Abell 2142, or A2142, is a huge,

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

luminous galaxy cluster in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Corona Borealis. It is the result of a still ongoing merger between two

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

clusters. The combined cluster is six

million One million (1,000,000), 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'' (''milione'' in modern Italian), from ''mille'', "thousand", plus the au ...

light years across, contains hundreds of

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

and enough gas to make a thousand more. It is "one of the most massive objects in the universe."

X-Ray image

The adjacent image was taken 20 August 1999 with the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 1 ...

's 0.3-10.0 k eV

Advanced CCD Imaging Spectrometer The Advanced CCD Imaging Spectrometer (ACIS), formerly 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 ''C ...

(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

in the cluster.

Quick facts

Abell 2142 is part of the

Abell catalogue The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift ''z'' ≤ 0.2. This catalog supplements a revision of George O. Abell's original "Northern Survey" of 1958, wh ...

of rich clusters of galaxies originally published by UCLA astronomer

George O. Abell George Ogden Abell (March 1, 1927 – October 7, 1983) was an American educator. Teaching at University of California, Los Angeles, UCLA, priorly he worked as a research astronomer, administrator, as a popularizer of science and of education, and ...

(1927-1983) in 1958. It has a heliocentric

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...

of 0.0909 (meaning it is moving away from us at 27,250 km/s) and a visual magnitude of 16.0. It is about 1.2 billion light years (380 M pc) away.Distance calculated from redshift.

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 energy In physics, the kinetic energy of an object is the energy that 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 accele ...

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 ''Asca'' is a genus of mites with worldwide distribution in the family Ascidae Ascidae is a family of mites in the order Mesostigmata. Description Ascidae are mites characterised by: seta ''st4'' usually on unsclerotised cuticle, peritrem ...

) did not have the capabilities of

Chandra Chandra ( sa, चन्द्र, Candra, shining' or 'moon), also known as Soma ( sa, सोम), is the Hindu god of the Moon, and is associated with the night, plants and vegetation. He is one of the Navagraha (nine planets of Hinduism) and ...

and XMM-Newton (two current

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, Massachusetts, 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.

References

{{DEFAULTSORT:Abell 2142 Corona Borealis 2142 Galaxy clusters Abell richness class 2

X-Ray image

Quick facts

Merger dynamics

See also

References