Ultimate Survivor: Massive Planet Spotted Closely Orbiting White Dwarf

An international team of researchers found what may be the first intact planet observed to be orbiting a white dwarf. Dubbed WD 1856 b, the planet is so close to the tiny star that it completes an orbit in just 34 hours.

Sun-like stars become red giants when they run out of fuel, expanding up to thousands of times and swallowing close-orbiting planets in the process. Eventually, the red giants shed about 80% of their mass and end up as white dwarfs that sometimes display rocky debris disks, likely from the objects that were torn apart in the process of forming the white dwarf.

Although there have been hints that massive planets may make their way to a close orbit with white dwarfs, it has been unclear whether these planets would survive the journey, since, no intact planets were previously discovered in close orbit of a white dwarf.

But in a new study, a research team has reported the discovery of a massive planet some 80 light-years away that possibly survived the process and is now orbiting so close to a white dwarf.

It was by scouring NASA's Transiting Exoplanet Survey Satellite (TESS) data that researchers found the unique pair. The TESS data showed that the star, WD 1856+534, was dimming by half every 1.4 days, signifying that something massive, perhaps a planet, was passing in front of it each time.

Upon further observations of the system, they found that it actually consists of a Jupiter-sized planet, WD 1856 b, orbiting very close to the white dwarf that's about the size of the Earth but still with half of the sun's mass. This means that the planet is about seven times larger than the white dwarf. What’s more, it is so close to the white dwarf that it completes an orbit 60 times faster than Mercury, which takes about 90 days to orbit the sun.

This makes WD 1856 b the first evidence of an intact planet surviving and, now essentially hugging, a white dwarf, showing that massive planets can indeed come into a close orbit with white dwarfs without being destroyed.

"We've never seen evidence before of a planet coming in so close to a white dwarf and surviving. It's a pleasant surprise," study lead researcher Andrew Vanderburg of the University of Wisconsin-Madison (UW-Madison) said in the university news release.

It is still unclear how the planet got that close to the white dwarf without getting destroyed, but, the researchers say it's possible that the white dwarf engulfed the other planets and destabilized WD 1865 b during its red giant phase. At the time, WD 1856 b was still orbiting much farther than its current orbit but the interaction with the red giant caused it to have an exaggerated oval orbit.

Eventually, over billions of years, the planet's orbit came closer and closer to the white dwarf until it ended up with the 1.4-day circular orbit, the researchers observed. What exactly led to this unique pair remains unclear.

"The white dwarf creation process destroys nearby planets, and anything that later gets too close is usually torn apart by the star's immense gravity," Vanderburg said in a NASA news release. "We still have many questions about how WD 1856 b arrived at its current location without meeting one of those fates."

With the first clear evidence for the peculiar pairing, the hope now is to search for other such systems and, perhaps even find whether they may harbor hospitable conditions.

The study is published in the journal Nature.