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Faint Triplets

October 7, 2012

Our Sun is a single star, traveling through the galaxy all alone. But many star systems are double or even triple. That includes the nearest star system to our own, Alpha Centauri. Its proximity, combined with the fact that two of its three stars are similar to the Sun, makes it one of the brightest stars in the night sky, although it’s too far south to see from most of the United States.

In contrast, the next-nearest triple star system is so dim that you need a telescope to see it. Luyten 789-6 resides in the faint constellation Aquarius. It’s 11 light-years from Earth, so it’s almost three times farther than Alpha Centauri.

The star system takes its name from Willem Luyten, an astronomer at the University of Minnesota who discovered it in the 1930s. It’s the 12th-closest star system to the Sun.

Luyten 789-6 is faint because it consists of three red dwarfs. Such stars generate energy just as the Sun does — through nuclear reactions in their cores that convert hydrogen into helium. But red dwarfs are much less massive than the Sun. That makes their cores much cooler, which in turn cools the pace of their nuclear reactions. That makes these stars the most feeble in the galaxy — they put out only a small fraction as much energy as the Sun does.

So even though it’s one of our closest neighbors, the triple-star system of Luyten 789-6 is so faint that no one knew of its existence until less than a century ago.


Script by Ken Croswell, Copyright 2012

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