One in three Sun-like stars has already eaten their planets

The Sun gave us life and the Sun will take it away. We have known for a long time that our particular star will not always be the calm and benevolent star that it is now. Quite the contrary, 5 billion years from nowWhen its hydrogen fuel runs out, it will undergo a dramatic series of changes that in the end will cause it to swell like a balloon and become a red giant, a star very different from the current one, and so large that it will surely swallow up the inner planets of our system.

However, and without the need to reach these extreme phases of stellar evolution, a team of researchers has just discovered that many stars similar to the Sun have

already devoured some of the planets that surround them. Many, but how many?

In a study just published in ‘
Nature Astronomy
‘and led by Lorenzo Spina, an astrophysicist at the Astronomical Observatory of Padua, in Italy, has addressed this question and the result is surprising: up to a third of stars similar to ours have already swallowed their planets. The find could help astronomers to rule out star systems in their searches that most likely no longer contain Earth-like worlds.

Scientists have known for decades, by measuring the composition of stars, that many of them have devoured the planets they had in orbit. Rocky worlds are indeed rich in heavy elements such as iron, silicon or titanium, while stars are made primarily of much lighter gases such as hydrogen, helium or oxygen. For this reason, when a planet is eaten, its heavy elements are scattered through the outermost layers of the star, and can be detected by astronomers, who look for the light absorption signals typical of those elements.

“If a star is abnormally rich in iron, but not in other elements such as carbon and oxygen,” explains Spina, “that can be interpreted as the signature that a planet has been swallowed up.”

To find out how often this happens, Spina and his colleagues looked at 107 binary systems made up of two stars similar to the Sun. Binary stars are born from the same cloud of gas and dust, so their chemical compositions should be almost identical. The researchers also chose pairs of stars with very similar masses and temperatures, so that they could be considered as twin stars.

Well, in 33 of these theoretically identical pairs one of the two stars showed very high levels of iron and lithium compared to those of his partner, which reinforces the hypothesis that they had absorbed some nearby world. Although stars similar to the Sun are already born with a considerable amount of lithium, they tend to burn it very soon, during their first 100 million years of life, so finding that element in older stars clearly indicated its planetary origin.

The researchers also found that these “abnormal chemical signatures»Appeared more frequently in the hottest stars. Which, according to Spina, makes perfect sense, since hot stars have thinner outer layers, so material from a devoured planet would be concentrated in a smaller volume and easier to detect.

In this way, Spina and his team concluded that between 20% and 35% of the stars similar to the Sun have already absorbed some of their ‘lands’. These types of events can happen in systems in which the gravitational interactions between planets end up ‘pushing’ some of them towards the central star, or at least bringing them close enough to it so that the star vaporizes and devours them. slowly.

The issue had already been the subject of other studies, but this new research is the first that, with a much larger sample, has managed to discover a generalized trend in a high percentage of stars similar to the Sun.

Despite this, Spina believes very unlikely that our Sun has already swallowed any planet in the past, since it has few heavy elements when compared to those of other similar stars that have. The study, as has been said, will help ‘planet hunters’ looking for a second Earth to rule out, from the outset, solar systems in which their stars show such an unnatural abundance of heavy elements.


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