There are stellar-mass and supermassive black holes. But very little evidence of anything in between. Where are all the intermediate-mass black holes that should be the building blocks of the biggest ones? Actually, the science has been accelerating rapidly and we now know of hundreds of them. The question marks in our understanding are slowly getting replaced with data. Let’s review what we now know about intermediate mass black holes and their origins.
Show Notes
- Funding Concerns
- Intermediate-Mass Black Holes
- Stellar-Mass Black Hole Mass
- Black Hole Formation Gaps
- Stellar Mass Black Hole Formation
- Supermassive Black Hole Mass
- Missing Intermediate-Mass Black Holes
- Black Hole Discovery Timeline
- LIGO’s Contribution
- Intermediate Mass Black Holes
- Globular Clusters as Potential Hosts
- Intermediate-Mass Black Hole Evidence
- Globular Cluster Formation
- DESI’s Role
- Dwarf Galaxy Discovery
- Active Galactic Nuclei in Dwarf Galaxies
- Intermediate Mass Black Holes
- Early Universe Complexity
- Theoretical Challenges
- Formation of Massive Objects
- Intermediate Mass Black Holes in Dwarf Galaxies
- Hypervelocity Star Ejection
- Formation of Mini Quasars
- Dwarf Galaxy Characteristics
- Intermediate-Mass Black Hole Evidence
Transcript
Fraser Cain: It’s the 365 Days of Astronomy podcast, coming in three, two, one. AstronomyCast, Episode 755, Intermediate Mass Black Holes. Welcome to AstronomyCast, our 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. I’m the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?
Dr. Pamela Gay: I am happy to be doing AstronomyCast.
Fraser Cain: As opposed to all of the other stuff that’s going on right now?
Dr. Pamela Gay: Yeah. Yeah. It’s one of these things where we try not to get too political on here, but what is happening to funding the science in the United States?
Yeah.
Fraser Cain: Yeah. I mean, for a lot of people who watch Universe Today, and I talk to the people, the fans and stuff, and they’re like, oh, I really like that you’re not very political, Fraser. But that’s about it.
I’m going to have to report on a 25% proposed cut to NASA, cancellation of most of everybody’s favorite science missions, the probable cancellation of the Artemis mission, Moon plans, the 54% cut to the National Science Foundation. That includes, like, we don’t know what the implications are going to be, but you know, things like, I don’t know, Vera Rubin Telescope. You know, there are all these incredible science projects that are in the works.
And then you layer on top of that, the cuts to the universities, you layer on top of that, the cuts to, you know, all of the DEI cancellations and cuts that are going on, as well as all of the people to administer this, as well as all the holds and freezes. Science is just going to lock up in the US at this point. That is my objective, non-political take on what’s about to happen.
And so it could be complicated. And you know, science, NASA specifically, has sort of dodged a whole bunch of bullets that have gone by so far. And now we’ve seen the budget request.
And so we haven’t seen what the actual Congress response is going to be, whether they’re going to just rubber stamp it or whether they’re going to push back and come up with their own version of the budget. So that is, that’s sort of like the final line of defense.
Dr. Pamela Gay: Yeah. And one of the things that I’ve realized talking to people is a lot of folks really don’t understand how scientists get their salaries and the fact that the vast majority of us are funded entirely through things that can be routed back to the government. And this is something that’s going to cause a significant proportion of scientists to leave the field entirely.
Fraser Cain: Yeah, yeah. I mean, I’m already talking with people who are saying, you know, I was going to be going to university in the US because it’s the best and now I’m not going to. Right?
So you’re going to have this brain drain of people not, you’re going to have this, this, people are going to be avoiding the US science. And then on top of that, people who are already scientists are going to find programs at other universities that are going to give a more stable funding environment. You’re going to see large, you know, very established teams of researchers have been working in, you know, very productive, either fragmenting because of lack of funding or rebuilding their operations in some other camp, you know, other nation like Canada.
Like, like we’re unfortunately for the US going to be the, uh, the inheritors of all of this chaos. We’re going to have, uh, you know, a lot of incredible researchers are going to come and come work in Canada because, you know, we don’t have any of these cuts. So anyway, let’s, let’s move on.
Uh, you know, I think this is going to be an episode like once the dust has settled and once we, once everything is kind of verified, like right now, everything is still kind of in, in the mix, but once everything is verified, I think we will do an episode which we’ll just sort of say, you know, here’s everything that happened and try to give you the most, uh, unbiased, but brutal, uh, reckoning of what has actually happened. So, so stay tuned for that in, in, in some number of weeks or months.
