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Par Ph. RECLUS

From stellar nucleosynthesis to elemental abundance: understanding the origins of sunlight and the production of elements in the periodic table

The production of elements in the periodic table and the origins of sunlight are closely linked to stellar nucleosynthesis. Nucleosynthesis requires high temperatures and densities, conditions found in the Big Bang, inside stars and in explosions. Understanding cosmic abundances and their evolution requires combining measurements from various sources and using different tools to understand the composition of cosmic matter. Recent years have seen significant advances in astrophysics, nuclear theories, laboratory experiments and cosmic messengers. Ejecta captured by Earth in sediments and identified by characteristic radioisotopes suggest that nearby nucleosynthesis occurred in recent history. Indications of nucleosynthesis in the local environment during the formation of the Sun are derived from meteoritic materials and deep-sea sediments. Spectroscopy and neutrino flux from hydrogen fusion processes in the Sun establish a refined model of how nuclear power generation shapes stars and our solar system. Observation of radioactive afterglow and the characteristic heavy element spectrum of a neutron star merger confirms the neutron-rich environments encountered in such rare explosions. Models are needed to explore nuclear fusion of heavier elements, while observations of γ rays from radioactive materials synthesized in stellar explosions support astrophysical models. It was possible to construct a database of isotopic compositions found in a variety of mineral phases using meteorites, which can be analyzed with high precision in terrestrial laboratories. Dust particles that formed in the immediate vicinity of cosmic nucleosynthesis sites are present in meteorites. The evolution of the cosmic composition results from the recycling of cosmic gas. New nucleosynthesis products must find their place in future generations of stars, with yields depending on the abundance of seed nuclei. Photons and neutrinos are not the only cosmic particles that serve as messengers of cosmic nucleosynthesis; Explosive nucleosynthesis ashes can also be discovered in stardust studies, with the very different isotopic composition of stardust grains identifying them as being of extra-solar origin. from the beginning of the galaxy until today.

 What is the general process by which a large diffuse cloud of gas transforms into a star and surrounding planets?

The formation of stars and planets from large clouds of diffuse gas: a comprehensive review of the process.

The formation of stars and planets from large clouds of diffuse gas involves a complex interplay of chemical, physical, and dynamic processes. Clouds are mostly composed of gas, with a small portion made up of submicron dust particles. Star formation is associated with dense molecular clouds where densities exceed 102nH cm−3. Compressions of these clouds generate turbulence, which can accelerate the production of molecules and produce the observed morphology. Turbulence also plays a key role in controlling the efficiency of star formation. MC formation occurs during large-scale compression of diffuse ISM driven by various mechanisms such as supernovae, magneto rotational instability, or gravitational instability in galactic disks of stars and gas. These cloud cores are dynamic objects with relatively short lifetimes, not exceeding a few mega years. At the protostellar stage, heating of interstellar grains in the envelope activates new chemical pathways that change the composition of future solid building blocks. The final section of the review focuses on observations and theory of chemistry in planet-forming disks and their relationship to observed volatile compositions in the Solar System. The envelope is dispersed on timescales of about 1 billion years, leaving the pre-main sequence star and a Kepler disk. The circumstellar disk is often called a proto-planetary disk or planet-forming disk where planets come together. The central star becomes hot enough for merger, marking the name change from protostar to pre-main sequence star. As the protostellar system evolves, more mass is found in the star and disk relative to the remnant envelope.

Name the two final states of stars much more massive than the Sun and describe their physical properties?

Stars much more massive than the Sun can end their lives in two different ways – like neutron stars or black holes. Neutron stars are incredibly dense objects that are created when a star collapses, while black holes are regions of space from which no light or matter can escape. Both of these objects have unique physical properties that make them fascinating to study. Neutron stars have incredibly strong magnetic fields and can spin rapidly, while black holes have an event horizon that marks their boundary and a singularity at their center.