Circinus Galaxy

The Circinus Galaxy (ESO 97-G13) is a Seyfert galaxy[2] in the constellation of Circinus. It is located 4 degrees below the Galactic plane, and, at a distance of 4.0 Mpc (13 Mly), and is one of the closest galaxies to the Milky Way.[3] The galaxy is undergoing tumultuous changes, as rings of gas are likely being ejected from the galaxy. Its outermost ring is 1400 light-years across while the inner ring is 260 light-years across. Although the Circinus galaxy can be seen using a small telescope, it was not noticed until 1977[4] because it lies close to the plane of the Milky Way and is obscured by galactic dust. The Circinus Galaxy is a Type II Seyfert galaxy and is one of the closest known active galaxies to the Milky Way, though it is probably slightly farther away than Centaurus A.

Circinus Galaxy produced supernova SN 1996cr, which was identified over a decade after it exploded. This supernova event was first observed during 2001 as a bright, variable object in a Chandra X-ray Observatory image, but it was not confirmed as a supernova until years later.

The Circinus Galaxy is one of twelve large galaxies in the "Council of Giants" surrounding the Local Group in the Local Sheet.[5]

Circinus Galaxy
Circinus Galaxy
A Hubble Space Telescope (HST) image of the Circinus Galaxy.
Observation data (J2000 epoch)
Right ascension 14h 13m 9.9s[1]
Declination−65° 20′ 21″[1]
Redshift426 ± 25 km/s
Distance4.0 Mpc [ 13 Mly ]
Apparent magnitude (V)12.1[1]
Apparent size (V)6′.9 × 3′.0[1]
Other designations
ESO 97-G13,[1] LEDA 50779


  1. ^ a b c d e f "NASA/IPAC Extragalactic Database". Results for ESO 97-13. Retrieved 2007-04-20.
  2. ^ "NAME Circinus Galaxy". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-04-20.
  3. ^ Maiolino, R.; Krabbe, A.; Thatte, N.; Genzel, R. (1998). "Seyfert Activity and Nuclear Star Formation in the Circinus Galaxy". The Astrophysical Journal. 493 (2): 650–65. arXiv:astro-ph/9709091. Bibcode:1998ApJ...493..650M. doi:10.1086/305150.
  4. ^ Inglis, Mike (2004). Astronomy of the Milky Way: Observer's Guide to the Southern Sky. New York, New York: Springer. p. 31. ISBN 978-1-85233-742-1.
  5. ^ McCall, Marshall L. (29 April 2013). "A Council of Giants". Monthly Notices of the Royal Astronomical Society (published 10 March 2014). 440 (1): 405–426. arXiv:1403.3667. Bibcode:2014MNRAS.440..405M. doi:10.1093/mnras/stu199.

External links

Coordinates: Sky map 14h 13m 9.9s, −65° 20′ 21″


Circinus is a small, faint constellation in the southern sky, first defined in 1756 by the French astronomer Nicolas-Louis de Lacaille. Its name is Latin for compass, referring to the drafting tool used for drawing circles (it should not be confused with Pyxis, a constellation that represents a mariner's compass which points north). Its brightest star is Alpha Circini, with an apparent magnitude of 3.19. Slightly variable, it is the brightest rapidly oscillating Ap star in the night sky. AX Circini is a Cepheid variable visible with the unaided eye, and BX Circini is a faint star thought to have been formed from the merger of two white dwarfs. Two sun-like stars have planetary systems: HD 134060 has two small planets, and HD 129445 has a Jupiter-like planet. Supernova SN 185 appeared in Circinus in 185 AD and was recorded by Chinese observers. Two novae have been observed more recently, in the 20th century.

The Milky Way runs through the constellation, featuring prominent objects such as the open cluster NGC 5823 and the planetary nebula NGC 5315. Circinus hosts a spiral galaxy, the Circinus Galaxy, which was discovered in 1977 and is the closest Seyfert galaxy to the Milky Way. The Alpha Circinids (ACI), a meteor shower also discovered in 1977, radiate from this constellation.

