Messier 77 (NGC 1068) is a barred spiral galaxy in Cetus. It has an active nucleus, which corresponds to the radio source Cetus A; M 77 is the prototype of the peculiar Seyfert galaxies.
Messier 77 was discovered by Pierre Mechain in 1780, who originally described it as a nebula. Mechain communicated his discovery to Charles Messier, who listed it as the 77th object in his catalog. Although both Messier and William Herschel described this galaxy as a star cluster, M 77 was one of the first recognized spiral galaxies, listed by Lord Rosse as one of the 14 "spiral nebulae" discovered up to 1850.
Halton Arp listed Messier 77 as No. 37 in his Catalogue of Peculiar Galaxies, describing it as a "Spiral with a Low Surface Brightness Companion On Arm".
Amateur Observation
A conspicuous spiral galaxy of visual magnitude 8.9, Messier 77 can be easily found 0.7° southeast of Delta Ceti. In amateur telescopes, the central 2' of this almost-face-on spiral galaxy dominate the view, and show remarkable detail with higher magnification in larger instruments. M 77 is an unusual galaxy, containing three distinct sets of spiral arms. It has a bright 7' x 6' disk elongated NNE-SSW, containing a very bright, exceptionally large core. The disk is mottled, with dark lanes and luminous fragments of spiral arms. At 175x, a starlike nucleus becomes visible in the core.
Messier 77 is the dominating member of a small physical group of galaxies, which includes NGC 1055 (Sb), NGC 1073 (SABc), UGC 2161 (Im), UGC 2275 (Sm), UGC 2302 (Sm), UGCA 44 (I). The nearby galaxies NGC 1087 (Sc), NGC 1090 (S-), and NGC 1094 (SABb-) are background objects, as their much higher redshifts indicate.
Properties and Structure
M 77 is about 60 million light years distant, and is receding from us at 1100 km/sec, as first measured by Vesto Slipher of Lowell Observatory in 1914; it was the second galaxy found with a large redshift (after the Sombrero galaxy, M 104). This magnificent galaxy is one of the largest in Messier's catalog: its bright part measures about 120,000 light years across, but its faint outer regions extend out to nearly 170,000 light years.
This galaxy is a magnificent spiral with broad, structured arms. In its inner region, these show a young stellar population, but away from the center, they are dominated by a smooth, yellowish, older stellar population. M 77's inner disk in inclined to our line of sight by 51°, and contains 27 billion solar masses - but the total mass of this galaxy must be of the order of 1 trillion solar masses.
Seyfert Activity
Messier 77 is the nearest and brightest of the Seyfert Galaxies, named after Carl K. Seyfert, who first described them in 1943. These systems have bright, starlike nuclei; peculiar emission-line spectra; and strong radio output. M 77's broad emission lines indicate giant gas clouds moving rapidly out of its core at several hundred km/sec. An enormous energy source is required to generate them, which must sit at the galaxy's core.
This core was found to be a strong radio source, discovered in 1952 and designated Cetus A. Optical investigations with the Hubble Space Telescope, and infrared observations with the 10-meter Keck telescope, have revealed Cetus A to be a pointlike source, less than 12 light-years in diameter, surrounded by a concentration of stars or interstellar matter 100 light years in extent.
In case of M 77, the central object responsible for the Seyfert activity has been found to be a supermassive black hole, with about 10 million solar masses. A giant disk containing water molecules, some 5 light-years in diameter, orbits this object. In the inner disk, surrounding the active nucleus, emission nebulae with intense star forming activity has been found. These star formation regions are perhaps the most luminous known within a distance of 100 million light years.
The active nuclei of Seyfert galaxies might be thought of as miniature quasars. Probably all types of active galactic nuclei, including Seyfert nuclei, radio galaxies, quasars, BL Lacertae objects, have the same physical cause: a central supermassive black hole which accumulates gaseous matter from its surrounding neighborhood. The variety of observed phenomena is simply a consequence of different viewing angles, and different rates of matter falling into these objects.