Slip into the Coma

By Phil Plait | June 10, 2008 10:14 am

Loner galaxies like the Milky Way are a bit unusual. We live out in the suburbs of space, but most galaxies prefer the hustle and bustle of the urban environment: the galaxy cluster. Clusters can have dozens of galaxies, but some are huge and have thousands of island universes swarming around inside them. We’re loosely affiliated with a cluster about 60 million light years away, the Virgo Cluster, but it’s only a middlin’-sized town.

The Coma Cluster is a metropolis.

Coma is about 300 million light years away or so, and has well over 1000 galaxies. It’s far enough away that you need a decent telescope to see even the brightest members, but when you point something like Hubble at it, well, you get the picture above, which was just released (the European version can be found here). That picture is only a section of the cluster, but you can still see hundreds of galaxies in it.

It’s worth taking a look at a few places up close. Check out this beauty:

That’s obviously a spiral galaxy, or something close to it. But it lacks the gorgeous spiral arms like we’re used to. Spiral arms are like traffic jams in a galaxy’s disk. When clouds slam into the jam, they collapse and form stars; the high-mass stars are very bright and light up the gas around them. This makes the spiral arms very obvious. But spirals with bright, clear arms are scarce in clusters. Why?

The galaxies in a cluster move around sort of like bees around a hive, each circling the center on their own orbit. The orbital speeds can be pretty fast due to the high mass and therefore strong gravity of the cluster. There is gas in between the galaxies, and they ram through this gas while they orbit the cluster. Any gas inside the galaxy is stripped away by this gas outside the galaxy, like the way you can blow a smell out of a car by opening the windows and letting outside air blow in.

So this galaxy is not really a spiral, it’s just a disk galaxy, or what astronomers call a lenticular (lens-shaped) galaxy. You see them all the time in clusters because their gas is stripped away, making the spiral arms harder to see. If you look closely you can just barely make out a spiral pattern in it, but that’s about it. The ring pattern halfway out from the center is odd, and to be honest I’m not sure I understand it. Some spirals do have rings (like M95) but their original is unclear. This one is pretty distinct, and it doesn’t look like it’s affiliated with any other structure in this image (the object at about 2 o’clock on the ring is probably a background galaxy). Interesting!

And you should expect interesting galaxies when you look in a dense cluster. To prove this point, check out this menagerie:

What a mess! You can see lenticulars, ellipticals, and a host of other weird shapes. I suspect a lot of the smaller galaxies (but not all) are background galaxies; much farther away than 300 million light years. But a lot of the galaxies you see here live in the Coma cluster. That flat, edge-on one at the lower right is particularly cool. It looks like it may have suffered some sort of collision a few hundred million years ago; the outer parts are puffed up, like a pizza crust. That sometimes happens when a big galaxy eats a smaller one. I’m guessing: I’m not sure, but it seems like a good bet.

Images like this are fun! It can be a lot of fun to grab a big version (6000×4260, 33Mb), or, if you can handle it, the monster full-size image (10816 x 7679, and 125 Mb! Holy Haleakala!) and just tool around. You can find all sorts of interesting things if you look carefully. How many stars do you see? How many small red dots, which may be galaxies billions of light years distant? How many are distorted from collisions? How many are bright blue, indicating they are bursting with star formation? Do you spy any gravitational lenses, arcs of light which are the distorted views of more distant galaxies? I found at least one in this image. I bet there are more!

Images like this are a treasure trove. Enjoy digging.

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures, Science

Comments (34)

  1. Matthew Reynolds

    This is like playing ‘Where’s Waldo?’, but with galaxy clusters.

    The full resolution picture is amazing. Definitely worth the load time.

  2. Powerdroid

    Phil,
    There’s something strange in the bottom picture of your post. (I know, that’s the point, right?). Near the upper edge on the right half of the image, there is an orange blob, or actually a pair of blobs. Then just off to the left of that, there is the same shape, only fainter. Is this real? Can you offer an explanation?

    Very curious,

    Powerdroid

  3. Powerdroid, that’s a good catch! Hmmm. I checked them out in the full-res version, and I’m not sure they’re exactly the same; the more vertical galaxy in the pair on the left looks bluer. But there are a LOT of other similarities (including a blue dot between them). It may be that the images weren’t aligned correctly when they were put into this mosaic. I’ll ask around and see if anyone knows anything.

  4. So,

    Now I know… Phil answered my question… THAT is where I was when I was in my coma for 30 days. It is kind of pretty, no wonder I didn’t wake up on time…

  5. rook

    Does anyone take photos such as this and create posters or pictures of them?

    Some of the pictures I see here and on APOTD I’d love to have in a larger format.

  6. Kaa

    Clusters can have dozens of galaxies, but some are huge and have thousands of island universes swarming around inside them.

    Say what? Island universes swarming around inside galactic clusters?

  7. Kaa– “island universe” is an old-fashioned term for galaxy. I’ve always liked it. It’s romantic. :-)

  8. Kaptain K

    Minor nit pick, but isn’t the local group; MW, M31, M33 and associated small galaxies, considered a cluster? If so, calling the Milky Way a loner would be an error!

