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PDF generated at: Fri, 25 Jan 2013 01:31:25 UTC Contents Articles Centaurus A 1 Andromeda Galaxy 7 Pleiades 20 Orion (constellation) 26 Orion Nebula 37 Eta Carinae 47 Comet Hale–Bopp 55 Alvarez hypothesis 64 References Article Sources and Contributors 67 Image Sources, Licenses and Contributors 69 Article Licenses License 71 Centaurus A 1 Centaurus A Centaurus A Centaurus A (NGC 5128) Observation data (J2000 epoch) Constellation Centaurus [1] Right ascension 13h 25m 27.6s [1] Declination -43° 01′ 09″ [1] Redshift 547 ± 5 km/s [2][1][3][4][5] Distance 10-16 Mly (3-5 Mpc) [1] [6] Type S0 pec or Ep [1] Apparent dimensions (V) 25′.7 × 20′.0 [7][8] Apparent magnitude (V) 6.84 Notable features Unusual dust lane Other designations [1] [1] [1] [9] NGC 5128, Arp 153, PGC 46957, 4U 1322-42, Caldwell 77 Centaurus A (also known as NGC 5128 or Caldwell 77) is a prominent galaxy in the constellation of Centaurus. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type (lenticular galaxy or a giant elliptical galaxy)[6] and distance (10-16 million light-years).[2][1][3][4][5] NGC 5128 is one of the closest radio galaxies to Earth, so its active galactic nucleus has been extensively studied by professional astronomers.[10] The galaxy is also the fifth brightest in the sky,[10] making it an ideal amateur astronomy target,[11] although the galaxy is only visible from low northern latitudes and the southern hemisphere. The center of the galaxy contains a supermassive black hole weighing in at 55 million solar masses,[12] which ejects a relativistic jet that is responsible for emissions in the X-ray and radio wavelengths. By taking radio observations of the jet separated by a decade, astronomers have determined that the inner parts of the jet are moving at about one half of the speed of light. X-rays are produced farther out as the jet collides with surrounding gases resulting in the creation of highly energetic particles. The radio jets of Centaurus A are over a million light years long.[13] Like other starburst galaxies, a collision is suspected to be responsible for the intense burst of star formation. Spitzer Space Telescope studies have confirmed that Centaurus A is colliding with and devouring a smaller spiral galaxy. Centaurus A 2 Morphology Centaurus A may be described as having a peculiar morphology. As seen from Earth, the galaxy looks like a lenticular or elliptical galaxy with a superimposed dust lane.[14] The peculiarity of this galaxy was first identified in 1847 by John Herschel, and the galaxy was included in the Atlas of Peculiar Galaxies (published in 1966) as one of the best examples of a "disturbed" galaxy with dust absorption.[15] The galaxy's strange morphology is generally recognized as the result of a merger between two smaller galaxies.[16] The bulge of this galaxy is composed mainly of evolved red stars.[14] The dusty disk, however, has been the site of more recent star formation;[10] over 100 star formation regions have been identified in the disk.[17] Supernovae One supernova has been detected in Centaurus A.[18] The supernova, named SN 1986G, was discovered within the dark dust lane of the galaxy by R. Evans in 1986.[19] It was later identified as a type Ia supernova,[20] which forms when a white dwarf's mass grows large enough to ignite carbon fusion in its center, touching off a runaway thermonuclear reaction, as may happen when a white dwarf in a binary star system strips gas away from the other star. SN 1986G was used to demonstrate that the spectra of type Ia supernovae are not all identical, and that type Ia supernovae may differ in the way that they change in brightness over time.[20] Distance Distance estimates to NGC 5128 established since the 1980s typically range between 3-5 Mpc.[2][1][3][4][5][21] Classical Cepheids discovered in the heavily-obscured dust lane of NGC 5128 yield a distance between ~3-3.5 Mpc, depending on the nature of the extinction law adopted and other considerations.[3][4] Mira variables[21] and Type II Cepheids[3][4] were also discovered in NGC 5128, the latter being rarely detected beyond local group.[22] The distance to NGC 5128 established from several indicators such as Mira variables and planetary nebulae favour a more distant value of ~3.8 Mpc.[6][5] 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.