Formation of the solar system and galaxies
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Solar System and Galaxy Formation: Planar Structures and Physical Processes
The formation of solar systems and galaxies is marked by the emergence of mostly two-dimensional, planar structures, such as the flat disks of galaxies and the ecliptic plane of our solar system. This planar geometry is primarily explained by the interplay of rotational kinetic forces and gravitational collapse, which cause matter to flatten into disks as it contracts under its own gravity. These processes are fundamental in shaping both solar systems and galaxies, despite the expectation from thermodynamics that matter would spread more evenly in three dimensions .
Galaxy Formation: Early Universe and Star Formation
Galaxies began forming rapidly in the early universe, with evidence showing that the first galaxies appeared within the first few hundred million years after the Big Bang. Observations from the James Webb Space Telescope have identified galaxies at redshifts z~10-13, indicating that these galaxies formed quickly, with intense star formation and compact structures. These early galaxies contributed significantly to cosmic reionization and were characterized by high star formation rate surface densities .
Massive, rapidly star-forming galaxies have also been found at redshifts greater than 6, often in close proximity to quasars. These galaxies exhibit star formation rates exceeding 100 solar masses per year, supporting the existence of massive elliptical galaxies observed at later times (z~4) . Dusty, star-forming galaxies (DSFGs) play a crucial role in the buildup of stellar mass and the evolution of massive galaxies, with their intense starbursts contributing significantly to the infrared background of the universe .
Physical Mechanisms: Gas, Gravity, and Feedback
The formation of galaxies involves the condensation of baryonic matter (normal matter) within dark matter halos. Gas cools and collapses under gravity, forming stars and galactic structures. The process is influenced by various feedback mechanisms, such as energy released from supernovae and active galactic nuclei, which can regulate or quench star formation Benson2010Cimatti2019. Explosive events, like the deaths of massive stars, can trigger further galaxy formation by propagating energy through the intergalactic medium, especially at certain epochs in the universe's history .
Evolution and Quenching of Star Formation
As galaxies evolve, their star formation activity changes. Observations show that in massive galaxies, star formation is often quenched from the inside out: the central regions stop forming stars first, while the outer regions continue for longer periods. This process leads to the development of dense, inactive bulges surrounded by more active disks, and is thought to occur over timescales of a few billion years . At the peak of cosmic star formation (z~2, known as "cosmic noon"), galaxies were gas-rich and experienced rapid growth, with internal processes and feedback shaping their evolution .
Simulations and Theoretical Models
Modern cosmological simulations have become essential tools for understanding galaxy formation. These simulations model the evolution of dark matter, gas, and stars from the early universe to the present, incorporating a wide range of physical processes. They have successfully reproduced many observed properties of galaxies and are used to test different cosmological models and feedback mechanisms Vogelsberger2019Benson2010. Theoretical frameworks, such as the cold dark matter paradigm, provide the basis for these simulations and help explain the large-scale structure of the universe Benson2010Cimatti2019.
Conclusion
The formation of the solar system and galaxies is governed by the interplay of gravity, rotation, gas dynamics, and feedback from star formation and black holes. Planar structures arise naturally from these processes, while the rapid formation and evolution of galaxies in the early universe set the stage for the diversity of galaxies observed today. Advances in observations and simulations continue to refine our understanding of these complex and fascinating processes Bushong2021Casey2014Robertson2022+7 MORE.
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