Space news: Giant Neptune-like exoplanet found orbiting white dwarf 1,500 light-years away in rare discovery

The study provides evidence that planets can survive the explosive transformation of a star into a white dwarf as most planets were thought to not survive this transition.


                            Space news: Giant Neptune-like exoplanet found orbiting white dwarf 1,500 light-years away in rare discovery
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Scientists have discovered a giant Neptune-like exoplanet orbiting a white dwarf or a dying star 1,500 light-years away. The discovery suggests that there could be many more planets around such stars waiting to be detected.

It is one of those chance discoveries, which opens up a new window into the final fate of planetary systems, explained Boris Gänsicke from the University of Warwick in the UK who was part of the study. 

The study provides evidence that planets can survive the explosive transformation of a star into a dwarf as most planets were thought to not survive this transition. This is because when most sun-like stars reach the ends of their lives, they destroy any closely orbiting planets, reducing them to their rocky cores and generating disks of debris. However, experts believe that at least 15 percent of white dwarfs have planets or debris around them.

In their hunt for planets circling white dwarfs, Gänsicke's team studied 7,000 white dwarfs and found that one star — WDJ0914+1914 — stood out.

When they looked deeper, they detected something unusual: the dying star, which has about five times the sun's temperature, has traces of hydrogen, oxygen and sulphur around it. What is more, these elements were found in levels similar to those circulating in giant planets like Neptune and Uranus, puzzling the team. 

The team used the X-shooter instrument on ESO's Very Large Telescope in the Chilean Atacama Desert to make sense of the puzzle. The results revealed that these elements were not originating from the star. Instead, they were escaping from a very large and icy exoplanet orbiting the white dwarf at a distance of 10 million kilometers. As they escaped, the elements formed a disc of gas around the dying star.

"It took a few weeks of very hard thinking to figure out that the only way to make such a disc is the evaporation of a giant planet," says Matthias Schreiber from the University of Valparaiso in Chile.
 
The evaporation of these elements could be due to the star’s extreme ultraviolet radiation. This radiation, the team says, could tear apart the planet’s outer layers, some of which escape from the planet and spiral into the white dwarf at a rate of 3,000 tonnes per second.

As the distance between the two objects was only 10 million kilometers, the authors believe that the planet moved closer to the star, at some point after it became a white dwarf. This led the research team to speculate that more than one planet may have survived the white dwarf's violent transition because the exoplanet's position could be the result of gravitational interactions with other planets in the system.

"This discovery of a planet orbiting closely around a burnt-out stellar core forcefully demonstrates that the universe is time and again challenging our minds to step beyond our established ideas," concludes Gänsicke.

The study has been published in Nature.

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