Sculpting a barred galaxy

By Phil Plait | June 17, 2010 7:19 am

I love big, splashy spiral galaxies. They are such eye candy, and of course their breadth and scale are magnificent. Sweeping, curved arms of stars and gas a hundred thousand light years long…

One of my favorites is NGC 253, a nearly edge-on spiral that lies roughly 11 million light years away in the constellation of Sculptor. I’ve seen it many, many times, but I was honestly surprised when a new image was released by the European Southern Observatory. I’ve never seen it like this:

eso_ngc253

Wow! Click to galactinate.

As you can see, it’s tilted pretty severely to our line of sight. You can clearly see the spiral arms, and the dust lanes wrapping around the galactic center. I was amazed to see the dust appears to be thicker on the top half than on the bottom. I was even more amazed to clearly see the bar — the elongated rectangular region in the center of the galaxy! That’s almost completely undetectable in a visible light image of the galaxy:

eso_ngc253_vis

That’s how I’m used to seeing it: loaded with dust that hides the shape of the galaxy itself. The top image, taken by the new VISTA 4.1 meter telescope, is in the infrared, which cuts through most of the dust and shows cooler, redder stars. The bar in the center of the galaxy is formed due to the way the gravity of all the stars of the galaxy shapes the way they orbit the center. In our solar system, the Sun outmasses everything else, and dominates the gravity of the system. This makes the system fairly simple. But in a galaxy the mass is spread out, and bizarre effects can occur as the combined mass of the stars affects the overall galaxy. Spiral arms are one outcome of this, and bars are another.

One way to form such a bar is to have a big galaxy collide and merge with another galaxy. Interestingly, NGC 253 is a starburst galaxy, which means it’s making new stars at a prodigious rate. This can also happen when two galaxies merge, and their gas clouds collide. On top of that, other studies looking at the velocities of stars and gas in the galaxy also indicate a merger. It seems pretty clear NGC 253 had a very violent event happen to it in the recent past. I suspect this may explain the thicker dust on one side than the other too. It could be the remnants of the smaller galaxy, or perhaps the collision triggered huge amounts of star formation along one arm — dust is created when young, massive stars die. Perhaps I’m way off here, but so many odd things happening in one galaxy with one clear explanation for so many of them makes me suspicious.

But the most important thing to me is that here we have a galaxy I thought I was at least passingly familiar with, and it turns out to have some major features about which I hadn’t a clue. I suppose I could be embarrassed by that, but instead, quite honestly, it makes me glad! I don’t think familiarity breeds contempt, necessarily, but it does tend to dull the sense of wonder. And here I get to re-kick start that wonder. It’s not often anyone gets a chance to do that.

ESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit


Related posts:

Barred for life
Ten Things You Don’t Know about the Milky Way
Incredible VISTA of the cosmos
The Orion VISTA


CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (21)

  1. I was amazed to see the dust appears to be thicker on the top half than on the bottom.

    From a layman’s perspective…

    What if we’re looking at the “bottom” of the galaxy. That is, the top part is the side closer to us. What if the dust is, as it appears to me, mostly on the outer edge. Wouldn’t that mean the dust in the “lower” part would be on the side facing away from us, and therefore less visible as it’s “behind” the stars?

  2. Noel

    yeah, what #1 said

    Could it be simply that the dust on top is closer to us than the bulk of the galaxy, making it appear darker, while the dust underneath is further away with most of the galaxy in front of it, so it appears lighter?

  3. @ Ken B:

    If you turn the image upside down, that explanation seems more possible. For some reason my brain interprets the orientation of the galaxy differently when it’s inverted. Upside down, it seems quite clear that the “top” in the original image is the edge closest to us, and the darker clumps of dust are just silhouetted against the background of the rest of the galaxy.

    Go ahead, flip your computer upside down!

  4. ToneDeF

    @Kuhnigget:

    I tried flipping my computer upside down, but it did not at all change the image on my monitor. Dang thing must be broken?

  5. @ Tonedef:

    The advantage of a laptop…smartypants.

  6. ToneDeF
  7. Messier Tidy Upper

    Beautiful image – both of them! :-)

    Perhaps I’m way off here, but so many odd things happening in one galaxy with one clear explanation for so many of them makes me suspicious.

    Why? I’d have thought having one clear explanation for the many oddities would be an elegant and good thing not something to be suspicious of?

    Galactic merger explains the barred spiral nature, the thicker dust on one side and the starburst phenomena – all that makes great sense to me. :-)

    Have they detected any sign of merging supermassive black holes or activity in its core eg. jets / Seyfert style Active Galactive Nucleus type stuff going on here?

    But the most important thing to me is that here we have a galaxy I thought I was at least passingly familiar with, and it turns out to have some major features about which I hadn’t a clue. I suppose I could be embarrassed by that, but instead, quite honestly, it makes me glad! I don’t think familiarity breeds contempt, necessarily, but it does tend to dull the sense of wonder. And here I get to re-kick start that wonder. It’s not often anyone gets a chance to do that.

    Yes. So true.

    Although I don’t know about the “not often” part because it seems there are *many* new discoveries and occassions that make me – for one – see things in a totally different light.
    Maybe you have to *make* more of these opportunities by deliberately looking closer or looking twice or thrice at what you think is familiar … ;-)

    One last thought – are they going to get the WISE (space observatory) guys to photograph and examine NGC 253 in (different band?) infra-red or the Fermi people to do the same in Gamma rays too? Hope so! What might their instruments add to our understanding and reveal anew about this barred spiral wonder I wonder? Has this already been done or is it planned?

