• Supercharged light from dying stars cause asteroids to break up into smaller pieces
  • The process repeats again and again until the asteroids are small enough to be unaffected
  • Essentially all the asteroids in the system would be destroyed in just a million years
  • The debris field left after the destruction can be studied by astronomers

About 90 percent of the stars in the Universe are main-sequence stars, including our own Sun. After such stars burn up all their hydrogen fuel, they enter the giant branch stage when they become hundreds of times more massive and ten thousand times more luminous, thereby producing intense electromagnetic radiation.

At this stage, which lasts for just a few million years before a star sheds its outer layers and becomes a white dwarf, the supercharged light that the star is emitting is strong enough to cause even distant asteroids to spin at high speeds until they essentially tear themselves apart. The process repeats itself again and again until the asteroid is small enough to be unaffected.

This process is called the YORP effect, named after the four scientists who contributed to the formation of the concept. It happens when the asteroids absorb intense radiation from the star and emit it in a different location. This then causes an imbalance that leads the asteroid to eventually spin at break-up speeds.

Pulverized Asteroids

In a new study published in the Monthly Notices of the Royal Astronomical Society, a pair of researchers analyzed these effects as well as how fast they happen and, found that the asteroids in a system would all be pulverized in a relatively short amount of time of just a million years. In fact, according to the researchers, all the asteroids in a system, except for the farthest and smallest ones, would be destroyed in just that short period.

The researchers further note that in many cases, there could be over 10 of these events before an asteroid is small enough to be unaffected by the YORP effect. It is much like in the classic arcade game, Asteroids, where bigger asteroids break up into smaller and smaller pieces after each event. Some of the debris can even be "double asteroids," or asteroids that revolve around each other as they orbit the star.

“For one solar-mass giant branch stars - like what our Sun will become – even exo-asteroid belt analogs 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,” lead author Dr. Dimitri Veras of the University of Warwick explained.

This effect, however, also depends on the "internal strength" and distance of an asteroid. Larger asteroids tend to be broken up more quickly because smaller asteroids have greater internal strength. The effect also lessens the farther an asteroid is from the star.

Debris Field

After the violent pulverization of the asteroids, what will be left is a debris disc formed around the white dwarf as a remnant of the quick and violent event. Such debris fields polluting white dwarfs are key to understanding the existence of debris-rich systems and major planets around white dwarfs.

“These results help locate debris fields in giant branch and white dwarf planetary systems, which is crucial to determining how white dwarfs are polluted. We need to know where the debris is by the time the star becomes a white dwarf to understand how discs are formed. So the YORP effect provides important context for determining where that debris would originate,” Dr. Veras said.

In the case of our own solar system, the researchers estimate that the Sun's supercharged light will pulverize the asteroid belt in six billion years.

Two Very Different Asteroids
Image of two different asteroids captured by NASA. NASA/JPL/JHUAPL