A ghost in the universe! Why are there 100 billion wandering planets in the Milky Way?

2021-09-13 | Cosmic Observation Record Original Collection4 |

In 2019, the sci-fi movie "The Wandering Earth", adapted from the novel of the same name by Liu Cixin, let many people know the smallness of the earth in the universe and the precariousness of human civilization.

Among them, the heavy element fusion engine is used to promote the earth, and the plot picture of "carrying the earth to wander" has become a classic scene in the history of science fiction movies.

But what I want to tell you is

In the eyes of most people, "Wandering Earth", which is full of science fiction, is actually the most "unsci-fi" plot in the whole movie, because the wandering planets really exist in the universe.

Astronomers tell us that there are 100 to 400 billion stars in the Milky Way galaxy, and they basically carry several planets around them, ranging from one or two, such as the neighboring galaxy 4.22 light-years away, and as many as seven or eight.For example, our solar system. Anyway, there are very few solitary star systems.

Therefore, the number of planets in the entire Milky Way galaxy is several times more than the number of stars, and can even reach a trillion level. Among these trillions of planets, some planets are not the same as the earth, and have been orbiting since the day of birth.The parent star revolves, but belongs to a wandering planet without a star, wandering in the universe all day long.

It's a long story for children without mothers

In astronomy, stars are the mothers of planets. Take our solar system as an example. After the molecular cloud containing heavy elements collapsed into the sun 4.6 billion years ago, the remaining heavy elements slowly became planets under the action of the sun's gravity., So there is no earth without the sun, but not all planets can stay in the galaxy.

In a newly born star system, in addition to being affected by the gravitational force of stars, planets are also affected by the gravitational force of their "colleagues" around them. In the simulations conducted by astronomers, multi-planetary systems such as the sun are evolving during the evolution process.In the early days, at least one planet would be affected by the gravitational slingshot of a nearby giant planet, and then would be ejected above the speed of the third universe, becoming a wandering planet sprinting out of the solar system.

In addition to the unlucky ones that were ejected, there are some wandering planets caused by innate factors. They should be called "brown dwarfs" to be exact, and they belong to failed stars.

In our universe, the lower limit of the mass of a star is 0.07 times the mass of the sun, which is approximately equivalent to 70 to 80 Jupiters. Only when this mass is reached, the hydrogen element in the core area can obtain sufficient pressure and temperature to produce a nuclear fusion reaction., To become a star in the true sense.

But there are quite a few planets in the universe, their mass has reached 0.06 times, or 0.065 times the mass of the sun, very embarrassingly at the critical point of the star, and it has been unable to break through.

These unlucky ones, although the mass is ridiculously large compared to the planets, they are still part of the planetary team, and they are also an important part of the wandering planets.

If the wandering planet has memory

Since its birth, it may not have received the light and heat from its parent star. It only accompanies the dark and silent space all day long, and the surface temperature is close to absolute zero. Although it is theoretically possible to "break into" a new one in the futureThe star system of China, anchored in its orbit and ended the wandering life, but in the universe where the average distance between stars is a few light years, the probability of this happening is wirelessly close to zero.

Among all wandering planets, the most unlucky ones are those born on the edge of galaxies, because the distance between stars and stars is only a few light years, and the distance between galaxies and galaxies is often hundreds of thousands of light years to millions of light yearsBetween years, so when the wandering planet at the edge of the galaxy enters the interstellar space in the opposite direction, it is like an ant falling into the Pacific Ocean. This life is over.

A paper published in the International Journal of Astrobiology in 2019 believes that if a wandering planet is a planet with an ocean at the beginning, its ocean will be frozen during the wandering process, thus becoming an isolated environmentThe blanket allows the ocean near the core area of ​​the planet to remain liquid, and even to produce life under the heat of the core area.

This kind of life, born under the ice layer and in the ocean, cannot be discovered by the outside world until it develops to a certain extent. Perhaps this is the reason why human beings have not been able to find alien life.


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