We’re familiar with regular binary stars. Two stars orbiting each other. Simple. Of course, the Universe has come up with every combination of things orbiting other things. And this week we look at the extreme version of this.
Blue Stragglers (Swinburne University)
Gamma Ray Bursts (NASA)
GRBs in hypernovae press release (ICRANet)
Cataclysmic variable stars (NASA)
Astronomers find closest black hole to Earth, hiding in plain sight (Science Magazine)
Scientists may have spotted a black hole and a neutron star colliding (Science Magazine)
Laser Interferometer Gravitational-Wave Observatory (LIGO) (Caltech)
Ep. 556: Multi Messenger Astronomy (Astronomy Cast)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 571, Extreme Binaries
Welcome to Astronomy Cast, a weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I’m Fraser Cain, publisher of “Universe Today.” With me, as always, Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how are you doing?
Pamela: I’m doing well. It is finally spring, as in I can go play in the garden.
Pamela: How are you doing up there in Vancouver Island?
Fraser: Vancouver Island, yeah. Things are great. The weather is absolutely gorgeous. And same thing, I have been out in the garden. The only downside, the robins get up at 4:00 in the morning, and they’re breeding at this point, so they’re just like, “Chirp, chirp, chirp.” And so I have one that has found the – He really likes the acoustics right outside my room.
Pamela: Oh no.
Fraser: And so, I’ve been getting up at 4:00 in the morning. And then I have to go, and I get up, and I have to close the window. And then try to get back to sleep, and then I can’t get back to sleep until – Yeah, I haven’t been getting a lot of sleep because this robin has been singing his little heart out every morning really loud right outside my window. So, hopefully, he’ll find a girlfriend and get lost. But until then, yeah, it’s pretty funny. But it’s spring. You just can’t go wrong.
Pamela: That is awesome.
Fraser: Yeah, absolutely. So, we’re familiar with regular binary stars, two stars orbiting each other. Simple. Of course, the universe has come up with every combination of things orbiting other things. And this week, we look at some extreme examples. All right, Pamela, so let’s just figure this out. What is a binary star?
Pamela: So, a binary star is a noun that needs a plural because a binary system is two separate stars. So, a binary star is a system that exists in two stars. And they can come in just about any kind of combination of regular star, compact object, advanced star, baby star. And they form in a whole myriad of different ways. They can either arise out of a single collapsing molecular cloud where they collapsed into their individual little solar systems side-by-side. Or they can gravitationally get caught up together through some activity in their advanced lives. So, when you’re looking at a system, statistically, it’s most common that it formed like that, but they didn’t have to.
Fraser: Right, right, and we can talk about that later on. But I’m imagining that standard formation, this gigantic cloud of gas and dust that’s swirling around, and you get – Instead of it all pulling into the middle, it pulls into two separate – What are the dynamics? Why doesn’t it all just turn into one big star in the middle? How can you get multiple stars orbiting around each other?
Pamela: So, you actually have two fragments in the same molecular cloud –
Pamela: – that are gravitationally pulling together. And it happens to be that these fragments are close enough that they’ll orbit one another. Different effects can bring them closer and closer over the years, but they form from two distinct fragments in the same molecular cloud. And the fact that molecular clouds is fragmenting is how we end up with separate stars. So, the fragmentation isn’t unusual. It’s just these two are close enough that they got caught up in each other’s gravity.
Fraser: Okay, and so then the vast majority of these situations, you end up with some amount of stuff, like a star’s worth amount or mostly a red dwarf’s amount of stuff. But every now and then, you end up with an extreme amount of stuff. These are very large blobs of gas and dust.
Pamela: And sometimes you just end up with two regular blobs that interact in ways that are extreme. So, when we talk about extreme binaries today, we’re gonna talk about a whole lot of different combinations.
Fraser: Right. So, it’s not just necessarily the amount of material that went into the star –
Fraser: – and the form that it took. But, in fact, these stars can interact with each other in really weird ways and cause really bizarre effects that we can see.
Okay, so let’s break this down then. As you define extreme then – We’ve defined binary, two stars orbiting each other. And a star can be all kinds of things. So, let’s define extreme. Give me – start classifying the kinds of extreme things that can happen.
