New exoplanet discoveries have been popping up with increasing regularity in recent years thanks to technological advances that allow scientists to spot evidence of their existence from afar. Spotting a dip in the brightness of a star is one of the easiest ways to find planets, but new research shows that it’s also possible to spot “dead” planets orbiting burned-out stars just by listening for them.
A new study published in Monthly Notices of the Royal Astronomical Society explains how metal-rich planetary cores that survive around white dwarf stars actually beam a radio signal into space that can be detected from Earth for hundreds of millions or even a billion years.››
When large stars die in a fiery blast they often claim the lives of planets orbiting them, or at the very least turn them into burnt-out husks of their former selves. However, when a planet’s core survives long enough for the star to become a white dwarf, the magnetic field of the dead star can form a circuit with said planets, beaming this dead planet “zombie” radio signal out into space.
The chances of this happening aren’t great since a planet has to be at the perfect distance from the star in order to form this circuit without being destroyed, but when it does happen it’s a telltale sign that an exoplanet is there.
“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,” Dr. Dimitri Veras of the University of Warwick said in a statement. “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.”
Spotting these signals in space can potentially tell researchers a lot about the history of various stars and the planets that surround them, while also giving astronomers a clue as to what lies ahead for our own solar system.