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Possible detection of a black hole with a mass that was thought to be impossible (quantamagazine.org)
189 points by theafh 53 days ago | hide | past | web | favorite | 101 comments



> (The million- and billion-solar-mass supermassive black holes that anchor galaxies’ centers formed differently, and rather mysteriously, in the early universe. LIGO and Virgo are not mechanically capable of detecting the collisions of supermassive black holes.)

Is this because those collisions would be too "loud", in the same way that I wouldn't expect my microphone to be able to pick up an earthquake?


Supermassive black holes are larger, so the characteristic timescale of their dynamics is longer, and the gravitational waves generated by their merger are correspondingly of lower frequency. More specifically, supermassive black holes binary (SMBHB) mergers usually ring at 0.1-1 millihertz, whereas LIGO's sensitivity is concentrated around more like 0.1-1 kilohertz, a typical frequency of stellar-mass black holes binary mergers. The ~6 orders of magnitude difference comes directly from the fact that supermassive black holes typically weigh in at millions of stellar masses.

See the plot here:

http://www.tapir.caltech.edu/~teviet/Waves/gwave_spectrum.ht...

(To convert from wavelength (meters) to frequency (hertz), take the speed of light and divide it by the wavelength.)


So it's like how you can easily see a small swell from a small boat but a larger swell can be almost undetectable.

Is this also why we don't just get ripped apart during one of these ripple events which are probably all around us as gravitational noise?

I wonder if this is why seemingly tiny vessels can cross large oceans just as easily as larger ones.


The reason we don't get "ripped apart" during these ripple events is simply that spacetime is so stiff that even absolutely monstrous amounts of gravitational energy lead to only the tiniest distortions in spacetime geometry. A black-hole collision may put out more power in gravitational waves than the entire optical luminosity of the visible universe, and the result when it reaches us will result in a distortion of less than the diameter of a proton.


http://www.astronomy.com/news/2019/07/colliding-supermassive...

> If the theories are wrong and there is no problem, supermassive black hole pairs should approach each other and merge frequently enough to create a background “hum” of gravitational waves. “This noise is called the gravitational wave background, and it's a bit like a chaotic chorus of crickets chirping in the night,” Goulding said. “You can't discern one cricket from another, but the volume of the noise helps you estimate how many crickets are out there.” But this hum is outside the hearing range of LIGO and VIRGO, though astronomers are looking forward to projects like LISA, a space-based gravitational wave detector that will “hear” at frequencies current instruments cannot.


I would think it is more like an antenna tuned to a different frequency.

I would expect they would need to be larger to detect the significantly lower frequency.


I'm a total illiterate in this context, so forgive the possibly stupid question, but the antenna analogy brought this to mind: is there any effect similar to heterodyning with respect to gravitational waves like we have in the electromagnetic ones? If yes, could some signals have been already recorded but elsewhere in the spectrum because they're the result of sum and/or subtraction with other known signals?


As far as I understand, that effect is just a result of the superposition characteristic of waves in general, so yeah it should also apply to gravitational waves. I think the difference is that there aren't a lot of sources of "carriers" in the gravitational wave universe.


The heterodyne effect comes from multiplication of signals. But you really just need to pass their superposition through a nonlinearity, because the Taylor series expansion will typically have an early term with the multiplication of the two signals' frequencies with a high coefficient. Of course, you'll have lot of artifacts from all the other terms of the expansion, but you can use a bandpass filter to drop all the unwanted terms.

Or so I think I remember. It's been a while.


There are no other devices capable of detecting spatial vibrations at the level of sensitivity required (strain of 1 part in 10^21).


"LIGO and Virgo are not mechanically capable of detecting the collisions of supermassive black holes"

Anyone have ideas why this might be?


The larger black holes have a lower frequency chirp. Supermassive black holes would produce a peak frequency so low it gets filtered out as noise.


It isn't filtered out as noise, but rather drowned out by noise.

