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.