The delicate aftermath of cosmic violence

By Phil Plait | May 4, 2011 6:57 am

My love affair with spiral galaxies is well documented here on this blog. Of course, I’m biased: I live in one.

But some of them demand a little more attention than others, like the oddly off-kilter NGC 2442, aka the Meat Hook Galaxy:

That gorgeous image (click to galactinate, or grab the ginormous 6756 x 5687 pixel version) is from the MPG/ESO 2.2 meter telescope in Chile, and it definitely shows why NGC 2442 is a weird one. The one arm at the bottom is long and stretched out, the top one is thicker and dotted with pink star-forming regions, and the nucleus is way off-center. What the heck happened to this galaxy?

Perhaps a close-up by Hubble will help:

[Note: this image is rotated 180° from the one above.] Again, we see lots of red gas clouds glowing, fired up by massive stars forming in them. Interestingly, to me this view of the galaxy looks like a single bird feather, with the individual vanes arcing down. Those vanes are actually streamers of gas and dust pulled out like taffy from the main arm. Given all this, it’s pretty clear that NGC 2442 suffered a very close pass or even a collision with another galaxy sometime in the relatively recent past.

But what galaxy? In the first image above you can see a small spiral galaxy off to the right. But in a much wider-scale image (reversed left to right of the one here) there is another galaxy above NGC 2442. It may have been either of these two… but I have my suspicions it’s the one on the right. In the first picture above, see how the small galaxy has no red star-birth regions in it? Many times, when smaller galaxies ram through big ones, all their gas and dust is stripped out by the bigger galaxy. The lack of gas in the small spiral is something of a tell.

In the Hubble image you can actually see smaller galaxies right through NGC 2442, too! That always gets me. So cool. But those are almost certainly much more distant background galaxies — NGC 2442 is roughly 50 million light years away, and those are more like hundreds of millions of light years distant. Even if they are near NGC 2442, they’re too small to have caused such a major disruption of the far larger galaxy anyway.

I’ll note that a radio survey of this region also detected a huge cloud of neutral hydrogen near NGC 2442 with about a billion times the mass of the Sun! That fits; it was probably free-floating hydrogen in the galaxy that got drawn or blown out by the passage of the smaller galaxy.

Pristine, symmetric spirals are so beautiful, but they are also lovely to behold when disrupted by a catastrophic collision, too. The energies and scales involved are mind-numbing, yet from a distance, and apparently frozen in time, they still possess a majesty and grand beauty.

Image credits: ESO; NASA/ESA and ESO


Related posts:

- Gorgeous galaxies celebrate Hubble’s 21st birthday
- When science and beauty collide
- Awesome Antennae!
- Felicia Day collides galaxies!

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (17)

Links to this Post

  1. Meet the Meathook Galaxy | Phathom | May 4, 2011
  1. Sam H

    So beautiful…what gets me is how that edge on spiral in the distance is visible through the thicker core regions as if it’s just a dirty window. I know it appears yellow because of the higher populations of red giants, older stars and the like toward the core (as it is with most galaxies of this type), but even here the stars must still be very spaced out (lol bad pun :) ) from each other.
    Question: in images like this, I’ve always suspected that the objects that appear to be individual stars in these galaxies at these distances are not actually individual stars, but clusters. Would this suspicion be true at all?

  2. I hear that Dr. Plait talks about spiral galaxies so much that his pub had him barred.

  3. Charles

    Sam,

    they might be individual stars in our galaxy. look past them, and you see this galaxy.

  4. Tom

    A 180 degree rotation doesn’t make sense… the long axis of the galaxy would still be at a mismatched viewing orientation compared to the first image. If I’m seeing this right, I’d say the Hubble image is rotated ~90 degrees clockwise from the first.

  5. @Alex (#2): *GROAN*

    Okay, I wish I had thought of it actually, and I am just jealous. :D

  6. David Draper

    Simply gorgeous. Thanks for sharing again and again, Phil.

    By the way …

    Happy Thtar Warth Day. … May the 4th be with you.
    :D

  7. Nick Kunka

    Dr. Plait,

    As usual, awesome images and awesome posts. I’ve always been curious though; are the images from Hubble and some of the larger telescopes like the Chilean one that gave us the first image color corrected or manipulated in any way to give us these beautiful images or is this a faithful image of what the universe and our galactic neighbors look like to the naked eye, but extremely magnified? Thanks!

