. 24/7 Space News .
Space Telescopes Probe Secrets Of Fossil Galaxy Clusters

XMM-Newton observations of the fossil galaxy cluster RX J1416.5+2315, show a cloud of hot gas emitting X-rays (in blue). The cloud, reaching temperatures of about 50 million degrees, extend over 3.5 million light years and surround a giant elliptical galaxy believed to have grown to its present size by cannibalising its neighbours. Image credit: Khosroshahi, Maughan, Ponman, Jones/ESA/ING
by Staff Writers
Birmingham, United Kingdom (SPX) Apr 27, 2006
Astronomers using ESA's XMM-Newton and NASA's Chandra space telescopes have discovered further evidence that dark matter permeates and dominates the behavior of a particular type of galaxy cluster called a fossil group.

Most of the galaxies in the universe reside in clusters, where they experience close encounters with their neighbors and interact gravitationally with dark matter - the mysterious substance that seems to comprise nearly one-quarter of the mass of the universe, but has not yet been directly observed.

The encounters cause the smaller galaxies to spiral in slowly toward the center of the group, where they eventually merge to form a single giant galaxy, which over time will consume all of its neighbors.

After the process runs its course, the result is an object astronomers call a fossil cluster: Almost all of the stars fall into the central galaxy, which in turn sits in the center of a surrounding dark-matter halo. Astronomers can infer the presence of the halo from the corresponding hot gas that fills its gravitational well and emits X-rays.

The team of international astronomers studied in detail a puzzling physical feature of the hottest and most massive fossil group, which according to theoretical models, simply could not have formed in the time available.

The group investigated, called RX J1416.4+2315, is dominated by a single elliptical galaxy located about 1.5 billion light-years away and radiating about 500 billion times more luminously than the Sun.

The XMM-Newton and Chandra X-ray observations, combined with optical and infrared analyses, revealed the group sits within a hot gas halo extending across 3 million light-years and heated to a temperature of about 50 million degrees, mainly due to shock heating as a result of gravitational collapse.

Such a high temperature - about twice as high as previously estimated, is characteristic of galaxy clusters. Another interesting feature is the cluster's large bulk - over 300 trillion solar masses, with only about 2 percent in the form of stars in galaxies and 15 percent as X-ray-emitting hot gas. The major contributor to the mass of the system, however, is dark matter, which gravitationally binds the other components.

According to the team's initial calculations, a fossil cluster as massive as RX J1416.4+2315 could not have formed during the whole age of the universe. The key to the process is a factor called dynamical friction, which causes a large galaxy to lose its orbital energy to the surrounding dark matter. This process is less effective, however, when galaxies are moving more quickly, which they do in massive clusters.

"Simple models to describe the dynamical friction assume that the merging galaxies move along circular orbits around the center of the cluster mass," said team leader Habib Khosroshahi of the University of Birmingham. "Instead, if we assume that galaxies fall towards the center of the developing cluster in an asymmetric way, such as along a filament � the cluster formation process may occur in a shorter time scale."

The hypothesis is supported by a highly elongated X-ray emission pattern observed in RX J1416.4+2315, Khosroshahi said.

"The study of massive fossil groups such as RX J1416.4+2315 is important to test our understanding of the formation of structure in the universe," he added. "Cosmological simulations are underway, which attempt to reproduce the properties we observe, in order to understand how these extreme systems develop."

The XMM-Newton observations of the fossil galaxy cluster RX J1416.4+2315 were performed in July 2003. Chandra's observations of the same object where made in September 2001. The findings will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

Related Links
Chandra at Harvard

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The DAWN Of A New Mission Marks Log Entry Number One
Pasadena CA (SPX) Apr 27, 2006
NASA's next planned venture into the solar system, Dawn is a collaborative effort of scientists, engineers and people in other disciplines at JPL, UCLA, Orbital Sciences Corp., the space agencies of Germany and Italy, and other universities and private companies in the United States and elsewhere.

  • Next Generation Soyuz TMA Getting Ready For Flight
  • Mikulski Calls for Balanced Space Program To Increase Support for NASA
  • ATK Gets NASA OK For More CLV Work
  • Muslim Countries Urged To Reach For The Stars

  • NASA Testing Prototype Software For Future Spaceflight
  • Spirit Surveys Local Terrian For Winter Of 2006
  • Phoenix Mars Lander Project Progressing Towards August 2007 Launch
  • Mars Express Views Nanedi Valles

  • Next Ariane 5 Launch Set For May 26
  • Cloud Satellite Launch Suffers One More Delay
  • Another No Go For Cloud Satellite Launch
  • NASA Still Looking To Launch Discovery In July

  • China Successfully Launches Remote Sensing Satellite
  • Geoinformation From Space Sharpens Population Density Maps
  • Israeli EO Bird EROS-B Safely In Orbit
  • SAIC Acquires Geo-Spatial Technologies

  • Xena Poses A Bright Mystery
  • Tenth Planet Only Slightly Bigger Than Pluto
  • New Horizons Payload Gets High Marks on Early Tests
  • "Zero G and I Feel Fine"

  • Space Telescopes Probe Secrets Of Fossil Galaxy Clusters
  • The DAWN Of A New Mission Marks Log Entry Number One
  • NASA Sees Hidden Structure Of Neutron Star In Starquake
  • Evidence Mounts For Companion Star To Our Sun

  • China Completes Radio Telescope For Moon-Probe Project
  • Pete Worden Is New NASA Ames Director
  • Lunar Rocks Suggest Meteorite Shower
  • NASA Seeking Lunar Exploration Ideas

  • Spirent To Supply Testing Equipment For Galileo
  • New Student-Designed System Tracks Firefighter And Special Forces
  • Russia And India Discuss Military Element For GLONASS
  • Germany's Gateway To The World

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2006 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA PortalReports are copyright European Space Agency. All NASA sourced material is public domain. Additionalcopyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement