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:5, Interesting)
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?
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:big shake-up (Score:1, Interesting)
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.
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 gravitational effects?
Re:Baryonic dark matter... (Score:3, Interesting)
Re:So there's more dust than previously thought... (Score:4, Interesting)
Re:So there's more dust than previously thought... (Score:5, Interesting)
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, 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.
Re:Doesn't this screw up lot of other things, too. (Score:3, Interesting)
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).
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: 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.
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.
Re:So there's more dust than previously thought... (Score:2, Interesting)
Example [astronomynotes.com]
Re:Because... (Score:2, Interesting)