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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."

139 comments

  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 Anonymous Coward · · Score: 2, Funny

      Hopefully there will be too much matter now and we can all build careers around theories of dark anti-matter.

    3. 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

    4. 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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    5. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 1, Informative
      Not exactly. Try the wikipedia article on dark matter 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 favors models in which the primary component of dark matter is new elementary particles, collectively called nonbaryonic dark matter.
      This article suggests a new model where much more of it might be dust and stars.
    6. Re:So there's more dust than previously thought... by BadAnalogyGuy · · Score: 2, Insightful

      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 dark matter as a theory.

    7. 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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    8. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      Score -3, Does Not Know What The Hell He Is Talking About

    9. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      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). As it has been defined, yes.

      However, the requirement for dark matter as a theoretical entity comes from observations that the mass required to explain motion on the galactic scale is far greater than the observable mass.

      If we now observe that we had previously missed 16.7%* of the total mass present, the amount of inferred dark matter must decrease accordingly.

      Obviously, this doesn't explain away the whole discrepancy. But it does make it somewhat smaller.

      *20/120 x 100
    10. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 1, Informative

      'Exotic' dark matter, which interacts only gravitationally, is a purely theoretical phenomenon. It was invented to try to account for the discrepancy between mass observed through gravitational effects, compared to optical methods.

      With optical methods we now observe more mass through optical methods, and that discrepancy is smaller. The need for the theoretical, exotic 'dark matter', which has never been observed, has been decreased, if this study's results turn out to be accurate.

    11. Re:So there's more dust than previously thought... by IdahoEv · · Score: 2, Informative

      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 dark matter exists than previously believed.

      It's not remotely enough of an increase to explain away all of the missing mass. IIRC there is a lot more dark matter than luminous matter, so an increase of 20% in the amount of luminous matter will only make a small difference.

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    12. 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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    13. Re:So there's more dust than previously thought... by Gerzel · · Score: 1

      Exactly!

      Those calculations prove that just as calculations previously proved that there must be a luminiferous either to transmit light!

    14. Re:So there's more dust than previously thought... by bemo56 · · Score: 0

      It might not be an answer to the unaccounted for "dark matter", but every now and then a astrologist comes forward and says there should be more mass in the universe but is not large enough to be explained by "dark matter". This "dust" could possibly be an answer to some of those theories.

      I'll enjoy watching this pan out
    15. 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...).

    16. Re:So there's more dust than previously thought... by Darfeld · · Score: 1

      This would be great! With that I bet we can achieve antigravity and light-speed travel...

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    17. 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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    18. 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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    19. 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.

    20. 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.
    21. Re:So there's more dust than previously thought... by Jump · · Score: 1

      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'.
    22. 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.

    23. Re:So there's more dust than previously thought... by Vectronic · · Score: 1

      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 trillions of miles or whatever in a light year...

      If the ray of light is bent/redirected, even if its basically infinitely small, means it could be thousands of miles of course by the time it gets here... its not like light travels in famillies, and there are parent photons making the child photons come back on course...

    24. 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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    25. 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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    26. Re:So there's more dust than previously thought... by Vectronic · · Score: 1

      Yeah im aware of that, but I would consider that, on some level, obscuring the light...

      From the wiki you suggested: http://en.wikipedia.org/wiki/Image:BlackHole_Lensing_2.gif

      Granted, the effect is magnified by billions of times with a blackhole, the source is still being obscured slightly as it passes various objects, even if those objects only effect the light via gravitation and not direct refraction, nothing we see is exactly what it (theoretically) looks like given that there isnt a pure vacuumous void absent of everything including the light itself...lol

      Its all distorted to some degree, which, I would also consider obscured.

    27. Re:So there's more dust than previously thought... by The_Wilschon · · Score: 1

      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.

      --
      SIGSEGV caught, terminating

      wait... not that kind of sig.
    28. 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.

      --
      SIGSEGV caught, terminating

      wait... not that kind of sig.
    29. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      No, msauve apparently meant the minimum of 20% additional mass of stars and its gravitational effects. How much mass was accounted to be in the form of dark matter again?

    30. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      if plasma pervades the universe and acts as a conductor then all galaxies would be on the same circuit, hence, the amount of energy observed coming from one galaxy is actually an amalgam of its' own energy and that of its' neighbors.
      dark matter is not needed the electric universe model.

    31. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      I should have scrolled down a bit before writing...

    32. Re:So there's more dust than previously thought... by DarkOx · · Score: 1

      every now and then a astrologist comes forward I think you possibly ment astronomer or astrophysicist, my astrologist is the guy the tells me I am going to bicker with all my friends who insists that my interpersonal relationships are almost soley governed by my sign.
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    33. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      (except to bend the light through gravitious pull). so it is interacting then...you can't have it both ways and "dark matter" is a load of flat-earth, global warming type hocus pocus.

    34. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      It's thought that a fluctuation in quantum mechanics caused what we consider the "Big Bang" and subsequently, the creation of the universe.

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

      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 observation equipment can scan ALL the frequencies of the EM spectrum. We can cover good portions of it, but not all...so there's some vital information missing. Also, cool objects emit vastly less broadband radiation, so objects like old dead dwarfs (red, white and black), "failed" stars like brown dwarfs, exoplanetary systems just to name a few do not contribute much to the "light" we receive from the rest of the universe. And light is really ALL we have to go on in observational astronomy. And let's not get started on neutrino mass... :)

    36. Re:So there's more dust than previously thought... by SurturZ · · Score: 2, Funny

      [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...

