Jupiter-sized planet discovered orbiting white dwarf star for first time

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A Jupiter-sized planet has been found orbiting the smouldering remains of a dead star eighty light years from Earth.

It’s going around so fast a year lasts less than one-and-a-half days. And it’s close to the habitable zone – with temperatures a comfy 60 degrees Fahrenheit.

The discovery gives an insight into what type of planets could harbour life and what will happen to our own earth when the sun becomes a white dwarf and dies out.

It also begs the question of how it survived the white dwarf’s death throes.

It supports the theory massive planets can migrate inwards – and survive the creation of a stellar graveyard.

They end up potentially hospitable to life – even after their star has died.

The upper limit of the planet’s temperature measured by NASA’s Spitzer Space Telescope is 17 C (63 F).

This is similar to the average temperature of Earth – boosting the search for extra-terrestrial life.

Lead author Dr Andrew Vanderburg, of the University of Wisconsin-Madison in the US, said: “We were using the TESS satellite to search for transiting debris around white dwarfs, and to try to understand how the process of planetary destruction happens.

“We were not necessarily expecting to find a planet that appeared to be intact.”

“Additionally, because we didn’t detect any light from the planet itself, even in the infrared, it tells us that the planet is extremely cool, among the coolest we’ve ever found.”

Until now, no planet in orbit around one had been detected directly.

A white dwarf is the collapsed core of a Sun-like star, left over after shedding its atmosphere.

They are typically the size of Earth, with masses about half that of our Sun.

Co author Dr Ian Crossfield, an astronomer at Kansas University, said: “This planet is roughly the size of Jupiter.

“But it also has a very short orbital period – a year on this planet is only 34 hours.

“So it’s quickly whipping around its white dwarf star.”

The gas giant, named WD 1586 b, is around 14 times the mass of Jupiter, report the international team.

Dr Vanderburg said: “Our discovery suggests WD 1856b must have originally orbited far away from the star, and then somehow journeyed inwards after the star became a white dwarf.

“Now that we know that planets can survive the journey without being broken up by the white dwarf’s gravity, we can look for other, smaller planets.”

Most ‘exoplanets’ – those beyond the solar system – orbit stars that will eventually form white dwarfs.

As they use up their reserves of hydrogen, they balloon into red giants, expanding and then engulfing any planets close by.

This makes it unlikely that any would remain to orbit the star in its white dwarf phase.

The finding published in Nature is based on data from NASA’s TESS (Transiting Exoplanet Survey Satellite) mission.

To avoid destruction when the white dwarf evolved into a red giant, the planet must have been more than the distance from Earth to the Sun away from the host star.

But it is unclear how it arrived in the close orbit observed – roughly 20 times closer than Mercury is to the Sun.

Computer simulations showed WD 1586 b was thrown into a close orbit due to interactions with other planets in the remnant planetary system.

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

“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. But it’s a big universe.

“Now we at least know some kinds of planets can survive and be found there, so that gives greater support and greater interest in continuing the search for even smaller planets around these white dwarfs.”

At first, WD 1856 b captured astronomers’ interest when they noticed a possible transiting object.

Explained Dr Crossfield: “TESS finds a planet by looking at a star, and it measures how bright the star is continuously for weeks.

“If a planet is orbiting the star, and if the planet passes between you and the star, some of that star’s light is going to be blocked.

“Then the star will get brighter again as the planet passes – we call this the ‘transit’ of the planet.

“And so, TESS looks for transiting exoplanet satellites. It tells you that something is there – but it doesn’t necessarily tell you what it is because it could be another dim star passing in front instead of a planet.”

He confirmed the discovery by studying the object’s infrared emissions with NASA’s now-defunct Spitzer Space Telescope in the months leading up to its decommission.

WD 1856 b is located in the northern constellation Draco. It’s believed to have been pulled in pulled in by the white dwarf’s gravity – long after it had shrunk.

Otherwise the planet would have been obliterated in its current orbit, said Dr Crossfield.

Earth is expected to be destroyed when the sun turns into a red giant five billion years from now.

Dr Crossfield said: “There’s a lot of open 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.

“Can planets actually survive that – or is that impossible? And until now, there weren’t any known planets around white dwarfs.”

Dr Steven Parsons, an astronomer at Sheffield University, who was not involved in the study, said: “This system opens up an entirely new field of exoplanetary research.”

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