The cold arms and hot, hot heart of the fuzzy maiden

By Phil Plait | January 5, 2011 12:15 pm

Hot (and cold) on the heels of my posting the infrared view of the nearby spiral M33, the European Space Agency just published this incredible picture of our other spiral neighbor, M31, the Andromeda Galaxy!

[Click to galactinate.]

Oh my. This is a composite of two orbiting observatory images: the far infrared using Herschel (colored orange), and the X-ray emission using XMM-Newton (blue). There’s so much to see! That’s not surprising, since at 2.5 million light years away, Andromeda is the closest big galaxy to us, and presents itself with loads of detail.

First, shown here is Robert Gendler’s magnificent visible-light image of the galaxy. You can see it’s tilted almost edge-on to us, but you can see the central bulge of old stars, the spiral arms winding out, the dark lanes of dust. This image has roughly the same orientation and border as the big one above, so you can compare them.

The infrared observations trace the presence of cold dust, created when stars are born and when they die. And by cold, I mean cold: much of it is just a few degrees above absolute zero. That dust is opaque in visible light, as you can see in Gendler’s shot. But it glows in infrared! The X-rays, on the other hand, are from incredibly hot gas heated to millions of degrees by neutron stars, black holes, and newly-born massive stars; you can see several individual objects in the galaxy’s core. In general, spiral galaxies have cores that long ago shut down when it comes to making new stars — the lack of dust there is another indication of this — but the compact remains of massive stars live on, and when they eat material that falls on them they heat up and generate X-rays.

[UPDATE: For some reason, the original picture from Herchel and XMM I put in this post got flipped (something I must have done when I Photohsopped it to change the image size). The orientation looked the same as in the original image, so I didn’t notice! The next paragraph, where I describe the companion galaxies as invisible in the IR image, is clearly wrong; I didn’t see them because I was looking in the wrong place. Embarrassing, but there you go. I made a mistake, so I’m correcting it. The incorrect paragraph is just below and is struck through; I added a new paragraph below it. Sorry about any confusion!]

Interestingly, the two dwarf galactic companions of Andromeda, named M32 and NGC 205 and which you can see in Gendler’s visible image above and just below M31’s core, are invisible in the IR/X-ray shot. Both are small elliptical galaxies, and the lack of dust and X-rays means they too are no longer making stars. It’s amazing what you can deduce just from glancing at these images!

Andromeda has two dwarf galactic companions named M32 and NGC 205 which you can see in Gendler’s visible image (one is above above and to the right, and the other just below M31’s core). They’re difficult to spot, but definitely in the IR/X-ray image as well. They must be so faint due to a lack of ongoing star formation, which is not surprising given that they are old elliptical galaxies which are generally pretty quiet in that regard. It’s amazing what you can deduce just from glancing at these images!

I can’t tell you how many times I’ve seen this galaxy with my own eyes. It’s up right now, in fact, high in the northern sky after sunset. The Andromeda Galaxy is about the same size as the Milky Way, 100,000 light years across, and can be seen from dark skies as a small bit of fuzz in the constellation of Andromeda (in mythology (or "Clash of the Titans") the maiden daughter of Cepheus and Cassiopeia, who was saved from the sea serpent by Perseus — which hopefully explains the title of this article). With binoculars you start to get an idea of the shape, and with even a small telescope it reveals itself as an elongated patch (the companions are easy to spot as well). With bigger telescopes the spiral arms become clearer, and of course deep exposures reveal the magnificence of a grand design spiral galaxy, one of the most awesome and gorgeous objects in the entire Universe.

And yet here is a new view of this old friend. And what a view! Scientists will be poring over these data for a long time to come, finding new ways to interpret this old gal. There’s nothing like a fresh perspective to liven up a relationship.

