Bang! A-boom-a-boomerang

By Phil Plait | February 23, 2010 7:37 am

Sometimes I’m surprised by something I thought I knew, and found out I didn’t, not really.

For your consideration: NGC 1427A, a dwarf galaxy.


[Click to unendwarfenate.]

I’ve seen pictures of this little guy before. It’s a small galaxy, maybe 20,000 light years across (the Milky Way is 5 times that size), and part of the Fornax cluster, a small but rich cluster of galaxies about 60 million light years away. The picture here was taken with the monster 8.2 meter Very Large Telescope in Chile, and uses filters that give a somewhat true-color appearance, though it also accentuates warm hydrogen (the pinkish glow).

Even though I’ve looked at it before, I don’t think I really saw it, because the boomerang shape is obvious, and to anyone familiar with galaxy dynamics the reason behind it is obvious too. Maybe it’ll help to know that this diminutive galaxy is screaming through the Fornax cluster at 600 kilometers per second, a ridiculously high speed.

See it now? NGC 1427A looks like it’s got a swept-back shape because it’s being swept back. In between galaxies there is an ethereally-thin fog of gas, but there’s enough there to have an effect on a passing galaxy. The boomerang shape of the galaxy is because that side is facing into the wind, so to speak, and being compressed. The pink curve in the image is due to rigorous star-formation going on there, where the gas clouds are collapsing from the pressure and birthing stars at a prodigious rate.

Looking at this image, it’s so obvious what’s going on I’m surprised I didn’t notice it before. I guess sometimes you miss stuff right under your nose if you’re not paying attention. If you consider 60 mega-light-years under your nose.

Tip o’ the Strömgren sphere to the ESO. Image credit: ESO. 10 extra BA points for anyone who knows what the title’s from. Don’t Google it! That’s cheating.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (32)


    Strömgren sphere is the sphere of ionized hydrogen (H II) around a young star of the spectral classes O or B.

    Oh, you mean the title? Err… I think that’s the name of the book written by Sir Patrick Moore, Chris Lintott, and Brian May.

  2. Here at Irvine dwarf galaxies are a *HUGE* research interest. There’s an issue in astrophysics known as the “missing satellites problem”. Basically, there should be orders of magnitude more dwarf galaxies than what we see if you believe the Lamda-CDM model for the universe.

    It could be they are there we just haven’t been able to observe them yet. (We keep finding them so this could be the case.) Or maybe there is new physics we don’t understand.

    But, not knowing the answer is why it is a problem. :)


    I just now checked out that “title” with Google… 😛

  4. The title is from an Abba song way back in ye olde 70’s. I think I have a vinyl LP with it around here somewhere. No record player though.

  5. And thanks, now I have that song in my head.

  6. Shawn

    Very beautiful. The dominate parts of it almost make it look like the Star Trek symbol :)


    @ Evolving Squid,

    You mean you actually bought that record, back then?! 😛 What possessed you, man?!

  8. I love the Hubble! Amazing.

  9. ABBAmania. I thought everyone had an ABBA record back then. I think Arrival sold almost a million copies in Oz in ’76. Madness I tell you madness. :)

  10. J_w23

    Hubble already got it 5 years ago:

    EDIT: the hubble heritage image is, the actual photo is from 2003.

  11. Matt T

    BA: I think you made a mistake in your post. 600 kps is technically ludicrous speed, but just barely.


    @ Shane,

    Madness was one of my favourite bands, back in the late ’7os/early ’80s.

  13. @Ivan3Man

    Ditto. I was lucky enough to see Madness at the V festival in Oz last year. Not bad for old buggers too.

  14. JM

    from the image it looks like most of the motion of the galaxy happens on the plane of the sky, but at those distances we can only measure radial velocities, not proper motions. How did we get the 600 kps figure? or is that just a lower limit?

    btw, cool picture.. GO VLT!

  15. Angus

    It looks vaguely like the Star Trek badges. COINCIDENCE? I think NOT. Clearly God made this galaxy in this shape to test the faith of those who worship false idols. And by false idols I mean Jean-Luc Picard.

