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An age-luminosity relations model of the oldest white dwarf stars reveals that the lower limit for the minimum age of the local Galactic disk is about 9.5 Gyrs. The white-dwarf luminosity function shows that the minimum age is more that the Hubble expansion age estimates. The emerging picture of the Galaxy shows that the halo formed about 14-17 Gyrs ago, the bulge globular clusters formed about 12-14 Gyrs ago, and a modest hiatus preceded star formation about 10 Gyrs ago.

Chandrasekhar showed that above a limiting mass, white dwarf stars will collapse under their own gravitational force. We use dimensional analysis to show that although the limiting mass is finite in three spatial dimensions (d = 3), it is zero in higher spatial dimensions. A star placed in a high-dimensional space is unstable and will either collapse to a black hole or disperse and become unbound. Thus, any universe - or part of a universe - with d greater than or equal to 4 will be profoundly different from one with d = 3.

The age of the millisecond binary dwarf PSR J1012+5307 is around 7000 million years. The age of its companion white dwarf is 0.3 gigayears. The age is calculated using a version of the evolution code of Eggleton. The cooling time scale of a very-low-mass white dwarf (VLMWD) is higher due to the absence of thermal flashes. A VLMWD with a hydrogen envelope is unable to exhibit thermal flashes when hydrogen content in the envelope remains high and gives a much longer phase with considerable hydrogen burning.