Astrophysics & Particle Physics-APPC 2026

Galaxies are immense collections of stars, gas, dust, dark matter, and cosmic structure held together by gravity. Galaxies are the basic building materials of the universe and contain billions to trillions of stars as well as planetary systems, stellar remnants, and interstellar material.Galaxies are mainly categorized as spiral, elliptical, or irregular, having unique morphologies, stellar populations, and dynamical features. Spiral galaxies, such as the Milky Way galaxy, have rotating disks and spiral arms with active star-forming regions. Elliptical galaxies are more spherical and consist of predominantly older stars, and irregular galaxies do not have a clear structure but tend to exhibit strong star formation activity.Galaxy formation and evolution are areas of study that tell us about the universe's history. Galaxies are created by matter gravitational collapse, mergers, and interactions that build their morphology, induce star formation, and shape the growth of supermassive black holes residing in their centers. Dark matter halos are essential in the formation of galaxies as they provide the gravitational structure that keeps galaxies intact.The interstellar medium made up of gas and dust in galaxies—enables star formation and chemical enrichment. Galactic evolution through stellar evolution creates heavier elements, enriching future generations of stars and cosmic chemical evolution. Galaxies are commonly investigated using multi-wavelength astronomy, such as optical, radio, infrared, X-ray, and gamma-ray observations.

Spectroscopy, photometry, and high-resolution imaging techniques assist in distance measurement, stellar populations, rotation dynamics, and dark matter content. Studying high-redshift galaxies enables astronomers to explore the distant universe and learn about the evolution of cosmic structures over billions of years.Studying galaxies helps scientists learn about star formation, galaxy interactions, dark matter, and cosmic structure evolution. Galaxies not only light up the universe's large-scale structure but also act as test beds for understanding basic astrophysical processes, from the life cycle of stars to supermassive black hole accretion.