Galaxies Twice As Bright As Previously Thought 139
Astronomers led by Simon Driver of Scotland's University of St. Andrews have discovered that interstellar dust shades us from as much as 50% of the light emitted by stars and galaxies. The scientists compared the number of galaxies we could see "edge-on" against the number which were "facing us," reasoning that dust would obscure more of the former, since we already receive less light from them. 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."
So there's more dust than previously thought... (Score:5, Interesting)
Re:So there's more dust than previously thought... (Score:4, Informative)
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hence, "obscure"
Re:So there's more dust than previously thought... (Score:5, 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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So diffusion, by means of gravitational pull is a form (or an act?) of obscuring the object by diffusing the light emitting/reflecting from the object.
It does not matter how fractionally small this diffusion is, the point is... it is diffusing the light.
And I really dont understand how you made the greater distance seem less important, like the flashlight gets effected more in its span of 10 feet than tr
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From the wiki you suggested: http://en.wikipedia.org/wiki/Image:BlackHole_Lensing_2.gif [wikipedia.org]
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
Re:So there's more dust than previously thought... (Score:4, Informative)
Re:So there's more dust than previously thought... (Score:5, Interesting)
Furthermore, the definition says nothing about "non interacting," and it seems to me that the real definition is more like "matter we know must exist because of its gravitational effects, but for which we can't account." (i.e. either we can't see it, or we're not looking correctly because we dont' know what we're looking for) Just as with the dust at hand, how do we know it is "non interacting," or that it "doesn't emit or reflect" radiation, if we don't know what it is?
If this newly found dust blocks light, what does it do with the visible light it absorbs? Seems to me, it must re-radiate it (at a lower frequency, like a black object in the sun?) So, if it re-radiates the energy it absorbs, then why hasn't that been noticed before? Is all this re-radiated energy just part of the cosmic microwave background radiation?
Re:So there's more dust than previously thought... (Score:5, Informative)
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.
Re:So there's more dust than previously thought... (Score:4, Informative)
Re:So there's more dust than previously thought... (Score:5, Interesting)
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Because... (Score:5, Interesting)
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).
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Simply not true (Score:2)
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
Re:So there's more dust than previously thought... (Score:5, Interesting)
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.
Re:So there's more dust than previously thought... (Score:5, Informative)
1)Dark matter is indeed postulated to account for the discrepancy between gravitational measurements of the mass distribution of galaxies vs evidence from other sources.
2)We know that dark matter can't be accounted for by large mass objects (like planets, asteroids, dust, etc) because CMB measurements tell us that the total amount of baryonic matter ('normal' matter made up of protons and neutrons) is a small fraction of the total matter in the universe (around 15%). So it must be made of heavy non-baryonic particles. This, by the way, is the reason why the discovery mentioned in TFA has little impact on dark matter. There is already an upper limit on the amount of baryonic mass in the universe, irrespective of what we see with telescopes.
3) We know that these particles can't interact electromagnetically or with the strong force, otherwise they would end up in atoms (either as part of the nucleus or orbiting the nucleus). In this case, these atoms would be much heavier than normal atoms and we would see evidence of them in the spectral lines of stars.
4)That leaves us with particles which interact only through the weak force, like neutrinos. We have also found that dark matter plays an important role in the formation of structure in the universe, and in order for structure to form in the way it has, the dark matter must be moving at non-relativistic speeds at that time. This rules out the neutrino, which would be moving at speeds very close to the speed of light at that time.
Wrong... (Score:4, Insightful)
Your circular logic fails to prove that dark matter exists.
Re: Dark Semantics (Score:5, Interesting)
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.
Same to you... (Score:2)
And here's your CMB [dfi.uem.br], predicted long before Big Bang cosmology, and more accurately, too.
Re:Same to you... (Score:4, Informative)
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.
Re:Wrong... (Score:4, Interesting)
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.
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The basis for every response here is - the study suggests this is a basic, fundamental, empirical fact of astronomy that a century of viewing galaxies has managed to overlook. In order to establish your upper limit, astrophysicists had to postulate exotic, undetectable forms of matter. Even then, all their calculations couldn't agree with cosmological data, so they had to bring up dark en
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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
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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...
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Unless an astrophycisst (sic - lazy) has actual numbers as to what % of the total matter is "dark"...
There are no such thing as actual numbers at astronomical distances.
The distance to a given star can only be accurately triangulated for relatively short distances (several light years). Beyond that astronomers use 'standard candles' - such as cepheid variable stars and supernovae - to estimate the distance to a star using the known luminosity of these adjacent objects.
That being said, if we determine that our observations of the luminosity of the given objects is incorrect due to this absorption then tha
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Where that discrepancy lies, that's the big hunt, but believing that dark matter exists is ridiculous.
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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.
