Centaurus A

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Galaxy
Centaurus A
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Superimposition of images in the submillimeter (APEX, orange) with X-ray (Chandra, blue) and visible areas
Superimposition of images in the submillimeter ( APEX , orange) with X-ray ( Chandra , blue) and visible areas
AladinLite
Constellation centaur
Position
equinox :  J2000.0 , epoch : J2000.0
Right ascension 13 h 25 m 27.6 s
declination −43 ° 01 ′ 09 ″
Appearance
Morphological type S0 pec; Sy2; BLLAC  
Brightness  (visual) 6.6 likes
Brightness  (B-band) 7.6 likes
Angular expansion 25.7 ′ × 20 ′
Position angle 35 °
Surface brightness 13.3 mag / arcmin²
Physical data
Affiliation M83 group , LGG 344  
Redshift +0.001825 ± 0.000017  
Radial velocity (+547 ± 5) km / s  
Stroke distance
v rad  / H 0 		(17 ± 1)  x  10 6  ly
(5.29 ± 0.39)  Mpc 
Dimensions one trillion (10 12 ) M ☉
diameter approx. 90,000 × 70,000 ly
history
discovery James Dunlop
Discovery date April 29, 1826
Catalog names
NGC  5128 • PGC  46957 • ESO  270-9 • MCG  -07-28-001 • IRAS  13225-4245 • 2MASX  J13252775-4301073 • SGC  132233-4245.4 • Arp  153 • GC  3525 • h  3501 • AM 1322-424 • PRC C -45 • HIPASS  J1324-42 • Dun  482; • LDCE

Centaurus A ( NGC 5128 ) is the name of a galaxy in the constellation Centaurus . NGC 5128 is a powerful radio source . NGC 5128 has an angular extent of 25.7 ′ × 20.0 ′ and an apparent magnitude of 6.6 mag. Centaurus A belongs to the roughly equally bright galaxy Messier 81 to the apparently brightest galaxies outside the local group and thus to the group of the brightest extragalactic objects in the sky. The distances are between 10 and 17 million light years . She is part of the M83 group . It is the closest radio galaxy and the third brightest radio source in the sky. There is still disagreement among experts about its morphological type , with some researchers classifying it as an elliptical type E (p) galaxy and another as a lens-shaped galaxy of type S0. Their characteristic optical feature is the clearly visible band of dust that crosses the galaxy. It is also a powerful source of X-rays and gamma rays . A relativistic jet is emitted from the core . Its proximity makes it one of the best-studied active galaxies. A black hole with a mass of 55 million solar masses is suspected in the center. Centaurus A's unusual activity can be explained by the fact that it collided with a small spiral galaxy a few 100 million years ago and took it in full. As a result, there was a violent star formation phase. In addition, gas masses were deflected from their original orbits and partially accumulated around the black hole in the center.

Halton Arp organized his catalog of unusual galaxies into groups according to purely morphological criteria. This galaxy belongs to the class of galaxies with internal absorption .

discovery

Source: Early Australian Optical and Radio Observations of Centaurus A.

  • 1826: NGC 5128 is discovered by James Dunlop on April 29th .
  • 1847: John Herschel catalogs the galaxy as an extraordinary looking nebula.
  • 1949: John Gatenby Bolton , Bruce Slee and Gordon Stanley locate NGC 5128 as one of the first extragalactic radio sources.
  • 1954: Walter Baade and Rudolph Minkowski propose that the extraordinary shape results from the union of a large elliptical galaxy and a small spiral galaxy.
  • 1970: discovery of X-ray emissions through the use of a sounding rocket
  • 1975–1976: Discovery of gamma radiation.
  • 1979 Discovery of the X-ray jet with the Einstein space telescope .
  • 1986 Discovery of the 1986G supernova.
  • 1996 Discovery of young, blue stars along the central dust band with the Hubble telescope.
  • 1999: More than 200 new point sources are located with the Chandra X-ray telescope.
  • 2006: The Spitzer Space Telescope discovers a parallelogram-shaped structure made of dust in the infrared range, which represents the remains of a spiral galaxy.
  • 2009: Detection of gamma radiation with very high energy (more than 100 GeV) with the HESS observatory in Namibia.
  • 2010: Several years of research with the Pierre Auger Observatory indicate that Centaurus A is a source of cosmic rays of the highest energy.

