You are here

Faint Neighbors

February 7, 2016

The brightest star visible in Lepus, the rabbit, is a stunner. It’s more than 30,000 times brighter than the Sun, so it’s easily visible to the unaided eye even though it’s more than 2,000 light-years away.

The constellation’s closest star is less than 20 light-years away. Yet it’s so feeble that you need a telescope to see it. And it has a small companion that’s even fainter: a cool ember known as a brown dwarf.

Gliese 229 is smaller and less massive than the Sun, which is the key to its faintness. A lightweight star burns through the nuclear fuel in its core much more slowly than a heavy star. That generates much less energy, so there’s not much for the star to radiate into space.

The brown dwarf companion — Gliese 229B — probably doesn’t produce any energy in its core. It’s a few dozen times the mass of Jupiter, the largest planet in the solar system. That’s just not big enough to ignite nuclear fusion and allow it to shine as a true star.

Gliese 229B probably formed like its bigger companion, from the collapse of a cloud of gas and dust. The cloud split apart, producing two separate objects. But there wasn’t enough material in Gliese 229B’s part of the cloud to make a star. Instead, it made a faint cosmic ember — a brown dwarf.

Lepus hops below the feet of Orion, which is high in the sky at nightfall. The rabbit’s brightest star is easy to spot, but Gliese 229 remains invisible — a close neighbor hidden from sight.


Script by Damond Benningfield, Copyright 2015

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.