Pamela: So, when I’m talking extreme events, I am talking about things that radically cause upheaval in the life of a star that could only happen because this is a binary system. That any singular star would not undergo these kinds of – well, really bad millennia.
Fraser: Right. So, you could have an enormous cloud of gas and dust that can generate a star with 50 times the mass of the sun. It’s an extreme star. It will then explode as a supernova in an extreme way. But that…
Pamela: Is not an extreme binary.
Fraser: That is not an extreme binary because it didn’t have a partner to do something even weirder. But let’s talk about what some of the recipes you can get. What are the ingredients? We’ll start with our ingredients, and then we’ll mix them into different recipes.
Pamela: So, I think the earliest discovered extreme combination that doesn’t actually involve an explosion is the blue straggler. These are stars that were noticed in globular clusters as being unusually young looking in their lives. And in trying to figure out the origins of these individual blue stars, nothing made sense. And at this point in astronomy, we had been teaching people and saying to ourselves that the space between stars is so great that no two stars will ever collide. And we were wrong. We were very wrong.
Fraser: Right. So, for the longest time, everyone said no, no. Come on, stars are small. Space is big. The chances of two stars impacting each other – Not gonna happen. Unless you’ve got a place where stars are buzzing around each other like angry bees, and you’ve got millions, billions of interaction opportunities all the time.
Pamela: And some of these interaction opportunities leave the binary star systems where the stars get closer and closer through a variety of different feedback mechanisms until one day, those two stars – They become one in one extreme merger.
Fraser: So, is that the blue straggler? Or is a blue straggler just a – Is it a head-on collision or is it most usually two stars have somehow ended up into orbit around each other and then they eventually just merge together into some…
Pamela: Well, this is the fascinating thing is we don’t know all the possible mechanisms by which you can get a blue straggler star for the very simple reason that we haven’t caught any in the act of becoming blue stragglers.
Now, we see plenty of super close objects, super close binary systems where it’s hard to differentiate between the two stars. So, it’s generally thought that these are stars that caught hold of each other or formed together and simply evolved into a single star. But that’s still a pretty extreme way to reignite your nucleosynthesis.
Fraser: Okay. So, that’s the one example. And you’ve got two stars, regular stars, of varying masses. They merge together. They get blue. They seem like a baby star where there should be no baby stars. And then, this star just continues on its life, and eventually it fades – does whatever it’s gonna do.
Pamela: Yeah. And this is just the beginning of this kind of star. This is the low-end, normal version. Now, as you increase the overall mass of this system, you get more and more extremes of this extreme in a binary star’s life.
Fraser: Okay. So, let’s swap out some taste – Let’s do some taste your ingredients then for this recipe.
Pamela: Well, there was a rather awesome supernova that we talked about in a rather recent episode where it was realized that they had a compact object – a standard, good, old-fashioned white dwarf that embedded itself in the atmosphere of its giant star companion. And from within that atmosphere, it acquired all the material necessary to go, boom, as a type 1a supernova. And the shockwave of this ignited the star it was now inside, creating an exceedingly bright supernova explosion.
Fraser: Right. And, I mean, it’s such a crazy idea. I mean, talk about extreme that you get this star – This white dwarf has gone inside the atmosphere of this other star. And then suddenly, it’s an all-you-can-eat buffet – when normally they’re sipping away from some partner – all-you-can-eat buffet and then, kaboom. And it didn’t take long, like a couple hundred years, and then it was, kaboom.
Pamela: And in these kinds of situations where you have these massive objects that are interacting together during supernovae may introduce a layer of noise to our understanding of distances within our universe that could artificially be causing us to see dark energy. We don’t know yet. I’m not saying there is no dark energy. I’m saying there is noise in the data.
Fraser: Right, that when you see – I guess to this point, we’ve talked about how a type 1a supernova is long thought to be very standard candle. It is when a white dwarf gobbles up enough material, and it explodes. Well, what do you do when a white dwarf explodes within another star? Or what do you do when a white dwarf has gone through some other process that force feeds it before it actually explodes? If you were using, and it’s a standard candle to measure the size of your universe, suddenly that’s no longer necessarily super accurate. So, can we scale up then? Can we feed other things to stars?
Pamela: Oh, yes.
Fraser: Oh, please.
