New Star Systems First of Their Kind

Researchers funded by the National Science Foundation (NSF) announced today in Astrophysical Journal Letters that they have discovered a faraway binary star system that could be the progenitor of a rare type of supernova.

The two yellow stars, which orbit each other and even share a large amount of stellar material, resemble a peanut. The Ohio State University astronomers and their colleagues believe the two stars in the system, 13 million light years away and tucked inside a small galaxy known as Holmberg IX, appear to be nearly identical, each 15 to 20 times the mass of our Sun.

This work was funded through an NSF continuing grant to support a systematic study of the most massive stars in the local universe. The study is expected to yield masses and radii for dozens of massive stars discovered in a variety of environments. The data produced can be used to test models of massive star atmospheres, winds, and how they evolve both as single stars and in binaries.

“To have discovered a pair of massive interacting stars in this configuration is truly exceptional–sort of like rare squared,” said NSF Program Manager Michael Briley. “There is a lot these stars can tell us about how they work and how they influence their environment. But the really exciting part is they may also hold the key to finally understanding why some massive yellow stars explode.”

Lead author Jose Prieto, an Ohio State graduate student who analyzed the new system as part of his doctoral dissertation, searched the historical record to see whether his group had found the first such binary. In a surprising twist, his search uncovered another similar system less than 230,000 light years away in the Small Magellanic Cloud, a small galaxy that orbits the Milky Way. The second binary star system was discovered in the 1980s but misidentified at the time. Prieto reassessed the data and realized the system was another yellow super-giant eclipsing binary. Prieto and his colleague suspect the yellow binary systems could be the progenitors of rare supernova linked to yellow supergiants.

Most stars end their life in a supernova at the cooler red end of the temperature scale and a few end in the hotter blue end, Pietro said. Astronomers didn't believe stars would end during the short transitional phase in between–until now.

“When two stars orbit each other very closely, they share material, and the evolution of one affects the other,” Prieto said. “It's possible two supergiants in such a system would evolve more slowly and spend more time in the yellow phase–long enough that one of them could explode as a yellow supergiant.”