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Beta Monocerotis

February 10, 2015

Beta Monocerotis is one of the most beautiful triple star systems in the heavens — three blue-white points of light that make a skinny triangle. But the system is even more remarkable than it looks — all three of its stars are among the brightest and most massive in the entire galaxy.

Two of the stars form a wide binary. Each star is roughly six times as massive as the Sun, and more than a thousand times brighter.

The third star probably orbits the other two. But it’s so far away from them that it takes about nine days for its light to cross the vast gulf between them. This star is the most impressive of the triplets. It’s a bit heavier than the others, and about twice as bright.

Like the Sun, all three stars will end their lives as cosmic embers known as white dwarfs. But they’ll get there a lot faster than the Sun. Heavier stars use up their nuclear fuel more quickly, so they live shorter lives. The three stars of Beta Monocerotis will live less than one percent as long as the Sun before they enter the final phases of life. For a short while, before they become white dwarfs, all three will shine much brighter than they are today.

For now, look for Beta Monocerotis in the southeast in early evening. Although it’s the brightest star of Monoceros, the unicorn, it’s quite faint, so you need dark skies to find it. But it’s to the lower left of Orion’s Belt, so there’s a bright marker to point the way.

More about the unicorn tomorrow.


Script by Damond Benningfield, Copyright 2014

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