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Astrophysicists Find First-Ever Evidence of Super-Remnants from Andromeda Galaxy

For the first time, astrophysicists have discovered the evidence of formation of gigantic remains due to frequent explosions on a dead star’s surface in the Andromeda Galaxy, located 2.5 million light-years from Earth.

A composite image of Liverpool Telescope data (bottom left) and Hubble Space Telescope data (top right) of the nova super-remnant.M31N 2008-12a is in the center. (Image credit: Matt Darnley, LJMU)

The size of the remains or “super-remnant” is almost 400 light-years across. To compare with, light from the Sun takes only 8 minutes to reach us.

When a white dwarf—the dead core of a star—is paired with a companion star in a binary system, it has the potential to cause a nova explosion.

With optimum conditions, the white dwarf can even absorb gas from its companion star and as soon as adequate material gets accumulated on the white dwarf’s surface, it sets off a thermonuclear explosion or “nova,” which is a million times brighter compared to Sun and initially moves at up to 10,000 km per second.

A group of astrophysicists including Dr Steven Williams from Lancaster University in the United Kingdom investigated the nova M31N 2008-12a in the Andromeda Galaxy, one of Earth’s closest neighbors.

The astrophysicists used Hubble Space Telescope imaging, in combination with spectroscopy from telescopes on Earth, to be able to reveal the nature of a gigantic super-remnant around the nova. Such an enormous remnant has been linked with a nova for the first time, and the study has been published in the journal Nature: https://www.nature.com/articles/s41586-018-0825-4.

Dr Williams took part in the Liverpool Telescope observations of the nova and also helped in interpreting the results.

This result is significant, as it is the first such remnant that has been found around a nova. This nova also has the most frequent explosions of any we know—once a year. The most frequent in our own Galaxy is only once every 10 years. It also has potential links to Type Ia supernovae, as this is how we would expect a nova system to behave when it is nearly massive enough to explode as a supernova.

Dr Steven Williams, Astrophysicist, Lancaster University

A Type Ia supernova emerges following the complete explosion of a white dwarf as it reaches a critical upper mass, in contrast to an explosion on its surface, similar to the nova observed in this study. Type Ia supernovae are comparatively rare. From the time Johannes Kepler observed the supernova 1604 shortly after it exploded and for the following year, named after him, no other supernova has been observed in the Milky Way Galaxy.

The researchers simulated the manner in which such a nova can form a vast, evacuated cavity surrounding the star, through continuous sweeping of the surrounding medium inside a shell at the edge of a growing super-remnant.

The models reveal that the super-remnant—the size of which huge compared to nearly all known remnants of supernova explosions—is consistent with being formed by repeated nova eruptions over millions of years.

According to Dr Matt Darnley from Liverpool John Moores University in the United Kingdom, who headed the study, “Studying M31N 2008-12a and its super-remnant could help us to understand how some white dwarfs grow to their critical upper mass and how they actually explode as a Type Ia Supernova once they get there. Type Ia supernovae are critical tools used to work out how the universe expands and grows.”

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