91福利

Prof. Wyn Evans (IoA Cambridge)

A Ghost Story: The Halo of the Milky Way Galaxy

The history of the Galaxy is imprinted in the kinematics and chemical
properties of the stars in the stellar halo. Their study allows us
partially to reconstruct the Galactic past because the time required
for stars in the halo to exchange their energies and momenta is very
long compared with the age of the Galaxy. This field has been
revolutionised in recent years by data from the Sloan Digital Sky
Survey Data, which has revealed a super-abundance of substructure.
There are ghostly streams from disrupting dwarf galaxies and globular
clusters, analogues of meteor streams along old cometary paths in the
Solar. There are ultrafaint phantom galaxies composed of old and faint
stars, so puny that the entire galaxy is outshone by a single red
giant star. There are smooth, flattened, halo populations, such as the
blue horizontal branch stars. Dominating the Galactic halo, there is
the magnificent double arch of the Sagittarius stream criss-crossing
the whole sky. These tracers enable the study of the assembly of the
Galaxy, as well as its present-day mass and gravitational field. The
quality of the data permit confrontation -- and conflict -- with
modern-day cosmological simulations of galaxy formation.