Actinide crystallization and fission reactions in cooling white dwarf stars

Understand

The first solids that form as a cooling white dwarf (WD) starts to crystallize are expected to be greatly enriched in actinides.

• This is because the melting points of WD matter scale as $Z^{5/3}$ and actinides have the largest charge $Z$.
• We estimate that the solids may be so enriched in actinides that they could support a fission chain reaction.
• This reaction could ignite carbon burning and lead to the explosion of an isolated WD in a thermonuclear supernova (SN Ia).