is it habitable?
It has been proposed that white dwarfs with surface temperatures of less than 10,000 Kelvins could harbor a habitable zone at a distance of c. 0.005 to 0.02 AU.
White dwarf
It has been proposed that white dwarfs with surface temperatures of less than 10,000 Kelvins could harbor a habitable zone at a distance of c. 0.005 to 0.02 AU that would last upwards of 3 billion years.
how does a white dwarf form? After the hydrogen-fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant. It the red giant  has insufficient mass to generate the core temperatures required to fuse carbon it forms a planetary nebula. The remaining core is the white dwarf. what metals does it contain? UNANSWERABLE when was it discovered? In 1910. and who discovered it? Henry Norris Russell, Edward Charles Pickering and Williamina Fleming. mention a few works published by the first person? He co-authored a two-volume textbook titled "Astronomy: A Revision of Young’s Manual of Astronomy" . how is the magnetic field of white dwarf? Since 1970 magnetic fields have been discovered in well over 200 white dwarfs, ranging  0.2 T to 100 kT.
wiki:19666804
White dwarf [SEP] Habitability
Another suggested constraint to this idea is the origin of those planets. Leaving aside formation from the accretion disk surrounding the white dwarf, there are two ways a planet could end in a close orbit around stars of this kind: by surviving being engulfed by the star during its red giant phase, and then spiralling inward, or inward migration after the white dwarf has formed. The former case is implausible for low-mass bodies, as they are unlikely to survive being absorbed by their stars. In the latter case, the planets would have to expel so much orbital energy as heat, through tidal interactions with the white dwarf, that they would likely end as uninhabitable embers.