See Figure 5a: https://arxiv.org/pdf/1604.00439.pdf


Because of the lower frequency that would result from the much larger mass collision of the supermassive black holes.

Ideally we would have much longer travel distances for the gravity wave detection experiment. They work by building a giant interferometer with lasers pointed at mirrors that try to estimate how spacetime gets bent by the gravity wave. This should be easier to do with larger distances and less sources of noise in space. LISA is one such project. So hopefully in a couple of decades will know a lot more about supermassive black holes and other huge phenomena after detecting their gravity waves!


Sgr A* is thought to be 4+ million solar masses.

GCIRS 13E, 3 ly away from Sag A*, is thought to be 1300 solar masses.


> But in 1967, three physicists at the Hebrew University in Jerusalem realized that when the core of a dying star is very heavy, it won’t gravitationally collapse into a black hole. Instead, the star will undergo a “pair-instability supernova,” an explosion that totally annihilates it in a matter of seconds, leaving nothing behind. “The star is completely dispersed into space,” the three physicists wrote.

Does this mean that maybe the big bang was just a unstable pair that did what they describe?


No. The “pair” in “pair instability collapse supernova” refers to positron-electron pair production.

Specifically, it refers to the situation where the star is hot enough that some of the photons inside it turn into positron-electron pairs which (because conservation laws) move slower than the original photon in the brief time before the positron is annihilated, and therefore contribute less pressure, which causes the start to collapse and get hotter, causing more photons which have the energy to create positron-electron pairs.

The big bang was too big to be a star, at all. If all the matter had been in the same place, it would’ve spontaneously turned directly into a black hole, if not for inflation, which I think is not yet well understood but had effects including causing spacetime to expand by an amount which makes “a lot” seem like “almost nothing” in comparison.


The big bang might as well be the almighty space chicken laying an egg for all we care before the moment space-time became a concept worth talking about


Sometimes referred to as "God". :)


You know. I get why this is down-modded... but in the end it's actually a beautifully succinct description of exactly why god is compelling to some people.

(Obligatory, "as an atheist" disclaimer)


As far as I can tell It's compelling because people tend to dislike uncertainty and making up stories and hypotheticals can feel like knowing. I don't have an issue with that per se, but the pretend "knowledge" tends to get intertwined with all sorts of claims that actually matter, and that bothers me.


It's funny it gets downmodded too, considering it wasn't even argument, only an observation. But I'm not here only for upvotes. If my score gets too high I get worried.

Edit: Thanks! Can we go a little lower plz.


Not really.

Lee Smolin has a nice accessible writeup on the Big Bang here[1], what we typically mean by "the Big Bang" and how we seek to replace the Big Bang concept with something better.

[1]: https://www.edge.org/response-detail/25371


To further clarify what other have been replaying: the big bang was not an explosion.


This title is sensationalist.

Of course there are black holes with a lot more than 50 solar masses. It's just that they aren't created in a single event by the death of a star.

https://en.wikipedia.org/wiki/List_of_most_massive_black_hol...


They can't be created from stars 50-130 solar masses, but they can be still created by joining 2 black holes of smaller masses, right?

The bet seems stupid when you consider black hole in center of Milky Way is supposed to be 4 million times solar mass.

So the prediction was wrong.


First, this article talks about a mass gap, not a mass ceiling. E.g. stars between 50-130 solar masses shouldn't form black-holes, they should explode. The bet is about finding black holes in this gap.

Second, the issue is LIGOs first 100 detections, not all detections. We know black holes in the mass gap could form by other means such as absorbing other black holes, it was assumed that this type of formation would be rare enough that it would not occur in the first 100 black holes detected by LIGO.

So that was the bet, and the loss of the bet was the occasion to write the article. Unfortunately, while all this information is in the article, several misleading points are also in the article:

* The headline of "a Black Hole So Big It ‘Should Not Exist'" is misleading

* The diagram is equally misleading, not showing a gap but a ceiling

* The mention of this only applying to the first 100 detections is buried at the end of the article, as is the fact that people are well aware that black holes can form via absorption and so enter the gap.

