First-ever planet found orbiting a dead star

PTI, Sep 17, 2020, 4:42 PM IST

Image Credit: NASA’s Goddard Space Flight Center

Washington: Scientists have, for the first time, discovered a Jupiter-sized planet orbiting a white dwarf or a dead star located about 80 light-years away.

The finding, published in the journal Nature, shows the likely presence of the planet, named WD 1856 b, orbiting the smaller star remnant every 34 hours.

“This planet is roughly the size of Jupiter, but it also has a very short orbital period — a year on this planet is only 1.4 days, so it’s quickly whipping around its white dwarf star,” said Ian Crossfield, assistant professor at the University of Kansas in the US.

A white dwarf is the vestige of a star that has ballooned into a red giant then collapsed back into a dense, dim core that is often about the size of Earth, so this planet is much larger than what is left of its star, the researchers said.

The process usually devours orbiting planets — but not in the case of WD 1856 b, which appears somehow to have avoided destruction, they said.

“This tells us white dwarfs can have planets, which is something we didn’t know before,” Crossfield said.

“There are people who now are looking for transiting planets around white dwarfs that could be potentially habitable. It’d be a pretty weird system, and you’d have to think about how the planets actually survived all that time,” he said.

The researchers noted that this finding proves that some kinds of planets can survive and be found around white dwarfs.

At first, WD 1856 b captured astronomers’ interest when they noticed a possible transiting object with NASA’s TESS Space Telescope survey.

TESS finds a planet by looking at a star, and measures how bright the star is continuously for weeks.

To confirm if WD 1856 b indeed was a planet orbiting the white dwarf, Crossfield studied the object’s infrared emissions with NASA’s now-defunct Spitzer Space Telescope in the months leading up to the satellite telescope’s decommission.

WD 1856 b is located about 80 light years away in the northern constellation Draco, the researchers said.

They believe the gaseous planet was pulled in by the white dwarf’s gravity long after the star had dwindled down from its red giant phase — otherwise the planet would have been obliterated in its current orbit.

The researchers noted that our Sun will become a white dwarf in around five billion years.

However, Crossfield said it remained unlikely that the Earth stood a chance of surviving the sun’s red-giant phase in the distant future.

There are a lot of questions about whether planets can survive the process of a star inflating up to become a red giant, swallowing up some of the inner planets, and then shrinking back down and just being left over as the white dwarf again, they said.