In a first, astronomers locate a huge planet orbiting a dead star

In a first, astronomers locate a huge planet orbiting a dead star

A tiny white dwarf, WD 1856, orbits a huge planet.

NASA Goddard

About 80 light-years from Earth is the white dwarf WD 1856, a dead star that entered its final stages of life about 6 billion years ago. This slow death is usually quite lonely. In the process of death, some stars will expand dramatically, becoming a huge “red giant”, such as Betelgeuse, and floods any of the planets in close orbit. Eventually, they consume all their fuel and collapse back into white dwarfs, having destroyed everything after them.

Not so for WD 1856. For the first time, astronomers have spotted a huge planet, about the size of Jupiter, orbiting a dead star. They named it WD 1856 b and it’s an amazing find – it avoided disaster and shows that dead stars could host planets with the right living conditions.

The study, published in the journal Nature on Wednesday, used data from NASA’s TESS satellite to track the planet and a series of ground-based telescopes to test WD 1856 for possible exoplanets. TESS, which examines stars for small drops in brightness that indicate possible planets, first examined the star in July and August 2019. A huge decrease in brightness was observed when the team examined WD 1856.

Astronomers have recently begun to study the idea that these dead stars could still host a number of planets. In December, researchers located a planet slowly devoured by a white dwarf about 1,500 light years away. However, this detection was based on light emitted by a disk of debris and gases surrounding the star, which researchers suggest must have been removed from a Poseidon-like planet.

The discovery, published in Nature today, is different because it records an immediate detection of the planet orbiting in front of its host star, which has not been achieved in the past for a white dwarf.

Each time a planet the size of Jupiter passes in front of WD 1856, as seen from Earth, light from the star falls by almost half. The process is incredibly short, however, because the planet completes a complete orbit every 1.4 days. The white dwarf itself is about 40% larger than Earth. As a result, the drop in brightness lasts just eight minutes and the planet is about 20 times closer to its star than mercury in our sun.

“This system is quite strange,” said Simon Campbell, an astrophysicist at Monash University in Australia. “In this case the planet is larger than its host by a factor of 7!”

Using data collected from ground-based telescopes, the team was also able to get an estimate of how huge the planet is. Infrared data from the Spitzer Space Telescope suggests that it is probably 14 times larger than Jupiter.

But if it is so close to its star, how did WD 1856 b survive the expansion phase? The team gave two possible explanations.

When the host star became a red giant, it may have disturbed the planets in its system, causing their orbits to escape. Naughty cosmic dance may have helped us fly a planetary body like WD 1856 b to the star, since it has been around ever since. Because he is such an old white dwarf, he also gives the planets enough time to bypass. Possibly, it could mean that there are other planets orbiting the white dwarf.

“While it is not impossible, I do not think we know how likely this is, as things get chaotic when you disturb the tracks,” Campbell said. “An observation like this is important here.”

Less likely, the researchers say, is the idea that the star was able to remove some outer layers and survive during the expansion phase. However, their current theories about this process probably suggest that it was not formed that way.

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Future observations, the team writes, should be able to confirm whether WD 1856 b is really a planet or whether it is a failed star known as the “brown dwarf”. They show it the upcoming but delayed James Webb telescope and the Gemini Observatory as keys to a better understanding of WD 1856 b. And, of course, if there are planets, then they may be able to host life.

“There are people now looking for planets to pass around white dwarfs that could possibly inhabit,” Ian Crossfield told a news release. “It would be a very strange system and you would have to think about how the planets really survived all this time.”

Of course, if we can wait a few billion years, the fate of our solar system will give us seats in the front row of the white dwarf. When our sun begins to die, it will swell to a size that extends beyond the orbit of Mars. Will be truly bulky. All four of the solar system’s inner planets will be incinerated in the expansion until, like WD 1856, it runs out of fuel and collapses back into a cool, white dwarf. Will outer planets like Jupiter, Saturn and Poseidon fall closer to the carnage? I’m sure we will not be close to find out.

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