Messier 61
A starburst spiral galaxy with eight observed supernovae.
Messier 61 (M61, NGC 4303, also called the Swelling Spiral Galaxy) is an intermediate barred spiral galaxy located in the Virgo Cluster. It was first spotted by Barnaba Oriani on May 5, 1779; Charles Messier observed it the same night but thought it was a comet, discovering it six days later. The galaxy lies about 45.61 million light-years from the Milky Way and belongs to the M61 Group, itself part of the Virgo II Groups—a chain of galaxies and clusters extending from the southern edge of the Virgo Supercluster.
One of the largest galaxies in the Virgo Cluster, M61 is a member of a smaller subgroup called the S Cloud. Its morphological classification, SAB(rs)bc, indicates a weakly barred spiral with a possible ring structure and moderately loose spiral arms. The galaxy hosts an active galactic nucleus and is classified as a starburst galaxy. At its center lies a massive nuclear star cluster with an estimated mass of 1 million solar masses and an age of 4 million years, alongside a candidate supermassive black hole of about 5 million solar masses. An older massive star cluster and a likely older starburst also reside there. Across M61’s disk, there is evidence of significant star formation and bright nebulae. Unlike most late-type spirals in the Virgo Cluster, M61 has an unusually high amount of neutral hydrogen. In 2026, a stellar stream was discovered north of the galaxy using the Vera C. Rubin Observatory.
M61 is one of the most prolific galaxies for supernovae, with eight observed so far: SN 1926A (Type II, magnitude 14), discovered by Max Wolf and Karl Wilhelm Reinmuth on May 9, 1926; SN 1961I (Type II, magnitude 13), found by Milton Humason on June 3, 1961; SN 1964F (Type II, magnitude 14), discovered by Leonida Rosino on June 30, 1964; SN 1999gn (Type II, magnitude 16), found by Alessandro Dimai on December 17, 1999; SN 2006ov (Type II, magnitude 14.9), discovered by Kōichi Itagaki on November 24, 2006; SN 2008in (Type II, magnitude 14.9), also found by Itagaki on December 26, 2008; SN 2014dt (Type Ia-pec, magnitude 13.6), discovered by Itagaki on October 29, 2014; and SN 2020jfo (Type II, magnitude 16.01), discovered by the Zwicky Transient Facility on May 6, 2020.
- Discoverer
- Barnaba Oriani
- Discovery date
- May 5, 1779
- Distance
- 45.61 million light years
- Morphological classification
- SAB(rs)bc
- Nuclear star cluster mass
- 1 million solar masses
- Nuclear star cluster age
- 4 million years
- Central supermassive black hole mass
- 5 million solar masses
Lore & Background
Messier 61 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. It is a member of the M61 Group of galaxies, which is part of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.
M61 is one of the largest members of the Virgo Cluster and belongs to a smaller subgroup known as the S Cloud. Its morphological classification of SAB(rs)bc indicates a weakly-barred spiral with the suggestion of a ring structure 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 1 million solar masses and an age of 4 million years, as well as a central candidate supermassive black hole weighing around 5 million solar masses. It cohabits with an older massive star cluster and a likely older starburst. Evidence of significant star formation and active bright nebulae appears across its disk. Unlike most late-type spiral galaxies within the Virgo Cluster, M61 shows an unusual abundance of neutral hydrogen. In 2026, a stellar stream was discovered north of Messier 61 using the Vera C. Rubin Observatory.
Eight supernovae have been observed in M61, making it one of the most prodigious galaxies for such cataclysmic events. These include SN 1926A, SN 1961I, SN 1964F, SN 1999gn, SN 2006ov, SN 2008in, SN 2014dt, and SN 2020jfo, all of which are Type II except SN 2014dt, which is Type Ia-pec.
Reader's Guide
Messier 61 is significant as one of the largest members of the Virgo Cluster and a starburst galaxy with an active galactic nucleus, indicating ongoing intense star formation and central black hole activity. Its classification as SAB(rs)bc places it among weakly-barred spirals with ring-like features. The galaxy's unusual abundance of neutral hydrogen for a late-type spiral in the Virgo Cluster sets it apart from similar galaxies. The discovery of a stellar stream north of M61 in 2026 using the Vera C. Rubin Observatory adds to its structural complexity. Its legacy is underscored by the observation of eight supernovae, making it one of the most prolific galaxies for such events. The supernovae span from 1926 to 2020, with discoverers including Max Wolf, Karl Wilhelm Reinmuth, Milton Humason, Leonida Rosino, Alessandro Dimai, Kōichi Itagaki, and the Zwicky Transient Facility. The galaxy's central supermassive black hole of about 5 million solar masses and its massive nuclear star cluster of 1 million solar masses and 4 million years old provide key insights into galactic evolution and starburst phenomena.
More in Messier Objects, Part 2 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced