Planets Can Emit Signal Even After Their Death, New Study Suggests

Astronomers have long thought that planet cores that remain after the planets die just float freely around the remnants of the dead star. However, a new study suggests that planets can emit signals even after they’ve died. Now scientists want to search for exoplanet cores that orbit white dwarf stars and track the signal they broadcast.

Researchers from the University of Warwick have found that the best exoplanets suitable for this research are those that orbit white dwarfs, because of the likelihood of surviving planetary cores following the explosion of the star. Their findings were published in the Monthly Notices of the Royal Astronomical Society.

Scientists found that the magnetic field that exists between the white dwarf star and planetary core that orbits it can form a unipolar inductor circuit, as the core is a conductor component due to its metallic composition. The radiation from the circuit is emitted as a radio wave and can be picked up by Earth’s radio telescopes.

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The new study aims to answer the time that planets can emit a signal after their outer layer, surface and atmosphere have disappeared. Different models they used tested several cases in which exoplanets died and continued broadcasting signals. The cases revealed that planetary cores can live from over 100 million years up to a billion years.

The team wants to use these results for observation time on telescopes such as Arecibo in Puerto Rico and the Green Bank Telescope in West Virginia, to find more planetary cores around white dwarfs.

“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,” Lead author Dr. Dimitri Veras from 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.”

“We will use the results of this work as guidelines for designs of radio searches for planetary cores around white dwarfs,” Professor Alexander Wolszczan from Pennsylvania State University, 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.”

“A discovery would also help reveal the history of these star systems, because for a core to have reached that stage it would have been violently stripped of its atmosphere and mantle at some point and then thrown towards the white dwarf. Such a core might also provide a glimpse into our own distant future, and how the solar system will eventually evolve,” Dr. Veras said.

The first discovery of the planets that can emit signals even after they’ve died was discovered orbiting a pulsar (the dense, spinning corpse of a star that died as a supernova), by Dr. Wolszczan in the 1990s. Back then, researchers used radio waves that the star emitted. The team plans to observe exoplanet cores in the similar electromagnetic spectrum, and hopefully they will make new discoveries.