Dr. Pamela Gay: But if you want to find out how scientists are actually paid, go listen to the most recent episode of EVSN at EVSN.TV. Oh, great.
Fraser Cain: There you go. There are stellar mass and supermassive black holes, but very little evidence of anything in between. Where are all the intermediate mass black holes that should be the building blocks of the biggest ones?
Actually, the science has been accelerating rapidly and we now know of hundreds of them. So, so let’s sort of give people a sense of the, just the gap between them. What is the typical mass of a stellar mass black hole?
Dr. Pamela Gay: So typical mass is a really weird thing to talk about because we are still doing a survey of, of all the stuff that’s out there. Like there weren’t confirmed black holes until this century and we’re only 25 years into this century. So we, we are fairly certain that there’s a large number of them that are in the few solar mass to 20-ish solar mass numbers.
Then there are more that are bigger. And then there’s another gap and there’s more that are even larger. So there’s this weird situation where if you have a star that is less than 10 to 20 solar masses, which is a fuzzy number, but mass loss is confusing.
It’s going to end up becoming a neutron star and create big nebula, big supernova, lots of mass loss. So it ends up tiny, tiny. If you have bigger than that 10 to 20 solar masses, most likely bigger than 20 solar masses, you end up with a supernova going off that creates a black hole in the center, big normal nebula.
Life is good. You have an object bigger than 50 to a hundred solar masses, most likely 50, and it’s going to collapse straight down into a black hole because gravity is like, nope, no supernova for you. But then you get even bigger and you end up with what’s called a pair instability where as that object tries to collapse, you end up with positrons and electrons getting formed, vast amounts of energy going off.
And so you end up with a completely different kind of star go boom and another gap in black hole formation.
Fraser Cain: Right. Right.
Dr. Pamela Gay: Because it looks like probably a gamma ray burst, right? Yeah. This is where they’re looking at hypernovas and stuff.
Fraser Cain: Yeah. Yeah. And because it’s all antimatter and matter in the middle, the whole star is just gone.
Dr. Pamela Gay: So you have these two different gaps and if your star is really big, you don’t end up with a black hole and, and at the same time we’re finding stuff with LIGO that seems to imply that either they’re still forming in those mass gap regions or things that shouldn’t have time to merge have merged and, and the universe not matching what we expected will be a theme in this episode.
Fraser Cain: Yeah. Yeah. Okay.
So those are the stellar mass black holes and now let’s shift to the supermassive black holes. What kind of mass regime do we see with them?
Dr. Pamela Gay: So, so here we’re looking at things that are larger than a hundred thousand solar masses and they go up to millions of solar masses.
Fraser Cain: Billions.
Dr. Pamela Gay: Billions of solar masses. Yeah. Yeah.
And, and so in this case we’re looking at a, we, we thought that they probably formed through mergers, but the universe hasn’t been around that long. We haven’t seen enough merger events. So maybe they form via turbulent infall of matter while galaxies are forming and then you end up with some mergers that get you to the giant ones, but there’s a whole lot of confusion there as well.
Fraser Cain: And so then astronomers have always been theorizing that there is, there’s gotta be something in between. There’s gotta be something like you don’t just get these supermassive black holes appearing overnight, that there has to be this accumulation, you get the small black holes merge with other small black holes, they form larger black holes and those make bigger black holes. And then you eventually get ones that are in the hundreds of times the mass of the sun, then thousands of times, then tens of thousands, and then hundreds of thousands, and then eventually you move into those millions of times the mass of the sun.
So it’s like this geometric progression of black holes eating other black holes to walk up that chain until finally you get those supermassive black holes. And the supermassive black holes, they’re at the hearts of galaxies, which is sort of like the bottom of the gravity well of the galaxy. And so it’s not surprising that they will collect down into the middles of these galaxies and then start to merge up.
But we don’t see, or haven’t traditionally seen, these in-between sizes.
Dr. Pamela Gay: 100,000 to 100,000 solar masses decided it wanted to be invisible.
Fraser Cain: Yeah, nowhere to be seen for the entire, essentially the entire history of astronomy. There has been this surprising gap where you would expect to see, like if you, I guess if you sort of think of a standard distribution curve, there should be lots of the middle sizes and then very few of the biggest ones, the heaviest ones. And yet, in fact, it’s like there’s lots of the light ones, lots of the big ones and nothing in between.
And that has always been a really big puzzle in astronomy.
