A Swift view of Andromeda

By Phil Plait | October 5, 2009 7:59 am

NASA’s Swift satellite is a modern success story: designed to peer at the Universe in ultraviolet, X-rays, and gamma rays, it is on constant lookout for gamma-ray bursts, explosions so vast they are second only to the Big Bang itself.

Swift scans the skies, constantly observing, always on its toes for that fleeting blast of high-energy light. But it also does other science as well; an orbiting camera like that has many uses. For three months in 2008, astronomers used Swift to target the nearest major spiral galaxy like our own: M31, the Andromeda Galaxy. And what they got was this gorgeous picture:


Wow. You absolutely want to click that to embiggen it most cromulently — you’ll get a whopping 4400 x 200 pixel version.

This image is incredible, both scientifically and logistically. It is the combination of 330 images, totaling 24 hours of solid observations, and amounted to a hefty 85 gigabytes of data. It covers three UV wavelengths: 192.8, 224.6, and 260 nanometers, which are just outside the range the human eye can see.

The image is huge; the full Moon would just fit over the apparent size of the central bulge of the galaxy. Over 20,000 individual sources of ultraviolet light can be found. Some science can be seen just with just a glance: for example, the light coming from the spiral arms is clumpy, and from the bulge it’s smooth. The arms are where you find patches of giant gas clouds forming newly born stars; the most massive of these blast out UV light and fierce winds which make the clouds themselves glow in UV.

But the bulge at the core is smooth, because stars there are old; star formation long ago ceased in the galactic center. The UV glow is mostly from tightly packed stars, not from gas. There are so many stars that the individual sources blend together into what looks like a continuous glow (not unlike a digital image itself, where individual pixels blend together to make what looks like a smooth picture).

This image is the most detailed ever taken of our big neighbor in the ultraviolet, and I have no doubt it will be used as an atlas for higher-resolution cameras aboard Hubble and future spacecraft. Pictures like this are scientifically incredibly useful; they are roadmaps we can use to plan out our travels ahead.

And they are also just very, very cool.

Image credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures

Comments (40)

  1. Gary Ansorge

    OK! NOW you’ve done it. This was so cool I just HAD to forward it to everybody I know. So don’t be unduly surprised if your visitor counter experiences a bump.

    GAry 7

  2. Totem

    Gorgeous image!

    I’m curious, btw… how close are ‘tightly packed stars’? I assume we’re still talkin a light year or two, or are they much closer than that?

  3. FC

    I frequently Tweet astronomy articles I really like. Just a minor quibble: does star formation in the galactic bulge truly cease completely? Isn’t S2 (the star and probably closest astronomical object to orbit the supermassive black hole in our galactic center) a young blue star (spectral type B1V)?

    Is it possible that as the SMB feeds off nearby material, much of this gets compressed and starts off small mini-bursts of star formation around the very center?

  4. DrFlimmer

    I just can’t help it: Andromeda doesn’t really look like a “normal” spiral to me. I always see two rings instead of two (or more) spiral arms.

  5. Beautiful. That’s all I can say right now.

  6. That will be my wallpaper for a long time :)..

  7. JC

    NASA used this as their pic of the day a couple of weeks ago, with a “rollover” so you can compare it with visible light images as well.


  8. “Oh my god, it’s full of stars!”

  9. Stunning! ’nuff said.

  10. Theron

    Ah, frick. Now I have to buy a wide screen monitor so I can use this as my screen saver. Thanks Phil – this is going to cost me.

  11. Gary

    What is the explanation for the ‘edges’ of M31 in the image being sharply defined and somewhat crenulated?

  12. kyew

    What’s causing that lens flare in the lower-right part of the image? I’m assuming it’s probably some local object between here and there, but is there a chance there’s something that bright way out there?

  13. mocular

    I second Gary’s question? What’s with the edges of the image?

  14. Gary and mocular, do you mean the image itself, or the image of the galaxy? If it’s the image itself, I’d point to:

    It is the combination of 330 images

  15. Torbjörn Larsson, OM

    You wrote a post?!

    Wait … that’s not it. I think the Swift reprieve from DEATH made my head all swirly. I see stars…

  16. Aerimus

    Very nice. But I think it’s slightly larger than 4400 x 200…

  17. Baka

    If I’m understanding Phil correctly, the full Moon is approximately as large as the central bulge of this galaxy when viewed from Earth. I find that remarkable because I wouldn’t have guessed any other galaxy to be so large. That’s easily viewable, including with details, from Earth. I’m guessing if I’m understanding this correctly, the only reason we don’t see a huge, awesome galaxy hanging in the sky on moonless nights is that we can’t see in the UV spectrum in which most of the detail is found. Is that right? If so, I wonder if other organisms (birds, insects, etc.) may have the ability to see in those wavelengths? What a different night sky they must see.

