AST 101 Lecture Notes - Lecture 29: Milky Way, Virgo Cluster, Local Group
Document Summary
Big bang- the event that began the universe according to modern cosmological theories. It occurred about 13. 7 billion years ago and generated the expanding motion that we observe today. Dark energy- a form of energy detected by its effect on the expansion of the universe, also knows as the cosmological constant. The nature and properties of dark energy are unknown. Dark matter- matter that emits no detectable radiation but whose presence can be deduced by its gravitational attraction on other bodies. Galaxy- a massive system of stars, gas, and dark matter held together by their mutual gravity. Typical galaxies have a mass between about 107 and 1013 solar masses. Galaxy cluster- a set of hundreds or thousands of galaxies held together by their mutual gravitational attraction. The milky way lies on the outskirts of the virgo cluster. Galaxy group- a system of from two to several dozen galaxies held together by their mutual gravitational attraction.
