Stephan's Quintet

Stephan's Quintet is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered.[2] The group, visible in the constellation Pegasus, was discovered by Édouard Stephan in 1877 at the Marseille Observatory.[3] The group is the most studied of all the compact galaxy groups.[2] The brightest member of the visual grouping is NGC 7320 that is shown to have extensive H II regions, identified as red blobs, where active star formation is occurring.

Stephan's Quintet
Stephan's Quintet Hubble 2009.full denoise
Observation data (Epoch J2000)
Right ascension 22h 35m 57.5s[1]
Declination+33° 57′ 36″[1]
Brightest memberNGC 7318B[1]
Number of galaxies5[1]
Other designations
HCG 92, Arp 319, VV 288,[1] SQ[2]


Four of the five galaxies in Stephan's Quintet form a physical association, Hickson Compact Group 92, and will likely merge with each other. Radio observations in the early 1970s revealed a mysterious filament of emission which lies in inter-galactic space between the galaxies in the group. This same region is also detected in the faint glow of ionized atomic hydrogen seen in the visible part of the spectrum as a green arc.

Two space telescopes have recently provided new insight into the nature of the filament, which is now believed to be a giant intergalactic shock-wave (similar to a sonic boom but traveling in intergalactic gas rather than air) caused by one galaxy (NGC 7318B) falling into the center of the group at several millions of kilometers per hour.

X-ray source

Stephan's Quintet X-ray + Optical
Stephan's Quintet. Image Credits: X-ray (blue): NASA/CXC/CfA/E. O'Sullivan Optical (brown): Canada-France-Hawaii-Telescope/Coelum.

As NGC 7318B collides with gas in the group, a huge shock wave bigger than the Milky Way spreads throughout the medium between the galaxies, heating some of the gas to temperatures of millions of degrees where they emit X-rays detectable with the NASA Chandra X-ray Observatory.

Molecular hydrogen emission

The NASA Spitzer Space Telescope, which detects infrared radiation, discovered a very powerful molecular hydrogen signal from the shock wave between the galaxies. This emission is one of the most turbulent formations of molecular hydrogen ever seen, and the strongest emission originates near the center of the green area in the visible light picture discussed earlier. This phenomenon was discovered by an international team led by scientists at the California Institute of Technology and including scientists from Australia, Germany and China. The detection of molecular hydrogen from the collision was initially unexpected because the hydrogen molecule is very fragile and is easily destroyed in shock waves of the kind expected in Stephan's Quintet. However, one solution is that when a shock front moves through a cloudy medium like the center of the group, millions of smaller shocks are produced in a turbulent layer, and this can allow molecular hydrogen to survive.

Stephans Quintet sdss-g Goran Nilsson & The Liverpool Telescope
Earthbound monochrome (sdss-g filtered) image of Stephan's Quintet from the Liverpool Telescope


NGC 7320 indicates a small redshift (790 km/s) while the other four exhibit large redshifts (near 6600 km/s). Since galactic redshift is proportional to distance, NGC 7320 is only a foreground projection[2] and is ~39 million lightyears[2] from Earth versus the 210-340 million lightyears of the other four.

NGC 7319 has a type 2 Seyfert nucleus.

The galaxies in the vicinity of Stephan's Quintet. The rectangle indicates the area covered by the 1998–99 Hubble Space Telescope image below.

A sixth galaxy, NGC 7320C, probably belongs to the Hickson association: it has a redshift similar to the Hickson galaxies, and a tidal tail appears to connect it with NGC 7319.

Detail of the quintet in a photo by Hubble Space Telescope, 1998–99. Credits: NASA/ESA.


