Abell 2142
Encyclopedia
Abell 2142, or A2142, is a huge, X-ray
luminous galaxy cluster
in the constellation
Corona Borealis
. It is the result of a still ongoing merger between two galaxy
clusters. The combined cluster is six million
light years
across, contains hundreds of galaxies and enough gas to make a thousand more. It is "one of the most massive objects in the universe."
's 0.3-10.0 keV Advanced CCD Imaging Spectrometer
(ACIS), and covers an area of 7.5 x 7.2 arc minutes
. It shows a colossal cosmic "weather system" produced by the collision of two giant clusters of galaxies. For the first time, the pressure fronts in the system have been traced in detail, and show a bright, but relatively cool 50 million degree Celsius central region (white) embedded in large elongated cloud of 70 million degree Celsius gas (magenta), all of which is roiling in a faint "atmosphere" of 100 million degree Celsius gas (faint magenta and dark blue). The bright source in the upper left is an active galaxy in the cluster.
of rich clusters of galaxies originally published by UCLA astronomer George O. Abell (1927-1983) in 1958. It has a heliocentric redshift
of 0.0909 (meaning it is moving away from us at 27,250 km/sec) and a visual magnitude
of 16.0. It is about 1.2 billion light years
(370 Mpc
) away.
of colliding objects heats the gas between subclusters, causing marked variations in gas temperature. These variations contain information on the stage, geometry and velocity of the merger. An accurate temperature map can provide a great deal of information on the nature of the underlying physical processes. Previous instruments (e.g., ROSAT
, ASCA
) did not have the capabilities of Chandra
and XMM-Newton
(two current X-ray
observatories) and were unable to map the region in detail.
Chandra has been able to measure variations of temperature, density, and pressure with high resolution. "Now we can begin to understand the physics of these mergers, which are among the most energetic events in the universe," said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics
, Cambridge, Mass., and leader of the international team involved in the analysis of the observations. "The pressure and density maps of the cluster show a sharp boundary that can only exist in the moving environment of a merger."
A2142's observed X-ray emissions are largely smooth and symmetric, suggesting it is a result of a merger between two galaxy clusters viewed at least 1–2 billion years after the initial core crossing. One would expect to observe uneven X-ray emission and obvious shock fronts if the merger was at an early stage. Markevitch et al. have proposed that the central galaxy (designated G1) of a more massive cluster has merged with the former central galaxy (G2) of the less massive cluster. The relatively cool central area suggests that the heating caused by previous shock fronts missed the central core, interacting instead with the surrounding gas.
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
luminous galaxy cluster
Galaxy cluster
A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Corona Borealis
Corona Borealis
Corona Borealis is a small constellation in the northern sky. Its name is Latin for "northern crown", a name inspired by its shape; its main stars form a semicircular arc. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and remains one of the 88 modern...
. It is the result of a still ongoing merger between two galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
clusters. The combined cluster is six million
Million
One million or one thousand thousand, is the natural number following 999,999 and preceding 1,000,001. The word is derived from the early Italian millione , from mille, "thousand", plus the augmentative suffix -one.In scientific notation, it is written as or just 106...
light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
across, contains hundreds of galaxies and enough gas to make a thousand more. It is "one of the most massive objects in the universe."
X-Ray Image
The image on the right was taken 20 August 1999 with the Chandra X-ray ObservatoryChandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
's 0.3-10.0 keV Advanced CCD Imaging Spectrometer
Advanced CCD Imaging Spectrometer
ACIS, the AXAF CCD Imaging Spectrometer, is an instrument built by a team from the Massachusetts Institute of Technology's Center for Space Research and the Pennsylvania State University for the Chandra X-ray Observatory...
(ACIS), and covers an area of 7.5 x 7.2 arc minutes
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
. It shows a colossal cosmic "weather system" produced by the collision of two giant clusters of galaxies. For the first time, the pressure fronts in the system have been traced in detail, and show a bright, but relatively cool 50 million degree Celsius central region (white) embedded in large elongated cloud of 70 million degree Celsius gas (magenta), all of which is roiling in a faint "atmosphere" of 100 million degree Celsius gas (faint magenta and dark blue). The bright source in the upper left is an active galaxy in the cluster.
Quick Facts
Abell 2142 is part of the Abell catalogueAbell catalogue
The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift z 18.0*Galactic-Latitude: Areas of the sky in the neighbourhood of the Milky Way were excluded from the study because the density of stars in those fields—not to mention...
of rich clusters of galaxies originally published by UCLA astronomer George O. Abell (1927-1983) in 1958. It has a heliocentric redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
of 0.0909 (meaning it is moving away from us at 27,250 km/sec) and a visual magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of 16.0. It is about 1.2 billion light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....
(370 Mpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
) away.
Merger Dynamics
A2142 has attracted attention because of its potential to shed light on the dynamics of mergers between galaxies. Clusters of galaxies grow through gravitational attraction of smaller groups and clusters. During a merger the kinetic energyKinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
of colliding objects heats the gas between subclusters, causing marked variations in gas temperature. These variations contain information on the stage, geometry and velocity of the merger. An accurate temperature map can provide a great deal of information on the nature of the underlying physical processes. Previous instruments (e.g., ROSAT
ROSAT
ROSAT was a German Aerospace Center-led satellite X-ray telescope, with instruments built by Germany, the UK and the US...
, ASCA
Advanced Satellite for Cosmology and Astrophysics
ASCA is the fourth cosmic X-ray astronomy mission by Japan's , and the second for which the United States is providing part of the scientific payload. The satellite was successfully launched on February 20, 1993. The first eight months of the ASCA mission were devoted to performance verification...
) did not have the capabilities of Chandra
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
and XMM-Newton
XMM-Newton
The XMM-Newton is an orbiting X-ray observatory launched by ESA in December 1999 on a Ariane 5 rocket...
(two current X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
observatories) and were unable to map the region in detail.
Chandra has been able to measure variations of temperature, density, and pressure with high resolution. "Now we can begin to understand the physics of these mergers, which are among the most energetic events in the universe," said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics
Harvard-Smithsonian Center for Astrophysics
The Harvard–Smithsonian Center for Astrophysics is one of the largest and most diverse astrophysical institutions in the world, where scientists carry out a broad program of research in astronomy, astrophysics, earth and space sciences, and science education...
, Cambridge, Mass., and leader of the international team involved in the analysis of the observations. "The pressure and density maps of the cluster show a sharp boundary that can only exist in the moving environment of a merger."
A2142's observed X-ray emissions are largely smooth and symmetric, suggesting it is a result of a merger between two galaxy clusters viewed at least 1–2 billion years after the initial core crossing. One would expect to observe uneven X-ray emission and obvious shock fronts if the merger was at an early stage. Markevitch et al. have proposed that the central galaxy (designated G1) of a more massive cluster has merged with the former central galaxy (G2) of the less massive cluster. The relatively cool central area suggests that the heating caused by previous shock fronts missed the central core, interacting instead with the surrounding gas.