Quoted from SEDS
Discovered 1780 by Pierre Méchain.
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 magnificent 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
magnificent 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 point like 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 super massive 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 NGCs 1055 (type Sb) and 1073
(type SABc), as well as UGCs 2161 (DDO 27, type Im), 2275 (DDO 28, type
Sm - designating a morphological type between spirals and irregulars)
and 2302 (DDO 29, type Sm), and the irregular galaxy UGCA 44 and the SBc
barred spiral Markarian 600. NGCs 1087 (Sc), 1090 (S-), and 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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