An astronomical demon creeps up the northeastern sky this evening — a close pair of stars in which one is cannibalizing the other.
The system is known as Algol. It’s in Perseus, the hero, which is in the northeast at nightfall and directly overhead in the wee hours of the morning.
“Algol” comes from an Arabic name that means the “demon.” It’s a shorter version of “head of the demon,” because the star represented the head of Medusa — a snake-headed monster who was decapitated by Perseus.
Algol consists of three stars, two of which are separated from each other by just a few million miles. One of those stars is several times as massive as the Sun, while the other is less massive than the Sun.
The less-massive star is in the final stages of life, while the more-massive star is still in the prime of life. And that’s a problem, because heavier stars age more quickly than their lighter-weight counterparts.
The solution is simple: stellar cannibalism. Algol’s less-massive star actually started out heavier than its companion. As it neared the end of its life, it puffed up to giant proportions. That loosened its grip on its outer layers, so gas in those layers began pouring onto the other star. Over millions of years, the two stars swapped enough gas that the lighter star became the heavier one.
So while Algol may not be a demon, it is a bit ghoulish — a perfect star to follow across the sky on a Halloween night.
Script by Damond Benningfield, Copyright 2012
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