Helium Detonation Appears To Have Triggered A White Dwarf Supernova

White dwarf stealing material from a companion star. European Space Agency and Justyn R. Maund (University of Cambridge)

An international team of astronomers has found evidence that a particular and important type of supernova explosion might sometimes be triggered when helium on the stellar surface detonates.

The study, published in Nature, focuses on a Type Ia supernova, a special kind of cosmic explosion where a white dwarf steals so much material from a companion star that it collapses on itself, producing the phenomenal explosion. Type Ia’s are important because they are about 5 billion times brighter than our Sun and they seem to have a steady luminosity so we can use them as standard candles, a sort of cosmic milestone to measure how far galaxies are.

“Studying Type Ia supernovae is important because they are a valuable tool researchers use to measure the expansion of the universe. A more precise understanding of their history and behavior will help all researchers obtain more accurate results,” co-author author Professor Mamoru Doi, from the University of Tokyo, said in a statement.

Type Ia supernovas occur about once per century per galaxy, but fortunately, the universe is filled with galaxies. The team used the Hyper Suprime-Cam camera on the Subaru Telescope in Hawaii to capture a large area of the sky at the same time.

“Among 100 supernovae we discovered in a single night, we identified a Type Ia supernova that had exploded only within a day before our observation. Surprising, this supernova showed a bright flash in the first day, which we thought must be related to the nature of the explosion," said Professor Keichi Maeda, from Kyoto University. "By comparing the observational data with what we calculated on how burning helium would affect brightness and color over time, we found both theory and observation were in good agreement.”

The question of how similar these explosions are is extremely important. It wouldn’t be good to suddenly realize our cosmic benchmarks are all wrong. It has been proposed that Type Ias that aren’t as bright might be showing helium and titanium signatures in their light. The particular supernova identified in the study seems to be a hybrid. It appears to be just as bright as the regular ones but it also shows a tell-tale titanium feature like less bright events.

At this point it’s unclear if this is a special case or we are learning something about the general population. The team is going to look for more Type Ia explosions to understand the role of this helium trigger.

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