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Hubble Space Telescope Detects Ring of Dark Matter
mknewman wrote with a link to a story on the NASA site indicating that they may have finally found dark matter using the Hubble telescope. We've discussed the stuff a few times in the last year, with the Hubble actually mapping out the dark matter in the universe in January. This, though, may be our first 'sighting' of the elusive substance. "NASA will hold a media teleconference at 1 p.m. EDT on May 15 to discuss the strongest evidence to date that dark matter exists. This evidence was found in a ghostly ring of dark matter in the cluster CL0024+17, discovered using NASA's Hubble Space Telescope. The ring is the first detection of dark matter with a unique structure different from the distribution of both the galaxies and the hot gas in the cluster. The discovery will be featured in the June 20 issue of the Astrophysical Journal."
Screenshot or it didn't happen!
I was about to write a comment panning this submission, because apparantly a one-paragraph press release - that doesn't give much room for an intelligent discussion - was the only information on this discovery. But I did find an abstract for a talk given at the American Astronomical Society Meeting 209, which was held in January this year.
Unfortunately I can't find the paper itself. So there is slightly more info, but not much :-(
It could happen. But if we piss off those robots and the genetically engineered humans, they may band together and start an extermination program of us humans. Then we'd have to flee the planet in a fleet of ships while the robots pursue us. Of course, with the genetically engineered humans, they'll look like us and they'd be used as spies. Of course, there may be a comuter scientist who falls in love with one of them and helps the robots take us out. Then he'll go insane and start imagining his robot lover.
I don't know if we really want to go there.
I prefer Flambe as apposed flamebait.
Given that the press conference isn't until May 15, I can't say for sure, but based on the brief blurb on the NASA website, it's almost certainly a gravitational lensing measurement.
It's true that dark matter doesn't interact directly with light, but it does curve space (ie. generate gravity), which light travels through. So light feels the gravitational effect of dark matter, a phenomenon known as "gravitational lensing". Essentially, the images of background galaxies going through a concentration of dark matter become magnified and distorted.
I don't know whether this is a strong lensing or weak lensing measurement. In strong lensing, the distortion is extreme and the images of the background get stretched into long tangential (and radial, though they're rarer) arcs like this. In the case of weak lensing, the distortion in any one image is small, but all images in a certain area are distorted coherently so you can statistically disentangle the signal.
Given the distorted images of the background galaxies, you can determine what mass distribution was responsible for those distortions, thereby producing a "mass map". It appears that in this case (again, based on the brief blurb), the mass map shows some sort of ring-like structure that isn't seen at any other wavelength (which non-dark matter would produce).
[TMB]
...last year: astronomers could see in the aftermath of two colliding galactic clusters.
The visible matter's momentum through space was impeded at quite a different rate than dark matter. This left four distinct zones of gravitational lensing, but only TWO were associated with visible matter. The other two were dark matter halos that had been separated from each galactic cluster.
"We find no luminiferous aether.
Not all scientific predictions are made equal."
that was a very useful prediction.
We predicted luminous aether: it was a logical theory. We had good reason to believe that light was a wave, we had no reason to imagine that a wave could exist without a physical medium (air, water, etc.)
It was a falsifiable theory.
For a long time people tried to prove it, but measurements weren't sensitive enough. Finally, a sensitive enough experiment was developed, and it found-- nothing!
This was far more useful than if they had found something.
On discovering that the theory was wrong, they didn't try to argue that it was really still correct. They puzzled about what it could mean: how can a wave exist without a substance to wave through?
Many incredibly significant scientific advances of the next few decades came out of this enigma. If there had been no luniniferous aether theory, there would have been no enigma, and perhaps many of these discoveries would not yet have come about.
The usefulness of a theory is not in whether it's correct or not. The usefulness of a theory comes from what you learn while trying to discover whether or not it is correct.