An international team of astronomers studied the star between 1993 and 2002 using the William Herschel Telescope. Nothing seemed out of the ordinary for the first seven years as Rho Cassiopeiae, one of only seven known yellow hypergiant stars in our galaxy, underwent periodic temperature fluctuations of a few hundred degrees. But during the summer of 2000, the star's temperature plummeted from 7,000 to 4,000 Kelvins over the course of just a few months. During this time, the astronomers also detected titanium oxide in the star's atmosphere. The scientists posit that the compound was part of a shell, which became detached from the star by a shock wave. The amount of ejected material--equal to 10,000 times the mass of the earth--was the largest ever observed in a single stellar eruption.
"Rho Cassiopeiae could end up in a supernova explosion at any time as it has almost consumed the nuclear fuel at its core," says team member Garik Israelian of the Instituto de Astrofisica de Canarias. "The monitoring of this and other unstable evolved stars may help us to shed some light on the very complicated evolutionary episodes that precede supernova explosions."