The article makes it look like existing knowledge of black hole formation is being challenged, when what is basically a statistical bet about 100 observations has been settled.

The combination of over simplification and sensationalization is a problem with mediocre science writing, of which this article is unfortunately an example.


Can't black holes also inhabit the gap by shrinking via Hawking radiation? Is that something we'd expect to occur given the current age of the universe or does it need longer timescales to occur?

Also, do we know if there were special conditions during the initial phases of the post-big-bang early universe which might change the conditions under which black holes may form? For instance, non-stellar material condensing into a black hole?


Hawking radiation shrinks the black holes the faster the smaller they are.

For microscopic black holes they evaporate in fractions of second, but a black hole the mass of our sun would evaporate in 10^67 years which is significantly more than the age of universe.

So I think the chance to detect a big black hole that evaporated significant percent of its mass is zero.


The collisions they're detecting are exactly the kind of events that can create something of the forbidden size. I think the claim is that those objects should not be near another black hole for a subsequent merger?


If you read the article, you'd find out that the supermassive black holes like those at the center of our galaxy were formed very early in the Universe's life, when the laws of physics were different.


It's the same laws but at higher energy level.

Depends on how you look at it I guess? Would you say the laws of physics on the moon are different because you can jump higher?


This "when the laws of physics were different" really pisses me off. It makes it sound like gravity pushes you away and magic is real and stuff.


QM has even stranger effects, so there's that...


Inaccurate, but a close enough approximation for values of "laws of physics" that equal "things we can experience in our universe."

Mathematically? No. Practically? Yes.


However, given that the whole point of the LIGO–Virgo experiment is to detect events where black holes merge and result in a single larger black hole, it is seriously weird that the article doesn't acknowledge that fact right away and then proceed to explain why the mass gap still exists.


So if I am understanding this correctly, lower threshold (in terms of mass) for a star to become a black hole is lower than what was earlier thought?


In all these situations there are forces and other forces that resist original force but under different ranges. It keeps the universe interesting!


Ah, the one Inigo dreamed of.


The title is misleading. Just to be clear, theory predicts that blacks holes shouldn't be created between 50 and 130 solar masses, but there are plenty of black holes >130 solar masses. This is just an observation of a black hole that falls inside the supposedly "forbidden" range.


Also misleading because it is not that the existence of these holes is physically impossible, rather that their formation was extraordinarily unlikely. They can exist along a range of masses, and it is technically possible to make nearly any mass in the range by merging holes. It just very difficult to imaging how such mergers would have happened.


> This is just an observation of a black hole that falls inside the supposedly "forbidden" range.

So you're saying it's of a mass that was thought to be impossible?


HN updated their title after I posted my comment. The title of the linked article is still misleading: "Possible Detection of a Black Hole So Big It ‘Should Not Exist’".


That's so incredibly frustrating. I can't tell you how many times I've seen this exact exchange when all it would take to prevent it is the slightest indicator that the previous title got memory-holed. The other issue is when you're looking for an article you saw earlier and can't find it. It's only a minorly bewildering inconvenience but as a user it feels a slap in the face to usability since it just isn't necessary.

I just saw in another thread that the links themselves are mutable, i.e. you could discuss one article and future readers of your comments saw a completely different version of the story.


Maybe he didn't word his post perfectly but he's still pointing out an important distinction. If you could conjure a star of 0.001 solar masses, or one of 1000 solar masses, the first would be a gaseous planet incapable of sustaining a nuclear chain reaction and the second would produce enough energy to overcome the force of gravity at its periphery, blowing away its outer mass and shrinking. Those masses are impossible for stars

A 1000M black hole would be stable, there's just no likely way to end up with one in the first place.


Ah but even the extremely unlikely is likely to happen many times in a universe with such a mind bogglingly large number of glasses and stars. Such as primitive life evolving into conscious intelligence capable of measuring the minute disturbances from distant black hole mergers. I would have been on the nature finds a way side of the wager.


