A recent breakthrough in astronomy has illuminated the mysterious dynamics of a binary star system, HD 135344 AB, where a giant planet was discovered orbiting the primary star— a star that had previously been overlooked. This discovery, documented in a recent study published in Astronomy and Astrophysics, reveals the fascinating ways in which planets form in binary systems. In the case of HD 135344 AB, while one of its stars continues to form planets, the other has already ceased the process, providing astronomers with an exceptional opportunity to study a planetary formation in its early stages.
This finding is significant because the discovery was made possible through the use of the Very Large Telescope (VLT) and its SPHERE exoplanet instrument, which allowed the team to directly image a planet that is roughly 10 times the mass of Jupiter. The results not only underscore the potential of advanced imaging technologies but also challenge previous assumptions about how planets evolve around binary stars.
The Surprising Discovery in HD 135344 AB
In the binary system HD 135344 AB, both stars are young, with the primary star classified as an A-type main-sequence star and its companion as an F-type main-sequence star. These two stars orbit each other widely, with separate protoplanetary disks. The intriguing aspect of this system is the fact that the primary star has already cleared away its disk, whereas its companion star still exhibits evidence of active planet formation.
Astronomers initially focused their attention on the secondary star, given the ongoing planet-forming processes visible in its disk. Features like spiral arms and central cavities pointed to planet-disk interactions. However, the primary star had been largely ignored due to the absence of a visible disk. This made it a prime target for direct imaging, which led to the stunning discovery of HD 135344 Ab, a young giant planet located at a distance of 15-20 astronomical units from its star.
A Lucky Break in Imaging the Planet
It took four years of meticulous observations to confirm the presence of HD 135344 Ab. As Tomas Stolker, lead author of the study and assistant professor at Leiden Observatory, put it, “Star A had never been investigated because it does not contain a disk. My colleagues and I were curious about whether it had already formed a planet. And so, after four years of careful measurements and some luck, the answer is yes.”
The challenge in detecting the planet was due to its small angular separation from its star, making it difficult to spot with high precision. “We’ve been lucky, though,” Stolker added. “The angle between the planet and the star is now so small that SPHERE can barely detect the planet.” This lucky timing allowed the team to capture images of the planet as it moved in its orbit, confirming that it was indeed a planet and not a background star.
Understanding the Formation of Giant Planets
The discovery of HD 135344 Ab also offers important insights into the process of planet formation. Scientists believe that the planet likely formed near the “snowline” of its star’s protoplanetary disk— a region where volatile materials like water, ammonia, and methane freeze and solidify. The snowline is thought to play a crucial role in the formation of giant planets because the availability of solid materials makes it easier for dust grains to stick together and grow into planets.
In their study, the researchers suggest that HD 135344 Ab might be part of a larger population of giant planets formed in the vicinity of the snowline. “These objects have remained challenging to detect since most surveys and observing strategies have not been optimized for such small separations,” the authors explain. The formation of these giant planets could provide valuable clues to the broader processes that shape planetary systems.
The Role of Astrometric Measurements
One of the key factors that enabled the detection of HD 135344 Ab was the high-precision astrometric measurements made by the team. “This study also highlights the importance of high-precision astrometric measurements to fully disentangle orbital from background motion in a region of non-stationary background stars,” the researchers noted. The ability to differentiate between the motion of the planet and that of background stars is crucial when studying distant objects like exoplanets.
As astronomers continue to improve their imaging techniques, the ability to detect planets at greater distances and with smaller separations will only increase. The upcoming release of data from the Gaia DR4 mission is expected to play a pivotal role in this process, with the potential to reveal more close-in giant planets in star-forming regions. “Gaia DR4 may reveal hints of similar close-in giant planets in star-forming regions, which will guide direct imaging searches and post-processing algorithms,” the researchers explain.
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