NGC 720 | |
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![]() NGC 720 by Chandra X-ray Observatory (left) and DSS (right) | |
Observation data (J2000 epoch) | |
Constellation | Cetus |
Right ascension | 01h 53m 00.5s [1] |
Declination | −13° 44′ 19″ [1] |
Redshift | 0.005821 +/- 0.000022 [1] |
Heliocentric radial velocity | 1,745 ± 7 km/s [1] |
Distance | 80 ± 20 Mly (24.4 ± 6.3 Mpc) [1] |
Apparent magnitude (V) | 10.2 |
Characteristics | |
Type | E5 [1] |
Apparent size (V) | 4.7′ × 2.4′ [1] |
Notable features | Strong X-rays source |
Other designations | |
MCG -02-05-068, PGC 6983 [1] |
NGC 720 is an elliptical galaxy located in the constellation Cetus. It is located at a distance of circa 80 million light years from Earth, which, given its apparent dimensions, means that NGC 720 is about 110,000 light years across. [1] It was discovered by William Herschel on October 3, 1785. [2] The galaxy is included in the Herschel 400 Catalogue. It lies about three and a half degrees south and slightly east from zeta Ceti. [3]
NGC 720 is an elliptical galaxy with elongated shape in the northwest to southeast axis as seen from Earth. [3] Observations by the Hubble Space Telescope of the core of NGC 720 did not reveal the presence of dust, disk, or inner spiral. [4] As observed in X-rays by the Chandra X-ray Observatory in 2000, the galaxy features a slightly flattened, or ellipsoidal triaxial halo of hot gas that has an orientation different from that of the optical image of the galaxy. Its shape cannot be accounted for based on the observed mass, even when using the Modified Newtonian dynamics theory of gravity, which excludes the need for dark matter. The observations by Chandra X-ray Observatory fit predictions of a cold dark matter model. [5] [6] The galaxy lacks emission in radio waves, meaning it does not host an active galactic nucleus. The total mass of the galaxy with its dark matter halo is estimated to be (3.1±0.4)×1012 M☉, with the total gas mass exceeding the stellar one. The observations of hot gas fit models that are nearly hydrostatic. [7] 42 X-ray point sources were detected in the galaxy, including a possible central source. Twelve of them are located within 2 arcsec of globular cluster candidates. NGC 720 features nine ultraluminous X-ray sources, the most found in an early type galaxy as of 2003. [8]
Observations made in 1996 suggested the galaxy had 660 ±190 globular clusters in the central 30kpc, a number considered small for such a galaxy. The allocation of the clusters resembled the ellipticity, position angle and surface brightness of the galaxy. [9] However, in 2012 it was observed that the blue globular clusters subpopulation had a similar slope with the X-ray surface brightness profile. [10] Further observations by the SLUGGS Survey (2016), with wider field data, raised the number of globular clusters in the galaxy to 1489 ± 96 and their distribution was less elliptical than the surface profile of the galaxy. The clusters have bimodal distribution as far as color is concerned, with the clusters characterised as red or blue, with the blue clusters having a stronger connection with the galactic halo. [11]
Optical long slit spectrography of the galaxy showed a strong age gradient along the semimajor axis of NGC 720, which has been explained on the grounds of two distinct population components. At the centre of the galaxy lie stars whose age is estimated to be 13 billion years (Gyrs) old up to 0.73 kpc, where stars with solar metallicity age (5 Gyrs) dominate. These older stars form a small bulge-like spheroid. At distances over 1 kpc dominate stars with age at 2,5 Gyrs. Based on the Mg2 gradient and its mass, it is proposed that NGC 720 underwent an unequal mass galaxy merger about 4 Gyrs ago. [12]
NGC 720 is the foremost galaxy in a small galaxy group, the NGC 720 group, which also includes the galaxy Arp 4. [13] NGC 720 lies at the centre of the group and the rest of the galaxies of the group are dwarf galaxies, which are at least 2 mag fainter than NGC 720. There is extended intragroup X-ray emission. The high fraction of early-type galaxies suggest that NGC 720 may be a fossil group, despite its low mass. [14] Further away lie the edge-on spiral galaxy NGC 681, NGC 701, and NGC 755. [13]
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.
Centaurus A is a galaxy in the constellation of Centaurus. It was discovered in 1826 by Scottish astronomer James Dunlop from his home in Parramatta, in New South Wales, Australia. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance. It is the closest radio galaxy to Earth, as well as the closest BL Lac object, so its active galactic nucleus has been extensively studied by professional astronomers. The galaxy is also the fifth-brightest in the sky, making it an ideal amateur astronomy target. It is only visible from the southern hemisphere and low northern latitudes.