  9. StevoR

    Yeah, I too nearly took the title here to be advice! It is pretty tempting to fall into a coma – or at least deep sleep at 3 am in the morning Adelaide (South Australia) time!

    Please be more careful with such titles Phil! ;-)

  10. alfaniner

    Pics like this remind me of a question I’ve been thinking about for some time.

    Why does everything in the Universe spin?

  11. StevoR (Steven Charles Raine)

    BTW. Thinking galaxies did you get my email or otherwise hear Bad Astronomer that the structure of our galaxy has been revised via the Spitzer scope – apparently we have lost two spiral arms!

    I also emailed you about an odd red supergiant recently studied in the Large Magellanic Cloud! Any thoughts on those ones?

  12. StevoR

    “BTW. Thinking galaxies did you get my email or otherwise hear Bad Astronomer that the structure of our galaxy has been revised via the Spitzer scope – apparently we have lost two spiral arms!”

    Relax though PZ! The ‘we’ that’s lost two spiral arms is just our Milky Way galaxy NOT the squid! ;-)

    Oh and back on topic – awesome images Phil of a very, ridiculously very, large area of space THX! :-)

    Plus I too like the “Island Universes” phrase. Wasn’t it Harlow Shapely who coined that one before we even knew what the “spiral nebulae” like Andromeda and theWhirlpool (M51) really were? :-D

  13. StevoR

    Of course, squid have tentacles not arms and they don’t really spiral either so much as coil about..

    … But hey, its too late /early here & I’m just trying to amuse …

  14. Amy

    Kaptain K: We’re in the Local Group, a dinky little huddle of galaxies that doesn’t merit the term “cluster”.

  15. Chip

    BA writes:
    “island universe is an old-fashioned term for galaxy. I’ve always liked it. It’s romantic.”

    I’ve got an old text book that uses the term “Andromeda Nebula”. I love the way that sounds, it flows beautifully, but unlike “Island Universe” which is poetical, “Andromeda Nebula” is now officially incorrect. ):

  16. Any gas inside the galaxy is stripped away by this gas outside the galaxy, like the way you can blow a smell out of a car by opening the windows and letting outside air blow in.

    That’s a great analogy, and one that will amuse my friends tremendously on this summer’s road trip, after we make the traditional stop at Taco Bell.

  17. Torbjörn Larsson, OM

    Why does everything in the Universe spin?

    Basically because most systems of matter you look at has been gravitationally bound from former more or less independent particles. It would be fantastically improbable if all their momenta cancel out exactly, so there is bound to be a remaining angular momentum (as well as regular momentum) pointing in some direction. (I.e. some axis of rotation for the system (as well as a direction of straight line motion).)

  18. Gary

    Am I the only one who gets seriously unnerved by these figures? Our own Sun scares m in a strange way by just how big it is. Our Galaxy is so big that for the next few hundred years the terms “Milky Way” and “universe” can pretty much be interchanged in terms of travel, because we ain’t getting out of it.

    And then we go and find other galaxies so far away that if we split up the distance into units of measurement that we have actual practical experience with, you and your great grandchildren wouldn’t live long enough to count it. And not just one. Hundreds.

    Doesn’t anyone else find the sheer…… size of everything we’re talking about here scary, or at the least intimidating? It even makes me sad, because I see these types of images all the time, but barring some immense leap in technology in the next 20 or so years, we’ll never actually get there to have a mooch around.

  19. Chip

    Gary – you should see the 1977 film “Powers of Ten”. It will blow your mind.
    http://www.imdb.com/title/tt0078106/

  20. Pop

    I downloaded the 125mb file and tried to look at it. Ayyie, my eyes, my eyes… It will take a long time for me go through this section by section. Many interesting points to look at. I just wish we could keep expanding and expanding pictures like this until we could see individual stars in a galaxy. To stand in a spot and see with the unaided eye a sight like these pictures present – ahh, the dream.

  21. Nicole

    Cool story! But I do have a problem with your opening lines…

    “Loner galaxies like the Milky Way are a bit unusual. We live out in the suburbs of space, but most galaxies prefer the hustle and bustle of the urban environment: the galaxy cluster.”

    I remember from my extragalactic class that something like 50% or more of galaxies live in groups, like our own Local Group, not in clusters. Only a few to a few 10s% live in clusters, and less in rich clusters. Thus we are not violating any Copernican principles if we note that he Milky Way lives in a group much like most other galaxies! Of course these are rough percentages depending on what your definition of galaxy is, from every tiny dwarf to the typical L-star galaxies like our own.

  22. Nicole

    Had to convince myself of what I just said with something in the literature… this review from 20 years ago mentions it, but maybe someone who is in the field can tell us a bit more….?

    http://adsabs.harvard.edu/abs/1988ARA%26A..26..631B

  23. Can’t gravitational lensing account for multiple images of the same object in one image or am I confused?

  24. Powerdroid

    Paul,
    So, you see it, too? I first thought that it was a little problem with the stitching of the mosaic pieces, as Phil suggested. But if that was the case, shouldn’t the two objects look exactly the same, like two pictures of the same thing, taken by the same camera, etc. Instead, one is much fainter than the other. Moreover, you don’t see any other items duplicated in the region, do you? I’m relatively uneducated on the topic, but I’m calling this a gravitational echo (that’s mostly a joke).

