NGC 4203

NGC 4203 is the New General Catalogue identifier for a lenticular galaxy in the northern constellation of Coma Berenices. It was discovered on March 20, 1787 by English astronomer William Herschel, and is situated 5.5° to the northwest of the 4th magnitude star Gamma Comae Berenices and can be viewed with a small telescope. The morphological classification of NGC 4203 is SAB0−, indicating that it has a lenticular form with tightly wound spiral arms and a weak bar structure at the nucleus.

This galaxy has a fairly large reservoir of neutral hydrogen containing on the order of a billion solar masses, but it is only undergoing a low rate of new star formation. Hence, the inner star formation of the galaxy is fairly old; roughly ten billion years on average. The neutral hydrogen is arranged in two ring-like structures, with the outer ring having nine times the mass of the inner. In the central region there is around $25,000,000$ of molecular hydrogen, plus dust structures within 300 pc of the nucleus. The gas in the outer disk may have been accreted from the inter-galactic medium, or captured during a close encounter with a dwarf galaxy.

The nucleus of the galaxy contains a low-ionization nuclear emission-line region of type 1.9. This is being generated by a supermassive black hole of an estimated $6$. An influx of gas of around $2e−2$ /yr is sufficient to explain the measured X-ray luminosity. The time-varying emissions from the region are perhaps best explained by an infalling red supergiant star that is losing mass to the black hole along a contrail.

NGC 4203 is a member of the Coma I Group which is part of the Virgo Supercluster.