Galaxies ppt

galaxies powerpoint presentations and ppt on galaxies
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Prof.EvanBaros,United Kingdom,Teacher
Published Date:26-07-2017
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Chapter 25 Galaxies and Dark MatterUnits of Chapter 25 25.5 The Universe on Large Scales The Sloan Digital Sky Survey 25.1 Dark Matter in the Universe 25.2 Galaxy Collisions 25.3 Galaxy Formation and Evolution XX25.4 Black Holes in Galaxies25.5 The Universe on Large Scales Galaxy clusters join in larger groupings, called superclusters. This is a 3- D map of the Local Supercluster, of which our Local Group is a part. It contains tens of thousands of galaxies.25.5 The Universe on Large Scales This slice of a larger galactic survey shows that, on the scale of 100–200 Mpc, there is structure in the Universe—walls and voids.25.5 The Universe on Large Scales This survey, extending out even farther, shows structure on the scale of 100–200 Mpc, but no sign of structure on a larger scale than that. The decreasing density of galaxies at the farthest distance is due to the difficulty of observing them.25.5 The Universe on Large Scales Quasars are all very distant, and the light coming to us from them has probably gone through many interesting regions. We can learn about the intervening space by careful study of quasar spectra.25.5 The Universe on Large Scales This “Lyman-alpha forest” is the result of quasar light passing through hundreds of gas clouds, each with a different redshift, on its way to us:25.5 The Universe on Large Scales This appeared at first to be a double quasar, but on closer inspection the two quasars turned out to be not just similar, but identical—down to their luminosity variations. This is not two quasars at all—it is two images of the same quasar:25.5 The Universe on Large Scales This could happen via gravitational lensing. From this we can learn about the quasar itself, as there is usually a time difference between the two paths. We can also learn about the lensing galaxy by analyzing the bending of the light.25.5 The Universe on Large Scales Here, the intervening galaxy has made four images of the distant quasar:25.5 The Universe on Large Scales These are two spectacular images of gravitational lensing: On the left is distant galaxies being imaged by a whole cluster. On the right is a cluster with images of what is probably a single galaxy.25.5 The Universe on Large Scales On the left is a visible image of a cluster of galaxies: on the right, to the same scale, is the dark matter distribution inferred from galaxy motion:25.5 The Universe on Large Scales This composite image shows two clusters of galaxies colliding, with the galaxies in white and the intracluster gas in red:Discovery 25-1: The Sloan Digital Sky Survey The Sloan Digital Sky Survey is being done by a dedicated telescope situated in New Mexico. Its purpose is to measure hundreds of millions of celestial objects, with five intensity points spanning the visible and near-infrared wavelengths. Approximately one million of these also have their redshifts measured, making possible very detailed redshift maps.Summary of Chapter 25 • Galaxy masses can be determined by rotation curves and galaxy clusters. • All measures show that a large amount of dark matter must exist. • Large galaxies probably formed from the merger of smaller ones. • Collisions are also important. • Merger of spiral galaxies probably results in an elliptical galaxy.Summary of Chapter 25 (cont.) • Quasars, active galaxies, and normal galaxies may represent an evolutionary sequence. • Galaxy clusters are gravitationally bound into superclusters. • The Universe has structure up to 100–200 Mpc; beyond that, there is no sign of it. • Quasars can be used as probes of intervening space, especially if there is galactic lensing.25.1 Dark Matter in the Universe Other galaxies have rotation curves similar to ours, allowing measurement of their mass:25.1 Dark Matter in the Universe Another way to measure the average mass of galaxies in a cluster is to calculate how much mass is required to keep the cluster gravitationally bound.25.1 Dark Matter in the Universe Galaxy mass measurements show that galaxies need between 3 and 10 times more mass than can be observed to explain their rotation curves. The discrepancy is even larger in galaxy clusters, which need 10 to 100 times more mass. The total needed is more than the sum of the dark matter associated with each galaxy.25.1 Dark Matter in the Universe This image may show a galaxy interacting with an unseen neighbor—a “dark galaxy”:

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