‘Bizarre’ planet orbiting dead star may preview fate of our solar system - CNN

New observations may offer fresh clues into how a giant exoplanet survived the violent death of its host star — and came to closely orbit its stellar remnants.

The findings could serve as a preview of the fate that may await our solar system’s largest planets — such as the gas giants Jupiter and Saturn — when the sun dies in 5 billion years.

Astronomers detected a baffling Jupiter-size planet in 2020 that was zipping around a dead white dwarf star. Located 80 light-years from our planet, WD 1856 b is seven times larger than its Earth-size star.

“This is one of the most bizarre planetary systems we know of,” said Dr. Christopher O’Connor, coauthor of a study published Wednesday in the journal Nature that detailed the observations. O’Connor is a postdoctoral fellow studying stellar and planetary astrophysics and dynamics at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics.

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WD 1856 b completes one orbit around the dead star every 34 hours and is less than 2 million miles (3 million kilometers) from its host.

When a massive sunlike star exhausts the hydrogen fuel at its core, it puffs up to more than 100 times its size before collapsing into a dense white dwarf. Given the close proximity of WD 1856 b to its star — 50 times closer than Earth is to our sun — astronomers were unsure how the planet survived its host’s destruction.

In order to retrace WD 1856 b’s unlikely journey of survival, O’Connor and his colleagues used the James Webb Space Telescope to capture the latest glimpses of the planet and measure its atmosphere, mass and temperature. Almost every finding the team made was unexpected — and suggested that huge planets can survive the demise of their host stars in ways previously thought impossible.

The planet’s tight orbit and the lopsided relative sizes of WD 1856 b and its host star motivated O’Connor and his colleagues to investigate further.

“For a theoretical astrophysicist, finding a strange object located where it ‘shouldn’t be’ feels a bit like an invitation from the universe to get creative in search of an explanation,” O’Connor wrote in an email.

But making observations with Webb was challenging. The team had limited chances to watch a transit, or the dip in starlight as a planet passes in front of its star. Dead white dwarfs are much dimmer than the planet-hosting stars normally observed with Webb, said study coauthor Victoria Boehm, a graduate student in the department of astronomy at Cornell University.

“To make things even harder, the planet’s transit only lasts 8 minutes, so it’s very much if you blink you miss it,” Boehm said in a statement. “Capturing enough light to see WD 1856 b’s spectrum, while also doing so quickly enough to not miss the transit, is something only Webb can do.”

But the spectrum, or data captured as light from the star passed through the planet’s atmosphere, revealed previously unknown information about WD 1856 b.

The team determined that the planet is between four and 11 times the mass of Jupiter.

Infrared light emitted by WD 1856 b suggested that it has a temperature of about 260 degrees Fahrenheit (127 degrees Celsius) — about 240 degrees hotter than if it were solely being heated by the dead star.

“That was really what started us on the track of figuring out the planet’s history from our data,” O’Connor said.

The team combined the new measurements with models of how giant planets like Jupiter and Saturn cool over time, which occurs at a predictable rate related to their mass.

The results showed that the planet originally orbited the star from a safer, much greater distance. But WD 1856 b heated up while migrating inward after the star died.

The researchers have two competing theories about how WD 1856 b ended up in its current, tight orbit.

The “engulfment model” suggests that the planet was actually swallowed by the host star as it ballooned in size before dying but managed to survive, O’Connor said. The “gravitational interaction model” alternatively proposes that WD 1856 b avoided the star’s death throes, but the gravitational influence of other objects in the system pushed it closer to the white dwarf, he added.