In the most remote confine of our solar system, where sunlight fades into a icy darkness, there is a vast kingdom surrounded by mystery: the oort cloud, a gigantic sphere, a kind of ‘cosmic shell’ that completely surrounds to … Our star and its planets, extending to almost a light year away. A place so huge and dark that even Voyager 1, the mythical probe that has been moving away from the earth since 1977 and traveling more than a million and a half km per day, would take 300 years to reach its limits.
The Oort cloud is a maze of thousands of millions, perhaps billion, of frozen bodies of all sizes: remains of the formation of our planetary system, expelled to that distant region for the seriousness of the giant planets. Most are potential comets, sleeping in the dark, waiting for a disturbance that wakes them up and throws them on a trip back to the sun. But there may also be something else there, frozen and unknown worlds that, for now, our technology does not It is able to detect.
Two spiral arms
And now, a new study carried out by researchers from the Southwest Research Institute In San Antonio (Texas) and the American Museum of Natural HistoryIn New York, he suggests that Oort’s cloud could have a pair of spiral arms that resemble a miniature galaxy.
We can think of the Oort cloud as a swarm of scattered ice balls, floating at huge distances from the sun, but still tied to it by its gravity. From time to time, some gravitational disturbance deviates one of these balls, pushes it towards the internal solar system and creates a long period comet that shines more and more as it approaches our burning star and its ice is sublimated forming the characteristic line.
However, the true form of Oort’s cloud remains a mystery, since it also depends on ‘external’ forces to our own system that are extremely difficult to calculate. The new study, which can already be consulted on the ‘Arxiv’ prepression server, tries to shed light on this invisible part of the solar system, or at least on its closest region, which is between 1,000 and 10,000 astronomical units of distance. (A UA is equivalent to the distance between the sun and the earth, 150 million km).
The influence of the galaxy
Known as ‘internal oort cloud’, this region is considered more populated than the ‘external oort cloud’, which extends from 10,000 to 100,000 UA. To understand the cloud structure, it is not enough to consider the gravitational forces of the planets. Of course, these forces have an impact, but there is a much more important actor in the orbital mechanics of these icy rocks: the galaxy itself.
And this is where the concept of ‘galactic tide comes into play. As the solar system moves through the galaxy, it suffers the gravitational forces of other objects, such as stars and black holes, which are closer or further from it. Like the Moon exerts a gravitational force on the water of the Earth, causing the tides, the galactic center, where most of the mass of the Milky Way is concentrated, it also affects the ‘ocean’ of loose cloud rocks of Oort.
Modeling this complex dynamic is a whole challenge, and the researchers, led by David Nesvorný, had to resort to a NASA supercomputer to execute its analytical model and then compare it with previous simulations of the Oort cloud structure. What they found hidden in the data was a surprise.
A miniature galaxy
According to its model, in effect, the Oort cloud resembles a spiral disk of about 15,000 A diameter, inclined about 30 degrees with respect to the ecliptic. But the most intriguing is that it has two long spiral arms that make it look like a miniature galaxy. Arms located almost perpendicular to the center and which are the result of the influence of the aforementioned galactic tide
The changes that produce these oscillations take a long time to occur, but according to the analysis of the researchers, they almost completely determine the shape of the internal Oort cloud. On the contrary, the gravitational attraction of the planets of the solar system itself or the stars of passage does not seem to have a significant effect.
According to the study, obtaining a faithful image of this two -arms spiral will be extremely difficult. To achieve this, the authors suggest that the direct observation of a large number of objects in that region of space would be needed, something that will be impossible in the short term, since there are currently no resources dedicated to this kind of observations.
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