Circinus (disambiguation)

Circinus may refer to:

Circinus, the Latin for a compass (drafting), a tool for drawing arcs and circles

Circinus (constellation), a small constellation of the southern winter sky, said to resemble a compass

Circinus Galaxy, a galaxy, also known as ESO 97-G13, in the Circinus constellation

Epsilon Circini

Epsilon Circini, Latinized from ε Circini, is a solitary star located in the southern constellation of Circinus. It is faintly visible to the naked eye, having an apparent visual magnitude of 4.86. The distance to this star, as determined by a measured annual parallax shift of 8.00 mas, is around 410 light years.

This is an evolved K-type giant star with a stellar classification of K2.5 III. The measured angular diameter of this star is 2.02±0.11 mas. At its estimated distance, this yields a physical size of about 27 times the radius of the Sun. It radiates about 244 times the solar luminosity from its outer atmosphere at an effective temperature of 4,576 K.

Eta Circini

Eta Circini, Latinized from η Circini, is the Bayer designation for a solitary star located in the southern constellation of Circinus. It is faintly visible to the naked eye with an apparent visual magnitude of 5.17. The distance to this star, as determined from an annual parallax shift of 11.82 mas, is around 276 light years.

This is an evolved G-type giant star with a stellar classification of G8 III. It is radiating an estimated 64 times the solar luminosity from its outer atmosphere at an effective temperature of 4,954 K.

Gamma Circini

Gamma Circini, Latinized from γ Circini, is a star system located in the constellation Circinus. It was noted as a double star by Herschel in 1835, who estimated their separation as 1 arc second. It is visible to the naked eye with an apparent visual magnitude of 4.51. Based upon an annual parallax shift of 7.27 mas, is it located at a distance of approximately 450 light years.

This is a wide binary star system and may even be a triple star. The two visible components orbit each other with a preliminary estimated period of 258 years and a large eccentricity of 0.931. As of 2014, the visible components have an angular separation of 0.80 arc seconds along a position angle of 359°.The primary star, component A, is a B-type subgiant star with a stellar classification of B5 VI. Based upon isochrone curve fitting it is hypothesized to be a pair of matching B5 stars, and is a Be variable with an uncertain maximum. It has an effective temperature of 15,135 K and an estimated mass six times that of the Sun. The companion, component B, is an F-type main sequence star with a stellar classification of F8 V. It has an effective temperature of 4,786 K.

List of galaxies

The following is a list of notable galaxies.

There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in our Local Supercluster and an estimated number of about one to two trillion in all of the observable universe.

The discovery of the nature of galaxies as distinct from other nebulae (interstellar clouds) was made in the 1920s. The first attempts at systematic catalogues of galaxies were made in the 1960s, with the Catalogue of Galaxies and Clusters of Galaxies listing 29,418 galaxies and galaxy clusters, and with the Morphological Catalogue of Galaxies, a putatively complete list of galaxies with photographic magnitude above 15, listing 30,642. In the 1980s, the Lyons Groups of Galaxies listed 485 galaxy groups with 3,933 member galaxies. Galaxy Zoo is a project aiming at a more comprehensive list: launched in July 2007, it has classified over one million galaxy images from The Sloan Digital Sky Survey, The Hubble Space Telescope and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey.There is no universal naming convention for galaxies, as they are mostly catalogued before it is established whether the object is or isn't a galaxy. Mostly they are identified by their celestial coordinates together with the name of the observing project (HUDF, SDSS, 3C, CFHQS, NGC/IC, etc.)

List of nearest galaxies

This is a list of known galaxies within 3.59 megaparsecs (11.7 million light-years) of the Solar System, in ascending order of distance.

This encompasses all of the about 50 Local Group galaxies, and some that are members of neighboring galaxy groups, the M81 Group and the Centaurus A/M83 Group, and some that are currently not in any defined galaxy group.

The list aims to reflect current knowledge: not all galaxies within the 3.59 Mpc radius have been discovered. Nearby dwarf galaxies are still being discovered, and galaxies located behind the central plane of the Milky Way are extremely difficult to discern. It is possible for any galaxy to mask another located beyond it.

Intergalactic distance measurements are subject to large uncertainties. Figures listed are composites of many measurements, some of which may have had their individual error bars tightened to the point of no longer overlapping with each other.

List of spiral galaxies

A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. A spiral galaxy maintains its spirals arms due to density wave theory.

