Jimmy Westlake: 1 morning, 2 ‘new’ stars
August 20, 2013
Steamboat Springs — Friday morning was a remarkable morning and unique to my 50-plus years of stargazing. Two "new" stars were visible in the sky at one time, a nova and a supernova. The nova is in our galaxy and is visible to the unaided eye. The supernova is in a distant galaxy and requires a medium-sized telescope to see. Both of these events are among nature's most violent and spectacular, so being able to witness both at the same time is unforgettable.
Nova Delphini 2013 was discovered by Japanese amateur astronomer Koichi Itagaki on Aug. 14. It rapidly increased in brightness until Friday morning, when it peaked at visual magnitude 4.3, easily visible to the unaided eye in the dark sky after moonset. The nova has faded slightly to magnitude 5.0 as of Sunday night and still would be visible to the unaided eye were it not for the bright moonlight this week.
Despite its name, a nova is not a new star at all but rather the explosion of a star in the advanced stages of life. A nova explosion is triggered when a red giant star dumps fresh hydrogen gas onto the surface of an orbiting white dwarf companion. The hydrogen gas is heated and compressed by the white dwarf's intense gravity until it reaches a temperature of about 10 million degrees and erupts in a thermonuclear explosion — a hydrogen bomb the size of the Earth. The star increases in brightness by a factor of 63,000 in a matter of hours and blazes into view in earthly skies as a "new star." During the following days and weeks, the erupting star fades back into obscurity. The red giant and white dwarf can survive this holocaust and repeat the nova process again in the future.
Many novae are discovered by astronomers every year, but very few cross the naked eye limit because of their extreme distance. Nova Delphini 2013 is a rare exception. It is the brightest nova to grace our skies since 2007. Look for it near the small constellation of Delphinus, the dolphin. Sagitta, the arrow constellation, points right to it. Binoculars will make spotting it easy.
Supernova 2013EJ was discovered by LOSS, the automated Lick Observatory Supernova Search, when it exploded in the distant galaxy M74 on the morning of July 25. Of course, at a distance of 30 million light-years, this star actually exploded 30 million years ago, and its light just now is arriving at Earth.
An ordinary nova explosion pales in comparison to a supernova. This particular type of supernova, called a Type 2, is caused when a massive star exhausts its thermonuclear fuel and reaches the end of its life. This causes a catastrophic implosion of the star's core and an explosion of its outer shell. The star increases in brightness by a factor of 100 billion or more, becoming visible from across the universe. It briefly can outshine the entire galaxy in which it resides and can release more energy in a few weeks than the sun will emit in its 10 billion-year lifetime.
No supernova has been visible in our galaxy since the year 1604, but supernovae in nearby galaxies can be seen with backyard telescopes every few years. The M74 supernova has peaked at magnitude 12.5 and will begin to fade during the coming weeks. It still is bright enough to be glimpsed in an 8-inch or larger telescope. M74 itself is a beautiful face-on spiral galaxy in the constellation Pisces.
Once this week's blue moon gets out of the way, try spotting these rare exploding stars for yourself.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His Celestial News column appears weekly in the Steamboat Today. Check out Westlake’s astrophotography website at http://www.jwestlake.com.