A planet has been found orbiting a dead star in a zone where it should have been incinerated when the star died. The discovery might give us a window into the future of our solar system.
When stars like our sun exhaust their fuel, they first expand to become a red giant, then collapse into a dense, Earth-sized remnant called a white dwarf.
Using the James Webb Space Telescope (JWST), at the University of Michigan and her colleagues detected a spike in heat near a white dwarf called WD 0310-688, about 34 light years away from us.
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That spike corresponds to a planet roughly three times the mass of Jupiter, orbiting its star at somewhere between 0.1 and two times the Earth-sun distance. The heat from this planet made the white dwarf appear about 21 per cent brighter in a process called infrared excess, although such excess could also be explained by a disc of dust in the system.
Only a handful of planets have been found orbiting white dwarfs before, and none at this distance from their star. Some have been spotted on much tighter orbits. This can be explained by a planet migrating inwards after the red giant phase, perhaps being pulled by another planet or passing star. Others have been found in more distant orbits where they can survive the red giant phase without being incinerated.
But it is harder to explain how a planet could end up in what the team calls a “forbidden zone”, where it should have been consumed by the expanding star. A possible explanation is the planet is in the process of moving towards the star, says Limbach. If confirmed, it would be a unique example of a white dwarf planet caught in such a migration.
“It’s really intriguing,” says at the Space Telescope Science Institute in Maryland. “It sort of breaks our basic understanding of where exoplanets should be.”
, at the University of California, San Diego and his colleagues found evidence of a planet orbiting at twice the Earth-sun distance around another white dwarf 3000 light years away.
The planet, roughly double the mass of Earth, was discovered through microlensing when the white dwarf passed in front of another star and the gravitational pull of the planet stretched the star’s light. It might once have been in an orbit similar to Earth’s before being pushed outwards during its star’s red giant phase, which suggests there is a chance Earth could narrowly avoid plummeting into the sun in the distant future, says Zhang.
More white dwarf planets are expected to be found in the coming years with continued JWST surveys and NASA’s upcoming Roman Space Telescope, which is set to launch in 2027 and will conduct a much broader microlensing survey.
“There seem to be more planets closer to white dwarfs than we were expecting,” says Limbach. “Maybe planets find their way in more often, and maybe that’s something that will happen in our solar system too.”
arXiv
