The dawn of exoplanet radio astronomy

Project level: Honours, PhD

Thousands of exoplanets have been discovered with optical astronomy, whether by using the Doppler effect to see the planet pulling its star back and forth (the radial velocity method, which won Didier Queloz & Michel Mayor the 2019 Nobel Prize in Physics), or looking for the dip in brightness as a planet passes in front of a star (the transit method). In our Solar System, the Sun, Earth, and the gas giants are bright sources of radio waves, which tell us a great deal about their magnetic fields and interactions, and for decades astronomers have searched for these effects in more distant planetary systems. Only a couple of the closest stars have been detected in radio waves - otherwise most radio sources are exotic stellar remnants, or black holes at the centres of galaxies. A handful of planets have been discovered by radio astronomy around neutron stars, but the search for radio emission from exoplanets around ordinary stars has until recently not yielded results.

A controversial new discovery by the LOFAR radio telescope in Europe may have opened the window to an important new way to discover and understand exoplanets. LOFAR has found the nearby old, quiet red dwarf GJ 1151 was found to emit circularly polarized radio waves, which we have interpreted as evidence of star-planet magnetic interaction. Excitingly, the Habitable-zone Planet Finder telescope went and looked for the predicted planet using radial velocity, and found a planet in just the predicted 2.02 day orbit. There are other systems we don't believe to be from planetary interactions, but might be new and interesting stellar astrophysics. With many more detections on the way from LOFAR, this could be the beginning of exoplanet radio astronomy. LOFAR is a pathfinder for the recently-approved Square Kilometre Array to be built in Australia, which will be nearly an order of magnitude more sensitive, with the potential to discover hundreds or thousands of these systems.

I have been involved in this project from the beginning, particularly in optical follow-up to search for these planets and understand these stars with ground-based telescopes and satellite data. I have also published theoretical work on what to expect from exoplanet radio observations.

There are Honours and PhD projects available in:

• Helping radial-velocity and TESS photometry follow-up of radio-detected stars
• Theoretical predictions of discoveries with the SKA

For more reading, see: New exoplanet search strategy claims first discovery