It is named Centaurus A as the brightest radio source in the constellation Centaur.

construction

In the optical spectrum , the galaxy, at an assumed distance of 12.4 million light years, has a diameter of 90,000 × 70,000 light years and the shape of an ellipsoid. It contains an Active Galactic Core . The central area consists mainly of older red stars. This area is traversed by a thin, heavily bent disk of dust, which also contains a lot of atomic and molecular gas. New stars have recently emerged in this. It is surrounded by extensive radio emission areas. Recordings with longer exposure times revealed further structures: There is a faintly visible extension along the main axis of the galaxy and a system of filaments and shell structures.

Central region

Graphic of the central area of ​​Centaurus A.

The galaxy has a very compact core that shows a remarkable variation in the intensity of radio and X-rays. This is likely due to mass accretion. In the vicinity of the core, absorption lines of atomic hydrogen in the spectrum show the presence of a larger proportion of matter falling towards the core. Starting from the core, there are linear jets in the X-ray and radio wave range that reach almost relativistic speeds within a few parsecs of the core.

At a distance of approximately 5 kiloparsecs, the jets widen in a mushroom shape. Then radio clouds extend up to a distance of 250 kiloparsecs.

A compact disc with a central cavity surrounds the core. The plane of this disk is perpendicular to the direction of the inner jets, while it is itself inclined to the galaxy's minor axis. This mechanism, which focuses the jet, is probably related to the disk that spans the core. It seems  to precess in periods of about 10 7 years. The central object is likely a medium-mass black hole. It is not yet clear whether the black hole was always in Centaurus A, whether it belonged to the original spiral galaxy, or whether it is the product of a merger of the black holes of their parent galaxies.

Dust tape

The distinctive ribbon of dust that runs through the elliptical galaxy is a disk seen from the side. It consists of a metal-rich population of stars, nebulae, and clouds of dust. The metallicity is similar to that in the solar neighborhood.

The disc has a position angle of approx. 122 °. Stars are formed in it in a "starburst" that apparently began 50 million years ago. During this burst, at least 100  H-II regions were created which are embedded in the disk. Bright blue stars (so-called OB associations) can be seen at the northeast and southeast edge of the dark band. The star formation rate there seems to be about 10 times higher than in the Milky Way.

The disc has a diameter of 8000 parsecs and a thickness of approx. 200 parsecs. Long-exposure images show that the disk is completely contained within the elliptical galaxy. The total mass of the gas in the disk is between 1.3 and 1.5 · 10 9 solar masses.

Compact Nuclear Disk

An analysis of the CO distribution revealed a disk around the core with a gas mass of 8.4 · 10 7 solar masses. The diameter is approx. 400 parsecs. Disks of this size seem to be a common part of active galaxies. The main axis of this disk has a position angle of 140 ° -145 °. This differs from the orientation of the dust belt, but is at right angles to the orientation of the jet. This suggests that the disc and jet are in communication.

Observations in the infrared and microwave range suggest that there is a temperature drop along the disc. This is expected if the excitation of the pane takes place mainly through high-energy radiation from the core area, which occurs at the inner edge of the pane.

Hot gas disc

Another smaller disk of hot gas was discovered through the Hubble telescope. It is not aligned to the axis of the black hole, but perpendicular to the outer dust belt of the galaxy, with a position angle of 33 °. It has a diameter of approx. 40 parsecs. With this diameter, it is significantly smaller than the gas disks that have been discovered in other galaxies. It could be the outer part of an accretion disk around the black hole. This disk of gas that supplies the black hole could have formed so recently that it is not yet aligned with the axis. Or it is influenced by the galaxy's gravitational forces rather than the black hole itself.

