Clearly visible in the upper left corner of the photo, Messier 106, or NGC 4258, is a “barred spiral” type galaxy recognizable (by enlarging the image) by its very bright central core…framed by a line of stars from which emerge blue-green spiral arms studded with white stars wrapped in a red-blue dust cloud.

It is located in the Hunting Dogs, a small constellation made up of only two stars that can be spotted quite easily south of the end of the handle of the “Great Casserole”. Discovered by Pierre Méchain in 1781, this galaxy was later added to the catalogue of his friend and colleague Charles Messier.

It is about 30,000 light-years in diameter and its distance is estimated at between 21 and 25 million light-years from Earth (by comparison, M31, the Andromeda galaxy M 31 is 2.5 million light-years away and its extension is 140,000 light-years). The slight inclination of its equatorial plane is comparable to that of the Andromeda galaxy M31: it is thus seen practically from the front. This makes it a very popular target for amateurs despite its small angular extension of 18 minutes and its apparent rather small magnitude of 8.4.

Thanks to the observations made in 1995 in the radio field, specialists suspect that M106 hosts in its center an enormous black hole whose mass, equal to 36 million times that of the Sun, would be confined in a sphere of diameter only 1000 larger. If this hypothesis proves true, this black hole would be the densest concentration of matter currently known.

It is thought that this type of galaxy with a very active and very bright nucleus draws its energy from the fall of matter on the central supermassive black hole. Already in 1943, Carl K. Seyfert (American astronomer, 1911-1960) had classified this galaxy as one of those galaxies with emission lines in their spectra from their nuclei, which are now called “Seyfert Galaxies”. These emissions occur throughout the entire electromagnetic spectrum, from radio waves to X-rays, including the visible range.

It should also be noted that the characteristics of the dense disc of matter surrounding this object made it possible to make a geometric measurement of its distance independently of other methods. This led to a distance of 23.8 ± 1.3 million light-years, which is considered to be consistent with the Cepheid data.

Among the other objects visible on this picture, we can see from top to bottom :
– NGC 4248, magnitude 12.6.

-NGC 4231 and NGC 4232, a little lower, one next to the other like two binoculars.

– NGC 4217, a spiral galaxy seen in profile with its gas band clearly visible, main companion of magnitude 12 located at the bottom, in the lower left corner of the picture.

– NGC 4220, another spiral galaxy seen in profile, of magnitude 12, in the lower right corner.