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Space Science

Galaxies Twice As Bright As Previously Thought 139

Posted by Soulskill
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."
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Galaxies Twice As Bright As Previously Thought

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  • by msauve (701917) on Sunday May 18, 2008 @10:23AM (#23453338)
    is there any reason this can't be the unaccounted "dark matter" astronomers are always talking about?
    • 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).
      • Re: (Score:3, Insightful)

        by Vectronic (1221470)
        "except to bend the light through gravitious pull"

        hence, "obscure" ... :P
        • by FooAtWFU (699187) on Sunday May 18, 2008 @12:29PM (#23454178) Homepage

          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.

          • Yes, as far as I am aware, "obscure" means to make less than whole, make unclear, or even make rare, etc.

            So diffusion, by means of gravitational pull is a form (or an act?) of obscuring the object by diffusing the light emitting/reflecting from the object.

            It does not matter how fractionally small this diffusion is, the point is... it is diffusing the light.

            And I really dont understand how you made the greater distance seem less important, like the flashlight gets effected more in its span of 10 feet than tr
            • Re: (Score:3, Informative)

              by no1home (1271260)
              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).
      • by msauve (701917) on Sunday May 18, 2008 @11:14AM (#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?
        • by zippthorne (748122) on Sunday May 18, 2008 @11:41AM (#23453842) Journal
          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.
        • Because... (Score:5, Interesting)

          by Jane Q. Public (1010737) on Sunday May 18, 2008 @01:53PM (#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).
          • Re: (Score:2, Interesting)

            by tpheiska (1145505)

            (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.
            • There are many ideas that have attempted to explain exactly that phenomenon, and one in particular arguably does so much better than "Dark Matter". That one is MoND (Modified Newtonian Dynamics).

              Further, MoND entails only a few very minor adjustments to known constants. Unlike the Dark Matter hypothesis, MoND does not require us to imagine that the universe is made mostly of stuff that we cannot see or interact with except via gravity. That latter is a pretty big leap of faith! So in a comparison of the
      • 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 shma (863063) on Sunday May 18, 2008 @03:02PM (#23455324)
          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.
          • Wrong... (Score:4, Insightful)

            by msauve (701917) on Sunday May 18, 2008 @04:54PM (#23456130)

            ...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 [venganza.org] plays with the gravitational "constant" to fool with us. Prove me wrong.

            Your circular logic fails to prove that dark matter exists.
            • Re: Dark Semantics (Score:5, Interesting)

              by hxnwix (652290) on Sunday May 18, 2008 @07:25PM (#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 [wikipedia.org]. 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.
              • How can pointing to a picture which claims to observe the unobservable not be funny?

                And here's your CMB [dfi.uem.br], predicted long before Big Bang cosmology, and more accurately, too.
                • Re:Same to you... (Score:4, Informative)

                  by hxnwix (652290) on Monday May 19, 2008 @12:38AM (#23458946) Journal

                  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.
            • Re:Wrong... (Score:4, Interesting)

              by wanerious (712877) on Sunday May 18, 2008 @11:38PM (#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 [venganza.org] 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 Squalish (542159)
                While I don't doubt there is a complicated, elegant rationale for a baryonic upper limit in your cosmology of choice...

                The basis for every response here is - the study suggests this is a basic, fundamental, empirical fact of astronomy that a century of viewing galaxies has managed to overlook. In order to establish your upper limit, astrophysicists had to postulate exotic, undetectable forms of matter. Even then, all their calculations couldn't agree with cosmological data, so they had to bring up dark en
                • by wanerious (712877)

                  The basis for every response here is - the study suggests this is a basic, fundamental, empirical fact of astronomy that a century of viewing galaxies has managed to overlook.

                  Well, overlook might be too strong a word. With the availability of modern databases, these new statistical studies can revise old estimates --- in this case, the old mass/light estimate for some galaxies.

                  In order to establish your upper limit, astrophysicists had to postulate exotic, undetectable forms of matter.