    37. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      Your grammatical abortion in the misuse of the word 'effected' makes my brain want to crawl out my ear to escape the signals coming from my eyes, relaying this message of implicit hatred toward the English language and effective human communication.

      Just sayin'.

    38. Re:So there's more dust than previously thought... by tpheiska · · Score: 2, Interesting

      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

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    39. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      Did anyone account all the e/m energy (photons) floating across the Universe, too? Light can be bent by gravity; assuming that, as from E=mc^2=hv (yes, it's a "nu", not a "vee", and it means the frequency), light has its own mass, it shall also produce some gravitational effects on its own: especially the "heaviest" radiations (x-rays, gamma.. is there an upper limit?).
      The overall "strength" of such a cumulative effect is unknown to me, so it might be an amazing problem to solve for any physicist; unless they already performed such an operation and found irrelevant the results.

    40. Re:So there's more dust than previously thought... by Lodragandraoidh · · Score: 1

      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 that throws all of the calculations out the window. Not only do they have more mass than anticipated, they are also closer to us than previously thought.
      --

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    41. Re:So there's more dust than previously thought... by Kashgarinn · · Score: 1

      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.

    42. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

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

      fixed that for you - and the "it can't be dark matter" dweebs.

    43. Re:So there's more dust than previously thought... by Anonymous Coward · · Score: 0

      zing!

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

    Do not look into galaxy with remaining eye!

    --
    Knowledge is power. Knowledge shared is power lost.
  3. Oh NOOOES! by hyperz69 · · Score: 1, Funny

    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!

    1. Re:Oh NOOOES! by sharperguy · · Score: 1

      Something tells me your not being totally serial.

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  4. Stars versus dark matter by anonieuweling · · Score: 3, Informative

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

  5. I have the answer... by Tastecicles · · Score: 1

    it's all those dead Xenomorphs.

    --
    Operation Guillotine is in effect.
    1. Re:I have the answer... by Chris+Mattern · · Score: 1

      Oh, for heaven's sake, call them Zerg. Nobody's called them Xenomorphs since Chau Sara was incinerated.

    2. Re:I have the answer... by Tastecicles · · Score: 1

      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.

      --
      Operation Guillotine is in effect.
  6. 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 Anonymous Coward · · Score: 1, Interesting

      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.

    2. Re:big shake-up by justthinkit · · Score: 1

      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 mass, plus or minus 200 to 2000% (we're not really sure)".

      We are going to need standard galaxy sizes, standard dust distribution, standard distance of comparison (the standard dust distributions alone will probably not be feasible to find) -- and then we will need 10 to 100 of these to do a statistically meaningful comparison.

      Haven't we got better things to do than invent theories based on too many assumptions for too little data? Personally, I've got LeBron to watch in 47 minutes.

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    3. 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.

    4. Re:big shake-up by Anonymous Coward · · Score: 0

      The hubble constant was estimated using systems with predictable true output, and correlating their redshifts, right? Doesn't this mean the whole size/age of universe thing is now messed up?

      I thought part of the reason we needed to invoke dark energy was the idea that the stars farther away look like they're accelerating. How does this new observation affect that?

    5. Re:big shake-up by Prof.Phreak · · Score: 1

      Indeed. Not to mention if this dust turns out to be non-uniform... how do we know the universe is expanding anyway?

      --

      "If anything can go wrong, it will." - Murphy

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

    Researchers found to be half as bright as previously thought.

    --
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  8. So god forgot to turn on the .... by 3seas · · Score: 1

    ....dust collector.

  9. ...shooting in the dark, so to speak... by BemoanAndMoan · · Score: 2, Insightful

    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.

    --

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    1. Re:...shooting in the dark, so to speak... by Falladir · · Score: 2, Insightful

      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.

    2. Re:...shooting in the dark, so to speak... by Tacvek · · Score: 2, Informative

      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 brightness. Distances to objects of known intensity are calculated from the apparent intensity of objects of known actual intensity. However the calculations are surely based on the inverse square law. However the amount of light lost to this dust means that the inverse squares law is not really accurate. That means that the distances to those reference objects have been overestimated. That in turn means the distances to the other objects are incorrect too. If our distance measurements are incorrect, it seems quite reasonable that out calculated orbits are incorrect too. The orbits may be many, many, many times closer to what they should be based on luminous matter alone. That means the total matter needed could drop an enormous amount. If the total amount of matter needed is then quite close to the amount of luminous matter needed, it may be that we do not need to invoke the existence of enormous amounts of exotic matter.

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  10. No shit sherlock! by Anonymous Coward · · Score: 0

    I guess all this really proves is how little we know about space despite professing to have studied it extensively.

  11. Baryonic dark matter... by msauve · · Score: 1

    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?

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
    1. Re:Baryonic dark matter... by cnettel · · Score: 2, Interesting

      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).

    2. Re:Baryonic dark matter... by Anonymous Coward · · Score: 2, Informative

      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.

    3. Re:Baryonic dark matter... by wanerious · · Score: 1

      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 "triangles" across the universe to get a sense of the overall geometry of the universe, much like measuring the interior angles of triangles on a sphere reveals its curved geometry. The observed size of the fluctuations tells us very precisely that the universe, globally, has a flat geometry.


