Why has star formation ceased in the galactic halo?
A)All of the galaxy's cool gas settled to the galactic plane long ago.
B)All the halo gas consists of elements with more protons than helium.
C)There are no white dwarf binaries to trigger star formation via their supernovae.
D)The halo has no gas at all.

Question

Quizplus · Accepted Answer

The galactic halo is an old and diffuse region surrounding the main disk of the galaxy. It contains little to no gas, and what gas is present is too warm to collapse and form new stars. The cool gas that was once present in the halo settled down to the galactic plane long ago, leaving the halo devoid of the necessary ingredients for star formation.

Why Has Star Formation Ceased in the Galactic Halo