Astrophysicists discover the first-ever evidence of a huge remnant formed around an exploding star – a shell of material almost 400 light-years across.

A small, dense dying star, about as massive as the Sun yet only slightly bigger than the Earth, has been constantly erupting for millions of years. We are talking about a white dwarf. A dead core of a star located in the Andromeda galaxy, 2.5 million light years from Earth.

When a white dwarf is paired with another star in a binary system, it pulls gas from the other star. So, the gas warms up and compresses, thus, eventually exploding to create a nova. The explosion causes the star to shine a million times brighter than our Sun and eject material at thousands of miles per second. The ejected material forms a remnant or shell surrounding the nova.

Allen Shafter and former SDSU postdoc. Martin Henze, along with a team of astrophysicists led by Matthew Darnley at Liverpool John Moores University in England, has been studying the nova M31N 2008-12a in the Andromeda Galaxy, one of our nearest neighbors.

“When we first discovered that M31N 2008-12a erupted every year, we were very surprised,” said Shafter. A more typical pattern is about every 10 years.

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They used Hubble Space Telescope imaging, along with ground-based telescopes, to help uncover the nature of a gigantic super-remnant surrounding the nova. This is the first time such a huge remnant has been linked with a nova. Researchers have published these findings in an article in the journal Nature.

Astronomers often use these type of novas, known as Type Ia novas, as standard candles in which to determine distances to other celestial objects.

Type Ia supernovae are among the most powerful and luminous objects in the universe. Astronomers believe they occur when a white dwarf exceeds its maximum allowable mass. Therefore, the entire white dwarf blows up instead of experiencing explosions on the surface as other novae do. These are relatively rare in our galaxy.

However, all that material left from the explosion will one day coalesce into a big cloud. That cloud will eventually break down into clumps to form stars and planets.

The discovery of more of these colossal-material makers and the super-shells they leave behind will help identify systems undergoing repeated eruptions and help astronomers determine how frequently Type Ia supernovae occur.

“They are, in effect, the measuring rods that allow us to map the visible universe,” said Allen Shafter an astrophysicist from San Diego State University who helped find M31N 2008-12a. “Despite their importance, we don’t fully understand where they come from.”

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Thumbnail image: An artist’s impression of a debris disc around a white dwarf. Image credit: Mark Garlick / University of Warwick / ESO / NASA