by Chris Peterson » Tue Nov 04, 2008 4:16 pm
JohnD wrote:Really?
When the blue galaxy is near enough for individual stars to be discriminated, and the red one isn't.
Surely the red one is ?twice? as far away, meaning that iteraction is unlikely.
There are no stars resolved in either galaxy. The "stars" you see in the blue galaxy are vast clumps of material, probably star forming regions. They happen in galaxies where shock waves cause a local collapse of material. Such shocks can be internally produced by galaxy dynamics (like arm motion), or externally produced by collisions. The fact that one galaxy shows such structure and the other doesn't can't be taken as an indication of their relative distances. Red shift measurements do show these galaxies to be interacting.
There's another ring galaxy in the famous image of Hoag's Object, but that doesn't mean that they have interacted.
No, but an old collision is the leading theory for how Hoag's Object formed; likewise for ring galaxies in general. Numerical simulations of collisions produce rings as one possible outcome.
[quote="JohnD"]Really?
When the blue galaxy is near enough for individual stars to be discriminated, and the red one isn't.
Surely the red one is ?twice? as far away, meaning that iteraction is unlikely.[/quote]
There are no stars resolved in either galaxy. The "stars" you see in the blue galaxy are vast clumps of material, probably star forming regions. They happen in galaxies where shock waves cause a local collapse of material. Such shocks can be internally produced by galaxy dynamics (like arm motion), or externally produced by collisions. The fact that one galaxy shows such structure and the other doesn't can't be taken as an indication of their relative distances. Red shift measurements do show these galaxies to be interacting.
[quote]There's another ring galaxy in the famous image of Hoag's Object, but that doesn't mean that they have interacted.[/quote]
No, but an old collision is the leading theory for how Hoag's Object formed; likewise for ring galaxies in general. Numerical simulations of collisions produce rings as one possible outcome.