It could be completely ionized by the radiation from the active galaxy core.

jet

Centaurus A's tremendous energy output comes from gas falling into the central black hole. Some of this matter is ejected in two jets facing each other at a considerable fraction of the speed of light. The details of this process are still unclear. The jets interact with the surrounding gas and likely affect the rate of star formation in the galaxy.

If one only looks at the core area, a bright, linear jet can be followed from the center in the radio area over a (projected) distance of 1 pc. This has a position angle of 51 °. VLBI observations show a weak counterjet. The jet itself contains nodular structures. Multi-year observations with the VLBI show significant structural changes in the nodes. In addition, movements can be seen at a speed of one tenth the speed of light. This observed movement represents slow movement patterns overlaid on the relativistic jet movement.

Two components within the jet appear to be slowly evolving. Another component exists very close to the nucleus, but it appears to be stationary. This suggests that the stationary nodes come about when stars or gas clouds in the galaxy cross the jet, causing shock waves. Since most of the jet lies within the main body of the galaxy, such an interaction is expected.

The opposite jet is much less visible than the jet in the northeast direction. The northern jet is very clear and contains several nodal structures, while the southern opposite jet was only recognized by the discovery of a few weakly visible nodes. This great difference in brightness can be explained by relativistic Doppler beaming, in which the radiation directed at us is amplified. It appears that the northeast jet is pointing at us at an angle of 50 ° -80 ° to the line of sight and is reaching a relativistic speed of 45% the speed of light.

The transition from the jet to the club-shaped cloud takes place at the location of the innermost optical shell structure. This transition is interpreted as a shock wave of the jet at the interface of the interstellar and intergalactic gas of the galaxy. The total length of the jet in the radio wave range extends over 10 arc minutes in the sky, or about 30,000 light years.

Globular clusters

It is estimated that over 1500  globular clusters surround NGC 5128. Examining the population of the star clusters provides clues as to how the galaxy evolved.

In an examination of 605 star clusters in the galaxy, 268 were found to be metal-poor, while 271 were determined to be metal-rich. (In astronomy, all elements heavier than helium are called metals.) The metal-rich globular clusters showed a rotational movement around the main axis of the galaxy, while the metal-poor ones showed hardly any signs of rotation. The bimodal (bimodal) distribution of the population of globular clusters is significant in relation to the assumed merger history of the galaxy. This distribution of metallicities was identified as a result of galaxy mergers . 68% of the star clusters in another sample were older than 8 billion years. A small part was less than 5 billion years old. This result suggests that there have been several epochs of star formation in the galaxy, each of which contributed to part of today's star population.

The brightness distribution of the clusters fits very well with the known distribution function of the class of gigantic elliptical galaxies. In addition, the distribution of the sizes and ellipticities of the globular clusters matches those found in the Milky Way system.

In an investigation of 125 globular clusters with the VLT, an attempt was made to determine the mass of each cluster and to correlate it with its brightness. For most star clusters, as expected, the brighter objects were also the more massive objects. However, some clusters were found to be far more massive than their brightness suggests. The more massive these globular clusters are, the greater the proportion of non-shining matter. These 'dark' globular clusters could either still harbor an unexpected amount of concentrated dark matter or a massive black hole.

This result shows that the formation and development of these globular clusters differs markedly from those of the “classical” globular clusters such as e.g. B. in the local group.

distance

The distances from NGC 5128, which have been determined since the 1980s, range from 3 to 5 Mpc. Measurements on classical Cepheids, which were discovered in the dust band of NGC 5128, resulted in distances between ≈3 and 3.5 Mpc, depending on an assumed extinction of the light and other factors. Other star types that can be used for distance determination, such as Mira variables and Type II Cepheids , were also discovered in NGC 5128. Other studies done on objects such as mira variables and planetary nebulae prefer a distance of around 3.8 Mpc.

