Using the formula for black hole density, a black hole of this mass would have an average density about the same as the near-vacuum atmosphere of Mars(!)
from which perspective? I have yet to wrap my head around it(this usually means I am wrong about something), but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects.
This is the origin of my favorite science fiction theory. (little to no actual science but you could write a fun space romp around it) If you get a large enough black hole where the tidal forces will not rip you to shreds instantly, you could just scoot across the event horizon right, now what happens? you can still move around, everything feels normal, but really you have lost half a dimension, everything "out" from the center is completely gone from the universe. Now the theory, back to our universe, What happened to time? why does time only go one way? we can accelerate and decelerate along the time axis, but can't reverse it. Where has our missing half of a time dimension gone?
> but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that.
That sounds more like a description of the stuff neutron stars are made of. I don't think that description really works for black holes - how exactly do you take a teaspoon out of a black hole?
> The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?
The linked Physics.SE answer does a decent job at explaining it, but the short of it is that for Schwarzchild black holes mass ~ event horizon radius, so if you define density as mass / (Schwarzchild volume) you get density ~ 1/(mass^2) - in other words, the more massive a black hole the less dense it is by that measure.
Small black holes are light, a large black hole with the mass of our visible universe would have an event horizon larger than the visible universe, because the area, not volume, scales linearly with the contained mass.
This reminds me of when I was a physics undergrad way back in the mid 80s. We used to spend nights drinking beer and hacking some simulations from the Computer Recreations section of Scientific American.
Once we wanted to simulate the dynamics of galaxies. I don'it think it was an SA article, but we did it the slow way by calculating the force on every star individually from each other star. It was excruciatingly slow and boring.
Then some time later, I don't recall where I picked that up, I updated the simulation to just model the force on each star coming from the galaxy's centre of mass.
I could simulate many more stars, have galaxies collide and see them spin off with their stars scattering around.
What struck me was that they looked like real galaxies we see out there.
I wasn't aware of the postulations made in the 60s/70s about there being supermassive black holes at the centre of galaxies, but to me, this simplified simulation was kind of like a smoking gun for that... from an 80286 IBM PC AT.
If we're assuming that the galaxy is radially symmetrical, doesn't it immediately follow that the combined gravitational force on a given star is the same as if we applied the force from a combined mass at the center?
This wouldn't work for something like the Solar system with a very sparse distribution of mass, but at the galaxy level it seems right even without the presence of a black hole.
Even when the distance between the centres of mass of two colliding galaxies become comparable to their size?
It's a long time ago, but what I remember was being fascinated by the shapes of the galaxies emerging from a collision under this centre-of-mass approximation, and that it created shapes we see out there. It was as if the main effect were a central mass in each galaxy dominating the dynamics.
Theoretically yes but although this black hole is big enough to make that more realistic, the redirected light would be have lost so much energy we’d likely be unable to observe it. We’d need an orbital hypertelescope to even stand a chance. Even then we wouldn’t see the earth because it would be drowned out by the sun.
The bigger problem is all the dust and other stars in the way. I’m not aware of any black holes close enough that would have a direct path for the light to cross without being absorbed and scattered.
The other problem is the angle at which the light must be redirected. The Cosmic Horseshoe is composed of two systems almost directly in line, the light comes from the farther system and bends infinitesimally around the black hole to come to us. I don't know if a 180 degree bend is possible.
Also, the foreground galaxy/supermassive black hole in the Cosmic Horseshoe is 5.6 billion light years away, so any light that could come from our solar system, go around the black hole, and come back to our hypothetical hypertelescope would be over 11 billion years old - almost triple the age of our sun.
Saggitarius A* in our own galaxy is, of course, directly in the elliptic and therefore badly occluded by dust, but it would be interesting to look at as it's only 27k light years away. In the absence of that pesky dust, it would give us a picture of the solar system as of the Paleolithic. Andromeda, at 2.5 million light years away, would give us 5-million-year-old light. There are other black holes in the Milky Way on the order of a thousand light years away which are not at the center of the galaxy but have masses comparable to or slightly larger than our sun, these are far closer (within a few thousand years) but have much smaller gravitational fields. Luminous intensity drops off with the square of the distance, but I'm not sure how the gravitational field strength affects the ability of a particular galaxy to bend light.
