What does our galaxy look like?
The Milky Way Galaxy consists of a thin disk about 100,000 light-years in diameter with a central bulge and a spherical region called the halo that surrounds the entire disk. The disk contains most of the gas and dust of the interstellar medium, while the
How do stars orbit in our galaxy?
Stars in the disk all orbit the galactic center in about the same plane and in the same direction. Halo and bulge stars also orbit the center of the galaxy, but their orbits are randomly inclined to the disk of the galaxy. Orbital motions of stars allow u
How is gas recycled in our galaxy?
Stars are born from the gravitational collapse of gas clumps in molecular clouds. Massive stars explode as supernovae when they die, creating hot bubbles in the interstellar medium that contain the new elements made by these stars. Eventually, this gas co
Where do stars tend to form in our galaxy?
Active star-forming regions, marked by the presence of hot, massive stars and ionization nebulae, are found mostly in spiral arms. In each arm, a spiral density wave causes gas clouds to crash into each other and to form clusters of new stars.
What do halo stars tell us about our galaxy's history?
The halo generally contains only old, low mass stars that have a much smaller proportion of heavy elements than stars in the disk. Halo stars therefore must have formed early in the galaxy's history, before the gas settled into a disk.
How did our galaxy form?
Halo stars probably formed in several different protogalactic clouds of hydrogen and helium gas. Gravity pulled those clouds together to form a single larger one. The collapse of this cloud continued until it formed a spinning disk around the galactic cen
disk
The portion of a spiral galaxy that looks like a disk and contains an interstellar medium with cool gas and dust; stars of many ages are found in the disk.
halo
(of a galaxy)� The spherical region surrounding the disk of a spiral galaxy.
interstellar medium
The gas and dust that fills the space between stars in a galaxy.
molecular clouds
Cool, dense interstellar clouds in which the low temperatures allow hydrogen atoms to pair up into hydrogen molecules (H2).
bubbles
An expanding shell of hot, ionized gas driven by stellar winds or supernovae, with very hot and very low density gas inside.
star-gas-star cycle
The process of galactic recycling in which stars expel gas into space, where it mixes with the interstellar medium and eventually forms new stars.
spiral arms
The bright, prominent arms, usually in a spiral pattern, found in most spiral galaxies.
spiral density wave
Gravitationally driven waves of enhanced density that move through a spiral galaxy and are responsible for maintaining its spiral arms.
protogalactic clouds
A huge, collapsing cloud of intergalactic gas from which an individual galaxy formed.