According to new research by University of Warwick and University of Colorado, Boulder scientists, electromagnetic radiation from stars at the end of their giant branch phase — lasting just a few million years before they collapse into white dwarfs – would be strong enough to spin even distant asteroids at high speed until they tear themselves apart; as a result, even Solar System’s asteroid belt will be easily pulverized by the Sun billions of years from now.
An artist’s impression of an asteroid belt around the bright star Vega. Image credit: NASA / JPL-Caltech.
After main sequence stars like our Sun have burnt all their hydrogen fuel, they then become hundreds of times larger during a giant branch phase and increase their luminosity 10,000-fold, giving out intense electromagnetic radiation.
When that expansion stops, a star sheds its outer layers, leaving behind a dense core known as a white dwarf.
The radiation from the star will be absorbed by orbiting asteroids, redistributed internally and then emitted from a different location, creating an imbalance.
This imbalance creates a torque effect that very gradually spins up the asteroid, eventually to break-up speed at one full rotation every two hours. This effect is known as the YORP effect, named after four scientists (Yarkovsky, O’Keefe, Radzievskii, Paddack) who contributed ideas to the concept.
Eventually, this torque will pull the asteroid apart into smaller pieces.
The process will then repeat itself in several stages and asteroids will break down into smaller and smaller objects after each destruction event.
In most cases, there will be more than ten fission events — or break-ups — before the pieces become too small to be affected.
“When a typical star reaches the giant branch stage, its luminosity reaches a maximum of between 1,000 and 10,000 times the luminosity of our Sun,” said lead author Dr. Dimitri Veras, a researcher at the University of Warwick.
“Then the star contracts down into an Earth-sized white dwarf very quickly, where its luminosity drops to levels below our Sun’s.”
“Hence, the YORP effect is very important during the giant branch phase, but almost non-existent after the star has become a white dwarf.”
“For one solar-mass giant branch stars — like what our Sun will become — even exo-asteroid belt analogues will be effectively destroyed.”
“The YORP effect in these systems is very violent and acts quickly, on the order of a million years.”
“Not only will our own asteroid belt be destroyed, but it will be done quickly and violently. And due solely to the light from our Sun.”
“The remains of these asteroids will eventually form a debris disk around the white dwarf, and the disk will be drawn into the star, ‘polluting it’.”
“This pollution can be detected from Earth by astronomers and analyzed to determine its composition.”
The study was published in the Monthly Notices of the Royal Astronomical Society.
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Dimitri Veras & Daniel J. Scheeres. 2020. Post-main-sequence debris from rotation-induced YORP break-up of small bodies — II. Multiple fissions, internal strengths, and binary production. MNRAS 492 (2): 2437-2445; doi: 10.1093/mnras/stz3565
