Universe: Every twelfth star has swallowed the planets

Signs of “contamination” from planetary or asteroid debris have already been detected in many stars. In such cases, the stellar atmosphere shows a clear richness in heavy elements, such as those found in rocky planets, but not in ordinary stars. However, it was previously unclear how often stars devour one of their own planets.

To find the answer to this question, you have to Fan Liu from Monash University in Melbourne and his team looked for pairs of stars that emerged from the same gas cloud. Using the European Astronomy Satellite “Gaya” They were able to identify 91 pairs whose distance and shared motion through space indicate that they were born together, so they are twin stars or double stars that must originally have had the same chemical composition, according to the paper just published in 2018. . Stady.

Weather differences

But as very careful observations using several large telescopes on Earth show, eight percent of these pairs show clear differences in the abundance of heavy elements in their atmospheres. Liu and his colleagues concluded that one of the two stars must have devoured a planet not long ago.

Computer simulations of planetary formation around young stars show that such catastrophes are not uncommon in the first 100 million years after the birth of a planetary system. “But such early events should not be detectable after several billion years,” the researchers emphasize. Because heavy elements sink into the interior of the star. However, the stars examined by the team are evolved stars that resemble our Sun in the normal phase of its life.

“Cosmic meals”

“It is possible that we see traces of later events, caused, for example, by perturbations from outside, such as another star passing close to us, or a large gaseous planet entering the inner system,” the team continues. The inner planets to bring them out of balance.

If a planet gets too close to its central star, it will be torn apart by its own gravity and its debris will fall onto the star. Such cosmic diets could be more common than previously thought, and thus play an important role in the late evolution of planetary systems.