                  It didn't work out quite that way. Observations strongly suggest a flat universe, and Big Bang nucleosynthesis, deuterium/lithium observations, and cosmological surveys all pointed to a total mass density of about a third necessary for flatness, with only 4-5% or so contributed by baryons. The

        • Re: (Score:3, Funny)

          by SurturZ (54334)
          [blockquote]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.[/blockquote]

          There has to be a Star Wars joke there somewhere about Dark Matter being a quicker, more seductive way to explain the missing mass, but for the moment it escapes me. (waves hand) this is not the mass you are looking for...
        • Unless an astrophycisst (sic - lazy) has actual numbers as to what % of the total matter is "dark"...

          There are no such thing as actual numbers at astronomical distances.

          The distance to a given star can only be accurately triangulated for relatively short distances (several light years). Beyond that astronomers use 'standard candles' - such as cepheid variable stars and supernovae - to estimate the distance to a star using the known luminosity of these adjacent objects.

          That being said, if we determine that our observations of the luminosity of the given objects is incorrect due to this absorption then tha

        • Dark matter should never have been postulated as real matter, or even hinted at it being real. It's basically a discrepancy between the models we use to mimick the real world and the real world.

          Where that discrepancy lies, that's the big hunt, but believing that dark matter exists is ridiculous.
    • Re: (Score:2, Funny)

      by Anonymous Coward
      Hopefully there will be too much matter now and we can all build careers around theories of dark anti-matter.
    • by ObjetDart (700355) on Sunday May 18, 2008 @10:34AM (#23453420)
      IANAA, but IIRC, the answer is no. It's been calculated that dark matter, whatever it is, must be nonbaryonic [wikipedia.org], so it can't be explained by extra interstellar dust, larger stars, etc.
      • Re: (Score:1, Informative)

        by Anonymous Coward
        Not exactly. Try the wikipedia article on dark matter [wikipedia.org] first.

        The composition of dark matter is unknown but may include ordinary and heavy neutrinos, recently postulated elementary particles such as WIMPs and axions, astronomical bodies such as dwarf stars and planets (collectively called MACHOs), primordial black holes and clouds of nonluminous gas. Also, matter that might exist in another universe but might affect ours via gravity would be consistent with some theories of brane cosmology. Current evidence

        • Re: (Score:2, Insightful)

          by BadAnalogyGuy (945258)
          From Wikipedia: The dark matter component has vastly more mass than the "visible" component of the universe

          From the summary: there is about 20 percent more mass in stars than previously thought

          Even if we assume that "vastly more mass" means 51% of all mass in the universe, we still have the problem of a lot of missing mass even with the increased estimations of stellar mass and interstellar dust.

          This study may increase our precision in our calculations of universe mass, but it is by no means eliminating dar
          • You are ignoring... (Score:3, Interesting)

            by msauve (701917)
            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 gravita
            • Re: (Score:1, Funny)

              by Anonymous Coward
              Mmmmh... iceburger...
            • Re: (Score:2, Insightful)

              Occam's tells us that we should select the theory that introduces the fewest assumptions. In this case, we can assume that the extra mass is accounted for by dark matter, or that the galaxies are emitting more light than we can see. Occam's doesn't appear to apply.
              • LOL. (Score:2, Insightful)

                by msauve (701917)
                You ignored the HUGE ASSUMPTION, unsupported by any facts (except gravitational effects), that any exotic black matter exists, in any quantity. THE ONLY REASON it is theorized is because nothing else had been identified which could cause those gravitational effects. Now there is evidence of previously unknown mass.

                You obviously don't know how to apply Occam if you prefer an unproven hypothetical to something which is observably evident.
                • Re: (Score:2, Insightful)

                  It is NOT observably evident. What is observably evident is a mass increase of 20 percent. That in no way accounts for all of the unobserved matter. And I'm not applying Occam's, I'm saying Occam's doesn't apply here. Both situations are hypothetical. Get a clue.
                  • Actually, the reduction of visible light, or to view it another way, extra mass in other galaxies seems to impact on a great many things and can't be taken in isolation. Once we nail down a more exact figure for the mass of other galaxies, then we need to recalculate the standard candles which in turn shifts the distances between galaxies. There may also be other effects related to potential quantity, and thus mass of interstellar dust.