  8. Mike

    New background!

  9. CW

    Am I the only one that can’t see the bar in these spiral galaxies? I see the bright center, and the swirling gasses, and finally the swirling arms.

  10. Messier Tidy Upper

    @9. CW : Look close to the core – the central yellow dot – the bar is ceratinly there as a straight line which slopes a slight tad upwards from left to right. Or follow the dark dusty spiral arm to where it appears to zig-zag down. I’m surprised you can’t see it.

  11. Messier Tidy Upper

    PS. CW you didn’t take your username here from the infra-red bright carbon giant star CW Leonis ( http://en.wikipedia.org/wiki/CW_Leo ) by any chance did you? ;-)

  12. mika

    Beautifully put, Phil. Yes, the joy of discovering the fact that there are still so many things in our universe we just don’t know – over and over again.

    It appears that the effects of mergers can take many forms. I wonder how exactly that warped spiral galaxy ESO 510-G13, for instance, got out of shape like that?

  13. Messier Tidy Upper

    @ ^ Mika :

    Afraid your link there isn’t working – at least not for me – have tried a few times & just got this message :

    Error Trying to Access Specified Page

    We are sorry you are experiencing problems. It appears this page’s address was either mistyped or no longer exists. Please double check the page’s address to make sure there was no misspelling. If you are still unsuccessful, please try searching for the page via our search engine. Thank you for your patience.

    :-(

  14. mika

    @Messier – yeah, you’re right. How strange, but no worries. Plenty of my fav spiral galaxy’s images here:
    http://images.google.co.uk/images?hl=en&source=imghp&q=spiral+galaxy+ESO+510-G13&gbv=2&aq=f&aqi=&aql=&oq=&gs_rfai=

  15. oldamateurastronomer

    @Messier Tidy Upper

    The problem with the first URL that Mika put up was that it had an extra ‘/’ at the tail end. Just re-click the URL and edit it in the address box at the top of your browser and the image he wanted everyone to see will appear!!
    ———–

    At 7.1 magnitude this magnificent spiral would have been well within the range of my scope, but I’m not sure if I ever looked for it. I was going through the DSOs that William Herschel observed before I had to quit observing,but NGC253 at just below -25 DEC may have been below the horizon from where he observed in England. What a missed opportunity – sigh!?!

  16. Messier Tidy Upper

    @^ Mika – Yes -that one works! Thanks. :-)

    @15. oldamateurastronomer : Thanks also. That’s worked. :-)

  17. ToneDeF:

    I tried flipping my computer upside down, but it did not at all change the image on my monitor. Dang thing must be broken?

    No, you just forgot to keep holding on to the computer after flipping it upside down.

    Messier Tidy Upper:

    Afraid your link there isn’t working

    Remove the trailing “/” on the URL, and try again, or just click here.

  18. Old Rockin' Dave

    “I was even more amazed to clearly see the bar — the elongated rectangular region in the center of the galaxy!”
    A bar at the center of a galaxy – Douglas Adams would have been pleased.

  19. I don’t know if you can type raw html with javascript in your blog, but it’s pretty easy to make “blink movies”, a blink back and forth between two images. Your page here is a nice candidate. Here’s an example of a blink movie http://sep.stanford.edu/sep/jon/family/jos/memories/andrew2.html from which anyone can copy the html.

  20. John Paradox

    Are ‘barred’ galaxies better places to find Pan-Galactic Gargle Blasters?

    asking the questions no one else dare ask:
    J/P=?

  21. Anchor

    “I was amazed to see the dust appears to be thicker on the top half than on the bottom.”

    Phil, and other posters here: that’s apparent in visible light too, and has been a diagnostic characteristic of NGC 253 and many other near-edge-on spirals for a long long time. Even amateurs studying NGC 253 visually through large-aperture telescopes have long been familiar with that aspect.

    The dust isn’t intrinsically thicker than the dust in the other arm. It’s just that the dust in that arm happens to be preferentially obscuring the starlight behind it in the disk, because that arm is in the relative foreground.

    The effect is commonly noticeable in literally thousands of spiral galaxy images in which the disks are nearly edge-on to our line of sight.

    KenB’s hunch is exactly right: when oriented this way, we’re looking at the bottom surface of the plane of the disk.

    Lots of people (including some professional astronomers!) still express skepticism that anyone can tell which side of the galaxy is closer merely from glancing at photos. But there’s not much of a trick to it, as long as there is a fair amount of dust inhabiting the disk, and it isn’t arranged in too wonky a pattern unassociated with the main plane, as some peculiar types will.

    It’s not at all hard to appreciate that an arm laced with dust situated BEHIND a galaxy’s general halo or hub of stars will have its dust considerably more “washed out” with intervening light sources than the foreground arm harboring dust clouds.

    Actually, this wonderful IR image shows that the morphology of NGC 253 bears a striking resemblance to that of our own Milky Way, complete with a modest bar AND what passes for a fair doppleganger to our so-called 3 kilo-parsec “arm”, which has been determined to form a complete ring much like that which contains the bar in NGC 253.

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