  16. Jon Hanford

    Notice the small reddish ring galaxy in about the 2 o’clock position from NGC 1427A!

    There’s also a couple of what appear to be very faint nucleated dwarf galaxies to the right of NGC 1427A. Quite a interesting field. :)

    Of course, NGC 1427A is most likely the result of a tidal encounter with NGC 1427 itself.

  17. Reera the Red

    One of my college roommates was a big ABBA fan and would play their music over and over, so I’ve got it embedded in my neurons. It’s mostly dormant, but as soon as I saw the title of this post I knew I’d have that song running through my head for the rest of the day. Thanks so much.

    Cool little galaxy, though.

  18. earth2allie

    Hooray for Abba!

    And, oh yeah, cool turbo speed boomerang! What I wanna know is: Who threw it?? Wouldn’t mind having one of those to toss around out on the science quad.

  19. Jon Hanford

    ESO has a really great image of this object too, and both the faint dwarfs and the ring galaxy are visible (using the VLT): (http:) // . Both images are fantastic!

  20. upgrayedd

    shawn #6 beat me to it, obviously proof of our future history of the galactic federation of planets…..

    angus #15, i dont worship jlp, i only pray to him, i worship data, cause he’s obviously the supreme being

    /waits for vulcans to make first contact

  21. TMB

    I love how, at the forward edge you can see an offset between the blue (young, recently-formed stars) and the red (ionized gas around extremely young and still forming regions). So star formation first happened at the shock at the leading edge, then its gas got used up making new stars and the shock proceeds further into the galaxt where there’s still gas.


  22. Jason

    How does one of these dwarf galaxies get moving so fast? Does it swing past a larger galaxy and get ejected into a different direction?

  23. Chris A.

    Er, Phil, I think you meant “vigorous star formation” in your second-to-last paragraph, not “rigorous star formation.” Unless the stars forming there are doing so according to a particularly strict set of rules (more so than the laws of physics?!).

  24. I had a similar reaction to the images of the Bug Nebula published soon after Hubble’s upgrades. I’d seen pictures before, but never really focused on the fact that you can actually see the MOTION of the thing. Every since, I’ve been scanning new photos (frequently here) to see if I can tell how they’re moving. It makes pretty photos stunning to get some small sense of the dynamics involved.

  25. The scale of these things…just amazing. Here’s a little galaxy, one called a dwarf. It takes only a few hundred human generations for light to get across it.

    I can’t imagine that. I trust that it’s factually correct, but I can’t imagine it.

  26. Brian Too

    Re: “Even though I’ve looked at it before, I don’t think I really saw it…”

    Well, you must admit it helps to have a view through an 8.2 metre VLT! Before you were probably looking at an image from a puny 5 metre scope (ahem).

    This has got to be a new golden age for telescopes and astronomers.

  27. Bad Wolf

    At 600 kps, I wonder – where is this galaxy going and why is it in such a hurry?

  28. Messier Tidy Upper

    @ ^ Bad Wolf :

    Rushing to merger?

    Gravity and the pull of other larger members of its cluster is probably the reason methinks.

    If you consider 60 mega-light-years under your nose.

    Actually I’d think its a lo-oong way *over* my nose. 😉

    Unless I’m looking at it through a telescope eyepiece in which case its just in front of and at about the same height as my nose! 😉

  29. JB of Brisbane

    Turn it sideways and it looks more like Apollo’s “hand” from “Who Mourns for Adonais?”.

  30. JupiterIsBig

    #15 Angus
    “It looks vaguely like the Star Trek badges. COINCIDENCE? I think NOT. Clearly God made this galaxy in this shape to test the faith of those who worship false idols. And by false idols I mean Jean-Luc Picard.”

    You Heretic – it was the Great Spaghetti Monster.

  31. Amanda

    Yay! I’m not the only one who thought of obscure Abba songs when they saw the title!

  32. sasapoljarevic

    it is not the only one that looks like this one ,i am pretty sure on it.:-)


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