'Shocking' things happen when supernova collides with nearby star

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.

The supernova, named iPTF14atg, is located 300 million light-years away in the galaxy IC 831. 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.

However, 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. This and other factors led many to conclude that most type Ia supernovae arise from the mergers of two white dwarf stars.

First author Yi Cao said of seeing the ultraviolet flash that he was fired up when he first saw a bright spot at the location of this supernova in the ultraviolet image.

Researcher Stefano Valenti said that as the data came in, he started to notice that this supernova was a weird one, it was a type Ia, but one with a slow-moving explosion.

According to the researchers, the supernova belongs to a subclass of SNe Ia sometimes called SN 2002cx-like. These supernovae may even be partially failed or incomplete explosions. In a normal type Ia the entire white dwarf blows up, but this class may leave a piece behind.

The new study builds on previous work by Andrew Howell and some of the study's coauthors showing that the type Ia SN 2011fe was likely the result of a merger of two white dwarf stars, while the SN Ia PTF11kx seemed to have a red giant companion star.

Howell said that "No wonder we've been so confused for decades. Apparently you can blow up stars in two different ways and still get nearly identical explosions."

The study appears in the May 21 issue of Nature.