In galactic collisions, might makes right

By Phil Plait | January 14, 2011 7:00 am

The Wide Field Infrared Survey Explorer (WISE) is an astronomy blogger’s gift that keeps on giving. Observing huge swaths of the sky in the infrared, it sends back the coolest images! Behold:

Yeah, click that to get the most cromulently embiggened 4000 x 4000 pixel version.

Those two galaxies are M82 (top) and M81 (bottom), and are both about 12 million light years away, relatively nearby as these things go. They are the two biggest galaxies in the M81 group, a collection of galaxies much like our own Local Group (dominated by our galaxy, the Milky Way, and Andromeda). M81 and M82 are almost certainly interacting with each, having had at least one pass sometime in the past, and may eventually merge in a billion years or so. Maybe less. Currently, they’re roughly 300,000 light years apart.

WISE sees them in the infrared, and in this picture blue represents the infrared wavelength of 3.4 microns, cyan is 4.6 microns, green is 12 microns, and red is 22 microns. For comparison, the reddest red your eyes can see is less than 1 micron, so these are well out into the IR.

Obviously, M81 looks very different than M82! M81 is a classic grand design spiral, roughly the same size or a bit smaller than the Milky Way. Most of the light you see comes from stars, which are bright at the shorter IR wavelengths.

M82, on the other hand, is a mess. I’ve included an image that’s a composite from Hubble (visible light), Chandra (X-rays), and Spitzer (IR). In visible light, M82 is cigar-shaped, but in X-ray and IR you can see all that schmutz coming out of it. It used to be thought that this was an exploding galaxy; that is, a series of exploding stars in the center caused this. However, it’s understood now that M82 is a starburst galaxy, undergoing a paroxysm of star birth. All that stuff is actually gas and dust blowing out of the galaxy due to the combined winds of the stars forming there.

In the WISE image, that warm dust is the dominant feature of the galaxy! A lot of it is comprised of PAHs — polycyclic aromatic hydrocarbons, complex organic molecules common in space. It’s not too bad to think of it as soot, or smoke… coming from a cigar-shaped galaxy. Hmmm.

Most likely, this burst of star formation was caused by M81′s close pass to M82. But then, why did M82 go all space-kablooie and M81 wound up all wound up? Perhaps it’s because M81 is more massive and bigger than M82, so it could hold its shape better. In a few hundred million years, when they pass again, I’m sure we’ll know more.

One thing to keep in mind about these galaxies is that they are visible using binoculars from a moderately dark site. I’ve seen ‘em myself. And some people have been documented as being able to see them with their unaided eyes, which is pretty amazing! The farthest object I’ve seen with my unaided eyes is Andromeda, which is about 2.5 million light years away, so clearly some folks have better eyes than I do.

But then, when we have WISE, Hubble, Chandra, Spitzer, and all the others, it’s really humanity’s eyes that see so far.

Image credit: NASA/JPL-Caltech/UCLA; NASA/ESA/CXC/JPL-Caltech


Related posts:

- Two nearby galaxies peek out through the dust
- Not all haloes are created equal
- AAS #6: Lonely stars between galaxies
- M81 up close and personal
- M82 stifles a cosmic belch
- Giant airplane-mounted telescopes sees first light


CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: M81, M82, WISE

Comments (25)

  1. Barney Nicholls

    I wonder how big each galaxy would appear in the night sky for an inhabitant of those galaxies.

    if we can see andromeda with the naked eye and thats 2.5 million light years away how big would that appear if it was only 300000, i guess about 8 times larger :)

  2. > dominated by our galaxy, the Milky Way, and Andromeda
    >

    Three galaxies, huh?

  3. Sir Craig

    You may think M82 is a mess, but when I take a look at that composite you’ve presented it couldn’t look lovelier. I really need to figure out how to recreate these kinds of images using Photoshop actions…

  4. @2 Dotan Cohen. I must have missed this reference because I’m not sure where you got the “three galaxies” thing. Phil only listed “our galaxy (the Milky Way) and Andromeda”. Makes sense if you make the Milky Way clause a sub-parenthetical (due to it already being in parentheses). :)

  5. Richard Drumm The Astronomy Bum

    I’ve always referred to M82 as the exploding cigar galaxy. Exploding with star formation works for me. No problem there! Never tried to see them with the unaided eye, though. Reeeeeally dark skies & young eyes might help…

  6. Pete Jackson

    “In a few hundred million years, when they pass again, I’m sure we’ll know more.”

