Messier 106, NGC 4258

Messier 106 (NGC 4258) is a spiral galaxy in the constellation Canes Venatici.

Messier 106 was discovered by Pierre Mechain in 1781, but not added to Charles Messier's catalog until 1947, by Helen Sawyer Hogg. It appears reasonable to assume that Mechain had intended to add it to a future edition, along with M 105 and M 107. William Herschel catalogued M 106 as H V.43 in 1788.

Observing Messier 106

In amateur telescopes, Messier 106 is a fine, bright, magnitude 8.4 galaxy. Its mottled, concentrated 5' x 3' central region contains a 1' diameter core with a bright, non-stellar nucleus. The outer halo is much fainter and more diffuse, extending to 19' x 8'. Hints of spiral structure can be glimpsed in the form of two brighter extensions from the central region out into the halo, the northern extension being more prominent. Both extensions have an indistinct dark streak. Several stars appear embedded in the outer arms on both sides.

Messier 106 is a large, massive type Sb spiral system, with a tightly wound structure tilted 25° to our line of sight. This orientation explains partly why this galaxy's dust lanes are so prominent. They form a spiral pattern which can be traced into its bright central core. The spiral arms end in bright blue knots, which are young star clusters dominated by very hot, luminous, massive stars which only have a lifetime of a few million years. Also conspicuous is the yellowish remnant of an older spiral arm, whose color indicates that its more massive stars ceased to shine long ago.

NGC 4217 is a possible companion galaxy of Messier 106, appearing 13' to the northeast.

Physical Properties

Messier 106 is about 22 to 25 million light years distant, and is receding at 537 km/sec. It may be a member of the Ursa Major cloud, a loose agglomeration of galaxies which also includes M 108 and M 109. A supernova (1981K) occured in M 106 in August of 1981 and reached 16th magnitude.

Since the 1950s, M 106 has been known as a source of radio emission, and appears much larger in radio radiation than in visible light. It is also a Seyfert galaxy: due to unusual emission lines in its spectrum, discovered by Carl Seyfert in 1943, we now suspect that matter in the galaxy is falling into a supermassive black hole at its center. This massive object contains a mass of 40 million Suns within a volume of about 1/24 to 1/12 light-years in radius.

The dense disk around this object works as a water maser (i.e., a microwave laser), seen by the 22 GHz line of H2O, and evidences warm, dense molecular gas. Water masers are useful to observe accretion disks in the nuclei of active galaxies.