Newly Discovered Star Shouldn't Exist, Says Theory

Reporting in Nature, researchers write of discovering one of the oldest stars in the Galaxy, formed some 13 billion years ago. But one current theory of star formation rules out stars of this chemical composition and mass. Astrophysicist Anna Frebel discusses how such an unusual star might be born.

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IRA FLATOW, host: You're listening to SCIENCE FRIDAY. I'm Ira Flatow. Next up, we're getting into the way-back machine, going back 13 billion years ago, near the time of the Big Bang, because this week in the journal Nature, astronomers reported the discovery of a very primitive star formed back then when the university had very few chemical elements, mostly just hydrogen, helium, a little dash of lithium.

There's just one little problem with this discovery: The star should not exist according to one current theory of star formation. But there it is. How did it get there? How did it form? Maybe it's back to the drawing board on our theories.

And what about the sun? It was born billions of years later than this early star. How different is it? Well, joining me to talk about this is my guest. She was not involved in the study, but she has found some very old stars herself. We're talking with Anna Frebel. She is a Clay Fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. Welcome to SCIENCE FRIDAY, Dr. Frebel.

Dr. ANNA FREBEL: Hi, thank you very much for having me.

FLATOW: Tell us what is so unusual about this star.

FREBEL: Well, in order to answer that question, let me just zoom out a little bit and sort of put what you said in my own words. The universe, as you mentioned, consisted only of hydrogen, helium and a little bit of lithium right at the Big Bang. That's what all was made in the Big Bang.

And over time, all the heavy elements we're made of - carbon and oxygen and iron - they were made over time in stars and supernovae. So the universe only very slowly built up some quantities of these heavier elements.

Now this new star has very little of especially iron and carbon, and so we then believe that the star must have formed very early on in the universe, and it's one of those stars that has one of the very least amounts of iron and carbon that we know of. And that's what makes it exciting for us. We can look back in time by studying the chemistry in these stars.

FLATOW: But it doesn't conform to the way we think stars have formed, I understand.

FREBEL: Well, the star formation in the early universe is actually a very big puzzle. Now, we know that star formation today is very complicated, and you would think that in the early universe, when fewer metals and heavy elements existed, it was easier - but, well, it is easier, but it's not easy.

And so there are actually several competing theories for star formation out there. And while we know that these stars exist, and certainly the new one exists, and there is some little quibble now with one theory, but there are several other theories that are not touched by the discovery of this star.

So we're definitely learning something new here, and I think it's very exciting to have a new star that looks slightly different from, for example, the stars that I have formed. So they're all kind of from similar generations, they're all from a similar family, and - but they all look a little bit different, and they all tell us something new about how star formation actually might have proceeded.

FLATOW: So can you give us an idea or a guess on how a star like this might have formed then?

FREBEL: Yes. So the very first generations of stars that formed in the universe, those were actually quite massive. They were probably 100 times bigger than the sun, more massive than the sun. And the reason for that is that the primordial material, just the hydrogen and helium, that couldn't really cool down enough.

So if you want to make a small star, it needs to - the gas from which it forms needs to become very cold, so it can clump together and essentially make a little ice cube. Now, the smaller your ice cube is supposed to be, your star, the colder it has to get.

And in the early universe, for the very first stars, there just wasn't enough cooling there. There weren't enough cooling mechanisms there. Metals such as carbon and oxygen, they act as cooling agents in a gas. They just radiate energy away. If you don't have that, your gas cannot get very cold and which means you make very big stars.

Now, the newly discovered star is most likely even lighter than the sun. So that means you have to get - you have to cool the gas in order to make that star before the star can actually form and start its nuclear fusion in the center.

And so there are different theories, and this has been going on in the field for several years now, how do we - how can we get the gas to cool. And one idea is that carbon and oxygen, the atoms, the carbon and oxygen atoms, do the job, and there are many stars that support that theory.

FLATOW: So they draw off the heat from the star.

FREBEL: That's - from the gas...

FLATOW: From the gas. Right.

FREBEL: ...right, so it can start forming an ice cube, a clump.

FLATOW: That's counterintuitive to hear that the stars get colder to get hotter.

FREBEL: Yes, yes, yes. Well, you first have to make the star. So as the gas gets cooler, the gas condenses, clumps together, gravitation acts on it. And at some point you kind of have a gas ball there that is dense enough that it can - as it - and then it keeps falling together based on gravity, and that heats it up in the very core, whereas the outsides are still rather cold.

And then at some point, nuclear fusion starts to burn and to ignite, and only then we actually call it a star. But you have to get to that stage. You have to make it small enough and dense enough in the center that hydrogen burning, so hydrogen gets converted to helium, can actually begin.

FLATOW: And so are there other particles or dust or whatever out there that can act as the cooling agent instead of having...

FREBEL: Exactly, exactly. So it could not just be carbon and oxygen atoms. It could also be dust grains. And dust grains, of course, consist also of some kind of heavy elements, but they are clustered together in little grains, and those grains can be made in supernovae explosions, for example the explosions of the very first stars.

And so this material gets created. The dust grains get made, and they get spilled out into the interstellar medium, and they act as cooling agents there, as well. And so according to that theory, this new star should well exist, even though there is now, you know, a little challenge to this idea that carbon and oxygen atoms are the major cooling channels, the major cooling mechanism, to form these low-mass stars in the early universe.