    If we can dodge all the bad things that can happen before then, many depicted on your Bad Universe TV documentaries!

    In the WISE picture, a lot of structure from the high latitude dust cloud belonging to our Milky Way galaxy, but lying in the direction of M81, can be seen to the left and right of M81. See:

    http://www.galaxyimages.com/UNP1.html

    And many years ago, I remember how linear dust filaments would appear superimposed on the nuclear regions of M81 as seen in classic references like the “Hubble Atlas of Galaxies” (Sandage 1961).

  7. Kaptain K

    I won’t say it helps dominate the “local group”, but (although quite a bit smaller than the Milky Way and M31) M33 (in Triangulum) is a good sized ” grand design spiral” just a little bit farther away than M31.

    FWIW: On a clear dark night, M31 was bright enough to catch my eye while I was driving, I pulled over into a rest area and, after my eyes adapted, I was just able to see M33.

  8. Chris A.

    @Barney Nichols (#1):

    “I wonder how big each galaxy would appear in the night sky for an inhabitant of those galaxies.”

    M81 is about 92,000 l.y. wide. At 300,000 l.y. it would span an angle of about 17 degrees. So, size-wise, if it were that close to us it would fit nicely within the box formed by Orion’s shoulder and knee/foot stars (Betelgeuse, Bellatrix, Rigel and Saiph) (although not appearing in that part of our sky, obviously)! Wouldn’t that be a sight!

    On another point: While M82 (the “Cigar” galaxy) _looks_ cigar-shaped, it is actually a spiral seen nearly edge on (tilted 80 degrees from face-on).

    (ref.: Mayya, Y. D.; Carrasco, L.; Luna, A. (2005). “The Discovery of Spiral Arms in the Starburst Galaxy M82″. The Astrophysical Journal 628 (1): L33–L36.)

  9. I’m one of those people who has seen M81 with the unaided eye. I was in Central Oregon in a vast swath of virtually-uninhabited desert on a high plateau. I was 30 at the time. So, yeah, really dark skies, and young eyes. I don’t think any of the group could see M82–probably because it is significantly smaller. (This was at the Oregon Star Party. Highly recommended.)

  10. Brian Too

    Ah false colour images, why do you tease me so?

  11. Sam H

    I just love the colour contrast :) !
    I found a site 100 km south of my city of Calgary in the summer, and from there I could see the nebulae in Sagittarius with my naked eye. And with Sadie (my 8-inch dob), I saw M101, Andromeda, Triangulum, M13, the Ring Nebula, the Omega, Lagoon and Eagle nebulae, and several star clusters (only thing I couldn’t find was the Bubble nebula…). But most spectacular were the great curls of our galaxy, just stretched above. Visible as day…so big that a small creature such as me could only get only the faintest hints of it’s inconceivable vastness.

    While the galaxy may not be crammed with alien civilizations as Carl Sagan believed, (probably only a few thousand of them out there at most), I hope that Gene Roddenberry was at least partially right about interstellar travel (google “Heim theory” and you’ll see what i mean).

  12. Messier Tidy Upper

    Gloriusly splendid image – I love it. :-)

    @8. Chris A. :

    @Barney Nichols (#1): “I wonder how big each galaxy would appear in the night sky for an inhabitant of those galaxies.”

    M81 is about 92,000 l.y. wide. At 300,000 l.y. it would span an angle of about 17 degrees. So, size-wise, if it were that close to us it would fit nicely within the box formed by Orion’s shoulder and knee/foot stars (Betelgeuse, Bellatrix, Rigel and Saiph) (although not appearing in that part of our sky, obviously)! Wouldn’t that be a sight!

    On another point: While M82 (the “Cigar” galaxy) _looks_ cigar-shaped, it is actually a spiral seen nearly edge on (tilted 80 degrees from face-on).

    (ref.: Mayya, Y. D.; Carrasco, L.; Luna, A. (2005).“The Discovery of Spiral Arms in the Starburst Galaxy M82″. The Astrophysical Journal 628 (1): L33–L36.)

