Desktop Project Part 12: The galactic deep diver M9

By Phil Plait | April 6, 2012 9:01 am

[The Desktop Project is my attempt to clear off all the amazing images I’ve been collecting on my computer’s desktop over the past few weeks – I’ll post one great picture every day until they’re gone. That way, I clear off my computer and you get to drink in a beautiful image and some science. Everyone wins!]

I love globular clusters. They’re amazing objects: hundreds of thousands of stars all orbiting each other like bees around a beehive, incredibly old (most are well over 10 billion years and counting), and are a laboratory of how stars age and die. And I used to love looking at them through my own telescope when I was a kid, avidly going from one to another.

M9, though, isn’t one that I remember observing. I’m not sure why. It’s easily bright enough to see, and big enough to get a sense of its globularness. But even if I had seen it, I don’t think it would’ve looked quite as amazing as this shot from Hubble:

[Click to hugely apiaryenate.]

Yegads. Funny though: all in all, as globulars go, M9 is rather unremarkable. It’s average in size, in distance (about 25,000 light years from Earth), and in most other ways. It does have the distinction of being the globular cluster nearest the center of the Milky Way, lying less than 6000 light years from the core. But that’s a bit of a cosmic coincidence: globulars orbit the Milky Way, so whichever one is closest is just a matter of orbital characteristics and time.

Still, hmmm. I imagine M9’s orbit must be pretty elliptical to bring it that close in, though. Some globulars orbit very far out on paths that never take them too close to the center. So perhaps in this way it is interesting. Why is its orbit shaped like that? Did it interact with some other object billions of years ago, changing a circular orbit into one that’s elongated? Its velocity through space is relatively high (PDF) as you might expect from an object at the bottom of its orbit– a position called perigalacticon, if you want to impress your friends at parties.

And yet, for all its unremarkableness, look at it! It’s gorgeous! Even the mundane in astronomy possess surpassing beauty. It’s another reason I love this science so much.

Image credit: NASA & ESA

Related Posts:

It’s full of stars!
A distant sparkling eruption of diamonds
Desktop Project Part 3: The massive massiveness of M54

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (9)

  1. llewelly

    Are any globular clusters (orbiting the Milky Way or elsewhere) known to be captured?

  2. Ilewelly brings up an interesting point. I would love to see some sort of graphic or animation that shows the trajectories of some of these more fascinating and alrger objects as they orbit and move around the milky way.

    All too often people just think of the Milky Way and Andromeda as galaxies (and our southern hemisphere upside-down friends may also think of the Magellanic clouds). However, there’s A LOT of stuff that is in our very local neighborhood. Almost like the NORAD tracking of all the space junk around our planet I would bet!

    So, who can oblige our curiosity?

  3. Tara Li

    I’d like to see a simulation of a pair of these intersecting. I expect that even as dense as they are, actual stellar collisions are pretty much out of the question. However, wouldn’t fairly close encounters result in many of the stars being ejected with significant speed, much like the debris from a particle collision in the LHC?

    And I agree with LarianLeQuella – it would be awesome to see a simulation of the movements of the Local Cluster and smaller elements like major globular clusters over deep time. I wonder if Wolfram Alpha can pull up something like that for me?

  4. Chris

    @3 Tara Li
    I was thinking the same thing. M9 has to intersect the plane of the Milky Way at some point. Direct collisions would still be very unlikely, but I’m sure the gravity would reek havoc on any star systems in the path. It would be fascinating to see how society evolved on a planet which sees M9 on a collision course.

  5. Chris A.

    @llewelly (et al.)
    “Are any globular clusters (orbiting the Milky Way or elsewhere) known to be captured?”

    Indeed. M54 is thought to have once belonged to the Sagittarius dwarf elliptical (SagDEG):

  6. dcsohl

    At 6000 light-years from the core, that means that its orbit must pass through the disc of the galaxy. How do globulars stay together while passing through a galaxy?

  7. T-storm

    Sooooooo how far apart are the stars in something like that? Space is incredibly overwhelming.

  8. CB

    “a position called perigalacticon”

    OMG, I’m so dumb. I always thought “perihelion” was such an odd word and could never remember what it meant. Then you bust out “perigalacticon” and I go “Oh crap, it’s ‘peri’ as in close, and ‘helion’ as in helios as in the freaking Sun!”

    Well I may not be impressing anyone at parties but I’m nevertheless a little bit less dumb. =D

  9. Sammy

    I was reading a thesis about dark matter in globular clusters and I ran into the term “anisotropy radius”. I figure it has something to do with the radius of an certain percentage of the stars in the cluster, but I could be wrong. Could you tell me what this term means?


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