French amateur astronomer StÃ©phane Lamott Bailey discovered a new supernova named SN 2011 dh in photos taken of the famed Whirlpool Galaxy near the Big Dipper early yesterday morning. The exploding star was not visible in pictures of the galaxy taken several nights before.
The Whirlpool, also known as M51, the 51st entry in 18th century astronomer Charles Messier’s catalog of deep sky objects, is one of the most picturesque galaxies in the sky and the first in which spiral structure was seen. Lord Rosse (a.k.a. William Parsons) used a 72-inch reflecting telescope to make a wonderful sketch of M51 back in 1845.
The galaxy is on every amateur astronomer’s “must see” list because it’s one of the closer spiral galaxies to our own with a recently revised distance of 23 million light years. That’s about 10 times farther away than the nearby Andromeda Galaxy. M51 is bright enough to see as a fuzzy patch through 7×50 or 10×50 binoculars and easy to find just off the end of the Handle of the Big Dipper. In a 6-inch telescope under dark skies, the brighter spiral whorls are visible, while 10-inch and larger scopes show them in grand fashion.
The newly discovered supernova is what astronomers call a Type II explosion. Type II supernovas occur in supergiant stars far more massive than the sun, when they run out of burnable nuclear fuel in their cores. With no outward push from heating to counteract the ever-present force of gravity, the star collapses in upon itself, creating shock waves that blast it to bits in a titanic explosion. The enormous energy released causes the star to suddenly brighten by millions of times.
The progenitor star was far too faint to see visually through a telescope, but now that’s it’s all fireworks, sky watchers with 8-inch and larger telescopes can spot the supernova. It’s currently at 14.2 magnitude, on the faint side to be sure, but may brighten in the coming nights since the explosion was caught early on
. The star is southeast of the galaxy’s center – 138″ east and 92″ south to be precise. For more photos and information, I encourage you to stop by Dave Bishop’s Bright Supernovae site. Scroll down until you see the entry for M51 on the left.
It’s a thrill to see a supernova in a bright, well-known galaxy. I’ll be updating the blog with more information, including my own observations, in the next couple days. Supernova SN 2011dh is special in another way. M51 is a favorite photographic target of amateur astronomers around the world. It’s likely someone or a few someones took pictures of the supernova as it rose from invisibility to its current brightness. These early photos can help shed light on the evolution and understanding of these spectacular events.
For naked eye sky watchers, the crescent moon has returned to the evening sky this week. You can catch it tonight below the two Gemini Twins, Castor and Pollux, low in the northwestern sky about an hour after sunset. Use binoculars for an even nicer view, especially of the ‘darker half’ illuminated only by light reflected from Earth called earthshine.