A halo can be studied by observing its effect on the passage of light from distant bright objects like quasars that are in line of sight beyond the galaxy in question.
[4] The stellar halo is a nearly spherical population of field stars and globular clusters.
The Milky Way's stellar halo contains globular clusters, RR Lyrae stars with low metallicity, and subdwarfs.
[5] Star formation in the stellar halo of the Milky Way ceased long ago.
[6] A galactic corona is a distribution of gas extending far away from the center of the galaxy.
Its existence is hypothesized in order to account for the gravitational potential that determines the dynamics of bodies within galaxies.
The nature of dark matter halos is an important area in current research in cosmology, in particular its relation to galactic formation and evolution.
[9] It represents the mass density of the dark matter halo as a function of
The invisible halo component cannot extend with this density profile indefinitely, however; this would lead to a diverging integral when calculating mass.
Most measurements that can be made are relatively insensitive to the outer halo's mass distribution.
The only dynamical variable related to the extent of the halo that can be constrained is the escape velocity: the fastest-moving stellar objects still gravitationally bound to the Galaxy can give a lower bound on the mass profile of the outer edges of the dark halo.
[10] The formation of stellar halos occurs naturally in a cold dark matter model of the universe in which the evolution of systems such as halos occurs from the bottom-up, meaning the large scale structure of galaxies is formed starting with small objects.
Halos, which are composed of both baryonic and dark matter, form by merging with each other.
Evidence suggests that the formation of galactic halos may also be due to the effects of increased gravity and the presence of primordial black holes.
[12] On the other hand, the halo of the Milky Way Galaxy is thought to derive from the Gaia Sausage.