  8. Arthur Maruyama

    @ Nick Kunka (#7):

    The short answer: unfortunately, no.

    If you ignore the foreground stars of the Milky Way and the background galaxies in the first picture, the view we are seeing in the first picture may be somewhat equivalent to our view of the Andromeda Galaxy. You can see the Andromeda Galaxy yourself IF you have clear, dark skies away from city lights and are in the northern hemisphere, but it more-or-less appears as a fuzzy star (which is basically the core). If you cheat a bit and use binoculars or even a largish (up to 10-inch in diameter) telescope, most of what you can see with your eyes will be a greenish-white haze surrounding the whiter core. Much of the details that you can get via astrophotography is more due to long exposure rather than magnification. These pictures from ESO and Hubble are further enhanced by the use of light filters to help bring out details of scientific interest such as the star-forming regions.

    Still purdy.

    And I agree with Tom (#4): you have to rotate the ESO picture roughly 90 degree clockwise rotation to get the Hubble view.

  9. Nick Kunka

    @Arthur: Thanks! So…if we could get up close enough to it, the colors would be true right? Nothing has been color enhanced artificially to turn a bunch of white stuff or stuff outside the visible spectrum visible or colorful for us?

  10. J. Rich

    Mihos & Bothun have an older paper modelling the interaction of NGC 2442. Their work suggests a recent strong interaction with the little guy you guessed (AM 0738-692) over the bigger neighbor:

    http://adsabs.harvard.edu/cgi-bin/bib_query?1997ApJ…481..741M

    Because it’s a little guy it didn’t perturb NGC 2442 as much as a lower mass-ratio interaction would have and NGC 2442 consequently doesn’t show as significant a kinematic disturbance or increase in star formation.

    A list of folks in the neighborhood for the curious:

    http://leda.univ-lyon1.fr/fG.cgi?n=0&c=o&p=B073633.0-692501&f=20&ob=ra
    http://tinyurl.com/3t5snao

    The larger elliptical to the NW (upper right) is NGC 2434:
    http://tinyurl.com/3dwn52c

    The smaller fellow to the NE (upper left) is AM 0738-692
    http://tinyurl.com/4557szn

    And further off is (way to the right and a little up, towards the edge) is NGC 2397
    http://tinyurl.com/3v2c7t6

  11. @ ^ J. Rich : Thanks – interesting comment and links there. Appreciated. :-)

    Superluminous (beyond just brilliant) galaxy images here – that Meathook galaxy has to be one of the best and most distinctive one’s I’ve seen on this blog which is saying a lot! ;-) 8)

  12. Reminds me also of these :

    http://blogs.discovermagazine.com/badastronomy/2011/02/17/the-milquetoasty-way/

    An ordinary entirely normal spiral NGC 2841 by way of contrast esp. with the lower image.

    http://blogs.discovermagazine.com/badastronomy/2011/02/04/a-galaxy-thats-all-hat-and-no-head/

    Bulge-less but beautiful NGC 3621.

    &

    http://blogs.discovermagazine.com/badastronomy/2010/06/21/gravitys-galactic-brushstrokes/

    an “aerial fly over” view of spiral galaxy Messier 66. Which is my personal all-time favourite astronomical image. :-)

  13. Sion

    I have a somewhat related question…looking at the radio survey image in the report you linked (http://iopscience.iop.org/0004-637X/555/1/232/fg2.h.gif) there is a diagonal, dotted line going out both directions from AM0738-692.

    What would this be? I see nothing like that in any of the other galaxies in the image and it doesn’t look like an artifact of processing. If this was the galaxy that interacted with NGC 2442, is this some sort of emission resulting from that?

  14. J. Rich

    @15 That is almost certainly an image artifact (or satellite?), it is incredibly linear and extends the length of the field. Compare DSS images and the lovely color image in the article and you do not see the same structure.

    http://archive.stsci.edu/cgi-bin/dss_form?target=AM0738-692&resolver=SIMBAD

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