Ongoing thermonuclear fusion on the surface of white dwarfs slows their cooling and changes how we calculate their age

By comparing more than 700 white dwarfs in two different globular clusters, astronomers realized there is ongoing thermonuclear fusion on their surfaces. The unexpected process leads to slower cooling of these white dwarfs which in turn could mean, that we might be wrong about their ages. And the ages of globular clusters they are part of.

The mass and temperature of white dwarf can be used to determine its age. But if some of the white dwarfs still retain thermonuclear fusion on their surfaces and cool more slowly than others, their age could differ.