      As said in the article, this only adds maybe 20% to the existing estimate of 4-5% of baryonic matter, so it won't change things much. Also, this dust should be emitting in the IR, so I'd be interested to see if this has been seen already by IR observations, and if not, why not.

  12. it's actually even worse than it is: they assumed by Anonymous Coward · · Score: 0

    that the number of galaxies axis-on to us was EQUAL to the number of galaxies edge-on.

    Perhaps foolish, since a galaxy can be face-on towards us in only a small-variation of orientations, but can be edge-on towards us in 360-degrees times whatever fudge-factor for "nearly-edge-on" is acceptable to gain the effect.

    Therefore, there aren't *equal* numbers of face-on & edge-on galaxies, there should have been MORE edge-on galaxies, and therefore the effect is probably significantly greater than even this bombshell declares.

    Mind You, IANAA, nor a mathematician, so ymmvs, eh?

    Also, *this* assumes that half-way-between was simply not counted, and was a significant portion of 'em:
    if they divided all the galaxies into Either facing, Or edge-on, then who knows at what angle the cut-off was.

    Essentially, though, it's the equal-distribution between sets that bugs me, since it's a staggering assumption...

  13. Olbers' paradox by $0.02 · · Score: 1

    This gives another perspective to it. http://en.wikipedia.org/wiki/Olbers'_paradox

    --
    If enithin kan gow rong it whil. (Murfey)
  14. Galaxies Twice As Bright... by FurtiveGlancer · · Score: 1

    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?

    --
    Invenio via vel creo
    1. Re:Galaxies Twice As Bright... by FooAtWFU · · Score: 1

      Because gas is nearing $4 a gallon!

      --
      The World Wide Web is dying. Soon, we shall have only the Internet.
    2. Re:Galaxies Twice As Bright... by Fumus · · Score: 1

      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?

    3. Re:Galaxies Twice As Bright... by bigd0880 · · Score: 1

      It looks like he is joking in his post. I do not think he is whining.

    4. Re:Galaxies Twice As Bright... by Fumus · · Score: 1

      I know. It just pisses me off every time I hear Americans bitching about gas prices.

  15. 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.

  16. WTF? by jav1231 · · Score: 1

    You can't SEE that one is brighter than before? :P

    1. Re:WTF? by Anonymous Coward · · Score: 0

      Turns out they just forgot to wipe the instruments.

  17. You are ignoring... by msauve · · Score: 2, Interesting

    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?

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
    1. Re:You are ignoring... by Anonymous Coward · · Score: 1, Funny

      Mmmmh... iceburger...

    2. Re:You are ignoring... by Ravon+Rodriguez · · 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.

      --
      Jesus loves me, he loves me a bunch, because he always puts Jiffy in my lunch.
    3. Re:You are ignoring... by shawb · · Score: 1

      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 oversimplification of gravity or nucleosynthesis on certain spacial scales could throw the equations WAY off.

      --
      I'll never make that mistake again, reading the experts' opinions. - Feynman
  18. Doesn't this screw up lot of other things, too... by msauve · · Score: 1

    Aren't all astronomical distance measurements, which are fundamentally based on brightness (except for parallax), now subject to revision?

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
  19. What a waste by Polski+Radon · · Score: 1

    The galaxies are still a waste of space.

  20. Obligatory 7th Century Zen reference by xactuary · · Score: 1
    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?

    --
    Say hello to my little sig.
  21. LOL. by msauve · · Score: 2, Insightful

    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.

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
    1. Re:LOL. by Ravon+Rodriguez · · 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.

      --
      Jesus loves me, he loves me a bunch, because he always puts Jiffy in my lunch.
    2. Re:LOL. by orclevegam · · Score: 1

      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 we observed in one area, and what was observed in another as well as issues with various models and predictions. If it now turns out that some of those observations will have different discrepancies, or possibly that some of the models will need to be adjusted slightly, it could have all kinds of effects as to the expected amount of "dark matter" we're currently trying to observe.

      First, we need to figure out what these observations mean, and what effects that have on established and well accepted theories and measurements. Once we've got that nailed down, then we can go on to see what this does to the less established theories like dark matter.

      --
      Curiosity was framed, Ignorance killed the cat.
  22. incorrect logic by Anonymous Coward · · Score: 0

    They assumed that the number of galaxies axis-on to us was EQUAL to the number of galaxies edge-on.

    Yes, and this is correct. We should expect that these two types of orientation would be observed equally; that is to say, the distribution of all possible orientations is is uniform. Another way of saying that is that there is no privileged position (no "special" galaxy) in the universe to which everything appears one way while appearing another way to observers anywhere else.

    ...a galaxy can be face-on towards us in only a small-variation of orientations, but can be edge-on towards us in 360-degrees times whatever fudge-factor for "nearly-edge-on" is acceptable to gain the effect.

    Galaxies, like any other orientable object, have a single axis of orientation. However we define it, all other axes are simple transformations of this it, so we just pick a convenient one such as "right handed" axis of rotation. Our line of sight provides an orientation to which we can compare the axes of galaxies, and the result is an angle, which is always a two-dimensional thing, no matter the number of dimensions in question.

    The problem with your reasoning is to think of face-on-edness as "only a small-variation of orientations" while you're willing to accept a large variation (in your words "360-degrees times whatever fudge-factor for "nearly-edge-on" is acceptable") for edge-on-edness. The angle is always just some number of degrees (radians). Just pick a threshold for "close enough": say, everything within 15 degrees of 0 (face on) and 90 (edge-on). If you want to consider *all* spiral galaxies (or individual stars, or whatever), just figure out if the angle is closer to 0 or 90. If every orientation of galaxies is equally represented in the universe, then the number in each category (edge- and axis-on) will be the same, no matter what angle you deem "good enough".