    Still curious,

    -Powerdroid

  25. Phil,

    Have there ever been any examples of a face to face galaxy collision? Almost like a stack of two pancakes merging? Would the gravitational pull of the two galaxy’s super-massive black holes cause it to look like a spiraling hourglass?

    - Alan

  26. L Ron Hubbub

    (the European version can be found here)

    So does the European version have…like…nudity in it or something?

  27. Fred

    I just discovered that the Hubble’s image is available to browse at Wiki Sky and seems to me at full resolution:
    http://wikisky.org/?ra=13.008&de=28.0489&zoom=11&img_source=IMG_all
    Amazing details!

  28. Ronn Blankenship

    @Chip, I and many others start out every semester’s introductory astronomy class by showing “Powers of Ten” the first night of class.

  29. Kullat Nunu

    As you can see in WikiSky, the image actually shows part of the outskirts of Coma Cluster. The two truly gigantic central galaxies NGC 4874 and NGC 4889 (both much bigger than M87) are not shown in the image.

  30. Tom Marking

    There is gas in between the galaxies, and they ram through this gas while they orbit the cluster. Any gas inside the galaxy is stripped away by this gas outside the galaxy, like the way you can blow a smell out of a car by opening the windows and letting outside air blow in.

    Hmmm, I would have thought that at the gas densities involved the gasses would pass through each other effortlessly. Let’s do a little calculation.

    Let RHO = gas density in number of atoms (typically Hydrogen) per cubic centimeter. A typical value for interstellar space is ~1 for this.

    Let R = the radius of an atom (we can use the Bohr radius of 5.29E-9 cm for this)

    Let L = mean free path of atom before collision with another atom (in centimers)

    So we have:

    PI * R^2 * L = 1 / RHO

    or

    L = 1 / (PI * RHO * R^2) = 1.14E16 cm = 0.012 light-years

    So if the gas particle is moving in the plane of the galactic disc (about 100,000 light-years across) it suffers about 8.3 million collisions. If it is moving perpendicular to the plane of the galactic disk (about 10,000 light-years thick of gas) it suffers 830,000 collisions. I guess these are enough collisions to strip off the gas from the galaxy. I was thinking if the number came up like 100,000 light-years then the gas particle will pass clean through the other galaxy without colliding with anything.

    There are also pockets of gas and dust in the galaxy where the particle density is much higher, say 1,000 atoms per cm^3 or 10,000 atoms per cm^3. The stripping process will be even more for these pockets of high gas density.

  31. Tom Marking

    It can be a lot of fun to grab a big version (6000×4260, 33Mb)

    There are several weird things in this JPEG file. Using Microsoft Paint check out the following:

    1.) 4424,1181 – Camera defect or really a blue glob of something?

    2.) 1885,1716 – Blue distant galaxy or blue foreground nebula in our galaxy?

    3.) 1653,1440 – Check out the foreground dust lanes in the biggest and brightest spiral galaxy. It really gives you a 3D effect with the dust in front of the galaxy.

    4.) 1041,2262 – Bright blue foreground star. You can see the 4 vane spikes telling you that Hubble’s secondary mirror is supported by 2 vanes that cross each other perpendicularly.

    5.) 5658,1852 – Elliptical galaxy in which you can almost resolve the stars, or perhaps they are globular clusters surrounding it.

    6.) 3928,2222 – You can make this one out to have a bar running from 7 o’clock to 2 o’clock so it’s a barred lenticular galaxy?

    7.) 1291,2866 – Whoa!, is that a foreground star in our galaxy or a supernova in the outskirts of the lenticular galaxy? Probably the former.

    8.) 5065,3101 – The blueist galaxy in the whole field. I wonder why it’s so blue.

    I didn’t see much evidence of obvious radio galaxies with black hole produced jets shooting out the sides but that’s a pretty awesome pic.

  32. Sergei

    1.) 4424,1181 – Camera defect or really a blue glob of something?

    Well, that one is real, though looks quite weired on Hubble’s shot. SDSS shows pretty strong signal from that spot and DSS2 also has something above noise level out there.
    Hubble image:
    http://www.wikisky.org/?ra=13.00563601413349&de=28.07489268436532&zoom=14&img_source=IMG_all
    SDSS:
    http://www.wikisky.org/?ra=13.00563601413349&de=28.07489268436532&zoom=14&img_source=SDSS
    DSS2:
    http://www.wikisky.org/?ra=13.00563601413349&de=28.07489268436532&zoom=14&img_source=DSS2

    I didn’t go through other cases. it is fun, but takes quite some time to locate the spot

  33. Tom Marking

    Well, that one is real, though looks quite weired on Hubble’s shot.

    Yeah, it looks much weirder on the Hubble shot. On the others it’s just an indistinct blue glob, probably a distant galaxy. I’m suspecting some type of defect in the Hubble camera or how the picture was put together. Whatever it is, it’s at:

    R.A. 13h 00m 20.36s Dec +28deg 04′ 30.1″

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