Pamela: Oh, yes. And it’s not necessarily that you’re feeding them into stars, but there was an amazing press release this week that came from a collaboration of collaborations in Europe where using a combination of x-ray and gamma-ray data and massive computer models, they realized that they can start to explain long-period gamma-ray bursts as what is one of the most extreme doesn’t start out with the black hole binary systems you can imagine.
In this particular situation, you start out with your standard carbon-oxygen-burning, massive star. You put it in a binary system with a neutron star, so it once upon a time, had a companion that was even bigger than it was.
Fraser: Right. So, you used to have two stars. One explodes. And now it’s a neutron star, and it’s orbiting around this other enormous star.
Pamela: And when that second enormous star runs out of the ability to generate energies and carbon and oxygen, its core collapses, and its outer layer fires outwards. And this mass that is getting shoveled directly towards that companion neutron star will, at the least, make that neutron star significantly more massive. And, in some instances, will even trigger that neutron star to spontaneously become a black hole. So, now we have one star’s explosion making a second star into a black hole because it can. But it gets worse.
Fraser: Or better. Come on, this is better. Yeah.
Pamela: It gets more extreme. Let’s just go with more extreme. That companion that was minding its own business, having a regular, every day Tuesday or whatever, that has now just become a more massive object, all the plasma and everything around it is going to generate a massive magnetic field with a temporary accretion disk that creates a jet. And it is the jet around the companion star that it turns out could be that gamma-ray burst we’re seeing.
So, when we see these long-period gamma-ray bursts, where optically they have a supernova remnant, and in x-rays and gamma-rays, they have this very short flare of high-energy particles, we’re seeing the gamma-rays and the x-rays associated with the older, original neutron star that may have become a black hole and the visible light associated with the supernova of that first carbon-oxygen massive star.
Fraser: I mean, I’m just wrapping my head around that, right? That you’ve got these two stars. One goes off, boom. Now it’s a neutron star going around the star. The second star explodes. As it explodes, it blows out this material. This material runs into the first neutron star. It explodes again, but it also is getting spun up. And this magnetic field that, as it explodes, it’s firing out these jets.
And these long-period gamma-ray bursts are no joke. We can have one hit us from across the Milky Way and sterilize life on earth. For us. Maybe the cyanobacteria at the bottom of the ocean will be fine, the water bearers. But surface life is in for a rough time. And you could be tens of thousands of light years away from this event, and that’s how extreme they are. That’s mind-bending.
Pamela: And so, these extreme binaries are causing extreme effects that they’re temporarily brighter than the entire rest of the galaxy. And that’s a thing to aspire towards.
Fraser: Yeah. So, what happens with black holes? I mean, I sound like a four-year old now. Come on, what if you add black holes to this mix?
Pamela: So, if you just had a black hole hanging out next to that initial star that went boom. It would simply go gobble, gobble, gobble, mine. It’s not exactly gonna become anything more extreme than a black hole. But that can also be generating a jet with a gamma-ray burst.
Fraser: Right. Well, and so this feeds into a piece of research that I think we talked about this idea that there have been super massive black holes seen orbiting each other billions of light years away. And there’s this regular flash that comes from this enormous, super massive black hole with 18 billion times the mass of the sun. And it has this accretion disk around it of all the material that’s falling in. And this second black hole that merely has about 150 million times the mass of the sun, is orbiting around it. And as it passes through the accretion disk, it is causing this flare that we can see – I think it’s 2 billion light years away. And so…
Pamela: So, in this case, we have binary black hole star A, former mass A, is creating the accretion disk. So, second star is passing through second former blob of mass. Black holes at this size are not former stars. They’re former families, galaxies –
Fraser: Who knows what they were.
Pamela: – plethora.
Fraser: Yeah, yeah, yeah. However you get 18 billion times the mass of the sun into one compact area.
Pamela: So, blob of mass that became a black hole A creates the accretion disk. Super massive black hole B, the smaller, passes through the accretion disk to create the flashes. And this can only happen in this double system.
Fraser: Yeah. And so, I mean, that’s on a vast scale. But there’s got to be versions of this on the more stellar scale.
Pamela: And the trick is finding all of these examples. What we have been able to find are the more mundane objects, the cataclysmic variable stars where you have a compact companion that is eating the mass from its either giant or main sequence companion star. That material gets dense enough on its way to be eaten that it explodes. It ignites in its own thermos-nuclear reactions. And the flare-up and light is that nova. The word nova is just new star.
