The Colliding Spiral Galaxies of Arp 274 (2009 April 7)

[Chris Peterson]

We all know these collisions happens over a very long period of time, hundred of millions of years as stated in the caption. But these two are 400 millions light years away; is that collision already over?

It depends on how you define "now": there really are different functional definitions. Certainly, by one that considers the time of flight of light, the collision is much more advanced than what we are currently seeing. From a practical standpoint, "now" meaning when we make the observation is almost always the more useful definition.

[rstevenson]

As I mentioned above, there is a note on another site which says the galaxies may not be interacting in the sense of "colliding". Since you may not have seen the link, here is a quote from that page...

Arp 274 was previously thought to be a set of interacting galaxies, galaxies that are "colliding" and gravitationally affecting one another. The [earlier] ground-based image ... of the same area of the sky certainly makes it seem that way. But, the new image by the Hubble, with far more detail, reveals that the three galaxies may just be galaxies located near each other, but not interacting together. The largest galaxy in the center, a barred spiral galaxy, appears to be extending an arm into the other spiral galaxy, on the right. Distortion of the shapes of the galaxies by gravity would indicate interaction, but this is simply not exhibited by these galaxies.

It would be interesting to see the galaxies "now" to see how close they have gotten. I assume various researchers are working with these images in more detail and answers will be forthcoming eventually.

Rob

[Chris Peterson]

As I mentioned above, there is a note on another site which says the galaxies may not be interacting in the sense of "colliding". Since you may not have seen the link, here is a quote from that page...

Arp 274 was previously thought to be a set of interacting galaxies, galaxies that are "colliding" and gravitationally affecting one another. The [earlier] ground-based image ... of the same area of the sky certainly makes it seem that way. But, the new image by the Hubble, with far more detail, reveals that the three galaxies may just be galaxies located near each other, but not interacting together. The largest galaxy in the center, a barred spiral galaxy, appears to be extending an arm into the other spiral galaxy, on the right. Distortion of the shapes of the galaxies by gravity would indicate interaction, but this is simply not exhibited by these galaxies.

It would be interesting to see the galaxies "now" to see how close they have gotten. I assume various researchers are working with these images in more detail and answers will be forthcoming eventually.

I agree that an interaction between the galaxies isn't obvious. This goes to what I said earlier, that usually the only way to tell for certain is with careful redshift measurements, and even then there could be significant uncertainty. If you don't see clear tidal distortion (which isn't obvious here), it is really hard to tell if galaxies are interacting.

[rstevenson]

Hi Chris,

It seems we were both responding almost simultaneously to the question above our two responses. But now that I have your attention ...

I asked way up in this thread about that small orange dot surrounded by fuzzy stuff which is to the top-left of the two main galaxies in this image. From this image I can't see whether it's a closer star which happens to be in front of a distant galaxy, or if it's perhaps a planetary nebula which happens to be in our line of site, or if it's a distant galaxy with a bright, well-defined central region. Since I'm in no way an astronomer, I wonder how one can find out more about such an object. If you were interested in it, how would you go about tracking down more info, or even if any other image of it exists?

Thanks for any hints you can offer.

Rob

[Chris Peterson]

I asked way up in this thread about that small orange dot surrounded by fuzzy stuff which is to the top-left of the two main galaxies in this image. From this image I can't see whether it's a closer star which happens to be in front of a distant galaxy, or if it's perhaps a planetary nebula which happens to be in our line of site, or if it's a distant galaxy with a bright, well-defined central region. Since I'm in no way an astronomer, I wonder how one can find out more about such an object. If you were interested in it, how would you go about tracking down more info, or even if any other image of it exists?

It's definitely a galaxy. In fact, if you look around it, you can see dozens of distant galaxies. On very deep shots like this, except for a few foreground stars (which usually show diffraction spikes), it's likely that every little speck you can see is a galaxy or a globular cluster. Individual stars don't show up at this scale unless they are in our own galaxy.

I would try tracking down an object like this using something like SIMBAD. However, when I do that using the approximate coordinates of 14h 35m 10s, +5° 21m 48s, that little galaxy doesn't show up. It's very likely that it hasn't been cataloged at all.

[rstevenson]

Thanks Chris. I've now bookmarked SIMBAD.

What caught my eye was that this object has such a well-defined (at least at this scale) center. Could be just an illusion of course, perhaps a ring of dust in the galaxy giving this impression.