The Dust of Magellan

By Phil Plait | September 6, 2006 7:22 am

When I saw the picture above, I was stopped in my tracks. I have looked at images of the Large Magellanic Cloud (a companion galaxy to the Milky Way) about a zillion times, and I am familiar with it. This one threw me. I just didn’t recognize it. I realized it was an infrared image, since it came from the Spitzer Space Telescope, and that nebula look different in IR than they do in optical light. But why was this one so odd?

Then it occurred to me to look up the dimensions of the image. It’s seven degrees across. That’s a huge chunk of real estate! Put it this way: take your hand. Make a fist. Hold it at arm’s length away. That’s roughly 7 degrees across.

This is a big image.

Normally, space telescopes don’t see much of the sky at once. Even the big Hubble images are small compared to, say, the Moon, which is a half degree across. But this image is 14 times the width of the Moon! The astronomers made this image by taking images and then stitching them together into a mosaic.

In this case, it was a lot of images. A whole lot: 300,000 of them. You read that right.

So they took a third of a million small images and mosaicked them into one monster. The version I display here is heavily reduced in size and compressed to keep the file size small. But if you want this image in all its glory (and you do), then go grab the 10 Mb version. It’s worth the wait.

Once you see the big version, things start to pop out at you. Near the top, the fuzziness appears to be cleared out in a circular shape (with a little uvula thingy hanging down). Why? I’m not sure. Maybe a bunch of stars blew up around the same time and cleared that region out. Maybe there were bright, hot stars whose winds did the job. Or maybe it’s an illusion, and that region isn’t a bubble at all. It’s tricky trying to interpret images.

In another spot, there is a blue star right next to a red one. They make a lovely couple, don’t you think? In reality, that star may not be blue at all; the color blue in the image corresponds to a wavelength three times what our eyes can see, and red is more than 20. So that star might actually be red to our eyes, and the red one might be invisible, glowing only in the IR! It might not even be a star at all; maybe it’s a distant luminous galaxy, apparent size shrunken by its terrible distance, with its light reddened hugely by dust inside of itself. Again, I don’t know, so I’m speculating a bit.

The image was taken as part of a Legacy project — 19 key projects for Spitzer. This one is to map dust in galaxies. This particular project has 50 scientists working on it (and no doubt a passel of grad students and postdocs, who also no doubt write the software to patch the 300,000 images together). A paper about the image won’t be out until November, so my speculation will have to wait until then for an answer. There’s obviously a lot of science in them thar dust, and a lot of beauty as well. That’ll hold me for a while.

CATEGORIZED UNDER: Astronomy, Cool stuff, NASA, Science

Comments (21)

Links to this Post

  1. MLP I; “The dust of Magellan” « The Ironism | September 7, 2006
  1. I swear I can see the Flying Spaghetti Monster in that first picture.

  2. DrFlimmer

    I liked this picture so much that it is the background of my desktop right now. It´s very great and that not only in size ;)

  3. Zavatar

    Okay, stupid question time:
    If te image is seven degrees across, does that mean that the Magellan Cloud is actually 7 degrees across in the night sky?

  4. Phil,

    Why do you assume it’s a carve-out, a bubble, rather than being dust? You wrote, ” fuzziness appears to be cleared out in a circular shape (with a little uvula thingy hanging down). Why? I’m not sure. Maybe a bunch of stars blew up around the same time and cleared that region out. ”

    Um, it’s a nebula… there’s intervening dust, which absorbs and then re-radiates… hm… which might show up in IR, or might not, depending…

    When a dark area with stars, in a roughly circular shape, appears superimposed on a colorful thing, my first thought is, dust. That means no, it’s not a carve-out; nothing blew up in the LMC; rather, there’s a more nearby bunch of stuff.

    The stuff could be ISM, or it could be a gas-cloud, but to be that kind of size… I’d guess it’s fairly close. The uvula is probably a gap in the dust cloud, not a hanging chad (if you will) in the LMC itself.

    Apologies if I’m barking up the wrong cloud with this.

    Eh N.

  5. Space Cadet

    I found the little anthropomorphism amusing, but Eh N’s description works as well. (You from Florida?)

    Anyway, cool pic.

  6. Eh nonymous, what you see glowing in that image is dust. Spitzer is an infrared telescope, and warm dust glow in the IR. So if you see a patch where the image is dark, it’s because there is no dust there (or the dust is so cold it doesn’t emit at those wavelengths). That’s why I think it may be a carved-out region. Plus, the LMC is lousy with supernova remnants and hot stars, so it is a good first assumption.

