Halo (astronomy)

In astronomy, a halo is a faint, diffuse region surrounding a galaxy, composed mostly of dark matter, old stars, and globular clusters. It extends far beyond the galaxy’s visible disk or bulge, providing a gravitational framework that influences the galaxy’s structure and motion. Halos help astronomers understand the distribution of dark matter and the formation history of galaxies, acting like a cosmic envelope that contains and shapes the visible parts of the galaxy within.