MSV-2035 Astronomy Document - Inside Design - FINAL - FINAL

Astronomy & Astrophysics 18 detectable in high-redshift galaxies, the UV-irradiated gas is an important tool for understanding the history of formation and evolution of structure in the Universe as well. Another realm of feedback from massive young stellar objects involves protostellar jet interaction with the ISM leading to particle acceleration and non-thermal radiation. This opens up a new window to investigate shock physics in stellar systems and contribution to the production of Galactic cosmic rays. The Central Molecular Zone (CMZ) provides an ideal laboratory for probing star formation processes under extreme conditions. The lack of (or inefficient) present-day star formation in the CMZ is surprising given its dense gas reservoir. Despite various proposed theoretical models, the star formation in the CMZ is not well characterized observationally. When we consider the IMF, a number of interesting unresolved aspects remain. Arobust observational finding is its near-universality in theMilkyWay and neighbouring galaxies. But is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF? How does it depend on the environment, on metallicity? How does it behave in extreme environments like the Galactic centre? These are some of the yet unanswered questions. 2.7 Cosmic Chemistry Deuterium, the two Big Bang nucleosynthesis in the first few minutes of the Universe is believed to have created 3 4 isotopes of Helium ( He and He) and a very small amount of Lithium as well as Beryllium (the so called “primordial composition”). Big Bang also predicts the light element abundance as a function of total baryon produced. Therefore, measuring the light element abundances in pristine environments is important to constrain Big Bang nucleosynthesis. Lithium (Li) with atomic number Z=3 is one of the first three light elements (others are hydrogen and helium) known to have been produced during the early Big Bang nucleosynthesis. Over the course of time, Li content in the physical Universe has increased by about a factor of four which is meager compared to rest of the elements, C, N, O, Fe, Ni. etc., which grew more than a million times, over the lifetime of the Universe. Stars are primary contributors to the significant enhancement of these heavier elements through mass ejections and stellar explosions. Li, however, seems to be an exception. The small increase of Li from its original value at the time of the Big Bang is mostly attributed to high energy cosmic ray bombardment of heavier nuclei like C and O in the interstellar medium, splitting them into 6 smaller atoms like Li. It is known that Li is destroyed at relatively low temperatures (~ 2 x 10 K) inside the stellar interiors. Further, mixing up with outer atmospheres leads to the destruction of initial Li over a star's lifetime. Contrary to this general understanding, a few evolved stars (about one in 100 in our Galaxy) are found to have very high Li content in their atmospheres, in some cases exceeding model predictions by a factor of 100,000. Understanding the Li production in such stars is of great importance in the study of stellar evolution and nucleosynthesis. Almost all other heavier elements in the periodic table are synthesised in the stellar interiors and envelopes during hydrostatic and explosive burning. Each stellar nucleosynthetic path has a different timescale and produces characteristic elemental abundance patterns. It is believed that the first set of stars formed (called “Population III” stars) had “primordial” composition. Subsequent generation of stars formed from the gas enriched by the previous generation of stars. Therefore, the observed abundance ratios and abundance patterns in a given object depend on the nature and duration of star formation activities in their host galaxies. As stellar lifetime is related to its mass, measuring the photospheric metallicities (or elemental abundances) of stars of different masses (and hence different ages) can be used to map how star formation and chemical enrichment proceeded in our Galaxy and other galaxies. Observations of the spectra of metal-poor stars in the Milky Way are the only available diagnostics for studying the nucleosynthesis in the early Galaxy, including the very first stars. These stars preserve the chemical fingerprint of the MEGA SCIENCE VISION-2035