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Adams, Walter Sydney

sirius stars dwarf spectroscopic

(1876–1956) US astronomer: discovered first white dwarf star.

Adams was born in Syria, where his American parents were missionaries, but he returned with them when he was 9 and was educated in the USA and in Europe.

Adams’s work was principally concerned with the spectroscopic study of stars. He showed how dwarf and giant stars could be distinguished by their spectra, and established the technique of spectroscopic parallax to deduce a star’s distance. In 1915 he observed the spectrum of Sirius B, the faint companion of Sirius, and discovered it to be an exceptionally hot star. Since it is only 8 light years distant he realized that it must therefore be very small (otherwise it would be brighter), and hence of very high density. Sirius B proved to be a ‘white dwarf’ and the first of a new class of stellar objects; such stars are the final stage in the evolution of stars of similar mass to the Sun, which have collapsed to form extremely dense objects.

Adams also searched for the relativistic spectral shift expected from a heavy star’s presumed intense gravitational field. This he succeeded in finding in 1924, thereby proving his hypothesis about the nature of Sirius B and strengthening the case for general relativity theory as well. Adams spent most of his working life at the Mount Wilson Observatory in southern California, and was its director from 1923 until 1946.

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