Not so for WD 1856. For the first time, astronomers have discovered a giant planet, about the size of Jupiter, orbiting the dead star. They have christened it WD 1856 b, and it is a surprising find – it avoided destruction and shows that dead stars could still host planets with the right conditions for life.
The study, published in the journal Nature on Wednesday, used data obtained from NASA’s planet-chasing TESS satellite and a series of ground-based telescopes to study WD 1856 for potential exoplanets. TESS, which studies stars for small declines in brightness meaning potential planets, first looked at the star during July and August 2019. A huge reduction in brightness was seen when the team looked at WD 1856.
Astronomers have recently begun to struggle with the idea that these dead stars can still host a number of planets. In December, researchers discoveredabout 1,500 light-years away. However, this detection was based on light emitted by a disk of dirt and gas surrounding the star, which scientists suggest must have been removed from a Neptune-like planet.
The discovery published in Nature today is different because it detects a direct detection of the planet orbiting its host star, which has not previously been achieved for a white dwarf.
Each time the planet Jupiter passes in front of WD 1856 as seen from Earth, the star’s light falls away by almost half. However, the process is incredibly short because the planet completes a full orbit every 1.4 days. The white dwarf itself is only about 40% larger than Earth. As a result, dipping in brightness lasts for only eight minutes, and the planet is about 20 times closer to its star than mercury is to our sun.
“This system is pretty weird,” said Simon Campbell, an astrophysicist at Monash University, Australia. “In this case, the planet is larger than its host star by a factor of 7!”
Using data collected by terrestrial telescopes, the team was also able to get an estimate of how massive the planet is. Infrared data fromsuggests that it is probably 14 times more massive than Jupiter.
But if it is so close to the star, how did the 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 and caused their orbits to skew. The disordered cosmic dance may have helped throw a planetary body like WD 1856 b toward the star, where it has been circulating ever since. Because it’s such an older white dwarf that also gives planets plenty of time to sit close. Potentially, this could mean that there are other planets orbiting the white dwarf as well.
“While it’s not impossible, I do not think we know how likely this is as things get chaotic when you disrupt lanes,” Campbell said. “This is where an observation like this is important.”
Less likely, the researchers say the idea was that the star was able to remove some outer layers and survive during the expansion phase. However, they conclude that our current theories about this process probably suggest that it was not formed in such a way.
Future observations, the team writes, should be able to confirm whether WD 1856 b is really a planet or not, or whether it is a failed star known as a “brown dwarf.” They point toand Gemini Observatory as keys to better understand WD 1856 b. And of course, if there are planets, they could possibly host life.
“There are people now looking for transiting planets around white dwarfs that could potentially be habitable,” Ian Crossfield said in a press release. “It would be a pretty weird system, and you’re going to have to think about how the planets actually survived all that time.”
Of course, if we can wait a few billion years, the fate of our own solar system will give us seats in the front row to the white dwarf aftermath. When our sun begins to die, it swells to a size that extends beyond Mars’ orbit. It will be really massive. All four of the solar system’s inner planets will be burned in the expansion until, like WD 1856, it runs out of fuel and collapses back into a cool, white dwarf. Will the outer planets, such as Jupiter, Saturn and Neptune, be thrown closer to the carnage? I’m sure we will not be there to find out.