Galactic destroyer?

[claymore]

Scientists have discovered that super massive black holes exist at the center of most galaxies.If black holes are born from the total collapse of a massive star { the generally accepted theory } why are n`t they all roughly the same size, do they get bigger as they draw in more and more material, if so will they eventually destroy their parent galaxy?

[jake-the-peg]

There is something called a schwartzchild radius.

This is the radius that a body would have to be compressed to to become a black hole

It is 2Gm/c� G is the Gravitational constant c the speed of light and m the mass.

So you see the size of a black hole is dependant on the mass.

When we talk about the size of a black hole of course we are talking about the "event horizon" not the singularity.

Have a look here
http://en.wikipedia.org/wiki/Schwarzschild_rad ius

[Loosehead]

Initially a black hoie is most commonly formed by a star of sufficient size as specified by the Chandrasakar limit, i think approx 8 times our own sun for example would be big enough. However there are much bigger stars. For the centre of the galaxy the black hole in question may well have also "eaten" many other stars too. The mass of a black hole gives the "size" as in the radius of the event horizon, as pointed out by jake, the size of the singularity itself is of course zero but the mass it has depends on the material it has acquired in its life and is hence variable.

Can the black hole comsume the galaxy? Yes if the material gets close enough, however in reality it's likely to eat what's available within reach, leaving a sort of "exclusion zone" around itself.

[beso]

The Black Holes also frequently eject jets of matter falling in from the parent galaxy . These jets exit at close to the speed of light.

If you are into galaxies check out http://www.galaxyzoo.org

The forums include some of the most spectacular galaxy photos you will ever see.

[mibn2cweus]

. . . or . . . Galactic creator?

. . . or . . . Which came first, the chicken or the egg?

. . . or . . . 'Co-evolution'

[Teddio]

If our Sun suddenly became a Black Hole it would make no difference to the orbit of the planets as the Gravitational Field Strength and the Gravitational Potential would remain the same. Most of the 10 thousand million or so stars in a typical galaxy will happily orbit their galactic centres without any fear of them being "sucked in".