Hubble sees ancient galaxies rejuvenating themselves

By Phil Plait | February 19, 2010 7:30 am

Every now and again I think I’ve pretty much seen it all when it comes to astronomical images, and I’m getting jaded.

And then I see a picture like this:

hst_hickson31

Yeah, I still get a thrill from seeing things like this! Click to massively embiggen.

The image shows what’s called the Hickson Compact Group 31, a small collection of galaxies. It’s a combination of images from Hubble (visible light, shown in red, green, and blue), Spitzer (infrared, shown as orange), and the Galaxy Explorer or GALEX (ultraviolet, seen here as purple).

If I saw this picture with no caption, I’d know I was seeing dwarf galaxies colliding; the shape and the glow from newly-forming stars is a dead giveaway. But I’d also guess that the galaxies were young; old galaxies tend not to have much gas in them, and there’s clearly plenty of that in those galaxies! But in fact the galaxies here are very old; there are globular clusters (spherical collections of perhaps a million stars each that tend to orbit outside of galaxies) in the group that can be dated to being 10 or so billion years old. That means these are old objects, reinvigorated by their collision.

In fact, star clusters inside the galaxies can be dated as well, and appear to be only a few million years old. Oddly, the gas content of the galaxies is very high, with about five times as much as the Milky Way has. That’s pretty weird; it should’ve been used up a long time ago. Apparently, these galaxies have lived very sedate lives until very recently. I’ll note that they are relatively close to us, about 166 million light years away. Usually, colliding dwarf galaxies like this are seen billions of light years away, so we really are seeing them as they appeared recently.

Apparently, the lower-case g-shaped object on the left is the result of two galaxies smashing into each other, and the longer galaxy above them is separate. The spiral to the right is part of this as well and may be involved in the gravitational dance; you can see a splotchy arm of material pointing right at it from the collision on the left. Typically in collisions the gravity of one galaxy draws matter out of the other, and that can collapse to form stars. The red glow is from gas excited by newly born stars, and the blue glow is from these stars themselves. The galaxies are pouring out ultraviolet light (the purple glow) which is another dead giveaway of vigorous star formation.

The background galaxies are gorgeous, too. There’s a phenomenal distant open spiral on the bottom, to the left of center, and what looks like yet another pair of interacting galaxies at the bottom left, obviously much farther away than the Hickson group. Take a minute to look around the high-res version to see what else you might find!

Yup. I guess you can teach old galaxies new tricks… and even sometimes jaded astronomers, too.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (17)

  1. Interesting picture from Hubble again!!

  2. Matt

    Sorry if I missed it, but what’s the big star/bright circle/whatever smack in the middle of the picture?

  3. you know, that “g” you speak of looks suspiciously like a cross. :P

  4. Zyggy

    Very cool!

    @ Lisa: I see a Norse hammer…or axe, with a couple of leather straps hanging from it. Hammer-Axedolieia? (sp?)

  5. Matt G.

    Awesome stuff! Just mind-blowing.

    Also that is clearly the easter bunny on the left and his easter egg on the right.

    The middle is uh… Jesus. I’m pretty sure this is all in the bible somewhere.

  6. John Paradox

    Regeneration… regeneration… where have I heard of that before? or who?
    ;)

    J/P=?

  7. I’d like to have a closer look at that orange blob sitting just above the colliding galaxies in the lower left-hand corner. Its features are not as crisp as many of the other background galaxies, but it does appear to have an arm of sorts pointing to the upper left, as well as a bulge on the center right. Perhaps a product of more colliding galaxies?

    EDIT: Also, at this resolution it appears to only (or mostly) emit infrared (orange). I’m guessing that two galaxies fairly depleted of their gas and/or colliding in such a way could account for the apparent lack of new star formation. Yea? Nay?

  8. DrFlimmer

    @ #2 Matt

    That’s a foreground star of the Milky Way. Nothing interesting ;) Everything that has such streaks is a MW star.

  9. If you look closely at the refraction spikes around that star, you can clearly see a rainbow. This is such obvious evidence of atmospheric chemtrail residue.

    //chortle!

  10. Matt

    @DrFlimmer

    Thanks. I’m a complete noob, it’s all interesting to me :)

  11. Mitch

    Looks like a floppy-eared bunny rabbit blowing the seeds off a dandelion. Either that or, you know, galaxies colliding. And stuff.

  12. Looking at the embiggened version is just so cool. There are so many small details and galaxies all over, that you don’t see at first.

  13. Jeffersonian

    This is so awesome.

    I have several questions about view like this. Example: Does “our” galaxy look like the one on the upper left when viewed from the right distance/angle? If so, why isn’t there tons more apparent light in our neighborhood?

  14. Messier Tidy Upper

    @ 13. jeffersonian ;

    Does “our” galaxy look like the one on the upper left when viewed from the right distance/angle?

    Not sure but it woulddepend on how loosely you translate the word “like” perhaps. Our galaxy does have a bit of awarp and is a large-ish bnarred spiral galaxy if thathelps any. That galaxy seen edge on is probably more spiral and more warped although its a bit hard to tell from that perspective.

    If so, why isn’t there tons more apparent light in our neighborhood?

    Its a *very* big neighbourhood is why! ;-)

    Also they may have more galaxies & more closely packed together in that galaxy cluster than in our Local Group of galaxies which has just three reasonably large spirals – Andromeda, the Milky Way and M33 the Triangulum or Pinwheel Galaxy.

    I’m not 100% sure but I think that mostly explains it although your question also evokes Olber’s Paradox of “why is the sky dark” which you may benefit from researching if you haven’t already.

    Try : http://en.wikipedia.org/wiki/Olbers%27_paradox

    @ 3. Lisa Says:

    you know, that “g” you speak of looks suspiciously like a cross.

    Eh? It does? :roll:

    Not to me it doesn’t.

    @ 8. DrFlimmer Says:

    @ #2 Matt : That’s a foreground star of the Milky Way. Nothing interesting Everything that has such streaks is a MW star.

    Hey, just because its a foreground star doesn’t mean it can’t be an *interesting* foreground star you know! ;-)

    Stellar astronomy can be pretty fascinating too, although perhaps not as visually dramatic as seen through a scope as the Deep Sky objects* eg. galaxies, star clusters, planetary nebulae, globular clusters, dark nebulae etc ..

    A few questions that spring to my mind as possibly interesting about that star include :

    1) What is called or designated?

    2) What is its spectral and lunminosity (dwarf, giant, supergiant) class?

    (I’d guess type A-K based on its not being very bluish or reddish. Right? )

    3) Is it a binary or multiple star system?

    4) Does it have any exoplanets known or suspected orbiting it?

    5) How old is it and how metal rich? Is it one of the ancient metal-poor population I stars or a metal rich younger populatuion II star?

    & that’s just for starters! ;-)

    —–

    * The Messier catalogue of deep sky objects does inculde one double star – M40.

  15. M.J.

    Would it be possible to hit fast forward and see how this all turns out?

  16. Susan

    Tidy, just turned it into my desk top.

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