    Thanks for that info. – neat to know. [Picturing it now.] :-)

  13. Messier Tidy Upper

    Wiki-links here in case they’re handy / interesting for folks :

    http://en.wikipedia.org/wiki/Messier_81

    &

    http://en.wikipedia.org/wiki/Messier_82

    &

    http://en.wikipedia.org/wiki/Messier_33

    For more info on some the galaxies mentioned here. :-)

  14. Messier Tidy Upper

    @7. Kaptain K :

    I won’t say it helps dominate the “local group”, but (although quite a bit smaller than the Milky Way and M31) M33 (in Triangulum) is a good sized ” grand design spiral” just a little bit farther away than M31.

    I don’t know about “dominate” but I’m pretty sure that the Triangulum galaxy (M33) the next largest and next most important member of the Local Group after our Milky Way and the Andromeda Galaxy.

    A past BA blog post lasty year noted the collision and interaction – continuing today (& more advanced than we see it across the gulfs of space) between the Triangulum and Andromeda galaxies.

  15. Messier Tidy Upper

    See :

    http://en.wikipedia.org/wiki/Local_Group

    For the wiki-basics on our Local group of galaxies.

    Plus see :

    http://wise.ssl.berkeley.edu/

    For the WISE homepage – with a familiar image starring (or should that be galaxy-ing) there.

    &

    http://www.youtube.com/watch?v=6eZm3LHlyrs

    for the Andromeda- Triangulum collision on Youtube.

  16. Mary

    Perhaps someone can help me out here. I was trying to explain how, in our expanding universe where objects are moving apart, some galaxies are on a collision course. The question was thoughtful. I am not so happy with my answer. Help, please.

  17. Messier Tidy Upper

    @ 16. Mary : While the cosmos as a whole is expanding, gravity still attracts and pulls nearby galaxies towards each other.

    Galaxies are arranged in clusters and superclusters which are areas that contain more matter (the galaxies & perhaps – I’m not 100% sure – also more dark matter too)

    Galaxies – like everything else are also moving rather than “staying still” and so when they come closer to each other, their mutual gravitational effects can pull them together leading to galactic collisions. In these collisions, the stars don’t (usually) collide but the galaxies pass through each other and then fall back towards each other and eventually merge. This will happen to our own Miliky Way and the Andromeda galaxy (M31) as the Bad Astronomer mentioned in his Death from the Sky book.

    Hope that helps. :-)

  18. Messier Tidy Upper

    See also :

    http://en.wikipedia.org/wiki/Galaxy_collision

    via wikipedia & also this wiki-page :

    http://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision

    while this blog has this particularly extreme example :

    [which I'm still searching for .. sorry. :-( ]

    of a large galactic “cannibal” that’s using its immense gravity to overcome the expansion of the universe.

  19. Messier Tidy Upper

    Sorry but I can’t seem to find the BA blog post I’m sure I remember seeing which was titled something like “Something, something & gluttonous is no way to go through life son” (with the somethings replaced by betetr words obviously!) and featuring a particularly extreme example of a Central Compact Elliptical “cannibal” galaxy.

    Tried a number of things – tags, search box options, etc .. with no success. :(

    Afraid I’m stumped on this – can anyone else remember that one & help here, please? BA?

  20. Mary

    Messier TidyUpper, thank you. I really appreciate your spending tbe time to provide an answer. I will search for that BA blog later today and have a look at the links you included.
    The question came after my explaining that Andromeda and our Milky Way will eventually collide. Well, as you said, pass through each other is a better word than collide. I don’t think it was wrong comparing galactic activity in an expanding universe to varying weather patterns on Earth. Within the context of overall global warming, there are weather incidents that may, if looked at in isolation, seem to contradict global warming. However, conditions in different locations (closeness to large bodies of water, mountain ranges, etc.) influence localized weather. This is not surprising and is, in no way, a contraindication to worldwide global warming. In the same way, colliding galaxies in no way contradict the fact that overall the universe is expanding.
    Thinking back, the anaolgy was okay, but I was not satisfied with a non astronomical explanation. I think I was a little brain fogged at the moment. Your information helps clarify things and I will get back to the questioner with a more specific/complete answer.
    Your input is much appreciated.

  21. Messier Tidy Upper

    @ ^ Mary : No worries, my pleasure. :-)

  22. Mary

    Thanks for the links, Messier Tidy Upper.
    Mary

  23. M81 is a very neat, symmetrical object, while M82 is a messier object!
    Sorry, couldn’t resist it.

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