Supernovae

So far, two supernovae have been discovered in Centaurus A.

In 1986 a supernova was discovered in the dust band of the galaxy by R. Evans (SN 1986G). It was categorized as Type Ia : An explosion of this type occurs as soon as a white dwarf has accumulated enough mass from its partner star that a thermonuclear reaction begins and destroys the star. It was discovered about a week before its maximum. The light of the supernova itself seems to have been greatly weakened by the dust band. Although the evolution of the supernova was typical of a Type Ia supernova, some unusual properties were discovered, such as: B. the expansion rate was relatively small.

A second supernova (SN 2016adj) was discovered in February 2016 by an amateur group (“Backyard Observatory Supernova Search”). Spectroscopic examinations indicate a Type II supernova.

Observations

Radio waves

and display information about the image
Overview of the radio structure of Centaurus A. The range of structures that can be observed with radio waves is impressive: The entire area of ​​radio wave emission extends over approx. 1.7 million light years (approx. 8 ° in the sky). Through observations of the VLBI art structures were of the jet and of the core are mapped smaller (corresponding to a resolution of 0.68 x 0.41 millimeters as a light year arc seconds ).
This view of the Centaurus A jets was taken in the radio wave range with a wavelength of 20 cm with the VLA. The position of the radio jet and the nodes within the jet coincide surprisingly well with the structures in the X-ray jet. This area of ​​the jet is known as the “Inner Lobe”.

Centaurus A's radio emissions are emitted from two regions. The outer radio source is symmetrical and rotated 40 degrees from the inner area. The outer radio source is 1.7 million light years in diameter, making it one of the largest objects of its kind in the sky. (For comparison: this is more than the distance between our Milky Way and the Andromeda Galaxy.) The apparent diameter is 8 degrees, which corresponds to sixteen full moon diameters. Although Centaurus A has unusually large radio columns for a radio galaxy, its radiation in the radio range is very low - 1000 times stronger than the radiation of a spiral galaxy, but only 1/1000 the strength of the optical radiation of its stars. Although it is a challenging task to observe the large-scale structures and the low surface brightness of the radio area, this is of great importance as no other radio galaxy allows these structures to be examined in such detail. The distribution of the strength of the radio emissions over the northern and southern areas is very asymmetrical.

These radio clouds are likely made up of hot thin gas expelled from the core. The radio radiation itself is generated by fast-moving electrons that move in the magnetic field of the radio clouds and emit synchrotron radiation . The electrons given off in the outer areas of the radio clouds were ejected from the nucleus 100 million years ago. Since then, the direction of the ejection has rotated 40 degrees counterclockwise. In addition, the strength of the radiation has changed.

The brightest part of the Northern Lobe is called the "Northern Middle Lobe", there is no southern counterpart to this. In the radio wave frequency range of 5 GHz, this section already accounts for 45% of the total radio emissions. The middle lobe is also associated with soft X-ray emissions.

The inner region extends symmetrically in two arms 16,000 light years each from the core. The inner radio waves contribute around 30% of the radio emissions in the 5 GHz range. The radio emission of the northern area is approx. 40% higher than that of the southern area. The polarization of the inner lobes is dramatically different from that of the middle and outer lobes. Outside the sharply delimited northern plume at a distance of 6.3 kpc from the core, it changes by 90 °.

With the help of VLBI (Very Long Baseline Interferometry) technology, the actually low resolution of telescopes in the radio wave range can be increased enormously by interconnecting several telescopes distributed across a continent. With the VLBA radio interferometer, this technique was used to study the structure of the jet in Centaurus A from 1992 to 2000. Two components (named C1 and C2) were discovered in the jet, which move with an apparent speed of 12% of the speed of light. In addition, a component C3 was observed that is closer to the core and stationary. Observations in the 22 GHz range showed that the jet is very straight and collimated down to a scale of 0.02 parsecs. The region in which the jet collimates (begins to focus) appears to be played out on a scale of 100 micro-arcseconds. In order to break up these structures, VLBI missions in space will be necessary.

