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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."
I heard it circles Uranus.
except, of course, all the astrophysicists who often pointed out that exactly this kind of discovery was just around the corner.
How we know is more important than what we know.
Screenshot or it didn't happen!
Is it just me, or are humans getting better and better at science as time progresses?
I mean, it seems likely that this would be the case, naturally. Nonetheless, it still strikes me.
We predict dark matter exists, then we show it exists. It seems pretty much assured that we will even find out what it is made of. This discovery further cements this feeling in my mind.
We figure there is a chemical of inheritance, we find DNA. We know there is a genome, we sequence it.
Everything seems to be a big puzzle, and we seem to be getting faster and more accurate with putting these puzzles together.
I feel fully confident in speculating, for instance, that we will solve the gene therapy issues in mere years. That we will have household humanoid robots by 2020 for under $50,000US. That we will enhance ourselves dramatically genetically and technologically by the end of the century.
Has science always been this inexorable in it's progress?
Read my Very Short "Stories"
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]
Why does the title read "Hubble Space Telescope Detects Ring of Dark Matter" when - as the first line of the summary states -, the HST actually only " may have finally found dark matter".
"Has found" and "may have found" are very different things. I "may have" the lotto ticket which is going to win me millions of dollars in Saturday's draw; on the other hand, I may not. To pre-emptively state a conclusion before it has been made is foolish and extremely unscientific and simply not an accurate description.
I challenge you to find much more information on Dark Matter... that isn't purely speculative. Whining about the lack of information is even worse than the wildest of speculations. Get in the game!
So far, it's all in the name; we can't really see it, ergo; dark. It has some sort of mass-effect in the universe, ergo; it matters. The only thing we can't agree on is what Dark Matter is. Let the speculations begin!
1. - Maybe it's a Quantum Substance and we've already determined it's nature by giving it a name. If it ever gets in the way, just shine a light on it and it disappears!
2. - What if it follows an Uncertainty Principle instead? Find a cloud of it, then put the lens-cap on the telescope. If I don't believe it's there when I take the lens-cap off, will it be gone? (Call it “Schroedinger's Haze”?)
3. - The residue of “unnecessary emotions” cast-off by an advanced species?
4. - Star farts?
I'd like to hear any better ideas... [ducks]
This post © Copyrite Duggeek, all rights reversed.
Not all scientific predictions are made equal.
The Raven
...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.
Part of the confusion is that there are 2 separate concepts that both go by the name "dark matter".
Dark matter in the broad sense is matter that we detect gravitationally but can't observe directly through any interaction with light (and if this measurement is from gravitational lensing, which I suspect, then it certainly falls into this catagory). We infer that it exists because the motions of stars and gas in galaxies, galaxies and hot gas in galaxy clusters, and the universe as a whole all act as though they are acting in the gravitational field produced by much more mass than what we can directly detect.
Some fraction of this dark matter is normal ("baryonic") matter that just happens to be very difficult to detect due to its temperature and density... for example, a lot of it is diffuse gas at ~100000K, which is too cool to emit X-rays but too hot to emit much line radiation.
However, from Big Bang nucleosynthesis calculations, we can estimate how much baryonic matter there is in the universe because the relative fractions of different isotopes of H, He, Li and Be are quite sensitive to the total amount of baryonic matter. And the total amount of matter required to account for the dynamics of the universe is about 6 times higher than the amount of baryons that Big Bang nucleosynthesis measurements indicate.
Therefore, there must be non-baryonic dark matter too, made of exotic particles (or neutrinos, but there most likely aren't enough of those either). This is also sometimes just called "dark matter", which is confusing.
Interestingly, galaxy clusters, like the one studied here, have most of their baryonic matter in the form of hot X-ray gas that is detectable... the density of baryonic matter we can detect within a galaxy cluster is about what you'd expect given the BBN calculations. So any dark matter in a galaxy cluster should be non-baryonic dark matter, which is why measurements like this are exciting.
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