Local Sheet

The Local Sheet in astronomy is a nearby extragalactic region of space where the Milky Way, the members of the Local Group and other galaxies share a similar peculiar velocity. This region lies within a radius of about 7 Mpc (23 Mly), 0.46 Mpc (1.5 Mly) thick, and galaxies beyond that distance show markedly different velocities. The Local Group has only a relatively small peculiar velocity of 66 km⋅s−1 with respect to the Local Sheet. Typical velocity dispersion of galaxies is only 40 km⋅s−1 in the radial direction. Nearly all nearby bright galaxies belong to the Local Sheet. The Local Sheet is part of the Local Volume and is in the Virgo Supercluster (Local Supercluster). The Local Sheet forms a wall of galaxies delineating one boundary of the Local Void.A significant component of the mean velocity of the galaxies in the Local Sheet appears as the result of the gravitational attraction of the Virgo Cluster of galaxies, resulting in a peculiar motion ~185 km⋅s−1 toward the cluster. A second component is directed away from the center of the Local Void; an expanding region of space spanning an estimated 45 Mpc (150 Mly) that is only sparsely populated with galaxies. This component has a velocity of 259 km⋅s−1. The Local Sheet is inclined 8° from the Local Supercluster (Virgo Supercluster).The so-called Council of Giants is a ring of twelve large galaxies surrounding the Local Group in the Local Sheet, with a radius of 3.75 Mpc (12.2 Mly). Ten of these are spirals, while the remaining two are ellipticals. The two ellipticals (Maffei 1 and Centaurus A) lie on opposite sides of the Local Group, and their formation may have prompted the development of the Local Group. The Local Sheet's own development outlines a concentration of dark matter in a filament.

* The mass is given as the logarithm of the mass in solar masses.

NGC 7552

NGC 7552 (also known as IC 5294) is a barred spiral galaxy in the constellation Grus. It is at a distance of circa 60 million light years from Earth, which, given its apparent dimensions, means that NGC 7552 is about 75,000 light years across. It forms with three other spiral galaxies the Grus Quartet.

Seyfert galaxy

Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material.Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way.Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943.

Theta Circini

Theta Circini (θ Cir), is a binary star located in the southern constellation of Circinus, to the northwest of Alpha Circini. It is faintly visible to the naked eye with an apparent visual magnitude of 5.110. Based upon an annual parallax shift of 11.82 mas, it is located at a distance of about 276 light years from the Sun.

This is an astrometric binary star system with an orbital period of about 39.6 years, an eccentricity of 0.3, and a semimajor axis of 85.64 mas. The pair show a combined stellar classification of B3 Ve, which matches a B-type main sequence star. The 'e' suffix on the class indicates this is a Be star. Alternate classifications include B4 Vnp and B4npe, with the 'n' indicating broad ("nebulous") absorption lines due to rotation and the 'p' meaning a chemically peculiar star. The two components appear to have similar visual magnitude, mass, and classification. The system behaves as a Gamma Cassiopeiae variable showing occasional outbursts of up to 0.27 in magnitude.

Zeta Circini

Zeta Circini, Latinized from ζ Circini, is the Bayer designation for a star located in the southern constellation of Circinus. With an apparent visual magnitude of 6.08, it is barely visible to the naked eye on a dark night. (According to the Bortle scale, it requires the lighting level of suburban skies or darker to be seen.) The distance to this star, as estimated using an annual parallax shift of 2.56 mas, is around 1,300 light years.

This is a B-type main sequence star with a stellar classification of B2/3 Vn,

where the 'n' suffix indicates broad ("nebulous") absorption lines due to rotation. It is a slowly pulsating B star with a frequency of 0.26877 d−1 and an amplitude of 0.0046 magnitude. The averaged quadratic field strength of the star's longitudinal magnetic field is (1.06±0.46)×10−2 T.The star is around 32 million years old and is spinning rapidly with a projected rotational velocity of 264 km/s. It has an estimated 5.5 times the mass of the Sun and 3.8 times the Sun's radius. Zeta Circini radiates around 602 times the solar luminosity from its outer atmosphere at an effective temperature of 16,788 K.

List of notable Seyfert galaxies
Seyfert 1
Seyfert 2

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.