[23] Messier 83 (the Southern Pinwheel Galaxy) is at the center of the other subgroup. These two groups are sometimes identified as one group[24][25] and sometimes identified as two groups.[26] 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.[27] The Centaurus A/M83 Group is located in the Virgo Supercluster. Amateur astronomy information Centaurus A is located approximately 4° north of Omega Centauri (a globular cluster visible with the naked eye).[11] 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,[11] and additional structure may be seen in larger telescopes.[11] Centaurus A is visible to the naked eye under exceptionally good conditions.[28] Centaurus A 3 Gallery The radio galaxy Centaurus Image taken by the Wide "Hubble's panchromatic A Hubble Space Telescope A, as seen by ALMA Field Imager attached to the vision... reveals the vibrant (HST) image of the dust disk in MPG/ESO 2.2-meter glow of young, blue star front of the nucleus of Centaurus [29] telescope at the La Silla clusters..." A. Credit: HST/NASA/ESA. Observatory. This image of the The heavily-obscured inner Chandra X-Ray view of central parts of (barred?) spiral disk at 24 μm as Cen A in X Rays Centaurus A reveals shown by the Spitzer IR showing one relativistic the telescope jet from the central black parallelogram-shaped hole remains of a smaller galaxy that was absorbed about 200 to 700 million years ago. Centaurus A 4 Video about Centaurus A jets. "False-colour image of the nearby radio galaxy Centaurus A, showing radio (red), 24-micrometre infrared (green) and 0.5-5 keV X-ray emission (blue). The jet can be seen to emit synchrotron emission in all three wavebands. The lobes only emit in the radio frequency range, and so appear red. Gas and dust in the galaxy emits thermal radiation in the infrared. Thermal X-ray radiation from hot gas and non-thermal emission from relativistic electrons can be seen in the blue 'shells' around the lobes, particularly to the [30] south (bottom)." References [1] "Distance Results for NGC 5128" (http:/ / nedwww. ipac. caltech. edu/ cgi-bin/ nDistance?name=NGC+ 5128). NASA/IPAC Extragalactic Database. Retrieved 2010-04-26. [2] J. L. Tonry, A. Dressler, J. P. Blakeslee, E. A. Ajhar, A. B. Fletcher, G. A. Luppino, M. R. Metzger, C. B. Moore (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". Astrophysical Journal 546 (2): 681–693. arXiv:astro-ph/0011223. Bibcode 2001ApJ...546..681T. doi:10.1086/318301. [3] Ferrarese Laura, Mould Jeremy R., Stetson Peter B., Tonry John L., Blakeslee John P., Ajhar Edward A. (2007). "The Discovery of Cepheids and a Distance to NGC 5128". The Astrophysical Journal 654: 186. arXiv:astro-ph/0605707. Bibcode 2007ApJ...654..186F. doi:10.1086/506612. [4] Majaess, D. (2010). "The Cepheids of Centaurus A (NGC 5128) and Implications for H0". Acta Astronomica 60: 121. arXiv:1006.2458. Bibcode 2010AcA....60..121M. [5] Harris, Gretchen L. H.; Rejkuba, Marina; Harris, William E. (2010). "The Distance to NGC 5128 (Centaurus A)". Publications of the Astronomical Society of Australia 27 (4): 457–462. arXiv:0911.3180. Bibcode 2010PASA...27..457H. doi:10.1071/AS09061. [6] Harris, Gretchen L. H. (2010). "NGC 5128: The Giant Beneath". Publications of the Astronomical Society of Australia 27 (4): 475. arXiv:1004.4907. Bibcode 2010PASA...27..475H. doi:10.1071/AS09063. [7] "SIMBAD-A" (http:/ / simbad. u-strasbg. fr/ simbad/ sim-id?Ident=Centaurus+ A). SIMBAD Astronomical Database. Retrieved 2009-11-29. [8] Armando, Gil de Paz; Boissier; Madore; Seibert; Boselli et al. (2007). "The GALEX Ultraviolet Atlas of Nearby Galaxies". Astrophysical Journal Supplement 173 (2): 185–255. arXiv:astro-ph/0606440. Bibcode 2007ApJS..173..185G. doi:10.1086/516636. [9] 4U catalog browse version. (http:/ / heasarc. gsfc. nasa. gov/ W3Browse/ uhuru/ uhuru4. html) Centaurus A 5 [10] F. P. Israel (1998). "Centaurus A - NGC 5128". Astronomy and Astrophysics Review 8 (4): 237–278. arXiv:astro-ph/9811051. Bibcode 1998A&ARv...8..237I. doi:10.1007/s001590050011. [11] D. J. Eicher (1988). The Universe from Your Backyard. Cambridge: Cambridge University Press. ISBN 0-521-36299-7. [12] "Radio Telescopes Capture Best-Ever Snapshot of Black Hole Jets" (http:/ / www. nasa. gov/ topics/ universe/ features/ radio-particle-jets. html). NASA. Retrieved 2012-10-02. [13] "Astronomy Picture of the Day - Centaurus Radio Jets Rising" (http:/ / apod. nasa. gov/ apod/ ap110413. html). NASA. 2011-04-13. Retrieved 2011-04-16. [14] A.