Red dwarfs are not failed stars. They are the lowest mass objects capable of nuclear fusion.
Brown dwarfs are capable of fusion of deuterium at an extremely low power output. Their inability to conduct more substantial fusion involving hydrogen-1 is what sets them apart from red dwarfs.
Brown dwarfs are capable of fusion of deuterium at an extremely low power output. Their inability to conduct more substantial fusion involving hydrogen-1 is what sets them apart from red dwarfs.