ASTRON 1101 Lecture Notes - Lecture 30: Local Group, Messier 87, Observable Universe

• School: Ohio State University
• Department: Astronomy
• Course: ASTRON 1101
• Professor: Barbara Ryden

Document Summary

Stars (plus gas, dust, and dark matter) are found in gravitationally bound galaxies. Galaxies are often found in gravitationally bound clusters. Galaxies come in a variety of sizes and shapes. Spiral galaxies make up ~75% of all luminous galaxies in the local universe: diameter: 5-50 kpc, luminosity: 100 million-100 billion lsun. Elliptical galaxies make up ~20% of all luminous galaxies in the local universe. They look like featureless elliptical blobs: diameter: 1-200 kpc, luminosity: 1 million-1 trillion lsun. Irregular galaxies make up ~5% of all luminous galaxies in the local universe. They look irregular: diameter: 1-10 kpc, luminosity: 1 million-10 billion lsun. It"s not just about the shape: different types of galaxy have different stellar proportions. Disks of spiral galaxies have lots of gas and dust; active star formation, ~2% heavy elements: population 1. Spheroids have little gas and dust; no star formation, ~0. 01% heavy elements: population.