Doing Physics in the Cores of Globular Star Clusters

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Stars up to about eight times the mass of our Sun end their lives as white dwarf stars (WDs). These stars have completed their nuclear evolution, converting their core of hydrogen into helium and then into carbon and oxygen. The star then contracts until the pressure of its electrons (the quantum mechanical electron degeneracy pressure) becomes high enough for the star to reach a balance between gravity (that wants to contract it) and pressure (that wants to expand it). The end point of this process is a star about half the mass of the Sun and about the radius of the Earth. The WD has depleted its potential source of nuclear fuel by this time, so it simply radiates its stored thermal energy out into space and cools slowly and predictably with time - WDS are good clocks. This provides a physical laboratory with conditions that cannot be reproduced on Earth; temperature about 100 million degrees, density of order of 1 million times that of water and a precise clock to boot. With this almost unique laboratory, it is possible to carry out exotic physical experiments.