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A new ultra-compact binary star

27 Jun 2018, 21:32 UTC
A new ultra-compact binary star
(200 words excerpt, click title or image to see full post)

Article by Gavin Ramsay, Astronomer at the Armagh Observatory and Planetarium
Approximately every other star in the Milky Way galaxy is in a ‘binary’ system. These binaries are made up of two stars orbiting around a common center of gravity. The time taken for the stars in the binary to make one revolution is called the ‘orbital period’. Binaries have a wide range of orbital period. The closest stellar system to the Sun is alpha Centauri which has two stars not unlike our Sun orbiting around one another every 80 years. Proxima Centauri, which is much smaller red dwarf star, orbits around these two stars once every 10,000 years.
About 50 years ago a small number of blue stars (known as AM CVn stars) were discovered which showed variations in their brightness on a timescale of tens of minutes. After 30 years it was conclusively shown that this variation was a signature of their orbital period. Such short periods can be reached because both stars are white dwarfs. These dwarfs are the dying remains of stars, having a mass around half that of the Sun, but are as small as the Earth, making them very dense. Because the stars are ...

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