Our solar system is far larger than the space occupied by the eight planets. It extends all the way to the Oort cloud. The Oort Cloud is 2.000 to 100.000 times farther from the Sun than the Earth. Its farthest edge reaches the midpoint between the Sun and Alpha Centauri, the closest star to us. So, if Alpha Centauri also has its own Oort cloud, the two stars are more or less body-to-body.
However, we don’t know how the Oort Cloud formed.
The Mystery of Oort Cloud Formation
The Oort cloud does not have as many large celestial bodies as the inner solar system. Traveling through it in a spacecraft, you may not encounter a single large celestial body. But it actually consists of about 100 billion small objects, mostly icy comets and rocky asteroids. The gravitational pull of the sun is so weak that they are easily pushed out of orbit and into interstellar space. We can’t see them directly, but there’s plenty of evidence of their existence, such as comets that periodically fall from the Oort cloud into the inner solar system.
There is some evidence for larger objects hiding in the Oort cloud. For several years, scientists studying the orbits of Neptune and several of its neighboring dwarf planets have suggested that there might be an unknown planet tugging on them there. It has about 10 times the mass of Earth and is known as Planet Nine.
The formation of the Oort cloud is a mystery. The first is its shape. You see, the planets and asteroids of the inner solar system are in a disk around the sun, whereas the Oort Cloud is a vast, diffuse sphere that surrounds the solar system in every direction. Its spherical shape cannot be explained by the current theory of the formation of the solar system.
Secondly, the origin of the celestial bodies in the Oort cloud is also a mystery. The prevailing view is that they are “leftovers” scattered from the nebular disk that made the planets of our solar system. There are indeed some objects in the Oort cloud from the inner solar system, but they only account for 1/10 to 1/3 of the total.
If you also assume that there is a celestial body as large as Planet Nine hiding there, the Oort cloud becomes more difficult to explain.
The sun may have had a brother
Recently, two astronomers from Harvard University in the United States came up with a way to solve these two mysteries at the same time. The gist of it is that the sun must be assumed to have had a twin brother in childhood.
Most astronomers believe that the cloud of gas and dust that gave birth to the sun may have also harbored many other stars. This cloud of gas and dust is like a star’s “nursery.” After these stars form, they form a star cluster (a relatively dense collection of stars, but unlike a galaxy, a star cluster has no center). The interstellar space within the cluster is also filled with a large number of “rogue objects”, such as asteroids, planets and interstellar comets. They are ejected from various star systems in violent star-forming events.
As far as the sun itself is concerned, its gravitational force is not enough to take these wandering celestial bodies into its arms, forming its current Oort cloud. But if the sun had a companion star when it was young (this is not uncommon, more than half of all sun-like stars have a companion star), and they form a binary star system, the situation is very different. The combined gravitational pull of the two sun brothers is much stronger than if they were alone, making it easier to capture small objects from interstellar space, or even large ones like the hypothetical Planet Nine.
This theory not only explains why there are so many celestial bodies in the Oort cloud, but also cleverly explains its shape. Because grabbing celestial bodies from interstellar space is random in all directions, a sphere around the sun is formed instead of a disk.
As for the Sun’s brother, it was lost later, most likely being pulled away by another passing star—a process that is also common in young star clusters. When it left, it may have also taken away some of the celestial bodies in the Oort cloud, making the Oort cloud we see now so “sparsely populated”.
How to prove that Sun had brothers?
To verify the authenticity of this conjecture, of course, it is best to point it to us in the vast sea of stars: “Here, that is the lost brother of the sun.” But unfortunately, if it exists, it is difficult for us to find it again. it’s gone. Because the stellar “club” the sun is in fell apart 4.5 billion years ago, and everything in the Milky Way has been stirred up too many times since then.
However, we can indirectly verify this conjecture based on other clues. If the sun did once have a companion star, the combination of the two could capture not only the envisioned Planet Nine, but also a large number of dwarf planets – which should still remain in the Oort cloud today.
Of course, there is no evidence for the existence of these dwarf planets, but that’s why we know so little about the Oort cloud. In 2021. the Large Synoptic Survey Telescope (LSST), completed in Chile, will scan the sky with unprecedented precision for such distant, faint objects. If LSST finds Planet Nine and a host of other dwarf planets in the Oort cloud, it would strongly suggest that our sun did indeed have a twin.