Feb 29, 2000
Galaxies in Collision
Right: The two large elliptical galaxies indicated by arrows in the center of this optical image are thought to be the central galaxies of two merging galaxy clusters. Together, the two merging clusters form a single object astronomers call Abell 2142. The optical image is overlaid with X-ray brightness contours. The bright source in the upper left is an active galaxy in the cluster.
The Chandra data provides the first detailed look at the late stages of this merger process. Previously, scientists had used the German-US Roentgen satellite to produce a broad-brush picture of the cluster. The elongated shape of the bright cloud suggested that two clouds were in the process of coalescing into one, but the details remained unclear. Chandra is able to measure variations of temperature, density, and pressure with unprecedented resolution.
"Now we can begin to understand the physics of these mergers, which are among the most energetic events in the universe," said Markevitch. "The pressure and density maps of the cluster show a sharp boundary that can only exist in the moving environment of a merger."
With this information scientists can make a comparison with computer simulations of cosmic mergers. This comparison, which is in the early stages, shows that this merger has progressed to an advanced stage. Strong shock waves predicted by the theory for the initial collision of clusters are not observed. It appears likely that these sub-clusters have collided two or three times in a billion years or more, and have nearly completed their merger.
These observations were made on August 20, 1999 using the Advanced CCD Imaging Spectrometer (ACIS). The team involved scientists from Harvard-Smithsonian; the Massachusetts Institute of Technology, Cambridge; NASAís Marshall Space Flight Center, Huntsville, Ala.; the University of Hawaii, Honolulu; the University of Birmingham, U.K.; the University of Wollongong, Australia; the Space Research Organization Netherlands; the University of Rome, Italy; and the Russian Academy of Sciences. The results will be published in an upcoming issue of the Astrophysical Journal.
The ACIS instrument was built for NASA by the Massachusetts Institute of Technology, Cambridge, and Pennsylvania State University, University Park. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.Web Links
Chandra home page -from Harvard
Chandra News -from NASA
Galaxy Clusters -a tutorial from Harvard's Chandra home page
X-Rays - Another Form of Light - the basics of X-rays from the Chandra home page at Harvard