It doesn't seem like there's a limit to how big they can get just a limit to how quickly they can get bigger due to what's called the Eddington Limit which explains how matter falling into the black hole emits radiation and if enough radiation around the accretion disk builds up, it can overcome the pull of the black hole and push matter away, at least until enough matter is pushed away that the radiation levels fall back under the limit and matter starts falling in again.
PBS Spacetime had an episode somewhat recently about a black hole which is growing at many (hundreds? thousands? I forget) times the Eddington Limit. And, as far as I remember, it isn't the only one to exceed the Eddington Limit - just the one with the record for how much it exceeded it.
I'll try to dig it up when I'm not at work (or if I remember the exact episode through the day).
Importantly, the Eddington limit does not apply to black hole mergers, theoretically allowing as much growth rate as you're able to feed in from smaller black holes.
So then the only theoretical limit on black hole mass would just be how fast you can put matter in black holes and/or merge existing black holes versus how fast the universe expands?
> [270B solar masses] is the maximum mass of a black hole that models predict, at least for luminous accreting SMBHs.
as well as:
> The limit is only 5×10^10 M [50B solar masses] for black holes with typical properties, but can reach 2.7×10^11 M [270B solar masses] at maximal prograde spin (a = 1).
However in the chapter before, it's stated:
> New discoveries suggest that many black holes, dubbed 'stupendously large', may exceed 100 billion or even 1 trillion M.
Poking around those articles (and knowing nothing really), it is interesting to note a couple references to a 50B solar-mass limit for “luminous accreting black holes hosted by disc galaxies.” (In your Phoenix cluster link). I guess these ones are easier to spot, based entirely on the word “luminous.”
There are other larger ones out there, looming in the darkness.
Yes - but it's basically the same as the total mass of the universe.
EDIT: I believe the above could be incorrect - if the universe has too much electrical charge or angular momentum. (And some other cosmological properties, so you couldn't get around the charge & spin issues.)
Might there be a black hole astrophysicist in the house, to comment on this?
With good quantization, I bet we can get it down to 8B and it will easily fit on consumer grade galaxy.
(Sorry, I had to, with all the AI flood, I really was about to skip this info after the first 3 characters)
Don't be sorry, that was pretty good
They very rare great HN joke.
How true this is
With good quantization you can get 36GB down to 8GB. To get 36B down to 8B you need good pruning.
I had a bit of a pause trying to figure out if someone named a model „black hole” from that title.
Hype is strong.
thanks for brightening the day :)
So you're saying it might fit on the S26?
Glad you wrote it, the title took me down the same path for a few seconds :-D
Researchers discovered the black hole has been consuming AI VC money, at the rate of $50M per day, and so finally explaining why it is gotten so big.
That sounds low...
that's too good, haha
But can you make it talk dirty to me
Using the formula for black hole density, a black hole of this mass would have an average density about the same as the near-vacuum atmosphere of Mars(!)
https://physics.stackexchange.com/questions/26515/what-is-ex...
That calculation of density is nice, but since we don’t know what’s inside a black hole, it doesn’t mean anything.
Passing the event horizon doesn’t mean you’ve reached the potentially ultra dense singularity, but it does mean you won’t escape.
And it would take 10 days from event horizon to the singularity.
from which perspective? I have yet to wrap my head around it(this usually means I am wrong about something), but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects.
https://modern-physics.org/time-dilation-near-massive-bodies...
This is the origin of my favorite science fiction theory. (little to no actual science but you could write a fun space romp around it) If you get a large enough black hole where the tidal forces will not rip you to shreds instantly, you could just scoot across the event horizon right, now what happens? you can still move around, everything feels normal, but really you have lost half a dimension, everything "out" from the center is completely gone from the universe. Now the theory, back to our universe, What happened to time? why does time only go one way? we can accelerate and decelerate along the time axis, but can't reverse it. Where has our missing half of a time dimension gone?