                    Dark Matter was postulated to account for a discrepancy between what w
            • by shawb (16347)
              There is theoretical evidence for the existance of exotic black matter: deuterium. According to our current models of nucleosynthesis in the big bang, if all of matter which gravitational observations predict is baryonic (I.E. neutrons, protons + electrons) then the high density during initial conditions would have fused the vast majority (if not all) of the deuterium into helium.

              It is also possible that our calculations are off with some portion of the equations: a fundamental misunderstanding or overs
              • by msauve (701917) on Sunday May 18, 2008 @01:04PM (#23454468)
                Science is about explaining observations (evidence) with testable theory, not claiming a theory to be evidence.

                The emperor has no clothes.
                • tell people to stop calling it the Dark Matter "theory"!!! It is only a hypothesis, not a theory, as I have pointed out on /. many times.

                  I have seen so many instances of people wrongly assuming that Dark Matter and String "Theory" are accepted fact, when neither of them are even good theories yet. It is distressing. Has science education failed that miserably in recent years?
                  • by Tim C (15259)
                    Has science education failed that miserably in recent years?

                    Yes, yes it has. See for example ID vs evolution.
          • by jabuzz (182671) on Sunday May 18, 2008 @01:37PM (#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.

          • You should get modded up just for mentioning that all of this is theoretical and that all of these "Theories" are based on incomplete data. Math is great, but math alone can not prove anything. If the math doesn't match the data then the math is wrong. I am suspicious of theories that shrug off new data.

            In my day, the universe was composed of matter and energy, and we liked it that way.
      • according to the Wikipedia article you cited, is calculated from observations of the cosmic microwave background radiation.

        But, this newly found dust, which blocks light, must do something with that energy - either gain mass or re-radiate it, right? Could not that re-radiation be a part of the CMB, which would in turn have an affect on the calculated amount of baryonic dark matter. If it's not part of the CMB, where is this lost energy accounted for?
        • Re: (Score:3, Interesting)

          by cnettel (836611)
          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).
          • Re: (Score:2, Informative)

            by Anonymous Coward
            Wow, your post is complete disinformation. I've never seen that on slashdot. Normally only a part of it is wrong.

            The CMB *has* the blackbody signature of an object at 2.725 kelvin. It is even the most precise blackbody ever found. The "shift" you're talking about is more accurately a multiplicative factor of about 1000. Multiplicative factors map a theoretical blackbody signature to another one with no distinction possible.
        • by wanerious (712877)

          But, this newly found dust, which blocks light, must do something with that energy - either gain mass or re-radiate it, right? Could not that re-radiation be a part of the CMB, which would in turn have an affect on the calculated amount of baryonic dark matter. If it's not part of the CMB, where is this lost energy accounted for?

          Nope. As stated in the article, dust that absorbs starlight re-radiates it in the infrared. The CMB is, as given by the name, microwave radiation, which corresponds to a temperature of about 3K. Any emission from dust that is warmer than the background universe must emit at a wavelength shorter than the CMB.

          What matters most in the calculation of baryonic upper limits is the variation of the CMB with position in the sky. The size of these fluctuations gives us a way to measure the interior angles of

      • Re: (Score:3, Informative)

        by IdahoEv (195056)
        What this will do is reduce the amount of dark matter that is necessary to explain the observed gravitational effects.

        Dark matter is theorized to exist because galaxies behave gravitationally as if they have more mass than we can account for based on the light we see; dark matter makes up the difference. Since this result demonstrates that there is more light-emitting matter than we previously believed, it explains a slightly larger proportion of the observed gravity. Hence, a slightly smaller amount of
      • by Gerzel (240421)
        Exactly!

        Those calculations prove that just as calculations previously proved that there must be a luminiferous either to transmit light!
    • Aren't all astronomical distance measurements [gsu.edu], which are fundamentally based on brightness (except for parallax), now subject to revision?
      • Re: (Score:3, Interesting)

        by Tacvek (948259)
        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 d
        • Furthermore... (Score:4, Interesting)

          by msauve (701917) on Sunday May 18, 2008 @02:29PM (#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).
      • I wouldn't think so, unless, for some reason, someone's distance methods only used a biased sample of edge-on galaxies. Also, I'm a little puzzled why this is surprising, since it's usually pretty easy to tell when an object's light has been absorbed by intervening dust ("reddened"). Dust preferentially absorbs/scatters shorter-wavelength light, so a standard technique when observing is to "de-redden" the data --- we know, based upon quantum probabilities, the ideal ratio of, say, H-alpha to H-beta. If t
    • by Jump (135604)

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

      Yes and no. Yes, because now that this is 'known' we have to remove some mass from the 'dark matter' budget and add it to dust and stars. However, 'normal' matter is only 4% and 92% of that is gas, not stars or dust. So increasing the contribution of 'stars' or 'dust' will not change the amount of missing (dark) matter significantly. So, no, in the the sense that it won't explain any significant part of the 'dark matter'.

