 A brown dwarf probably forms in the same way as a star, from the collapse of a cloud of gas and dust. The heat of that collapse makes the brown dwarf shine. But a brown dwarf isn't massive enough to fuse hydrogen in its core to make helium, the power source of most true stars. It may briefly fuse a heavy form of hydrogen, but that doesn't produce nearly as much energy. So brown dwarfs are also known as failed stars.