AST- 105 1st EditionLecture 22Outline of Last LectureI. Spheroidal ComponentsII. Galactic CenterIII. The Galactic NucleusIV. Mass of GalaxyV. The HaloOutline of Current LectureI. Dark MatterII. Globular Cluster DynamicsIII. Cluster EvolutionIV. Close BinariesV. Blue Stragglers Current Lecture I. Dark Mattera. As much as 90% of the mass of the Galaxy may be made up of dark matter.b. The physical nature of the dark matter is still not known.1. Most of it is thought to be in the form of WIMPS1. i.e. Exotic Subatomic particles2. Experiments are underway to detect these particles1. e.g. at the Large Haaron Colliderin EuropeII. Globular Cluster Dynamicsa. Contain up to a few million stars.1. Density is highest in the core2. Density is lowest in the halob. Each star feels gravity of all the other stars1. Causes each star to orbit cluster center in a rosette pattern2. Orbits have random planes and directionsIII. Cluster Evolutiona. Cluster Evolution- close encounters occur between pairs of stars1. Orbits are deflected by gravitational attraction2. Some stars are kicked into core, while others are kicked into halob. Core Collapse- core shrinks and becomes much denser.IV. Close Binariesa. Close binaries are formed by gravitational interactions in the core1. Will be X-ray binary if one star is a white dwarf, neutron star or black hole2. Overabundance observed in clustersb. Gravitational interactions between binaries and singles can eject both from cluster.1. Ejected stars join galactic halo2. Clusters may be X-ray binary factoriesV. Blue Stragglersa. Most cluster stars are low-mass, red, old starsb. Standard Theory:1. All cluster stars were born about 10^10 years ago, however, observe smallnumbers of higher-mass, blue, apparently young stars known as blue stragglers.1. Stellar evolution theory says these should not exist now- should have evolved to red giants then white dwarfs.c. Theory for Blue Stragglers:1. Formed for stellar collisions leading to mergers2. Produces “reborn” blue, higher mass stars3. Hubble Space Telescope detected large numbers of blue stragglers in cluster cores, where collision rate is
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