Centaurus A
Encyclopedia
Centaurus A is a prominent galaxy in the constellation
of Centaurus
. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type (lenticular galaxy
or a giant elliptical galaxy) and distance (10-16 million light-year
s). NGC 5128 is one of the closest radio galaxies to Earth, 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, although the galaxy is only visible from low northern latitudes and the southern hemisphere.
A relativistic jet
which extracts energy from the vicinity of what is believed to be a supermassive black hole
at the center of the galaxy is responsible for emissions in the X-ray
and radio
wavelengths. By taking radio observations of the jet separated by a decade, astronomers have determined that the inner parts of the jet are moving at about one half of the speed of light
. X-rays are produced farther out as the jet collides with surrounding gases resulting in the creation of highly energetic particles. The radio jets of Centaurus A are over a million light years long.
As observed in other starburst galaxies
, a collision is responsible for the intense burst of star formation. Using the Spitzer Space Telescope
astronomers confirm that Centaurus A is going through a galaxy collision by devouring a spiral galaxy.
morphology. As seen from Earth, the galaxy looks like a lenticular
or elliptical galaxy
with a superimposed dust lane. The peculiarity of this galaxy was first identified in 1847 by John Herschel
, and the galaxy was included in the Atlas of Peculiar Galaxies
(published in 1966) as one of the best examples of a "disturbed" galaxy with dust absorption. The galaxy's strange morphology is generally recognized as the result of a merger
between two smaller galaxies.
The bulge of this galaxy is composed mainly of evolved red stars. The dusty disk, however, has been the site of more recent star formation
; over 100 star formation regions have been identified in the disk.
has been detected in Centaurus A.
The supernova, named SN 1986G
, was discovered within the dark dust lane of the galaxy by R. Evans
in 1986.
It was later identified as a type Ia supernova
,
which forms when a white dwarf
's mass grows large enough to ignite carbon fusion in its center, touching off a runaway
thermonuclear reaction, as may happen when a white dwarf in a binary star
system strips gas away from the other star. SN 1986G was used to demonstrate that the spectra of type Ia supernovae are not all identical, and that type Ia supernovae may differ in the way that they change in brightness over time.
. The distance to NGC 5128 established from several indicators such as Mira variables and planetary nebulae favour a more distant value of ~3.8 Mpc.
.
(a globular cluster
visible with the naked eye). Because the galaxy has a high surface brightness and relatively large angular size, it is an ideal target for amateur astronomy observations. The bright central bulge and dark dust lane are visible even in finderscopes and large binoculars, and additional structure may be seen in larger telescopes.
Centaurus A is visible to the naked eye under exceptionally good conditions.
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Centaurus
Centaurus
Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.-Stars:...
. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type (lenticular galaxy
Lenticular galaxy
A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies which have used up or lost most of their interstellar matter and therefore have very little ongoing...
or a giant elliptical galaxy) and distance (10-16 million light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s). NGC 5128 is one of the closest radio galaxies to Earth, so its active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
has been extensively studied by professional astronomers. The galaxy is also the fifth brightest in the sky, making it an ideal amateur astronomy target, although the galaxy is only visible from low northern latitudes and the southern hemisphere.
A relativistic jet
Relativistic jet
Relativistic jets are extremely powerful jets of plasma which emerge from presumed massive objects at the centers of some active galaxies, notably radio galaxies and quasars. Their lengths can reach several thousand or even hundreds of thousands of light years...
which extracts energy from the vicinity of what is believed to be a supermassive black hole
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
at the center of the galaxy is responsible for emissions in the X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
and radio
Radio spectrum
Radio spectrum refers to the part of the electromagnetic spectrum corresponding to radio frequencies – that is, frequencies lower than around 300 GHz ....
wavelengths. By taking radio observations of the jet separated by a decade, astronomers have determined that the inner parts of the jet are moving at about one half of the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. X-rays are produced farther out as the jet collides with surrounding gases resulting in the creation of highly energetic particles. The radio jets of Centaurus A are over a million light years long.
As observed in other starburst galaxies
Starburst galaxy
A starburst galaxy is a galaxy in the process of an exceptionally high rate of star formation, compared to the usual star formation rate seen in most galaxies. Galaxies are often observed to have a burst of star formation after a collision or close encounter between two galaxies...
, a collision is responsible for the intense burst of star formation. Using the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
astronomers confirm that Centaurus A is going through a galaxy collision by devouring a spiral galaxy.
Morphology
Centaurus A may be described as having a peculiarPeculiar galaxy
A peculiar galaxy is a galaxy which is unusual in its size, shape, or composition. Peculiar galaxies come about as a result of interactions between galaxies, and they may contain atypical amounts of dust or gas, may have higher or lower surface brightness than a typical galaxy, or may have...
morphology. As seen from Earth, the galaxy looks like a lenticular
Lenticular galaxy
A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies which have used up or lost most of their interstellar matter and therefore have very little ongoing...
or elliptical galaxy
Elliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
with a superimposed dust lane. The peculiarity of this galaxy was first identified in 1847 by John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
, and the galaxy was included in the Atlas of Peculiar Galaxies
Atlas of Peculiar Galaxies
The Atlas of Peculiar Galaxies is a catalog of peculiar galaxies produced by Halton Arp. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology....
