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Space Science

Galaxies Twice As Bright As Previously Thought 139

Astronomers led by Simon Driver of Scotland's University of St. Andrews have discovered that interstellar dust shades us from as much as 50% of the light emitted by stars and galaxies. The scientists compared the number of galaxies we could see "edge-on" against the number which were "facing us," reasoning that dust would obscure more of the former, since we already receive less light from them. notes, "In fact, the researchers counted about 70 percent fewer edge-on galaxies than face-on galaxies." A NYTimes report provides some additional details: "Interstellar dust absorbs the visible light emitted by stars and then re-radiates it as infrared, or heat, radiation. But when astronomers measured this heat glow from distant galaxies, the dust appeared to be putting out more energy than the stars. 'You can't get more energy out than you put in, so we knew something was very wrong,' said Dr. Driver. The results also mean that there is about 20 percent more mass in stars than previously thought."
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Galaxies Twice As Bright As Previously Thought

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  • by msauve ( 701917 ) on Sunday May 18, 2008 @11:23AM (#23453338)
    is there any reason this can't be the unaccounted "dark matter" astronomers are always talking about?
  • by ObjetDart ( 700355 ) on Sunday May 18, 2008 @11:34AM (#23453420)
    IANAA, but IIRC, the answer is no. It's been calculated that dark matter, whatever it is, must be nonbaryonic [], so it can't be explained by extra interstellar dust, larger stars, etc.
  • big shake-up (Score:5, Interesting)

    by Bombula ( 670389 ) on Sunday May 18, 2008 @11:59AM (#23453560)
    Although the article does a good job of being nonchalant and avoiding hyperbole, it seems that there are going to be some major implications from this 'correction'. Some are alluded to in the article - that stars are brighter than expected and that some of the 'missing mass' in the universe has apparently been found. But doesn't that open up a big can of worms? Aren't recent dark matter and dark energy theories calibrated to older and - apparently - now inaccurate data about how matter/mass there is in the universe?

    Anyone case to elaborate on what kind of shake-up this is going to have for astronomy and cosmology?

  • by msauve ( 701917 ) on Sunday May 18, 2008 @12:14PM (#23453660)
    According to the Wikipedia article, dark matter "does not emit or reflect enough electromagnetic radiation to be observed directly." Why does that exclude this dust, which at the time that statement was made was unobserved, and therefore fit into the definition?

    Furthermore, the definition says nothing about "non interacting," and it seems to me that the real definition is more like "matter we know must exist because of its gravitational effects, but for which we can't account." (i.e. either we can't see it, or we're not looking correctly because we dont' know what we're looking for) Just as with the dust at hand, how do we know it is "non interacting," or that it "doesn't emit or reflect" radiation, if we don't know what it is?

    If this newly found dust blocks light, what does it do with the visible light it absorbs? Seems to me, it must re-radiate it (at a lower frequency, like a black object in the sun?) So, if it re-radiates the energy it absorbs, then why hasn't that been noticed before? Is all this re-radiated energy just part of the cosmic microwave background radiation?
  • Re:big shake-up (Score:1, Interesting)

    by Anonymous Coward on Sunday May 18, 2008 @12:26PM (#23453750)
    Does this have any affect on the estimations of the universe's rate of expansion? I understand that's based on measuring the brighness of supernova.
  • by Anonymous Coward on Sunday May 18, 2008 @12:53PM (#23453920)
    I'm not discounting the importance of this work scientifically, but the implications of dust in making a galaxy appear dim has been known for a long time, and this work no way gives us definitive answers to the nagging dust extinction issues.

    Therefore it is questionable whether this is a popular-science news worthy finding. As someone who has worked closely in the field, I feel the way the report has been written only serves to fool the public into thinking something is really different about the current state of astronomy.

    But then the public doesn't really care, you know. I wonder why astronomy news are so abundant in public, when most of them really have little implications for society and worse yet, the popular science articles often miss the gists of whatever the science discoveries really mean.

    PR in astronomy is excellent in that they do fairly well on improving their public image, but often horrendous in conveying the substance of what they really do.
  • You are ignoring... (Score:3, Interesting)

    by msauve ( 701917 ) on Sunday May 18, 2008 @01:01PM (#23453996)
    The "20% more mass in stars" may just be the tip of the iceburg. The article doesn't mention the amount of mass in the dust itself.

    Since there is no evidence for exotic black matter (other than observed gravitational effects), doesn't Occam force us to assume that the gravitational effects which we do observe are likely due to what we know about?