    Zavatar: yes, you are right. I saw the LMC for the first time in 2004 (with the Small MC too) just hanging over me in the Australian sky. It was incredible. They are big objects, far bigger than, say, the Andromeda galaxy, and a lot brighter too.

  7. Tom K

    A good companion to this picture is the January 26, 2006 Astronomy Photo of the Day. Here’s the URL (unless it gets blocked):
    http://antwrp.gsfc.nasa.gov/apod/ap060123.html

    They used only a mere 1,500 images to create this one, though.

  8. Down at the bottom of the page is the full-res version: 13,250 x 13,250 pixels at a whopping 59 MB.

    That’s a little better than that piddling 10 MB version.

  9. Tom K

    I don’t know if I can post an image here, but I took a look at the APOD picture referenced above, and it appears that part of Phil’s speculation about the blue-red pair of stars is correct. Whatever the red one is, it doesn’t appear to show up in the APOD picture.

    I cropped, resized and rotated approximately the same area of the two pictures. Here’s a URL, again hopefully not blocked:
    http://img430.imageshack.us/img430/2372/lmcstarsmg2.jpg

  10. Tom K

    Upon further review (and examining the 59MB file referenced above by Austin) I believe that the red star does show up in the APOD photo, just much dimmer. It’s below the green bar artifact in the APOD photo. It also still appears very star-like, so I don’t think it’s a background galaxy.

  11. It’s hard to tell from those images what’s going on, unfortunately. And if the red object appears pointlike to Spitzer, it certainly will to a ground-based ‘scope!

  12. Navneeth

    If I remember the article at the Spitzer webstie correctly, this picture represents only one-third of the entire galaxy.

  13. Justin

    The red object is probably not a star. Red is the 24 micron MIPS data, and stars just don’t show up at such long wavelengths. Even relatively nearby galaxies tend to be point sources, though (resolution is about 6″). It could be an extremely dust-enshrouded star, I guess, but a background galaxy seems much more likely.

  14. ioresult

    The Bad Astronomer said:
    It might not even be a star at all; maybe it’s a distant luminous galaxy, apparent size shrunken by its terrible distance, with its light reddened hugely by dust inside of itself.

    OR its light reddened hugely by the doppler/redshift effect due to the object’s cosmological distance, maybe?

  15. Mendeli

    I was thinking about using that picture as a background image for a spaceship action game. I think it will probably be okay since its going to be a free game anyways. That picture will be just perfect for background graphics, I think. I’ll ditch my crappy photoshop star dust thingie :)

  16. icemith

    Beautiful photo.

    I’m waiting now for the Left photo to make up the stereo pair!

    Can someone get that taken from Pluto. I know it’s another 300000 shots, but it would make a good baseline. Even better, get another lot in 120 years time when Pluto is on the other side of the Sun. Now that would be a decent stereo shot!

    Ivan.

  17. icemith

    Double post I know, but would a *stereo* shot in the infra-red spectrum, yield any useful information? Or even a meaningful image? I do not recall any IR shots that are not normally fuzzy and indistinct. Maybe on the scale that the LMC shot is processed, that may not apply.

    Ivan.

  18. icemith

    Make that triple. My head is full of questions, just can’t help it.

    Re the stereoscopic view, would the starry background be sufficiently separated from the main subject, the LMC, (or any other subject for that matter), to resolve that subject much more clearly, as it should stand out somewhat. I’m guessing that anyway.

    It may even show which stars, galaxies – well, star systems anyway, and whispy clouds of dust or whatever, is in reality, in front. And what’s with the small dark, I hesitate to say *black*, voids amidst the carpet of blue? They could be resolved as unlit opaque dust , or actually holes right through to nothingness. any other ideas?

    Ivan.

  19. Irishman

    Zavatar said:
    >If te image is seven degrees across, does that mean that the Magellan Cloud is actually 7 degrees across in the night sky?

    Yes, that is what is meant. The combination of the size of the Megallanic Cloud and the distance away gives a size that covers 7 degrees of the sky.

    Eh Nonymous said:
    >Why do you assume it’s a carve-out, a bubble, rather than being dust? You wrote, ” fuzziness appears to be cleared out in a circular shape (with a little uvula thingy hanging down). Why? I’m not sure. Maybe a bunch of stars blew up around the same time and cleared that region out. ”

    >Um, it’s a nebula… there’s intervening dust, which absorbs and then re-radiates… hm… which might show up in IR, or might not, depending…

    Besides the answer Phil already gave, look at the image. See all those bright spots in the black background? Distant stars or even more distant galaxies. If it were intervening dust that somehow wasn’t hot enough to glow in the IR image, then it would be black with no stars visible.

  20. Bertrum

    Any one else see the space monkey just above the centre of the image?

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