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

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

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 first constellati ...

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 ...

. It was discovered in 1826 by

Scottish Scottish usually refers to something of, from, or related to Scotland, including: *Scottish Gaelic, a Celtic Goidelic language of the Indo-European language family native to Scotland *Scottish English *Scottish national identity, the Scottish ide ...

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 Param ...

from his home in

Parramatta Parramatta (; ) is a suburb (Australia), suburb and major commercial centre in Greater Western Sydney. Parramatta is located approximately west of the Sydney central business district, Sydney CBD, on the banks of the Parramatta River. It is co ...

, 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 published 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 Galaxy morphological classification, type of galaxy intermediate between an elliptical galaxy, elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-s ...

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 three main galaxy morphological classification, classes of galaxy described by Edwin Hubble in his Hub ...

) and distance (11–13 million

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s). It is the closest

radio galaxy 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 Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, as well as the closest

BL Lac object 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 l ...

, so its

active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such e ...

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 ...

with a mass of 55 million

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es, which ejects a

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

that is responsible for emissions in the

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

and

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

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 exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

. 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. It is also one of the nearest large

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 format ...

, of which 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 and experimental photographer who invented the blueprint and did botanical work. ...

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. Early life and education Baade was born the son of a teacher in North Rhine-Westphalia, Germany. He fin ...

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 Mi ...

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 HEAO Program, High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to ho ...

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 ...

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, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...

, 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 . In Earth's atmosphe ...

. 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 corners ...

, 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, the Capstone, or Bama) is a Public university, public research university in Tuscaloosa, Alabama, United States. Established in 1820 and opened to students in 1831, the University of ...

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 of one hundred to one hundred thousand (102–105) solar masses: significantly higher than stellar black holes but lower than the hundred thousand to more than ...

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 is remembered for his 1966 book ''Atlas of Peculiar Galaxies'', which catalogued unusual-looking galaxies and presented their images. Arp was als ...

's ''

Atlas of Peculiar Galaxies The ''Atlas of Peculiar Galaxies'' is a Astronomical catalog, 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 Institut ...

'' (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 a company, business organization, or one of their operating units is transferred to or consolidated with another entity. They may happen through direct absorpt ...

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 interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

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

Novae and supernovae

Two

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

e have been detected in Centaurus A. The first supernova, named SN 1986G, was discovered within the dark dust lane of the galaxy by

Robert Evans Robert Evans (born Robert J. Shapera; June 29, 1930 – October 26, 2019) was an American film producer who worked on ''Rosemary's Baby (film), Rosemary's Baby'' (1968), ''Love Story (1970 film), Love Story'' (1970), ''The Godfather'' (1972), ...

on 3 May 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 Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

's mass grows large enough to ignite carbon fusion in its center, touching off a

runaway Runaway, Runaways or Run Away may refer to: Engineering * Runaway reaction, a chemical reaction releasing more heat than what can be removed and becoming uncontrollable * Thermal runaway, self-increase of the reaction rate of an exothermic proce ...

thermonuclear reaction, as may happen when a white dwarf in a

binary star A binary star or binary star system 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 as separate stars us ...

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, designated SN 2016adj, 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 weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

. 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 spectru ...

). In addition to these supernovae, a

luminous red nova A luminous red nova (abbr. ''LRN'', pl. ''luminous red novae'', pl.abbr. ''LRNe'') is a stellar explosion thought to be caused by the merging of two stars. They are characterised by a distinct red colour, and a light curve that fades slowly with ...

, designated AT2020nqq (type ILRT, mag. 17.8), was discovered on 27 June 2020. Centaurus A is close enough that classical

nova A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white ...

e can also be detected. The first confirmed nova in this galaxy was discovered by BlackGEM at magnitude 18.47 on 23 December 2024, and designated AT 2024aeql.

Distance

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

Classical Cepheids Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial Stellar pulsation, pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenth ...

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 wave ...

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 period-luminosity relationshi ...

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, where Earth is located. 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 ...

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

s and

planetary nebula A planetary nebula 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 planets. The ...

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, 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 (constellation), Hydra and Centaurus. Nicolas-Louis de Lacail ...

(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 Local Supercluster (LSC or LS), or Virgo Supercluster is a formerly defined supercluster containing the Virgo Cluster and Local Group, which itself contains the Milky Way and Andromeda galaxies, as well as others. At least 100 galaxy group ...

. 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 that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

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 Astronomical interferometer, 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, wh ...

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 clus ...

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. Claims have been made that 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'', an upcoming film by Sally Potter * ''Alma'' (Oswald de Andrade novel), 1922 * ''Alma'' (Le Clézio novel), 2017 * ''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 massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

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 colors and pseudo colors respectively refers to a group of color Signal processing, rendering methods used to display images in colors which were recorded in the visible spectrum, visible or non-visible parts of the electromagnetic spe ...

image of Centaurus A, showing

(red), 24-micrometre

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

(green) and 0.5–5

keV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

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)

* ttp://www.universetoday.com/wp-content/uploads/2006/07/ngc5128.jpg High-resolution image of Centaurus Ashowing 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 BL Lacertae objects Centaurus A/M83 Group Centaurus NGC objects 46957

153 Year 153 ( CLIII) was a common year starting on Sunday 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 condita''). The denomination 153 for this y ...

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