    Why would it be incorrect to say this newly discovered dust has mass x (equal to the necessary dark matter mass), which scientists can determine from it's gravitational effects?
  • by cnettel ( 836611 ) on Sunday May 18, 2008 @01:09PM (#23454056)
    The CMB has overall a black-body (heat) signature. It's shifted, however, most reasonably explained with the expansion of the universe and the associated Doppler effects. An object at the current "background temperature" would NOT emit radiation with the background signature. Nothing with a well-defined temperature would emit anything like it today, unless it's exotic in some way... That makes the assumption of non-interaction just as plausible (from a layman perspective).
  • by FooAtWFU ( 699187 ) on Sunday May 18, 2008 @01:32PM (#23454198) Homepage
    There's already way too much matter. They took a look at the physics, and they expected that there should be an equal amount of matter and anti-matter out there from when the Universe got created, but as far as they can tell, there isn't. So some process at the beginning of the Universe made slightly more Matter than Antimatter, and this asymmetry is already one of the greatest unsolved problems of physics.
  • by EtaCarinae ( 1149927 ) on Sunday May 18, 2008 @01:35PM (#23454216)
    Perhaps this will have implications for some of the standard candles []? If objects suddenly aren't that far off, they will shrink in size and kinetic energy estimates will drop making the case for dark matter weaker.
  • Dark matter is non-interacting. It only exerts a gravitational force.
    No, not at all.

    Dark Matter is a theoretical answer to "the universe has more matter than it looks like." If the universe, in fact, actually has more matter, then there's less, possibly zero, need for the hand-waving "Dark matter" theory.

    Unless an astrophycisst (sic - lazy) has actual numbers as to what % of the total matter is "dark", we won't know what effect, if any, this discovery has on the dark-matter theory.
  • by jabuzz ( 182671 ) on Sunday May 18, 2008 @02:37PM (#23454726) Homepage
    The point is that the new model shows that what was previously thought to be sown up, the shortfall between the observed matter, and the amount required to account for the observed behavior is not quite as sown up as we thought.

    So while this discovery does not mean that we have now observed all the mass necessary, it does mean that it would be prudent to look again very hard at how we have derived the mass of the universe in case we have left out mass along the line.

    There are also other challenges on dark matter. The reason the whole concept exists is that there does not appear to be enough visible matter to explain the rotation of galaxies. However even this has recently being challenged, with the argument that using Newtonian dynamics to model galactic rotation is flawed, and if you do the same modeling using General Relativity (much much harder to do) the missing mass appears to vanish. I am the first to admit that there are issues with the paper that proposes this. However it is an important new avenue of research.

    There is also the possibility that we might have gravity wrong, at very low accelerations which would also make dark matter go away.

    My personal feeling is that dark matter is about as likely as the ether, and in reality we have not counted the mass accurately and are miss-applying theories.

    Then again I think Copenhagen interpretation is hokum as well.

  • by Tacvek ( 948259 ) on Sunday May 18, 2008 @02:48PM (#23454812) Journal
    That seems reasonable. It may be that some of the things requiring unusual theories like quantum gravity or gobs of non-baryonic matter, may in fact just be due to inaccurate distance measurements. My understanding is that much of those theories are due to unusual observed movements, that don't seem to correspond to gravity on regular matter. But if are distance calculations are wrong, then perhaps that was all there was too it. The fact that this 20% is only a minuscule fraction of the amount of alleged dark matter existing is immaterial if the calculations for the total amount of mass that should exist are based on significantly flawed numbers. This I would not be shocked to see a major drop in the amount of non-luminous (dark) matter needed if the numbers are re-run.
  • Because... (Score:5, Interesting)

    by Jane Q. Public ( 1010737 ) on Sunday May 18, 2008 @02:53PM (#23454860)
    So-called "dark matter" (which so far is only a hypothesis, not even a real theory), DOES NOT INTERACT with our "normal" universe, except through gravity. Therefore, it does not absorb light. It could bend light (gravitational lensing) but not absorb it.

    Personally, I find the idea of "dark matter", as currently envisioned, to be little more than superstitious hand-waving. I think the concept is unlikely in the extreme to be shown valid, and instead that other sources will be found for the observed effects (like, as the other responder pointed out, more mass than previously thought in existing stars).
  • Furthermore... (Score:4, Interesting)

    by msauve ( 701917 ) on Sunday May 18, 2008 @03:29PM (#23455102)
    since the article was concluded more light dimming for "edge on" galaxies, then there should be a futher test: current distance measuring objects and metrics (Cepheid Variables, etc.) should show that "edge" galaxies are further away than "face" galaxies, on average. (this wouldn't affect galaxies measured by red shift, which would equally off).

    Surely, there's a database somewhere with distances and galaxy types which could be easily looked at to see if that's true.

