Astronomers discover upper mass limit for black holes

Sep 11, 2008

There appears to be an upper limit to how big the universe's most massive black holes can get, according to new research led by a Yale University astrophysicist.

Once considered rare and exotic objects, black holes are now known to exist throughout the universe, with the largest and most massive found at the centers of the largest galaxies. These "ultra-massive" black holes have been shown to have masses upwards of one billion times that of our own Sun. Now, Priyamvada Natarajan, an associate professor of astronomy and physics at Yale University and a fellow at the Radcliffe Institute for Advanced Study, has shown that even the biggest of these gravitational monsters can't keep growing forever. Instead, they appear to curb their own growth – once they accumulate about 10 billion times the mass of the Sun.

These ultra-massive black holes, found at the centers of giant elliptical galaxies in huge galaxy clusters, are the biggest in the known universe. Even the large black hole at the center of our own Milky Way galaxy is thousands of times less massive than these behemoths. But these gigantic black holes, which accumulate mass by sucking in matter from neighboring gas, dust and stars, seem unable to grow beyond this limit regardless of where – and when – they appear in the universe. "It's not just happening today," said Natarajan. "They shut off at every epoch in the universe."

The study, to appear in the Monthly Notices of the Royal Astronomical Society (MNRAS), represents the first time an upper mass limit has been derived for black holes. Natarajan used existing optical and X-ray data of these ultra-massive black holes to show that, in order for those various observations to be consistent, the black holes must essentially shut off at some point in their evolution.

One possible explanation put forth by Natarajan is that the black holes eventually reach the point when they radiate so much energy as they consume their surroundings that they end up interfering with the very gas supply that feeds them, which may interrupt nearby star formation. The new findings have implications for the future study of galaxy formation, since many of the largest galaxies in the universe appear to co-evolve along with the black holes at their centers.

"Evidence has been mounting for the key role that black holes play in the process of galaxy formation," said Natarajan. "But it now appears that they are likely the prima donnas of this space opera."

Source: Yale University

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googleplex
3 / 5 (2) Sep 11, 2008
So if they radiate more energy than they abosrb then can they be seen? Presumably if they are that size 10 bn solar mass then the hawking radiation (or whatever its called) will be very bright.
zevkirsh
5 / 5 (1) Sep 11, 2008

Arthur_Dent
5 / 5 (3) Sep 12, 2008
There is a profound difference between

* CANNOT exceed this size, and

* NORMALLY DOES NOT exceed this size.

If 2 "maximum" size black holes collide, as in 2 galaxies colliding, they won't repel each other.

It may be uncommon, may even not have happened yet, but don't use the word "can't" to mean "doesn't normally".

Cheers.
Modernmystic
not rated yet Sep 12, 2008
Thank you Arthur. Moreover did I REALLY hear the article say the "energy they produce"??? Sure micro black holes will be blazing away like mad due to hawking radiation, but the bigger the hole the LESS energy they give off.

How is it that the most massive ones in the universe give off enough energy to interfere with their growth?

I seriously doubt there is a theoretical limit on how big they can be. As Arthur said I don't thing that two of these things zooming at each other at 1000s of km/s are going to be stopped by the miniscule number of virtual particles that are escaping the horizon.
D666
5 / 5 (2) Sep 12, 2008

How is it that the most massive ones in the universe give off enough energy to interfere with their growth?


It doesn't actually say that they stop growing because they give off more energy than they produce. It says that after a certain point, the energy they are emitting (which doesn't have to be Hawing radiation, it can simply be the radiation produced by matter being torn apart due to tidal forces) begins to seriously interfere with their ability to eat more. Think "solar wind", strong enough to blow all nearby matter away. Voila! instant diet.
Modernmystic
not rated yet Sep 12, 2008
It doesn't actually say that they stop growing because they give off more energy than they produce. It says that after a certain point, the energy they are emitting (which doesn't have to be Hawing radiation, it can simply be the radiation produced by matter being torn apart due to tidal forces) begins to seriously interfere with their ability to eat more. Think "solar wind", strong enough to blow all nearby matter away. Voila! instant diet.


Actually with more surface area you'd think that any energy given off by tearing apart stars would be more and more disprate per unit of measure...since stars can only grow so large and since the event horizon only grows....

I'm still having a problem seeing this concept.
D666
not rated yet Sep 12, 2008

I'm still having a problem seeing this concept.


Well, I don't have any observational data to work with, nor have I seen the math. But it doesn't strongly contradict any prevalent theories, so I'm inclined to just provisionally accept it, barring further evidence. It's an interesting take, though.
gopher65
5 / 5 (1) Sep 12, 2008
Actually with more surface area you'd think that any energy given off by tearing apart stars would be more and more disprate per unit of measure...since stars can only grow so large and since the event horizon only grows....

The volume (and therefore the mass) of the black hole grows by cubes, and the surface area grows by squares. As well, a sphere is the shape that allows the greatest amount of volume with the least amount of surface area (that might actually *be* the definition of a sphere).

This means that ratio of mass/surfacearea grows very quickly, and in a non-linear fashion.

So I'm not sure that the energy being given off by stuff in orbit around the black hole (which is I think what this article is talking about, not Hawking Radiation) would decrease per unit volume as the black hole grew in size. I think that the black hole would eventually reach a point where its accretion disk would be blasting out so much energy that only bread crumbs (so to speak) would end up reaching the black hole; everything else would just get blasted in some random directly.

Since the accretion disk would be so far from the black hole at this point (it would move outward as the mass increased, not as the surface area increased), only things that were blasted from the accretion disk in a very narrow direction would ever reach the black hole. Everything else would either be blasted in the general direction of the hole, but miss the event horizon, or it would be blasted in the opposite direction and be freed. The black hole would be effectively starved.

Of course, as Dent pointed out above, this wouldn't stop direct collisions. It would only stop dust and gas (the main food source) from being eaten, thereby slowing the growth of the black hole to a crawl.
Velanarris
not rated yet Sep 13, 2008
Well when a black hole breaches this limit via direct contact with another super massive black hole wouldn't there possibly be an instant explosion of energy due to the theorized mechanics of blackholes.

Effectively they'd blast their companion galaxies to pieces thus stopping their feeding all together where they'd eventually evaporate to nothing.

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