3 ms·

So this is one of them "shower thoughts", you know, those stupid things you think about while working on something else.That is, purely science fiction. Can an

by somat 3y ago

So this is one of them "shower thoughts", you know, those stupid things you think about while working on something else.That is, purely science fiction. Can an analog be drawn between galaxies and solar system creation theories, with several orders of magnitudes in time required for formation due to scale difference. That is, the galaxies we see with their billions of stars are actually young proto accretion disks. while mature galaxies will have most of the mass localized in a small(1-2) number of points with a few(~10) point masses orbiting it. a sort of galaxy sized solar system if you will. However due to the scale of things involved all these late stage point masses would be black holes.

deanCommie 3y ago
I'm here for shower thoughts-driven discourse. But I missed the point. Stars eventually wind up as black holes. So it stands to reason so would galaxies. But then why would they be all over the early universe?
- consilient 3y ago
  > Stars eventually wind up as black holes. The vast majority of stars will end up as white dwarfs. Stars need to be about 10 times the mass of the sun to undergo core collapse, and about 25 solar masses (or more, depending on composition) to form black holes. > So it stands to reason so would galaxies. Galaxies are loosely bound clouds of dust with a few stars here and there, relatively speaking; stars are dense roiling balls of plasma. Their dynamics are extremely different.
- mr_toad 3y ago
  > But then why would they be all over the early universe? Stars can form quite quickly (relative to the age of the universe), possibly as early as 150 million years after the Big Bang. And the earliest massive stars would have had very short lifespans.
cooper_ganglia 3y ago
[flagged]
- kragen 3y ago
  please elucidate which part, if any, of this is correct
dotnet00 3y ago
It is worth considering that a black hole's hold on its galaxy is not as strong as a sun-like star's on its accretion disk. Our Sun is 99% of the mass of the solar system, our Sagittarius A* is ~4 million solar masses, while our Milky Way is 800 billion solar masses. On top of that, black hole growth rate slows to nearly a stop at ~270 billion solar masses, so even if a black hole manages to meet the rare conditions to get that heavy, it would still be dwarfed by its galaxy.
- Moldoteck 3y ago
  Is the upper limit due to hawking radiation?
  - adgjlsfhk1 3y ago
    it isn't. hawking radiation slows as the black hole size increases. I believe it's more just that it's very unlikely for too much mass to pass by a black hole
    - Moldoteck 3y ago
      wow, i've assumed that if bh increases, ther's more space for howking radiation to escape so bh will loose more mass... I guess physics and intuition aren't going that well together in some cases)
  - dotnet00 3y ago
    Something to do with the spin rate and the stability of the accretion disk. I don't fully understand it, just something I picked up off wikipedia.
- brabel 3y ago
  But at the same time, I think it's been shown the the size of a galaxy almost always reflects the size of its central black hole... that is, the influence of the central black hole seems to be way, way bigger than what you would expect from the black hole's gravity alone.
Laremere 3y ago
Not an astronomer, but there's at least one important thing to consider: Stars form in denser regions of gas. However once they grow large enough to start fusion, the solar wind will blow away the gas, halting growth of that star system. So stars have a kind of limit when it comes to size. That's what makes these early universe large black holes problematic (read, exciting new science): we know black holes the mass of stars can form by a super nova. However the only way we know that these super massive black holes can form is by smaller black merging. There's simply not enough time for black holes as large as we think jwst has seen to form in the age of the universe we think we're looking at. Something in the physics has to give.
- Keysh 3y ago
  ... the only way we know that these super massive black holes can form is by smaller black merging. The main way supermassive black holes in the centers of galaxies grow is by accreting gas, not by mergers with other black holes. (But you can still have potential problems with not being able to accrete enough gas in a short enough time to explain early SMBHs, unless the initial "seed" BHs are larger than those formed by conventional supernovae.)

by somat 3y ago

deanCommie 3y ago

I'm here for shower thoughts-driven discourse. But I missed the point. Stars eventually wind up as black holes. So it stands to reason so would galaxies. But then why would they be all over the early universe?

consilient 3y ago
> Stars eventually wind up as black holes. The vast majority of stars will end up as white dwarfs. Stars need to be about 10 times the mass of the sun to undergo core collapse, and about 25 solar masses (or more, depending on composition) to form black holes. > So it stands to reason so would galaxies. Galaxies are loosely bound clouds of dust with a few stars here and there, relatively speaking; stars are dense roiling balls of plasma. Their dynamics are extremely different.
mr_toad 3y ago
> But then why would they be all over the early universe? Stars can form quite quickly (relative to the age of the universe), possibly as early as 150 million years after the Big Bang. And the earliest massive stars would have had very short lifespans.

cooper_ganglia 3y ago

[flagged]

kragen 3y ago
please elucidate which part, if any, of this is correct

dotnet00 3y ago

It is worth considering that a black hole's hold on its galaxy is not as strong as a sun-like star's on its accretion disk. Our Sun is 99% of the mass of the solar system, our Sagittarius A* is ~4 million solar masses, while our Milky Way is 800 billion solar masses. On top of that, black hole growth rate slows to nearly a stop at ~270 billion solar masses, so even if a black hole manages to meet the rare conditions to get that heavy, it would still be dwarfed by its galaxy.

Moldoteck 3y ago
Is the upper limit due to hawking radiation?
- adgjlsfhk1 3y ago
  it isn't. hawking radiation slows as the black hole size increases. I believe it's more just that it's very unlikely for too much mass to pass by a black hole
  - Moldoteck 3y ago
    wow, i've assumed that if bh increases, ther's more space for howking radiation to escape so bh will loose more mass... I guess physics and intuition aren't going that well together in some cases)
- dotnet00 3y ago
  Something to do with the spin rate and the stability of the accretion disk. I don't fully understand it, just something I picked up off wikipedia.
brabel 3y ago
But at the same time, I think it's been shown the the size of a galaxy almost always reflects the size of its central black hole... that is, the influence of the central black hole seems to be way, way bigger than what you would expect from the black hole's gravity alone.

Laremere 3y ago

Not an astronomer, but there's at least one important thing to consider: Stars form in denser regions of gas. However once they grow large enough to start fusion, the solar wind will blow away the gas, halting growth of that star system. So stars have a kind of limit when it comes to size. That's what makes these early universe large black holes problematic (read, exciting new science): we know black holes the mass of stars can form by a super nova. However the only way we know that these super massive black holes can form is by smaller black merging. There's simply not enough time for black holes as large as we think jwst has seen to form in the age of the universe we think we're looking at. Something in the physics has to give.

Keysh 3y ago
... the only way we know that these super massive black holes can form is by smaller black merging. The main way supermassive black holes in the centers of galaxies grow is by accreting gas, not by mergers with other black holes. (But you can still have potential problems with not being able to accrete enough gas in a short enough time to explain early SMBHs, unless the initial "seed" BHs are larger than those formed by conventional supernovae.)