Today, let’s look at the spiral galaxy M83, a lovely cosmic lotus blossom and one of the showpieces in the southern deep sky.
Barely visible from northern latitudes, M83 lies roughly 15 million light-years away in the constellation Hydra. It’s one of the 25 brightest galaxies in the sky, and one of the closest and brightest barred spiral galaxies. At magnitude 7.6, it’s easily visible with binoculars and small telescopes about 18° due south of the bright star Spica, in Virgo, and just north of the star Menkent in the constellation Centaurus.
This galaxy was first seen by French astronomer and cartographer Nicolas Louis de Lacaille in 1752 during an expedition to the Cape of Good Hope. Charles Messier later added it to his list of nebulous objects in 1781. Messier observed from Paris in the days of dark sky. But this is a difficult object for northern observers because it’s low on the horizon. A little light pollution makes it nearly impossible to see. Southern stargazers have a much better view.
M83 forms a small physical group, called the M83 group, along with the peculiar radio galaxy Centaurus A (also called NGC 5128). The shape of M83 lies between that of a normal and barred spiral galaxy. In photographs like the one at the top of the page, it displays well-defined spiral arms flecked with red and blue knots. The red are diffuse gaseous nebulae where new stars form and which glow from the energy of hot young stars. The blue are congregations of new stars that have blown away the gas and dust of the nebulae from which they formed.
An average galaxy produces roughly one supernova every 300 years. But six supernovae have been discovered in M83 in the last 85 years.The brightest supernova in M83 was discovered by the amateur astronomer J.C. Bennett from Pretoria, South Africa. His was the first discovery of a supernova by an amateur astronomer in the 20th century.
(Image of M83 above is courtesy of Warren A. Keller (billionsandbillions.com), and was acquired at the Star Shadows Remote Observatory in collaboration with Steve Mazlin, Steve Menaker, and Jack Harvey).