NGC 7424
| NGC 7424 | |
|---|---|
| 300px | |
| Observation data (J2000 epoch) | |
| Constellation | Grus |
| Right ascension | 22h 57m 18s[1] |
| Declination | −41° 04′ 14″ [1] |
| Redshift | 0.003132 (939 ± 2 km/s) [1] |
| Distance | 37.5 Mly (11.5 Mpc)[2] |
| Type | SAB(rs)cd [1] |
| Apparent dimensions (V) | 9.5 x 8.1 arcmin [1] |
| Apparent magnitude (V) | 11.0 [1] |
| Notable features | similar to the Milky Way |
| Other designations | |
| PGC 070096 | |
NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the southern constellation Grus (the Crane). Its structure and diameter (about 100,000 light-years) make it similar to our own galaxy, the Milky Way.[3] 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.
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.[4]
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.[5] 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.[6][7] 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.[8]
Ultraluminous X-ray sources
In May and June 2002 Roberto Soria and his colleagues at the Harvard-Smithsonian Center for Astrophysics discovered two Ultraluminous X-ray sources (ULXs) with the Chandra X-ray Observatory. ULXs are objects that emit tremendous amounts of X-rays (> 1032 watts or 1039 erg/s), assuming they radiate isotropically (the same in all directions). This amount is larger than currently understood stellar processes (including supernovae) but smaller than the amount of X-rays emitted by active galactic nuclei, which accounts for their alternate name, Intermediate-luminosity X-ray Objects (IXOs). The source designated ULX1 was found in a relatively empty interarm region, far from any bright clusters or star-forming complexes, and showed a 75% increase in X-ray luminosity over the course of 20 days. ULX2 was found in an exceptionally bright young stellar complex, and showed an order of magnitude increase over the same time period.[2]
References
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- ↑ 2.0 2.1 Lua error in package.lua at line 80: module 'strict' not found.
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