Using the Hubble Space Telescope, two teams have been in hot pursuit of some of the coolest objects in the universe.
Those objects, known as brown dwarfs, straddle a heavenly boundary: They're too massive to be planets yet too scrawny to be stars. Brown dwarfs are thought to arise the same way stars do—from the collapse of giant gas clouds.
They don't become stars, however, because they're not big enough to sustain fusion. Instead, they quickly fizzle and become hard to detect. To find some of the lowest-mass brown dwarfs known, both research groups relied on Hubble's near-infrared camera. The objects are too dim to be seen in visible light.