Dr. Pamela Gay: And this is where we have to be fair to history and say that prior to the early 2000s, prior to the late 1990s, people were labeling the centers of galaxies monsters. We didn’t have this unified idea of active galactic nuclei and CIFRT-1, CIFRT-2s and quasars all being actively feeding black holes. They literally were just saying monsters be here.
And stellar mass black holes, we didn’t have the X-ray and gamma ray data we have today. So we had like Cygnus X-1, I think is the correct license plate for this one stellar mass object that we said, that’s probably a black hole. But in the late 1990s, we suddenly started to be able to use the Hubble Space Telescope’s spectral capabilities to look in the cores of galaxies, look at the radial velocities of things really close into the core and stay there.
That is so high in velocity that the only way you can explain that is with a supermassive black hole. And we also had Andrea Goetz and her team looking at motions in the core of our galaxy and saying these stars can only be moving like this if there is something that is a supermassive black hole. So supermassive black holes really only started to find in the 1990s.
It would take Fermi and Chandra and a whole lot of work confirming things in the radio to figure out stellar mass black holes are actually a thing and they’re kind of everywhere. So we’re really only looking at 20 years, not even.
Fraser Cain: So I would say one of the big revolutions came with the LIGO observatory.
Dr. Pamela Gay: So with LIGO, we are able to see the release of energy when high mass objects on the small side of what we call high mass decide to merge. So it sounds stupid, but here we’re talking about neutron stars. So neutron stars and black holes are the largest stellar remnants.
And the sensitivity of LIGO is really just tuned by nature to be seeing the neutron star mergers and stellar mass black hole mergers. And here I have to check my dates. In 2019, rather, May 21st, 2019, there was a merger that caused a wave of space time that compressed the separation between the mirrors and the LIGO system as it passed through our planet.
There was a gravitational wave released that could best be understood as the merger of an 85 solar mass stellar mass black hole and a 65 solar mass stellar mass black hole into a 142 solar mass intermediate black hole. Now this is a kind of squirrely result because that 85 solar mass black hole doesn’t fit what we expected to exist and we can’t fully explain it except as the merger of two smaller black holes and the universe hasn’t been around long enough to justify that. So we’re confused.
Fraser Cain: Right. Right. And that’s sort of back to that thing you were saying that there is no direct mechanism for getting you black holes of that 85 times the solar mass that that you can have lighter ones and you can get maybe heavier ones, but it’s that there’s that gap where they shouldn’t be forming because these stars are expecting to just completely blow up and yet there there is one.
And so then you have to say, OK, well, there had to be two smaller black holes that came together to produce that black hole, which is weird because it takes time. You need to kind of take time. Yeah.
Yeah. Yeah. But there it is.
There it is. You know, the universe does. The universe doesn’t ask for our permission to show us stuff that that are unexpected.
So OK, so then you’ve got this this new tool, LIGO, for being able to detect the collisions, the mergers of black holes. And now it’s finding this point almost a black hole merger almost every day. It’s such a productive observatory.
And so now we’re seeing all of these black holes that are out there or at least the ones that are emerging. We’re not seeing all the ones that are out there, the ones that are quiet, that are silently moving through the cosmos, interacting with nobody apart from its gravity. But you know, don’t worry about those.
I’m sure it’ll be fine. But what about the intermediate mass black holes? We’ve got one at one hundred and twenty five, but that’s that’s not one hundred thousand.
That’s not two hundred thousand. Where are the intermediate mass black holes? Can anybody find them?
Dr. Pamela Gay: Well, so so technically anything over a hundred is an intermediate mass black hole. Now, globular clusters may offer a solution. And this gets highly controversial because.
Several attempts to say this globular cluster or that globular cluster must have an intermediate mass black hole have been confounded by realizing, no, they actually are filled with stellar mass black holes in their core whose additive mass allows things to get flung around as though there were an intermediate mass black hole. The result that is so far standing up the best is Omega Sun, which is a super weird globular cluster. It appears to have had multiple epochs of star formation.
It’s the biggest, the biggest, it’s chunky, it’s best seen from equatorial regions. So if you live in the extreme north, you’re probably not going to see it. It’s a gorgeous globular cluster that likes to defy expectations.
And because it’s a weirdo, people keep looking at it with the Hubble Space Telescope. And a team of researchers realized there is data over enough of the history of the Hubble Space Telescope, which is now 35, which really made me feel old to learn.
Fraser Cain: Don’t feel old.