  18. sailor

    You post a lot of wonderful images here Phil. They would make an awesome big calender if someone so felt like.

  19. Dan

    Sweet zombie jesus!

    “…the full Moon would just fit over the apparent size of the central bulge of the galaxy.” Does that mean that if we could see this image in the sky with the naked eye, and the full moon happened to eclipse the center bulge, we’d still see these huge spiraling arms dominating much of the sky!? Freaking wow!

    Phil this blog is great!

  20. I was attracted to the halation around the foreground star on the lower right and saw (in the embiggened version) the 3 lens flares associated with the 3 UV filters used to make the image! It also looks like the 3 images weren’t stacked well for that section, unlike the others… It looks like coma or tracking error, but I think it’s just a mis-registration of the images.

    Intensely cool image! Go & Digg it!

    Baka & Dan: You’re right, this thing is large. However, you can just see a dim smudge with the naked eye, which is the core of the galaxy. No details, unfortunately, as the spiral arms are just too dim for our eyes to make an image. You can take a nice picture of this galaxy with a little practice, some modest equipment & some dark skies. A zoom lens of 200 – 300 mm is sufficient, no telescope needed. A tracking mount, is required, though. A large telescope with a low power eyepiece will show some detail, but this is expensive.
    Here’s my latest feeble try with a 135mm telephoto:

    I’ll stick with Cat’s Eye Nebula (NGC 6543) for my wallpaper. It’s an image that just keeps on giving.

  21. Kees

    200 pixels? Missed a zero there Phil. Anyway, awesome image. Very much desktopped.

  22. J. D. Mack

    In the upper left quadrant, there are a couple of green streaks (in the dark area between the arms). Were these likely meteors, some sort of photographic artifact, or something else?

  23. Larry

    Beautiful, yes, but fun and educational as well.. Go to APOD (http://antwrp.gsfc.nasa.gov/apod/ap090917.html) to see the SWIFT image of M33 with a visual wavelengths overlay. Flick back and forth to see why two sets of wavelengths are better than one: hot stars are bright in UV, dim in the visual, and vice versa. Correlate visually dark dust with UV bright star formation, all by rolling your mouse over the picture. Fast and easy spectroscopy was never so much fun.

  24. I can see Kevin Sorbo’s ego!

  25. Wendy


  26. Michelle

    This was so cool I actually sent a copy to my dad and made it my wallpaper. Phil, you post so many awe inspiring photos that my wallpaper changes constantly!

  27. APOD had that last week, and I promptly made it my desktop, though it doesn’t do it a bit of justice. Sometimes I close all my windows just to stare at it. Amazing.

  28. JC

    Relative Size of Moon to Andromeda Galaxy

    Someone at NASA made a photshop of how big the Moon is relative to M31, assuming M31 was bright enough for us to see like this. Hopefully this gives those asking a visual reference.

  29. Synopsis

    @JC Thanks! my dad asked me a couple of weeks ago why we don’t see sights like that, and now I have an answer for him (well, in addition to light pollution); Andromeda just isn’t bright enough to see in visible light!

    Curse these pathetic human eyes.

  30. Sandy L

    I really want to go there!

  31. Baka

    Thanks to Richard Drumm who answered my question about the relative size of this galaxy and the Moon. Also, thanks for the link to the NASA image comparing the two, JC. Muchly appreciated.

  32. Stump

    Reply to J. D. Mack

    I believe the green “streaks” are stars that are moving and leaving behind a trail of hot gas. Don’t quote me on that, though.

  33. Linus

    J. D. Mack: My guess is that is is artifact from the mosaic process. I.e. misaligned pictures.

    This is though only a guess.

  34. Kopeliadis

    Big Bang was not an explosion … ūüėČ
    it just has a bad reputation by name.

  35. mike burkhart

    Like I said KEEP THOSE IMAGES COMEING !!!!!!! this is a better view then I get thro my telescope even at the maximum magnafaction by the way andromeda will be in our backyard billons of years form now its getting closer to the milky way and the two will merge to become one big galaxy

  36. This was so cool I actually sent a copy to my dad and made it my wallpaper. Phil, you post so many awe inspiring photos that my wallpaper changes constantly!


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