What exactly are we looking at?

[Belcher]

Excuse the possibly stupid question, but this one keeps going around my head.

Now I understand that the only stars we see in our night skies are only the contents of our own galaxy. OK, I get that. But what about when we see other galaxies? Typical images of something like the Andromeda galaxy is surrounded by numerous stars. So am I right in thinking that the stars in these images are all our own stars in the foreground of Andromeda? But then, what about Andromeda itself? The wispy arms are visible, but it looks mostly nebulous with few visible stars. Being a great fan of Stargate, we are told that the space between galaxies is vast and void of other stars. Fact or fiction? So if for example we were viewing from right on the outer edge of our own galaxy looking outwards, would we see a very dark sky with barely no stars, and clear galaxies on inky black backgrounds?

Random bizarre question eh !!!

[JulianO]

Yes - well depends on your magnification. Its easy to resolve stars in the Milky way, it is very hard to resolve them in Andromeda without very powerful telescopes.

It's like living in a city, you can see the houses and people, and in the distance you can see a faint glow of another city. WIth enough magnification you can make out the bigger houses in that city.

If the scale of our galaxy is likened to 30-40km, Andromeda is nearly 1000km away, so its a huge difference in scale.

[ollypenrice]

Take a widefield image with the Andromeda galaxy in the middle. Take a star count per square degree outside the galaxy. Now assume (not unreasonably) that such a star count will lie in front of the galaxy as well and see how the two counts compare, remembering that it will be hard to see foreground stars against bright galaxy.

You need some serious kit to resolve stars within M31 itself. The most famous astrophoto of all time does just that. Edwin Hubble had the cheek to graffiti it with the letters VAR!! http://obs.carnegiescience.edu/PAST/m31var

Olly

[will-i-am]

I think i'm right in saying there are stars outside of galaxies which have been cast out because of galaxies colliding.

[JulianO]

I think i'm right in saying there are stars outside of galaxies which have been cast out because of galaxies colliding.

Yes - there are indeed - but they're definitely in the minority.

[cowasaki]

I think i'm right in saying there are stars outside of galaxies which have been cast out because of galaxies colliding.

There are all manner of objects floating around outside of galaxies....

[sologuitarist61]

I'm sure that compared to galaxy density then the amount stars that are between the galaxies is small, Having said that, there must be quite a few who tread a lonely path in the void having been kicked out through interactions with other stars or galactic merges etc.

[VigdisVZ]

There are all manner of objects floating around outside of galaxies....

Dwarf galaxies, rogue planets, forgotten stars, dark matter, dust, radiation and maybe Chtulhu?

[sologuitarist61]

Dwarf galaxies, rogue planets, forgotten stars, dark matter, dust, radiation and maybe Chtulhu?

Forgot about dark matter - in that case there is more between the galaxies than inside them!!

[JulianO]

Forgot about dark matter - in that case there is more between the galaxies than inside them!!

Well more around galaxies than in them, typically haloes extending to about 10x the galaxy size. There isn't that much in intergalactic space.