Astrophysics & Particle Physics-APPC 2026

The Interstellar Medium (ISM) is matter found between stars in a galaxy, made up of gas, dust, cosmic rays, and magnetic fields. It is central to star formation, galactic dynamics, and chemical evolution, connecting stellar life cycles to galaxy structure and evolution.The ISM is made up of molecular clouds, atomic gas, and ionized gas. Molecular clouds are dense and cold regions of stellar nurseries where gravitational collapse creates new stars and planetary systems. Atomic and ionized gas areas occupy greater volumes and get affected by stellar radiation, supernova shock waves, and cosmic rays, and they control the thermal and dynamic structure of the galaxy.Dust grains within the ISM absorb as well as scatter light, adding to interstellar reddening and extinction. Dust also supplies surfaces for astrochemical reactions, allowing for molecules to form like water, carbon monoxide, and complex organic molecules. These molecules are vital to the study of chemical enrichment and the origin of life-building material.The ISM is full of magnetic fields, which impact gas dynamics, star formation, and the spread of cosmic rays.

Stellar input, such as winds, supernova explosions, and radiation pressure, puts energy into the ISM, powering turbulence, gas heating, and the formation of galactic structures like bubbles, shells, and filaments.Observations of the ISM utilize radio, infrared, optical, ultraviolet, and X-ray astronomy. Methods like spectroscopy and emission-line mapping enable astronomers to determine chemical composition, density, temperature, and kinematics of interstellar dust and gas.Most importantly, by observing the ISM, scientists are able to learn about the evolution of galaxies, star formation, molecular chemistry, and the cycle of matter in the universe. The Interstellar Medium is the conduit between dying stars and new star birth, sculpting the cosmic community that nourishes galaxies and governs astrophysical activity.