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Galaxies Twice As Bright As Previously Thought
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."
is there any reason this can't be the unaccounted "dark matter" astronomers are always talking about?
"National Security is the chief cause of national insecurity." - Celine's First Law
Do not look into galaxy with remaining eye!
Knowledge is power. Knowledge shared is power lost.
More mass in stars, so less dark matter...
Anyone case to elaborate on what kind of shake-up this is going to have for astronomy and cosmology?
A-Bomb
Researchers found to be half as bright as previously thought.
You must write The Book, and then tear away belief. Only you can save the light of man --Gary Numan
Wow, a simple, seemingly obvious (as always, in hindsight) observation that throws a lot of carefully balanced highly theoretical equations out of whack.
Of course, it could prove to be equally inaccurate by failing to take into account some other grand unknown that in turn will prove to be obvious, but I can't help but feel sorry thinking of all those academics sitting around a table of hardly-touched pints and muttering "well, fuck..." to no one in particular.
--
"You're only as smart as the guys you think are smarter than you."
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.
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
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).
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
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
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.
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
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).
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
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
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.
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.
Your circular logic fails to prove that dark matter exists.
"National Security is the chief cause of national insecurity." - Celine's First Law
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.
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.