    Therefore, there aren't *equal* numbers of face-on & edge-on galaxies, there should have been MORE edge-on galaxies... ...Mind You, IANAA, nor a mathematician...

    If you still don't follow the math (which is just logic, so give it another go!), maybe you can see the error from a related but qualitatively different argument:

    You claim that from our vantage point in the universe, here on earth in the Milky Way in The Place The Milky Way Inhabits, there are more galaxies pointing away from us (edge-on) than toward us. If your mathematical reasoning were correct, the same would be true of every other place in the universe. So you're claiming that more galaxies point away from any point in the universe than point toward it. Those galaxies have to point somewhere though! So this should provide intuition that your idea of "pointing toward" is narrow compared to your idea of "pointing away". The only alternative to that is that you really think that this point in the universe is different from all the other points (i.e. we have the privileged position in the universe). Essentially, though, it's the equal-distribution between sets that bugs me, since it's a staggering assumption... You seem to be denying the Copernican Principle here, so perhaps my second line of reasoning is lost on you, and you will have to rely on the first.

    It's just as easy to say that we have a different kind of place in the universe as it is to say that the distribution of spiral galaxy orientations is NOT uniform. They are in fact exactly the same thing, because galaxies that point away from certain places in the universe have to point toward other places.

    it's a staggering assumption...

    It is true that we can only examine Nature and if we don't agree, we, and not Nature, are in the wrong. However, it is not at all an *assumption* as you so naively put it. Perhaps it is also an assumption that it is the sun that goes around the earth, to someone unfamiliar with the evidence that it the other

    1. Re:incorrect logic by Anonymous Coward · · Score: 0

      I guess geometrical intuition must be inversely proportional to the amount of prose, because you are offbase and writing a lot about it.

      We live in 3 spatial dimensions, so there are more ways to be edge-on than face-on.

      To discretize a bit, imagine a die: 1,6 are the galactic poles, and 2,3,4,5 are the rim. Throw a "galaxy" on the floor, you'll see that it lands edge-on 2/3 of the time.

      To reason about the continuous case, choose a random unit vector u, and look at the distribution of abs(arccos(u.x)). You'll see that it isn't a uniformly distributed angle between 0 and 90 degrees.

    2. Re:incorrect logic by Anonymous Coward · · Score: 0

      I guess geometrical intuition must be inversely proportional to the amount of prose, because you are offbase and writing a lot about it. It almost always takes more effort to correct something that's wrong than it did to create the wrongness to begin with. That's the very reason most scientists tend not to debunk junk science, and why they write "come to office hours" on fundamentally wrong homework problems instead of trying to write it all out. (Also, the temptation can be very great to respond to such self-assured wrongness and insults with further insults.)

      We live in 3 spatial dimensions, so there are more ways to be edge-on than face-on. A case in point. You just made a (very...) wrong statement in one sentence and backed it up with three more bits of incorrect reasoning. I could just state the correct answer and then do some hand-waving or irrelevant statements, but in this case you've already seen the correct answer and you just don't seem to be comfortable with it. So a) we could just contradict each other, b) I could let your incorrect statement stand, or c) I would have to illustrate the situation in more detail.

      To discretize a bit, imagine a die:... Inapt analogy. This is the same error made by the OP. There are more "edge" sides than "face" sides, but there are not any more angles between the galactic axis and the line of sight (the gravity vector, in your analogy). If the die example isn't clear (it's misleading and inappropriate), picture the continuous case of a perfectly balanced marble with an axis drawn through it, rolled randomly on a perfectly flat surface.

      To reason about the continuous case... ...
      You'll see that it isn't a uniformly distributed angle between 0 and 90 degrees. That's incorrect. The area swept isn't uniformly distributed between two equal angles chosen with respect to an axis, but the angles themselves are equal; angles are two-dimensional things. There's the axis in question (treat as 2 coincident anti-parallel vectors) and the displacement vector from the observation point to the galaxy in question. (Not even the dimensionality of the vector space in question matters. That's why the same old dot product for R2 works the same way for R3 and R50 and every other real vector space.)

      You understand (at least) one chunk of geometry, but you're trying to use it to reason about a situation in which it just isn't the right model. It's an incorrect model (only one), and it leads to incorrect physical intuition about the situation.

      If you're interested in why the area is irrelevant and why the angle is always the same, I tried to explain it a couple more ways here:

      http://science.slashdot.org/comments.pl?sid=556574&cid=23458768
    3. Re:incorrect logic by Anonymous Coward · · Score: 0

      picture the continuous case of a perfectly balanced marble with an axis drawn through it, rolled randomly on a perfectly flat surface.
      That's a great analogy. Now mark in black the region the marble needs to land to be face-on. Mark in red the region it needs to land to be edge-on. The black region is two small dots at the poles, the red region is a ring around the equator. It is very clear that the red region has larger area than the black region, hence a tiny galaxy contained in a randomly thrown marble has a bigger chance of landing edge-on than face-on, which is what a bunch of people are trying to hammer into your head.

