Kyoto, Japan --  White dwarfs are the compact remnants of stars that have stopped nuclear burning, a fate that will eventually befall our sun. These extremely dense objects are degenerate stars because their structure is counterintuitive: the heavier they are, the smaller they are.

White dwarfs often form binary systems, in which two stars orbit one another. The majority of these are ancient even by galactic standards, and have cooled to surface temperatures of about 4,000 degrees Kelvin. However, recent studies have revealed a class of short period binary systems in which the stars orbit each other faster than once per hour. Contrary to theoretical models, these stars are inflated to twice the size as expected due to surface temperatures of 10 to 30 thousand degrees Kelvin.

This inspired a team of researchers, led by Lucy Olivia McNeill of Kyoto University, to investigate the theory of tides and use it to predict the temperature increase of white dwarfs in short period binary orbits. Tidal forces often deform celestial bodies in binary orbits, determining their orbital evolution.

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