Have Astrophysicists Spotted Evidence For ‘Dark Stars’?

Data from the Webb Space Telescope may hold evidence of ancient "dark stars," which would’ve been powered by dark matter, not nuclear fusion.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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• 0:17Ira Flatow?

  Science Friday is supported by MathWorks, creator of MATLAB and Simulink software for technical computing and model-based design. MathWorks, accelerating the pace of discovery in engineering and science. Learn more at mathworks.com. Hi, I'm Ira Flatow, and you're listening to Science Friday.

• 0:40Ira Flatow?

  Today on the podcast, one theory about the early days of our universe, and how stars then might not be like stars we have now.

• 0:50Speaker 02

  This dark matter annihilation takes place throughout the star, which, by the way, is really weird-looking. Its radius is 10 times the distance between the Earth and the Sun. These are cool, big, puffy beasts.

• 1:03Ira Flatow?

  Scientists think they may have discovered a new kind of star. They named it a dark star, but it actually shines very brightly. I know it sounds weird. Considering that the star is believed to be powered by dark matter, not nuclear fusion, weirdness is par for the course in cosmology, is it not? It goes without saying, this idea is controversial, but a team of astrophysicists say they have spotted evidence for the existence of these dark stars in data collected by the James Webb Space Telescope. The study was published in the Proceedings of the National Academy of Sciences. Joining me now are two of the authors of that research. Dr.

• 1:44Ira Flatow?

  Katherine Fries is a theoretical astrophysicist and professor of physics, University of Texas at Austin. She first proposed the existence of dark stars in 2007. And Dr. Cosmin Ilie, an assistant professor of physics and astronomy at Colgate University. Welcome to Science Friday.

• 2:02Speaker 02

  Thank you. Thank you. It's great to be here.

• 2:05Ira Flatow?

  Oh, it's nice to have you. Dr. Fries, what exactly is a dark star?

• 2:11Speaker 02

  A dark star would be the very first kind of star that formed in the history of the universe when it was about 200 million years old. They're made of hydrogen and helium from the Big Bang, almost entirely of ordinary stuff, but they're powered by dark matter. The way the first stars form is inside proto galaxies that weigh about a million times as much as the sun. And smack in the middle of these objects, there is a lot of dark matter. And it turns out that if the dark matter is made of particles that annihilate among themselves, then when two particles annihilate, they turn into something else. And the stuff that comes out interacts with the hydrogen and gets stuck inside this collapsing

• 2:55Speaker 02

  cloud and turns it instead into a star.

• 2:59Ira Flatow?

  So it's shining brightly then?

• 3:01Speaker 02

  It starts out small, weighing about the same as the sun, but it keeps growing and growing and growing until it gets a million times as massive as the sun and a billion times as bright. And if you're a billion times as bright as the sun, yes, I would say it's shining brightly.

• 3:13Ira Flatow?

  But Dr. Iliya, you say you have four candidates. What do they look like? What's the signature for them?

• 3:20Speaker 03

  Okay, so physically, if you look at the image, they look like red dots. Okay? They're part of this plethora of objects called red dots. Some of them are called blue monsters. They're really compact objects, very compact, meaning a few hundred parsecs or less, which emit insane amounts of light. So if they're really galaxies, they have to have packed those stars incredibly efficiently. Like in a small amount of space, you have to have many, many stars.

• 3:50Ira Flatow?

  Right.

• 3:51Speaker 03

  For this reason, our interpretation is, well, if it's actually a star, it could have the same signatures as a galaxy. And that's what we're showing, both with spectroscopy in this latest study and with photometry in the 2023 study.

• 4:07Speaker 02

  The predictions that we made back in 2012 were how much light would come out of these things at different wavelengths. It's called a spectrum. And then we compared that to the JWST filters. And we said, yes, these things would stick out. We would be able to see them in the JWST. And so this spectrum, how much light at different wavelengths, was a specific prediction and it matches. So that is really exciting. But the third property is the one that I'm gonna let Kazmin describe, which is a helium line in the spectrum.

• 4:43Speaker 03

  Yeah, definitely. So there's a telltale signature in the spectra of dark stars. An absorption feature, meaning, you know, if you take the spectrum, there's a dip in the spectrum. That means there's a lack of light compared to the light that comes in the, you know, narrowing wavelengths, a lack of an absorption feature. But a specific wavelength, that line is expected to be there for dark stars. Why? Well, because in their atmospheres, they do have sufficient helium, but more than that, the temperatures of those objects is in such a way that that helium is seemingly ionized, that means it lost an electron out of the two it has. And more than that, that electron that still remains there

• 5:27Speaker 03

  is in a specific excited state. So it takes a combination of factors for an object to actually have this feature as an absorption feature.

• 5:36Speaker 02

  This helium-21640 line is a smoking gun for dark stars. If it's in there, then it is not an early galaxy. It is a dark star. And as we keep, as we keep scanning the JWC, look, we don't have, we don't even have to do an observing survey because the data are coming in and we can watch as it comes in and say, aha, there's a candidate. And then we look at the details and does it have that dip right there? Or not?

• 6:03Ira Flatow?

  When you say it's powered by dark matter, Dr. Fries, what does that mean?

• 6:08Speaker 02

  That means the, if the dark matter is of the type that self annihilates, two dark matter particles hit each other and turn into something else. The things that it turns into, which would be particles of light or electrons, hit the hydrogen inside the collapsing hydrogen cloud and they get captured. So it's kind of a heat dump. Into the dark star. The energy that used to be in the mass of the dark matter particles instead becomes energy that powers the dark star. And this is completely different from fusion. I mean, fusion takes place in the hot cores of stars.

