Sun mist

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The solar nebula (also called solar or presolar primordial nebula ) is an interstellar molecular cloud in the prevailing cosmogony , from which the solar system was once formed. Such clouds are also called nebulae in astronomy . Like all molecular clouds, the solar nebula consisted primarily of gas and relatively little dust . The matter of the sun as well as the planets and other bodies in the solar system orbiting around it originate from here .

Historical hypotheses

The hypothesis of such an ancient nebula was first put forward by Emanuel Swedenborg in 1734 and introduced by Immanuel Kant in his work General Natural History and Theory of Heaven in 1755 . Kant assumed that in this nebula, due to the interaction of its particles, an initially somewhat predominant sense of rotation had established itself and that the primal nebula therefore rotated more and more pronounced and flattened.

In 1796, Pierre-Simon Laplace independently presented a relatively similar model. It appeared in the last volume of his five-volume work Exposition du systeme du monde (Representation of the World System) and is known today as the Nebular Hypothesis . However, Laplace assumed an already existing sun, whose heated atmosphere assumed a lenticular shape for analogous reasons. In the course of the cooling and the corresponding compression of the gas envelope, centrifugal force over time predominated in its outermost area , and several gas rings, which had compressed to form the planets, separated one after the other.

The cosmogony of Kant and the nebular hypothesis of Laplace are often simply referred to as the Kant-Laplace theory .

In the meantime, a near-collision theory had become very popular, according to which the planets were formed by a near-collision between the sun and another star, at which mass was torn out of the stars. Today this theory is considered obsolete.

Today's assumptions

According to current knowledge, the process of star formation from a molecular cloud follows Kant's considerations in essential points. It is believed that even the solar system to these "usual way" originated , d. H. like star systems in general.

Today it is assumed that the solar nebula was only a fragment of a much larger molecular cloud, the primordial cloud . In addition to the solar system, thousands of other star systems have emerged from this , so that a star cluster has formed. This has spread over the galaxy in the further course .

The solar nebula was initially about 100  AU in diameter and two to three times the mass of the sun . At a certain moment, gravitational compression caused the core of the molecular cloud to collapse . This resulted in a protostar , the "primordial sun". The collapse was initially isotropic from all sides, later a circumstellar accretion disk formed. The sun continued to grow from their material, and the planets also emerged from this. In the case of the solar system, only a single star system has arisen, not a double or multiple star system , as is often the case.

About the composition of the chemical elements and compounds in the solar nebula, in addition to the sun and the planets and a. meteorites also provide information.

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