So you're saying it's of a mass that was thought to be impossible?
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.
A 1000M black hole would be stable, there's just no likely way to end up with one in the first place.
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.
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.
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".
* pedantic quibble with title * criticism of style of website on mobile
it makes this kind of a silly place.
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"!
> 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
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.
Can HN ELI5 what a black hole actually is and explain how they even come into existence, let alone that binaries can combine??
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.
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.
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?
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.
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.
> 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.
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.
Yes: radiation pressure is directed outwards (this is how main-sequence stars maintain hydrostatic equilibrium against gravity, which tends inwards).
You'd want blackholes with 100 solar masses though, as the collision will apparently shed significant part of the mass in gravitational waves.
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.
How so?
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.
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.
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.
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 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
Edit: the mechanics of this are left as an exercise to the reader.