Mar 2 2012

From The Space Library

RELEASE: 12-068 DARK MATTER CORE DEFIES EXPLANATION IN NASA HUBBLE IMAGE

WASHINGTON -- 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. 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.

RELEASE: 12-069 COMMUNITY COLLEGE SCHOLARS SELECTED TO DESIGN ROBOTIC ROVERS

WASHINGTON -- Community college students will have the chance to design robotic rovers in cooperation with NASA. Ninety-two students from schools in 24 states have been selected to travel to a NASA center to develop rovers through the National Community College Aerospace Scholars program. The initiative provides hands-on opportunities to inspire interest in science, technology, engineering and mathematics (STEM) disciplines. Students will visit either NASA's Jet Propulsion Laboratory in Pasadena, Calif., from May 1-3, or NASA's Johnson Space Center in Houston from May 9-11. The teams will establish fictional companies pursuing Mars exploration. Each team will develop, design and build a prototype rover, then use their prototypes to navigate a course, collect rocks and water and return to a home base. "I am so proud of the Community College Aerospace Scholars program," said Leland Melvin, NASA's associate administrator for education. "Community colleges offer NASA a great pool of STEM talent critical to our scientific and exploration initiatives. They also serve a large portion of our nation's minority students. Engaging these underserved and underrepresented learners in STEM initiatives helps NASA build a more inclusive and diverse workforce for the future." Participants were selected based on completion of interactive web-based assignments throughout the school year. The on-site experience this spring includes a tour of NASA facilities and briefings from agency scientists and engineers. The program is based on the Texas Aerospace Scholars program, originally created in partnership with NASA and the Texas educational community. Aerospace Scholars programs are designed to encourage students to enter careers in science and engineering and ultimately join the nation's technical workforce.

MEDIA ADVISORY: M12-034 NASA INVITES PUBLIC TO EVENT HONORING WOMEN'S HISTORY MONTH

WASHINGTON -- NASA invites the public to an event featuring senior government leaders, scientists and innovators in celebration of Women's History Month. The "Women, Aerospace and Innovation" program will be held from 9 a.m. to 3 p.m. EST on March 8 at the George Washington University's Jack Morton Auditorium and Marvin Center at 805 21st St. NW in Washington. The program will feature panel discussions with women in senior government positions and breakout sessions where students and early career professionals can meet NASA scientists and researchers. New videos from the Women@NASA website will be featured during the day, highlighting the role women play at NASA.