A NASA satellite has spied two supernova bursting in one galaxy in less than a month.
For the first time ever, astronomers have observed two supernovas bursting within a few weeks of each other in the same galaxy.
On May 19, 2007, NASA's SWIFT satellite spied a supernova in a distant galaxy named MCG +05-43-16. The SWIFT satellite, designed to move quickly to catch a different kind of explosion, the more powerful and distant gamma-ray bursts, captured the supernova, named SN 2007ck, with its Ultraviolet/Optical Telescope as it flared to brightness. SN 2007ck was a Type II supernova, which means the explosion occurred when a massive star ran out of fuel, triggering the gravitational collapse of its core and a rebounding shockwave.
Then, just a few weeks later on June 4, 2007, a second supernova was spied in this same obscure galaxy. SWIFT spied the bright light of Supernova 2007co. This time the supernova was of a different type. Supernova 2007co came from a Type Ia event. In a Type Ia explosion, a white dwarf star has been accreting material from a binary companion star until it becomes unstable and explodes in a supernova.
These supernova in galaxy MCG +05-43-16, which is 300 million light-years from Earth in the constellation Hercules, were imaged together by the SWIFT satellite. In the image shown here, Supernova 2007ck is the orangish spot at nine o'clock, and Supernova 2007co is the whitish blue spot between four and five o'clock. (Click on the picture below for a larger view.) The picture is a combination of red, green, and blue images taken on June 9 and 12. You can see how the more recent supernova is the brightest object in the galaxy while the older supernova has already started to fade.
Finding two supernovae in one galaxy in such a short period of time is unusual. "Most galaxies have a supernova every 25 to 100 years, so it's remarkable to have a galaxy with two supernovae discovered just 16 days apart," says Stefan Immler, an astronomer with NASA's Goddard Space Flight Center.
Astronomers point out that while the occurrence of these two supernovae in one galaxy is rare, it is merely a coincidence. Imagine that we are positioned out in galaxy MCG +05-43-16 close to SN 2007ck. While we would see SN 2007ck, we would not see the next supernova within days, as we did here on Earth. If we were in that galaxy, we would not see the next supernova for tens of thousands of years, because the two supernova are tens of thousands of years apart within the galaxy and the optical signal from the explosions can only travel at the speed of light. It is merely because of a particular position here in this galaxy on this planet that we happen to see the explosions appearing close together in time.
