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Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now. Groups and clusters may contain ten to thousands of individual galaxies. The clusters themselves are often associated with larger, non-gravitationally bound, groups called superclusters.
Serpens is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International Astronomical Union. It is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput to the west and Serpens Cauda to the east. Between these two halves lies the constellation of Ophiuchus, the "Serpent-Bearer". In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in Serpens Caput and Nu Serpentis in Serpens Cauda.
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy. The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
Messier 87 is a supergiant elliptical galaxy in the constellation Virgo that contains several trillion stars. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters—about 15,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs, traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.
A blazar is an active galactic nucleus (AGN) with a relativistic jet directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from Earth. Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales. Some blazar jets appear to exhibit superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.
A BL Lacertae object or BL Lac object is a type of active galactic nucleus (AGN) or a galaxy with such an AGN, named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and large-amplitude flux variability and significant optical polarization. Because of these properties, the prototype of the class was originally thought to be a variable star. When compared to the more luminous active nuclei (quasars) with strong emission lines, BL Lac objects have spectra dominated by a relatively featureless non-thermal emission continuum over the entire electromagnetic range. This lack of spectral lines historically hindered identification of the nature and distance of such objects.
Messier 88 is a spiral galaxy about 50 to 60 million light-years away from Earth in the constellation Coma Berenices. It was discovered by Charles Messier in 1781.
Abell 1413 is a massive and rich type I galaxy cluster straddling the border between the constellations Leo and Coma Berenices, with the projected comoving distance of approximately 640 Mpc (2.1 billion ly). The cluster is especially notable due to the presence of its very large brightest cluster galaxy (BCG), one of the most extreme examples of its type, as well as one of the largest galaxies known. The cluster was first noted by George O. Abell in 1958.
NGC 3309 is a giant elliptical galaxy located about 200 million light-years away in the constellation Hydra. NGC 3309 was discovered by astronomer John Herschel on March 24, 1835. The galaxy forms a pair with NGC 3311 which lies about 72,000 ly (22 kpc) away. Both galaxies dominate the center of the Hydra Cluster.
NGC 3311 is a supergiant elliptical galaxy located about 190 million light-years away in the constellation Hydra. The galaxy was discovered by astronomer John Herschel on March 30, 1835. NGC 3311 is the brightest member of the Hydra Cluster and forms a pair with NGC 3309 which along with NGC 3311, dominate the central region of the Hydra Cluster.
NGC 3312 is a large and highly inclined spiral galaxy located about 194 million light-years away in the constellation Hydra. The galaxy was discovered by astronomer John Herschel on March 26, 1835. It was later rediscovered by astronomer Guillaume Bigourdan on February 26, 1887. NGC 3312 was later listed and equated with IC 629 because the two objects share essentially the same celestial coordinates. NGC 3312 is the largest spiral galaxy in the Hydra Cluster and is also classified as a LINER galaxy.
NGC 708 is an elliptical galaxy located 240 million light-years away in the constellation Andromeda and was discovered by astronomer William Herschel on September 21, 1786. It is classified as a cD galaxy and is the brightest member of Abell 262. NGC 708 is a weak FR I radio galaxy and is also classified as a type 2 Seyfert galaxy.
NGC 4636 is an elliptical galaxy located in the constellation Virgo. It is a member of the NGC 4753 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster. It is located at a distance of about 55 million light years from Earth, which, given its apparent dimensions, means that NGC 4636 is about 105,000 light years across.
NGC 759 is an elliptical galaxy located 230 million light-years away in the constellation Andromeda. NGC 759 was discovered by astronomer by Heinrich d'Arrest on September 17, 1865. It is a member of Abell 262.
NGC 5846 is an elliptical galaxy located in the constellation Virgo. It is located at a distance of circa 90 million light years from Earth, which, given its apparent dimensions, means that NGC 5846 is about 110,000 light years across. It was discovered by William Herschel on February 24, 1786. It lies near 110 Virginis and is part of the Herschel 400 Catalogue. It is a member of the NGC 5846 Group of galaxies, itself one of the Virgo III Groups strung out to the east of the Virgo Supercluster of galaxies.
NGC 4065 is an elliptical galaxy located 300 million light-years away in the constellation Coma Berenices. The galaxy was discovered by astronomer William Herschel on April 27, 1785. It was then rediscovered by John Herschel on April 29, 1832 and was listed as NGC 4057. NGC 4065 is the brightest member of the NGC 4065 Group.
NGC 4066 is an elliptical galaxy located 340 million light-years away in the constellation Coma Berenices. The galaxy was discovered by astronomer William Herschel on April 27, 1785. NGC 4066 is a member of the NGC 4065 Group.
NGC 4070 is an elliptical galaxy located 340 million light-years away in the constellation Coma Berenices. NGC 4070 was discovered by astronomer William Herschel on April 27, 1785. It was rediscovered by John Herschel on April 29, 1832 and was listed as NGC 4059. The galaxy is a member of the NGC 4065 Group.
AP Librae is a BL Lacertae object located at a distance of 700 million light years in the southern constellation of Libra. In the visual band it is one of the most active blazars known. AP Lib is surrounded by an extended source with a spectrum characteristic of a red-shifted giant elliptical galaxy. The derived visual magnitude of this region is 15.0, and it follows a radially decreasing brightness that is characteristic of an elliptical. Seven fainter galaxies are visible within an angular radius of 9′, suggesting it is the brightest member of a galactic cluster.
References
- ↑ Maccagni, D.; Tarenghi, M.; Cooke, B. A.; Maccacaro, T.; Pye, J. P.; Ricketts, M. J. (1978). "An X-ray and optical study of seven clusters of galaxies". Astronomy and Astrophysics. 62 (1–2): 127–33. Bibcode:1978A&A....62..127M.
- ↑ Remillard, R. A.; Tuohy, I. R.; Brissenden, R. J. V.; Buckley, D. A. H.; Schwartz, D. A.; Feigelson, E. D.; Tapia, S. (1989). "Two X-ray-selected BL Lacertae objects observed with the HEAO 1 scanning modulation collimator". Astrophysical Journal, Part 1. 345: 140–47. Bibcode:1989ApJ...345..140R. doi:10.1086/167888. ISSN 0004-637X.
- ↑ Pesce, Joseph E.; Falomo, Renato.; Treves, Aldo (1994). "Imaging and spectroscopy of galaxies in the fields of five BL Lacertae objects". Astronomical Journal. 107 (2): 494–502. Bibcode:1994AJ....107..494P. doi: 10.1086/116871 . ISSN 0004-6256.
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