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تسجيل مستخدم جديدAstrochemistry and compositions of planetary systems
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Planets form and obtain their compositions in disks of gas and dust around young stars. The chemical compositions of these planet-forming disks regulate all aspects of planetary compositions from bulk elemental inventories to access to water and reactive organics, i.e. a planets hospitality to life and its chemical origins. Disk chemical structures are in their turn governed by a combination of {it in situ} chemical processes, and inheritance of molecules from the preceding evolutionary stages of the star formation process. In this review we present our current understanding of the chemical processes active in pre- and protostellar environments that set the initial conditions for disks, and the disk chemical processes that evolve the chemical conditions during the first million years of planet formation. We review recent observational, laboratory and theoretical discoveries that have led to the present view of the chemical environment within which planets form, and their effects on the compositions of nascent planetary systems. We also discuss the many unknowns that remain and outline some possible pathways to addressing them.
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Most stars form in dense stellar environments. It is speculated that some dense star clusters may host intermediate-mass black holes (IMBHs), which may have formed from runaway collisions between high-mass stars, or from the mergers of less massive b
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Star and planet formation are inextricably linked. In the earliest phases of the collapse of a protostar a disc forms around the young star and such discs are observed for the first several million years of a stars life. It is within these circumstel
lar, or protoplanetary, discs that the first stages of planet formation occur. Recent observations from ALMA suggest that planet formation may already be well under way after only 1 Myr of a stars life. However, stars do not form in isolation; they form from the collapse and fragmentation of giant molecular clouds several parsecs in size. This results in young stars forming in groups - often referred to as clusters. In these star-forming regions the stellar density is much higher than the location of the Sun, and other stars in the Galactic disc that host exoplanets. As such, the environment where stars form has the potential to influence the planet formation process. In star-forming regions, protoplanetary discs can be truncated or destroyed by interactions with passing stars, as well as photoevaporation from the radiation fields of very massive stars. Once formed, the planets themselves can have their orbits altered by dynamical encounters - either directly from passing stars or through secondary effects such as the Kozai-Lidov mechanism. In this contribution, I review the different processes that can affect planet formation and stability in star-forming regions. I discuss each process in light of the typical range of stellar densities observed for star-forming regions. I finish by discussing these effects in the context of theories for the birth environment of the Solar System.
Revealing the mechanisms shaping the architecture of planetary systems is crucial for our understanding of their formation and evolution. In this context, it has been recently proposed that stellar clustering might be the key in shaping the orbital a
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