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Space Science

The Starry Sky Just Got Starrier 186

Posted by samzenpus
from the twinkle-twinkle dept.
An anonymous reader writes "Astronomers have surveyed eight elliptical galaxies, and found that we've vastly underestimated the number of dim red dwarf stars in these giant galaxies. When they used the new number of red dwarfs in their calculations, they tripled the total number of known stars in the universe."
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The Starry Sky Just Got Starrier

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  • Re:first? or third? (Score:4, Informative)

    by John Hasler (414242) on Wednesday December 01, 2010 @06:29PM (#34411864) Homepage

    They don't determine the mass of a galaxy by counting stars.

  • Re:first? or third? (Score:2, Informative)

    by Bigjeff5 (1143585) on Wednesday December 01, 2010 @06:33PM (#34411892)

    It won't boost as much as you think. It increases the number of stars, but red dwarfs are small and not very massive. They are usually stars that went nova but were too small to collapse and form a black hole.

    A handful of super-massive black holes could probably cover this tripling of the stars.

    Even if the amount of matter tripled, however, it still would not eliminate dark matter. Currently, visible matter accounts for 4.6% of the matter in the observable universe. Dark matter accounts for 23% (the rest is dark energy). Tripling the visible matter would bump it up to 13.8% of matter in the universe, and would bring dark matter down to 13.8%, or roughly equal.

    That's still a hell of a lot of dark matter that is currently invisible, and is still plenty to screw up astronomical observations.

  • Re:first? or third? (Score:5, Informative)

    by spun (1352) <`moc.oohay' `ta' `yranoituloverevol'> on Wednesday December 01, 2010 @07:04PM (#34412142) Journal

    No, it's out there. Things like the bullet cluster pretty much prove that there must be large amounts of some sort of weakly interacting matter. Basically, two galaxies collide. Normal matter in one galaxy interacts with normal mater in the other, slowing it down. But something massive wasn't slowed down and kept right on trucking along the same path at the same speed as before. We only know it is there because of the gravitational lensing it produces. So, we have direct evidence of matter that we can not see, and that does not interact with other stuff except through gravity. Call it whatever you like, it's out there. And that is just one piece of evidence. Galaxy rotation and the CMB are others.

  • Re:first? or third? (Score:4, Informative)

    by icebike (68054) on Wednesday December 01, 2010 @07:17PM (#34412262)

    Five to one or twenty to one, you still have a significant amount of mass.

    Then, as you mention, you have to add all the hard to detect planets for another small fraction. (If weren't seeing the star you can bet they weren't measuring its wobble). Admittedly its probably a small addition relative to the stars themselves.

  • Re:first? or third? (Score:5, Informative)

    by mog007 (677810) <Mog007.gmail@com> on Wednesday December 01, 2010 @09:15PM (#34413108)

    Dark matter and dark energy are two totally different things. They're placeholders for vastly different phenomena. Dark matter explains why galaxies rotate at the speeds they do, even though their visible mass is much, MUCH, lower than the spinning speed shows it should be. Dark energy is the pressure that's causing the universe to accelerate outward. The universe isn't just expanding, the rate of the expansion is increasing, not decreasing as you would expect. Some force is being exerted on the fabric of the universe that's causing it to expand at a faster rate every second.

    So, to recap:
    Dark matter = mass that's causing galaxies to spin faster than they should be
    Dark energy = force that's pushing the universe apart

  • Re:first? or third? (Score:4, Informative)

    by wvmarle (1070040) on Wednesday December 01, 2010 @10:01PM (#34413342)

    It probably depends on what you're talking about really, from WP:

    dark matter accounts for 23% of the mass-energy density of the observable universe, while the ordinary matter accounts for only 4.6% (the remainder is attributed to dark energy).[2] From these figures, dark matter constitutes 80% of the matter in the universe, while ordinary matter makes up only 20%.

    So ordinary matter accounts for 4.6% (1/20th) of all mass+energy in the universe - this I suppose has to do with Einstein's E=mc2 that allows for mass to be converted to energy and the other way around. And looking at actual mass, not taking the energy into account, this would end up at 1/5th. So both numbers are in a way correct, depending on context. I thought actually it was about 90% dark matter, so let's call that number the average. Then at least I'm not wrong myself.

    Now I don't really know what they mean with the "dark energy" part or how that's measured, the "dark matter" I understand somewhat as it has to do with gravity.

    Anyway this whole "dark matter" thing sounds to me like the hypothetical "aether" - we don't know what it is so make up something to make the formulas work. So now we found that there is 3-4 times as much "visible" matter in our universe than we thought before. Oh well that's quite some "dark matter" that has come to light. I'm quite sure the rest will follow sooner or later.

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