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NGC 5128
Centaurus A, MCG-07-28-001
RA 13:25:24
Dec -43° 00.6'
Galaxy |
James Dunlop discovered this interesting and
very peculiar galaxy from Paramatta, New South Wales, and included it as No. 482
in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a
very singular double nebula, about 2.5' long, and 1' broad, a little unequal:
there is a pretty bright small star in the south extremity of the southernmost
of the two, resembling a bright nucleus: the norther and rather smaller nebula
is faint in the middle, and has the appearance of a condensation of the nebulous
matter near each extremity. These two nebulae are completely distinct from each
other, and no connection of the nebulous matters between them. There is a very
minute star in the dark space between the preceding extremities of the nebula:
they are extended in the parallel of the equator nearly." He drew a sketch
of the object, and observed it 7 times.
Sir John Herschel observed it at the Cape of
Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "A
most wonderful object; a nebula very bright; very large; little elongated, very
gradually much brighter in the middle; of an elliptic figure, cut away in the
middle by a perfectly definite straight cut 40 arcsec broad; pos = 120.3 ;
dimensions of the nebula 5' x 4' The internal edges have a gleaming light like
the moonlight touching the outline in a transparency." On his next sweep
he observed it again, describing it as "Two nebulae, or two portions of one
separated by a division or cut. The cut is broad and sharp. The two nebulae
are very nearly alike. Perhaps the slit is larger towards the N.p. end, where
there is a star between them. There is certainly a very feeble trace of nebula,
an island as it were, running from this star between the sides of the slit.
N.B. No 'moonlight effect' seen between the edges. Night very fine. Pos of
the slit 120.3 The place taken is that of the star within the slit." His
final observation recorded it as "A nebula consisting of two lateral
portions, and no doubt of a small streak of nebula along the middle of the slit
or interval between them, having a star at its extremity. Position of the slit
124.7 ; of the star, with another star near the nebula and south of it 332.3 ;
others stars also laid down. A most superb calm night; objects admirably
defined. Shown to a bystander (J.R.) who saw it as figured and described."
Herschel carefully sketched the galaxy, and commented on it as "a very
problematic object, and must be regarded at present to form a genus apart, since
it evidently differes from mere 'double nebulae,' not only in the singular
relation of its two halves to each other, (having each a well and an illdefined
side, their sharply terminated edges being turned towards each other and exactly
parallel) but also by the intervention of the delicate nebulous streak
intermediate between them and lying in exactly the same general direction. It
may perhaps be considered that the nebulae V.24 [NGC 4565] and I.43 [NGC 4594]
offer some analogy of structure to this; but of so it is a very remote one, the
nebulae constituting these objects being in both instances very unequal in size
and brightness, and being individually merely elongated nebulae of the ordinary
type, which these are not. On the other hand we have, in the completely
resolved cluster,[NGC 6451], an object which, removed to such a distance as to
appear nebulous, would present a considerably approach to it in point of general
aspect."
There has been much controversy since Herschel's musings above
over the nature of this object. In 1849, Sir John Herschel wrote in his "Outlines
of Astronomy" that it was "two semi-ovals of elliptically formed
nebula appearing to be cut asunder and separated by a broad obscure band
parallel to the larger axis of the nebula, in the midst of which a faint streak
of light parallel to the sides of the cut appears." In 1918, H D Curtis of
Lick Observatory classified it as an edge-on spiral galaxy with dark lanes.
Burnham notes that in a Helwan Observatory publication of 1921 it is described
as a "large patch of structureless and possibly gaseous nebulosity, cut in
two by a wide belt of obscuring matter, through which appear several stars and
wisps of nebulosity." Hubble, in 1922, classified it as a local
nebulosity. In 1932, Shapley and Ames included it in their famous catalogue of
galaxies as an irregular system. Burnham notes that the "dark band is
approximately 1' wide where it crosses in front of the nucleus, widening to
about 2' on the southeast side of the galaxy. On the northwest the band becomes
weaker and less regular, breaking into a chaotic mass of bright and dark clouds.
The course of the dark lane is from PA 135 to 315 ."
Hartung describes it as a "bright round
luminous haze about 5' across, bisected by a clean dark bar about 1' wide in PA
130 in which is a faint luminous streak coming in N.p. Many stars are in the
field, one being immersed in the southern region of theg nebula and one in the
dark rift. Even a 3-inch shows this object plainly."
