Sextans A

Sextans A
Irregular galaxy Sextans A. The bright Milky Way foreground stars appear yellowish in this view. Beyond them lie the stars of Sextans A with young blue star clusters clearly visible.
Observation data (J2000 epoch)
Constellation	Sextans
Right ascension	10h 11m 00.8s[1]
Declination	-04° 41′ 34″[1]
Redshift	324 ± 2 km/s[1]
Distance	4.31 ± 0.13 Mly (1.32 ± 0.04 Mpc)[2][3][4]
Type	IBm[1]
Apparent dimensions (V)	5′.9 × 4′.9[1]
Apparent magnitude (V)	11.9[1]
Notable features	Square in shape
Other designations
UGCA 205,[1] DDO 75,[1] PGC 29653[1]
See also: Galaxy, List of galaxies

Sextans A ( as known as UGCA 205 ), is a tiny dwarf irregular galaxy. It spans about 5000 light-years across, and is located within the Local Group of galaxies, which includes our Milky Way galaxy. At 4.3 million light-years away from Earth, Sextans A is one of most distant members of the Local Group, and is notable for its peculiar square shape. Massive short-lived stars exploded in supernovae that caused more star formation, triggering yet more supernovae, ultimately resulting in an expanding shell. Young blue stars now highlight areas and shell edges high in current star formation, which from the perspective of observers on Earth appears roughly square.^[5]

References

1. ^ ^{a b c d e f g h i} "NASA/IPAC Extragalactic Database". Results for Sextans A. http://nedwww.ipac.caltech.edu/. Retrieved 2006-11-18. 
2. ^ Dolphin, Andrew E. et al. (March 2003). "Deep Hubble Space Telescope Imaging of Sextans A. II. Cepheids and Distance". The Astronomical Journal 125 (3): 1261–1290. arXiv:astro-ph/0211486. Bibcode 2003AJ....125.1261D. doi:10.1086/346279. http://www.iop.org/EJ/article/1538-3881/125/3/1261/202477.html. 
3. ^ I. D. Karachentsev, V. E. Karachentseva, W. K. Hutchmeier, D. I. Makarov (2004). "A Catalog of Neighboring Galaxies" (abstract). Astronomical Journal 127 (4): 2031–2068. Bibcode 2004AJ....127.2031K. doi:10.1086/382905. 
4. ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics 49 (1): 3–18. Bibcode 2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. 
5. ^ http://apod.nasa.gov/apod/ap981103.html