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Black Holes May Not Grow Beyond Certain Limit
xyz writes "Do black holes increase in size indefinitely? According to an analysis by astronomers at Yale and the European Southern Observatory, the maximum size a black hole may reach is only few tens of billion of solar masses. The limit was calculated using an analysis of what may happen to the gas surrounding a black hole which has reached few tens of billions of solar masses. It is thought that black holes of such size heat the surrounding gas to a temperature where the radiation pressure begins blowing outer layers into space."
Not quite sucking them in and spitting them out. Rather it's when the inflowing matter creates so much heat it clears out all the remaining matter in the area. Creates a "dry galaxy" (their term, not mine). So nothing left nearby for it to suck in and thereby grow.
An analogy would be how when a star forms it coalesces to a point that it produces enough energy to clear the area (T Tauri wind?). The star growth is then capped.
The world is made by those who show up for the job.
What happens, roughly, is that stars that stray too close to the black hole are torn apart by the tidal forces, their constituent gas adding to a large torus of gas orbiting the black hole. Some fraction of this torus loses enough angular momentum to either fall into the event horizon of the black hole, lost "forever" (astronomically speaking), or a grazing collision that gives it enough energy to avoid being sucked in. This gas can form a galactic wind of sorts: that flow becomes collimated by the high spin rate of the black hole and the torus of gas around it. This produces jets like those seen emanating from the core of M87. That gas, with its high temperature and flow rate, will not cool to a low enough temperature to coalesce into new stars any time "soon" (astronomically speaking.)
Now, there are flows that involve gas being ejected from the disk of the galaxy with less energy, which can rain back down onto the disk and contribute to newly-formed stars. But these "champagne flows" are usully caused not by the energetics of the central black holes, but rather the collective stellar winds from the stars in the disk; for example, the galactic superwind of M82
In both cases, the thermal energy of the ejecta is insufficient to explain the gravitational anomalies you mention.
"I guess the moral of the story is, don't paint your airship with rocket fuel." -- Addison Bain
There are 10^11 stars in the galaxy. That used to be a huge number. But it's only a hundred billion. It's less than the national deficit! We used to call them astronomical numbers. Now we should call them economical numbers.
Richard Feynman, US educator & physicist (1918 - 1988)
http://www.quotationspage.com/quote/26930.html
It's not totally crazy - when talking about black holes, the "size" of the black hole refers to it's Schwarzschild radius, which is directly proportional to its mass. Though you're probably right that in this case it's just a mistake!
Well, I'll admit this sounds intuitive with the Penrose-Hawking singularity theorems applied to the Big Bang.
No, it has nothing to do with singularities (or the Big Bang). It has more to do with matter which orbits black holes.
Now, I'm not a physicist either but I have read a lot that speculates the Big Bang was a singularity that created a hot unstable mess. All the mass of the universe in a singularity suddenly starts blowing out and producing massive heat. Although what was around this singularity is nothing--not even space.
Don't think of the singularity as a point that blew matter in all directions. As you correctly note, there is nothing "around" a singularity. For now limit consideration to an infinite universe, which is preferred by standard inflation scnearios. Then a singularity isn't even really a single point. The universe is still infinite in extent, it's just that the matter/energy in it is of infinite density. (See here.) Think of the Big Bang as where space expands making the matter less dense, rather than some single location that spews matter away from itself.
As always, it brings up interesting questions about what was before that epoch since it is kind of clear that such a singularity could not be possibly be stable for any amount of time (as this research indicates).
To reiterate, this research has nothing to do with the singularity inside of black holes. It has to do with matter which is outside black holes not being able to make its way in, due to the pressure created by other infalling matter. The black hole itself does not emit any appreciable matter/radiation (other than a very tiny amount of Hawking radiation).
All I could think of was that I really wish they called micro black holes that exist for minute fractions of a second something other than "black holes." It scares people unnaturally.
I agree. "Micro black hole" is a terrible name. I prefer "Death, Tiny Destroyer of Worlds".