© NASATwo young brown dwarfs, objects that fall somewhere between planets and stars in terms of their temperature and mass.
Brown dwarfs are misfits because they fall somewhere between planets and stars in terms of their temperature and mass. They are cooler and more lightweight than stars and more massive (and normally warmer) than planets. This has generated a debate among astronomers: Do brown dwarfs form like planets or like stars?
Brown dwarfs are born of the same dense, dusty clouds that spawn stars and planets. But while they may share the same galactic nursery, brown dwarfs are often called "failed" stars because they lack the mass of their hotter, brighter stellar siblings. Without that mass, the gas at their core does not get hot enough to trigger the nuclear fusion that burns hydrogen -- the main component of these molecular clouds -- into helium. Unable to ignite as stars, brown dwarfs end up as cooler, less luminous objects that are more difficult to detect -- a challenge that was overcome in this case by Spitzer's heat-sensitive infrared vision.
