Light on, light off—this is how one could describe the behavior of the nova, which goes by the name RS Ophiuchi (RS Oph). Every 15 years or so, a dramatic explosion occurs in the constellation of the Serpent Bearer. Birthplaces of a nova are systems in which two very different stars live in a parasitic relationship: A white dwarf, a small, burned-out and tremendously dense star—a teaspoon of its matter weighs about 1 ton—orbits a red giant, an old star that will soon burn up.