Over the past 13.8 billion years, under the effect of gravity, matter has aggregated, compacted, contracted and collapsed to form hundreds of billions of objects traveling through the cosmos , alone or within gravitationally bound systems. Despite the vastness of the Universe, the trajectories of many of these objects intersect, and collisions become inevitable.
The standard cosmological model — the Λ-CDM model — describes the formation of cosmic objects in a hierarchical increment, that is, from smaller objects to larger ones. Thus, the first collapse and merge to form the second, according to an increasing scale of size. Indeed, this model implies the existence of cold, massive and slow dark matter compared to the speed of light, implying this rising hierarchical dynamics.
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The collision of two stars will light up the night sky in 2022
During the evolution of the Universe, the cosmic catalog has therefore been enriched with many objects such as planets, stars, galaxies, black holes, etc. As a general rule, these objects evolve within systems bound by gravitation, within which there is a cohesion that locally opposes the phenomenon of expansion of the Universe. Although the distances are usually large between these objects, collisions are actually frequent.
Around 4.5 billion years ago, when the Solar System began to form, models suggest that there were certainly more than eight planets. For example, simulations show that a fifth gas giant probably existed between Jupiter and Neptune; however, it would have been ejected during the cleaning of the orbits by the other planets.
The majority hypothesis regarding the formation of the Moon involves a collision between a Mars-sized body and the young Earth. This event would have propelled millions of tons of debris into the peripheral environment; this cloud of dust and rock would then have aggregated and contracted to form the Moon.
This scenario has been confirmed by numerous clues, in particular by the study of lunar samples brought back by the Apollo missions. Similarly, the Martian satellites Phobos and Deimos are believed to have originated from the collision of Mars with a large cosmic object.
According to current planetary formation models, rocky planets collide frequently during the formation of a solar system. When they come into contact with each other, this leads to the formation of a single larger planet, with a cloud of debris contracting to form one or more satellites that decrease in size with distance. The Pluto-Charon system is a typical example of this phenomenon.
According to the International Astronomical Union, a brown dwarf is an object whose mass is insufficient to trigger the thermonuclear fusion reactions of hydrogen, but sufficient to trigger those of deuterium. It is thus an object too small to be considered a star, and too massive to be considered a giant planet. Its mass is, according to the models, between 13 and 75 Jovian masses (mass of Jupiter); i.e. between 1% and 7.5% of the mass of the Sun.
Brown dwarfs are about 75% hydrogen. During the collision between two brown dwarfs, if the total mass of the object resulting from the fusion exceeds the threshold of 0.075 solar masses, then the new object is massive enough to trigger thermonuclear hydrogen fusion reactions, and becomes so a real star. In this case, the post-merger object is a red dwarf, specifically an M-type star.
Stars are objects with a wide variety of masses. The less massive appear red, cold and burn their hydrogen less quickly. The more massive ones appear blue, hot and fuse their hydrogen faster; they therefore have a shorter lifespan. The age of a stellar cluster can thus be determined by studying the distribution of the masses of its stars.
In a few star clusters, some observed stars are more blue, massive, and hotter than they should be given the evolution of other stars on the Hertzsprung-Russell diagram. Theoretical models suggest that these late blue stars — called blue straggler — come from the collision of stars within the host cluster.
Indeed, when two stars merge, the resulting object is more massive. For example, if two 0.7 and 0.8 solar mass red dwarfs merge, they can form a 1.5 solar mass blue star, even if the star cluster is too old to contain 1.5 solar mass stars.
Late blues are frequently seen in the dense stellar environment of globular clusters. Such a scenario shows that even when a star has exhausted its fuel and lost mass, the formation of a new, more massive star is still possible through fusion.
White dwarfs are dense objects resulting from the evolution of a… (continued on next page)
