Planets are born from the matter around stars, but a recent new study points out that at least a quarter of the stars in the universe will be recycled and swallowed shortly after the planets are born. These all show that our solar system and the earth are both ordinary , And extraordinary.
How rare is the solar system? Since the first discovery 30 years ago that there are also exoplanets that revolve around stars other than the sun, we know that many stars in the Milky Way also have planetary systems, but they are different from the solar system in many ways.
First of all, the eight planets in the solar system revolve around the sun in a stable and nearly circular orbit. This shows that the orbits of the planets have not changed much since they were formed. However, observing other planetary systems, you will find that most of them have experienced a rather chaotic past. Perhaps the relatively quiet growth history of the solar system is one of the reasons for the reproduction of life on Earth. When looking for exoplanets that may nurture life, if we have a way to judge planetary systems with similar growth experience, we can narrow the target range.
Secondly, about 75% of the stars in the Milky Way are M-type main sequence stars (red dwarfs), which are smaller and colder than the sun and have a longer life span. However, our sun is a G-type main sequence star (yellow dwarf). Only 7% of stars belong to type G stars. Now astronomers have also discovered that 20 to 35% of sun-like stars in the universe will devour their planets at a certain moment in their lives.
Rocky planets are rich in heavy elements such as iron, silicon and titanium, while stars mainly contain lighter substances such as hydrogen, helium, oxygen, and carbon. When a planet is swallowed, its heavy elements fall on the outer layer of the star, leaving obvious absorption characteristics in the latter’s spectrum. If a star is abnormally rich in iron but does not contain other elements such as carbon and oxygen, this can be explained. To devour the planet.
The team of the National Institute of Astrophysics of Italy inspected 107 binary star systems composed of sun-like stars. The chemical composition of the two stars in the binary system should be similar. However, the researchers found that 33 of these systems have a certain star ratio. Half stars are more iron-rich; secondly, iron-rich stars also contain more lithium than their companion stars. Generally, lithium will gradually disappear during the star’s life cycle (for example, the composition of the sun and the earth are highly similar, but the sun’s lithium content is higher than The earth’s lithium content is 100 times lower), the abnormally high lithium content detected in stars must be different.
Third, the iron content of these stars is even higher than that of other sun-like stars in the Milky Way. Various chemical differences can indicate that these stars have swallowed their own planets.
The number of G-type stars similar to the sun is running out. At least a quarter of the systems are in chaotic environment. Even if planets are born, they may not be able to grow up peacefully. This also makes the peaceful growth of the solar system even more valuable. Although in terms of the number of stars in the Milky Way, there are millions of stars in the galaxy that are similar to the sun, but if there is no suitable screening method, looking for Earth 2.0 is still like finding a needle in a haystack.
The new paper was published in the journal Nature Astronomy.
(The first picture is a schematic diagram, source: NASA)