    • Yes. The dark matter is not only deduced but unseen matter, the deduction that leads us to conclude that it exists also leads us to expect it to have a significantly different distribution in galaxies than the luminous matter does. Simply increasing the mass of all or most stars by 20% cannot account for the observed effects which have been attributed to dark matter.
    • Re: (Score:1, Informative)

      by scratchpaper (1175477)
      Hi everyone, I teach astronomy, and I see this all the time: the term "dark matter" is almost always misconstrued to be some strange, exotic form of matter. In reality, its just an umbrella term meaning ANY kind of matter that, for one reason or another, is obscured from our observations. So yes, IS dust clouds could be a significant contributor to the "missing matter" that we think is out there. Really, anything we can't directly observe. Think about it: no detector is 100% efficient, and no observatio
  • Warning! (Score:5, Funny)

    by Daimanta (1140543) on Sunday May 18, 2008 @10:27AM (#23453356) Journal
    Do not look into galaxy with remaining eye!
  • Oh NOOOES! (Score:1, Funny)

    by hyperz69 (1226464)
    Interstellar dust shades us from as much as 50% of the light emitted by stars and galaxies. It's universal darkening. Time to call Al Gore and head out into space. Those space aliens may not care what all the ion fuel is doing to the space environment, but Al will teach them!
  • by anonieuweling (536832) on Sunday May 18, 2008 @10:29AM (#23453372)
    More mass in stars, so less dark matter...
  • it's all those dead Xenomorphs.
    • Oh, for heaven's sake, call them Zerg. Nobody's called them Xenomorphs since Chau Sara was incinerated.
      • Let's see. I can be eaten by the grue or I can get a scantily clad Wonder Woman wannabe to blow it out of the airlock...

        Saying that, she can blow me out the airlock any time she likes.
  • big shake-up (Score:5, Interesting)

    by Bombula (670389) on Sunday May 18, 2008 @10:59AM (#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?

    • Re: (Score:1, Interesting)

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

      And just before we start shaking, can someone point me to the calculation for the exact ratio of "full face" to "oblique" galaxies we were expecting to see? Starting with a definition of how full is "full". 51%? 90%? 99%? 99.99% I think it is more likely a random differentiation, like say 98.7654321%, or "Gee, it looks pretty full on to me, Jim". All of which makes the findings more like "20% more m
    • Indeed. Not to mention if this dust turns out to be non-uniform... how do we know the universe is expanding anyway?
  • by AstronomicUID (929210) <atreides2k5@ g m a i l . c om> on Sunday May 18, 2008 @11:00AM (#23453564) Homepage
    Researchers found to be half as bright as previously thought.
    • I found this to be quite humorous, not "troll" at all. Please, modders, do not assume "troll" just because you didn't get the joke.
      • Re: (Score:2, Funny)

        My theory is that some observers did not get the joke because the dimming effects of interstellar dust partially obscured its hilarity. This effect could be increased if observers are viewing the joke edge-on. Some hilarious jokes may even be completely undetectable to some observers. If my theory is true, most comments on /. may actually be twice as funny as they seem.
  • ....dust collector.
  • Wow, a simple, seemingly obvious (as always, in hindsight) observation that throws a lot of carefully balanced highly theoretical equations out of whack.

    Of course, it could prove to be equally inaccurate by failing to take into account some other grand unknown that in turn will prove to be obvious, but I can't help but feel sorry thinking of all those academics sitting around a table of hardly-touched pints and muttering "well, fuck..." to no one in particular.

