Supernova hits star, reveals its origin

A team of astronomers has witnessed a supernova smashing into a nearby star, shocking it and creating an ultraviolet glow that reveals the size of the companion.

In a type Ia supernova, a white dwarf star explodes after it gains matter from a companion star in the same binary star system. One of the leading theories is that the supernova happens when two white dwarf stars merge. But a competing theory says that the companion could be a normal or giant star that survives the explosion, although not without some damage.

The supernova is expected to hit the companion star, creating a shock wave that glows in ultraviolet light. This had been theorized in 2010 but such an effect had never been seen.

"I was fired up when I first saw a bright spot at the location of this supernova in the ultraviolet image. I knew this was likely what we had been hoping for," said study first author Yi Cao from California Institute of Technology (Caltech).

The origin of type Ia supernovae, the standard candles used to reveal the presence of dark energy in the universe, is one of astronomy's most beguiling mysteries.

Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star -- and how it triggers the explosion -- have remained elusive for decades. The supernova, named iPTF14atg, is located 300 million light years away in the galaxy IC831.

"The better we understand the origin of type Ia supernovae, the better we can use them as standard candles for cosmology," the authors concluded.

The study that appeared in the journal Nature was led by Cao but included physics postdoctoral fellows Iair Arcavi and Stefano Valenti, and physics faculty member Andrew Howell of University of California Santa Barbara and Las Cumbres Observatory Global Telescope Network (LCOGT).