Debris remains show:

One in 12 stars has already devoured planets

Around one in twelve stars has already devoured at least one planet during its normal life phase. This is shown by observations of 91 stellar twins by an international research team.

Despite their common origin in a gas cloud, these pairs of stars show remarkable differences in their chemical composition. These differences can only be explained by cosmic events, scientists report in the scientific journal "Nature".

"Pollution" by debris from planets 
Astronomers have discovered signs of "pollution" by debris from planets or asteroids in numerous stars. In such cases, the atmosphere of the stars shows a clear enrichment with heavy elements that are typically found in rocky planets but not in normal stars. However, the frequency with which stars devour their planets was previously unclear.

Pairs of stars studied
To find answers to this question, Fan Liu from Monash University in Melbourne and colleagues have searched for pairs of stars that have emerged from the same gas cloud. With the help of the European astronomy satellite "Gaia", they identified 91 pairs whose distance and common movement through space indicate that they were formed together - in other words, they are stellar twins that originally had the same chemical composition.

However, further detailed observations with several large telescopes showed that eight percent of these pairs have significant differences in the abundance of heavy elements in their atmospheres. This leads to the conclusion that one of the stars must have swallowed a planet not too long ago.

Computer simulations of planet formation around young stars show that such events are not uncommon in the first hundred million years after the formation of a planetary system. "However, such events should no longer be detectable after several billion years," emphasize Liu and his colleagues. 

"Traces of later events"
"We therefore probably see the traces of later events," the researchers continue, "triggered, for example, by external disturbances - such as another star passing nearby or a large gas planet entering the inner system." Such disturbances can upset the orbits of the inner planets.

Such cosmic events could occur more frequently than previously assumed and play an important role in the late evolution of planetary systems.