No, it is of a mass that according to our still standing understanding of astrophysics, is impossible to create by the collapse of "a single star".

But you can very well have this mass by the colapse of two black holes, or by one black hole that ends up consuming one or more stars nearby in due time.


If there were prior observed cases, then it certainly wouldn't be thought to be impossible. Instead it's just that theory can't yet explain how.

In the same way that it is, or was, ludicrous when people say it's impossible that bumble bees can fly, when clearly they can. Instead our understanding of their flight mechanics was incomplete.


For those wondering what the heck you are talking about, it appears that this criticism is of the title of the actual article, which is "Possible Detection of a Black Hole So Big It ‘Should Not Exist’".

I don't know if that was also the HN title at some point, but now the HN title is "Possible detection of a black hole with a mass that was thought to be impossible".


on hackernews the top voted comment is always either

* pedantic quibble with title * criticism of style of website on mobile

it makes this kind of a silly place.


That made me curious to look at the current top comments. Here they are:

https://news.ycombinator.com/item?id=20822461

https://news.ycombinator.com/item?id=20822567

https://news.ycombinator.com/item?id=20823089

https://news.ycombinator.com/item?id=20820337

https://news.ycombinator.com/item?id=20822562

https://news.ycombinator.com/item?id=20821984

https://news.ycombinator.com/item?id=20823146

https://news.ycombinator.com/item?id=20823164

https://news.ycombinator.com/item?id=20823170

https://news.ycombinator.com/item?id=20823062

https://news.ycombinator.com/item?id=20821332

https://news.ycombinator.com/item?id=20818721

https://news.ycombinator.com/item?id=20820497

https://news.ycombinator.com/item?id=20822627

https://news.ycombinator.com/item?id=20820161

https://news.ycombinator.com/item?id=20822859

https://news.ycombinator.com/item?id=20818811

https://news.ycombinator.com/item?id=20819619

https://news.ycombinator.com/item?id=20821850

https://news.ycombinator.com/item?id=20818903

https://news.ycombinator.com/item?id=20819782

https://news.ycombinator.com/item?id=20821601

Of those, https://news.ycombinator.com/item?id=20818721 is a website style complaint; you get a point for that one. But it's also a classic example that standard moderation would mark as off topic. After doing that, the new top comment is https://news.ycombinator.com/item?id=20820028, which is a fine comment. So for this cross-section of stories your description covers 1/30 prior to standard moderation and 0/30 after. That's actually better than most claims of "always"!


Don't forget the "I agree with you substantively, but aesthetically I must object" genre of political critique.


Misleading indeed. And I’m surprised the article did not talk about binary black hole mergers being potential sources of such black holes, since that seems like the most plausible theory.


I thought it did talk about binary black hole merges as one source. Here's a quote from the article which seems to match what you describe:

> Inside a globular cluster, a 50-solar-mass black hole could merge with a 30-solar-mass one, for instance, and then the resulting giant could merge again. This second-generation merger is what LIGO/Virgo might have detected


Argh, you are right - the ad fold made it seem like the article ended, yet there were two more paragraphs below it.

Still, rereading the article, the main body seemed a bit coy. It kept talking about how such black holes should not exist, yet I kept thinking “hasn't LIGO detected formation of 60+ solar mass black holes via mergers?”

But perhaps I’m in an extra criticizing mood before my morning coffee.


Did you read the whole article? It did talk about that. It gave a whole explanation.


Ok, so now i realize that i have absolutely no idea what a black even actually is.

Can HN ELI5 what a black hole actually is and explain how they even come into existence, let alone that binaries can combine??


I'm not an astrophysicist but I think I can provide a reasonably accurate answer anyway.

Basically, you get a black hole when you push matter together tight enough. This happens when some stars die, and the processes inside the star can't counteract its own gravity.

Light is affected by gravity. A black hole is an object whose gravitational "pull" is so powerful that inside a certain radius, everything gets inevitably pulled into it. This causes the event horizon, where even light can't get away.