      So you're wrong with the conviction of being right which in general can be quite dangerous. I hope no one is putting you in charge of something important.
    4. Re:incorrect logic by Anonymous Coward · · Score: 0

      The black region [face-on, where the axis protrudes the marble] is two small dots at the poles, the red region [the edge-on region] is a ring around the equator. It is very clear that the red region has larger area than the black region, Yes; this is exactly the relative areas idea described in the other posts. But now:

      hence [the marble] has a bigger chance of landing edge-on than face-on This is inapplicable and misleading: the angle between the marble's axis and the surface's normal is *not* more likely to be 90 degrees than 0 degrees! Rotation scales the area in question, but it does not scale the angle in question, and it is the angle that determines orientation. All possible orientations of the marble are equally likely, which is the same as saying that all possible angles are equally likely. You're claiming that different axial rotations contribute many successful orientations at 90 degrees from normal, but that different axial rotations contribute only one successful orientation at 0 degrees from normal.

      So you're wrong with the conviction of being right which in general can be quite dangerous. I hope no one is putting you in charge of something important. Your petulance is noted. My conviction comes from my knowledge of mathematics. I think you either did not bother to read my other arguments or the exposition contained there went over your head. If you had read/understood it, you would have done at least one of a) explained why you thought the reasoning was wrong, b) berated me for those arguments instead of the clinging to my grudging modification of your die analogy, or c) been convinced and acknowledged as much or responded with silence. You did none of these things.

      [the unequal area analogy] is what a bunch of people are trying to hammer into your head. I think I've demonstrated amply that I understand the geometry of that situation, starting with my very first response. I also think I've illustrated both why it is inapplicable and what the correct analysis is instead.

      I don't find your reply constructive, but I'm not sure how constructive you meant it to be either. Read/think about it more, be more articulate, or bite your lip. You could be a little less caustic too, but I'd settle for the first two.
    5. Re:incorrect logic by Anonymous Coward · · Score: 0

      All I can say is paint a rim on a hundred marbles, throw them all on the floor, and count how many land face-on vs edge-on. If you're unable to see what would happen in your head, then only an experiment will do.

  23. 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
  24. Actually, they don't want to admit it but... by jpellino · · Score: 1

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

    --
    "Win treats sysadmins better than users. Mac treats users better than sysadmins. Linux treats everyone like sysadmins."
  25. Re:Doesn't this screw up lot of other things, too. by Tacvek · · Score: 2, Interesting

    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.

    --
    Stylish sheet to fix many problems in Slashdot's D3: https://gist.github.com/801524
  26. Re:$4 a Gallon by FurtiveGlancer · · Score: 1

    If hydrazine is cheaper, maybe we should all drive rocket powered cars! Tailgaters beware!

    --
    Invenio via vel creo
  27. 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).

    1. Re:Because... by Anonymous Coward · · Score: 0

      I'd consider this fairly solid evidence of the existence of non-baryonic matter.

    2. Re:Because... by tpheiska · · Score: 2, Interesting

      (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.
      --
      "wahts woring iwth my tyoping?"
  28. Re:it's actually even worse than it is: they assum by naasking · · Score: 1

    You can also rotate the face-on galaxies about their axes too, so the assumption seems sound to me.

    --
    Higher Logics: where programming meets science.
  29. Then PLEASE... by Jane+Q.+Public · · Score: 1

    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?

    1. Re:Then PLEASE... by Tim+C · · Score: 1

      Has science education failed that miserably in recent years?

      Yes, yes it has. See for example ID vs evolution.

      --
      It's official. Most of you are morons.
  30. Mod up, please. by Jane+Q.+Public · · Score: 1

    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.

    1. Re:Mod up, please. by memorycardfull · · 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.

  31. 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
    1. Re:Furthermore... by X10 · · Score: 0

      Surely, there's a database somewhere with distances and galaxy types which could be easily looked at to see if that's true. I think the uncertainty in distances of galaxies is greater than the difference in distance for facing and edge-on galaxies.

      --
      no, I don't have a sig
  32. 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.

    --
    Equine Mammals Are Considerably Smaller
  33. Because it has always ended badly. by Jane+Q.+Public · · Score: 2, Funny

    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.

    And the time before that, Andromeda called little Sagittarius an ugly dwarf, which started a huge row, and Tucana ended up giving us all the Boötes.

    So, this has not exactly turned out to be the best of neigborhoods. I mean, with friends like these, who needs NGCs? No wonder everybody has been putting up those dust fences.

  34. Re:Doesn't this screw up lot of other things, too. by Anonymous Coward · · Score: 0

    Not quite. It has implications for standard candles, but astronomers are working on standard rulers.

    There are few distance measurements based (or hinged) *purely* on amplitude (e.g. the mass-brightness relation), and those are studied regularly because they are unsafe for any number of reasons, not least of which is lensing and absorption by cold gas clouds (this is the Cepheid variable extinction problem).

    The worry that these relations can be unreliable led to the Tully-Fisher relation, which attempted to correlate mass-brightness with redshift introduced in rotating galaxies. This was very clever and useful, since it was readily demonstrated that galactic rotation speeds are directly related to galactic mass (which is measurable in a variety of ways), and also, relevantly, led to the discovery that galaxies were often much less luminous than expected from the mass-luminosity relationship.

    Thus, "dark" (literally non-luminous) matter accounted for a substantial amount of mass -- enough to speed up galaxy rotation and inter-galaxy orbital motions (and deepen lensing, and influence the thermalization of inter-galactic matter with respect to the CMBR, and otherwise show up in tests for mass).

