English: White dwarfs are either dominated by a hydrogen or a helium atmosphere, this is seen in the Hertzsprung–Russell diagram of the Gaia Data Release 2 (Gaia Collaboration 2018). There is also another feature in this diagram that is explained as the core-crystallization of white dwarfs that releases additional energy during the cooling (Tremblay et al. 2019).
To create this diagram I used ESA's Gaia Archive and the following selection method: G-mag<20, plx>15, astrometric_sigma5d_max<0.5
The stars plotted here are therefore closer than 217 light-years (67 parsec).