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Galaxies Twice As Bright As Previously Thought

Posted by Soulskill on from the intergalactic-dust-buster dept.

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. SPACE.com 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."

29 of 139 comments (clear)

  1. So there's more dust than previously thought... by msauve · · Score: 4, Interesting

    is there any reason this can't be the unaccounted "dark matter" astronomers are always talking about?

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    1. Re:So there's more dust than previously thought... by BadAnalogyGuy · · Score: 4, Informative

      Dark matter is non-interacting. It only exerts a gravitational force. It would not obscure the light of galaxies (except to bend the light through gravitious pull).

    2. Re:So there's more dust than previously thought... by Vectronic · · Score: 3, Insightful

      "except to bend the light through gravitious pull"

      hence, "obscure" ... :P

    3. Re:So there's more dust than previously thought... by ObjetDart · · Score: 4, Interesting

      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.

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    4. Re:So there's more dust than previously thought... by msauve · · Score: 4, Interesting

      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?

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      "National Security is the chief cause of national insecurity." - Celine's First Law
    5. Re:So there's more dust than previously thought... by zippthorne · · Score: 5, Informative

      He wasn't suggesting that the DUST is the dark matter. He was suggesting that the stars' unaccounted-for mass is, at least part of, the "dark" matter: the matter that we cannot observe except by it's gravitational effects.

      The article suggests two things by stating that the dust is obscuring galaxies more than previously thought:

      1) there is more mass in the galaxies than previously thought (to be generating the light we don't see)

      2) there is more mass in the dust than previously thought.

      "dark" matter is in it's essence, unaccounted for matter. In a sense, Neptune was a "dark" planet until it was observed. Astronomers have suggested that the reason we haven't observed the "missing mass" is that it is not observable. The article does, in fact, suggest that at least part of the missing mass may be unobservable for mundane reasons rather than new physics.

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    6. Re:So there's more dust than previously thought... by cnettel · · Score: 3, Informative

      Just to make things clear, even a doubling of the amount of mass in stars would only reduce the amount of dark matter by a few percent (and then we have the dark energy...).

    7. Re:So there's more dust than previously thought... by FooAtWFU · · Score: 4, Informative

      Have you measured the effect of gravity on light recently? You ever notice how your flashlight beam actually falls towards the ground when you aim it straight out? No? That's because it's trivially small.

      To obscure light, matter would need to absorb it. Assuming that it cannot, the closest to "obscuring" that gravitational interactions could do is to bend it a little so it's facing a different direction. Lensing, and all that fun. I suppose in the worst case, a patch of dark matter could act to randomly diffuse the light going through it, but since it IS matter and it is gravitationally bound, it tends to form clusters like other matter, and you're not going to see diffusion over the million-light-year gaps between the galaxies being observed.

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    8. Re:So there's more dust than previously thought... by FooAtWFU · · Score: 3, Interesting

      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.

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    9. Re:So there's more dust than previously thought... by EtaCarinae · · Score: 5, Interesting

      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.

    10. Re:So there's more dust than previously thought... by Planesdragon · · Score: 5, Interesting

      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.
    11. Re:So there's more dust than previously thought... by jabuzz · · Score: 5, Interesting

      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.

    12. Re:So there's more dust than previously thought... by no1home · · Score: 3, Informative

      It's not so much obscuring as mildly redirecting. It's called gravitational lensing. (http://en.wikipedia.org/wiki/Gravitational_lensing) This is what causes effects like the halo around a distant back lit object or the optical illusion of two copies of the same object (star, galaxy).

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    13. Re:So there's more dust than previously thought... by shma · · Score: 5, Informative

      There seem to be a lot of questions about dark matter, so I'll do my best to answer them.

      1)Dark matter is indeed postulated to account for the discrepancy between gravitational measurements of the mass distribution of galaxies vs evidence from other sources.

      2)We know that dark matter can't be accounted for by large mass objects (like planets, asteroids, dust, etc) because CMB measurements tell us that the total amount of baryonic matter ('normal' matter made up of protons and neutrons) is a small fraction of the total matter in the universe (around 15%). So it must be made of heavy non-baryonic particles. This, by the way, is the reason why the discovery mentioned in TFA has little impact on dark matter. There is already an upper limit on the amount of baryonic mass in the universe, irrespective of what we see with telescopes.