Members of the Hickson Compact Group 92
Name Type[4] R.A. (J2000)[4] Dec. (J2000)[4] Redshift (km/s)[4] Apparent Magnitude[4]
NGC 7317 E4  22h 35m 51.9s +33° 56′ 42″ 6599 ± 26 +14.6
NGC 7318a
(UGC 12099)
E2 pec  22h 35m 56.7s +33° 57′ 56″ 6630 ± 23 +14.3
NGC 7318b
(UGC 12100)
SB(s)bc pec  22h 35m 58.4s +33° 57′ 57″ 5774 ± 24 +13.9
NGC 7319 SB(s)bc pec  22h 36m 03.5s +33° 58′ 33″ 6747 ± 7 +14.1
NGC 7320c (R)SAB(s)0/a  22h 36m 20.4s +33° 59′ 06″ 5985 ± 9 +16.7

See also


  1. ^ a b c d e "NASA/IPAC Extragalactic Database". Results for HCG 92. Retrieved 2006-09-18.
  2. ^ a b c d e Moles, M.; Marquez, I.; Sulentic, J. W. (1998). "The observational status of Stephan's Quintet". Astronomy and Astrophysics. 334: 473–481. arXiv:astro-ph/9802328. Bibcode:1998A&A...334..473M.
  3. ^ Stephan, M. E. (1877). "Nebulæ (new) discovered and observed at the observatory of Marseille, 1876 and 1877, M. Stephan". Monthly Notices of the Royal Astronomical Society. 37: 334–339. Bibcode:1877MNRAS..37..334S. doi:10.1093/mnras/37.6.334.
  4. ^ a b c d e "NASA/IPAC Extragalactic Database". Results for various galaxies. Retrieved 2006-10-20.


External links

Coordinates: Sky map 22h 35m 57.5s, +33° 57′ 36″

Astrophysical X-ray source

Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays.

There are a number of types of astrophysical objects which emit X-rays, from galaxy clusters, through black holes in active galactic nuclei (AGN) to galactic objects such as supernova remnants, stars, and binary stars containing a white dwarf (cataclysmic variable stars and super soft X-ray sources), neutron star or black hole (X-ray binaries). Some solar system bodies emit X-rays, the most notable being the Moon, although most of the X-ray brightness of the Moon arises from reflected solar X-rays. A combination of many unresolved X-ray sources is thought to produce the observed X-ray background. The X-ray continuum can arise from bremsstrahlung, either magnetic or ordinary Coulomb, black-body radiation, synchrotron radiation, inverse Compton scattering of lower-energy photons by relativistic electrons, knock-on collisions of fast protons with atomic electrons, and atomic recombination, with or without additional electron transitions.Furthermore, celestial entities in space are discussed as celestial X-ray sources. The origin of all observed astronomical X-ray sources is in, near to, or associated with a coronal cloud or gas at coronal cloud temperatures for however long or brief a period.

Atlas of Peculiar Galaxies

The Atlas of Peculiar Galaxies is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The primary goal of the catalog was to present photographs of examples of the different kinds of peculiar structures found among galaxies.

Galaxy group

A galaxy group or group of galaxies (GrG) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way (about 1010 times the luminosity of the Sun); collections of galaxies larger than groups that are first-order clustering are called galaxy clusters. The groups and clusters of galaxies can themselves be clustered, into superclusters of galaxies.

The Milky Way galaxy is part of a group of galaxies called the Local Group.

Hickson Compact Group

A Hickson Compact Group (abbreviation: HCG) is a collection of galaxies designated as published by Paul Hickson in 1982.The most famous group on Hickson's list of 100 objects is HCG 92, Stephan's Quintet.

List of NGC objects (7001–7840)

This is a list of NGC objects 7001–7840 from the New General Catalogue (NGC). The astronomical catalogue is composed mainly of star clusters, nebulae, and galaxies. Other objects in the catalogue can be found in the other subpages of the list of NGC objects.

The constellation information in these tables is taken from The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer, which was accessed using the "VizieR Service". Galaxy types are identified using the NASA/IPAC Extragalactic Database. The other data of these tables are from the SIMBAD Astronomical Database unless otherwise stated.

List of astronomical objects named after people

There are probably a few thousand astronomical objects named after people. These include the names of a few thousand asteroids and hundreds of comets. Also, many topological features on solar system bodies have been named after people, including many hundreds of craters on the Moon, Mars and other planets and satellites. In addition to craters there are also various other topological features such as mountains, valleys, ridges on the Moon and other bodies which are also named after people. Finally, several stars are named after people (according to the IAU), such as Barnard's star (Star-registry companies keep lists of stars they claim to have named after people. The IAU does not recognize those claims.). There's also a number of Deep-Sky objects named after astronomers and scientists. The list below shows most of them.