And so, with these cataclysmic variables, this can happen extraordinarily dramatically. And they come in all different flavors, from just a standard white dwarf that will have things crackling around it to neutron stars. And black holes aren’t exactly cataclysmic variables, but the energetics of these systems are constantly flaring out in x-rays and generating jets that are just a smaller version of what we see in super massive black holes. And with the super massive black hole, it’s not exactly a binary system. It’s stealing mass from the entire rest of the galaxy. But in these extreme binary systems, we have the black hole, happily, hungrily eating things from any neighbor that gets too near.
Now, that’s the catch is black holes don’t always eat. We actually had a triple system that showed up in the news recently that was only found because astronomers were looking at a double star, what they thought was a pair of stars that were probably orbiting each other. And when they went to resolve the orbit of that pair, they discovered no, they can only explain these motions if they add in a third invisible black hole that was not eating. So, not eating black holes happen.
Fraser: Right. And so, I think that – I mean, okay, fine. I don’t think we want to do another show on extreme multiple star objects, so I’m gonna let two stars and a black hole in to this show this one time. So, just this analysis, being able to see this, is one of the ways that black holes are even seen, that we even know that they exist, right? How do you know that a thing that has gravity so powerful that nothing, not even light, can escape it – How can you even – Because that sounds invisible. And so, thanks to the fact that they do form in binary systems, and sometimes in a trinary system, we can discover them in the first place.
Pamela: And the irony is there could be a whole lot more out there that we don’t know about because they are orbiting a single star, and we haven’t done the necessary detailed astrometry to see that otherwise singular star move.
Fraser: Are they orbiting the star? Or is the star orbiting them?
Pamela: It’s mutual. It’s mutual. The vector points both directions. Well, the different vectors each point in a specific direction. But, physics. Physics is mutual.
Fraser: And so, this is the kind of candidate object that’s something like GAIA would find, right?
Fraser: To find these objects spinning around each other.
Pamela: They’d have to be wide enough to get sufficient motion. But yes, there could be a whole lot of non-jet, extreme, dizzy, eating black holes out there in binary systems that we don’t see ‘cause we’re just not looking.
Fraser: It’s interesting to think about that, that you look out into space, and you see a star. And, in fact, I think with that triple system, you can see it with your own eyes, I think.
Pamela: You can see the combined light of the two regular stars.
Fraser: Yeah, with your eyes.
Pamela: In a dark site.
Fraser: Right. It’s like magnitude six or five or something.
Pamela: It’s close to magnitude six.
Fraser: And so, just that idea that you can look up into space, and you can see what you think is a star is actually two stars whizzing around each other – is actually, actually two stars whizzing around a black hole. The black hole is the system. And these two stars are the hangers-on. But from our eyes, we just see a star, what looks like a star. But, actually, we’re not seeing the true reality of what’s in that system. Blows your mind just to think about that.
Pamela: And there’s so many things out there like this where you go from eyeballs to telescope to bigger telescope, and they just keep splitting. Yeah, anyone who says double stars are boring doesn’t understand. There’s black holes out there, folks.
Fraser: So, we talked about extreme objects interacting with other regular objects. You’ve got a black hole neutrons – Sorry, black hole orbiting through the stars. But these extreme objects will get into shenanigans with each other, as well.
Pamela: Oh, yes. And this is where they were first detected by James Taylor and his graduate student whose name has escaped me, and I feel like a horrible human being. I am sorry, James Taylor’s graduate student who went on to get a Nobel Prize, so I think it’s okay.
They discovered this work while they were at the University of Massachusetts, I think. And they were studying binary stars, and they found a system where the period of the system was evolving in a way that could only be explained if gravitational waves were carrying energy away from the system. Now, since that discovery, we have finally, finally gotten gravitational wave detectors to actually work. Still bitter.
Fraser: Why you’re bitter. You’re gonna have to, at some point, you’re just gonna have to relent and just give in. I can understand that it’s gobbling up the budget.
Pamela: I need something to put fire in my belly. If this is what it is, it’s a fairly innocent thing.
Fraser: The source of your rage is the fact that gravitational waves aren’t delivering the kind of science you were hoping for as quickly as you would like.
Pamela: It’s just the timeline.
