Hot Embrace

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From up close, the star system W Ursae Majoris would look like a glowing, spinning hourglass. The system is in the constellation Ursa Major, the great bear, which is high in the north on May evenings. The bear's body and tail form the Big Dipper. You need a telescope to find W Ursae Majoris, but it's so far away that even a telescope won't show you what this remarkable system looks like.

W Ursae Majoris is a binary "” two stars locked in a mutual orbit. Half or more of all star systems are binaries. Individual stars like the Sun are a minority.

Most binary stars orbit each other once every few months or years. But some are so close to each other that they complete an orbit in just days or even hours. In some of these cases, one star can "œsteal" hot gas from its companion.

W Ursae Majoris is the prototype of a class of stars that take the stealing business to extremes. The stars are so close that they touch each other, forming a contact binary. Each star looks like a teardrop, with the drops joined at the narrow ends like an hourglass. The stars in these systems are exchanging gas with each other. In essence, they consist of two stellar cores that share a single coating of hot gas.

Both of the stars of W Ursae Majoris are roughly the same size, mass, and color as the Sun. They orbit each other once every eight hours -- locked in an embrace that could continue for millions of years.

We'll talk about a much brighter binary system tomorrow.

Script by Damond Benningfield, Copyright 2005, 2008

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