    The bright side (no pun intended) is that at large ranges (extragalactic distances), luminosity was not really an especially interesting tool for distance measurement as much as a check on relationships among more useful tools (expansion and dynamical parallax and angular relationships generally, cosmic redshift, eclipsing studies, and so forth). Generally, SNIa light curves are useful.

    These problems led to the discovery of the Diamater-sigma relation for elliptical galaxies, which, as observational tools improve, is liable to become the most useful tool in extra-galactic distance measurements, as it avoids some problems in Tully-Fisher, which has some important assumptions about galactic rotation (and is not useful for nonrotating galaxies).

    Finally, amplitude attenuation by normal matter has workarounds, since you can track absorption-reemission spectral lines, and since normal matter clouds are often transparent in a variety of frequencies (typically IR and radio) which still permit useful magnitude-distance calculations.

  35. What about the Supernovas then? by tagew · · Score: 1

    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

  36. Re:what what? by Mental+Maelstrom · · Score: 0, Troll

    True. This is quite a scandal! I mean - "how could science be wrong!?!?". LOL.

    I wonder how soon will they discover carbon dating is twice as erronous as previously though...

  37. 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.
    --
    "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.

    2. Re:Wrong... by Squalish · · Score: 1

      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 energy - which they can barely begin to agree on, much less explain.

      Occam's razor, combined with articles like this, offers a strong suggestion to those of us not versed in your particular specialty, that you're simply missing out on some fundamental observation. Perhaps in 2031 a physicist will smack themselves over the head and go "But of course WMAP came out even, the intergalactic dust that we'd always assumed was trivial ended up diffusing the CMB!!" or some other obvious-in-retrospect observation, and the entire need for 'dark energy' and 'dark matter' will cease to exist... Myths that helped astronomers of their day reason out what they observed much as the Zodiac did millenia earlier.

      One question - could this observation (that there exists a larger-than-expected galactic halo of interstellar dust (rather than dark matter)) at least be used to explain the galactic rotation rate problem?

      --
      People in Soviet Russia, however, appear to be afflicted with amusing juxtapositions of the aforementioned situation
    3. Re:Wrong... by wanerious · · Score: 1

      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 realization that the matter was somehow exotic was slowly revealed as we tried to study its properties. Of course its not "undetectable", since it is clearly manifest in the rotation curve anomalies of galaxies, the dynamics of clusters, and the lensing effects on cosmological scales.

      Even then, all their calculations couldn't agree with cosmological data, so they had to bring up dark energy - which they can barely begin to agree on, much less explain.


      I think pretty much everyone agrees with the concept and dynamic effect of "dark energy" (horrible name!), but you are right that no one has a good explanation for it as of now. It's a very exciting time in cosmology.

      Occam's razor, combined with articles like this, offers a strong suggestion to those of us not versed in your particular specialty, that you're simply missing out on some fundamental observation. Perhaps in 2031 a physicist will smack themselves over the head and go "But of course WMAP came out even, the intergalactic dust that we'd always assumed was trivial ended up diffusing the CMB!!" or some other obvious-in-retrospect observation, and the entire need for 'dark energy' and 'dark matter' will cease to exist... Myths that helped astronomers of their day reason out what they observed much as the Zodiac did millenia earlier.


      It is too true that whatever model we construct to explain nature today will be refined, and perhaps overturned, in the future. But we can't just throw up our hands and wait for those relevations to happen. On the contrary, the spirit of Occam is alive and well in cosmology. Is there a simpler explanation that will unify the above phenomena? (rotation curves, cluster dynamics, lensing) If so, a legion of astrophysicists would like to follow your lead. I'd be very surprised if something like dark matter were not to exist. It's very hard to imagine something that acts *exactly* like clouds of weakly-interacting matter that is *not* clouds of weakly-interacting matter.

      One question - could this observation (that there exists a larger-than-expected galactic halo of interstellar dust (rather than dark matter)) at least be used to explain the galactic rotation rate problem?


      No --- the anomalous curves exist for almost all sampled spirals (in fact, there was a recent report that there was one interesting spiral that did *not* exhibit such a curve), and notably, for *ours*. Such an enhanced ring of dust would obscure observations of the outskirts of our own galaxy in a striking and obvious way, and it would be easily seen in neighboring galaxies as well. Further, the rotation problem is such that an amount of mass equal to about 8-9 times the stellar mass of galaxies has to be postulated. There is no evidence of anywhere near that much dust even in this latest survey.

  38. Distance ... by PinkyGigglebrain · · Score: 1

    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?

  39. Why would facing galaxies be obscured more? by X10 · · Score: 0

    I don't think that dust obscures galaxies facing us more than galaxies we see edge-on. Dust reduces the light we see by a percentage. Galaxies we see edge-on seem brighter in the middle, but the percentage remains the same.

    --
    no, I don't have a sig
  40. Re:incorrect logic^2 by msauve · · Score: 1

    if you want to consider *all* spiral galaxies (or individual stars, or whatever), just figure out if the angle is closer to 0 or 90. If every orientation of galaxies is equally represented in the universe, then the number in each category (edge- and axis-on) will be the same, no matter what angle you deem "good enough".
    If I understand your argument, you are incorrect.

