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Understanding how large stars capture planets and take them out of orbit
What is “star nursery”
The Earth’s Sun is four light years from the nearest star, and only our planetary system is its company. However, this is not entirely typical for the Universe: most often, young stars appear in groups called “stellar nurseries”. These are dense nebulae in which hundreds of thousands of young stars interact with each other, exchange energy, and after a few million years they disperse throughout the galaxy. A new study by two British scientists shows how large stars in such formations can steal planets from each other.
Creation of new planets around stars
Almost immediately after the birth of young stars, planetary systems begin to form around them. Their sources are fine dust particles (each no more than 0,1 mm in diameter). They revolve around a star in a disk from which planets gradually form. On a galactic scale, this process is quite fast. Planets can form in less than 1 million years from the birth of a star, while it is still interacting with similar celestial bodies in a stellar nursery. Planets are constructed so rapidly because of the dense nebula, in which particles can more easily coalesce.
Interception of planets
After formation, a planet that has arisen around a young star can be intercepted by large stars. These giants are heavier, more massive and brighter than the Sun, but their lives are much shorter – a few million years compared to 10-11 billion. By the force of their gravity, they are able to “drag” the planets from the mother’s orbit and capture them from “free floating” in the “stellar manger”.
Appearance of “beasts”
In 2021, researchers from Stockholm University discovered that in one “stellar nursery” on the outskirts of the Milky Way there are two planets – one revolves around a star nine times heavier than the Sun, and the other ten times heavier. They were called “beasts”. Initially, they tried to explain their formation as follows: they formed from clots of gas, like Jupiter and Saturn in the solar system. However, this version was rejected due to the fact that in the “manger” bright ultraviolet radiation from nearby stars would not allow particles to connect in this way.
A new explanation for the formation of the “beasts”, put forward by British scientists, is that they ended up in their orbits due to a planetary “robbery”: they were born around small stars, but were captured by larger ones.
The researchers emphasize that “beast”-like celestial bodies are usually in wide orbits and are not at all like spherical, closely spaced planets in our solar system. Perhaps it also has a stolen, yet undiscovered planet, but the existing eight definitely formed around the Sun.