In our galaxy, finding exoplanets is a critically vital endeavor. The more exoplanets we discover, the greater our knowledge of our own Solar System and the origins of life in the universe will be. Over 4,000 exoplanets have been verified as of this writing, but a new discoveries may broaden our search and enable us to uncover exoplanets that have been too difficult to find in the past.
The recently found exoplanet, which has a mass equal to Saturn's, circles a tiny, chilly red dwarf star that is 35 light-years distant and is exactly at the lower mass limit for main sequence stars. However, this situation is so novel in many ways than only the planet and star.
The unique aspect of this finding is how it was made possible by the use of a radio telescope to follow the star's motion across the Milky Way and see the gravitational wobble caused by an orbiting exoplanet. This very challenging feat, known as the astrometric approach, has never before been used effectively with a radio telescope.
It's not a novel concept to look for an exoplanet using an orbital wobble. You see, a planetary system's orbital center is not located in the star's center. Instead, the system's bodies circle a single gravitational center known as the barycentre. For instance, the Solar System's barycenter is located slightly beyond the Sun's surface, mostly as a result of the gravitational pull of Jupiter and Saturn.
This impact may be seen in the way light wavelengths are compressed or stretched when the star moves when we see other stars with huge, tightly orbiting exoplanets. Doppler spectroscopy, often known as the radial velocity method, is one of the more used techniques for discovering exoplanets.
The astrological method is a bit unique. The Milky Way's stars move around the galaxy rather than being stationary in space, and astrometry is the study of this motion. Therefore, the astrometric method searches for deviations from a straight line of movement rather than considering variations in wavelengths.
Exoplanets with wider orbits around their stars, which Doppler spectroscopy cannot detect, may be found using this technique.
According to astronomer Gisela Ortiz-Leon of the Max Planck Institute for Radio Astronomy in Germany, "Our technique complements the radial velocity method, which is more sensitive to planets circling in tight orbits, while ours is more sensitive to big planets in orbits distant from the star."
"In fact, only a handful planets with traits like the planet we discovered have been discovered using these other methods. These traits include planet mass, orbital size, and host star mass. We think that the VLBA and the astrometry method in general might find a lot more planets that are comparable."
The US is home to a large network of 10 radio antennas known as the Very Long Baseline Array (VLBA). The study team, under the direction of astronomer Salvador Curiel of the National Autonomous University of Mexico, traced a tiny star known as TVLM 513-46546 through space for 18 months beginning in June 2018.
Data were painstakingly and carefully analyzed, and it became clear that the star was not moving in a perfectly straight line but rather was pursuing a twisting course. The periodicity and amplitude of the wiggle indicated the presence of a planet with an orbit of 221 days and a mass of between 38 and 46 percent of Jupiter, making it somewhat more massive than Saturn, which has a mass of around 30 percent of Jupiter.
"We were startled to discover a lower mass, Saturn-like planet in a reasonably compact orbit since giant planets like Jupiter and Saturn are predicted to be uncommon orbiting tiny stars like this one, and the astrometric approach is excellent at detecting Jupiter-like planets in wide orbits. We anticipated discovering a planet with a larger orbit, more massive than Jupiter "said Curiel.
The astrometric method is more often employed to investigate binary stars since they are gravitationally attracted to one another more strongly than planets are. Although it has been used to research exoplanets that are already known, the astrometric approach has only ever been used once to find an exoplanet using a radio telescope.
But earlier this year, a different team of researchers reported using a radio telescope for the first time to find an exoplanet. Instead of using astrometry, they did it by observing the circular polarization of radio waves produced as a planet moved across the magnetic field of a red dwarf.
Consequently, despite the fact that the discovery was difficult for Curiel's team, their eventual success demonstrates the potential of both radio telescopes and the astrometric methodology for discovering planets that other methods overlook.
The Gaia telescope is currently surveying the Milky Way and producing the most precise and thorough astrometric map of the galaxy to date; it is anticipated that this data will completely open up the field of astrometric exoplanet detection and lead to the discovery of tens of thousands of new exoplanets.
The Astronomical Journal has published the study.
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