• 6:50Speaker 02

  This dark matter annihilation takes place throughout the star, which by the way is really weird looking. Its radius is 10 times the distance between the earth and the sun. These are cool, big, puffy beasts. They're, they're very unusual and but because they're so cool, it's possible for them to keep accreting matter, to keep having more mass flow onto them and getting bigger and bigger and bigger. So that's, this dark matter power is the key to why they can grow so large.

• 7:18Ira Flatow?

  If you don't know what dark matter is made of, how do you base a theory around the behavior of it?

• 7:24Speaker 02

  The key is there's, you're, you're dumping heat into these early clouds and turning them into stars. That for us is the key. We don't really care what type of dark matter will do that. We don't care the origin of the heat source. So we used as an example, the annihilating dark matter. That works. We've also since then looked at other types of dark matter. Self-interacting dark matter also works. We want to generalize what we have to all kinds of different, all different kinds of dark matter. All we, all we, we need the heat to get into the star.

• 7:55Ira Flatow?

  Mm hmm. Well, if these are dark stars and they exist, does it help you explain, Dr. Fries, anything else about the universe?

• 8:05Speaker 02

  It, it's an interesting concept to imagine that maybe the way, the nature of the dark matter will be discovered by understanding the dark stars. By, by discovering a dark star and then it's clear it has to be powered by dark matter. And then you can study how many dark stars there are, of what mass and so forth. And based on that, you could even figure out what the mass of the dark matter particle is, or the interaction strength of the dark matter particles. So discovering these, these stars as a probe of the dark matter, which is 85% of the total mass content of the universe. So that, that's an exciting prospect. I also want to say that make a connection to, um, the, the connection between different types of physics.

• 8:49Speaker 02

  Back in the day, people were trying to understand what powers the sun. If the sun were just collapsing and that's the only place it got any energy, it would have died in a million years. Well, that's wrong. The sun has already lived five billion. Along comes nuclear physics and says, "Well, we can give you fusion. Put that in the center of the star. Now you have a way to keep it alive for 10 billion years." And we're saying, "Well, okay, what about particle physics? Let's put that inside the star. What does that do? And that can power a different kind of star, a dark star, for who knows how long, millions to billions of years. So this connection between different branches of physics is pretty interesting.

• 9:28Speaker 03

  I want to go back to the data, to the web. And the fact that the web, in its few years of existence, already is placing enormous stresses on previous theories of the formations of the first stars and galaxies. There's too many, too massive, too compact, very early galaxies, such as those blue monsters, to be explained with regular astrophysics. So now we have a choice, either to modify the astrophysics in ways that are strange, let's say, or to introduce new flavors of physics, new particles in the mix, such as dark matter, and see what this dark matter does to the first stars. And eventually, if dark stars do exist,

• 10:12Speaker 03

  they actually could solve some of those puzzles posed by the web data.

• 10:17Speaker 02

  The other cause of concern we haven't mentioned, which is huge, Cosmin, is that once the dark stars die, because there's no more dark matter fuel, then they collapse to black holes. There's the big black hole problem of the early universe. There are these supermassive black holes that are also seen in the James Webb data and other data that are just enormous. So you've got a billion solar mass, supermassive black holes. They're weighing a billion times as much as the sun, already very early in the history of the universe. How do you make those? We really help with that problem because... Supermassive dark stars that collapse to, let's say, a black hole that weighs a million

• 11:00Speaker 02

  times as much as the sun, that's a really good seed to merge some of those together or accrete mass onto them. And you can end up explaining where these early giant supermassive black holes came from. This is a huge area of research and people are struggling to try to explain where these things came from.

• 11:18Ira Flatow?

  Yeah. Dr. Ilié, what would you need to confirm this or firm up your data?

• 11:24Speaker 03

  Basically, as we mentioned before, the smoking gun signature is this 1640 absorption feature, which in one of the four objects we analyzed in the study we're discussing today, we found, albeit not conclusive, at what astronomers called signal to noise ratio, for us, it's a level two to three. So that's not conclusive. If we scan more objects and we analyze more data, hopefully, one of those would be irrefutable, meaning at a level of five or higher. And with that, then would, in my mind, have a confirmation of the existence of those objects.

• 12:01Ira Flatow?

  Well, do you think that your research, this paper, is going to convince others in the field of this idea?

• 12:07Speaker 02

  You know, it's hard to determine what other people are going to do. So I never know how to answer a question. I mean, if you have the right idea and you have something new and intelligent to say, people, they pay attention. And if you have the answer, they're going to get it, you know? As theorists, we invent a lot of stuff. We have ideas, right? But guess what? Within five minutes, they die because they, some observation breaks them. This is the other way around. Every few years, the new problem comes along that we're automatically solving. And we're like, how is this possible? There must be something to this. So for us, these are exciting times.

• 12:46Ira Flatow?

  Well, I could go on talking about this all day because, as I say, it's one of our favorite subjects on Science Friday. But we have run out of time. So I'd like to thank both of you, Dr. Katherine Fries, professor of physics at the University of Texas at Austin, Dr. Cosmin Ilié, an assistant professor of physics and astronomy at Colgate University.

• 13:06Speaker 02

  Thank you. This has been fun.

• 13:08Speaker 03

  Thank you. It was a real pleasure.

• 13:16Ira Flatow?

  Hey, thanks for listening. And if you have a comment or question or a story idea, our listener line, it's always open. Call 877-4-CY-FRY, 877-the-number-4-CY-FRY. This episode was produced by Charles Berkquist. I'm Ira Flatow. We'll see you soon.