Scientists get first look at nova before, during, and after explosion

Astronomers have successfully observed and captured images of a tiny white dwarf star with a low and unstable mass-transfer rate both before and after it exploded as a classical nova for the first time, according to research published earlier this week in the journal Nature.

As part of their study, Przemek Mróz of the Warsaw University Observatory in Poland and his colleagues monitored V1213 Cen (Nova Centauri 2009), a nova located 20,000 light years from Earth, during both its pre- and post-eruption phases using ground-based telescopes in Chile.

During their long-term sky survey, the team was able to see what the star system looked like in the six years prior to its explosion in May 2009, and compared that to observations conducted after it went nova, according to CNN and BBC News reports. They found that the white dwarf was a full two orders of magnitude brighter after it erupted than it was beforehand.

“Classical novae attract attention during eruptions, when they are bright and easy to observe,” Mróz told CNN. “Because of their unpredictable nature, very little is known about pre-eruption behavior of novae. This is the first case that the evolution of a classical nova can be investigated so precisely with long-term pre- and post-eruption observations.”

Authors say that their findings support a ‘hibernation-based’ model

Prior to its eruption, V1213 Cen was part of a close binary star system in which it orbited a red dwarf star at an extremely close distance. As the white dwarf gathered matter from its companion star over time, it triggered an explosive thermonuclear surface reaction, jettisoning the additional material it collected while leaving behind the now much brighter white dwarf.

“The entire system survives the nova explosion… so the whole process starts again. After thousands of years, our nova will awake and explode again but no one will be able to see it,” Mróz explained to BBC News. This is a drastic difference from a Type Ia supernova, which involves a much larger explosion that causes the white dwarf to be completely obliterated.

He and his colleagues observed light being emitted by the binary system, indicative of the mass being accumulated by the white dwarf, prior to and following its dramatic increase in brightness seven years ago. What they found, Mróz said, was that the mass transfer rate was extremely low and unstable before the eruption, and much higher and far more stable afterwards.

“That means that the  explosion we observed changed the properties of the binary,” he told the British media outlet, adding that the findings support a “hibernation-based” model for classical novae – in other words, the system essentially goes dark and the white dwarf temporarily stops stealing gas from its companion star during the long period of time leading up to the eruption.

His team’s research predicts that the pre-nova matter transfer rate is slow, while the post-nova transfer rate is relatively fast, Mróz added. However, other experts are not convinced – Christian Knigge of the University of Southampton, for example, told BBC News that the team’s findings are “circumstantial” and that he wants to see more data before determining what the end-result of the classical nova will be in terms of brightness.

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Image credit: Warsaw University Observatory

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