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Astronomy 3040 Astrobiology Spring_2016 Day-6 Homework -1 Due Monday, Feb. 8 Chapter 2: 1, 3, 16 23, 24, 26 29, 30, 33 44 53, 54, 56 The appendices will be useful Project http://www.ulalaunch.com/docs/product_sheet/Delt aIVPayloadPlannersGuide2007.pdf This is the Delta-IV payload guide overview. 20MB. Planetary quarantine program. Becoming a Star The protostar’s energy source is gravitational energy. Temperature rises in the core. Hydrogen fusion begins in the core, and the star begins its life on the main sequence. Very low-mass stars (< 0.08 M) never start hydrogen fusion. These are called brown dwarfs. Protostars to Stars Evolutionary Tracks An individual star follows an evolutionary track on the H-R diagram. This is the path of the temperature and luminosity with time. Protostars get less luminous and hotter. The star first appears as a T Tauri star. The star moves on the Hayashi track and arrives on the main sequence. Since L = (area) (T4), the star contracts. Star Clusters Star formation can make star clusters. These are gravitationally bound groups of stars. Some stars are more massive, others less so. Higher-mass stars evolve faster. Clusters are good laboratories for testing our ideas of star formation and evolution. Star Clusters and Stellar Evolution Star clusters are bound groups of stars, all made at the same time. Each star evolves at a rate set by its mass. High-mass stars evolve more quickly. Young clusters still have massive stars on MS. In older clusters, massive stars have died. Location of main sequence turnoff gives cluster age. Cluster Trends Globular clusters (probe halo): All old. All low in heavy elements. Open clusters (probe disk): Contain dozens to hundreds of stars. Clusters are young, old, and in between. Rich in heavy elements. Omega Centaurus M35 Main Sequence Lifetimes Mass (M) Luminosity (L) 17.5 52,500 Lifetime in billion years 0.01 2.0 14 1.1 1.0 1.0 10 0.67 0.15 53 0.21 0.011 290 Galaxy Formation The Milky Way offers clues to galaxy formation. All halo stars have some heavy elements, so at least one prior generation of stars must have existed. Halo objects were formed before interstellar gas was all concentrated into the disk. Later star formation was all in the disk. A Normal Spiral Galaxy Satellite Galaxies The Milky Way probably formed by the merger of many smaller protogalaxies. Several of these are still orbiting the Milky Way as satellite galaxies. These can contain significant amounts of gas. The gas delivered by the protogalaxies was a significant source of star formation. Evidence for different chemical evolution timescale. H-R Diagrams Compared to the universe, the Earth is less than a grain of sand on a beach Our Sun, A Slightly Bigger than most, Star The Sun is the Largest Object in the Solar System The Sun contains more than 99.85% of the total mass of the solar system If you put all the planets in the solar system, they would not fill up the volume of the Sun 110 Earths or 10 Jupiters fit across the diameter of the Sun How big is the Sun? The Sun goes through periods of relative activity and inactivity March 5, 2009 21:48:43 CST