Pamela: It’s the timelines. When you’re told that something is supposed to be done by 2000, and it doesn’t happen until 2002…
Fraser: Just turned out it was hard.
Pamela: I know.
Fraser: All right.
Fraser: At some point, we need to have some kind of party where you just embrace gravitational waves, and we can just move forward. Maybe like a therapy – Can we have a therapy session? I’ll help you work through this. We’ll talk about what happens next because there’s lots of good stuff coming. Anyways, no problem.
Pamela: Anyways, it has been determined that compact objects of a myriad of different masses are all periodically just going from being two objects to one in a release of massive gravitational waves and, in some cases, bursts of light. And that’s the amazing thing is that we’re able to theoretically channel all of the detectors of the world, from the particle detectors to the light detectors to the gravitational wave detectors, to do what is now being called multi-messenger astronomy, which admittedly gives us one of the worst acronyms in astronomy.
Fraser: Well, we did a whole show on this.
Pamela: And so, go check out the entire show –
Fraser: Yeah, yeah.
Pamela: – because this is the new extreme extreme, except for the case of the supernova triggering another star to become a black hole. That, to me, is still more extreme, but personal choice.
Fraser: Yeah, I mean, it’s funny to me that that hasn’t been picked up by the news as big and as important as it probably is. So, I mean, maybe the findings – Talk about the source of long-period gamma-ray bursts. I mean, 2017, we learned the source of short-period gamma-ray bursts being colliding neutron stars. But long-period was still a mystery. Now it looks like we probably have the – We might have a serious answer for this. And yet, I have been waiting for press releases to come out to talk about this, and nobody has. It’s weird to me.
Pamela: I think it’s because it’s plague times.
Pamela: And everyone has been distracted trying to deal with everything else going on.
Fraser: Yeah, I think if true, it’s one of the biggest stories of the year. And yet, it’s – So, I mentioned this. I warned you that I’m gonna steal your thunder on this –
Pamela: That’s okay.
Fraser: – and absolutely make a video on this because it’s so exciting.
Pamela: I do the quick news. You do the in-depth looks. We’re good.
Fraser: Yeah. Well no, just normally I feel like I’m the one who sees this stuff, but you just nailed a huge story that was completely off my radar. So, thank you.
But the fact that we can use these enormous black holes coming together in the final moments of being separate entities and watch how the space time ripples outward. But even more magical is with those neutron stars, we can confirm this collision in both the visible and in the gravitational realm is game changing.
Pamela: We have, in the past 20 years, pretty much thrown out everything except for the basic dynamics in the astronomy textbook I started with. The whole Gmm/r 2, that is still true. But the story we tell of how objects interact with one another has been completely revolutionized, as we’ve realized that space is mostly empty, but things find a way to interact.
Fraser: Right, yeah.
Pamela: And it’s kind of awesome.
Fraser: Yeah, it really is. Cool. Super fun topic. I hope this gives everybody a lot of really interesting new rabbit holes to go down. Do you have some names for us this week?
Pamela: I do, as always. We’re just so grateful to have an audience of patrons out there who support us in everything we do. As always, we would not be here without the generous contributions of people like you. It takes a lot of people behind the scenes, by which I mean two people, but two people we adore. And we like to make sure they can eat. Actually, it’s more than two nowadays. It takes a whole bunch of people behind the scenes to make sure we do everything we do.
This episode is going to be produced by Richard Drumm. We’re gonna have all of our show content put together by Beth Johnson. Allie Pelfrey’s in the background making sure all of our YouTube channels stay on target. And we’re able to pay our humans a fair wage because you support this show. Thank you.
And this week, in particular, I would like to thank Ryan James, Brian Nelson, Kristin Brooks, Eric Farenger, Martin Dawson, Kseniya Panfilenko, Dwayne Isaac, Froto Tennabau, Shannon Humber, Justin Proctor, Thomas Tubman, David Gates, Rachel Fry, Erin Sagav, Fredrik Sjoge, Claudia Mastroianni, Neuterdude, and Paul L. Hayden. Thank you, all of you, for everything you do that allows us to do everything we do. We are indebted to your support.
Fraser: And we’ll see you all next week.
Pamela: Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a creative common attribution license. So, love it, share it, and remix it. But, please, credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, astronomycast.com.
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