To date, 5,084 exoplanets have been confirmed in 3,811 planetary systems, with another 8,912 candidates awaiting confirmation.
These discoveries have provided astronomers with detailed sampling of the types of planets that exist in our universe, ranging from gas giants several times the size of Jupiter to smaller, rocky bodies like Earth.
So far, the vast majority of them have been detected using indirect methods – such as the transit method (transient photometry) and the radial velocity method (Doppler spectroscopy) – while the rest have been detected using various other methods.
And in a recent study, an international team of astronomers used the National Science Foundation’s (NSF) Very Long Baseline Array (VLBA) network to discover a Jupiter-like planet orbiting in a binary system (GJ 896AB) located about 20 light-years from Earth. .
Using a method known as Astrometry, the team was able to detect this planet by the “oscillation” it makes as it orbits around the two larger stars in the system. Moreover, this method allowed the team to create the first 3D structure of a binary system and a planet orbiting one of its stars.
The research team was led by Salvador Coriel Ramirez, a researcher at the Institute of Astronomy at the National Autonomous University of Mexico (UNAM). He was joined by colleagues from UNAM and researchers from the Max Planck Institute for Radio Astronomy (MPIFR) and the National Radio Astronomy Observatory (NRAO).
The paper describing their research, titled “The Three-Dimensional Orbital Geometry of a Binary Dwarf System and its Planetary Companion,” was published Sept. 1 in The Astronomical Journal.
The system under study, GJ 896AB, consists of two red dwarf stars orbiting each other. The larger of the two, which orbits a Jupiter-like exoplanet (GJ 896 Ab), has a mass about 44 percent as much as our sun, while the smaller has a mass of about 17 percent.
They are separated by close to the distance between Neptune and the Sun (about 30 AU) and have an orbital period of 229 years. As Corell explained in an NRAO press release, the 3D mapping they did could not be achieved using other exoplanet detection methods.
“Since most stars are in binary or multiple systems, being able to understand systems like this one will help us understand planet formation in general,” he said.
In addition, M-type (red dwarf) stars are the most common in the universe, accounting for about 75 percent of the stars in the Milky Way alone.
These low-mass, faint stars can remain in their main-sequence phase for up to 10 trillion years and are notable for supporting smaller rocky planets—such as Proxima b and d and the seven-planet system TRAPPIST-1.
In their study, Curiel and colleagues combined VLBA data obtained between 2006 and 2011 (and new data obtained in 2020) with observations made on the system between 1941 and 2017.
The accuracy provided by the ten VLBA telescopes across the United States produced extremely accurate measurements of the positions of the stars over time.
They then performed a comprehensive analysis of the data that revealed the stars’ orbital motions and their combined motions through space. This process, whereby the position of the stars and their proper motion are measured, is known as stellar scaling.
Their detailed assessment of the larger star’s motion showed a slight wobble caused by the star’s gravitational influence, revealing a planet orbiting it. Based on the level of gravitational influence, the team calculated that the planet is a gas giant, roughly twice the mass of Jupiter.
They also determined that it orbits its parent star at a distance slightly less than the distance between Venus and the Sun, has an orbital period of 284 days, and is included approximately 148 degrees from the two stars’ orbits.
“This means that the planet is moving around the main star in the opposite direction to the secondary star around the main star,” said co-author Gisela Ortiz-Leon, a researcher with UNAM and MPIA….This is the first time such a dynamic structure has been observed in a planet associated with a binary system. compressed presumably formed in the same protoplanetary disk.”
Astrometric technology will be a valuable tool for characterizing more planetary systems, which will benefit from observatories such as the planned Very Large Next Generation Array (ngVLA).
This massive network will consist of 244 18-meter (59 ft) dishes spread over 8,860 kilometers (5,505 miles), with an additional short-spaced group of 19 6-meter (20 ft) dishes at the telescope’s core.
The improved sensitivity will allow astronomers to detect smaller, rocky planets orbiting near their stars – where “Earth-like” planets are most likely to reside.
“Further detailed studies of this and similar systems can help us gain important insights into how planets form in binary systems. There are alternative theories of the formation mechanism, and more data could indicate which one is more likely,” said co-author Joel Sanchez Bermúdez of UNAM.
In particular, current models suggest that such a large planet is unlikely to be a companion to such a small star, so perhaps these models need adjusting.
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