Day 14 notes

Louis Lackey

Day 14 Notes

Chapter 14- our galaxy

Section 14.1- the milky way revealed

            We view our galaxy edge-on. There is a disk, bulge, halo, and globular clusters. The milky way is a spiral galaxy and has arms. The orbits of stars in the bulge and halo are random. The orbits of stars bob up and down because the gravity of disk stars pulls them back and forth. Orbital velocity Mr=r*v^2/G M is mass within the orbit.

Section 14.2 Galactic recycling

            Stars have a cycle of fusion, death, bubbles, accretion, and birth. Large stars create complex elements in this cycle. Low mass stars return mass to space through solar winds and nebulae. High mass stars supernova and explode new elements into space. H2 gas forms as hot gas cools allowing electrons to join the protons. Molecular clouds form when the gas cools enough to allow molecules to form. Gravity forms stars from the molecules completing the gas to star cycle.

Stars make elements from fusion

Dying stars expel new elements in bubbles

Hot gas cools allowing hydrogen to form

Further cooling allows molecules

Gravity forms new systems

            Most star formation happens in the spiral arms. The arms have molecular clouds, hot stars, and ionization nebulae. Gas clouds get squeezed as they move into the arms. The squeezing triggers star formation. Young stars flow out of the arms.

Section 12.3 the history of the Milky Way

            Halo stars have almost no heavy elements, 0.02 compared to 2 %. Halo stars formed before disc stars and didn’t continue forming. Our galaxy probably formed from a giant gas cloud.

Section 12.4 the mysterious galactic center

            Stars appear to be orbiting a massive black hole at the center of the galaxy.