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."

Comments

Interesting repercussions

[AKAImBatman]

I am not an astrophysicist (IANAAP?), but this would seem to have some interesting implications for galactic mechanics. For one, does this means that stars are continously recycled by the black hole believed to be at the center of each galaxy? i.e. They get sucked in, crushed, then ejected as gassous emmisions which then collect and reform as a new star.

Wouldn't this also create a "galactic wind" similar to the solar wind experienced inside a solar system? Could such a wind (as weak as it may be on a micro scale) be responsible for the universe's apparent anti-gravity effect? It seems to me that if a galactic wind did exist, it would cause the galaxies to repel each other as the particles communicate back the forces of the particle collisions over billions of years.

Speaking of Black Holes, I was just listening to an interview with Brian Greene on NPR this morning. It seems that he has released a children's book designed to help children understand Relativity. Specifically, the link between gravity and time. Amazon has a nice video* where Mr. Greene explains the story and how he attempts to create an emotional connection between readers and the physics of Relativity.

* Full Disclosure: I did NOT include a referral code. This is a clean link
** Someone should really make a joke out of LHC doomsday and how we're all saved. I couldn't come up with anything funny.

Re:Interesting repercussions

[KillerBob]

Side note: makes much more sense then the big bang theory, which reeks of creationism.

Until somebody asks where it all came from in the first place. Then you're back at square one, with the same problem that the Big Bang theory has.

Unless you adopt the Hindu/Buddhist take on the cosmology... it wasn't created, it didn't magically poof into existence out of nothing: it just is. Always has been, always will be, and goes through periodic cycles of growth and destruction, without end.

Re:Interesting repercussions

[SBacks]

Why does everyone assume that nothingness is the default? From everything we've observed of the universe, it tends towards chaos and disorder (entropy). Nothingness is the complete lack of entropy, so why would should that be considered stable?

And, by the way, there are branches of cosmology that contend that the universe, has, in fact, always been and will always be. It comes from the idea that as you measure time further and further backwards, you find yourself measuring time forwards again. It has something to do with string theory, but the math is way beyond me.

Re:Interesting repercussions

[interiot]

If something denser, like a star were to fall in, I doubt that the radiation pressure would push it away.

It's not just that it pushes gas away, it also gets to the point where it prevents star formation in its vicinity:

Furthermore, it appears that black holes can keep the gas too hot to settle in large quantities back to the galaxy's nucleus or to form stars through most of the galaxy's bulk. ... "So galaxies reach the point where you don't make stars."

But stars can still form elsewhere and be pulled in, yes. These black holes would be ~one tenth the mass of our galaxy, so they should be able to capture other galaxies that orbit it and eventually fall in.

Re:Interesting repercussions

[steelfood]

Or perhaps nothingness is a state of equilibrium.

Re:Interesting repercussions

[Ambitwistor]

See here for what the heat death of the universe would be like.

Agreed, Very Interesting repercussions

[eldavojohn]

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.

Well, I'll admit this sounds intuitive with the Penrose-Hawking singularity theorems applied to the Big Bang. 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.

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).

** Someone should really make a joke out of LHC doomsday and how we're all saved. I couldn't come up with anything funny.

I was trying to relay what I had read about the micro black holes the LHC is trying to create to a female coworker. I failed. She told me someone in India committed suicide facing the LHC being turned on. 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.

Re:Tens of billion?

[megamerican]

Stop spreading FUD, it's only a single ten of trillion.

You are forgetting the unfunded liabilities the American taxpayer is on the hook for which is $60+ trillion.

Colliding black holes

[CubicleView]

I'm sure I'm basing this on some bad sci fi movie or other, but can't two of these maxed out black holes merge together (in theory at least) to form a larger one?

Just Like MRIs

[Anonymous Coward]

What we today call MRI (Magnetic Resonance Imaging) used to be called NMRI (Nuclear Magnetic Resonance Imaging). As with "Black Holes", people were afraid of anything "nuclear"; hence the name change.

