Paul Ledoux (8 August 1914 – 6 October 1988) was a Belgian astrophysicist best known for his work on stellar stability and variability. With Theodore Walraven, he co-authored a seminal work on stellar oscillations. In 1964 Ledoux was awarded the

Francqui Prize The Francqui Prize is a prestigious Belgian scholarly and scientific prize named after Émile Francqui. Normally annually since 1933, the Francqui Foundation awards it in recognition of the achievements of a scholar or scientist, who at the star ...

for Exact Sciences, and was awarded the

Eddington Medal The Eddington Medal is awarded by the Royal Astronomical Society for investigations of outstanding merit in theoretical astrophysics. It is named after Sir Arthur Eddington. First awarded in 1953, the frequency of the prize has varied over the ye ...

of the

Royal Astronomical Society The Royal Astronomical Society (RAS) is a learned society and charitable organisation, charity that encourages and promotes the study of astronomy, planetary science, solar-system science, geophysics and closely related branches of science. Its ...

in 1972 for investigations into problems of stellar stability and

variable stars A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

. He was awarded the Janssen Medal of the French Academy of Sciences in 1976.

Ledoux criterion

In stellar astrophysics, Ledoux's name is now associated with the criterion under which material in a star becomes unstable to convection in the presence of a gradient of chemical composition. In homogeneous material, the Schwarzschild criterion shows that material is unstable to convection if the radiation field alone would establish a steeper temperature gradient steeper than the adiabatic (or isentropic) temperature gradient. However, Ledoux showed that a composition gradient stabilises or destabilises the material against convection. In convectively-stable regions destabilised by the composition gradient, one expects ''thermohaline mixing''; in convectively-unstable regions that are stabilised, one expects double-diffusive mixing, known in stellar astrophysics as ''semiconvection''.

References

20th-century Belgian astronomers 1914 births 1988 deaths {{Belgium-scientist-stub