    It would also be interesting to know how much this affects the Hubbel constant.

    Finally, the conclusions seem to only recognize the effect within other galaxies, but there would be no reason to think similar dimming doesn't occur from interstellar dust within the Milky Way. If so, then extragalactic objects should be dimmer (and more distant based on flawed calculations) on average when they lie in certain directions. (e.g. most dimming when looking through the galactic center near Sagittarius).
  • Re: Dark Semantics (Score:5, Interesting)

    by hxnwix ( 652290 ) on Sunday May 18, 2008 @08:25PM (#23457052) Journal

    the onus is on you to prove that portion of it correct by finding some of this imaginary non-baryonic mass...Your circular logic fails to prove that dark matter exists.
    I assume you're going for +5 funny, but here is your dark matter []. From wikipedia: Composite image of the Bullet cluster shows distribution of ordinary matter, inferred from X-ray emissions, in red and total mass, inferred from gravitational lensing, in blue.

    The various discrepancies referred to by the GP are interesting because they represent quantifiable gaps in cosmological theory. The discrepancy between observation and Newtonian prediction of the period of Mercury's orbit could be explained by unsatisfactory inventions such as the interstellar ether; similarly, dark matter began as a stopgap invention.

    However, as the GP mentioned, surprising evidence is cropping up that the universe contains vast quantities of weakly-interacting matter. That doesn't mean we should throw our hands up as you do and claim it's the flying spaghetti monster. We ought to continue observing, theorizing, predicting, checking and refining our understanding of the universe. Perhaps non-intuitive sorts of matter do exist! Or, the investigation of it might lead to theories superseding the current ones as relativity replaced Newtonian physics.
  • Re:Wrong... (Score:4, Interesting)

    by wanerious ( 712877 ) on Monday May 19, 2008 @12:38AM (#23458644) Homepage

    What you mean to say is that the theory of life, the universe and everything which you subscribe to breaks if there is no exotic dark matter. There is no proven "upper limit on the amount of baryonic mass in the universe," there are only theories and hypothesis which make that claim as part of their model. I won't try and prove a negative by saying that theory is necessarily wrong, but the onus is on you to prove that portion of it correct by finding some of this imaginary non-baryonic mass. Myself, I'll claim that the Flying Spaghetti Monster [] plays with the gravitational "constant" to fool with us. Prove me wrong. Your circular logic fails to prove that dark matter exists.
    You might have a point if, in science, we were in the habit of proving things. Nothing is ever "proved" in science. Nobody cooked up the idea of "dark matter" and went out trying to find supporting observations; rather, the anomalies in a number of different phenomena leads one to this idea. "Dark Matter" is the simplest explanation we can imagine for these many different observations. Altering the gravitational constant in a specific, scale-dependent way may allow you to solve the galactic rotation curve problem, for a particular galaxy, but you'd need to invent an entirely new change of the constant at galactic cluster scales, where the dark matter effects are also observed. Worse still, the Bullet Cluster observations imply a lensing effect of the dark matter halo, so not only do you need to fiddle with the *magnitude* of the gravitational constant, but also its *direction* in a way to precisely fit the data. We (I am an astrophysicist) tend to think that the Bullet Cluster, for all practical purposes, ends the viability of various modified gravity hypotheses. Some people still work on them, but they're getting harder and harder to justify in general.

    The upper limit on the amount of baryonic matter is computed with increasing precision based upon WMAP and other CMB observations. It's something like 4-5% of the total mass of the universe. You should avail yourself of the procedure used to get the result. It's a beautiful calculation.

  • by tpheiska ( 1145505 ) on Monday May 19, 2008 @02:52AM (#23459226)
    It's also a thing with the mass distribution. With a system where things rotate around a central mass (ie. the solar system) the speed of the objects can be easily estimated. Now, in a galaxy, if all the mass is in the objects we can see we should be able to deduct the speeds of the objects (faster near the center, slower in the edges). This is not the case. The stars seem to be rotating around the center of the galaxy with nearly equal velocities. This can thus far only be explained by a dark matter halo that gives additional speed to the outer stars.

    Example []
  • Re:Because... (Score:2, Interesting)

    by tpheiska ( 1145505 ) on Monday May 19, 2008 @02:54AM (#23459242)

    (like, as the other responder pointed out, more mass than previously thought in existing stars).
    Won't work. Nothing that we have seen or deducted so far has not been able to explain the velocity discrepancies of stars orbiting the center of the galaxy. Also, more mass somewhere is propably the easiest thing to check, for example the effects could be seen in binary systems.

"If it's not loud, it doesn't work!" -- Blank Reg, from "Max Headroom"