SDSS J1228+1040 b

SDSS J1228+1040 b is a disputed extrasolar planetesimal orbiting the white dwarf SDSS J1228+1040. It was discovered in 2019 using the variable calcium Ca II emission line.

Unlike other planetesimals around white dwarfs, the planetesimal SDSS J1228+1040 b needs high internal strength and a high density to not be tidally disrupted. The researchers calculate a density of 7.7 g/cm3 or less. This density is close to the density of iron and it is speculated that this planetesimal is the core of a larger body. This larger parent body possibly got its crust and mantle stripped by the white dwarf, leaving the core behind. This crust and mantle material would then form the debris disk, which is now detected around the white dwarf.

At first the size of the planetesimal was estimated to be between 4 and 600 km or between 2 and 200 km for an eccentric orbit, but newer accretion models suggest a minimal radius of 72 km and a lifetime of 1500 years before it is completely sublimated.

The white dwarf SDSS J1228+1040 is surrounded by a debris disk, detected as both spectroscopic metal lines and infrared excess. The white dwarf also shows emission lines. While absorption lines represent metals that are already pollute the atmosphere of the white dwarf, the emission lines are interpreted as sublimated metal gas inside the disk. In the case of SDSS J1228+1040 it is suggested that the gas is sublimated on the surface of the planetesimal. The gas component also shows long-term variability over the 15 years observations. This is interpreted as precession of an assumed to be eccentric orbit of the planetesimal. Other gaseous disks around white dwarfs show similar long-term variability.

A study questions the existence of the planetesimal and instead suggests that the disk is precessing under the forces of general relativity and gas pressure. This eccentricity of the disk should dissipate within 200 years, meaning that the disk must have formed recently.