Re:Just Like MRIs

[ppanon]

Ignoring the fact that non-profit groups might have the same reasons for cutting corners

It's less of an issue. For-profit corporations in the US are required by law to maximize profit for shareholders. Non-profits usually have different priorities. Sure there's still a lot of potential for individual greed gumming up the works, but non-profit organization eliminates a whole class of failure modes. For some types of enterprises, society is willing to accept the risk of those failure modes in exchange for the increased efficiency that they can provide in delivering a desired product. However a very strong argument can be made that the production of energy through nuclear fission has sufficiently bad potential consequences (thousands or millions dying and trillions' worth of land and resources unavailable for decades vs. a few thousand people out of work) that the greater efficiencies sometimes available through for-profit organizations are not worth the risk.

Stable Structure?

[corsec67]

What if there was a black hole, at this size limit, inside of a very dense cloud of gas?

Would it look like an enormous gas planet to an outside observer?
If the gas cloud was dense enough, could fusion start, creating a star with a hollow region between the "star" part and the black hole, held in place by this "radiation pressure"?

Hmm, what if the external part started becoming solid? Would it be like a planet, but inside out with "gravity" provided by the pressure from the black hole? Of course the radiation on the inside would be huge. Would the outside have tolerable gravity levels, due to the empty space inside?

Heh, I think I have one sentence there that isn't a question.

He's quoting Feynman-

[Petskull]

He's quoting Feynman:

"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

Also: Economical Number
A number n is called an economical number if the number of digits in the prime factorization of n (including powers) uses fewer digits than the number of digits in n. The first few economical numbers are 125, 128, 243, 256, 343, 512, 625, 729, ... (Sloane's A046759). Pinch shows that, under a plausible hypothesis related to the twin prime conjecture, there are arbitrarily long sequences of consecutive economical numbers, and exhibits such a sequence of length nine starting at 1034429177995381247.
http://mathworld.wolfram.com/EconomicalNumber.html

not so fast!

[Lord Ender]

You can test these theories like you test software. Consider an edge case.

Suppose there exist two of these "maximum" density black holes on a collision course. Sure, the "radiation pressure" may exceed gravity at some point for low-momentum gas particles, but that doesn't mean the pressure would be so much greater than gravity that it would halt an oncoming super black hole (with corresponding super momentum!).

It seems in such a scenario it would be possible to form a black hole with double the "maximum" mass.

No matter ejected from inside the hole

[iamlucky13]

They're not saying that matter is ejected from inside the hole, so no, stars wouldn't be recycled. Also, they are not saying black holes at galactic cores are at this limit. Sagittarius A*, for example, which lies at the center of the Milky Way, is estimated to be only 3.7 million solar masses...orders of magnitude below this theoretical maximum. Also, such a wind as you suggest should be observable as it interacts with free gas and dust in the Milky Way. This may sound hard to believe, but it is in fact regularly observed in supernova remnants and massive stars like in the Crescent Nebula.

So what they're actually decribing is gas, dust, etc in the accretion disc orbiting near but not yet swallowed by the black hole. As stated, this gas becomes superheated and expands as it swirls ever closer to the hole. They claim that at some point the heat grows so intense that like a Wolf-Rayet star at the Eddington limit, it just blows all of the remaining gas away from itself to form a big bubble of relative emptiness. The article fairly descriptively labels this as a "dry" black hole. Actually, going back to the star recycling concept, this effect may be so dramatic as to actually prevent star formation in the host galaxy for the predictable future.

At this point I think the description is a little sloppy, since the black hole would then be devoid of material to compress and heat, and therefore the "black hole wind" (AC's insert crude fart joke here) effect is now gone. Theoretically then, feeding is able to occur at slow rates, and reading between the lines of the article, it sounds like the researchers agree about that. However, it would not allow the super-fast feeding behavior that results in the distant strobes known as quasars, which are believed to be such super-massive black holes below this limit.

Ultimately what they're suggesting is that quasars can't last forever because eventually their growth slows down to practically nothing, and then you have a relatively quiet, but huge black hole. Please keep in mind, however, that the end of the article disclaims this as being speculative physics. It makes sense, and it seems to fit the data, but it hasn't been thoroughly validated yet.

Re:Where does the energy come from? Hmmm?

[Dan Ost]

Black holes do radiate particles (search for "hawking radiation" on Wikipedia), but that's not what they're talking about here. As matter falls into the black hole, it gets superheated and radiates lots of EM. Thus, it isn't radiation from the black hole that clears out the surrounding space, but radiation from the matter falling into the black hole.