NGC 891

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NGC 891
Spiral Galaxy NGC 891
Observation data (J2000 epoch)
Constellation Andromeda
Right ascension 02h 22m 33.4s[1]
Declination +42° 20′ 57″[1]
Redshift 528 ± 4 km/s[1]
Distance 27.3 ± 1.8 Mly (8.4 ± 0.5 Mpc)[2]
Type SA(s)b?[1]
Apparent dimensions (V) 13′.5 × 2′.5[1]
Apparent magnitude (V) 10.8[1]
Other designations
UGC 1831, PGC 9031,[1] Caldwell 23
See also: Galaxy, List of galaxies

NGC 891 (also known as Caldwell 23) is an edge-on unbarred spiral galaxy (actually barred) about 30 million light-years away in the constellation Andromeda. It was discovered by William Herschel on October 6, 1784. The galaxy is a member of the NGC 1023 group of galaxies in the Local Supercluster. It has an H II nucleus.[3]

The object is visible in small to moderate size telescopes as a faint elongated smear of light with a dust lane visible in larger apertures.

In 1999, the Hubble Space Telescope imaged NGC 891 in infrared.

In 2005, due to its attractiveness and scientific interest, NGC 891 was selected to be the first light image of the Large Binocular Telescope.[4] In 2012, it was again used as a first light image of the Discovery Channel Telescope with the Large Monolithic Imager.[5]

Supernova SN 1986J was discovered on August 21, 1986 at apparent magnitude 14.[6]

Peculiarities[edit source | edit]

NGC 891 looks as we think the Milky Way would look like when viewed edge-on (some astronomers have even noted how similar look our galaxy as seen from the Southern Hemisphere and NGC 891[7]) and in fact both galaxies are considered very similar in terms of luminosity and size;[8] studies of the dynamics of its molecular hydrogen have also proven the likely presence of a central bar.[9] Despite this, recent high-resolution images of its dusty disk show unusual filamentary. These patterns are extending into the halo of the galaxy, away from its galactic disk. Scientists presume that supernova explosions caused this interstellar dust to be thrown out of the galactic disk toward the halo.[10]

It may also be possible that the light pressure from surrounding stars causes this phenomenon.[11]

A close-up infrared Hubble Space Telescope (HST) image of NGC 891. Credit: HST/NASA/ESA.

The galaxy is a member of a small group of galaxies, sometimes called the NGC 1023 Group. Other galaxies in this group are the NGCs 925, 949, 959, 1003, 1023, and 1058, and the UGCs 1807, 1865 (DDO 19), 2014 (DDO 22), 2023 (DDO 25), 2034 (DDO 24), and 2259.[12] Its outskirts are populated by multiple low-surface brightness, coherent, and vast substructures, like giant streams that loop around the parent galaxy up to distances of approximately 50 kpc. The bulge and the disk are surrounded by a flat and thick cocoon-like stellar structure. These have vertical and radial distances of up to 15 kpc and 40 kpc, respectively[13] and are interpreted as the remmant of a satellite galaxy disrupted and in the process of being absorbed by NGC 891[14]


NGC 891 (North part) close up by HST, 3.24′ view. Credit: NASA/STScI/WikiSky

Trivia[edit source | edit]

There're a number of galaxies that are easy to see from the Milky Way, but that for hypothetical observers located in NGC 891 would be invisible, at least in the optical, due to its inclination as they lie in the Zone of Avoidance of this galaxy and thus their light is blocked by NGC 891's interstellar dust. Examples of this include not only our galaxy but also the Andromeda Galaxy, that would appear so edge-on as we see NGC 891, and most notably the Virgo Cluster.[7]

In popular culture[edit source | edit]

The soundtrack of the 1974 film Dark Star by John Carpenter features an instrumental piece called When Twilight Falls On NGC 891.[15]

The first solo album by Edgar Froese, Aqua, contained a track called "NGC 891".

See also[edit source | edit]

References[edit source | edit]

  1. ^ a b c d e f g "NASA/IPAC Extragalactic Database". Results for NGC 891. Retrieved 2006-11-18. 
  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. ^ Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". Astrophysical Journal Supplement 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041. 
  4. ^ "LBT - First Light, Description". Large Binocular Telescope Corporation. 2008. Archived from the original on 2010-11-06. 
  5. ^ Vitron, Tom. "Lowell's NSF-funded Large Monolithic Imager sees first light". Lowell Observatory. Retrieved 27 September 2012. 
  6. ^ "List of Supernovae". Harvard-Smithsonian Center for Astrophysics (IAU). Retrieved 2010-05-19. 
  7. ^ a b The Milky Way in relation to other galaxies
  8. ^ Karachentsev, Igor D.; Karachentseva, Valentina E.; Huchtmeier, Walter K.; Makarov, Dmitry I. (2003). "A Catalog of Neighboring Galaxies". The Astronomical Journal 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905. 
  9. ^ Garcia-Burillo, S.; Guelin, M. (1995). "The distorted kinematics of molecular gas in the center of NGC 891.". Astronomy & Astrophysics 299: 657. Bibcode:1995A&A...299..657G. 
  10. ^ "Interstellar Dust Bunnies of NGC 891". Astronomy Picture of the Day. 2002. Retrieved 2011-01-29. 
  11. ^ "NGC 891 in Andromeda". Wilhelm-Förster Observatory, Berlin. 2001. Retrieved 2011-01-29. 
  12. ^ "NGC 891". SEDS. 2009. Retrieved 2011-01-29. 
  13. ^ Mouhcine; Ibata; Rejkuba (2010). "A panoramic view of the Milky Way analogue NGC 891". arXiv:1002.0461 [astro-ph.GA].
  14. ^ Shih, Hsin-Yi; Méndez, Roberto H. (2010). "Possible Stellar Streams in the Edge-on Spiral NGC 891 Discovered from Kinematics of Planetary Nebulae.". The Astrophysical Journal Letters 725 (1): L97–L100. Bibcode:2010ApJ...725L..97S. doi:10.1088/2041-8205/725/1/L97. 
  15. ^ The Cinema of John Carpenter. Wallflower Press. 2004. p. 53. Retrieved 2011-06-08. 

External links[edit source | edit]

Coordinates: Sky map 02h 22m 33.4s, +42° 20′ 57″