Carles Badenes Studies Supernova ‘Crime Scene,’ a White Dwarf to Blame

Using archival data from the Japan-led Suzaku X-ray satellite, the University of Pittsburgh’s Carles Badenes, along with astronomers at NASA’s Goddard Space Flight Center, have established the pre-explosion mass of a white dwarf star that blew up thousands of years ago. The findings strongly suggest that the explosion involved only a single white dwarf, ruling out a well-established alternative scenario involving a pair of merging white dwarfs.

The study, published in March in The Astrophysical Journal Letters, is part of a continuing program of Suzaku research aimed at helping astronomers better understand the diversity of type Ia supernovae, an important class of stellar explosion used in probing the distant universe. This finding shows that at least some type Ia supernovae must have surviving stellar companions, and the team emphasizes that the search for these stars should continue.

The researchers analyzed archival observations of a supernova remnant named 3C 397, which is located about 33,000 light-years away in the constellation Aquila. Astronomers estimate this cloud of stellar debris has been expanding for between 1,000 and 2,000 years.

“White dwarfs remain stable as long as they never tip the scales too closely to 1.4 solar masses,” says Badenes, an assistant professor in Pitt’s Department of Physics and Astronomy. “White dwarfs near this limit are on the verge of a catastrophic explosion. All it takes is a little more mass.”

All low- and medium-mass stars similar to the sun will end their days as white dwarfs. A typical white dwarf is about as massive as our sun yet roughly the size of Earth. This makes white dwarfs among the densest objects known, surpassed only by neutron stars and black holes.

Until recently, astronomers thought the most likely way for a white dwarf to gain mass would be as a member of a close binary system with a normal sun-like star. By accumulating matter from its companion over millions of years, a white dwarf nudges itself closer to the limit and eventually explodes. While the companion stars are expected to survive, various lines of evidence, including the general failure to find these stars in remnants or to detect signs of their presence in the light of recently observed supernovae, suggested the need for an alternative model.

NASA recently appointed Badenes as the U.S. representative to the Supernova Remnant Working Group of the Athena Study Science Team—the next big international mission for X-ray astronomy.