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How so?
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Definitely a dumb question but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that.
The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?
> but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that.
That sounds more like a description of the stuff neutron stars are made of. I don't think that description really works for black holes - how exactly do you take a teaspoon out of a black hole?
> The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?
The linked Physics.SE answer does a decent job at explaining it, but the short of it is that for Schwarzchild black holes mass ~ event horizon radius, so if you define density as mass / (Schwarzchild volume) you get density ~ 1/(mass^2) - in other words, the more massive a black hole the less dense it is by that measure.
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Black holes become less dense as they get bigger.
Radius is linearly proportional to the mass: r = 2GM/c²
(So volume grows faster than mass)
Small black holes are light, a large black hole with the mass of our visible universe would have an event horizon larger than the visible universe, because the area, not volume, scales linearly with the contained mass.
This reminds me of when I was a physics undergrad way back in the mid 80s. We used to spend nights drinking beer and hacking some simulations from the Computer Recreations section of Scientific American.
Once we wanted to simulate the dynamics of galaxies. I don'it think it was an SA article, but we did it the slow way by calculating the force on every star individually from each other star. It was excruciatingly slow and boring.
Then some time later, I don't recall where I picked that up, I updated the simulation to just model the force on each star coming from the galaxy's centre of mass.
I could simulate many more stars, have galaxies collide and see them spin off with their stars scattering around.
What struck me was that they looked like real galaxies we see out there.
I wasn't aware of the postulations made in the 60s/70s about there being supermassive black holes at the centre of galaxies, but to me, this simplified simulation was kind of like a smoking gun for that... from an 80286 IBM PC AT.
Even the largest SMBHs mass is a minute fraction of their host galaxies' total mass so it is not the case that everything is just orbiting the SMBH.
If we're assuming that the galaxy is radially symmetrical, doesn't it immediately follow that the combined gravitational force on a given star is the same as if we applied the force from a combined mass at the center?
This wouldn't work for something like the Solar system with a very sparse distribution of mass, but at the galaxy level it seems right even without the presence of a black hole.
Even when the distance between the centres of mass of two colliding galaxies become comparable to their size?
It's a long time ago, but what I remember was being fascinated by the shapes of the galaxies emerging from a collision under this centre-of-mass approximation, and that it created shapes we see out there. It was as if the main effect were a central mass in each galaxy dominating the dynamics.
With all the lensing going on out there, is it possible for us to observe the light from our sun (and potentially our planet) billions of years ago?
A cool achievement would be, observe the moon/earth separation event(s)
Theoretically yes but although this black hole is big enough to make that more realistic, the redirected light would be have lost so much energy we’d likely be unable to observe it. We’d need an orbital hypertelescope to even stand a chance. Even then we wouldn’t see the earth because it would be drowned out by the sun.
The bigger problem is all the dust and other stars in the way. I’m not aware of any black holes close enough that would have a direct path for the light to cross without being absorbed and scattered.
The other problem is the angle at which the light must be redirected. The Cosmic Horseshoe is composed of two systems almost directly in line, the light comes from the farther system and bends infinitesimally around the black hole to come to us. I don't know if a 180 degree bend is possible.
Also, the foreground galaxy/supermassive black hole in the Cosmic Horseshoe is 5.6 billion light years away, so any light that could come from our solar system, go around the black hole, and come back to our hypothetical hypertelescope would be over 11 billion years old - almost triple the age of our sun.
Saggitarius A* in our own galaxy is, of course, directly in the elliptic and therefore badly occluded by dust, but it would be interesting to look at as it's only 27k light years away. In the absence of that pesky dust, it would give us a picture of the solar system as of the Paleolithic. Andromeda, at 2.5 million light years away, would give us 5-million-year-old light. There are other black holes in the Milky Way on the order of a thousand light years away which are not at the center of the galaxy but have masses comparable to or slightly larger than our sun, these are far closer (within a few thousand years) but have much smaller gravitational fields. Luminous intensity drops off with the square of the distance, but I'm not sure how the gravitational field strength affects the ability of a particular galaxy to bend light.