Image credits: IR: ESA/Herschel/PACS/SPIRE/J.Fritz; X-ray: U.Gent/XMM-Newton/EPIC/W. Pietsch, MPE; optical: Robert Gendler

Related posts:

Andromeda born out of a massive collision?
The first spectacular views of the sky from WISE (has an IR pic of Andromeda as well)
Herschel eyes the infrared southern cross
Open wide and say awwwww


Comments (37)

  1. Jason

    This is a beautiful picture, even if it isn’t visible light

  2. It’s the Eye of Sauron!


  3. Gareth

    Hah! Brian Cox beat you to it! This pic was shown on BBC 2 last night on Brian Cox & Dara O’Briain’s Stargazing LIVE show! ;o)

  4. Scott E.

    Question regarding the Herschel image (

    What are the red dots? Are those natural red dots or something placed onto the image after?

  5. *right-clicks*

    New desktop background…

  6. Shawn

    My high school Astronomy students and I just got done discussing the reasons for viewing objects in other-than-visible EM spectra. This picture is a perfect example of how this works. It’s an amazing and gorgeous example of non-visible astronomy.

  7. praetorianus_65

    Actually, Andromeda is probably larger than the Milky Way but may be just as heavy.
    Size of Andromeda:
    Mass of the Milky Way:

  8. Chris A.

    Just once, I would like to get an indication of how much of the e-m spectrum (yes, I know, it’s essentially infinite in span) we’ve been able to cover when receiving photons from a given celestial object using various detectors. In other words, I want to see a graph spanning gamma to radio, with the abscissa showing the percentage of the energy detected at each wavelength/frequency. Have we come anywhere close to “filling in” all the gaps between x-ray, UV, visible, IR, etc.?

    I ask this, because I have this fantasy of seeing an image of an astronomical target that has been imaged across the entire spectrum, with the colors we can see mapped from gamma to radio. The Great Observatories image of M101 from IYA2009, although nice, was disappointing to me because they reduced the results from each contributing telescope (Chandra, Spitzer, and Hubble) to a monochrome color (blue, red, and yellow, respectively) before combining them. I want to “see” the entire E-M spectrum compressed to the range of colors my eye can see, with all the subtle variations of color representative of the various strong and weak emissions across the whole range. But perhaps our coverage of the spectrum is too sparse for this to work.

  9. Lukas

    just wow! im getting goosebumps, this will be my new desktop background until the next awesome thing get caught on picture.

  10. Sir Chaos

    Careful, Phil… don´t let your wife catch you eyeing maidens, fuzzy or not. 😉

  11. Will

    I LOVE stuff like this for desktop backgrounds.

    However, it is not large enough to make a good background for my work machine, which has two 1680 x 1050 monitors. Even the “high-res” version available at the ESA article is only 2000 pixels wide.

    Can anyone recommend a good source for larger images like this to use as multi-monitor desktop backgrounds? The ideal size would be at least 3360 x 1050.

  12. JohnW

    “Andromeda (in mythology (or “Clash of the Titans”)”

    Mmmm, Judi Bowker.

    That’s just unreal, but am I the only one thinking the arms don’t look very spirally?

  13. David

    Actually the two images are inverted with respect to each other and the two companion galaxies are still present in the IR/Xray image. They are not invisible afterall.

  14. David (14): Hmm, I think you’re correct. Something may have happened when I cropped the IR image. I’ll dig into this and see what’s what. I was very surprised not to see any emission from the the two companions…

  15. David

    No problem. Glad to contribute something.

  16. David– looks like you were right, the image got mirror flipped. I corrected the image, struck through the incorrect text, and added new text. Thanks for pointing that out!

  17. Matt B.

    I had this idea while reading Buzz Aldrin’s Encounter with Tiber that to indicate in a “video” message to aliens which side of the images is the front (since they can’t presume the data are laid out left to right or vice versa), you could include a picture of something in space. But what you show would have to look similar enough to them as to us, and be asymmetrical. I figure a picture of the Andromeda Galaxy is perfect for trying to talk to aliens in the Milky Way, but for the encoding used in the book (base 8), I would want to reduce the picture to 1-bit color, so only pure red, yellow, green, cyan, blue, magenta, black and white would be seen. Is there a Photoshop-ish program that will do that to a 16-bit-color picture?