Microwaves

Centaurus A with ALMA

With the ALMA observatory in Chile, the galaxy was examined in the millimeter and submillimeter wavelength range in 2012. The picture opposite was recorded in wavelengths of 1.3 mm. This radiation is emitted from carbon monoxide gas. The movement of the gas in the galaxy causes slight changes in the wavelength of the radiation due to the Doppler effect. This movement is coded in this picture using the color: green areas come towards the viewer, while the orange areas on the right-hand side move away from the viewer.

In the picture in the info box, the submillimeter data, created with the LABOCA instrument on the APEX telescope at a wavelength of 870 micrometers, are shown in orange. In the sub-millimeter wavelength, one sees not only thermal radiation from the central dust disk, but also the radiation from the central radio source and radiation from the so-called inner radio columns, which are located north and south of the dust disk. This radiation comes from the movement of fast electrons along magnetic field lines (synchrotron radiation). An analysis shows that the material in the jets is ejected at almost half the speed of light.

By examining the emissions in the 870 micrometer range, the temperature of the cold dust disc could be determined to be 17-20 Kelvin. This is comparable to the dust temperature of the disk of the Milky Way. The total mass of the gas was determined to be 2.8 · 10 9 solar masses.

Infrared

Centaurus A in near infrared light, recorded by the New Technology Telescope
Far infrared image taken with the Herschel Space Telescope

The core of Centaurus A is covered by the dust band in the optical area. Only infrared wavelengths can penetrate the dust layers and thus reveal the actual structure of the galaxy. The near-infrared image of the NTT telescope shows the galaxy in wavelengths that are four times longer than visible light. The region between the two parallel dust bands is weakened a million times in the optical wavelength range. The star density increases steadily towards the center, as one would normally expect in elliptical galaxies. However, bands of dust are unusual in these galaxies. New stars form in the densest areas of the dust band. These can be identified in optical images (e.g. the Hubble image) at the edge of the dust belt. Measurements of the Doppler shift in the infrared range of the different regions of the band showed that the dust disk orbits the center at a speed of 250 km / s. During the collision, the stars of the original galaxy were dispersed throughout the galaxy, while some of the dust and gas clouds from the original spiral galaxy were deflected into the center of the elliptical galaxy. There they formed an accretion disk around the black hole. The energy released is then emitted in the high-energy wavelengths. Observations with the Spitzer Space Telescope revealed a parallelogram-like structure in the central dust band. This strange shape is explained by the fact that Centaurus A swallowed a small spiral galaxy and its disk was bent and twisted during the recording process.

With the Spitzer space telescope, a shell-shaped expanding structure around the core with a radius of 500 parsecs was found in 2006. It is the first shell structure around a galaxy core that was discovered in the mid-infrared range. It cannot be seen in the optical. The shell is oriented perpendicular to the gas and dust disk and is not oriented along the radio jet. Astronomers estimate that the shell is a few million years old and contains around one million solar masses. This shell structure could have been created by a starburst, in which stars with a total mass of several thousand solar masses were formed. Another possible explanation is that the radiation intensity of the active core supplies the shell with energy.

Between 1999 and 2002, two fields in Centaurus A were photographed 20 times in the near infrared with the ISAAC instrument of the VLT observatory in order to find variable stars. Over 1000 of them have been found, most of them so-called mira stars  - old stars that change their brightness over months. Such measurements help u. a. in the process of determining the distances of galaxies more precisely.

Optically

Central area of ​​Centaurus A as observed with the Hubble Space Telescope

The radial course of brightness across the galaxy follows a De Vaucouleurs profile, which is characteristic of elliptical galaxies.