What's inside the event horizon is not known, as far as I know, except that it has mass, charge and angular momentum

Black holes colliding is essentially no different from any other two objects colliding in space, except for the cataclysmic scale. They behave pretty much like any other object of their mass would, which means you can have two black holes orbiting each other in a binary system just like two stars would.


I really loved this ELI5, thank you.


I guess it was more of an ELI5 for kids with exceptional vocabulary. :P

One thing I neglected to mention is that the effect of gravity gets weaker with distance, so conversely it must get stronger the closer matter is pressed together. And as it gets stronger, the object gets denser because (in the absence of counteracting forces) its matter is further pulled together, and it becomes a loop until you get a black hole. Beyond that things get weird and we don't know what exactly is going on, but we do know that it happens.


So what the heck is gravity???

And assuming youre pulling mayter together so strongly, what happens to the spatial size of the atoms being pulled into that black hole? Does the physical size of the atoms change? Do they transmogrify into some other substance? Are black holes hot? Or cold?


As far as I understand it, you can think of spacetime as having a shape. All objects travelling through spacetime must conform to its shape. Einstein's insight was that objects with mass affect this shape of spacetime, and thus there is an apparent force because spacetime itself bends and thus any path through spacetime in that region also changes. It's very weird, but also kind of neat. The effect is very weak though which is why it's only really noticeable around very massive objects.

If it helps, draw a line on paper and bend the paper in various ways and observe how the line changes. You should also be able to find demonstrations on YouTube using a stretched canvas.

As for the size of matter, atoms aren't actually the smallest thing we know of, so there's (relatively speaking) a lot of empty space even inside an atom that you can squeeze out.

As for what happens inside black holes under mind-boggling pressures, while there's reason to suspect that there is such a thing as "the smallest possible space" (a quantum of space) that would act as a limit, but it's not been possible to confirm yet, so it's only speculative, and as such the only intellectually honest answer is "I don't know".

As for the temperature of a black hole, I don't know. I think Hawking radiation implies they have one, but you'll need to find out yourself.


Couldn't it evaporate into this size, or consume enough stars / other material to grow so large? Universe is young, but not so young this should be impossible


Wrt. evaporation: no. Here is a handy online black hole calculator

http://xaonon.dyndns.org/hawking/

Punch in 130 solar masses, and you get a lifetime (before evaporation) of around 10^72 years. Age of the universe is 10^10 years, so evaporation is utterly negligible.


This was my first question, too. Disappointing that HN downvotes good-faith, on-topic questions.


I agree except the word "just". It's really interesting that it exists contrary to current theories.


The article discusses that there are multiple theories explaining the possibility of alternative modes of formation.


Is there an ELICU (college undergrad) as to why 50 to 130 is forbidden but below and above is allowed?


How’s the one the article mentions?

> A pair-instability supernova happens when the core grows so hot that light begins to spontaneously convert into electron-positron pairs. The light’s radiation pressure had kept the star’s core intact; when the light transforms into matter, the resulting pressure drop causes the core to rapidly shrink and become even hotter, further accelerating pair production and causing a runaway effect. Eventually the core gets so hot that oxygen ignites. This fully reverses the core’s implosion, so that it explodes instead. For cores with a mass between about 65 and 130 times that of our sun (according to current estimates), the star is completely obliterated. Cores between about 50 and 65 solar masses pulsate, shedding mass in a series of explosions until they drop below the range where pair instability occurs. Thus there should be no black holes with masses in the 50-to-130-solar-mass range.


It kinda hand waves over a number of parts and is more simplified than what I was looking for.

To give a very very simplified summary of my reading and the questions I have remaining, it seems to be there are two equations for what is going on here. One is the force of gravitational and light radiation collapse that results in the initial increase in heat and the other is for the force of oxygen explosion.

At under 50 solar mass, the oxygen explosion is 0 and so it forms.

