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Space Science

Dim Galaxy Could Give Clues to Dark Matter 40

chamblah writes "Reuters is reporting that the dimmest galaxy has been found. 'In fact, it is dimmest galaxy ever detected, which means it could give clues to the mysterious dark matter that appears to be pushing regular matter around.' Since this galaxy is '...100 times dimmer than the night sky', it could only be detected using 'instruments involved in the Sloan Digital Sky Survey, the sky-mapping project.' The galaxy is also part of the Andromeda galaxy, only 2 million light years from us. The article goes on to explain how finding these dim galaxies can be useful, 'Andromeda IX fits the profile for the small, dim galaxies that cosmic theorists predict should exist as leftovers from the formation of big galaxies.'"
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Dim Galaxy Could Give Clues to Dark Matter

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  • by Anonymous Coward on Tuesday June 01, 2004 @02:07PM (#9305740)
    They're just eco-friendly and power saving.
    • It is dim because their bulbs aren't bright enough.
  • by Daniel Dvorkin ( 106857 ) * on Tuesday June 01, 2004 @03:00PM (#9306450) Homepage Journal
    It's not "part of" Andromeda; it's a satellite galaxy, like the Magellanic Clouds are to the Milky Way. It wouldn't make a whole lot of sense to talk about a dim galaxy that's part of a regular galaxy, anyway ...
    • Alright, I hope this doesn't come off as condescending, but IAAA (grad student, at least), and *one* dim, tiny dwarf galaxy will tell us very little about dark matter.

      You can measure its velocity dispersion to infer its total mass, and you can measure its light and spectra to attempt to infer its mass in baryons (protons, neutrons, and electrons), and you can measure the spectral lines to determine its metallicity, but this has nothing to do with inferring dark matter.

      Dark Matter is inferred, at least when it comes to galaxies and clusters of galaxies (to keep it simple), because the mass required to provide the galaxy/cluster with the internal velocities observed is much more than what we see in starlight. Therefore, some of the matter is non-luminous, or "dark". Dark matter exists, on AVERAGE, so that 1/7 of the total mass in a galaxy is in baryons, and 6/7 is in dark matter. This ratio varies widely for different galaxies, and I do not see how *one* galaxy is going to tell us anything?

      Also, if this satellite galaxy is less than ~100 kpc from Andromeda, the main galaxy's dark halo will envelop the satellite, too, further complicating the matter.
  • Yessir (Score:5, Funny)

    by Wylfing ( 144940 ) <brian AT wylfing DOT net> on Tuesday June 01, 2004 @03:06PM (#9306532) Homepage Journal
    The galaxy is also part of the Andromeda galaxy

    Exactly, just like I-90 is part of the Honda freeway!

  • So ... I've R'd TFA, but I'm still not an astrophysicist ...

    Does one infer from this that the 'missing' dark matter is possibly just a bunch of stuff we haven't been able to see yet? Or is the magnitude of the dark matter just too big to be accounted for by dim structures in space?

    Just askin'.
    • thats right. Based on gravity pulls the astronomers are not able to explain, only with what we can see, the movements of stars and galaxies, on the other hand if there were dark things(which not emit, nor reflect enough light to be observed by us) hanging around, the whole puzzle would fit perfectly(or much better at least). So, finding a galaxy that faint, it means scientist would eventually find all that dark matter.

      If a tree falls in the forest and no one is near to hear it...does it still emits a sound
    • Well, technically dark matter IS 'just a bunch of stuff we haven't been able to see yet'. The speculation is that it might not be 'see-able' the way regular matter is.

      Anyway, this still does not seem to explain the first reason for coming up with the dark matter idea anyway. That being the way the galaxies rotate: spiral galaxies have a (visible) more or less discoidal disposition of matter (in a plane), but appear to rotate as if they were more like spheres (that is, the radial dependence of the speed cor
    • Forgive the scepticism, but it may be worth noting that there are electrical discharge theories of the cosmos that do not need to invoke "dark matter" at all (though these theories are, for reasons unknown, not accepted by mainstream astrophysicists and cosmologists). The point being that maybe there ain't no such thing as "dark matter".
      • "there are electrical discharge theories of the cosmos that do not need to invoke "dark matter" at all" I was all ready to mod you up but, alas, no examples or links....
        • sorry, didn't have the links on-hand when I posted and just figured ppl would google for them. Here are a couple of good ones. I bring up Electrical Discharge Theory at all just because too few ppl think to question basic assumptions. In this case, most everyone presumes there's "dark matter" just because most physicists and astronomers tell them so, but history tells us that physicists and astronomers have been w
    • Re:OK ... (Score:3, Informative)

      by Aglassis ( 10161 )
      Tthe rotation of the Galaxies doesn't follow Kepler's Laws of planetary motion (which should apply if you consider all the stars in the galaxy to be planets). The easiest way to look at this is to compare the rotational velocities of the stars in the galaxy (which can be determined by taking the red/blue shift of the galaxy in general to determine its velocity relative to you and then taking the redshift of stars in the galaxy that are roughly parallel to your line of sight). Kepler's Third Law says that
  • > Reuters is reporting that the dimmest galaxy has been found

    Yeah, I always that galaxy wasn't too bright...
  • Scientists have now found the brightest dark-sucker [] galaxy to date...
  • by JohnPM ( 163131 ) on Wednesday June 02, 2004 @05:09AM (#9312851) Homepage
    ...the mysterious dark matter that appears to be pushing regular matter around

    That must be the extra mysterious version of dark matter that works opposite to gravity (pushes).

    The normally mysterious version of dark matter is simply dark and mysterious. It pulls.

(1) Never draw what you can copy. (2) Never copy what you can trace. (3) Never trace what you can cut out and paste down.