Is there an upper limit to how big a black hole can get?

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Is there an upper limit to how big a black hole can get?

Postby Kwoodhouse on April 5th, 2018, 12:11 am 

I've read articles on black holes that show the biggest black holes are estimated to be anywhere from 6 to 40 billion solar masses which is pretty ridiculous in size but is there a point a black hole would reach where it just would stop growing and start losing more mass to things like quasars than it could gain?
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Re: Is there an upper limit to how big a black hole can get?

Postby Watson on April 5th, 2018, 12:18 am 

You should post the sources? It would be helpful if we could refer to the same article.
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Re: Is there an upper limit to how big a black hole can get?

Postby Kwoodhouse on April 5th, 2018, 12:33 am 

Sorry I didn't really think the article was that relevant it was just one I came across that made me thinkbut i'll link it anyway

https://www.space.com/18668-biggest-black-hole-discovery.html

also I looked up if they do have a size limit and got this

https://www.newscientist.com/article/dn28647-black-holes-have-a-size-limit-of-50-billion-suns/

the way they explain it doesn't really seem to say they do have a size limit though just that if it got big enough that it wouldn't be able to support a gas disc so it wouldn't grow as fast
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Re: Is there an upper limit to how big a black hole can get?

Postby mitchellmckain on April 5th, 2018, 5:00 pm 

Kwoodhouse » April 4th, 2018, 11:11 pm wrote:Is there an upper limit to how big a black hole can get?

No.

Kwoodhouse » April 4th, 2018, 11:11 pm wrote:I've read articles on black holes that show the biggest black holes are estimated to be anywhere from 6 to 40 billion solar masses which is pretty ridiculous in size but is there a point a black hole would reach where it just would stop growing and start losing more mass to things like quasars than it could gain?

If the 6 to 40 billion solar masses was about theoretical limits then the lower limit on this should be 2.17 solar masses, for that is what you would get if a neutron star absorbed any matter exceeding this amount which would cause it to collapse under its own gravity into a black hole. Thus neutrons stars are restricted to a rather narrow mass range since they must have 1.4 solar masses in order to become a neutron star (from the supernova of a star with at least 8 solar masses). So perhaps the 6 to 40 billion solar masses is from actual examples of black holes that are known to exist because of their gravitational effects.

If a theoretical upper limit on the mass of black holes in the universe is even possible then it would only be a limit on what we expect to see according to known process which produce black holes. These limits will change (grow wider) with the increasing age of the universe. More time means black holes can gobble more mass and isolated black holes lose mass over time and thus the lower number will decrease and the higher number will increase.

The only means by which black holes can lose mass is by Hawking radiation and that decreases with mass. Thus if really small black holes existed for some reason, then if they do not quickly gobble up more mass, they will be shorted lived, losing all their mass to Hawking radiation.
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Re: Is there an upper limit to how big a black hole can get?

Postby Kwoodhouse on April 5th, 2018, 7:24 pm 

How much mass can a black hole actually lose to radiation then and how does the rate at which they lose mass change with size.

Does it increase proportionally such as a fixed or semistable % of its size lost to radiation over time, or does it change exponentially so that the amount it loses relative to its size increase the larger it gets which would perhaps indicate the possibility of a upper limit or it could neither of these scenarios.

If black holes do not have an upper limit though the implications of that possibilly could be that the entire known universe could theoretically be consumed and merged into a single body. Although that's hard to imagine.
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Re: Is there an upper limit to how big a black hole can get?

Postby Watson on April 5th, 2018, 7:30 pm 

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Re: Is there an upper limit to how big a black hole can get?

Postby Watson on April 5th, 2018, 8:59 pm 

From that link:
Hawking showed how the strong gravitational field around a black hole can affect the production of matching pairs of particles and anti-particles, as is happening all the time in apparently empty space according to quantum theory. If the particles are created just outside the event horizon of a black hole, then it is possible that the positive member of the pair (say, an electron) may escape - observed as thermal radiation emitting from the black hole - while the negative particle (say, a positron, with its negative energy and negative mass) may fall back into the black hole, and in this way the black hole would gradually lose mass. This was perhaps one of the first ever examples of a theory which synthesized, at least to some extent, quantum mechanics and general relativity.


Hawking Radiation has always suggested to me, that the event horizon is a well defined boundary where by one virtual particle is trapped in the BH, yet the close by counterpart particle is able to escape. That seems to suggest the event horizon is a sharp boundary, with in or out options, only .
Yet most other notions of gravitation attractions near the event horizon seem to suggest a more graduated EH, depending on what is objects are near or falling into the BH
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Re: Is there an upper limit to how big a black hole can get?

Postby mitchellmckain on April 5th, 2018, 10:51 pm 

The rate of emission appears to be inversely proportional to the mass squared.

Wikipedia wrote:For a black hole of one solar mass (M☉ = 1.98892×10^30 kg), we get an evaporation time of 2.098×10^67 years—much longer than the current age of the universe at (13.799±0.021)×10^9 years.


So when we consider the heat death of the universe, the black holes are, by far, the last thing to go.
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