Adam Solomon: A Young Astrophysicist Studies Old Dwarfs Brown dwarfs are basically failed stars. In normal stars, the swirling balls of gas present during the star's formation become so big that they press in on themselves, forming a central core that is dense enough to cause hydrogen atoms to fuse. This nuclear fusion is what causes stars to produce heat and light. Because brown dwarfs are smaller, lacking sufficient mass to start a fusion reaction, they radiate only very little light. That makes them hard to find, so they haven't been studied much until recently.