2023-09-20 11:35:57
Artistic representation of the planet 8 Ursae Minoris b, also known as “Halla”, in the middle of the debris field after a violent two-star merger. – WM KECK OBSERVATORY
MADRID, 20 Sep. (EUROPA PRESS) –
NASA’s TESS exoplanet search mission has discovered a planet that should have been gobbled up by the red giant star that, somehow, continues to orbit.
Planet 8 Ursae Minoris b orbits a star about 530 light years away that is dying. The star, a bloated red giant, would have been expected to expand beyond the planet’s orbit before receding to its current, still-giant size.
In other words, the star would have engulfed and destroyed any planet orbiting near it. However, the planet remains in a stable and almost circular orbit, NASA reports.
The discovery of this seemingly impossible situation, based on precise measurements made with the Transiting Exoplanet Survey Satellite (TESS), shows that the formation and destruction of planets is probably much more complex and unpredictable than many scientists might have thought.
As stars like our Sun approach the end of their lives, they begin to use up their nuclear fuel. They become red giants and expand to their maximum size. If that had happened in this case, the star would have grown from its center by up to 0.7 astronomical units, that is, approximately three quarters of the distance between the Earth and the Sun. It would have swallowed and destroyed any nearby planets in orbit in the process.
But planet b, a large gas world, is about 0.5 astronomical units, or AU, away. Because the planet could not have survived the dive, University of Hawaii astronomer Marc Hon, who published his discovery in Natureinstead proposes two other possibilities: The planet is actually the survivor of a merger between two stars, or it is a new planet, formed from the debris left by that merger.
The first scenario begins with two stars the size of our Sun in orbits close to each other, and the planet orbits both. One of the stars “evolves” a little faster than the other, going through its red giant phase, shedding its outer layers and becoming a white dwarf, the small but high-mass remnant of a star. The other barely reaches the red giant stage before the two collide; What remains is the red giant we see today. This merger, however, prevents the red giant from expanding further, preventing the destruction of the planet in orbit.
In the second scenario, the violent merger of the two stars expels a large amount of dust and gas, which forms a disk around the remaining red giant. This “protoplanetary” disk provides the raw material for the fusion of a new planet. It is a late-stage second life species for a planetary system, although the star is still nearing its end.
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