Supernova star collision reveals type Ia formation

Observations shed new light on the birth of Type Ia supernovae and their binary pairings

Illustration showing the explosion of a Type Ia supernova (dark brown). Material is ejected and slams into its companion star (light blue).
Credit: Courtesy of Dan Kasen

A supernova has been witnessed smashing into a nearby star, revealing new information about a class of supernova called Type Ia; the exact origins of which have so far eluded astronomers.

It is known that Type Ia supernovae occur when a white dwarf in a binary star system impacts with its companion, but the properties of that second star remain so far uncertain.

This latest observation sheds new light on the problem, as astronomers have witnessed a supernova colliding with a nearby star, creating an ultraviolet glow that reveals the size of its companion.

Supernova iPTF14atg is located 300 million lightyears away in galaxy IC 831.

The observation supports a theory put forward in 2010 that says Type Ia supernovae can occur when a white dwarf explodes after gaining matter from a companion star, such as a normal or giant star. Although this theory was suggested five years ago, such an event had never been observed, supporting the more prominent theory that the Type Ias occur when two white dwarf stars merge.

This latest study was led by graduate student Yi Cao at the California Institute of Technology (Caltech).

“As you can imagine, I was fired up when I first saw a bright spot at the location of this supernova in the ultraviolet image,” he says. “I knew this was likely what we had been hoping for. Hot, blue supernovae are not supposed to happen in old, dead galaxies. And yet, as our robotic telescopes gathered the data, we watched in amazement as the blue supernova morphed into a Type Ia supernova.”

The team observed the event using LCOGT (Las Cumbres Observatory Global Telescope Network), a fleet of robotic telescopes that are able track the supernova as Earth rotates, restricting the observations only to night time.

“As the data came in, I started to notice that this supernova was a weird one,” said team member Stefano Valenti, a physics postdoctoral fellow at Caltech. “It was a Type Ia, but one with a slow-moving explosion.” 

According to the team, the supernova belongs to a subclass called SN 2002cx-like, which are often partially failed explosions that leave a piece of the white dwarf behind.

The study builds on previous work by team member Andrew Howell, physics faculty member at the University of California, Santa Barbara and LCOGT, which suggests that a Type Ia supernova could have a red giant star as its binary companion.

“We are finally beginning to see how differences in the progenitor stars relate to differences in the explosion,” says Howell. “This is exciting because the better we understand the origin of type Ia supernovae, the better we can use them as standard candles for cosmology.”


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