    For sake of example and clear terminology, picture a disc galaxy as being a disc in the earth, the edge aligned with the equator, and observers are equally spaced throughout the sky. It is then "face-on" for observers near the celestial poles (+90 and -90 declination), and "edge-on" for observers near the galactic equator (0 declination). This is exactly analogous to a single observer watching multiple randomly oriented discs.

    If we simply chose which an observer is closer to (pole or equator), we will divide observers into two sets, those within 45 degrees of the equator ("edge on"), and those within 45 degrees of the poles ("face on").

    It should be very clear, just by looking at a globe, that the angular area of the former is much greater than that of the latter. In fact, without doing any spherical geometry, I can tell that it is more than twice as large.

    Let's call the area within 45 degrees of one pole 1 unit, which gives us 2 units of "face on" observers. For "edge on" observers, we have 1 unit at 0 degrees longitude, and other, non-overlapping areas centered at 90, 180, and 270. That gives us twice as many "edge on" observers as "face on" observers, and there are still unaccounted areas within 45 degrees of the equator.

    You claim that from our vantage point in the universe, here on earth in the Milky Way in The Place The Milky Way Inhabits, there are more galaxies pointing away from us (edge-on) than toward us.
    The OP is correct, depending upon how "face/edge-edness" is defined. If one takes a simple but incorrect approach, as you have ("everything within 15 degrees of 0 (face on) and 90 (edge-on)", the conclusions can be subject to significant error. I believe that was his point.
    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
  41. 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.
  42. Calculated Distances have to be fixed by yoyoq · · Score: 1

    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.

  43. Same to you... by msauve · · Score: 1

    How can pointing to a picture which claims to observe the unobservable not be funny?

    And here's your CMB, predicted long before Big Bang cosmology, and more accurately, too.

    --
    "National Security is the chief cause of national insecurity." - Celine's First Law
    1. 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.
    2. Re:Same to you... by EvilErik · · Score: 0

      (Score:5, Science. It works, bitches)

  44. Re:incorrect logic^2 by Anonymous Coward · · Score: 0

    Spherical geometry isn't hard.

    The fraction of a sphere within angle x of a pole is 1-cos(x).
    The fraction of a sphere within angle x of the equator is sin(x).

    With x = 45 degrees, the fractions are approximately 0.293 and 0.707.
    With x = 15 degrees, the fractions are approximately 0.034 and 0.259.

  45. Re:Doesn't this screw up lot of other things, too. by wanerious · · Score: 1

    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 there isn't as much H-beta as we expect, based upon the H-alpha, we associate this with dust. We can even calculate the column density of dust in this way. Surely this has been done for most of these galaxies.

  46. Re:incorrect logic^2 by Anonymous Coward · · Score: 0

    If I understand your argument, you are incorrect. You have not understood the argument:

    [you establish a globe and sky analogy] ...This is exactly analogous to a single observer watching multiple randomly oriented discs. ...
    It should be very clear, just by looking at a globe, that the angular area of the former is much greater than that of the latter. This is the error, and it is exactly the one made by the GP and shared by a few of the other posters here. The areas you describe are indeed unequal, but they do not contain different distributions of edge/face-on spiral galaxies. Within each area, the ratio of edge- to face-on spiral galaxies is the same (1:1) even though the total number of galaxies subtended by the solid angle is proportional to the area.

    To illustrate this, let's just choose the same coordinate styles, but in different orientations (i.e. we'll choose different coordinate systems). You choose Earth's polar axis and divide the galaxies into two groups of different sizes: the conic section within 45 degrees of the poles, and everything else. If I choose any other axis but yours, I have the same relative areas, but they have different galaxies in them. The choice of coordinate system would either change the answer we got or move galaxies around in the space! This must not be the right approach. If you don't see why right off, let's drop it because the globe analogy is a red herring; try a different approach:

    Forget the areas and solid angles and spherical coordinates, because they seem to be confusing the issue. Consider a thin shell of galaxies (1 layer thick), at some radial distance from a point (your vantage point). There are no poles or equators or confusing coordinate systems. No matter which direction you look, you are always looking *away* from your position, toward a galaxy on the thin shell. If the galaxies have random orientations, the same number will point "away" as will point toward you.

    The large-scale structure of the universe is isotropic, so no matter which shell you choose and thus which observation point you choose, the picture is the same. If more galaxies point away from certain points than others, then some points have more galaxies pointing toward them than others since galaxies have to point somewhere! I'm not sure how I can motivate this any further.

    If one takes a simple but incorrect approach, as you have ("everything within 15 degrees of 0 (face on) and 90 (edge-on)" This is the correct approach, and I took special care to explain the two-dimensional nature of angles so as to assuage the OP's error. Sorry if that wasn't clear.

    ...the conclusions can be subject to significant error. I believe that was his point. Indeed, an incorrect approach could lead to significant error, and the OP thought he was illustrating such an error. But he was the one in error, and the professional cosmologists did not make a basic (undergrad vector analysis) error while choosing my isotropic and uniform "misinterpretation" instead. It bothers me to argue by authority, so I took the effort to explain the situation rather than say "cosmologists are smart and if they don't see a problem at primary/undergrad analytical geometry level then you're wrong if you think they missed such a simple thing."

    Remember: galaxies can't point away from every point at once, and the distribution of galaxies is isotropic,. (The distribution of galaxies themselves isn't locally isotropic because of clusters and superclusters and voids and supervoids, but those structures are isotropically distributed; that's why I used the term "large-scale structure" earlier.)
  47. Re:incorrect logic^2 by Anonymous Coward · · Score: 0

    Spherical geometry isn't hard. No, but it isn't relevant to the matter at hand either, so even if the parent had articulated with mathematical language rather than qualitative English, the geometry wouldn't be any more applicable to the physical situation.

