Messier 106

Lore & Background

Messier 106 was discovered by Pierre Méchain in 1781. It lies at a distance of about 22 to 25 million light-years from Earth. The galaxy contains an active nucleus classified as a Type 2 Seyfert, and the presence of a central supermassive black hole has been demonstrated from radio-wavelength observations of the rotation of a disk of molecular gas orbiting within the inner light-year around the black hole. NGC 4217 is a possible companion galaxy. Besides its two visible arms, M106 has two 'anomalous arms' detectable using an X-ray telescope.

M106 has a water vapor megamaser seen by the 22-GHz line of ortho-H2O, which evidences dense and warm molecular gas. The water masers in M106 enabled the first case of a direct measurement of the distance to a galaxy, providing an independent anchor for the cosmic distance ladder. The galaxy has a slightly warped, thin, almost edge-on Keplerian disc on a subparsec scale, surrounding a central area with mass 4×10^7 M☉. The supermassive black hole at the core has a mass of (3.9±0.1)×10^7 M☉.

Two supernovae have been observed in M106: SN 1981K (Type II, mag. 17), reported by E. Hummel and verified by Paul Wild from archival photos dated 3 November 1981; and SN 2014bc (Type II, mag. 14.8), discovered by the PS1 Science Consortium 3Pi survey on 19 May 2014.

Reader's Guide

Messier 106 holds significant importance in astrophysics primarily through its water vapor megamaser, which enabled the first direct measurement of distance to a galaxy, thereby providing an independent anchor for the cosmic distance ladder. This achievement was crucial because before this, Cepheid variables from other galaxies could not be used to measure distances reliably due to differing metallicities. M106 contains Cepheid variables similar to both the metallicities of the Milky Way and other galaxies' Cepheids. By measuring the distance of Cepheids with metallicities similar to our galaxy, astronomers were able to recalibrate other Cepheids with different metallicities, a key fundamental step in improving quantification of distances to other galaxies in the universe. Additionally, the galaxy's active nucleus and supermassive black hole, with a mass of (3.9±0.1)×10^7 M☉, have been studied through radio observations of a rotating molecular gas disk. The presence of two anomalous arms detectable in X-rays and two recorded supernovae further contribute to its scientific value as a nearby, well-studied spiral galaxy.