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Key Facts & Information

  • Centaurus A or NGC 5128 is a galaxy found in the constellation of Centaurus. Centaurus A lies around 10 to 16 million light years away from us and has an estimated diameter of 60 000 light years and an apparent magnitude of 6.84. It might be an ancient cannibalistic galaxy devouring a smaller, nearby galaxy. Centaurus A is the largest and nearest radio galaxy. There is a massive source of radio wavelengths in the constellation Centaurus. It is also the fifth brightest galaxy in the sky, but is only visible from low northern latitudes and the southern hemisphere.
  • Centaurus A is believed to be a result of two galaxies smashing into each other. One is an older elliptical galaxy that merges with a smaller spiral galaxy.
  • The epic radio lobes, which spread millions of light years towards the opposite direction from the dust band, are probably a result of this collision.
  • It shoots two gigantic jets with high-energy radiation from the galaxy’s center due to the black hole with a mass of 55 million solar masses swallowing the falling matter.
  • It has an active nucleus, meaning that matter falls into the supermassive black hole in its center and shoots electrons from its poles at half the speed of light. This creates massive relativistic jets that spread thousands of light years into space.
  • The speed of the inner parts of the moving jets were determined by taking radio observations of the jet separated by a decade.
  • The X-ray jets of Centaurus A are produced farther out as the jet collides with surrounding gases, which results in the creation of highly energetic particles.
  • These X-ray jets are thousands of light years long and the radio jets are over a million light years long.
  • Evidence of starburst, which is a process of formation of new blue stars in the dust band, and the edges of the two massive radio lobes were also found. Similar with the other galaxies, a collision is expected to be the reason for the intense starburst formation.

Formation

  • Arguments were still made by the scientists whether to classify the Centaurus A as an elliptical galaxy or a lenticular galaxy due to its strange appearance.
  • Based on research studies conducted in visible light, the galaxy seems to have a structure of elliptical galaxies, wherein these galaxies do not usually have bonds of interstellar gas and dust known as a dust lane or bond.
  • A dust lane is a cloud-like smudge that hides the bulge of the Milky Way as we look at it in the night sky. The dust bond is a usual feature in spiral galaxies, but is also found in Centaurus A.
  • In 1954, it was first hypothesized that the galaxy’s strange structures and its emissions were due to the collision of two galaxies.
  • Simulation models suggest there is a possibility that a more massive elliptical galaxy merged in a smaller spiral galaxy somewhere 200 and 700 million years ago.

Observational History

  • It was discovered by Scottish astronomer James Dunlop in April 29, 1826, from his home in Parramatta, South Wales, Australia.
  • In 1847, the galaxy was described by John Herschel 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, Centaurus A was localized as one of the first extragalactic radio sources by John Gatenby Bolton, Bruce Slee, and Gordon Stanley. It was the first and the brightest source of radio emissions in the Centaurus constellation.
  • In 1954, Walter Baade and Rudolph Minkowski suggested that the peculiar structure of the galaxy is caused by the collision of a giant galaxy and a small spiral galaxy.
  • In 1970, the X-ray emissions were first detected using a sounding rocket.
  • In 1975 to 1976, gamma ray emissions from Centaurus A were observed through the Imaging Atmospheric Cerenkov Technique.
  • In 1979, an X-ray jet emanating from the nucleus was detected by the Einstein Observatory.
  • In 1989, young blue stars were found along the central dust band with the Hubble Space Telescope.
  • In 1999, the Chandra X-ray Observatory identified more than 200 new point sources.
  • In 2006, the Spitzer Space Telescope found a parallelogram-shaped structure of dust in near infrared images of the Centaurus A, photographs of the light coming from the galaxy in a broad spectrum ranging from infrared to ultraviolet light, and also radio and microwaves. This revealed the unique feature of Centaurus A and the striking radio lobes that spread its relativistic jets.

