NGC 4639

NGC 4639 is a barred spiral galaxy located in the equatorial constellation of Virgo. It was discovered by German-born astronomer William Herschel on 12 April 1784. John L. E. Dreyer described it as "pretty bright, small, extended, mottled but not resolved, 12th magnitude star 1 arcmin to southeast".^[7] This is a relatively nearby galaxy,^[8] lying approximately 72 million light-years away from the Milky Way.^[3] It is a companion to NGC 4654, and the two appear to have interacted roughly 500 million years ago.^[9] NGC 4639 is a member of the Virgo Cluster.^[10]

NGC 4639
NGC 4639 imaged by the Hubble Space Telescope[1]
Observation data (J2000 epoch)
Constellation	Virgo
Right ascension	12h 42m 52.37814s[2]
Declination	+13° 15′ 26.7129″[2]
Heliocentric radial velocity	989 km/s[3]
Distance	72.02 ± 0.23 Mly (22.08 ± 0.07 Mpc)[3]
Group or cluster	Virgo Cluster
Apparent magnitude (V)	12.2[4]
Characteristics
Type	SAB(rs)bc[5]
Apparent size (V)	2′.8 × 1′.9[4]
Notable features	Seyfert type 1
Other designations
IRAS 12403+1331, LEDA 42741, MCG+02-32-189, NGC 4639, UGC 7884, VCC 1943,[6] PGC 42741[4]

The morphological classification of this galaxy is SAB(rs)bc,^[5] indicating a spiral galaxy with a weak bar (SAB), an incomplete ring around the bar (rs), and moderate to loosely-wound spiral arms (bc). NGC 4639 has a mildly active galactic nucleus of the Seyfert type 1; one of the weakest known. The compact central source has been detected by its X-ray emission, and is variable on timescales of months to years.^[8] There is a supermassive black hole at the core^[11] with an estimated mass of 7.9×10⁶ M_☉.^[12]

Supernovae

Two supernovae have been observed in NGC 4639:

• SN 1990N (type Ia, mag. 15.5) was discovered by E. Thouvenot on 22 June 1990, two weeks before reaching peak brightness.^[13][14][15] It was positioned 63.2″ east and 1.8″ south of the galaxy core.^[13] The brightness and proximity of this supernova event has allowed it to be used as a standard candle.^[15]
• SN 2018imf (type IIP, mag. 15.8) was discovered by Kōichi Itagaki on 14 November 2018.^[16] [Note: while officially associated with NGC 4639, this supernova is actually much closer to the neighboring galaxy VCC 1931.]