Only a few years ago, astronomers discovered the first asteroids and comets of interstellar origin in our solar system. Now a model study suggests that such extrasolar chunks are by no means rare – quite the contrary: the Oort cloud, a distant storehouse of icy comets at the outer edge of our solar system, even those There may be more interstellar objects than people that formed in our own system. Overall, about one percent of all the carbon and oxygen in the Milky Way may also be contained in interstellar lumps.
It’s only been clear for a few years that our solar system has been regularly receiving visitors from outside: in the autumn of 2017, astronomers observed a cigar-shaped object that passed the Sun at high speed and Then disappeared again into the depths of space. Evaluation of the observational data allowed only one conclusion: the part named ‘Oumuamua was of interstellar origin and passing only through our solar system. In 2019, researchers discovered a second interstellar guest. This time, however, it was a comet with a considerable amount of ice, as evidenced by the tail-like bulge and rupture of a fragment. A more detailed analysis of the interstellar comet, Baptism 2I/Borisov, also showed that its material showed no trace of the path of an earlier nearby star – so the Sun’s flyby may have been its first flight through the vicinity of a star. .
Oort cloud in sight
The observations of these two “travellers” raise the question of how often such interstellar visitors come, and also how many of them may have been in our star’s sphere of influence in the early days of the Solar System. According to popular theory, our Sun formed together with other stars in a common gas cloud. The density of young stars and the gravitational interactions they cause may cause celestial bodies to deflect more frequently from the outer region of the accretion disk around young stars and eject into interstellar space. As a result, there may be far more interstellar chunks than long thought. Based on these ideas, Amir Siraj and Avi Loeb from the Center for Astrophysics | Harvard & Smithsonian (CFA) calculates how many interstellar visitors and permanent guests may be hiding in the vastness of the Oort Cloud.
“Before the discovery of the first interstellar comet, we had no idea how many interstellar objects were in our solar system,” Siraj says. “But theories about the formation of planetary systems suggest that there will be fewer visitors than permanent residents in any case.” For their model, Siraj and Loeb started with the characteristics and trajectory of Comet 2I/Borisov, as well as what is known about the Oort cloud and the behavior of its “inhabitants”. This storehouse of long-period comets and other icy fragments begins at over 2000 times the Sun-Earth distance and can extend up to 1.6 light years. This means that this bowl-shaped region is not only huge, it is also located in a region in which solar gravity is much weaker than inside it.
More Interstellar Guests Than Household Stuff
From their model calculations, the two astronomers concluded that this distant region may be more strongly characterized by traveling interstellar objects than previously assumed. “There could be quite a few more visitors,” Siraj said. In particular, they determined that the number of interstellar fragments probably exceeds the number of parent objects in the outer part of the Oort cloud. “Interstellar objects are rare in the planetary region of the Solar System, but our results clearly show that they are more common in the deeper depths of the Oort Cloud than material from the Solar System,” says Loeb. Because these interstellar guests are so small and dark that they are not visible with our telescopes at such a distance, they remain hidden from us, explain astronomers.
Also interesting: Based on their calculations, Siraj and Loeb believe that a relatively high proportion of our galaxy’s heavy elements are bound up in interstellar material. “About one percent of carbon and oxygen can be found in interstellar objects,” the team reports. This could mean that during the formation of stars and planetary systems, much more material is thrown into space than in current models of planet formation. “Therefore interstellar objects may impose interesting restrictions on the formation processes of planetary systems,” Siraj says. Conversely, large material losses mean that there must be a higher “building material stock” than initially calculated.
Quell: Amir Siraj und Avi Loeb (Center for Astronomy | Harvard and Smithsonian, Cambridge), Monthly Notices of the Royal Astronomical Society Letters, doi:10.1093/mnrsl/slab084