The inner area was examined more closely with the Hubble space telescope . Newly formed star clusters with hot young stars were discovered at the edge of the dust disk . The dust disc itself has an angle of 10 to 20 degrees to our line of sight.

Centaurus A in the ultraviolet wavelength range, recorded with GALEX

The normal optical photographs only show the inner area of ​​the galaxy. The Australian astronomer David Malin was able to examine the edge areas of the galaxy more precisely using a special technique. This shows the enormous size of the galaxy. A shell structure of multiple shells was also discovered, which is due to the collision with another galaxy.

Ultraviolet

Diagram of the individual components of the Centaurus A galaxy

Ultraviolet radiation is almost completely filtered out by the Earth's atmosphere. That is why telescopes such as the GALEX Observatory were started to examine objects such as Centaurus A in these wavelengths. In particular, very young and hot giant stars shine in this wavelength range.

With the GALEX observatory, a ribbon-like structure was discovered in the ultraviolet range that winds more than 35 parsecs northeast of the galaxy. This band is associated with nodular structures found in the radio and X-ray range. There is a whole complex of gas with optical emission lines, active star formation, cold gas and dust clouds that extend to the outer edge of the galaxy. In the GALEX image on the right, the emissions from this region can be seen in the upper left area (referred to as the “North Transition Region”) as blue bands.

It can also be seen that the central dust band of NGC 5128 is a strong source of UV radiation. The GALEX instruments are set up in such a way that they are particularly sensitive to the radiation from O and B stars , which can be found in areas where star formation occurs. These emissions could come from an active starburst in which stars are formed at a rate of 2 solar masses per year and which has lasted for 50 to 100 million years.

It seems plausible that the active galaxy core was also active during the starburst. A galactic wind propelled by the central starburst region affects the North Transition Region. This can drive star formation in the dense gas in this region.

X-rays

Centaurus A in the X-ray light.
In this picture, low-energy X-rays are shown in red, medium energies in green and highest energies in blue. The blue and red bands that are oriented perpendicular to the jet are bands of dust that absorb X-rays.

Observations with the Chandra X-ray telescope show a 30,000 light-year jet emanating from the core of the galaxy. The brightness of the nucleus in the X-ray range can change within a few days, which is why the source can only be a maximum of a hundredth of a light year in size. The X-rays from the nucleus likely come from an accretion disk around a massive black hole.

The jet of matter or jet directed from the center becomes visible in this wavelength. In the lower right part of the galaxy, the reflection from a shock wave appears. This is generated by the fact that the ejected material collides with gas from the vicinity of the galaxy.

Using the Chandra space telescope , researchers examined point-shaped X-ray sources in Centaurus A in 2013. Most of the sources were compact objects - either black holes or neutron stars that extracted gas from their companion star. These compact objects are formed from massive stars - black holes form from heavier stars than the ones that become neutron stars.

The results showed that the masses of the compact objects fell into two categories - either up to twice as massive as the sun, or more than five times more massive than the sun. These two groups correspond to neutron stars and black holes. This gap in the mass range gives an indication of how stars explode. Since the masses of the stars are distributed over a continuous range, it is normally expected that the mass range of black holes begins where the range of neutron stars ends (from approx. 2 solar masses). This unequal mass distribution was already discovered in the Milky Way. The observations of Centaurus A confirm this mass gap also in more distant galaxies.

Gamma radiation

The energy of the emitted gamma radiation exceeds that of the radio waves by more than a factor of 10. High-energy gamma rays that were recorded by the Fermi space telescope are shown here in purple.

Gamma radiation cannot be directly detected on earth. Therefore, space telescopes have to carry out observations, or short flashes of light are measured in the atmosphere when high-energy gamma radiation hits the Earth's air envelope. The HESS observatory in Namibia measures this radiation .

