White dwarf's glowing disc observed

Astronomers have used ESO’s Very Large Telescope (VLT) to study the remains of a white dwarf and the asteroid it ripped apart in detail.

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Artist’s impression of a glowing disc of debris surrounding a white dwarf, showing how Saturn could theoretically fit in the space between the dead star and its glowing disc.
Credit: Mark Garlick and University of Warwick/ESO

A team of astronomers have conducted a study of observations of white dwarf SDSS J1228+1040 between 2003 and 2015, providing an unprecedented look at white dwarf formation.

The study has revealed a disc-like structure of glowing material around the dead star formed by the debris of materials it ripped apart during its formation.

Large stars explode as supernovae towards the end of their lives, but smaller stars like our Sun use up all their fuel, expand as red giants and expel their outer layers into space. What remains is a hot, dense core called a white dwarf. It has long been asked whether the planets and other bodies in that star’s system would survive such a process and this latest study is helping to answer the question.

Observations revealed an asteroid torn apart by the tidal forces that formed the disc of material now visible around the remaining white dwarf. Only seven white dwarfs surrounded by discs of gaseous material have ever been found.

This disc was formed in a similar way to the rings around Saturn, but the white dwarf is seven times smaller than the ringed planet and 2,500 times greater in mass. The distance between the white dwarf and its disc is much greater: Saturn and its rings could fit in the gap between them.

The study was led by Christopher Manser at the University of Warwick and used the Ultraviolet and Visual Echelle Spectrograph (UVES) and X-shooter, both attached to the VLT.

These observations have allowed the team to observe the white dwarf’s disc precess under the dead star’s gravitational field. Precession is when a rotating body’s rotational axis is shifted by another force. The team also observed that the disc is lopsided and not completely circular.

The discoveries help piece together clues as to what happens when stars reach the end of their lives, but also in understanding the processes that occur in exoplanetary systems. The data can be used to help predict the fate of our own Solar System when the Sun dies in about seven billion years.

“When we discovered this debris disc orbiting the white dwarf back in 2006, we could not have imagined the exquisite details that are now visible in this image, constructed from twelve years of data. It was definitely worth the wait,” says Boris Gänsicke, a co-author of the study.


 

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