Black Holes May Not Grow Beyond Certain Limit 201
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."
Re:Interesting repercussions (Score:4, Informative)
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.
Re:Interesting repercussions (Score:3, Informative)
I'm not an astrophysicist either, but as far as I can tell nothing about this hypothesis contradicts the idea that once matter crosses the event horizon it doesn't come out again, except as radiation. They aren't saying that the black hole begins "ejecting" gas, just that at that mass it gives off enough radiation to prevent any more gas from falling in.
I'm not sure I buy that as setting an upper limit on the size of a black hole. It just means the rate of growth would slow, and potentially reach equilibrium with regards to the surrounding gas. If something denser, like a star were to fall in, I doubt that the radiation pressure would push it away.
But who knows. I don't.
You are completely correct. Good work.
Re:Interesting repercussions (Score:5, Informative)
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 [nasa.gov]. 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 [nasa.gov]
In both cases, the thermal energy of the ejecta is insufficient to explain the gravitational anomalies you mention.
Re:What if our universe were one big black hole? (Score:3, Informative)
I saw an interesting interview with Michio Kaku here [youtube.com], and he talks about just this.
Re:Tens of billion? (Score:5, Informative)
Richard Feynman, US educator & physicist (1918 - 1988)
http://www.quotationspage.com/quote/26930.html [quotationspage.com]
Re:Interesting repercussions (Score:1, Informative)
Not quite right either. Nothing escapes a black hole except gravity. The radiation produced by a quasar comes from the super-heating of the gases as they are compressed rushing into the black hole.
What this article is saying is that the radiation (light/x-ray, etc.) pressure from this glowing super-heated gas is pushing away other incoming gases at a rate that "chokes off" the process.
Re:slashdot editor fail... (Score:3, Informative)
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!
Re:Agreed, Very Interesting repercussions (Score:4, Informative)
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 [ucla.edu].) 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".
Re:Interesting repercussions (Score:3, Informative)
Do they always assume that? I've always heard the phrase "heat death of the universe," which doesn't imply nothing...exactly, but it would be close.
Thanks to almighty laws of thermodynamics, we could theoretically reach a point where every bit of matter has been broken down into mere energy, and every quantum of energy is so far away from every other quantum of energy that no interaction ever happens again - everything stays in the lowest possible energy state, at the lowest level of organization.
If you could suddenly teleport to that time in the future, what you'd see for light years in every direction would be nothing at all. Sure, there'd be *something* since energy can't be destroyed.
It just wouldn't be doing much...probably not enough to detect.
Re:Interesting repercussions (Score:3, Informative)
I don't waste my time arguing with creationist nutjobs like arminw, but just for the sake of scientific accuracy, you should know that cosmological redshift is NOT quantized into discrete redshifts. The people who claim so don't even understand what "quantization" means.
In the past there has been some weak evidence of a periodicity in redshifts in small samples of galaxies. "Periodicity in redshift" means that galaxies are more likely to be found at multiples of certain redshifts than others. It does not mean that the redshifts are quantized, meaning they only occur in discrete multiples. Even if you accept the claimed periodicity, there are most certainly plenty of galaxies (the vast majority, in fact) which occur at redshifts other than periodic multiples.
The studies which purported to find periodicities didn't all agree with each other as to which redshifts were the peaks. That's a hallmark of data-mining a spurious signal out of noise, a classic outcome of small-sample statistics. When you take into account any of the following factors (1) large sample sizes (we now observe far more galaxies than when those original claims were made), (2) the existence of large scale structure (you're going to see more galaxies at certain distances if that's where a supergalactic cluster is located), (3) sample selection bias, the "effect" goes away.
You should also note that periodicities in redshift do not contradict the evidence in favor of the expansion of the universe, either. Even if they existed, the most direct interpretation is that there is inhomogeneous large scale structure formation (which we already know there is, see point 2 above).