[Spacetectonics (OP)]

The  resent cosmological studies show that black holes are mostly located at the center of the galaxies (i.e)milky way .if this is true,

My question is why and if this has anything to do with gravity?

[lean bean]

I'm no expert, so of the top off my head I would say... we are finding evidence of black holes at galaxy centres because they are easier to locate from their influence on their surroundings because of their extra large masses. Maybe  later with better  technology  we will be finding the smaller ones just as numerous in the other areas of a galaxy.  Also, the centres are more dense,starwise, and have had more time to form black holes with this material. But aho beware, I could be wrong

[Ethos_]

The  resent cosmological studies show that black holes are mostly located at the center of the galaxies (i.e)milky way .if this is true,

My question is why and if this has anything to do with gravity?

Absolutely my friend, gravity is the culprit. And of course, a galaxy provides sufficient material upon which the black hole can feed. When the galaxy first forms, the black hole can feed vigorously because it has a great supply of bodies to diet upon. After a brief feeding frenzy, in galactic terms, the local supply of material will become diminished and the black hole will find itself with fewer and fewer bodies to feed upon leaving it more solitary as time passes. At this point, the gravitational center will generate the typical spiral galaxy we have seen in great abundance all around the universe.

[CliffordK]

I presume that if one built a computer simulation with 1000 objects of various masses in "space", close enough for gravitational interaction, one would find over time that the light objects would be orbiting around the heavy objects.

In fact, if you think of our Sun, and Jupiter, the two objects orbit around a common center of mass, which turns out to be very near the sun's corona. 

In a 2 body system, a planet the size of Earth might be quite content orbiting Jupiter, even at a fairly great distance.  However, once you add additional planets, and a heavy body such as our sun, your earth-like object would likely eventually get thrown into an orbit around the sun.

The planets certainly interact with each other causing orbital resonance

Anyway, say if you created an artificial galaxy with a billion stars and one super massive black hole, somewhere out along one of the spiral arms, the galaxy would eventually rearrange itself around the supermassive black hole.

Of course, that doesn't mean that if one had several black holes of varying sizes in a galaxy that they would all move to the middle of the galaxy.  The black holes for the most part would maintain their previous orbital momentum, although perhaps disturbing other local stars, or entering into binary orbits, or small clusters.

[evan_au]

Some theories suggest that a black hole forms the seed of a new galaxy; the galaxy then grows around the black hole as a balance between gravitational attraction and outward pressure due to gas outflows and radiation pressure from the accretion disk.

Current thinking is that a galactic black hole would have a mass of around 0.1% of the mass of the galactic bulge.

http://en.wikipedia.org/wiki/M-sigma_relation#Origin

[imatfaal]

off topic branch re magnetic field started by Clive S has been moved to New Theories