ASTR 1346 1st Edition Lecture 17 Outline of Last Lecture I Hubble s Galaxy Classification A Spirals B Barred Spirals Outline of Current Lecture I Hubble s Galaxy Classification A Ellipticals B Lenticulars C Irregulars II Distribution of Galaxies A Group B Cluster C Supercluster D Voids Filaments and Walls Current Lecture l A Ellipticals show little internal structure They have an elliptical shape no disks spiral arms or dust lanes and their brightest stars are red They range from E0 circular E1 slightly flattened up to E7 flattest Ellipticals are a few thousand to a few million light years in diameter There is a halo of old stars with little cool gas or dust B Lenticulars are intermediate They re between E7 ellipticals and Sa spirals They re classified by SO if no bar and SB if with bar They have a thin disk and flattened bulge with no gas or spiral arms C Irregulars have the shortest range of sizes with an irregular and chaotic structure They have lots of star formations and blue stars and are separated into 2 different types Irr 1 are smaller than spirals but larger than dwarf ellipticals Irr 2 are rarer and have more of an explosive appearance ll A A group galaxy is a poor cluster with a few dozen bright galaxies There is either regular spherical or irregular asymmetrical Regular is usually rich and contains mostly elliptical and lenticular galaxies Irregular is usually poor and contains more These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute spiral and irregular galaxies There are more than 3 000 galaxy cluster that have been cataloged to date The local group contains 3 spiral galaxies Milky Way M31 M33 It has 40 45 galaxies elliptical irregular and poor B Clusters are rich clusters that have hundreds to thousands of bright galaxies Rich clusters contains thousands of galaxies with one or more giant elliptical galaxies in the center ex Virgo About 2 500 mostly dwarf galaxies are centered on two bright ellipticals Coma Cluster is rich and regular C Superclusters have clusters of cluster and contains dozens of individual clusters Superclusters are the largest coherent structures seen in the Universe The local cluster is roughly centered on the Virgo Cluster and contains tens of thousands of galaxies D Voids have fewer galaxies Vast chains of superclusters are called filaments and long chains of filaments are called walls