By Ron Cowen
Astronomers have discovered the most luminous supernova ever recorded. At its peak, the stellar explosion, which erupted in a galaxy 4.7 billion light-years from Earth, was 100 billion times as bright as the sun.
Robert Quimby was hunting for supernovas with a tiny telescope, the 18-inch ROTSE-IIIb at McDonald Observatory near Fort Davis, Texas, when he spotted the explosion. Follow-up observations with the same observatory’s 10-meter Hobberly-Eberly Telescope hinted that light emitted by doubly ionized oxygen atoms in the supernova was shifted from its normal position in the spectrum to much longer, or redder, wavelengths. This suggestion of high redshift indicated that the supernova, found in 2005 and dubbed SN 2005ap, came from a remote galaxy. It had to be extremely luminous to be seen at such great distances.
“It [was] so luminous that I originally doubted the distance,” says Quimby, now at the California Institute of Technology in Pasadena.
A colleague of Quimby’s observed the supernova’s fading glow with the 10-m Keck I telescope atop Hawaii’s Mauna Kea. That spectrum showed emissions characteristic of both redshifted oxygen and magnesium, convincing Quimby that the supernova really is distant. He and his colleagues report the findings in the Oct. 20 Astrophysical Journal Letters.
SN 2005ap is classified as a type II supernova, marking the collapse of a massive star. It’s about twice as luminous as the previous record holder, SN 2006gy, another type II supernova found by Quimby using the same small telescope (SN: 5/12/07, p. 293).