Between 2004 and 2008, the observatory was able to detect a weak signal from the center of Centaurus A within 115 hours of observation. The radiation intensity reached about 0.8% of the Crab Nebula. No changes in radiation were detected in the HESS observations. Since Centaurus A is a very close Active Galaxy, it is very possible that Cherenkov telescopes like HESS will one day also be able to resolve the galaxy's inner jet in detail.

The gamma radiation emanating from the radio bubbles (detected by Fermi's LAT instrument) is generated by particles that collide with the microwave background and accelerate to energies in the TeV range ( inverse Compton effect ). The analysis of measurements carried out by the LAT in the energy range greater than 100 MeV within 10 months revealed a point source in the core area. This coincides with the position of the radio core of Centaurus A. No change in the radiation intensity was observed here.

Astronomers assume that the radiation emanates from the inner edge of the gas disk that encircles the black hole. The X-rays are emitted from regions further out.

Cosmic rays

The Pierre Auger Observatory observes the sky for collisions with high-energy cosmic rays. This radiation has energies of 10 17 to 10 20  eV and cannot be observed with normal observatories. It consists mainly of protons. If a high-energy particle hits the earth, it collides with the atoms of the atmosphere. This creates a cascade of secondary particles that can be discovered with this observatory. These events are very rare. The discovery of the sources of cosmic rays is a subject of ongoing research. Of 69 events detected in the energy range above 55 EeV, 15 were in a region around Centaurus A. Centaurus A as a source of high energy cosmic rays has not yet been adequately confirmed.

The spectrum of cosmic rays extends up to energies above 10 18  eV. Above a limit of approx. 6 · 10 19  eV (for protons) this energy is lost through interaction with the cosmic microwave background . This is called the Greisen-Zatsepin-Kuzmin effect (GZK effect). This effect ensures that the spectrum of cosmic rays drops dramatically above this energy. The few cosmic radiation particles discovered, whose energy was above this limit, must have originated within the local universe, at a distance of a few megaparsecs from Earth.

Neutrinos

Neutrinos are neutral particles that hardly react with normal matter. Because they are neither absorbed nor scattered over long distances, they could provide information about the physics of events at the edge of the observable universe. Neutrinos can be generated in energy-intensive astrophysical events. Active galaxy nuclei and their jets could serve as a possible source of high-energy neutrinos, along with other objects. Several scenarios have been proposed for how jets in active galaxy nuclei generate these neutrinos: Charged particles such as protons are accelerated to very high energies in the jet. These high-energy protons interact with the cosmic microwave background or other particles in the environment. This creates a cascade of lighter particles and, through further decay, charged pions . When they decay, these generate high-energy neutrinos.

Centaurus A has not yet been able to clearly detect neutrinos , although a detector such as IceCube could detect the expected neutrino flows. This could be because Centaurus A is not a typical neutrino source, or the models overestimate the rate of neutrino production.

Amateur observations

Star map showing the position of NGC 5128

Centaurus A is about 4 ° north of Omega Centauri (a globular cluster that is visible to the naked eye ). Due to its high surface brightness and relatively large angular size, it is an ideal object for amateur astronomers. The bright central core and the dark band of dust are visible even in the viewfinder and in large binoculars. Other structures can be seen with larger telescopes. The brightness is 7.0 magnitudes. Centaurus A appears to be visible to the naked eye under exceptionally good conditions. This makes it one of the most distant objects that can be seen without an instrument. In equatorial and southern latitudes, the galaxy can be easily found by star hopping from Omega Centaurus. The dust band is not visible in small telescopes; it can be seen from an opening of 4 inches and good visibility conditions. In large amateur instruments larger than 12 inches, the dust band can easily be seen.

