Centaurus A (also known as NGC 5128 or Caldwell 77) is a

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Centaurus Centaurus is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one o ...

. It was discovered in 1826 by Scottish astronomer

James Dunlop James Dunlop FRSE (31 October 1793 – 22 September 1848) was a Scottish astronomer, noted for his work in Australia. He was employed by Sir Thomas Brisbane to work as astronomer's assistant at his private observatory, once located at Paramat ...

from his home in

Parramatta Parramatta () is a suburb and major Central business district, commercial centre in Greater Western Sydney, located in the state of New South Wales, Australia. It is located approximately west of the Sydney central business district on the ban ...

, in New South Wales, Australia. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its

Hubble type The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a t ...

(

lenticular galaxy A lenticular galaxy (denoted S0) is a type of galaxy intermediate between an elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. L ...

or a giant

elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The R ...

) and distance (10–16 million

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s). NGC 5128 is one of the closest

radio galaxies A radio galaxy is a galaxy with giant regions of radio emission extending well beyond its visible structure. These energetic radio lobes are powered by jets from its active galactic nucleus. They have luminosities up to 1039 W at radio wav ...

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, so its

active galactic nucleus 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 pr ...

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 center of the galaxy contains a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...

with a mass of 55 million

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es, which ejects a

relativistic jet An astrophysical jet is an astronomical phenomenon where outflows of ionised matter are emitted as an extended beam along the axis of rotation. When this greatly accelerated matter in the beam approaches the speed of light, astrophysical jets bec ...

that is responsible for emissions in the

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

and

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...

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 half of the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...

. X-rays are produced farther out as the jet collides with surrounding gases, resulting in the creation of highly energetic particles. The X-ray jets of Centaurus A are thousands of light-years long, while the radio jets are over a million light-years long. As in other

starburst galaxies A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formatio ...

, a galactic collision is suspected to be responsible for an intense burst of star formation. Models have suggested that Centaurus A was a large elliptical galaxy that collided with a smaller spiral galaxy, with which it will eventually merge. For that reason, the galaxy has been of particular interest to astronomers for years. While collisions of spiral galaxies are relatively common, the effects of a collision between an elliptical and a spiral galaxy are not fully understood.

Observational history

NGC 5128 was discovered on 29 April 1826 by

during a survey at the Parramatta Observatory. In 1847

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...

described the galaxy as "two semi-ovals of elliptically formed nebula appearing to be cut asunder and separated by a broad obscure band parallel to the larger axis of the nebula, in the midst of which a faint streak of light parallel to the sides of the cut appears." In 1949 John Gatenby Bolton, Bruce Slee and Gordon Stanley localized NGC 5128 as one of the first extragalactic radio sources. Five years later,

Walter Baade Wilhelm Heinrich Walter Baade (March 24, 1893 – June 25, 1960) was a German astronomer who worked in the United States from 1931 to 1959. Biography The son of a teacher, Baade finished school in 1912. He then studied maths, physics and astro ...

and

Rudolph Minkowski Rudolph Minkowski (born Rudolf Leo Bernhard Minkowski ; ; May 28, 1895 – January 4, 1976) was a German-American astronomer. Biography Minkowski was the son of Marie Johanna Siegel and physiologist Oskar Minkowski. His uncle was Hermann Min ...

suggested that the peculiar structure is the result of a merge event of a giant elliptical galaxy and a small spiral galaxy. The first detection of X-ray emissions, using a sounding rocket, was performed in 1970. In 1975–76 gamma-ray emissions from Centaurus A were observed through the atmospheric Cherenkov technique. The

Einstein Observatory Einstein Observatory (HEAO-2) was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to honor Albert E ...

detected an X-ray jet emanating from the nucleus in 1979. Ten years later, young blue stars were found along the central dust band with the Hubble Space Telescope. The

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 1 ...

identified in 1999 more than 200 new point sources. Another space telescope, the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

, found a parallelogram-shaped structure of dust in near infrared images of Centaurus A in 2006. Evidence of gamma emissions with very high energy (more than 100 GeV) was detected by the H.E.S.S-Observatorium in Namibia in 2009. The following year, Centaurus A was identified as a source of cosmic rays of highest energies, after years of observations by

Pierre Auger Observatory The Pierre Auger Observatory is an international cosmic ray observatory in Argentina designed to detect ultra-high-energy cosmic rays: sub-atomic particles traveling nearly at the speed of light and each with energies beyond 1018 eV. In Ear ...

