We’ve discovered a planet orbiting an exploded star for the first time

https://www.newscientist.com/article/2226112-weve-discovered-a-planet-orbiting-an-exploded-star-for-the-first-time/

This artist's concept shows a hypothetical 'rejuvenated' planet,a gas giant that has reclaimed its youthful infrared glow. NASA's Spitzer Space Telescope found tentative evidence for one such planet around a dead star, or white dwarf, called PG 0010+280.

An artist’s impression of the planet orbiting a white dwarf

NASA/JPL-Caltech

A giant planet is orbiting the remnants of an exploded star – called a white dwarf – 1200 light years away from Earth. The discovery is the first time an entire planet has been found orbiting a white dwarf.

The first hint that there may be planets orbiting white dwarfs came earlier this year, when researchers found a small piece of planet in orbit around a white dwarf. Now the same team has discovered evidence of a giant intact planet, similar in size to Jupiter.

Boris Gänsicke at the University of Warwick in the UK and his colleagues  detected a mysterious disc of gas surrounding a white dwarf. The gas disc contained hydrogen, oxygen and sulphur – a mixture that most likely came from the planet, whose atmosphere is being evaporated by radiation from the white dwarf.

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The giant planet has an orbital period of 10 days and is surprisingly close to the white dwarf, suggesting it migrated inwards, says Gänsicke. A possible explanation is that the presence of other planets may have pushed it inwards.

Alternatively, another planet may have been absorbed by the exploding star, causing the orbit of the newly discovered planet to be pulled inwards, says Ben Zuckerman at the University of California, Los Angeles, who wasn’t involved with the work.

“This confirms what we have been thinking for the past 25 years – white dwarfs have proper planetary systems around them,” says Gänsicke. Jupiter and Saturn also migrated in and out during the early days of our solar system. Understanding other solar systems in space could help us understand how our own developed, he says.

Stars of low to medium mass like the sun become white dwarfs after they have burned up all their fuel and expelled all their outer material, leaving behind only the core of the star. This very hot white dwarf cools down gradually over the next billion years or so. Our sun is about 5 billion years away from becoming a white dwarf, says Zuckerman.

“This is an exciting discovery,” says Carl Melis at the University of California, San Diego. He says it is surprising that giant planets would be able to survive in such close orbit to the remnants of their host star.

Journal reference: Nature, DOI: 10.1038/s41586-019-1789-8

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