The Light Of Dying Stars Can Pulverize Asteroids

Artist's illustration of an asteroid breaking apart in space. NASA/JPL-Caltech

Even stars that don’t end their lives in supernovae can spell catastrophe for the smallest members of their solar system. New research suggests that the light of dying stars is enough to pulverize asteroids located hundreds of times further than the Earth-Sun distance from their star.

The study, published in the Monthly Notices of the Royal Astronomical Society, looked at the consequence of the YORP effect in stellar systems. Named after the four scientists that contributed to the idea (Yarkovsky, O'Keefe, Radzievskii, and Paddack), the YORP effect is when an asteroid spins itself to death due to stellar radiation.

Starlight has a small but not zero momentum. As we have seen with the successful solar sail tests in the last decade or so, photons from the Sun can push objects around. When starlight hits an asteroid, it is absorbed, redistributed internally, and then reemitted at a different location. 

Asteroids are large piles of space rocks that often remain together due to weak gravity; however, they are not well mixed, so the heating from stellar radiation and the subsequent emissions are not balanced. This imbalance in the emissions produces a small torque. Over time and with the star getting brighter and brighter, the torque increases. Since the gravity exerted on the asteroids is too weak to counterbalance the forces pulling the asteroids apart, the space rocks become dust. 

“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. 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,” lead author Dr Dimitri Veras, from the University of Warwick’s Astronomy and Astrophysics Group, said in a statement.

The work provides insight into the future of our Solar System. In about 6 billion years, our Sun will have run out of fuel, shedding its outer layers and collapsing into a white dwarf. This will mean bye to the asteroid belt in record time.

“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," said Dr Veras.

The simulations suggest that the size of the debris will plateau when objects are less than 100 meters (330 feet) across, as these often have quite high internal strength. The researchers think that by studying emissions from the asteroid debris around white dwarfs, it might be possible to gain insight into what the stellar system used to be like before the star died.

 

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