The Sombrero Galaxy is a peculiar galaxy of unclear classification in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from the Milky Way galaxy. It 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 has an isophotal diameter of approximately 29.09 to 32.32 kiloparsecs, making it slightly bigger in size than the Milky Way.
Messier 84 or M84, also known as NGC 4374, is a giant elliptical or lenticular galaxy in the constellation Virgo. Charles Messier discovered the object in 1781 in a systematic search for "nebulous objects" in the night sky. It is the 84th object in the Messier Catalogue and in the heavily populated core of the Virgo Cluster of galaxies, part of the local supercluster.
Messier 89 is an elliptical galaxy in the constellation Virgo. It was discovered by Charles Messier on March 18, 1781. M89 is a member of the Virgo Cluster of galaxies.
NGC 1427 is a low-luminosity elliptical galaxy located approximately 71 million light-years away from Earth. It was discovered by John Frederick William Herschel on November 28, 1837. It is a member of the Fornax Cluster. The galaxy has a stellar mass of 7.9 × 1010M☉, and a total mass of 9.4 × 1010M☉. However, the mass of the dark matter halo surrounding the galaxy is around 4.3 × 1012M☉.
NGC 5170 is a large, nearby, edge-on spiral galaxy in the equatorial constellation of Virgo. It was discovered on February 7, 1785 by William Herschel. This galaxy is located at a distance of 83.5 million light years and is receding at a heliocentric radial velocity of 1,502 km/s. It 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.
NGC 1553 is a prototypical lenticular galaxy in the constellation Dorado. It is the second brightest member of the Dorado Group of galaxies. British astronomer John Herschel discovered NGC 1553 on December 5, 1834 using an 18.7 inch reflector.
NGC 1399 is a large elliptical galaxy in the Southern constellation Fornax, the central galaxy in the Fornax Cluster. The galaxy is 66 million light-years away from Earth. With a diameter of 130 000 light-years, it is one of the largest galaxies in the Fornax Cluster and slightly larger than the Milky Way. William Herschel discovered this galaxy on October 22, 1835.
NGC 6388 is a globular cluster of stars located in the southern constellation of Scorpius. The cluster was discovered by Scottish astronomer James Dunlop on May 13, 1826 using a 20 cm (9 in) reflector telescope. It was later determined to be a globular cluster by English astronomer John Herschel, who was able to resolve it into individual stars. NGC 6388 is located at a distance of approximately 35,600 light-years (10.90 kpc) from the Sun. Due to its apparent visual magnitude of +6.8, binoculars or a small telescope are required to view it.
NGC 1407 is an elliptical galaxy in Eridanus. It is at a distance of 76 million light-years from Earth. It is the brightest galaxy in the NGC 1407 Group, part of the Eridanus Group, with NGC 1407 being its brightest member. NGC 1400, the second-brightest of the group lies 11.8 arcmin away.
NGC 4494 is an elliptical galaxy located in the constellation Coma Berenices. It is located at a distance of circa 45 million light years from Earth, which, given its apparent dimensions, means that NGC 4494 is about 60,000 light years across. It was discovered by William Herschel in 1785.
NGC 3311 is a super-giant 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 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 1395 is an elliptical galaxy located in the constellation Eridanus. It is located at a distance of circa 75 million light years from Earth, which, given its apparent dimensions, means that NGC 1395 is about 130,000 light years across. It was discovered by William Herschel on November 17, 1784. It is a member of the Eridanus Cluster.
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 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 4278 is an elliptical galaxy located in the constellation Coma Berenices. It is located at a distance of circa 55 million light years from Earth, which, given its apparent dimensions, means that NGC 4278 is about 65,000 light years across. It was discovered by William Herschel on March 13, 1785. NGC 4278 is part of the Herschel 400 Catalogue and can be found about one and 3/4 of a degree northwest of Gamma Comae Berenices even with a small telescope.
NGC 4318 is a small lenticular galaxy located about 72 million light-years away in the constellation Virgo. It was discovered by astronomer John Herschel on January 18, 1828. NGC 4318 is a member of the Virgo W′ group, a group of galaxies in the background of the Virgo Cluster that is centered on the giant elliptical galaxy NGC 4365.
NGC 1132 is an elliptical galaxy located in the constellation Eridanus. The galaxy was discovered by John Herschel on November 23, 1827. It is located at a distance of about 318 million light-years away from Earth.