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How big would the diameter of this be ? Something like 8 light days ?
The Schwarzschild radius would be approximately 106 billion kilometers or about 7 light days (r = 2GM/c²).
Sounds about right. Wiki has a correctly scaled picture with the two biggest known black hole event horizons and the solar system:
https://en.wikipedia.org/wiki/TON_618
Event horizon radius would be about roughly 1000 times the distance between Earth/Sun.
About 9000 times the mass of the supermassive black hole at the center of our galaxy (Sagittarius A*).
Mind boggling. Wish they included images of the scale compared to our sun, solar system, galaxy etc to help me wrap my head around this beast.
Unfortunately a picture would not clarify anything with that sort of object. A video will: https://www.youtube.com/watch?v=0FH9cgRhQ-k
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Cosmic Horseshoe galaxy, with pics
https://en.m.wikipedia.org/wiki/Cosmic_Horseshoe
A bit off topic: Is there any theoretical upper limit on the mass of a black hole?
It doesn't seem like there's a limit to how big they can get just a limit to how quickly they can get bigger due to what's called the Eddington Limit which explains how matter falling into the black hole emits radiation and if enough radiation around the accretion disk builds up, it can overcome the pull of the black hole and push matter away, at least until enough matter is pushed away that the radiation levels fall back under the limit and matter starts falling in again.
PBS Spacetime had an episode somewhat recently about a black hole which is growing at many (hundreds? thousands? I forget) times the Eddington Limit. And, as far as I remember, it isn't the only one to exceed the Eddington Limit - just the one with the record for how much it exceeded it.
I'll try to dig it up when I'm not at work (or if I remember the exact episode through the day).
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Importantly, the Eddington limit does not apply to black hole mergers, theoretically allowing as much growth rate as you're able to feed in from smaller black holes.
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So then the only theoretical limit on black hole mass would just be how fast you can put matter in black holes and/or merge existing black holes versus how fast the universe expands?
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https://en.wikipedia.org/wiki/List_of_most_massive_black_hol... shows the maximal theoretical limit as 270B solar masses.
To expand on this, as stated in your source:
> [270B solar masses] is the maximum mass of a black hole that models predict, at least for luminous accreting SMBHs.
as well as:
> The limit is only 5×10^10 M [50B solar masses] for black holes with typical properties, but can reach 2.7×10^11 M [270B solar masses] at maximal prograde spin (a = 1).
However in the chapter before, it's stated:
> New discoveries suggest that many black holes, dubbed 'stupendously large', may exceed 100 billion or even 1 trillion M.
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So what happens if two such black holes collide?
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Given things like https://en.wikipedia.org/wiki/TON_618 and https://en.wikipedia.org/wiki/Phoenix_Cluster#Supermassive_b..., probably not. Seems like you can just keep shoving mass into it.
Poking around those articles (and knowing nothing really), it is interesting to note a couple references to a 50B solar-mass limit for “luminous accreting black holes hosted by disc galaxies.” (In your Phoenix cluster link). I guess these ones are easier to spot, based entirely on the word “luminous.”
There are other larger ones out there, looming in the darkness.
Those supermassive black holes are very old, from a time when the universe was much denser - they likely collapsed directly without any star formation
There is this whole theory that the observable universe is inside a black hole.
So the upper limit is the weight of the universe.
Yes - but it's basically the same as the total mass of the universe.
EDIT: I believe the above could be incorrect - if the universe has too much electrical charge or angular momentum. (And some other cosmological properties, so you couldn't get around the charge & spin issues.)
Might there be a black hole astrophysicist in the house, to comment on this?
https://youtu.be/EGzvGgNmaiY?t=58s