Astronomers have discovered a planet that appears to have survived a doomsday scenario. The “hot Jupiter” orbits a giant star that logically should engulf it, but the team has some hypotheses about how it might still be standing.
Whether still habitable or not, the Earth itself has a severe limit on how long it can live—in about five billion years, the Sun will run out of combustible hydrogen fuel and start fusing helium. This would cause it to swell into a red giant, increasing its size and engulfing Mercury, Venus and Earth. Eventually it will blow off its outer layers, leaving behind a white dwarf that will gradually cool down to the background temperature of space over trillions of years.
A similar fate awaits countless worlds orbiting other stars. But now, astronomers have discovered a “zombie” planet that seems to have defied all odds to survive such a catastrophe. This dramatic story takes place in a star system relatively close to Earth, only about 520 light-years away.
The lucky planet, named Halla, orbits a giant star called Baekdu in the constellation Ursa Minor. Baekdusan is almost 11 times as wide as the sun but only 1.6 times as massive as the sun, and Halla orbits it fairly close, less than half the distance between Earth and the sun.
In the new study, astronomers examined the star in more detail and found that it was already fusing helium, suggesting it had previously gone through a red giant phase. According to their calculations, Mt. Baekdu will swell far beyond Halla’s current orbit by then.
Dr Dan Huber, second author of the study, said: “When a star exhausts its core hydrogen fuel, it expands to 1.5 times the planet’s current orbital distance, engulfing it completely in the process, before shrinking back to its current size. “. “Being engulfed by a star usually has catastrophic consequences for a planet in close orbit. We were completely surprised when we realized that Halla was able to survive near its giant star.”
So how did it survive being engulfed? The most likely explanation, scientists say, is that this is not the case. Instead, they hypothesize that Armageddon was averted by a second star that once existed in the system. As the two stars grew older, they sucked material from each other, preventing expansion until they finally merged into what is now Mount Paektu. This process does not involve growth and phagocytosis.
The alternative is that Hara wasn’t there that long. When the two stars collided, they likely created clouds of gas that cooled to form Hanla as the new “second-generation” planets in the system.
Whatever happened, it’s an interesting system that could teach astronomers about the life and death of planets and stars.
The study was published in the journal nature. An animation of the merging and nascent scenes can be seen in the video below.