List of galaxy groups and clusters

This page lists some galaxy groups and galaxy clusters.

Defining the limits of galaxy clusters is imprecise as many clusters are still forming. In particular, clusters close to the Milky Way tend to be classified as galaxy clusters even when they are much smaller than more distant clusters.

Marseille Observatory

Marseille Observatory (French: Observatoire de Marseille) is an astronomical observatory located in Marseille, France, with a history that goes back to the early 18th century. In its incarnation in 1877, it was the discovery site of a group of galaxies known as Stephan's Quintet, discovered by its director Édouard Stephan. Marseille Observatory is now run as a joint research unit by Aix-Marseille University and the French National Center for Scientific Research (CNRS).

In 2000, Marseille Observatory merged with the Laboratoire d'Astrophysique Spatiale to become the Laboratoire d'Astrophysique de Marseille (LAM) within the broader Observatoire Astronomique Marseille Provence which also included the Haute-Provence Observatory.

In 2008, LAM was relocated to a new 10,000 square meter facility in the Technopôle Chateau-Gombert in Marseille. The facility includes two major technology platforms for qualification of space instruments and for fabrication and metrology of optical mirrors. LAM astronomers specialize in cosmology and galaxy evolution, exoplanets and Solar System, and R&D in optics and instrumentation.

In 2012, the Observatoire Astronomique Marseille Provence merged with other earth-sciences research institutes from Aix-Marseille University and became a new entity called the Observatoire des Science de l'Univers Institut Pythéas (OSU-IP) which now includes 6 major labs for earth and universe sciences: CEREGE, IMBE, MIO, LAM. LPED, MIO as well as the Haute-Provence Observatory.

NGC 6845

NGC 6845 (also known as Klemola 30) is an interacting system of four galaxies in the constellation Telescopium. The cluster has certain similarities with Stephan's Quintet. Its distance is estimated to be about 90 Mpc.

The components of the galaxy cluster are the two spiral galaxies NGC 6845A and NGC 6845B as well as the two lenticular galaxies NGC 6845C and NGC 6845D. The four galaxies occupy an area of about 4' x 2' in the sky. The largest galaxy in this compact galaxy cluster is NGC 6845A, a barred spiral galaxy. SN 2008DA was a Type II supernova observed in NGC 6845A in June 2008. The dwarf galaxy ATCA J2001-4659, which is found around 4.4' northeast of NGC 6845B, was identified as a companion of NGC 6845.NGC 6845 was discovered on July 7, 1834 by John Herschel.

NGC 7317

NGC 7317 is an elliptical galaxy that is a member of the Stephan's Quintet in the constellation Pegasus.

NGC 7318

NGC 7318 (also known as UGC 12099/UGC 12100 or HCG 92d/b) are a pair of colliding galaxies about 300 million light-years from Earth. They appear in the Constellation Pegasus and are members of the Stephan's Quintet.

The Spitzer Space Telescope revealed the presence of a huge intergalactic shock wave, shown by a green arc produced by one galaxy falling into another at millions of kilometers per hour. As NGC 7318B collides with NGC 7318A, gas spread throughout the cluster, atoms of hydrogen are heated in the shock wave, producing the green glow. The molecular hydrogen visible in the collision is one of the most turbulent forms known. This phenomenon was discovered by an international team of scientists of the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg. This collision can help provide a view into what happened in the early universe, around 10 billion years ago.

NGC 7319

NGC 7319 is a highly distorted barred spiral galaxy that is a member of the Stephan's Quintet located in the constellation Pegasus. The galaxy's arms, dust and gas have been highly disturbed as a result of the interaction with the other members of the Quintet.

NGC 7320

NGC 7320 is a spiral galaxy in the Stephan's Quintet. However, it is not an actual member of the galaxy group, but a much closer line-of-sight galaxy at a distance of about 40 million light years. Other galaxies of Stephan's Quintet are some 300 million light-year distant.

NGC 7320c

NGC 7320c is a galaxy member of the Stephan's Quintet located in the constellation Pegasus.

