Slashdot Mirror

← Back to Stories (view on slashdot.org)

Hubble Space Telescope Detects Ring of Dark Matter

Posted by Zonk on from the i-can't-see-it-someone-get-a-light dept.

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."

3 of 176 comments (clear)

  1. More info by IWannaBeAnAC · · Score: 5, Informative

    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.

    Authors: Jee, Myungkook J.; Ford, H. C.; Illingworth, G. D.; White, R. L.; Broadhurst, T. J.; Coe, D. A.; Meurer, G. R.; van der Wel, A.; ACS Science Team We present a comprehensive mass reconstruction of the z = 0.4 rich galaxy cluster CL0024+17 from Advanced Camera for Surveys data, unifying both strongand weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies ( 120 per arcmin^2) across the cluster enables the derivation of a high-resolution parameter-free mass map. The strongly-lensed objects tightly constrain the mass structure of the cluster inner region on an absolute scale, breaking the mass-sheet degeneracy. The mass reconstruction of CL0024+17 obtained in such a way is remarkable. It reveals a ring-like dark matter substructure at r 75" surrounding a soft, dense core at r<50". We interpret this peculiar sub-structure as the result of a high-speed line-of-sight collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated by the cluster bimodal velocity distribution. Our numerical simulation with purely collisionless particles demonstrates that such density ripples can arise by radially expanding, decelerating particles that originally comprised the pre-collision cores. ACS was developed under NASA contract NAS5-32865, and this research was supported by NASA grant NAG5-7697.

    Unfortunately I can't find the paper itself. So there is slightly more info, but not much :-(

  2. how you see dark matter by TMB · · Score: 5, Informative

    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]

  3. Dark matter was already detected by Burz · · Score: 5, Informative

    ...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.