Structure

  • Centaurus A’s central bulge mainly consists of older red stars.
  • Research conducted in the ultraviolet spectrum displays an abundance of blue stars that indicate a very high new star formation activity, starburst.
  • Blue stars are young hot stars found in nebular clouds and remnants of galactic collisions.
  • Strong emissions in radio wavelengths were detected from constellation Centaurus and the Centaurus A was dubbed to be the source of the emissions.
  • Further research revealed two enormous radio lobes perpendicular to the plane of the dust lane that measure 650 000 and 1 350 000 light years in diameter.
  • Centaurus A also hosts a supermassive black hole with an estimation of 55 solar masses.
  • The black hole is surrounded by a disk of hot gas with a diameter of around 130 light years.
  • Its black hole is currently in the process of “feeding” which means that the hot gas is spiraling towards it.
  • As the gas spirals down towards the event horizon, the hot swirling matter forms what is known as an accretion disk.
  • Two jets shooting symmetrically from the galaxy’s nucleus were revealed through the use of X-ray imaging. The emission of gamma radiation, which is more than ten times greater than the radio output of the galaxy, was detected by the researchers from the Naval Research Laboratory.
  • A number of sources of X-ray radiation were also found by scientists and are believed to come from the neutron stars and active stellar-mass black holes.
  • Microwave wavelength observations revealed the direction in which the galaxy spins.
  • Other types of stars are also found within the Centaurus A, such as the Mira variables and Type II Cepheids.
  • Mira variables are a type of old red giants, which undergo helium fusion inside their core and shed a lot of their mass to the surrounding space.
  • They are pulsating stars with varying brightness over time, and their loss of mass will result in becoming dwarfs over the course of several million years.
  • Cepheid variables, on the other hand, are also a type of pulsating star, which are often used to determine the distances between galaxies.

Supernovae

  • Along with all the new stars created by Centaurus A, it’s also losing some stars. Centaurus A has two detected supernovae, SN 1986G and SN2016adj
  • SN 1986G
    • SN 1986G was discovered in 1986 within the dark dust lane by Robert Owen Evans.
    • It was later identified as Type Ia supernova wherein it forms when a dwarf’s mass grows large enough for it to ignite carbon fusion inside its core.
    • Thermonuclear reaction may happen when a binary system’s white dwarf strips gas away from another star.
    • Since it takes over 10 million years for light to reach us, these stars exploded more than 10 million years ago.
    • SN 1986G demonstrates that the spectra of type Ia supernovae are not all identical, in which case they may differ in a way that they change in brightness over time.
  • SN 2016adj
    • SN 2016adj, on the other hand, was discovered by Backyard Observatory Supernova Search in February 2016.
    • It was initially classified as a type II supernova due to its H-alpha emission line.
    • SN 2016adj was later classified as type IIb supernova, which is a type of violent explosion resulting from a rapid collapse of a core of massive stars eight times larger than the Sun.

Locating Centaurus A

  • Centaurus A is the fifth brightest galaxy but even so, it is only visible to the naked eye in certain circumstances.
  • The galaxy is only visible from the southern hemisphere and low northern latitudes.
  • Centaurus A can be found near the center of the constellation Centaurus, around 4° north of the Omega Centauri, a globular cluster.
  • The galaxy is an ideal target for amateur astronomy due to its high surface brightness.
  • Its bright central bulge and dark dust lane are both visible even just with the use of finderscopes and large binoculars, its additional structures may be seen in large telescopes.
  • NGC 5128 is part of the Virgo Supercluster that contains more than a hundred galaxy groups and galaxy cluster, including our Milky Way.
  • The Virgo Supercluster is part of the Laniakea Supercluster that contains 100,000 galaxies.
  • Centaurus A is the fifth brightest galaxy seen from Earth.

Did You Know?

  • Aside from NGC 5128 in the New Generation Catalog, Centaurus A is also known as Arp 153, PGC 46957, 4U 13322-42, and Caldwell 77.
  • It is nicknamed the Hamburger galaxy due to its unique appearance, which it shares with Sarah’s Galaxy or the NGC 3628, and edge-on spiral galaxy located in the constellation of Leo.
  • James Dunlop included it in his “A Catalog of Nebulae and Clusters of Stars in the Southern Hemisphere observed in New South Wales” as number 482 and published in the Philosophical Transactions of the Royal Society, Volume 11 in 1828.
  • In a binary system, the white dwarfs sometimes steal some of the mass from the other star until it has gained so much mass that it is kickstarted to burn again.
  • Critical mass refers to the event in which stars gain too much mass in order to maintain their stability.
  • The core of the galaxy spans only 10 light days, making it one of the smallest extragalactic radio sources known.
  • Centaurus A was included in Halton Arp’s Atlas of Peculiar Galaxies in 1996 as it appears like an elliptical or lenticular galaxy when viewed from Earth.