    --

    "You're only as smart as the guys yo
    • Re: (Score:3, Insightful)

      by Falladir (1026636)
      I suspect that the theories you're speaking of aren't actually *that* carefully balanced. A factor of 2 might seem huge, but we currently think there's several times more dark matter than normal matter in the universe, so I don't think this will put *that* much of a dent in the status quo.
      • Re: (Score:3, Informative)

        by Tacvek (948259)
        The dark matter theory comes from the caculated amount of total matter that should exist. As it is, a significant change in the amount of luminous matter would not change the amount of dark matter needed to reach that total by very much. However, what exactly is that total amount of energy based on? Presumably the amount of matter needed to correct the orbits of large systems. However, this throws distance measurements into doubt. My understanding is that distance measurements are based in part on observed
  • This gives another perspective to it. http://en.wikipedia.org/wiki/Olbers'_paradox [wikipedia.org]
  • No thanks to us, apparently.

    I love the line about "10,000 nearby galaxies." If they're so close, why don't we visit more often?

    • by FooAtWFU (699187)
      Because gas is nearing $4 a gallon!
      • by Fumus (1258966)
        1 US gallon = 3.78541178 liters
        4.00 USD = 8.69120 PLN

        1 LITER of gasoline costs over 4,5 PLN in Poland. That's $8 a gallon.
        And you're whining about high gas prices?
      • If hydrazine is cheaper, maybe we should all drive rocket powered cars! Tailgaters beware!
    • Really! Last time, Leo I and Leo II got into it over seniority, and ruined the whole event. Cetus tried to get everyone to get back in their chairs and calm down, and Triangulum made a few good points, but ultimately that was the end of our little get-together.

      The time before that, Barnard's brought too much wine, which resulted in that whole inappropriate Sextans thing, remember? Canis Major tried to stick his huge Phoenix into Virgo and little Ursa Minor, and Draco was caught Fornaxing with Carina.

      A
  • by Anonymous Coward on Sunday May 18, 2008 @11:53AM (#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.
  • by jav1231 (539129)
    You can't SEE that one is brighter than before? :P
  • The galaxies are still a waste of space.
  • Shen Hsiu's stanza read:

    Our body is the Bodhi-tree,

    And our mind a mirror bright.

    Carefully we wipe them hour by hour,

    And let no dust alight.

    To which Hui Neng (our hero, poetry slam winner, and hence, Zen's sixth Patriarch) answered:

    There is no Bodhi-tree,

    Nor stand of a mirror bright.

    Since all is void,

    Where can the dust alight?

  • .. it was the sunglasses those rock-star astronomers were wearing.

  • by florescent_beige (608235) on Sunday May 18, 2008 @02:36PM (#23455152) Journal
    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.
  • So I'm probably totally wrong here, but since light output from supernovas in distant galaxies are used to measure the distance to these galaxies, wouldn't a discovery like this have severe implications on the topography of the universe - ie. the galaxies we know the distance to based on supernova measurements could be closer than they really are? Or? /Tage
  • If we use the brightness of Type Ia Supernovae to determine the distance to neighboring galaxies wouldn't this discovery, if validated, mean that everything is closer than we thought?

    And how would this affect the calculations of how the galaxy's gravity affects everything else?

    If everything is closer than thought that would mean that the gravitational influence of the object would be greater than currently calculated?
  • most distance calculations are based on luminosity, so if thats off, all the distances would have to be recalculated. thats interesting because that distance is also used in dark matter calculations.
  • Astrologers will take this in their stride.
  • So stars we know about may have 20% more mass than we thought, galaxies we know about have more stars (that are more massive), there are a crapload of galaxies that we are unaware of, and countless distances that we have measured are huge over estimates all because of this effect. Yet every poster in this topic that is (or pretends to be) a physicist claims that all this has little impact on the amount of dark matter in the universe.

    I don't want to sound cynical, but this thread gives me little hope for t

  • The dark energy hypothesis is that galaxies appear further away than expected with linear expansion. Expansion seems to be accelerating then, driven by some massive unknown repulsive force called "dark energy". But if there is an alternative explanation why stars appear too dim, then dark energy may not be needed.

Sigmund Freud is alleged to have said that in the last analysis the entire field of psychology may reduce to biological electrochemistry.

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