Messier 61

Messier 61 (also known as M61, NGC 4303, or the Swelling Spiral Galaxy) is an intermediate barred spiral galaxy in the Virgo Cluster of galaxies. It was first discovered by Barnaba Oriani on May 5, 1779, six days before Charles Messier discovered the same galaxy. Messier had observed it on the same night as Oriani but had mistaken it for a comet. Its distance has been estimated to be 45.61 million light years from the Milky Way Galaxy. It is a member of the M61 Group of galaxies, which is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.

Properties

M61 is one of the largest members of Virgo Cluster, and belongs to a smaller subgroup known as the S Cloud. The morphological classification of SAB(rs)bc indicates a weakly-barred spiral (SAB) with the suggestion of a ring structure (rs) and moderate to loosely wound spiral arms. It has an active galactic nucleus and is classified as a starburst galaxy containing a massive nuclear star cluster with an estimated mass of 10⁵ solar masses and an age of 4 million years, as well as a central candidate supermassive black hole weighing around 5×10⁶ M_☉ solar masses. It cohabits with an older massive star cluster as well as a likely older starburst. Evidence of significant star formation and active bright nebulae appears across M61's disk. Unlike most late-type spiral galaxies within the Virgo Cluster, M61 shows an unusual abundance of neutral hydrogen (H I).

Supernovae

Eight supernovae have been observed in M61, making it one of the most prodigious galaxies for such cataclysmic events. These include:

SN 1926A (type II, mag. 14) was discovered by Max Wolf and Karl Wilhelm Reinmuth on 9 May 1926.
SN 1961I (Type II, mag. 13) was discovered by Milton Humason on 3 June 1961.
SN 1964F (Type II, mag. 14) was discovered by Leonida Rosino on 30 June 1964.
SN 1999gn (Type II, mag. 16) was discovered by Alessandro Dimai on 17 December 1999.
SN 2006ov (Type II, mag. 14.9) was discovered by Kōichi Itagaki on 24 November 2006.
SN 2008in (Type II, mag. 14.9) was discovered by Kōichi Itagaki on 26 December 2008.
SN 2014dt (type Ia-pec, mag. 13.6) was discovered by Kōichi Itagaki on 29 October 2014.
SN 2020jfo (Type II, mag. 16) was discovered by the Zwicky Transient Facility on 6 May 2020.