Houston writes: "Visually its bright 7th
mag glow is some 10' in diameter with a wide belt of dark material dividing it
in two slightly unequal halves. This belt shows well in a 4-inch telescope, and
Ron Morales of Tucson, Arizona, has seen it with 7x35 binoculars." Houston
also reports Morales' description as "very bright, large, round object, cut
through the middle by a wide, dark lane."
Steve Coe, in “SACNEWS On-Line for May
1996”, observing with a 17.5" f/4.5 Dobsonian, notes: NGC 5128 is
bright, large, round and has a bright middle at 100X. The dark band across this
galaxy is easy at 135X. There are several stars superimposed across the face of
this object. This bizarre galaxy has been photographed many times because of
the tormented shape of the dark lane across the bright body of this object. On
that clear, sharp night so long ago, I was able to pick out some of that
structure in moments of good seeing at 135X and 165X. You might hear this
galaxy spoken of as Centaurus A, because of it is also a strong radio source and
it got that designation from a radio survey done in the 1950s at Cambridge
University in Britain. Wait for a great night then see if you can observe some
of that fine detail at 13 hr 25.5 min and -43 01.
Harrington notes that it is "bright and
large enough to be seen in 7x binoculars. When high in the sky the galaxy
displays its dust lane well through giant glasses and small telescopes.
Increasing to 10-inch or larger instruments, the lane begins to reveal
irregularities along its fringes."
Simon Tsang notes that in a 13-inch "the
two bright hemispheres are separated by a dark lane of uneven width visible even
at moderate powers. This dark lane is wider and more conspicuous than the dark
lane in the Sombrero."
Tom Lorenzin, in the e-version of "1000+
The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: “7.2M;
10' x 8' extent; very large; at first glance this looks like two separate
objects; closer scrutiny shows large glow with broad equatorial dust lane; 9M
stars on SE edge and to SW, 10' from core; !good supernova prospect! see photo
at HAG-50.”
Todd Gross, in a contribution to the IAAC,
observing with 80mm APO refractor, describes it as “Best at around 70x,
this was fairly easy to find only because it was near Omega Centauri (globular).
I just ran the scope up to the north for a few degrees and looked for the
nebulosity. It was a bit difficult at first, requiring averted vision to see the
dark lane that runs roughly west to east and splits the approximately round
patch in two pieces. Dark lane visible at 32 & 69x. Round patch of galaxy
is relatively large, but at this aperture and focal length it still appears
reasonably small, not as huge as Omega Centauri nearly, the largest globular I
have ever seen.”
AJ Crayon, using an 8” f6 Newtonain,
notes: “is a spiral galaxy. It is 8m 3'x5' with no dust lane, has a bright
middle of 2'x1' in position angle east with a star south of the bright middle at
100x.
Other names: “ARP153,E270-09”.
Inclination: (face-on, in degrees) 44 Total photoelectric blue mag 7.84 Total
colour index 1.00 Logarithm of the angular diameter D25 (arcminutes) 2.41 Blue
photographic magnitude 7.18 This galaxy is included in a sample of galaxies with
velocity less than 500km/s with respect to the centroid of the Local Group.
[Nearby Galaxies. Schmidt K.-H., Priebe A., Boller T. (Astron. Nachr. 314, 371
(1993))]
Sidney van den Bergh (1961, Astronomical
Journal, Vol 66) notes that this galaxy could be a radio source. He remarks: "Dark
patches and bright knots. Similar to NGC 1316 and NGC 1275?"
Sandage and Tammann (1975, Astrophysical
Journal, 196, 313-328) includes this galaxy in the NGC 5128 Group. Members
include NGC 4945, NGC 5068, NGC 5102, NGC 5128 & NGC 5236.
This galaxy is a member of the fairly nearby
Centaurus group of galaxies, which includes NGC 4945, 5102, 5128, 5236 and NGC
5253. Listed as No. 153 in Arp's "Atlas of Peculiar Galaxies"
(Astrophysical Journal Supplement, vol. 14, 1966.)
15.5-inch f/9 Newtonian : At
220x this beautiful object is well shown, with its complete, bold dark band
bisecting the nebula into uneven halves. The northern section is shorter and
fatter than the southern half, which is a thin, bright band. The dark band is
clearly broadest at the eastern tip, whilst the western tip has a star located
just inside the extent of the band. The northern section contains two stars in
the nebulosity. It bears a striking resemblance to a hamburger! (suburban
skies) [AS] |
