Help classify a million galaxies!

Galaxy Zoo

I saw this on The Sky at Night and it’s unexpectedly addictive!

Basically you have a quick tutorial on galaxy classifications, undertake a test to see if you’re up to the task, then you’re presented with pictures of galaxies to classify! :cool:

Oh, I like this! I’ve started classifying, too. Is it just me, or are all the ellipticals some kind of yellow, and all the spirals some kind of blue?

That’s pretty cool. I just did a few hundred. Most of the images are pretty blurry and hard to classify, but it’s fun trying anyway. :slight_smile:

Well I got 15/15 on the test, but in the actual classification business, I’m not sure that I don’t totally suck. I seem to be getting far more ellipticals than anything, unless some of them are just so blurry I can’t make out the spiral.

They’re hard to make out most of the time. I try and see if I can notice subtle spiral arms or a faint central bar, but even then it’s hard. A blurry spiral or barred galaxy at a great distance can look just about the same as an elliptical one, just as an edge on galaxy could be just about anything. I have found, as Jaochai has, that elliptical galaxies do tend to have a more reddish hue to them, while spirals tend more towards the blue end of the spectrum, based on the few that were easily and clearly identifiable as such. That’s still no guarantee though. At least the mergers are relatively easy to spot. :slight_smile:

This is due to the fact that elliptical galaxies tend to be older than spiral galaxies, and that spiral galaxies tend to have higher rates of active star formation, due to their higher dust content. A young star starts off extremely blue and as it ages, it reddens. So given that a spiral galaxy will still be making new stars, whilst the elliptical will simply have a passively aging population of stars, it makes sense that a spiral should look bluer than an elliptical.

And just to add, this is a project with real scientific value; computers can do a lot of things very well, very fast and very reliably. Identifying galaxy structure isn’t one of them however, and the best computer for doing that is the combination of the human eye and brain, and the lack of good basic galaxy classification has been something that has plagued the SDSS for a while now.

Help classify a million galaxies…!?

I was too cheap to name a star after my wife for Christmas… :eek: :frowning:

That makes sense. Now that you mention it, in any large, clear picture of an elliptical galaxy (such as found in NASA’s image archive) you never really see much in the way of dust lanes; they just look like a big star with a large halo. Dust lanes being stellar nurseries, not having any means no new stars. Now I’m curious if ellipticals might be formed around non-rotating supermassive black holes.

Also makes sense, though many of those images are just too fuzzy to make out many specific details; some of the ones I classified seemed to be so distant that they were barely a small, dim amber blob that could just as easily be a nebula.

As far as we can tell, not really. Ellipticals are essentially an end-point of galaxy evolution; as galaxies merge, their substructure (things like spiral arms) gets washed out, till you end up with what is essentially a big blob, an elliptical galaxy. There’s nothing special about which galaxies will merge to form ellipticals, and so there’s no reason why a priori, ellipticals should have non-rotating supermassive blackholes. In fact, seeing as angular momentum should be conserved, we expect blackholes at the centres of ellipticals to be rotating.

I do know some colleagues who’ve done some work on this by looking at the power output of powerful radio galaxies that are hosted by large ellipticals, and to get those sorts of power outputs from the black hole, the theory says that said black holes must be rotating at or close to their maximum rotation velocity.

alright! 5 down… 100 Billion more to go!

Alright, I’m getting more confident with this. Also, the moderators have made it clear not to stress over making mistakes…

In that spirit, here’s a very pretty spiral I just analyzed.

This is very fun. Thanks, sandra_nz!

There are fourteen classifications of galaxies

  1. galaxies that belong to the Emperor
  2. embalmed galaxies
  3. galaxies that are trained
  4. suckling galaxies
  5. mermaid galaxies
  6. fabulous galaxies
  7. stray galaxies
  8. galaxies included in the present classification
  9. galaxies that tremble as if they were mad
  10. innumerable galaxies
  11. galaxies drawn with a very fine camelhair brush
  12. others
  13. galaxies that have just broken a flower vase
  14. galaxies that from a long way off look like flies

Fun site

Does this look like a merge?

They could have warned y’all about barred spirals. Knorf’s is a barred spiral. The bars can sometimes make the galaxy look like it’s spiraling in one direction, when the outer arms are actually spiraling in towards the bars in the other direction.

I’d say possibly, but at the first stage of merging. There’s some distortion, and it looks like the two galaxies might be beginning to share a common stellar envelope, but its very difficult to tell just from an optical image.

AHunter3, considering the galaxyzoo people have asked a bunch of us laypeople to help analyze, it is quite understandable that they would greatly simplify the criteria for categorization.