. In 2016 a review of data from Chandra and

XMM-Newton ''XMM-Newton'', also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket. It is the second cornerst ...

, unusual high flares of energy were found in NGC 5128 and the galaxy NGC 4636. Jimmy Irwin of

University of Alabama The University of Alabama (informally known as Alabama, UA, or Bama) is a Public university, public research university in Tuscaloosa, Alabama. Established in 1820 and opened to students in 1831, the University of Alabama is the oldest and la ...

hypothesized the discovery as potentially a black hole in a yet unknown process or an

intermediate-mass black hole An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes. Several IMBH candidate obje ...

Morphology

Centaurus A may be described as having a peculiar morphology. As seen from Earth, the galaxy looks like a lenticular or

with a superimposed dust lane. The peculiarity of this galaxy was first identified in 1847 by

, and the galaxy was included in

Halton Arp Halton Christian "Chip" Arp (March 21, 1927 – December 28, 2013) was an American astronomer. He was known for his 1966 ''Atlas of Peculiar Galaxies'', which (it was later theorized) catalogues many examples of interacting and merging galaxie ...

's ''

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 ...

'' (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 Mergers and acquisitions (M&A) are business transactions in which the ownership of companies, other business organizations, or their operating units are transferred to or consolidated with another company or business organization. As an aspect ...

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 is the process by which dense regions within molecular clouds in The "medium" is present further soon.-->interstellar space

; over 100 star formation regions have been identified in the disk.

Supernovae

Two

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

e have been detected in Centaurus A. The first 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 A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white ...

, which forms when a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

'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 A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

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 second supernova, dubbed SN2016adj, was discovered by Backyard Observatory Supernova Search in February 2016 and was initially classified as a Type II supernova based on its H-alpha

emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

. A subsequent classification found the spectrum best resembled the Type Ib core-collapse supernova 1999dn. (See

Type Ib and Ic supernovae Type Ib and Type Ic supernovae are categories of supernovae that are caused by the stellar core collapse of massive stars. These stars have shed or been stripped of their outer envelope of hydrogen, and, when compared to the spectrum ...

Distance

Distance estimates to Centaurus A established since the 1980s typically range between 3–5 Mpc.

Classical Cepheids Classical Cepheids (also known as Population I Cepheids, Type I Cepheids, or Delta Cepheid variables) are a type of Cepheid variable star. They are population I variable stars that exhibit regular radial pulsations with periods of a few days to a ...

discovered in the heavily obscured dust lane of Centaurus A yield a distance between ~3–3.5 Mpc, depending on the nature of the extinction law adopted and other considerations.

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelen ...

s and

Type II Cepheid Type II Cepheids are variable stars which pulsate with periods typically between 1 and 50 days. They are population II stars: old, typically metal-poor, low mass objects. Like all Cepheid variables, Type IIs exhibit a relationship between the st ...

s were also discovered in Centaurus A, the latter being rarely detected beyond the

Local Group The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a "dumbbell" shape: the Milky Way and its satellites form ...

. The distance to Centaurus A established from several indicators such as

s and

planetary nebula A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to ...

e 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 The Centaurus A/M83 Group is a complex group of galaxies in the constellations Hydra, Centaurus, and Virgo. The group may be roughly divided into two subgroups. The Cen A Subgroup, at a distance of 11.9 Mly (3.66 Mpc), is centered on Centauru ...

, a nearby

group of galaxies 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 ...

Messier 83 Messier 83 or M83, also known as the Southern Pinwheel Galaxy and NGC 5236, is a barred spiral galaxy approximately 15 million light-years away in the constellation borders of Hydra and Centaurus. Nicolas-Louis de Lacaille discovered M83 on 23 ...

