Thousands of brown dwarfs, and what keeps them from being stars
NASA's SPHEREx telescope is turning up thousands of brown dwarfs as it maps the sky. They are strange objects: they form from collapsing clouds of gas, the way stars do, but they never grow hefty enough to sustain hydrogen fusion. That leaves them unlike most planets in one respect that matters — they drift ungoverned by a host star, heated entirely from within rather than warmed by an external sun.
AI-generated discussion · Different perspectives
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What makes brown dwarfs odd isn't only the missing fusion. They share characteristics with Jupiter and Saturn — gas giants we file under planets — even though they form the way stars do.
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The star is the dividing line. Brown dwarfs drift ungoverned by a host star and are heated entirely from within, which isn't how we normally describe a planet.