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A group of researchers used numerical simulations to show that interstellar objects like ‘Oumuamua, a fast-moving cigar-shaped object of extrasolar origin discovered on October 19, 2017 by the Pan-STARRS 1 telescope in Hawai’i, can be produced through the tides. fragmentation and expelled during close encounters of their parent bodies with their host stars.
An um Oumuamua type object produced by a simulation of the tidal disruption scenario. Image credit: Y. Zhang / NAOC / M. Kornmesser / ESO.
“‘ Oumuamua is nothing like anything else in our Solar System, “said first author Dr. Yun Zhang, a researcher at the National Astronomical Observatories, the Chinese Academy of Sciences.
“Its dry surface, unusually elongated shape, and puzzling movement even led some scientists to wonder if it was an alien probe.”
“It is truly a mysterious object, but some signs, such as its colors and the absence of radio emission, point to‘ Oumuamua being a natural object. “
“Our goal is to create a comprehensive setting, based on well-understood physical principles, to put together all the tantalizing clues,” added Professor Douglas Lin of the University of California, Santa Cruz, co-author of the study.
Astronomers hoped that the first interstellar object they detected was a frozen body like a comet.
Frozen objects like those that populate the Oort cloud evolve at very great distances from their host stars, are rich in volatiles and are often driven from their host systems by gravitational interactions. They are also highly visible due to the sublimation of volatile compounds, which creates the coma of a comet when the Sun warms it up.
However, Oumuamua’s dry appearance is similar to rocky bodies like asteroids in the Solar System, indicating a different ejection scenario.
Other researchers have calculated that there must be an extremely large population of interstellar objects similar to Oumuamua.
“The discovery of‘ Oumuamua implies that the population of rocky interstellar objects is much larger than previously thought, “said Dr. Zhang.
“On average, each planetary system should expel a total of around one hundred billion objects like‘ Oumuamua. We need to build a very common scenario to produce this type of object. “
When a smaller body passes very close to a much larger one, the tidal forces of the larger body can break the smaller one, as happened with Comet Shoemaker-Levy 9 when it approached Jupiter.
Tidal disruption processes can eject some debris into interstellar space, which has been suggested as a possible origin for ‘Oumuamua.
But whether that process could explain the puzzling characteristics of um Oumuamua was still highly uncertain.
This illustration shows the tidal disruption process that can result in Oumuamua-like objects. Image credit: Y. Zhang / NAOC.
The study authors performed high-resolution computer simulations to model the structural dynamics of an object flying close to a star.
They discovered that if the object gets close enough to the star, the star can break it into extremely elongated fragments that are then ejected into interstellar space.
“The elongated shape is more convincing when we consider the variation in material resistance during the stellar encounter. The long axis to short axis ratio can be even greater than ten to one, “said Dr. Zhang.
The team’s thermal modeling showed that the surface of the fragments resulting from the interruption of the initial body would melt at a very short distance from the star and would re-condense at greater distances, thus forming a cohesive crust that would guarantee the structural stability of the Extended form.
“The diffusion of heat during the stellar tidal disruption process also consumes large amounts of volatiles, which not only explains the colors of ‘Oumuamua’s surface and the absence of visible coma, but also clarifies the inferred dryness of the interstellar population, “said Dr. Zhang.
“However, some high-temperature sublimation volatiles buried below the surface, such as water ice, may remain in condensed form.”
‘Oumuamua’s observations showed no cometary activity, and only water ice is a possible source of degassing to explain its non-gravitational movement.
If scenario Oumuamua was produced and ejected by the team’s scenario, a lot of wastewater ice could be activated during its passage through the Solar System.
The resulting degassing would cause accelerations that coincide with the um Oumuamua kite trajectory.
“The tidal fragmentation scenario not only provides a way to form a single‘ Oumuamua, but it also represents the vast population of asteroid-like interstellar objects, “said Dr. Zhang.
The calculations demonstrate the efficiency of the tidal forces in the production of this type of object.
Prospective parents, including long-lived comets, debris disks, and even super Earths, could transform into ‘Oumuamua-sized pieces during stellar encounters.
This work also supports estimates of a large population of ‘Oumuamua type interstellar objects.
Given that these objects can cross the domains of habitable zones, the possibility that they can transport matter capable of generating life, called panspermia, cannot be ruled out.
“This is a very new field. These interstellar objects could provide critical clues to how planetary systems form and evolve, “said Dr. Zhang.
“‘ Oumuamua is just the tip of the iceberg. We anticipate that many more interstellar visitors with similar features will be discovered by future observation with the upcoming Vera C. Rubin Observatory, ”said Professor Lin.
The team’s work was published in the magazine. Astronomy of nature.
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Y. Zhang and D.N.C. Lin Tidal fragmentation as the origin of 1I / 2017 U1 (‘Oumuamua). Nat astron, published online April 13, 2020; doi: 10.1038 / s41550-020-1065-8
