Messier 77

Discovered 1780 by Pierre Méchain.

Messier 77 (M77, NGC 1068) is a conspicuous spiral galaxy situated in constellation Cetus. With its bright Active Galactic Nucleus (AGN), it is the prototype of an active galaxy, and a famous group of these objects called "Seyfert Galaxies," after their discoverer.

When Pierre Méchain discovered this object on October 29, 1780, he described it as a nebula. Charles Messier included it as No. 77 in his catalog on December 17, 1780, and misclassified it a cluster with nebulosity, perhaps because of foreground stars, or possibly mistaking some of its knots for faint stars. M77 is one of the first recognized spiral galaxies, and listed by Lord Rosse as one of 14 "spiral nebulae" discovered to 1850.

This magnificient galaxy is one of the biggest galaxies in Messier's catalog, its bright part measuring about 120,000 light years, but its faint extensions (which are well visible e.g. in the DSSM image) going perhaps out to nearly 170,000 light years. Its appearance is that of a magnificient spiral with broad structured arms, which in the inner region show a quite young stellar population, but more away from the center, are dominated by a smooth yellowish older stellar population.

M77 is about 60 million light years distant, approximately the same distance but another direction as the Virgo Cluster, and is receding from us at about 1100 km/sec, as was first measured by Vesto M. Slipher of Lowell Observatory in 1914; it was the second galaxy with a large measured redshift after the Sombrero galaxy, M104 (R. Brent Tully's Nearby Galaxies Catalog gives a somewhat smaller value for the distance, 47 million light years, and values in other sources are spread both below and above the Virgo Cluster value; the higher values would make M77 the most remote Messier object).

From investigations of the inner disk's rotational velocities, E.M. Burbidge, G.R. Burbidge and K.H. Prendergast (1959) found that M77's inner disk in inclined against the line of sight by 51 degrees. They estimated the inner disk's mass at 27 billion solar masses, while the total mass of this galaxy must be of the order of 1 trillion solar masses.

This galaxy is unique and peculiar because of several reasons. First of all, its spectrum shows peculiar features in the form of broad emission lines, indicating that giant gas clouds are rapidly moving out of this galaxy's core, at several 100 km/sec. This feature was first discovered by Edward A. Fath of Lick Observatory in 1908 (Fath 1909) who identified six "Planetary Nebula type" emission lines (H Beta, [O II] 3727, [N III] 3869, [O III] 4363, 4959, 5007), confirmed by Vesto M. Slipher at Lowell Observatory in a much better spectrum in 1917 (Slipher 1917) and particularly mentioned by Edwin P. Hubble in his historic paper on "extragalactic nebulae" of 1926 (Hubble, 1926). It classifies M77 as a Seyfert galaxy of type II (type I Seyfert galaxies exhibit an even larger expansion velocity of several 1000 km/sec); it is the nearest and brightest representative of this class of active galaxies. This remarkable class of galaxies is named after its discoverer, Carl K. Seyfert, who described them first in 1943 (Seyfert 1943).

An enormous energy source is required to generate this velocity, which must sit in the galaxy's core or nucleus. This core was found to be a strong radio source, which was discovered by Berbard Yarnton Mills in 1952 and designated Cetus A, and listed as 3C 71 in the Third Cambridge Catalogue of Radio Sources. It was investigated optically with the Hubble Space Telescope. Infrared investigations with the 10-meter Keck telescope by Caltech astronomers have revealed a strong pointlike source, less than 12 light-years in diameter, and surrounded by an elongated structure of 100 light years extension (a concentration of stars or interstellar matter); these structures were not apparent in the Hubble images in the visible light. M77, as well as other Seyfert galaxies, has been known to be bright infrared radiators since some time.

It were Donald E. Osterbrook and R.A.R. Parker in 1965 who brought up the hypothesis that the active nuclei of Seyfert galaxies might be thought of as miniature quasars (quasi-stellar radio sources), according to Burnham. This view has been confirmed now by decade-long research: Probably all types of active galactic nuclei (AGNs), including Seyfert nuclei, radio galaxies, quasars, BL Lacertae objects, and others, are caused by the same physical reason, a central supermassive object 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 supply falling into the objects.

In case of M77, the central object which is responsible for the Seyfert activity has been found to have a mass of about 10 million solar masses, via IR observations from Caltech. Radio astronomers of the National Radio Astronomy Observatory (NRAO) and the 100-meter-diameter radio telescope of the Max Planck Institute for Radio Astronomy at Effelsberg, Germany found a giant disk of some 5 light-years diameter orbiting this object, which contains water molecules (NRAO PR of January 15, 2000).

In the inner disk of M77 surrounding the active nucleus, near the active center, M.F. Walker has found emission nabulae with considerable expansion velocities. Intense star forming activity in an inner bar was found to take place by the Ultraviolet Imaging Telescope on its Astro-1 Space Shuttle mission. These star formation regions are among the brightest known, and perhaps the most luminous within a distance of 100 million light years from us.

Halton Arp has included M77 as No. 37 in his Catalogue of Peculiar Galaxies as "Spiral with a Low Surface Brightness Companion On Arm".

M77 is the dominating member of a small physical group of galaxies, which includes NGC 1055 (type Sb) and NGC 1073 (type SABc), as well as UGC 2161 (DDO 27, type Im), UGC 2275 (DDO 28, type Sm - designating a morphological type between spirals and irregulars) and UGC 2302 (DDO 29, type Sm), and the irregular galaxy UGCA 44 and the SBc barred spiral Markarian 600. NGC 1087 (Sc), NGC 1090 (S-), and NGC 1094 (SABb-) are nearby background galaxies, as their much higher redshift indicates (Info from Burnham, Tully, and the Sky Catalogue 2000.0).

M77 can be easily found 0.7 degrees ESE from the 4-th mag star Delta Ceti. Its central 2 arc minutes dominate the view of this almost face-on spiral galaxy in amateur telescopes, and shows remarkable detail with higher magnification in larger instruments. NGC 1055 is situated about 0.5 deg NNW of M77, and visible as a 3' long edge-on spindle, aligned about east to west, of about mag 10.6. 11th-mag NGC 1073 is about 1 deg NNE of M77, a face-on disk of 5' diameter, with a prominent 2x1' bar elongated at about position angle 60 deg.

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