Dr. Pamela Gay: So with many, many, many observations, researchers were able to identify seven stars in the core of Omega Sun that are moving so fast that they should, unless there’s an intermediate mass black hole in there, they should be moving at escape velocities and leaving instead of orbiting in the core. Their orbits are consistent with an 8,200 solar mass black hole being in the heart of Omega Sun. So far, no one has been able to disprove these results.
This is the one I’m going to go with.
Fraser Cain: Right. But that is, you know, now we’re talking, that is an intermediate mass black hole. That is something that you couldn’t get without mergers upon mergers upon mergers.
And of course, in a globular cluster, these are places that are incredibly dense, lots of stars, lots of time for things to find each other. And this is where you would you would find them. So and as you said, this is the strongest case, but there have been other examples where it feels like you can, where astronomers say they see almost like the gravitational wake of these intermediate mass black holes moving through globular clusters, distorting the movements of the other stars around them.
But obviously, it’s a very tricky observation to make. And so they haven’t held up as strongly. So up until this point, I think, you know, we’ve I’ve been covering this on Universe Today.
We’ve had lots of these like tentative discoveries. Is this some indirect evidence? I don’t know.
There’s, you know, but now the evidence is starting to build.
Dr. Pamela Gay: And this is where we get the dark energy spectroscopic instrument DESI. And it is my new favorite thing. Gaia had been my favorite thing.
DESI is now my favorite thing.
Fraser Cain: In this brief break between Gaia and Vera Rubin, we get a new favorite thing.
Dr. Pamela Gay: Yeah. And DESI is a instrument that is going through and taking spectra of galaxies in numbers that are ludicrous. They looked at their initial data.
This is not the full survey. This is preliminary release. They started with spectra of 410,000 galaxies.
They found 115,000 of these were dwarf galaxies. And because they have such high resolution and tiny fiber optics, they’re able to resolve smaller things than could be resolved in the past, which means we can start to see and understand smaller things than we could understand in the past. Things that in the past just got blurred out by the stars and things around the cores of galaxies.
Fraser Cain: Yeah.
Dr. Pamela Gay: And they were able to find that of these 115,000 dwarf galaxies, 2,500 have active galactic nuclei, which is not something we’ve really expected. And they also found 300 intermediate mass black holes.
Fraser Cain: Mini quasars at the centers of dwarf galaxies that are active. They are feeding and they are blasting out radiation in exactly the same thing that we see with quasars, just at a much smaller level. And so what kinds of masses do we think we’re looking at in these dwarf galaxies?
Dr. Pamela Gay: This is the thousands to tens of thousands that- Done. Yeah. We got there.
Fraser Cain: Yes.
Dr. Pamela Gay: And what I love is we’re now having to figure out between the data from the James Webb Space Telescope that’s like, hey, galaxies formed way before anyone thought. We are now having, because of DESI results saying here are these intermediate mass black holes everywhere that are actively eating, because of the LIGO results saying, hey, we have mass gap black holes. We’re having to start thinking about things that weren’t even the topics of graduate school conversation at the beginning of this century.
Things like intermediate mass black holes that maybe came out of primordial prior to the cosmic microwave background release times. We’re having to talk about, well, are these things forming as the galaxies form through turbulence at all sizes?
Fraser Cain: Direct collapse. Yeah. Are we seeing first generation stars being able to be much larger and more massive than anyone thought, producing larger remnants, going straight to intermediate mass black holes?
Like these mysteries are compounding.
Dr. Pamela Gay: And so we’re at this really cool point where theorists are going nuts. We’re trying to figure out, okay, realistically, what fits the data the best? And we’re going to see the extremely broad brushstrokes that we used to explain the bulk of evolution of stars and galaxies in our universe getting radically evolved as we add in new details about things that happened early on, those first stars, what happened prior to the formation of the cosmic microwave background.
All of these things caused effects we are finally able to see for the first time. So it’s not that we were wrong in the past. In some cases we were wrong.
It’s that we’re now realizing our ideas about the universe were way too limited because as you said, the universe doesn’t ask permission and it was more creative than we were. And it’s really cool.
Fraser Cain: Yeah. Yeah. And like it really feels like we’re seeing other examples like the little red dots that were discovered by James Webb, that the large structures of the universe formed really early on that mass came together quickly and that, as you said, something had to overcome that turbulence in order to be able to bring this material closer together.
Because we just, we don’t see that happening in stars today, you know, beyond a hundred times the mass of the sun, the outflows of radiation become so strong that no new mass can fall in. Well, how do you get us, how do you get a, even an intermediate mass black hole with tens of thousands of times the mass of the sun within, well, how do you get a billion mass black hole within the first 800 million years of the beginning of the universe, right? Like that’s crazy.
