Brown Dwarf is a star so small—some are hardly more massive than a large planet—that it never lit up. Astronomers scarcely even bothered to look for planets around such runts. Yet they have now seen hints of mini solar systems forming around brown dwarfs and similarly unlikely objects.
Ron Miller

Key Concepts

• Few if any astronomers expected the sheer diver­sity of planets beyond our solar system. The most extreme systems are those that orbit neutron stars, white dwarfs and brown dwarfs.
• Neutron stars are born in supernova explosions, and planets orbiting them probably congealed from the debris. The bodies orbiting white dwarfs are the hardy survivors of the demise of a sunlike star. And brown dwarfs, themselves barely more massive than planets, nonetheless appear to be sites of planet formation.

Among the most poignant sights in the heavens are white dwarfs. Although they have a mass comparable to our sun’s, they are among the dimmest of all stars and becoming ever dimmer; they do not follow the usual pattern relating stellar mass to brightness. Astronomers think white dwarfs must not be stars so much as the corpses of stars. Each white dwarf was once much like our sun and shone with the same brilliance. But then it began to run out of fuel and entered its stormy death throes, swelling to 100 times its previous size and brightening 10,000-fold, before shedding its outer layers and shriveling to a glowing cinder the size of Earth. For the rest of eternity, it will sit inertly, slowly fading to blackness.

As if this story were not gloomy enough, it gets worse. We and our colleagues have found more than a dozen white dwarfs in our galaxy that are orbited by asteroids, comets and perhaps even planets—entire graveyards of worlds. While the stars were still alive, they rose every day in the skies of these worlds. They gently warmed the soil and stirred the wind. Living organisms may have soaked up their rays. But when the stars died, they vaporized or engulfed and incinerated their inner planets, leaving only the bodies that resided in the chilly outposts. Over time the dwarfs shredded and consumed many of the survivors as well. These decimated systems offer a grim look at the fate of our own solar system when the sun dies five billion years from now.

   
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