    The fraction of galaxies subtended by an angle changes only the number of galaxies in question; not their orientation relative to the viewer and not the distribution of orientations in each subtended angle. All you'd have to do to change which galaxies you thought were pointing a certain way would be to choose a different axis by which to project your celestial sphere: the small portion near the poles could just as easily have been chosen as part of the large portion near the equator. Choice of coordinate system should not have any effect on the answer you get, and if it does you know you're doing something wrong.

    I went over this in a bit more detail here:

    http://science.slashdot.org/comments.pl?sid=556574&cid=23458768/
  48. One things for sure by cavebison · · Score: 1

    Astrologers will take this in their stride.

  49. dust, redshift, distance by Anonymous Coward · · Score: 0

    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. The universe is isotropic and homogeneous, so since we see the same number of face as edge galaxies in every direction, the edge spirals would be at higher redshift. We know the redshift of every galaxy from the closest on out. (In fact, Andromeda is the galaxy closest to us at about 2 million light years, and one of only a few that has a "negative redshift", i.e. blueshift. All the blueshifted galaxies are very close to the Milky Way.)

    Redshift measurements are actually sensitive enough to compare much smaller differences in velocity: spiral galaxies' rotation curves, even that of the Milky Way, are measured by comparing Doppler shifts of the 21cm neutral hydrogen line. Interstellar dust is transparent at this wavelength. Even if we're observing a wavelength in the far infrared as in this study, any absorption or emission effects would simply be superimposed on top of the already shifted spectrum and not affect the shift itself.

    It would also be interesting to know how much this affects the Hubbel constant. Here's how that would work:
    The Hubble constant can be calculated by correlating redshift values with other means (the distance ladder), often using brightness. So anything we associated with a redshift value that looks farther away than it is will indicate that redshift is *higher* at that distance than we thought, according to the correction factor they propose in the paper. (That factor depends on the position of the object within a spiral galaxy, the orientation of the galaxy, the age of the galaxy, and probably a couple other things I'm forgetting.)

    Depending on how much each measurement changed, how many measurements were involved, and the pattern that emerged, they could do several things to the value of the Hubble constant. 1) not change it at all, 2) revise its value downward.

    But, the value of the Hubble constant we have now is corroborated by other measurement methods that don't depend on pinning distances on luminosities. We also have the Sunyaev-Zeldovich effect and gravitational lensing, so I don't think it will change our estimate of the Hubble constant much at all, and certainly not much compared to the uncertainty.

    there would be no reason to think similar dimming doesn't occur from interstellar dust within the Milky Way. Quite right. It's called extinction:
    http://en.wikipedia.org/wiki/Extinction_(astronomy)

    If so, then extragalactic objects should be dimmer (and more distant based on flawed calculations) on average when they lie in certain directions. Right idea, but backward at the last step. If we look at a star through more dust than we thought, it is actually brighter than we thought. We know what kind of star (or supernova or whatever) it is through spectral analysis, so brighter means closer. If we're looking at galaxies through our own galaxy's dust, then we're using redshift and the the dust doesn't affect that.
  50. Bad title by Anonymous Coward · · Score: 0

    Blocking "as much as" 50% of the light means that the galaxies are "up to" 100% brighter than previously realized. And we all know to be skeptical when we hear "up to." That's an upper bound, but no marketer will say "you'll save less than 15% by switching to Geico."

  51. T is for Theory by huckamania · · Score: 1

    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.

  52. Esoteric topic vs Yes men by pokerdad · · Score: 1

    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 the human race. Either the subject matter is so esoteric that the experts who are here cannot explain it to an audience of nerds (and if this is true, what chance does the non-nerd have?) or the experts are so set in their ways that nothing can change them. The reason I weep for humanity is that you can see how similar problems exist on so many other issues; that either the intelligent layman has no chance to understand (and what could that mean when the unintelligent layman has to pass laws on a given topic, though obviously not this one), or the experts aren't really experts at all, just yes men who will parrot whatever in vogue theory they come across.

  53. Does this eliminate "dark energy" then? by peter303 · · Score: 1

    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.

    1. Re:Does this eliminate "dark energy" then? by RolfRomeo · · Score: 1

      Then consider the increasing amount of dust between the object and the observer with distance, and you can slap another variable onto the formulaes.

    2. Re:Does this eliminate "dark energy" then? by RolfRomeo · · Score: 1

      More specifically, now that my head has cleared a bit: Wouldn't, as a consequence of this discovery, the intensity of light for far-away stars and galaxies fall of by an additional factor of 1/D_obscure*r, where D_obscure(=D)is a function of the average density of dust per l.y. (or integrated over the distance if you will) in the current direction, and of course with the optical properties of the dust. I propose Pettersen's 1st: (1. draft :) ) The intensity of light received from a distant stellar body that is obstructed by stellar dust is proportional with 1/(D*r^3). D as loosely defined above. --- Also as grandparent mentions, this could have profound effects for black energy, as the move from r^2 to r^3 should mitigate the need for acceleration to explain distances. IANAP

  54. Simply not true by Jane+Q.+Public · · Score: 1

    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 two hypotheses, Occam's Razor argues very strongly in favor of MoND.