The European LOFAR radio telescope, one of the largest in the world, observes very low-energy light, invisible to the human eye and to any optical telescope. It has the particularity of operating at very low frequencies (between 10 and 250 megahertz) in an essentially unexplored energy range. Operated by ASTRON in the Netherlands and in its European neighbors, notably in France, it consists of a network of fifty thousand antennas spread throughout Europe. The French part of the network is located in Nançay, in the Cher department, within the radio astronomy station of the Paris Observatory - PSL (Observatoire de Paris - PSL / CNRS / University of Orléans).
Using LOFAR, an international team has detected radio waves emanating from the boreal constellation of Bouvier, a region of the sky dominated by the star Arcturus, 50 light years away. This signal could be the first radio transmission from a planet beyond our Solar System. It came from the system τ Boötes which contains a binary star and a gas giant exoplanet very close to its star (a "hot Jupiter"), named τ Boötes b, which the theory predicts to be a good candidate for the production of intense radio waves.
The intensity and polarization of the signal argue in favor of an emission from this exoplanet.
Last year, the scientific team used LOFAR to observe Jupiter. Its highly attenuated radio signal, scaled to the scale of an exoplanet a few dozen light years away, served as a "pattern" for the search for radio emissions from exoplanets.
The analysis of about a hundred hours of observations revealed the signature expected in the data of τ Boötes. This signature is weak, and the planetary origin of the signal is still uncertain, so the need for follow-up observations is crucial.
The detection of such a radio emission makes it possible to probe the magnetic field, thus the interior of an exoplanet, as well as the physics of star - planet interactions. The magnetic field, protecting the planet from the stellar wind radiation, could promote habitability.
The observation of other "hot Jupiters" in the systems 55 Cancri and Ups. Andromedae did not reveal any comparable emission.
The authors have already started a new monitoring campaign of τ Boötes using several low-frequency radio telescopes, including the latest one, NenuFAR, at the Nançay radio astronomy station.
Bibliography
- « The search for radio emission from the exoplanetary systems 55
Cancri, Ups. Andromedae, and τ Boötis using LOFAR beam-formed
Observations », par Jake D. Turner et al., paru en ligne sur le site de la revue Astronomy & Astrophysics - « The search for radio emission from exoplanets using LOFAR beam-formed observations: Jupiter as an Exoplanet », par Jake D. Turner, Jean-Mathias Grießmeier, Philippe Zarka, & Iaroslavna Vasylieva, Astronomy & Astrophysics, 624, A40, 2019.