PR Newswire: news distribution, targeting and monitoring
Mar 2 2012

WASHINGTON, March 2, 2012 /PRNewswire-USNewswire/ -- Astronomers using data from NASA's Hubble Telescope have observed what appears to be a clump of dark matter left behind from a wreck between massive clusters of galaxies. The result could challenge current theories about dark matter that predict galaxies should be anchored to the invisible substance even during the shock of a collision.

(Logo: http://photos.prnewswire.com/prnh/20081007/38461LOGO)

Abell 520 is a gigantic merger of galaxy clusters located 2.4 billion light-years away. Dark matter is not visible, although its presence and distribution is found indirectly through its effects. Dark matter can act like a magnifying glass, bending and distorting light from galaxies and clusters behind it. Astronomers can use this effect, called gravitational lensing, to infer the presence of dark matter in massive galaxy clusters.

This technique revealed the dark matter in Abell 520 had collected into a "dark core," containing far fewer galaxies than would be expected if the dark matter and galaxies were anchored together. Most of the galaxies apparently have sailed far away from the collision.

"This result is a puzzle," said astronomer James Jee of the University of California in Davis, lead author of paper about the results available online in The Astrophysical Journal. "Dark matter is not behaving as predicted, and it's not obviously clear what is going on. It is difficult to explain this Hubble observation with the current theories of galaxy formation and dark matter."

Initial detections of dark matter in the cluster, made in 2007, were so unusual that astronomers shrugged them off as unreal, because of poor data. New results from NASA's Hubble Space Telescope confirm that dark matter and galaxies separated in Abell 520.

One way to study the overall properties of dark matter is by analyzing collisions between galaxy clusters, the largest structures in the universe. When galaxy clusters crash, astronomers expect galaxies to tag along with the dark matter, like a dog on a leash. Clouds of hot, X-ray emitting intergalactic gas, however, plow into one another, slow down, and lag behind the impact.

That theory was supported by visible-light and X-ray observations of a colossal collision between two galaxy clusters called the Bullet Cluster. The galactic grouping has become an example of how dark matter should behave.

Studies of Abell 520 showed that dark matter's behavior may not be so simple. Using the original observations, astronomers found the system's core was rich in dark matter and hot gas, but contained no luminous galaxies, which normally would be seen in the same location as the dark matter. NASA's Chandra X-ray Observatory was used to detect the hot gas. Astronomers used the Canada-France-Hawaii Telescope and Subaru Telescope atop Mauna Kea to infer the location of dark matter by measuring the gravitationally lensed light from more distant background galaxies.

The astronomers then turned to the Hubble's Wide Field Planetary Camera 2, which can detect subtle distortions in the images of background galaxies and use this information to map dark matter. To astronomers' surprise, the Hubble observations helped confirm the 2007 findings.

"We know of maybe six examples of high-speed galaxy cluster collisions where the dark matter has been mapped," Jee said. "But the Bullet Cluster and Abell 520 are the two that show the clearest evidence of recent mergers, and they are inconsistent with each other. No single theory explains the different behavior of dark matter in those two collisions. We need more examples."

The team proposed numerous explanations for the findings, but each is unsettling for astronomers. In one scenario, which would have staggering implications, some dark matter may be what astronomers call "sticky." Like two snowballs smashing together, normal matter slams together during a collision and slows down. However, dark matter blobs are thought to pass through each other during an encounter without slowing down. This scenario proposes that some dark matter interacts with itself and stays behind during an encounter.

Another possible explanation for the discrepancy is that Abell 520 has resulted from a more complicated interaction than the Bullet Cluster encounter. Abell 520 may have formed from a collision between three galaxy clusters, instead of just two colliding systems in the case of the Bullet Cluster.

A third possibility is that the core contained many galaxies, but they were too dim to be seen, even by Hubble. Those galaxies would have to have formed dramatically fewer stars than other normal galaxies. Armed with the Hubble data, the group will try to create a computer simulation to reconstruct the collision and see if it yields some answers to dark matter's weird behavior.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For more information about Hubble visit: http://www.nasa.gov/hubble

For images and more information about Abell 520's dark core, visit: http://hubblesite.org/news/2012/10

For more information about dark matter, visit: http://go.nasa.gov/dJzOp1

SOURCE NASA



RELATED LINKS
http://www.nasa.gov

Questions?

Can I help you? Drop me a line and let me know. 

Blogger Services

Customized Newsfeeds

Don't let the name PR Newswire for Journalists dissuade you. This is a great service for bloggers. Any content creator -- whether you're a journalist, freelancer or blogger -- can set up a customized profile to receive releases based on preferences. You also have access to hi-res photos, media-only content such as media advisories and embargoed releases, and experts via ProfNet.

ProfNet

Need expert sources? Check out ProfNet, a service that helps journalists, bloggers, authors, and other content creators connect with experts -- at no charge. Sending a query is easy: Just fill out a form detailing the kind of expertise you need, how you want to be contacted, and your deadline. ProfNet will do the rest. You also can sign up for a weekly "tip sheet" of experts and story ideas. Visit ProfNet for more info or go directly to the query form.

ProfNet Connect

ProfNet Connect is a free, interactive online community where PR professionals, experts, and media professionals can network and engage with one another. Via profiles, forums and blogs, subject-matter experts can position themselves as the go-to source for content creators and journalists. In turn, content creators can search the site by keyword to find the experts they need. The site also features enhanced profile capabilities, allowing users to easily add multimedia components -- photos, videos, white papers and more -- to their profiles.

News Widget

Our widget allows you to display PR Newswire content on your site with very little back-end programming required.  You not only get the headline, but also the body of text of the news release, keeping the user on your site at all times.  In order to do so, the difference between our Widget and other widgets is at the end of the sign-up process, you will be provided with two pieces of source code -- one for the page where the Widget itself will be displayed and one for the pages that will display the body of text of each news release.  In addition, the sign-up process allows you to have 100 percent control over every aspect of the Widget's appearance, so that the Widget can blend in fully with the look and feel of your site. Still not convinced? Here's what one blogger had to say about the widget.

Search
  
  1. Home
  2. News Unfiltered
  3. Blog Posts
  4. Blogger Services
  5. Blogger Events
  6. Contact Us