Like the Greek god Chronos, a large number of stars devoured their children. A third of stars, like our Sun, are known to have swallowed at least one planet of their own.
Quoted from Science Mag, Wednesday (1/8/2021) these findings can help astronomers rule out star systems that are unlikely to contain Earth-like planets.
"This will probably be one of the classic papers on this subject," commented Eric Mamajek, an astronomer at NASA's Jet Propulsion Laboratory who was not involved in the study.
Researchers have known for decades that stars can sometimes swallow their offspring. Rocky planets are rich in heavy elements such as iron, silicon, and titanium. While stars contain lighter materials such as hydrogen, helium, oxygen, and carbon. When a planet is swallowed, its heavy elements scatter in the outer layers of the star, leaving signs of absorption in its light.
"If a star is anomalously rich in iron but not in other elements such as carbon and oxygen, this could be interpreted as a sign of swallowing a planet," said Lorenzo Spina, an astrophysicist with the Padua Astronomical Observatory who led the study.
He and his colleagues investigated how often this happens by looking at 107 binary systems containing two Sun-like stars. Binary stars are born from the same cloud of gas and dust, so their chemical composition must be nearly the same. The team also selected pairs that were very close in terms of mass and temperature to each other.
In these 33 pairs, one of them showed increased iron levels compared to the other. This is a sign of planetary cannibalism. This same partner is also rich in lithium, giving further credence to the planetary 'chewing' hypothesis.
Although Sun-like stars are born with large amounts of lithium, they burn it in the first 100 million years of their life. So seeing it on an older star in the study sample suggests it may have come from a planet.
The team also found that abnormal chemical signatures appear more frequently in the hottest stars. That makes sense, because hot stars have thin outer layers—and planetary matter will be concentrated in smaller volumes, leaving more conspicuous marks.
Using these different lines of evidence, the team was able to model that between 20% and 35% of Sun-like stars consume some of their Earth-like offspring.
Such an event could occur in systems where gravitational interactions between the planets would be flung towards a central star or bringing it close enough for the star to slowly evaporate and devour it.
"This is clearly a strong trend. Planetary consumption has been studied before. But this new paper provides a much larger sample size and clear statistical evidence for the phenomenon," Spina said.
He thought that it was unlikely that our Sun would ever engulf any planet, because it was depleted of heavy elements compared to other planets in its class.