Astrophysics & Particle Physics-APPC 2026

Galactic halos are extensive, approximately spherical areas around galaxies that extend many kiloparsecs beyond their observable disks or bulges. Galactic halos consist of diffuse stars, globular clusters, hot gas, and dark matter and are important in the formation, dynamics, and evolution of galaxies.Galactic halos differ in mass and size depending on the host galaxy. For instance, the Milky Way halo reaches hundreds of kiloparsecs and has halo stars, globular clusters, and dark matter.

Analyzing the kinematics of globular clusters and halo stars enables astronomers to trace the distribution of dark matter and learn about the merger history of the galaxy.Halos also play an important role in understanding galaxy formation models. The hierarchical model predicts that halos are built up via accretion and mergers, absorbing smaller galaxies and their star populations. Spectroscopy, photometry, and gravitational lensing observations both inform us about the stellar and dark matter content of halos.Accordingly, galactic halos are large regions extending around galaxies that contain stellar populations, globular clusters, diffuse gas, and dark matter. Understanding halos is crucial for learning about galaxy formation, evolution, and distribution of dark matter in the universe.