(published in 1966) as one of the best examples of a "disturbed" galaxy with dust absorption. The galaxy's strange morphology is generally recognized as the result of a merger
Interacting galaxy
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy's disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision.-Satellite interaction:A giant...
between two smaller galaxies.
The bulge of this galaxy is composed mainly of evolved red stars. The dusty disk, however, has been the site of more recent star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
; over 100 star formation regions have been identified in the disk.
Supernovae
One supernovaSupernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
has been detected in Centaurus A.
The supernova, named SN 1986G
SN 1986G
SN 1986G was a supernova that was observed on May 3, 1986 by Robert Evans. Its host galaxy was Centaurus A about 15 million light-years away in the constellation Centaurus. Since Centaurus A is about 15 million light-years away from us, this supernova happened 15 million years ago.SN 1986G was a...
, was discovered within the dark dust lane of the galaxy by R. Evans
Robert Evans (astronomer)
Robert Owen Evans is a minister of the Uniting Church in Australia and an amateur astronomer who holds the all-time record for visual discoveries of supernovae ....
in 1986.
It was later identified as a type Ia supernova
Type Ia supernova
A Type Ia supernova is a sub-category of supernovae, which in turn are a sub-category of cataclysmic variable stars, that results from the violent explosion of a white dwarf star. A white dwarf is the remnant of a star that has completed its normal life cycle and has ceased nuclear fusion...
,
which forms when a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
's mass grows large enough to ignite carbon fusion in its center, touching off a runaway
Thermal runaway
Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result...
thermonuclear reaction, as may happen when a white dwarf in a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
system strips gas away from the other star. SN 1986G was used to demonstrate that the spectra of type Ia supernovae are not all identical, and that type Ia supernovae may differ in the way that they change in brightness over time.
Distance
Distance estimates to NGC 5128 established since the 1980s typically range between 3-5 Mpc. Classical Cepheids discovered in the heavily-obscured dust lane of NGC 5128 yield a distance between ~3-3.5 Mpc, depending on the nature of the extinction law adopted and other considerations. Mira variables and Type II Cepheids were also discovered in NGC 5128, the latter being rarely detected beyond local groupLocal Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
. The distance to NGC 5128 established from several indicators such as Mira variables and planetary nebulae favour a more distant value of ~3.8 Mpc.
Nearby galaxies and galaxy group information
Centaurus A is at the center of one of two subgroups within the Centaurus A/M83 Group, a nearby group of galaxies. Messier 83 (the Southern Pinwheel Galaxy) is at the center of the other subgroup. These two groups are sometimes identified as one group and sometimes identified as two groups. However, the galaxies around Centaurus A and the galaxies around M83 are physically close to each other, and both subgroups appear not to be moving relative to each other. The Centaurus A/M83 Group is located in the Virgo SuperclusterVirgo Supercluster
The Virgo Supercluster or Local Supercluster is the irregular supercluster that contains the Virgo Cluster in addition to the Local Group, which in turn contains the Milky Way and Andromeda galaxies. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs...
.
Amateur astronomy information
Centaurus A is located approximately 4° north of Omega CentauriOmega Centauri
Omega Centauri or NGC 5139 is a globular clusterin the constellation of Centaurus, discovered by Edmond Halley in 1677 who listed it as a nebula. Omega Centauri had been listed in Ptolemy's catalog 2000 years ago as a star. Lacaille included it in his catalog as number I.5...
(a globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
visible with the naked eye). Because the galaxy has a high surface brightness and relatively large angular size, it is an ideal target for amateur astronomy observations. The bright central bulge and dark dust lane are visible even in finderscopes and large binoculars, and additional structure may be seen in larger telescopes.
Centaurus A is visible to the naked eye under exceptionally good conditions.
See also
- Messier 87Messier 87Messier 87 is a supergiant elliptical galaxy. It was discovered in 1781 by the French astronomer Charles Messier, who cataloged it as a nebulous feature. The second brightest galaxy within the northern Virgo Cluster, it is located about 16.4 million parsecs from Earth...
- a giant elliptical galaxy that is also a strong radio source - NGC 1316NGC 1316NGC 1316 is a lenticular galaxy about 70 million light-years away in the constellation Fornax. NGC 1316 is a radio galaxy. It is the fourth-brightest radio source in the sky .-Structure and formation:...
- a similar lenticular galaxy that is also a strong radio source
External links
- Helmut Steinle Centaurus A project
- SEDS: Peculiar Galaxy NGC 5128
- ESA/Hubble images of Centaurus A
- NASA's APOD: The Galaxy Within Centaurus A (3/4/06)
- NASA's APOD: X-Rays from an Active Galaxy (7/5/03)
- High-resolution image of Centaurus A showing the discrete elements of galactic core
- Centaurus A at UniverseToday.com
- NGC5128 Centaurus A