But I think, you know, a little controversy is always great. It gets us excited. We will go back to the drawing board, and future conferences I'm sure will have a lot of discussions about this. So it's - you know, new data is always exciting, especially when you think about the early universe, which happened such a long time ago, and these stars are one of the few actual data points we can get from this time back then.

FLATOW: Now, scientists, whether you talk to them about not finding the Higgs boson or not understanding a star formation, they get more excited about the negative results than they do about the positive results.

FREBEL: Yeah, because it definitely rules out things. You know, we - everyone has lots of ideas on how it happened, and that's great because we want to find out. But we need the data to rule out all these, you know, sometimes more or less crazy ideas.

(SOUNDBITE OF LAUGHTER)

FREBEL: So it really helps to find something that, you know, looks yet a little bit different because it sparks a lot of new ideas, and hence we can fill in the puzzle of the universe.

FLATOW: If we have in biology biodiversity, what would we call star diversity?

FREBEL: It's definitely chemical diversity...

FLATOW: Yeah, chemical diversity.

FREBEL: ...because we are studying the chemical abundances in these stars because we believe they have been preserved in the outer layers of the stars since the time of their birth.

FLATOW: As Carl Sagan used to call them, star stuff, we're all made of star stuff.

FREBEL: Yes, we are.

(SOUNDBITE OF LAUGHTER)

FREBEL: Yes, as I said, all the elements have been made in stars and supernovae. And the clue with this new star, as well as the ones that I have previously found, is that they were right at the beginning of the stuff. So perhaps only one or two generations of supernovae made the very first amounts of heavy elements, and then these little stars formed from the slightly enriched primordial material, and they're preserved exactly as chemical fingerprint in their surface and transported it with them until today.

And so they are in the Milky Way galaxy today. They're shining right there for us every night, and we use the world's biggest telescopes to observe these fossil stars.

FLATOW: You have one heck of a job. 1-800-989-8255. Let's go to Ed(ph) in Minneapolis. Hi, Ed.

ED: Hi, Ira.

FLATOW: Hi there.

ED: Yeah, my phone is starting to cut out here, so just quickly, I'm just curious. I didn't hear where the star was located at, how old it is and, you know, if it's from the beginning of the universe, how do they really figure that it's from back then?

FLATOW: OK, good question. Where - how close is it? Where is it? Can we see it? And how old is it?

FREBEL: Yeah, I'm not exactly sure what the exact coordinates are right now, but it's a reasonably bright star. If you have a small amateur telescope, you can probably see it from your backyard, depending on where you live, you know, Northern or Southern Hemisphere. I think this one is located in the Southern Hemisphere. It is not too far away. I heard it's about 4,000 light years away. And that, for our galaxy, kind of means just the beginning of the outskirts, so not too close, not too far away. And...

FLATOW: And is it in a constellation we can look toward?

FREBEL: I actually have to admit that I don't know the constellation.

FLATOW: I heard it was in Leo.

FREBEL: It's - that is probably true. For us, astronomers, we are a little bit geeky. We usually don't really go by the constellation. So we have, you know, the coordinates that we dial into our telescope and just go.

FLATOW: I know because...

(SOUNDBITE OF LAUGHTER)

FLATOW: ...I read your paper and it had all the geeky coordinates and didn't tell me where - how far away it was even in there. And I found...

FREBEL: That is true. But it's 4,000 light years away. And...

FLATOW: How - well, let me stop you there. Because, you know, if something is that old, near the beginning of the universe, how come it's so close, relatively speaking?

FREBEL: Yeah. That is the beauty of this work with these old stars. If I can just zoom out for a second again, the way we think that large galaxies like the Milky Way form is through a hierarchical assembly. Now, that sounds like a mouthful, but what it means is you start in the early universe with a small galaxy. And it - like a little kid, it wants to grow bigger, and it does so by eating up other, even smaller galaxies and gas and stars and whatever it can find. So it grows and grows and grows, and eats up all these smaller systems.

And any of these old fossil stars that we're finding, based on their chemistry, we can tell that they're formed in the very early universe, probably in a small galaxy. And then that galaxy was likely eaten up by, you know, a bigger one. And so it got deposited into a new bigger one. And then perhaps, that one itself got eaten up, again, by yet another bigger one. And so it's slowly made its way, over cosmic timescales, into the Milky Way, into the outskirts of our galaxy where we see it today.

FLATOW: So we're in the stomach of some other galaxy.

FREBEL: Yeah. Well...

(SOUNDBITE OF LAUGHTER)

FREBEL: We have definitely eaten up some galaxies. This is actually still happening today. We have evidence of that, too. A huge star streams in the outskirts of the Milky Way. They look very pretty in photos, but it's actually quite a violent process.

(SOUNDBITE OF LAUGHTER)

FLATOW: Well, Dr. Frebel, this is quite fascinating. I think we all learned a lot about star stuff today. And I want to thank you for taking time to be with us today. And good luck in your work.

FREBEL: Thank you very much. Bye-bye.

FLATOW: And you can - bye-bye. Have a good weekend. Anna Frebel is the Clay fellow at the Harvard-Smithsonian Center for Astrophysics, a famous place in Cambridge, Massachusetts.

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