(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 Supercluster The Virgo Supercluster (Virgo SC) or the Local Supercluster (LSC or LS) is a mass concentration of galaxies containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least ...

. In addition to dwarf galaxies, Centaurus A, like most galaxies, has a population of

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

s. Some objects that appear to be globular clusters are hypothesized to be the tidally stripped cores of former galaxies. The most extreme example is the object VHH81-01, whose central black hole is estimated to be around .

Observations

Radio waves

In July 2021 the

Event Horizon Telescope The Event Horizon Telescope (EHT) is a large telescope array consisting of a global network of radio telescopes. The EHT project combines data from several very-long-baseline interferometry (VLBI) stations around Earth, which form a combined arr ...

released a resolved image of Centaurus A showing the jet coming from the black hole at its center.

Visibility

Centaurus A is located approximately 4° north of

Omega Centauri Omega Centauri (ω Cen, NGC 5139, or Caldwell 80) is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of , it is the largest-known globular clust ...

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.

Gallery

Centaurus A halo.jpg, Wide field view of Centaurus A showing its extended halo of stars Radio galaxy Centaurus A by ALMA.jpg, The radio galaxy Centaurus A, as seen by

ALMA Alma or ALMA may refer to: Arts and entertainment * ''Alma'' (film), a 2009 Spanish short animated film * ''Alma'' (Oswald de Andrade novel), 1922 * ''Alma'' (Le Clézio novel), 2017 * ''Alma'' (play), a 1996 drama by Joshua Sobol about Alma ...

CentaurusA3.jpg, The heavily obscured inner (barred?) spiral disk at 24 μm as shown by the Spitzer IR telescope NGC 5128.jpg, Chandra X-ray view of Cen A in X-rays showing one

from the central

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

Firestorm of Star Birth in Galaxy Centaurus A.jpg, "Hubble's panchromatic vision... reveals the vibrant glow of young, blue star clusters..." CenA-nearIR.jpg, Image of the central parts of Centaurus A showing the parallelogram-shaped remains of a smaller galaxy that was absorbed about 200 to 700 million years ago Centauros a-spc.png, "

False-colour False color (or pseudo color) refers to a group of color Signal processing, rendering methods used to display images in color which were recorded in the visible spectrum, visible or non-visible parts of the electromagnetic spectrum. A false-c ...

image of Centaurus A, showing

(red), 24-micrometre

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

(green) and 0.5–5

keV Kev can refer to: Given name * Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991 * Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter * Kev Coghlan (born 1988), Scottish Grand Prix motor ...

emission (blue) CentaurusA Center EN.PNG, Central part of the galaxy Centaurus A jets.ogv, Video about Centaurus A jets Centaurus a Mark Johnston.jpg, Amateur astronomer photo of Centaurus A

References

Sources

* STScI
Hubble Provides Multiple Views of How to Feed a Black Hole
Press release: ''Space Telescope Science Institute''. 14 March 1998. * Chandra X-Ray Observatory Photo Albu
Centaurus A Jet

External links

ESA/Hubble images of Centaurus A

* ttp://apod.gsfc.nasa.gov/apod/ap060304.html NASA's APOD: The Galaxy Within Centaurus A (March 4, 2006)
NASA's APOD: Centaurus A (July 12, 2018)

High-resolution image of Centaurus A
showing the discrete elements of galactic core
Centaurus A
at UniverseToday.com

NGC 5128
at DOCdb (Deep Sky Observer's Companion) *
Centaurus A at Constellation Guide
{{DEFAULTSORT:Centaurus A Lenticular galaxies Peculiar galaxies Radio galaxies Starburst galaxies Centaurus A/M83 Group Centaurus (constellation) NGC objects 46957

153 Year 153 ( CLIII) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Rusticus and Rufinus (or, less frequently, year 906 '' Ab urbe cond ...

077b Polar-ring galaxies Astronomical objects discovered in 1826 Articles containing video clips