What Is A “Zombie” Star?

Faraway planets orbiting dead stars can broadcast “zombie” radio waves for a billion years after planetary death, according to new research by the Royal Astronomical Society. The planets orbit stars at the very end of their lifespan, known as “white drawfs.” The radio waves can be detected on Earth.

“There is a sweet spot for detecting these planetary cores: a core too close to the white dwarf would be destroyed by tidal forces, and a core too far away would not be detectable,” Dimitri Veras, one of the new study’s authors, said. “Also, if the magnetic field is too strong, it would push the core into the white dwarf, destroying it…Hence, we should only look for planets around those white dwarfs with weaker magnetic fields at a separation between about 3 solar radii and the Mercury-Sun distance.”

Veras said space researchers have never discovered the “bare core” of a planet orbiting a white dwarf before. However, tracking these planets via their radio waves might lead to these discoveries in the future.

“We will use the results of this work as guidelines for designs of radio searches for planetary cores around white dwarfs,” Penn State researcher Alexander Wolszczan said. “Given the existing evidence for a presence of planetary debris around many of them, we think that our chances for exciting discoveries are quite good.”