Oumuamua could have been formed by stellar 'tidal forces'

Its name means "distant visitor", since it is the first interstellar object (that we have detected) to visit our solar system. Given its exotic character, the origin of Oumuamua has become a source of speculation since its discovery by a Hawaiian telescope in October 2017.

This interstellar object has the elongated shape of a large 'cosmic cigarette' of 400 metres in length and shows a chaotic rotation, which puzzles scientists. Given its rapid displacement (at 95,000 kilometres per hour), we know it is impossible for it to have formed in our solar system. The fact that it has no tail, like other asteroids, also throws off experts. Dark red and very dense, probably because it contains a lot of metal, Oumuamua is nothing like any known object.

Although the hypothesis most supported by scientists is that it is nothing more than a peculiar interstellar asteroid, some others, like certain members of the Harvard-Smithsonian Astrophysics Center, they proposed that it was actually a light probe from an extra-terrestrial civilization. However, there is no detectable electromagnetic radiation or any other evidence to show that this conclusion, not without controversy, is more than a mere (and sensational) intuition.

Now, a new study published on April 13 in Nature Astronomy offers one of the first full answers to questions about how Oumuamua was formed and where it came from.

The research consisted of computer simulations to show how objects like Oumuamua can form under the influence of tidal forces similar to those of the Earth’s oceans but, in this case, stellar ones. This hypothesis of formation, according to the authors of the study, would explain all the unusual characteristics of Oumuamua.

To understand this, we must start from the hypothesis that Oumuamua has had a solar system of origin: "Interstellar objects similar to Oumuamua can be formed through extensive fragmentation during close encounters with their host stars, and then ejected into interstellar space," the document cites.

Fragmentation caused by a "stellar tide"

When a smaller body passes very close to a much larger one, the tidal forces of the larger body can break the smaller one, which is what happened with the Comet Shoemaker-Levy 9 when it approached Jupiter. According to computer simulations, if an object gets close enough to its star, it can break it into extremely elongated fragments "in a long-to-short-axis ratio that may be even greater than ten to one", as the document explains; and then it would be ejected into interstellar space. This process, which they have called a stellar tide, is what has been suggested as a possible origin for Oumuamua.

Moreover, to the disappointment of some, again, researchers insist: "The absence of radio broadcasts points to the fact that Oumuamua is a natural object".

Additionally, the researchers applied a thermal modelling of the surface of Oumuamua, which is also consistent with its fracture hypothesis: the initial fragments would melt at a very short distance from the star and would condense again at greater distances, thus forming a cohesive crust that would guarantee the structural stability of the elongated shape.

Other objects like Oumuamua

On the other hand, researchers have also calculated that there must be an extremely large population of interstellar objects like Oumuamua, and that this is just the tip of the iceberg. "The discovery of Oumuamua implies that the population of rocky interstellar objects is much larger than we previously thought. On average, we believe that each planetary system should eject about one hundred billion objects like Oumuamua.”

The researchers' calculations demonstrate the efficiency of stellar tidal forces in the production of these types of objects. This also means that other objects, such as long-lasting comets, debris discs and even super earths, could be transformed into Oumuamua-shaped pieces during their stellar encounters.

Oumuamua has allowed astrophysicists and astrobiologists to open very new fields of work: since these objects can cross the domains of habitable zones (as has happened in our case) the possibility that they can transport matter capable of generating life (the theory of panspermia) cannot be ruled out. Additionally, these interstellar objects could provide clues as to how planetary systems form and evolve.