Videos

Web links

Commons : Centaurus A  - collection of images, videos and audio files

literature

  • Jeff Kanipe and Dennis Webb: The Arp Atlas of Peculiar Galaxies - A Chronicle and Observer's Guide , Richmond 2006, ISBN 978-0-943396-76-7

Individual evidence

  1. ↑ a b c d e NASA / IPAC EXTRAGALACTIC DATABASE
  2. ↑ a b c d e SEDS : NGC 5128
  3. ↑ a b Gretchen LH Harris: NGC 5128: The Giant Beneath . In: Publications of the Astronomical Society of Australia . tape 27 , no. 4 , 2010, p. 475 , doi : 10.1071 / AS09063 , arxiv : 1004.4907 .
  4. ^ Francis Reddy: Radio Telescopes Capture Best-Ever Snapshot of Black Hole Jets. May 20, 2011, accessed June 27, 2015 .
  5. ↑ Cappellari et al. a .: The mass of the black hole in Centaurus A from SINFONI AO-assisted integral-field observations of stellar kinematics . December 4, 2008, arxiv : 0812.1000 (English).
  6. ↑ Peter Robertson, Glen Cozens, Wayne Orchiston, Bruce Slee, Harry Wendt: Early Australian Optical and Radio Observations of Centaurus A . In: Publications of the Astronomical Society of Australia . tape 27 , no. 04 , January 1, 2010, ISSN  1323-3580 , p. 402-430 , doi : 10.1071 / AS09071 , arxiv : 1012.5137v1 .
  7. ^ JG Bolton, GJ Stanley, OB Slee: Positions of Three Discrete Sources of Galactic Radio-Frequency Radiation . In: Nature (Ed.): Nature . tape 164 , no. 4159 . Nature, 1949, pp. 101-102 .
  8. ↑ CS Bowyer, M. Lampton, J. Mack, F. de Mendonca: Detection of X-Ray Emission from 3C 273 and NGC 5128 . In: Astrophysical Journal . tape 161 , 1970, doi : 10.1086 / 180559 .
  9. ^ EJ Schreier, E. Feigelson, J. Delvaille, R. Giacconi, DA Schwartz: EINSTEIN Observations of The X-Ray Structure of Centaurus A: Evidence For The Radio-Lobe Energy Source . In: Astrophysical Journal . tape 234 , Part 2 - Letters to the Editor , 1979, pp. 39-43 , doi : 10.1086 / 183105 .
  10. ↑ HubbleSite - NewsCenter - Hubble Provides Multiple Views of How to Feed a Black Hole (05/14/1998) - Background Info. In: hubblesite.org. Retrieved October 14, 2015 .
  11. ↑ RP force JM Kregenow, WR Forman, C. Jones, SS Murray: Chandra Observations of the X-ray point source population in Centaurus A . In: The Astrophysical Journal . tape 560 , no. 2 , October 20, 2001, p. 675-688 , doi : 10.1086 / 323056 .
  12. ↑ Alice C. Quillen, Mairi H. Brookes, Jocelyn Keene, Daniel Stern, Charles R. Lawrence: Spitzer Observations of the Dusty Warped disc of Centaurus A . In: The Astrophysical Journal . tape 645 , no. 2 , July 10, 2006, p. 1092-1101 , doi : 10.1086 / 504418 .
  13. ^ A b F. Aharonian, AG Akhperjanian, G. Anton, U. Barres de Almeida, AR Bazer-Bachi: DISCOVERY OF VERY HIGH ENERGY γ-RAY EMISSION FROM CENTAURUS A WITH HESS In: The Astrophysical Journal . tape 695 , no. 1 , April 10, 2009, p. L40-L44 , doi : 10.1088 / 0004-637x / 695/1 / l40 .
  14. ↑ J. Abraham, P. Abreu, M. Aglietta, C. Aguirre, D. Allard: Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei . In: Astroparticle Physics . tape 29 , no. 3 , April 1, 2008, p. 188–204 , doi : 10.1016 / j.astropartphys.2008.01.002 .
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  40. ↑ Inner Radio Lobes of Centaurus A (NGC 5128). ( Memento of the original from September 16, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / images.nrao.edu
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