At 50 to 65 solar mass, the oxygen explosion is enough to throw off mass but not enough to obliterate the star, which eventually moves it to the 50 solar mass range.

At 65 to 130 solar mass, the oxygen explosion is violent enough to destroy the star without a black hole.

At 130+ solar mass, the oxygen explosion is too weak to overcome the gravitational collapse force and a black hole forms (but masses this large seem to be rare).

What I'm wondering is why are those the specific numbers. Is it really just a case of 'take the equations, plug in the numbers, and this is what you get', or is there some explanation that is easier to conceptualize.

For example, the 50 cut off seems to be that is the threshold needed to even have oxygen ignite. But for 50 to 65, why isn't the explosion enough to destroy the star? At this point, the force from gravity holding the star together would be less than at 65+ solar mass, so why isn't the core obliterated? Is it because there is a different sort of oxygen explosion that only happens under the force of 65+ solar mass that is much stronger than the one that happens at 50 solar mass?

And as for the 130 threshold, shouldn't the more solar mass mean the more oxygen to explode, so shouldn't the force of the explosion continue to be higher than the force of the gravitational collapse? The article clearly claims this isn't the case, but doesn't explain why.

P.S.

Now that I'm reading over it again, I think there might be three forces and I misunderstood the direction of the light radiation force that invalidates all of the above. It appears the light radiation is pushing outward, same direction as the oxygen explosion. If I consider all three forces it might be the model I'm looking for.


> Now that I'm reading over it again, I think there might be three forces and I misunderstood the direction of the light radiation force that invalidates all of the above. It appears the light radiation is pushing outward, same direction as the oxygen explosion. If I consider all three forces it might be the model I'm looking for.

Yes: radiation pressure is directed outwards (this is how main-sequence stars maintain hydrostatic equilibrium against gravity, which tends inwards).


What if two blackholes with 50 solar masses collide into each other?


AFAIK, nothing prevents that.

You'd want blackholes with 100 solar masses though, as the collision will apparently shed significant part of the mass in gravitational waves.


So does that mean during a collision between blackholes mass actually does/can escape a blackhole? I thought mass couldn't escape, at least not in any observable way that we can detect. [I don't know a ton about astrophysics, so apologies if this question doesn't make sense].


Mass (or rather, energy) escaping a black hole through gravitational waves has been detected experimentally. Similarly, Hawking radiation allows for black holes to emit energy as well (though this is due to quantum effects near the event horizon).


No, it cannot.

The only energy that can escape in the collision comes from the kinetic energy of the two bodies, and from their colliding accretion discs, and energy bound up in magnetic fields outside the holes.

It is interesting that the kinetic energy of a black hole is technically outside the hole.

Energy radiated as a consequence of pair production on the event horizon would fluctuate as the surface changed shape and area, but not much.


> It is interesting that the kinetic energy of a black hole is technically outside the hole.

How so?


The fact is that the energy is radiated away as gravity waves. Since energy cannot escape the event horizon, the energy must be outside it.

Of course it starts as what seems like gravitational potential energy as they first approach, and then looks increasingly kinetic as they spiral in, but the distinction doesn't really mean much. That we can detect it means some of the energy reaches us--and the whole rest of the universe, in an expanding sphere.


It's not. Even in Newtonian mechanics kinetic energy is an observer-dependent quantity; in General Relativity we care about the stress-energy-momentum tensor, and you can slice that up into kinetic and potential energies as you wish by applying coordinates.

The vast majority of the stress-energy in the immediate neighbourhood of an accreting black hole formed by stellar collapse is found inside the horizon, even if there is a substantial accretion structure.

General Relativity doesn't make any predictions about the forms stress-energy-momentum can take; we get that from matter theories like classical (but relativistic) Maxwell's equations, quantum electrodynamics, or the full Standard Model. (One also runs into "toy" or "test" forms of matter -- various idealized space-filling fluids or dusts, mainly, that approximate matter in the large: huge numbers of stars or huge numbers of galaxies, for example). So General Relativity also has nothing much to say about kinetic energy vs potential energy: just that they each must contribute to the Einstein Field Equations and that typically means being encoded in the stress-energy tensor.