      3) We know that these particles can't interact electromagnetically or with the strong force, otherwise they would end up in atoms (either as part of the nucleus or orbiting the nucleus). In this case, these atoms would be much heavier than normal atoms and we would see evidence of them in the spectral lines of stars.

      4)That leaves us with particles which interact only through the weak force, like neutrinos. We have also found that dark matter plays an important role in the formation of structure in the universe, and in order for structure to form in the way it has, the dark matter must be moving at non-relativistic speeds at that time. This rules out the neutrino, which would be moving at speeds very close to the speed of light at that time.

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    14. Re:So there's more dust than previously thought... by The_Wilschon · · Score: 3, Informative

      Fine, but that's pretty clearly not what TFA meant by "obscured". So context-ignoring semantic wrangling aside, gravitational lensing is not particularly relevant here.

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  2. Warning! by Daimanta · · Score: 4, Funny

    Do not look into galaxy with remaining eye!

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    Knowledge is power. Knowledge shared is power lost.
  3. Stars versus dark matter by anonieuweling · · Score: 3, Informative

    More mass in stars, so less dark matter...

  4. big shake-up by Bombula · · Score: 4, Interesting
    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?

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    1. Re:big shake-up by khallow · · Score: 3, Informative

      I believe you've nailed the major implication of this research. Assuming it turns out to be true, it may provide an alternate explanation for why distant supernova (type 1A) appear more distant than expected from their red shift.

  5. In other news... by AstronomicUID · · Score: 4, Funny

    Researchers found to be half as bright as previously thought.

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  6. why is this a news? by Anonymous Coward · · Score: 5, Interesting

    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.

  7. Tail wagging the dog... by msauve · · Score: 4, Insightful

    Science is about explaining observations (evidence) with testable theory, not claiming a theory to be evidence.

    The emperor has no clothes.

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
  8. Because... by Jane+Q.+Public · · Score: 4, Interesting

    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).

  9. Furthermore... by msauve · · Score: 3, Interesting

    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).

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
  10. Not Intergalactic Dust... by florescent_beige · · Score: 4, Informative

    From reading TFA, the dust they are talking about is *within* the galaxies. Because of it galaxies don't emit as brightly edge-wise.

    But perpendicular to the plane there is little dust absorption. So the brightness of galaxies viewed this way shouldn't need much correction. Since most galaxies are viewed this way due to the bias caused by this effect, why would there need to be a major rethink of stellar brightness? I'm not getting it.

    Maybe it's galactic density that needs correction.

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  11. Wrong... by msauve · · Score: 3, Insightful

    ...We know that dark matter can't be accounted for by large mass objects (like planets, asteroids, dust, etc) because CMB measurements tell us that the total amount of baryonic matter ('normal' matter made up of protons and neutrons) is a small fraction of the total matter
    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.
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    "National Security is the chief cause of national insecurity." - Celine's First Law
    1. Re:Wrong... by wanerious · · Score: 3, Interesting

      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.

  12. Re: Dark Semantics by hxnwix · · Score: 5, Interesting

    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.
  13. Re:Same to you... by hxnwix · · Score: 3, Informative

    How can pointing to a picture which claims to observe the unobservable not be funny? Dark matter is postulated to be observable solely by its gravitational interaction with directly observable matter and energy. In this case, the Bullet cluster image represents empirical data: matter not visible in the image but within the frame of the image and in front of other visible objects is deflecting electromagnetic radiation emitted from those background objects.

    Similarly, you can't see electrons, but if you collect a large amount of them, you can observe the force caused by the static charge upon observable objects. If you move them, you can detect the generated magnetic field.

    And here's your CMB [dfi.uem.br], predicted long before Big Bang cosmology, and more accurately, too. That's a non sequitur. The +5 rated post to which you originally replied pointed out that CMB anisotropy indicates the presence of cold dark matter; the link you supply deals with average CMB black body spectra and does not mention dark matter even once.