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Moon and Spica

June 14, 2016

For the stars of Spica, life is a never-ending give and take. The stars tug at each other and bombard each other with strong winds. And one of the stars may cause the other to vibrate like the string of a cello.

Spica is the leading light of the constellation Virgo. It stands close to the Moon as darkness falls tonight.

What we see as Spica is actually two heavy stars. One is about 11 times the mass of the Sun, while the other is about seven times the Sun’s mass. Each star is also much bigger than the Sun, and hundreds or thousands of times brighter.

The stars are so close together that they orbit each other in just four days. Since both stars are big and hot, they produce powerful “winds” of charged particles. The winds collide between the stars, producing X-rays. The combination of the winds and X-rays heats the side of each star that faces the other.

And the gravity of each star pulls more strongly at the side of the companion star that faces it. That distorts the stars, so each one is shaped more like an egg than a ball, with the small ends pointing toward each other.

A recent study found that gravity may have one more effect. The larger star pulses in and out. Astronomers have discovered at least three sets of pulsations — like notes played on three different strings of a musical instrument. One of those notes may be caused by the gravitational pull of the smaller star — plucking the strings of its bigger companion.

Script by Damond Benningfield

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