The perfectly elastic bouncing of microscopic particles of a gas each bouncing in one dimension between opposite sides of the inside of a gas container produces a beautiful relationship between the kinetic energy of a gas and its pressure. https://en.wikipedia.org/wiki/Kinetic_theory_of_gases#Pressu... (PV = 2/3 K)

Assuming isotropic pressure at time t, we encode an identical contribution into the pressure components of the stress-energy tensor (the green diagonals here https://en.wikipedia.org/wiki/Stress–energy_tensor#/media/Fi... ) for every point within the gas cylinder.

The inner regions of massive stars have a lot of pressure; collapsars like neutron stars have even more pressure deep within them. In a runaway collapse that leads to the formation of a black hole, pressure typically dominates the stress-energy tensor, driving the formation of the event horizon.

By contrast, a Schwarzschild black hole is a vacuum solution of the Einstein Field Equation, meaning that the stress-energy tensor is everywhere zero. Thus there is no pressure. The source of the "central" mass inside the horizon of a Schwarzschild is best thought of as gravity self-gravitating, or if you like, "it's just defined as curvature alone until you throw a test object in".

If we perturb the Schwarzschild black hole by throwing neutral test objects through the horizon, the stress-energy tensor inside the horizon must be somewhere nonzero, but once through the horizon (ignoring quantum effects) the nonzero stress-energy stays in there, and everywhere outside the stress-energy tensor returns to zero.

An astrophysical black hole by stellar collapse locks up stress-energy in the same way: once it's inside the event horizon, it stays there (ignoring quantum effects, principally Hawking radiation). Stress-energy outside the horizon might cross the horizon in various ways, or it might form some long lived arrangement sufficiently far from the horizon. You wouldn't say that a white dwarf partner in a white-dwarf/black-hole binary forms "the kinetic [or other] energy of a black hole", would you? If not, then neither does any matter near -- but outside -- the horizon.

The no-hair theorem(s) mean(s) that in general you cannot distinguish between an uncharged, zero-angular-momentum black hole formed by stellar collapse (or black hole mergers) and a Schwarzschild (vacuum) black hole (say, formed primordially from nothing but gravitational radiation), even in binaries. A binary of uncharged, no-angular-momentum black holes may be two Schwarzschild BHs or two astrophysical BHs or one of each. The momentum-energy that leaves the binary cannot come from the stress-energy tensor of a Schwarzschild black hole, because it's zero everywhere in the horizon. If no-hair is true, it can't come from the stress-energy tensor in the interior of a black hole formed by stellar collapse, either. A very large primordial BH will have had a bunch of things fall into it (if nothing else, lots of CMB photons), but can still have essentially no stress-energy inside. Primordial black holes are not especially crazy: that's one possible way to explain supermassive black holes ( https://en.wikipedia.org/wiki/Supermassive_black_hole#Format... and note it's possible that primordial black holes can start with and retain essentially zero angular momentum).

A pair of primordial SMBHs, each near the centre of mass of merging galaxy clusters, may have eaten a bunch of stellar masses worth of dust and gas in their lifetimes, but not nearly enough to account for the gravitational radiation that will be emitted late in their inspiral, let alone during the merger and ringdown. Instead, it is the angular momentum of the binary system (as a whole, since in this sketch neither BH rotates) that must power the gravitational radiation during the inspiral.


The chances of two random black holes ever colliding with each other (not a binary-pair situation) is astronomically rare. On cosmic scales, black holes are microscopic. They are far smaller than stars of similar masses, but have we ever seen two random stars just collide?

Two black holes colliding would be like two bullets colliding if fired randomly from guns on different continents. The likelihood is so low that any detection within our sphere of observation would be very suspect.


We have not seen stars collide, but black hole mergers seem to be a regular thing now that we have a detector.