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Re:So there's more dust than previously thought... (Score:4, Interesting)
Re:So there's more dust than previously thought... (Score:5, Interesting)
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From the summary: there is about 20 percent more mass in stars than previously thought
Even if we assume that "vastly more mass" means 51% of all mass in the universe, we still have the problem of a lot of missing mass even with the increased estimations of stellar mass and interstellar dust.
This study may increase our precision in our calculations of universe mass, but it is by no means eliminating dar
You are ignoring... (Score:3, Interesting)
Since there is no evidence for exotic black matter (other than observed gravitational effects), doesn't Occam force us to assume that the gravitational effects which we do observe are likely due to what we know about?
Why would it be incorrect to say this newly discovered dust has mass x (equal to the necessary dark matter mass), which scientists can determine from it's gravita
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LOL. (Score:2, Insightful)
You obviously don't know how to apply Occam if you prefer an unproven hypothetical to something which is observably evident.
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Dark Matter was postulated to account for a discrepancy between what w
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It is also possible that our calculations are off with some portion of the equations: a fundamental misunderstanding or overs
Tail wagging the dog... (Score:5, Insightful)
The emperor has no clothes.
Then PLEASE... (Score:2)
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?
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Yes, yes it has. See for example ID vs evolution.
Re:So there's more dust than previously thought... (Score:5, Interesting)
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.
T is for Theory (Score:2)
In my day, the universe was composed of matter and energy, and we liked it that way.
Baryonic dark matter... (Score:2)
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?
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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.
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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
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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
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Those calculations prove that just as calculations previously proved that there must be a luminiferous either to transmit light!
Doesn't this screw up lot of other things, too... (Score:2)
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Furthermore... (Score:4, Interesting)
Surely, there's a database somewhere with distances and galaxy types which could be easily looked at to see if that's true.
It would also be interesting to know how much this affects the Hubbel constant.
Finally, the conclusions seem to only recognize the effect within other galaxies, but there would be no reason to think similar dimming doesn't occur from interstellar dust within the Milky Way. If so, then extragalactic objects should be dimmer (and more distant based on flawed calculations) on average when they lie in certain directions. (e.g. most dimming when looking through the galactic center near Sagittarius).
Re:Doesn't this screw up lot of other things, too. (Score:2)
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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'.
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Warning! (Score:5, Funny)
Oh NOOOES! (Score:1, Funny)
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Stars versus dark matter (Score:3, Informative)
I have the answer... (Score:2)
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Saying that, she can blow me out the airlock any time she likes.
big shake-up (Score:5, Interesting)
Anyone case to elaborate on what kind of shake-up this is going to have for astronomy and cosmology?
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Re:big shake-up (Score:4, Informative)
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And just before we start shaking, can someone point me to the calculation for the exact ratio of "full face" to "oblique" galaxies we were expecting to see? Starting with a definition of how full is "full". 51%? 90%? 99%? 99.99% I think it is more likely a random differentiation, like say 98.7654321%, or "Gee, it looks pretty full on to me, Jim". All of which makes the findings more like "20% more m
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Re:incorrect logic^2 (Score:2)
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 observe
In other news... (Score:4, Funny)
Mod up, please. (Score:2)
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So god forgot to turn on the .... (Score:2)
...shooting in the dark, so to speak... (Score:2, Insightful)
Of course, it could prove to be equally inaccurate by failing to take into account some other grand unknown that in turn will prove to be obvious, but I can't help but feel sorry thinking of all those academics sitting around a table of hardly-touched pints and muttering "well, fuck..." to no one in particular.
--
"You're only as smart as the guys yo
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Olbers' paradox (Score:1)
Galaxies Twice As Bright... (Score:2)
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?
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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?
Re:$4 a Gallon (Score:2)
Because it has always ended badly. (Score:3, Funny)
The time before that, Barnard's brought too much wine, which resulted in that whole inappropriate Sextans thing, remember? Canis Major tried to stick his huge Phoenix into Virgo and little Ursa Minor, and Draco was caught Fornaxing with Carina.
A
why is this a news? (Score:5, Interesting)
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.
WTF? (Score:2)
What a waste (Score:1)
Obligatory 7th Century Zen reference (Score:1)
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?
Actually, they don't want to admit it but... (Score:2)
Not Intergalactic Dust... (Score:5, Informative)
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.
What about the Supernovas then? (Score:1)
Distance ... (Score:2)
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?
Calculated Distances have to be fixed (Score:1)
One things for sure (Score:1)
Esoteric topic vs Yes men (Score:2)
So stars we know about may have 20% more mass than we thought, galaxies we know about have more stars (that are more massive), there are a crapload of galaxies that we are unaware of, and countless distances that we have measured are huge over estimates all because of this effect. Yet every poster in this topic that is (or pretends to be) a physicist claims that all this has little impact on the amount of dark matter in the universe.
I don't want to sound cynical, but this thread gives me little hope for t
Does this eliminate "dark energy" then? (Score:2)