h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

the solar system....everything is normal, all the planets going around and around, then for no reason at all the sun vanishes,

without gravity what happens

does the earth go whizzing off into space the insatant the sun vanishes or is there some kind of wave front formed that travels out and the earth whizzes off 8 mins. later??????

The effects of gravity travel at the speed of light, nothing would happen until 8 minutes later.

It is assumed it moves at the speed of light, I don´t believe it has been proven yet.

Not *proven* but demonstrated. This team used the gravitational lensing effect of Jupiter as it moved in front of a quasar, then worked backwards and calculated the speed of gravity to be about C.

http://www.newscientist.com/article/mg17723774.600-how-fast-is-gravity.html

I'm with Einstein on this, in my experience he tends to be right most of the time.

so on a larger scale

if the blackhole at the centre of the galaxy which we all spin around suddenly dissapeared the galaxy wouldn't fly apart and dissipate, it would fly apart from the centre outwards like a huge explosion????

is that right???

Well the effect would travel from the centre outwards, but the matter is all moving very slowly compared to the speed of light, so on the galactic scale I don't think it would make much difference.

Yes the mass from the remaining stars would probably mean the galaxy would dissipate quite slowly.

The black hole at the centre of our galaxy is "supermassive", but it is very small compared with the size of the galaxy, only about 3%, so it doesn't have a huge effect on the galaxy.

Yeah, the mass from the rest of the Galaxy would likely be enough to keep it in check.