Researchers from the Institute of Astrophysics of Andalusia (IAA-CSIC) are leading an ambitious radio observation project that shows that extrasolar planets can be detected with radio telescopes.
For two decades it has been known that the magnetic interaction between Jupiter and one of its largest moons, Io, generates a large amount of radio emission similar to terrestrial auroras (produced, in turn, by the interaction of electrically charged particles from the Sun with the Earth’s atmosphere). After the discovery of the planet Proxima b around the star closest to us, Proxima Centauri, a group of researchers from the IAA-CSIC set out to check whether radio interactions also occur in this neighboring solar system. Their finding opens a new path in the study of extrasolar planets.
“This type of radio emission is possible because the Proxima planetary system has particular properties: it is a much more active star than our Sun and the planet Proxima b is very close to it; in fact, it is ten times closer to its star than Mercury is to the Sun”, points out Miguel Pérez-Torres, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who is leading the study.
The observation campaign was carried out with the ATCA (Australia Telescope Compact Array), a radio telescope made up of six twenty-two-meter antennas, and lasted for seventeen terrestrial days. As planet Proxima b makes a complete revolution around its star every 11.2 days (much less than the 365 days of Earth’s orbit), the researchers observed the emission from the Proxima planetary system for the equivalent of a year and a half.
“We detected radio emission during most of the observation campaign, with times of more intense emission. These peaks were detected twice for each orbital period, when the planet is, seen from Earth, more separated from its star -says José Francisco Gómez, IAA-CSIC researcher who participates in the study-. The data we have obtained agrees very well with what models of interaction between the star and the planet predict”.
This is a pioneering work, since it shows for the first time that the existence of a planet outside the Solar System can be detected by observing the periodic variations of the system with radio telescopes. “This opens a new path for the study of other planets that, in some cases, could not be detected by other techniques, and that is very promising when we think about the exceptionally sensitive radio telescopes that are in development, such as the Square Kilometer Array (SKA)”, indicates Miguel Pérez-Torres (IAA-CSIC).
This work has also made it possible to detect several radio flashes lasting just a few minutes, which respond to brief episodes of activity in the star, as well as a stellar flare that lasted for three days and whose radio brightness was ten times higher than the usual of the star.
“These results are also interesting in regards to the possibility of Proxima b harboring life. These radio wave flares must have been very strong for us to detect them, and some have lasted for days. Forms of life like those on Earth could not possibly survive this type of event”, points out José Francisco Gómez (IAA-CSIC).
In this study have participated, in addition to researchers from the IAA-CSIC, also researchers from the Institut de Ciències del Espai (ICE-CSIC) in Barcelona, the Osservatorio de Catania (INAF, Italy), the Universidad de Chile, and from the North-West University in South Africa.
FOUR YEARS OBSERVING PROXIMA FROM THE IAA-CSIC
In 2016, the international observation campaign RedDots, in which the IAA-CSIC participated, focused four telescopes on the star closest to us after the Sun, Proxima Centauri. They sought to detect the slight gravitational pull that a possible planet would exert on the star, which forces it to draw a small orbit and is translated into oscillations in its light. This is how Proxima b was found, a planet with a minimum mass equivalent to 1.3 times that of the Earth and that revolves around Proxima Centauri every 11.2 days within the habitable zone, or the region around a star with favorable conditions for the existence of liquid water on the surface.
In 2017, researchers from the Institute of Astrophysics of Andalusia (IAA-CSIC) discovered a dust belt around Proxima through observations with the ALMA interferometer. Similar to the Kuiper Belt of our Solar System, it represented the discovery of remnant material from the formation of the planetary system closest to ours.
In January 2020, the discovery, also with the participation of the IAA-CSIC, of a possible second planet around Proxima Centauri was announced, thanks to data collected from Chile with the UVES and HARPS spectrographs of the European Southern Observatory (ESO). The observations, which spanned a total of seventeen years, revealed the presence of a signal with a period of 5.2 years compatible with the existence of a second planet around Proxima Centauri with a minimum mass of about six times that of Earth.
“A project of this kind could only be carried out because IAA specialists in various fields (physics of the atmospheres of the planets of the Solar System, stellar physics, search and study of exoplanets and processes of the interstellar medium) have joined forces and knowledge. This includes their experience both in theoretical modeling and in multi-wavelength observations, from radio to optical and infrared”, concludes Antxon Alberdi, director of the IAA-CSIC and participant in the study.
Video: Model of the auroral emission arising from the interaction between the planet Proxima b (the small circle in the movie) and its host star Proxima Centauri (the big circle). During its revolution around Proxima Centauri, the planet Proxima b impacts the host star magnetosphere (the green lines in the movie), accelerating charged electrons that propagate towards the magnetic poles of the star (orange lines). This process leads to abundant radio emission, which can be seen from Earth only when the star occupies particular phases of its rotation. The radio emission is also polarized, so that when the emission comes from the Northern hemisphere of the star magnetosphere, the light is polarized clockwise (RCP in the movie) and, when the emission comes from the Southern hemisphere, the light is polarized anti-clockwise (LCP in the movie). Credits: Corrado Trigilio (INAF, Italy).
Reference: M. Pérez-Torres, J. F. Gómez et al. “Monitoring the radio emission of Proxima Centauri”. Astronomy & Astrophysics, 645, A77 (2021). http://www.aanda.org/10.1051/0004-6361/202039052
Provided by IAA-CSIC