NGC 1313

NGC 1313 (also known as the Topsy Turvy Galaxy^[2]) is a field galaxy^[3] and an irregular galaxy^[4] discovered by the Scottish astronomer James Dunlop on 27 September 1826.^[5] It has a diameter of about 50,000 light-years, or about half the size of the Milky Way.^[6]

NGC 1313
A Very Large Telescope (VLT) image of NGC 1313. Credit: ESO.
Observation data (J2000.0 epoch)
Constellation	Reticulum
Right ascension	03h 18m 15.4s [1]
Declination	−66° 29′ 50″ [1]
Redshift	0.001568 [1]
Distance	12.886 Mly[1]
Characteristics
Type	SB(s)d[1]
Apparent size (V)	9.1 x 7.1 arcmin[1]
Other designations
Topsy Turvy Galaxy, PGC 12286, ESO 082- G 011

NGC 1313 lies within the Virgo Supercluster.^[7]

In 2007, a rare WO star was discovered in NGC 1313,^[8] currently known by its only designation of [HC2007] 31. It is of spectral type WO3.^[8] The derived absolute magnitude is about -5,^[8] which is very high for a single WO star. (WOs usually have absolute magnitudes of about -1 to -4) This means that the WO is likely part of a binary or a small stellar association.^[8]

Supernovae

Two supernovae have been observed in NGC 2841:

• SN 1962M (type II, mag. 11.7) was discovered by José Sérsic on 26 November 1962.^[9][10]
• SN 1978K (type IIn, mag. 16) was discovered by Stuart Ryder in January 1990 and originally reported as a nova.^[11] However, a search of archival photographs revealed an outburst on 31 July 1978, and all data indicated that it was a very unusual type II supernova.^[12]

Features

NGC 1313 has a strikingly uneven shape and its axis of rotation is not exactly in its centre.^[13] NGC 1313 also shows strong starburst activity^[14] and associated supershells.^[15] NGC 1313 is dominated by scattered patches of intense star formation, which gives the galaxy a rather ragged appearance.^[16] The uneven shape, the ragged appearance and the strong starburst can all be explained by a galactic collision in the past.^[17] However, NGC 1313 seems to be an isolated galaxy and has no direct neighbours. Therefore, it is not clear whether it has swallowed a small companion in its past.^[2]

Young, blue stars are scattered across the galaxy.^[18] This is evidence of infant mortality in which the young open clusters quickly became gravitationally "unglued", scattering their resident stars into the galaxy.^[19] The galaxy bears some resemblance to the Magellanic Clouds^[20] and hosts two ultraluminous X-ray sources, called NGC 1313 X-1 and X-2.^[21] The former is a rare intermediate-mass black hole.^[22][23]