Well, so there has to be some kind of direct mechanism that’s coming together, that’s forcing matter and energy into these small regions and allowing them to turn into black holes on scales that were vastly quicker than anybody had ever thought. And this is the regime that we’re now apparently living in. So there’s one piece of research, I don’t know if you had prepared this, but astronomers have found stars getting ejected on hypervelocity trajectories out of the small Magellanic cloud, which is our closest example of a dwarf galaxy.
And that you can’t get this without there being an intermediate mass black hole that’s going through three body interactions, hurling stars at us.
Dr. Pamela Gay: Yeah. And that’s one of those results where people are like, let me see if I can come up with something else. So it’s one of those results that isn’t a, it absolutely has to be this.
It is one of those results where it’s like the easiest way to explain this is with an intermediate mass black hole. So yeah, it turns out the Magellanic clouds fling stars. And one star has been seen moving with a sufficiently high velocity that the easiest way to explain it is you have two stars left behind in the tight binary and it got flung out in the process.
So you probably had an intermediate mass, a black hole and a binary system and it got shredded.
Fraser Cain: Right. Tore one of them away and the other one got a slingshot out of the galaxy. And so it’s interesting, you know, the fact that so many of these intermediate quasars, I don’t know how you describe them.
We need a new term for the mini quasars anyway, mini quasars. These mini quasars have been found at the hearts of many dwarf galaxies. Then you can start to make this assumption that in the way we know that there is a supermassive black hole at the heart of every large galaxy, there could very well be an intermediate mass black hole at the heart of every dwarf galaxy.
Dr. Pamela Gay: And this is where dwarf galaxies are super weird. And we are learning you can’t actually say every dwarf galaxy regarding anything. There was a point in time where we were like, dwarf galaxies have extremely high light to dark matter ratios.
And then we found some that appear to have no dark matter.
Fraser Cain: Yes. Yeah. Or stars.
Dr. Pamela Gay: Yeah. Dwarf galaxies are weirdo leftover chunks of stuff and things that, yes, some of them appear to have intermediate mass black holes that are actively feeding. Others appear to have had a single epoch of star formation and be in terms of their stellar population identical to a globular cluster, but with radically different motions and strange dark matter ratios.
They are weird. They’re the small leftover bits that apparently do what they feel like.
Fraser Cain: So this is satisfying, I think, for me, that we are finding at sort of three different methodologies that we have available to us now through gravitational waves, through examining the motions of stars in globular clusters, and through looking at the radiation that’s coming from the centers of dwarf galaxies, growing evidence that there are a lot of intermediate mass black holes. And one of the biggest mysteries in astronomy feels like it’s now starting to give up its secrets. We’re starting to learn the true answer to this question, which is just, it’s so great.
Dr. Pamela Gay: And it’s a really interesting time because every time we get an increase in computational ability and an increase in telescopic ability, we see these revolutions. The last one was with the Digital Sky Survey. Gaia did a lot for motions and figuring out where things are in stellar populations.
But when it comes to galaxies, DESI is that next revolution, and I’m here for it.
Fraser Cain: Me too. Thanks, Pamela.
Dr. Pamela Gay: Thank you, Fraser. And thank you so much to our patrons. We would not be here without you, because it turns out we need a small herd of people to make us sound good.
This week, I would like to thank AstroBob, AstroSets, Bebop Apocalypse, Bob Zatzke, Brett Moorman, Danny McGlitchie, David Troge, Diane Philippon, Dr. Whoa, Flower Guy, Frederick Salvo, Galactic President Scooper, Star McScoops-a-Lot, Jeff McDonald, Glenn McDavid, Gold, Gordon Dewis, James Signorowicz, Jarvis Earl, Jim Schooler, Jordan Turner, J.P. Sullivanm, just me and the cat, Justin Proctor, Christian Golding, Kinsaya Penflanko, Matthew Horstman, Maxim Leavitt, Michael Wichman, Nate Detweiler, OldBoomer847, Paul D. Disney, Peter, Rajevs, Akari, Robert Cordova, Robert Hundle, Robert Plasma, Sergio Sansevero, Sersom Scone, Scott Bieber, Scott Briggs, Sean Matz, Semyon Torfason, Siggy Kemmler, Stephen Veidt, Stephen Coffey, The Mysterious Mark, Tricor, Van Ruckman, and Zero Chill. Thank you all so very much.
Fraser Cain: Thanks, everyone. We’ll see you next week. Bye bye.