NGC 7331 Group

NGC 7331 Group is a group of galaxies in the constellation Pegasus. Spiral galaxy NGC 7331 is the brightest member of the group. This group is also called the Deer Lick Group, and contains four other members; NGC 7335, NGC 7336, NGC 7337 and NGC 7340, affectionately referred to as the "fleas".

Pegasus (constellation)

Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and is one of the 88 constellations recognised today.

With an apparent magnitude varying between 2.37 and 2.45, the brightest star in Pegasus is the orange supergiant Epsilon Pegasi, also known as Enif, which marks the horse's muzzle. Alpha (Markab), Beta (Scheat), and Gamma (Algenib), together with Alpha Andromedae (Alpheratz, once also designated Delta Pegasi) form the large asterism known as the Square of Pegasus. Twelve star systems have been found to have exoplanets. 51 Pegasi was the first Sun-like star discovered to have an exoplanet companion.

Robert's Quartet

Robert's Quartet is a compact galaxy group approximately 160 million light-years away in the constellation Phoenix. It is a family of four very different galaxies whose proximity to each other has caused the creation of about 200 star-forming regions and pulled out a stream of gas and dust 100,000 light years long. Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel on the 30 September 1834.The quartet is one of the best examples of compact galaxy groups. Because such groups contain four to eight galaxies in a very small region they are excellent laboratories for the study of galactic interactions and their effects, in particular on the formation of stars. The quartet has a total visual magnitude of almost 13. The brightest member of the group is NGC 92, having the blue magnitude of 13.8. On the sky, the four galaxies are all within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years. It was named by Halton Arp and Barry F. Madore, who compiled A Catalogue of Southern Peculiar Galaxies and Associations in 1987. Arp and Madore named Robert's Quartet after Robert Freedman who generated many of the updated positions of galaxies in the catalogue.

Seyfert's Sextet

Seyfert's Sextet is a group of galaxies about 190 million light-years away in the constellation Serpens. The group appears to contain six members, but one of the galaxies is a background object and another "galaxy" is actually a separated part of one of the other galaxies. The gravitational interaction among these galaxies should continue for hundreds of millions of years. Ultimately, the galaxies will merge to form a single giant elliptical galaxy.

Édouard Stephan

Édouard Jean-Marie Stephan (31 August 1837 – 31 December 1923) was a French astronomer. His surname is sometimes spelled Stéphan in some literature, but this is apparently erroneous.

He was born in Sainte Pezenne (today one of the districts of the town of Niort) and attended the Ecole Normale Superieure, and graduated at the top of his class in 1862.He was the director of the Marseille Observatory from 1864 to 1907 (until 1872 he was subordinate to Urbain le Verrier). In the early part of his career there, he had limited opportunities to do observations because he was preoccupied with improving the observatory. He discovered the asteroid 89 Julia in 1866. In 1867 he used the new telescope to observe a transit of Mercury.Between 1870 and 1875, Stephan systematically studied nebulae, precisely recording their positions and discovering many new ones. His goal was to enable the exact measurement of stellar proper motions by creating a reference system of fixed objects.In 1873, Stephan was the first person to attempt to measure the angular diameter of a star using interferometry, converting the 80 cm telescope at Marseille Observatory into an interferometer. He did this by obscuring the reflector with a mask containing two vertical slits.

The star he chose to perform this experiment was Sirius. He did not succeed in resolving any stellar disks, but by 1874 had obtained an upper limit to stellar diameters of 0.158" (the true angular diameter of Sirius is 0.0059 arcseconds, and for comparison, the angular diameter of Alpha Centauri and Betelgeuse are 0.0145 and 0.05 arcseconds respectively).In 1881 he discovered NGC 5, and he discovered the galaxy NGC 6027 the following year using the 80 cm reflector.Among others, he discovered Stephan's Quintet, also known as "Arp 319", a group of five galaxies. Stephan made this discovery with the first telescope equipped with a reflection coated mirror.In 1884 the French Academy of Sciences awarded him the Valz Prize (Prix Valz). His name is associated with the periodic comet 38P/Stephan-Oterma, although Jérôme Coggia saw it first.

He became a Chevalier of the Légion d'honneur in 1868 and an Officier of the Légion d'honneur in 1879.

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