Astronomy - February 2014

WWW.ASTRONOMY.COM 29

supergiants). Like top tennis players, there
aren’t many, but they have high visibility.
This mass-luminosity relationship also
works in the other direction. A star that’s
only one-tenth the mass of the Sun — a
small red dwarf — will shine with only 0.08
percent of our star’s brightness. Because of
this lackluster luminosity, red dwarfs are
hard to see. There’s not one you can pick
out without reaching for some optics. In the
north, Barnard’s Star, 6 light-years distant
and with a modest apparent magnitude of
9.5, is the nearest. In the south, Proxima
Centauri is closer (4.23 light-years) but even
harder to identify at magnitude 11. But

what does this have to do with intelligent

alien beings?

Only this: Red dwarfs might be the low-

lights of the cosmos, but what they lack in

luminance they make up in numbers. They

easily dominate the galaxy, constituting the

majority of its stellar population. This

shouldn’t surprise you, as natural processes

frequently result in more small things than

large (think field mice versus elephants).

According to Georgia State astronomer

Todd Henry, 74 percent of the stars in the

solar neighborhood — our corner of the

Milky Way — are red dwarfs. They might

be small, but collectively they make up

more of the galaxy’s mass than any other

type of star.

Despite the stars’ ubiquity, SETI

researchers have spent little time searching

the environs of these pint-sized suns. That’s

because scientists believed red dwarfs had

some discomfiting characteristics that

would make them unlikely hosts for truly

advanced life.

The negatives

The first dwarf downside is that these stars

have low power output. If habitable worlds

exist around red dwarfs, they will have to

be star-huggers. Otherwise, they won’t be