  18. Chief

    Very nice, question though, the blue stars near the core seem to be very big in relation to the diameter of the galaxy. Is it a trick of the observed “light”. I assume it is around 100K L/yrs across. Must be a trick with the optics and amount of “light” generated by each object.

  19. Leo Serrano

    What are those blue blobs -very faint- in the picture! They are above and below the galactic plane! I counted three above and perhaps four at the bottom. artifact from the pics?
    Cool pics though!

  20. Messier Tidy Upper

    The Andromeda Galaxy is about the same size as the Milky Way, 100,000 light years across,

    I thought Andromeda was a bit larger than our Milky Way Galaxy? No?

    Great image anyhow. :-)

  21. Messier Tidy Upper

    Wikipedia suggests M31 *is* indeed the largest in our Local Group see :

    & Kaler photographic map image for it is here :

    & my fave video on Andromeda – and its eventual collision with our Galaxy plus much more here :

    Hope these are interesting / handy for folks. :-)

  22. jess tauber

    I’ve seen the Kalium galaxy several times, but only on TV…

  23. QuietDesperation

    Years ago I wrote a program to randomly generate images of galaxies. I was doing 3D landscape generation, and plopping a real image of a galaxy in the sky just looked wrong- it also needed to be CGI. A big bug in the color selection routine produced similar results.

  24. I think the infrared image alone looks fantastic. It’s probably just the color, but with the spiral of the galactic structure it looks pretty impressive. I’d like to see a high res version of that.

  25. M. B. Cilek

    this is just great..
    ıt is what I wanted to see..friends and especially you Phil, please do me a favor and provide me with tha names 2-3 heavyweight astrophysicists who will bother to read a 2 page document which will carry my new theory on “Galactic Rotation Curves”.. if they like it (I am sure they will be amazed) they can endorse it for publication on Arxiv..I am asking you because I am an outsider to this field and need your help..pls contact me,
    strawberry at

  26. Joseph G

    This might be a clueless question, but why would dust that’s a few degrees above absolute zero show up so well in the infrared? Wouldn’t it be radiating most strongly in radio frequencies? I thought objects that were a few hundred kelvins or so were the ones that radiated most strongly in the infrared?

  27. Joseph G

    Ooh, another noob question: How can such detailed images be made of X-ray sources? Are there actually lenses and mirrors that can refract and reflect x-rays without lots of absorption or aberration?

  28. Joseph G

    @#18 Matt B: I’m sure you could do it with Photoshop or Gimp, but I’m not sure exactly what you’re looking to do. And we don’t even know what colors, if any, aliens would see. if orientation is all we’re looking to establish, wouldn’t it make more sense to just have a monochrome image based on IR, visible and UV light, averaged together? Just so they can recognize what it is and how it’s oriented?
    Or maybe I don’t understand what you’re talking about (knowing me, this is quite possible).

  29. «bønez_brigade»
  30. Richard Woods

    @ #29 Joseph G

    From — “X-rays mirrors can be built, but only if the angle from the plane of reflection is very low (typically 10 arc-minutes to 2 degrees). These are called glancing incidence mirrors.”

    There are a variety of designs for X-ray telescopes (, but XMM-Newton, like Chandra X-ray Observatory, uses the Wolter I grazing-incidence design. See

  31. Joseph G

    @32 Richard Woods: Thanks!
    Wow, human ingenuity never ceases to amaze me.

  32. bottom-up

    I know this is late but in the xray only image it appears that there is a rather large spheroid of shocked gas surrounding the galaxy’s core, Shades of Larry Niven. Too bad the Ringworld would be too small to spot at this distance!

    Question. Which edge is closest to us, the upper right or the lower left? My eyes insist on interpreting the image either way with no effort at all; just a quick flick of the old Mark one eyeballs and the image inverts.


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