Astronomers have found that most (about half or even 85% ) of the bright spots we see in the night sky are multiple stars: that is, pairs or trios of stars (and even larger groups); they are simply so far away that we only see a single point. So is the Sun exceptional for being a unique star?
But the truth is possible that in the past it was not like that, and that the Sun really had a partner. It may seem implausible but it is the hypothesis recently proposed by a group of astronomers to explain the existence of the Oort cloud , a vast region on the outskirts of the solar system in which there are hundreds of billions of icy bodies, and whose origin does not it is entirely clear. Their findings have been published in ” Astrophysical Journal Letters .”
«We show that a binary companion of the same mass as the Sun – write the authors, led by Amir Siraj , a researcher at Harvard University (USA) – located at a separation of 103 AUs (one AU is the distance between Earth and the Sun) would have increased the probability of observing the population that we find in the Oort cloud.
The mystery of the Oort cloud
The Oort cloud is a region of unknown extent, reaching a distance of thousands or hundreds of thousands of times the separation between the Earth and the Sun. It is believed that there is a large population of comets and other icy objects of considerable size, because, from time to time, gravity pulls them into the solar system, allowing us to view them with telescopes or impacting planets.
Although it may seem hard to believe, it is still not entirely clear how this gigantic cloud of space “debris” formed . It is considered that the gravity of the gaseous planets expelled them from the interior of the solar system, during their formation, or that the Sun was stealing objects from other nearby stars.
In both cases, scientists have run simulations to find out if these hypotheses can explain what we observe today, but they have not been very successful. The numbers don’t say that these options are impossible, but they do say that they are unlikely.
“Capture models suffer because the truth is that it is very difficult to capture enough objects”, explained Siraj in ” Cosmosmagazine.com “. At least from what we know of the solar system so far, it seems likely that some piece of the puzzle is missing.
So Amir Siraj’s team has tried something else. They have drawn simulations in which they have incorporated another star into the solar system. Thus, they have been able to verify that it is easier to explain the existence of the Oort cloud if the solar system was inhabited by a binary star : this multiple system would have been more efficient in capturing the objects that today form the Oort cloud.
The existence of this new Sun could also shed some light on the enigma of Planet 9, a hypothetical world four or five times more massive than Earth and located at a great distance from the Sun. It has never been glimpsed, but its influence seems to be sensed in a part of the population of trans-Neptunian objects, an army of small bodies situated beyond Neptune.
Astronomers are looking for it, but how it could have gotten to its supposed position cannot yet be explained: One possibility is that it formed very far away, or that, again, gravity drove it to the outskirts of the inner solar system . The first is very difficult to explain and the second does not fit, as the numbers show … Unless another star is added to the solar system, as Amir Siraj’s team has found out.
If it existed to this day, this additional star would not make Earth’s sky look like Tatooine’s. According to the researchers, it would be so far away, about 150,000 million kilometers, that it would be rather a very bright point, but less than the full Moon.
Assuming there had been another sister sun, some process would have to explain its disappearance. According to Siraj, the separation most likely occurred in the first 100 million years of the solar system’s life. A gravitational interaction with another nearby star would have ejected the Sun’s brother into interstellar space.
“It ‘s a good idea,” he said in ” Cosmosmagaine.com ” Mike Brown, an astronomer at the California Institute of Technology, which is engaged in the search for Planet 9. “The general idea that the sun began as a binary is not controversial. ‘
In Siraj’s opinion, progress can be made in the confirmation or rejection of these ideas when the Vera C. Rubin Observatory in Chile comes into operation in 2021. It will be able to search the sky in search of Planet 9 and is expected to find a significant population of dwarf planets on the outskirts of the solar system. This could be an important clue that the Sun had a companion star in the past.