M 83

Spiral Galaxy M83 (NGC 5236), type SABc, in Hydra

Southern Pinwheel

Right Ascension 13 : 37.0 (h:m)

Declination -29 : 52 (deg:m)

Distance 15000 (kly)

Visual Brightness 7.6 (mag)

Apparent Dimension 11x10 (arc min)

Right Ascension	13 : 37.0 (h:m)
Declination	-29 : 52 (deg:m)
Distance	15000 (kly)
Visual Brightness	7.6 (mag)
Apparent Dimension	11x10 (arc min)

M83 was classified as intermediate between normal and barred spiral galaxies by G. de Vaucouleurs, in his classification this is SAB(s)c.

Clicca sull'immagine per ingrandirla

It is magnificient in our image, has very well defined spiral arms and displays a very dynamic appearance, appealing by the red and blue knots tracing the arms. The red knots are apparently diffuse gaseous nebulae in which star formation is just taking place, and which are excited to shine by its very hot young stars. The blue regions represent young stellar populations which have formed shortly (i.e., some million or some dozens of million years ago). The dust lanes may be traced well into the central region to the nucleus which has only 20" diameter.

Our image was obtained by David Malin with the 3.9-meter Anglo Australian Telescope and is courtesy of David Malin and the Anglo Australian Telescope Board.

David Malin, in his older publications, always gave a distance of about 25 million light years, as he does in his book A View of the Universe in chapter 4, while in his Galaxis chapter 8, he joins the lot of those claiming a distance of about 10 million light years, and gives an argument, namely that the brightest stars can be viewed as individuals over this distance. M83 recedes at 337 km/sec, implying a bit larger distance from Hubble's law (H0=75 yields about 15 million light years, uncorrected for the disturbation by the Virgo cluster of galaxies, the Virgo centric flow, but in excellent agreement with the value of 15.3 million light years given in R. Brent Tully's Nearby Galaxies Catalog).

This galaxy is sometimes called the "Southern Pinwheel". It forms a small physical group with the peculiar radio galaxy Centaurus A (NGC 5128) and the unusual galaxy NGC 5253 in Centaurus.

Five or six supernovae were reported in M83 up to now, more than in any other Messier galaxy:

1923A was observed by C.O. Lampland at Lowell Observatory at mag 14.
1945B appeared on July 13, 1945 and reached mag 14.2). This supernova was only detected in 1990 by W. Liller on photographic plates taken at Harvard's station at Bloemfontein (South Africa), and could be traced from July 13 to August 7 IAU Circular 5091.
1950B was observed by G. Haro and reached mag 14.5 in its maximum,
1957D was discovered by H.S. Gates on December 13, 1957 and reached only mag 15.0, it was about 3' NNE of the nucleus.
Supernova 1968L was discovered visually by amateur astronomer Jack C. Bennett of Pretoria, South Africa, when sweeping for comets; this was a type I, located 5" preceding the nucleus and reached mag 11 to 12.
1983N appeared on July 3, 1983 and became as bright as 12.5 mag.

For years, M83 had been the galaxy with most discovered supernovae, but recently came up with the same number of 6, or even one more if 1945B should be an error.

M83 was discovered by Abbe Nicholas Louis de la Caille at the Cape of Good Hope in 1751-52, it was his object Lacaille I.6. Thus it became the first galaxy discovered beyond the Local Group. Its spiral structure was noted and sketched by William Lassell who described it as a "three-branched spiral".