Black Holes and Galaxy formation

[LowlyPion]

... Astronomers have devised two theories to explain this relationship.

The first theory says that in the very early universe, galaxies were all fairly small, and they were born with black holes equal to 0.15 percent of their mass. These galaxy fragments quickly merged to form bigger galaxies. As they did, the black holes in their cores merged, too, maintaining the ratio of black-hole mass to the mass of all the gas and stars.

The second theory says that the black holes started relatively small, then grew as the galaxies formed around them. However, the process that increases the size of the black hole releases copius amounts of energy back into the galaxy. This energy interacts with the galaxy to regulate the galaxy's ability to make stars. The energy release also shuts off the black hole's own fuel supply by pushing away the surrounding clouds of gas and dust.

In other words, at a specific ratio of black-hole mass to galaxy mass, the black hole effectively stops both the galaxy and itself from getting any larger. This remarkable process happens when that ratio is 0.15 percent.

Observations and computer simulations made over the last decade seem to favor the second explanation. ...

http://blackholes.stardate.org/resources/articles/article.php?id=9

This presupposes that dark matter and dark energy interactions play no role?

 

[neutralseer]

Dark Energy didn't start playing a role in Cosmic history until roughly ~10 billion years after the big bang. Thus it doesn't have much to say about galaxy evolution (though it is important in the evolution of galactic clusters). As for Dark matter (DM), mmm, it seems like it would play some role, but I'm not sure.

Warning: the following is just my educated guess.

I'm guessing it plays more of a passive background role. The dark matter in a galaxy is really smoothly spread out and only becomes important (dynamically) a certain distance away. It's possible that that distance is located outside the bulge? Thus, within the bulge there is more normal matter (i.e. stars, gas), hence the focus on the black hole mass and the normal matter mass.

Still, in the initial formation of galaxies DM is very important...so I don't think we can ignore DM entirely. Sorry for my inconclusive answer. I hope someone more knowledgeable will come to save the day.

 

[ray b]

do we have a chicken/egg problem here?

stars form in a galaxy and a galaxy forms around a black hole
BUT you need a star to go boom to form a black hole

so what came first a star or a galaxy

or were there primal BHs or nongalaxy stars

 

[Janus]

do we have a chicken/egg problem here?

stars form in a galaxy and a galaxy forms around a black hole
BUT you need a star to go boom to form a black hole

so what came first a star or a galaxy

or were there primal BHs or nongalaxy stars

You don't need a star to go boom to form a black hole, all you need is enough mass packed into a small enough area. While some black holes are formed when stars go supernova, it is not the only way they can be formed.

 

[LowlyPion]

I ran across this somewhat related article about stars forming close to massive black holes.

How Puzzling Stars Formed near Galactic Black Hole
Gas clouds pulled into orbit around black holes could survive long enough to make stars

http://www.sciam.com/article.cfm?id=how-stars-formed-near-black-hole&sc=rss

 

[Chronos]

Black holes forming from stellar collapses may be fairly rare. Most supernova's blow off too much mass to collapse into a black nole. A neutron star is more likely.

 

[neutralseer]

LowlyPion,
That Sciam article is about something else entirely. It's about stars that form really close to the Super Massive Black Hole (SMBH). Here, "really close" means well within the SMBH's sphere of influence. A SMBH's sphere of influence is the volume in which most of the gravitational potential is due to the SMBH, not the surrounding stars,gas, and dark matter. Thus, the formation of these stars are directly affected by the SMBH's gravity.

The strange thing about the relationship between galactic bulges and SMBH's--the subject of the article you initially linked to--is that most of the Bulge lies far outside of the SMBH's sphere of influence (a SMBH's sphere of influence is less than 100 ly while the bulge is several 1000 ly). Thus, how the relation came about is not immediately obvious.

 

[Chronos]

Here is a recent relevant paper:
http://arxiv.org/abs/0808.1254
The Co-evolution of Galaxies, Black Holes, and AGN in a Hierarchical Universe