Coma Cluster
Credit: X-ray: NASA/CXC/MPE/J.Sanders et al, Optical: SDSS
A new composite image, with Chandra data in pink and optical data
from the Sloan Digital Sky Survey appearing in white and blue, features
these spectacular arms (mouse over the image for their location). In
this image, the Chandra data have been processed so extra detail can be
seen.
The X-ray emission
is from multimillion-degree gas and the optical data shows galaxies
in the Coma Cluster, which contain only about 1/6 the mass in hot gas.
Only the brightest X-ray emission is shown here, to emphasize the arms,
but the hot gas is present over the entire field of view.
Researchers think that these arms were most likely formed when
smaller galaxy clusters had their gas stripped away by the head wind
created by the motion of the cluster through the hot gas, in much the
same way that the headwind created by a roller coaster blows the hats
off riders.
Coma is an unusual galaxy cluster because it contains not one, but two giant elliptical galaxies near its center. These two giant elliptical galaxies
are probably the vestiges from each of the two largest clusters that
merged with Coma in the past. The researchers also uncovered other signs
of past collisions and mergers in the data.
From their length, and the speed of sound in the hot gas (~4 million
km/hr), the newly discovered X-ray arms are estimated to be about 300
million years old, and they appear to have a rather smooth shape. This
gives researchers some clues about the conditions of the hot gas in
Coma. Most theoretical models expect that mergers between clusters like
those in Coma will produce strong turbulence, like ocean water that has
been churned by many passing ships. Instead, the smooth shape of these
lengthy arms points to a rather calm setting for the hot gas in the Coma
cluster, even after many mergers.
Large-scale magnetic fields are likely responsible for the small
amount of turbulence that is present in Coma. Estimating the amount of
turbulence in a galaxy cluster has been a challenging problem for
astrophysicists. Researchers have found a range of answers, some of them
conflicting, and so observations of other clusters are needed.
Two of the arms appear to be connected to a group of galaxies located
about two million light years from the center of Coma. One or both of
these arms connects to a larger structure seen in the XMM-Newton data,
and spans a distance or at least 1.5 million light years. A very thin
tail also appears behind one of the galaxies in Coma. This is probably
evidence of gas being stripped from a single galaxy, in addition to the
groups or clusters that have merged there.
These new results on the Coma cluster, which incorporate over six
days worth of Chandra observing time, will appear in the September 20,
2013, issue of the journal Science. The first author of the paper is
Jeremy Sanders from the Max Planck Institute for Extraterrestrial
Physics in Garching, Germany. The co-authors are Andy Fabian from
Cambridge University in the UK; Eugene Churazov from the Max Planck
Institute for Astrophysics in Garching, Germany; Alexander Schekochihin
from University of Oxford in the UK; Aurora Simionescu from the
Institute of Space and Astronautical Science in Sagamihara, Japan;
Stephen Walker from Cambridge University in the UK and Norbert Werner
from Stanford University in Stanford, CA.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra Program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and
flight operations from Cambridge, Mass.
Fast Facts for Coma Cluster
Scale: Image is 23 arcmin on a side (about 2 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000: RA 12h 59m 48s | Dec +27° 58' 00
Constellation: Coma Berenices
Observation Date: 13 pointings between November, 1999 and April, 2012
Observation Time: 151 hours 35 min (6 days, 7 hours, 35 min)
Obs. ID: 555, 1112-1114, 9714, 13993-13996, 14406, 14410, 14411, 14415
Instrument: ACIS
References: Sanders, J.S., et al, 2013, Science (in press)
Color Code: X-ray (Pink); Optical (Red, Green, Blue)
Distance Estimate: About 318 million light years (z = 0.0231)
