ISLAMABAD: Astronomers have made a remarkable discovery by identifying an exoplanet named Halla that managed to survive the violent transformation of its hot star. This star, larger than our sun, had exhausted its hydrogen fuel and was being fueled by helium when the surprising revelation was made. The findings about this gaseous Jupiter-like planet, located 520 light-years away from Earth in the Ursa Minor constellation, were published in the journal Nature. Halla was first detected in 2015 by astronomers from Korea.
Halla is classified as a “hot Jupiter,” a category of exoplanets that share similarities in size with Jupiter and orbit their host stars at close proximity, resulting in higher temperatures. What astonished scientists is that Halla survived despite its star undergoing a transition that typically obliterates nearby planets.
Using Nasa’s Transiting Exoplanet Survey Satellite, scientists observed the star named Baekdu and discovered that it had depleted its hydrogen reserves and was being supplied with helium at its core. This suggests that the star had expanded into a red giant at one point. Normally, the engulfment of a star has catastrophic consequences for planets in close orbits. However, Halla managed to endure in close proximity to its giant star, defying expectations.
Halla Survives in Immediate Vicinity of Giant Star
Dr. Dan Huber, study coauthor and associate professor at the Institute for Astronomy of the University of Hawaii at Manoa, expressed surprise, stating, “When we realized that Halla had managed to survive in the immediate vicinity of its giant star, it was a complete surprise. As it exhausted its core hydrogen fuel, the star would have inflated up to 1.5 times the planet’s current orbital distance—engulfing it completely in the process—before shrinking to its current size.”
This discovery raises compelling questions about the fate of planetary systems with companion stars. In our own solar system, it is projected that the sun will reach the end of its life in 5 billion years and expand to a size that could engulf and obliterate planets. With this in mind, researchers are eager to determine how systems with companion stars and their orbital planets fare.
The team of astronomers also conducted follow-up observations in 2021 and 2022, confirming the planet’s stable orbit for over a decade. Halla completes its orbit in 93 Earth days. Dr. Marc Hon, lead author of the study, noted the importance of multiple telescopes on Maunakea in validating the existence of Halla and the subsequent inquiry into how the planet managed to survive.
Astronomers are now investigating the possibility of Halla withstanding such a cataclysmic stellar event. While it is commonly believed that planets initially orbit at a distance from their stars and then move closer over time, scientists are questioning whether this applies to Halla. Dr. Huber stated, “We just don’t think Halla could have survived being absorbed by an expanding red giant star.” It is plausible that Halla was never in danger to begin with, as the system may have originally consisted of two stars that merged, preventing either from expanding enough to engulf the planet.
Alternatively, experts propose the intriguing notion that Halla is a young planet formed from a gas cloud resulting from the collision of two stars, making it a second-generation planet created within the system.
