| NGC 4861 | |
| Epoch: | J2000 |
| Constellation Name: | Canes Venatici |
| Ra: | [1] |
| Z: | 0.002785 |
| H Radial V: | 835[2] |
| Dist Ly: | 10.662+/- |
| Group Cluster: | Virgo Cluster |
| Type: | SB(s)m Im/BCD |
| Appmag B: | 12.90 |
| Appmag V: | 12.32 |
| Size V: | 0.797′ × 0.692′ |
| Names: | Arp 266, UGC 8098, MCG+06-29-003, PGC 44536[3] |
NGC 4861, also known as Arp 266, is a galaxy in the constellation Canes Venatici. It was discovered by William Herschel on May 1, 1785.[4]
Morphological classification of NGC 4861 has proved relatively difficult. Its mass, size, and rotational velocity are consistent with it being a spiral galaxy. However, due to its highly irregular shape, it may also be classified as a dwarf irregular galaxy.[5] In fact, since dwarf galaxies are less massive and have lower gravitational potentials, gases and other material for star formation can move within them much faster, causing the galaxy to become a specific type of starburst galaxy, called a blue compact dwarf galaxy.[5] [3] It has also been described as a "comet-like" galaxy due to its resemblance to a comet.
Two ultraluminous X-ray sources (ULXs) have been found within NGC 4861. The first, NGC 4861 X1, is associated with a dense H II region. The second, NGC 4861 X2, seems to be within a small star cluster near the "comet head" of NGC 4861. Assuming it is a star cluster, it has a mass of and an age of 5 million years. Compared to other star clusters with which ULXs are associated, its mass is quite low.[6]