Right ascension 22 57 18 Distance 37.5 Mly (11.5 Mpc) Apparent size (V) 9.5 x 8.1 arcmin Constellation Grus | Declination −41° 04′ 14″ Type SAB(rs)cd Magnitude 11 Apparent magnitude (V) 11 | |
Redshift 0.003132 (939 ± 2 km/s) Similar NGC 7090, NGC 7793, NGC 1532, NGC 7582, NGC 7217 | ||
NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the southern constellation Grus (the Crane). Its size (about 100,000 light-years) makes it similar to our own galaxy, the Milky Way. It is called a "grand design" galaxy because of its well defined spiral arms. One supernova and two ultraluminous X-ray sources have been discovered in NGC 7424.
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Characteristics
NGC 7424 is intermediate between normal spirals (SA) and strongly barred galaxies (SB). Other features include the presence of a central ring-like structure and a relatively low core brightness relative to the arms. The redder color of the prominent bar indicates an older population of stars while the bright blue color of the loose arms indicates the presence of ionised hydrogen and clusters of massive young stars. NGC 7424 is listed as a member of the IC 1459 Grus Group of galaxies, but is suspected of being a "field galaxy"; that is, not gravitationally bound to any group.
Supernova 2001ig
SN 2001ig was a rare Type IIb supernova discovered by Australian amateur Robert Evans on the outer edge of NGC 7424 on 10 December 2001. Type IIb supernovae (SNe) initially exhibit spectral lines of hydrogen (like typical Type II's), but these disappear after a short time to be replaced by lines of oxygen, calcium and magnesium (like typical Type Ib's and Ic's).
On 28 May 2002 Cambridge University astrophysicist Stuart Ryder et al. found what they believe is the binary companion to SN 2001ig. It is a massive O or B class star that had an eccentric orbit around the progenitor, a Wolf-Rayet star. They believe that the companion periodically stripped the outer hydrogen-rich envelope of the progenitor, accounting for the observed spectral changes. Princeton University fellow Alicia Soderberg et al. also believe that the progenitor was a Wolf-Rayet star, but suggest that the periodic mass loss was a result of the intense stellar wind these stars produce.