How old a white dwarf?
Such an age discrepancy stood out especially for the well-studied star cluster NGC-6791. The main sequence method pegged its age of birth to about 8 billion years ago, while the white dwarf method yielded a much younger age of just 6 billion years. The universe is about 13.7 billion years old. Now the latest model developed by Garcia-Berro and his colleagues has shown that the illusion of white dwarf youth depends on the release of gravitational potential energy, which creates heat and prolongs the cooling phase. Such potential energy is freed when elements settle out within the white dwarf or end up physically separated. An element known as neon-22 sinks slowly into the white dwarf interior as “one of the ashes” left over from the star’s helium-burning phase, the researchers said. More cooling of the core allows the solid elements carbon-12 and oxygen-16 to separate. “Once you have neon-22 sedimentation and carbon-oxygen phase separation, both processes release potential gravitational
