Transcript Slide 1
Formation of Stars and Galaxies Introduction 1. Timeline and Big Bang The Instruments 1. Optical Telescopes a) Use different regions of Electromagnetic Spectrum i. Visible EM region ii. Infrared EM region iii.Ultraviolet EM region b) Types i. Refracting ii. Reflecting iii.Catadioptric 2. Radio Telescopes 3. X-Ray and Gamma-Ray Telescopes The Objects 1. Stars 2. Nabula 3. Galaxies ( More than 100 billion ) i. Have 10 million to one trillion stars ii. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances of the order of millions of parsecs (mpc). Types of Galaxy i. Elliptic ii. Spiral iii. Barred-Spiral iv. Irregular M87 NGC4414 NGC1300 NGC1427A Hubble’s Tuning Fork ….. more 4. Groups , Clusters and Superclusters i. Group A group of galaxies contain about < 50 galaxies, a diameter of 1 to 2 megaparsecs, masses contained in groups is typically ~ 1013 solar masses and the model applied is CDM. ii. Cluster A cluster of galaxies contain 50 to 1000 galaxies, hot X-ray emitting gas, clusters typically have masses from 1014 to 1015 solar masses and large amounts of dark matter a diameter from 2 to 10 Mpc . A group is a member of cluster iii. Supercluster A superstructure can have extents of order 100 Mpc, have masses above 105 solar masses. A cluster is member of supercluster 5. Filaments of galaxies are 50 to 80 mpc in length 6. Black Holes and Supermassive Black Holes i. If a collapsing star of over 3 solar masses does not eject matter, it becomes a black hole. ii. a mass of an order of magnitude between 105 and 1010 of solar masses. Most, if not all galaxies, including the Milky Way, contain supermassive black holes at their galactic centers. 7. Dark Matter and Dark Energy ….. more 8. Voids A void billion light years across was found in 2007 9. Walls i. Great Wall (cfA2) of galaxies, a very large structure discovered in1989 is 500 million l years long, 200 million l years wide and 15 million l years thick. ii. Sloan Great Wall of galaxies , the largest structure discovered in 2003 is 1.37 billion light years but is not a structure in the strict sense Big Bang and Models of Cosmology 1. Lambda - CDM ( Cold Dark Matter ) It explains cosmic microwave background observations, as well as large scale structure observations and supernova observations of the accelerating expansion of the universe. Cold Dark Matter is explained as being cold its velocity is non-relativistic (v<<c) ,can not cool by radiating photons and collisionless (i.e., the dark matter particles interact with each other and other particles only through gravity). 2. WDM ( Warm Dark Matter ) Recently WDM predicted the Black Hole formation at the centrer at the center of galaxy. 3. HDM (Hot Dark Matter) It is represented primarily by neutrinos, does not apparently account for the pattern of galaxies observed in the Universe. Discovery of dim dwarf galaxies filling void negates HDM. The two models CDM and WDM are still competing with each other and computer simulations don’t discard them. Galaxies Formation 1. Models and Computer Simulations 2. Primordial Fluctuations Large clumps of gases and protogalaxies are formed 3. Central Quiescent theory Inside Dark Matter halos galaxies are formed by slow accretion. Massive galaxies should be bright. 4. Collisional Starburst Scenario Galaxies are formed quickly by collisions between small clumps of matter , produces could trigger a huge burst of star formation. 5. Supermassive Black Holes at the center small "seed" black holes, which formed in the very early universe, served as gravitational "roots" for the clouds of gas around them 6. Top-Down Formation 7. Bottom-Up Formation 8. Formation of Spiral Galaxies Lambda-CDM Model supports it. Slow star formation 9. Formation of Elliptical Galaxies Formed by merger of Galaxies and quick star formation. Have supermassive black holes at the centers. 10. Formation of Barred-Spiral Galaxies possible cause of bar creation is tidal disruptions between galaxies. The bar structure decays over time Star Formation 1. Accretion of gases and shrinkage under gravity at 1. 10 kelvin or less forms a protostar. 2. Shrinkage continues and temperature rises. 3. At few million kelvin therminuclear reactions of hydrogen start. Protostars less than 0.08 solar masses (0.08M) can never start thermonuclear process. 4. Time of shrinkage and burning of hydrogen depends on mass of protostar. 5. After hydrostatic and thermal equibrium star becomes a stable star and occupies the main sequence of H-R diagram. ……. Diagram Nucleosynthesis of Stars 1. After consuming hydrogen if the star is less than Chandrashekhar limit of 1.4Mass of the sun, it will become a white dwarf having volume about earth 2. At 100 million kelvin at the core helium burning starts producing carbon and oxygen. 3. At 600 million kelvin and mass equl to 4 M carbon burning begins producing neon, oxygen and magnesium 4. At 1.2 billion kelvin neon burning begins 5. At 1.5 billion oxygen starts burning. Pricipal prouct is sulpher , it also produces silicon, phosphorus and magnesium 6. At about 2.7 billion kelvin silicon burning starts it produces iron and further burning stops. Any star with more than 10M can develop iron core. 7. When density reaches more than 4x1017 kg/m3 a neutron star is born. If mass >3.0M it will become a black hole. 8. For 25M carbon burns for 600 years, neon for 1 year, oxygen for 6 months and silicon in 1 day. END