A galaxy is a massive, gravitationally bound system that consists of stars, stellar remnants, interstellar gas, dust, and dark matter. These components are held together by mutual gravitational attraction. Galaxies are the fundamental building blocks of the universe and come in a variety of shapes and sizes.
Galaxies are thought to have formed from the gravitational collapse of protogalactic clouds of gas and dust. The structure of a typical galaxy includes:
Central Bulge: Contains older stars and often a supermassive black hole at the center.
Disc: Contains gas, dust, and both young and old stars, arranged in spiral arms or in a more elliptical distribution.
Halo: Contains globular clusters, old stars, and dark matter, extending beyond the main body of the galaxy.
Study Guide
When studying galaxies, it's important to focus on the following key points:
Understand the different types of galaxies and their distinguishing features.
Energy - A. Energy is involved in all physical and chemical processes. It is conserved, and can be transformed from one form to another and into work. At the atomic and nuclear levels energy is not continuous but exists in discrete amounts. Energy and mass are related through Einstein's equation E=mc 2 . B. The properties of atomic nuclei are responsible for energy-related phenomena such as radioactivity, fission and fusion. C. Changes in entropy and energy that accompany chemical reactions influence reaction paths. Chemical reactions result in the release or absorption of energy. D. The theory of electromagnetism explains that electricity and magnetism are closely related. Electric charges are the source of electric fields. Moving charges generate magnetic fields. E. Waves are the propagation of a disturbance. They transport energy and momentum but do not transport matter.
Relate temperature to the average molecular kinetic energy.