Located 63.4 light-years from Earth in the constellation Pictor is the young and bright blue star, Beta Pictoris. In 2008, observations conducted from the ESO’s Paranal Observatory in Chile confirmed the presence of an extrasolar planet. This planet was Beta Pictoris b, a Super-Jupiter with an orbital period of up between 6890 and 8890 days (~19 to 24 years) that was confirmed by directly imaging it as it passed behind the star.
In August of 2019, a second planet was detected (another Super-Jupiter) orbiting closer to Beta Pictoris. However, due to its proximity to its parent star, it could only be studied through indirect means (radial velocity measurements). After conducting a reanalysis of data obtained by the VLT, astronomers with the GRAVITY collaboration were able to confirm the existence of Beta Pictoris c through direct imaging.
The researchers responsible for the research detailed their findings in two studies that appeared in the October 2nd issue of Astronomy & Astrophysics. The first was led by Mathias Nowack of the Kavli Institute for Cosmology (University of Cambridge) while the second was led by Anne-Marie Lagrange of the Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA) and the Paris Observatory.
As they explain in their first study, the GRAVITY collaboration combined light from four of the VLT’s large telescopes to conduct the very first direct observations of Beta Pictoris c. This was not only the first time that a planet was directly imaged this close to its parent star, it was also the first time that direct imaging was used to confirm a detection made using the Radial Velocity (aka. Doppler Spectroscopy) method.
For decades, astronomers have relied on radial velocity measurements to detect the presence of exoplanets. With hundreds of candidates discovered to date, it has been the second-most popular method (after the Transit Method) and is often combined with transits to confirm the existence of exoplanets. However, never before have candidates discovered using the radial velocity method been confirmed by direct observation.
This was only possible because of the GRAVITY instrument, a second-generation device that is part of the VLT’s Interferometer (VLTI). This instruments combines light from four VLT telescopes – either the four Unit Telescopes or the four Auxiliary Telescopes, each of which are assisted by Adaptive Optics (AO) – and then combines them into a virtual telescope, allowing for unprecedented detail and sensitivity.
As Frank Eisenhauer, the lead scientist of the GRAVITY project at the Max Planck Institute for Extraterrestrial Physics (MPE), said in a recent institute statement:
“It is amazing, what level of detail and sensitivity we can achieve with GRAVITY. We are just starting to explore stunning new worlds, from the supermassive black hole at the centre of our galaxy to planets outside the solar system.”
At the same time, the team was only able to observe Beta Pictoris c because new radial velocity measurements were able to precisely establish the orbital motion of the planet. This was the subject of the second paper, where they show how a combination of high-contrast imaging, long baseline interferometry, and radial velocity data allowed them to precisely predict the position of Beta Pictoris b so that GRAVITY was able to find it.
Their observations also allowed them to further constrain the orbital and physical properties of Beta Pictoris b and c and predict the closest approaches of both planets as well. What this revealed, however, was rather puzzling to the GRAVITY team. Beta Pictoris c is about 8 times as massive as Jupiter and is roughly 2.7 AU away from its star – about the same distance…
Read More: Those are Exoplanets. You’re Looking at Actual Exoplanets 63 Light-Years Away!