Astronomers have discovered that planets orbiting white dwarfs — dense stellar remnants — can retain conditions for life despite the fact that their stars have passed the red giant stage.
White dwarfs form after a Sun-like star exhausts its hydrogen reserves, loses a significant portion of its mass, and turns into a dense core the size of Earth. There are about 10 billion such objects in our galaxy, and their number is only set to grow.
Scientists have already discovered a planet that survived orbiting a white dwarf, and are now studying whether liquid water can persist on such worlds. The main difficulty is the proximity of the habitable zone to the star: it is 10 to 100 times closer than Earth is to the Sun, which creates the risk of strong tidal heating. However, as the example of Jupiter’s moons has shown, moderate heat can help preserve subglacial oceans.
Another factor is the survival of the planet during the red giant stage. To preserve water, planets must be far from the star and gradually migrate closer as it cools.
Although no Earth-like planets have yet been found in the habitable zone of a white dwarf, new telescopes, including the James Webb, may discover such worlds. This will expand scientists’ understanding of possible places for life to exist in the Universe, showing that even “dead” stars remain promising targets for astrobiology.
