Scientists explain ‘impossible’ nova explosions

Scientists have proven a theory which explains why nuclear explosions on the surface of white dwarf stars appear to be “impossibly” bright and powerful.

Researchers from Michigan State University found that powerful shockwaves can amplify the nuclear explosions beyond normal expectations.

A white dwarf is the leftovers of a brightly burning star which has exhausted its nuclear fuel. Near the end of its nuclear burning stage, it expels most of its outer material, creating a planetary nebula – gas ejected from the star at the end of its lifetime – and leaving only the hot core remaining.

In a typical year, there are around 50 nuclear explosions on the surface of white dwarfs in our galaxy, but some of those explosions suggest much more energy than the small star should be able to generate.

Published in Nature Astronomy, the researchers explain the science behind the seemingly impossible explosions, called novae.

“Astronomers have long thought the energy from novae was dominated by the white dwarf, controlling how much light and energy are emitted,” said Dr Laura Chomiuk, an astronomer and study co-author.

“What we discovered, however, was a completely different source of energy – shockwaves that can dominate the entire explosion.”

Using robotic telescopes, NASA’s Fermi Gamma-ray Space Telescope, as well as an international group of volunteer astronomers, Dr Chomiuk was able to record unparalleled data on the nuclear novae.

The team found that when the nuclear explosions begin on the surface of white dwarfs, they eject a cooler, slower wave of material which is followed by a faster, hotter wave.

It is the collision of these two waves which results in the explosion which is brighter and more hot than could otherwise be explained.

“Novae are little laboratories in our galactic backyard that we can use to study some of the most luminous explosions in the universe,” Chomiuk said.

“As future novae happen, we’ll be able to observe them to better understand how shocks light up and fuel explosions. We really want to find out how common and energetic shocks are.”
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