Andromeda Galaxy

[rov1200]

The pictures we can see through our telescopes of the Andromeda Galaxy are 2.5million years old.

How do we know what has happened in since then? Could that galaxy move towards our own milky way. And what happens when galaxies collide?

[jake-the-peg]

We know the speed of it's motion then and it's direction so we know where it will be.

It will start to colide with ours in about 3 billion years or so.

About the time the sun goes supergiant and distroys the earth

http://en.wikipedia.o...93Milky_Way_collision

[jake-the-peg]

Here's some rather pretty pictures of some galaxies that are colliding right now.

http://www.google.co....QwAA&biw=1280&bih=832

[Davethedog]

Jake, not "right" now but x millon years ago? Or are they still colliding after millions of years?

[R1Geezer]

we cannot know what has happenned until the light reaches us. The Galaxy is a local one and is on a collision course with our own.

Yes dave, anything we see is only as it was a certain time ago, eg the Sun is as it was 8 minutes ago.

[jomifl]

It can be argued that as nothing travels faster than light then time also cannot do so What we see is 'now' no matter how long 'ago' it happened in theory.

[jake-the-peg]

Lets not get started on what "now" means eh?

[flobadob]

If two galaxies collide now, but there is no light with which to see it, does it make a sound?

[jomifl]

Yes Jake, lets wait 'til it gets here.

[rov1200]

If the Andromeda Galaxy is due to merge with the Milky Way in about 3 billion years hence and our Sun is due to expire in about 5billion years maybe they should readjust life on Earth will probably disappear nearer to the first figure.

[R1Geezer]

no, rov, the collision of the Galaxy will be a fairly non violent affair, obviosly there will be some collisiions but mostly they will embrace the spaces between the stars and start an oscilation dance, probably resulting in a large globular Galaxy rather than a spiral. Possibly a giant black hole binary could result.

[jake-the-peg]

A fairly non violent affair?

Hmm

Given that both sprial galaxies have a supermassive black hole at their hearts one wonders what the result of their collision might be.

At the very least I would expect a huge Gamma ray burst

[R1Geezer]

I read about this somewhere before jake but this link describes the output of a simulation:
http://www.universeto...t-happens-to-the-sun/

[R1Geezer]

If the 2 supermassive black holes did merge then yes a GRB is to be expected but they seem to be saying that the twin black holes would co exist.

[jake-the-peg]

Yes I wouldn't actually expect the two black holes to collide.

But if they did there would be a lot of matter pulled in and a lot of activity

[R1Geezer]

Absolutely jake.

The new Galaxy already has a name: Milkdromeda! not sure if I prefer Andromaway though!

[heathfield]

Binary black holes?.... Wheee!

[society]

Did you take those pictures, Jake? :-)

[mibn2cweus]

This is one of my favourites among merging galaxies . . . don't ask me why ~ http://upload.wikimed.../06/Warped_galaxy.jpg

[Old_Geezer]

Dark matter aside, most of a galaxy is "empty" space, so two can combine and blend with few actual collisions. We can not know what has happened to Andromeda since the light that reaches us now, left that galaxy. Our present understanding says that information can not get to us faster than the speed of light.