I would posit the difference is that you have to be looking at a the stars at the time of collision, but for black holes we have an omnidirectional detector with high SNR.


We have seen binary pairs collide, objects that were orbiting each other and who in all probability started their lives as a pair of objects and share a common formation story. We have not seen two non-associated stars born in different places randomly cross paths, which is the sort of merger necessary to form some sizes of black holes.


Binary’s don’t always start from the same nebula. Over millions of years stars move around quite a bit and can form or break apart binary’s.


To form a binary, for one star to capture another, requires some careful planning. (A binary pair grabbing a passing star and exchanging momentum.) They don't just get close and start orbiting each other. If a star was captured by another, it wouldn't be a tight pair that may one day merge. They would be very far apart, so far that merger would take far longer than the age of the universe.


That assumes their are only 2 stars involved. Add a 3rd or more and things get unstable.

“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud," Stahler said. "And the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years." https://www.space.com/37186-sun-long-lost-twin-nemesis.html


Because the black hole can't form from a star of 50 to 130 solar masses but it can, for example, start at 40 solar masses, collapse into a black hole, and then accumulate another 20 solar masses over its lifetime to become a black hole of 60 solar masses.

Edit: the mechanics of this are left as an exercise to the reader.


Non clickbait headline: ‘Possible detection of Black Hole that grew after formation.’

Honestly, I would have been more intrigued by the less clickbait headline for novelty if nothing else.


Maybe this works from your perspective but for everyone else who doesn't immediately understand that "after formation" is something strange and not normal the title helps people understand that this is an interesting and novel topic and worth exploring more.


So, stars between 50-130 solar masses don’t directly form black holes because they blow themselves apart at the end of their lives. I got that from the article. Is the idea that a black hole less than 50 solar masses should usually evaporate before it can gain enough mass to fall into that gap?

Edit: or is it just that there shouldn’t be enough around for a smaller black hole to “eat” to become that big?


Black Hole evaporation is incredibly slow in the 1+ Solar Mass range (~2.1 * 10^67+ years). http://xaonon.dyndns.org/hawking/

Also, another astrophysics took the other side of the bet as a 50/50. So, it was not considered all that unlikely.

PS: There is normally a limit to how fast black holes can eat, but that’s irrelevant when two black holes collide.


[flagged]


Your comment is oddly confrontational and assumes a lot. Also relies on a societal change that the parent commenter is by no means responsible for.


The tone may be confrontational, but the meaning is basically true.


It frustrates me when people complain about the quality of writing they're not paying for.


Is it not okay for me to complain about the quality of Baum's "The Wizard of Oz", which I downloaded for free from https://www.gutenberg.org/ebooks/55 ?

But, more to the point, Quanta is a nonprofit foundation-funded publication. It doesn't have subscriptions or advertisement. If we take your advice, does that mean it's unacceptable to complain about the quality of any Quanta article at all?

Doesn't their non-profit status means they receive some (indirect) financial support from us already?


I can't find any indication this publication offers a subscription, and I'm not sure how you know /u/Retric doesn't subscribe to various outlets already.


The accurate headline would be: "So Medium-Sized It Should Not Exist"


"So Medium-Sized It Might Have Been Fairly Uncommon"


There’s really no such thing as “should not exist”, only “this challenges our assumptions”. Anything is possible, it might make the human mind uncomfortable but it’s true. Our ability to comprehend and measure things is so unfathomably finite that it’s almost laughable to think we can be sure of anything.


Or, hear me out, "The IMPOSSIBLE black hole that science can't explain".


Thought to be impossible*

Title is fine -- this is great story. The media are notorious for often make a hames of scientific reporting but this isn't too bad.


> Systems programming is the development and management of software that serves as a platform for other software to be built upon.

What a wonderfully concise definition. I was never sure exactly where to draw the line; "You know, it's, uh, programming where you have to manage memory. They use C for it. It's lower-level, and stuff. It's operating systems but not just operating systems."




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