NASA’s TESS and Spitzer missions just discovered a strange sight — maybe the first example of a giant world orbiting extremely close to a small, dead star.
The object, called WD 1856 b, is roughly the same size as Jupiter, with possibly up to 14 times its mass. About every day and a half, it orbits a white dwarf, a star containing half the Sun’s mass in a space only slightly larger than Earth.
TESS hunts for regular dips in starlight caused when planets pass in front of, or transit, their stars. TESS discovered WD 1856 b’s transits, which were then confirmed by Spitzer.
Finding a potential planet so close to a white dwarf is surprising. Stars like WD 1856 often start out looking much like our Sun. But as they age, they transform into red giants, engulfing any nearby planets. Then their atmospheres blow away, revealing their dead white dwarf cores.
So, WD 1856 b likely formed much farther away from its star. Scientists think there are several ways it may have moved inward, closer to where we find it today. Then the effects of the star’s gravity would have nudged it into its current orbit.
For example, it’s possible the system had additional massive planets. As the star evolved and disrupted the planets’ orbits, their gravitational interactions could have kicked WD 1856 b closer inward.
Although the possible planet orbits the white dwarf, there are two other small, distant stars in the system. Perhaps their combined gravitational influence could have altered its orbit over time. Or, perhaps a massive object from deep space, such as another star, could have thrown the entire system into disarray.
No matter the cause, the system then settled into its current state over billions of years. Scientists think this finding could help us understand how other star systems, including our own, may evolve.
In the meantime, though, TESS will continue its search for more potential worlds like WD 1856 b … and possibly find even stranger ones.