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
