Using the National Science Foundation’s Very Long Baseline Array (VLBA) supersharp radio “vision”, astronomers discovered a Saturnsmall in orbit around a small cold star 35 light years from Earth. This is the first discovery of an extrasolar planet with a radio telescope that uses a technique that requires extremely precise measurements of the position of a star in the sky, and only the second discovery of the planet for that technique and for radio telescopes.
The technique has long been known, but has proven difficult to use. It involves tracking the actual movement of the star in space, hence the detection of a tiny “wobble” in that movement caused by the gravitational effect of the planet. The star and the planet orbit around a position that represents the center of mass for both combined. The planet is indirectly revealed if that position, called the center of gravity, is far enough away from the star’s center to cause a wobble that a telescope detects.
Animations side by side of the star and the planet in orbit around their common center of gravity (center of gravity) and of the couple moving through space while they orbit, creating the “wobble” of the star that revealed the planet. Credit: Bill Saxton, NRAO / AUI / NSF
This technique, called the astrometric technique, should be particularly good for detection Jupiter-as planets in orbits distant from the star. This is because when a huge planet orbits a star, the oscillation produced in the star increases with a greater separation between the planet and the star, and at a certain distance from the star, the bigger the planet, the bigger the swing produced.
Beginning in June 2018 and continuing for a year and a half, astronomers tracked down a star called TVLM 513-46546, a cold dwarf with less than one-tenth the mass of our Sun. In addition, they used data from nine previous VLBA observations. of the star between March 2010 and August 2011.
An extensive analysis of the data from those periods of time revealed a revealing vibration in the movement of the star indicating the presence of a planet comparable in mass to Saturn, in orbit around the star once every 221 days. This planet is closer to the star than Mercury is to the sun.
Beautiful little stars like TVLM 513–46546 are the most numerous star type in ours Milky Way The galaxy and many of them have discovered smaller planets, comparable to those of Earth and Mars.
Conception of the artist of the dwarf star TVLM-513-46546 and his newly discovered planetary companion. Credit: Luis A. Curiel Ramirez
“Giant planets, like Jupiter and Saturn, should be rare around small stars like this, and the astrometric technique is best for finding Jupiter-like planets in large orbits, so we were surprised to find a lower mass, similar to Saturn planet in a relatively compact orbit. We expected to find a more massive, Jupiter-like planet in a wider orbit, “said Salvador Curiel, of the National Autonomous University of Mexico.” To detect the orbital movements of this mass planetary companion under Jupiter in a such a compact orbit was a big challenge, “he added.
More than 4,200 planets have been discovered in orbit around stars other than the Sun, but the planet around TVLM 513–46546 is only the second to be found using the astrometric technique. Another highly successful method, called the radial velocity technique, also relies on the planet’s gravitational effect on the star. This technique detects the slight acceleration of the star, towards or away from the Earth, caused by the movement of the star around the center of gravity.
“Our method integrates the radial velocity method which is more sensitive to planets in orbit in nearby orbits, while ours is more sensitive to massive planets in orbits further away from the star,” said Gisela Ortiz-Leon of the Max Planck Institute for Radio Astronomy in Germany. “In fact, these other techniques have found only a few planets with characteristics such as the mass of the planet, the orbital size and the host stellar mass, similar to the planet we have found. We believe that VLBA, and astrometry technique in general, could reveal many other similar planets. “
A third technique, called the transit method, also very effective, detects the slight darkening of the light of the star when a planet passes in front of it, seen from Earth.
The Very Long Baseline Array (VLBA) astrometry has detected an “oscillation” in the motion of a small star caused by the gravitational effect of a size of Saturn exoplanet. First radio discovery of an exoplanet with this technique. Credit: NRAO / AUI / NSF
The astrometric method was successful in detecting nearby binary star systems and was recognized as early as the 19th century as a potential means of discovering extrasolar planets. Over the years a series of discoveries of this type have been announced, which have failed to survive further checks. The difficulty was that the stellar wobble produced by a planet is so small when viewed from Earth that it requires extraordinary precision in positional measurements.
“The VLBA, with antennas separated by as many as 5,000 miles, has provided us with the great resolution power and the extremely high precision necessary for this discovery,” said Amy Mioduszewski, of the National Astronomical Observatory of Radio. “In addition, the improvements made to the sensitivity of the VLBA have given us the quality of the data that made it possible to do this job now,” he added.
Curiel, Ortiz-Leon, Mioduszewski and Rosa Torres of the University of Guadalajara in Mexico reported their results in Astronomical diary.
Reference: “An astrometric planetary candidate at M9 Dwarf TVLM 513–46546” by Salvador Curiel, Gisela N. Ortiz-León, Amy J. Mioduszewski and Rosa M. Torres, 4 August 2020, Astronomical diary.
DOI: 10.3847 / 1538-3881 / ab9e6e
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