objects that we can see at the edge of detectability. We find those stars. They have chemical ages, which are beyond the most ancient quasar systems. If you put a redshift, as astronomers like to do, as a substitute for distance or age, the highest redshift objects that astronomers know about where you measure a redshift is somewhere around seven to 10. We argue seven to 10, all right? Well, it turns out that if you take the ages of our stars, which we can determine from the radioactive decay of certain heavy elements like uranium and thorium, and turn that in redshift, the equivalent chemical redshift is about 30. So our stars were born before the most distant objects that those guys will ever see. So we're doing that. So there is no relationship between the age of the universe and the formation of more complex elements. Oh, I mean, there is a relationship. Absolutely, there is a relationship. The first ones formed early, probably 12, no more than a billion years after the Big Bang, some probably a few hundred million after the Big Bang, and continuously have been forming in certain places ever since. So we see stars formed today in our Milky Way, in the disk of our Milky Way. So we cover the whole 13-ish billion years of history. But the part of the history that matters for this problem is all crammed into the first 500 million to a billion years. Thank you very much. Yes. More questions? Okay, very good. So before we finish, can I have the students who just arrived from the diploma students? Can you raise your hand just for a second? Very good, very good. So let me tell you something that you don't know, but this is a tradition here, is that at the end of each colloquium, we, after the question session, everybody is asked to do the room and go for some refreshments, except for the students. The students come here and ask questions to the speaker. Any questions you want to ask that you may be shy to ask in front of the audience? So don't be shy, just let everybody leave. The students come and you can ask anything you want. What is the periodic table, for instance? Or you can ask, what happened? Were there light elements or lithium? And so how did it happen at the beginning of the big man? Or what happened with the, how is it the process that the heavy elements are being produced, anything you want? And if you don't come up with that questions, just ask some personal questions. I think the speaker is a very, very friendly person. He can answer many questions. So let's now do this. So let's thank Timothy for such a great presentation. Thank you.