Sirius B

star

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Last updated

July 13, 2026

Quick Summary

Sirius is the brightest star in the night sky, located in the constellation Canis Major. It is a binary star system, meaning it consists of two stars orbiting each other. The primary star, Sirius A, is a blue-white star significantly more luminous and hotter than our Sun.1

The companion star, Sirius B, is a white dwarf. White dwarfs are the dense remnants of stars that have exhausted their nuclear fuel. Sirius B was the first white dwarf ever discovered. Despite being as massive as the Sun, Sirius B is much smaller and incredibly dense. The two stars orbit each other with a period of about 50 years.12

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Sirius
This companion star, Sirius B, is about as massive as the Sun, though much more condensed, and was the first white dwarf star to be discovered.
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This companion star, Sirius B, is about as massive as the Sun, though much more condensed, and was the first white dwarf star to be discovered.
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star
White dwarfs
…a faint object (now called Sirius B), about 10,000 times fainter than Sirius (now called Sirius A) or 500 times fainter than the Sun. Its mass is slightly less than that of the Sun, and its size a little less than that of Earth. Its colour and spectrum correspond roughly…
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…a faint object (now called Sirius B), about 10,000 times fainter than Sirius (now called Sirius A) or 500 times fainter than the Sun. Its mass is slightly less than that of the Sun, and its size a little less than that of Earth. Its colour and spectrum correspond roughly…
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astronomy
Testing relativity
…determined the gravitational redshift of Sirius B, the white dwarf companion of Sirius. (White dwarfs were expected to have much higher gravitational redshifts than stars like the Sun.) The confirmation of the gravitational redshift not only bolstered general relativity but also helped support Eddington’s theory of stellar structure, which predicted…
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…determined the gravitational redshift of Sirius B, the white dwarf companion of Sirius. (White dwarfs were expected to have much higher gravitational redshifts than stars like the Sun.) The confirmation of the gravitational redshift not only bolstered general relativity but also helped support Eddington’s theory of stellar structure, which predicted…
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