In December 2019, the Zwicky Transient Facility (ZTF) discovered a new supernova, SN2019yvg. Discovering a supernova isn’t particularly unusual for this telescope, but this particular supernova was a weirdo. In follow-up observations, NASA’s Neil Gehrels Swift Observatory spotted an ultraviolet flash such as has only been seen once before. 

Why ultraviolet flashes are rare, we have no idea, but time should literally allow us to tell as the gas in the supernova remnant thins and allows us to look deep into the supernova remnant to see what remains.

According to the press release: Miller and his team believe this is an important clue to understanding why white dwarfs explode, which has been a long-standing mystery in the field. Currently, there are multiple competing hypotheses. Miller is particularly interested in exploring four different hypotheses, which match his team’s data analysis from SN2019yvq.

Potential scenarios that could cause a white dwarf to explode with a UV flash are:

• A white dwarf consumes material from its companion star and becomes so massive and unstable that it explodes. The white dwarf’s expelled material and the companion star collide, causing a flash of UV emission;
• Extremely hot radioactive material in the white dwarf’s core mixes with its outer layers, causing the outer shell to reach higher temperatures than usual;
• An outer layer of helium ignites carbon within the white dwarf, causing an extremely hot double explosion and a UV flash;
• Two white dwarfs merge, triggering an explosion with colliding ejecta that emit UV radiation. 

“Within a year,” Miller said, “we’ll be able to figure out which one of these four is the most likely explanation.”

More Information

Northwestern University press release 

“The Spectacular Ultraviolet Flash from the Peculiar Type Ia Supernova 2019yvq,” A. A. Miller et al., 2020 July 23, Astrophysical Journal (Preprint on arxiv.org)