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Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine [email protected] Schedule • December 8 • December 9 – Presentations – 5-10 minutes – On how you would teach something you learned in class to your students • December 13 – Final – Covers everything from midterm – Can bring in one sheet of paper with anything you wanted written on it – Also, your mineral identification sheets Unit of distance in Astronomy • A light-year is the distance that light travels in a year • 10,000,000,000,000,000 meters • 5,878,625,373,184 miles Life of a Star • A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2) • Temperatures like 10-50 K Region is approximately 50 light years across Condensing • Molecular clouds tends to be lumpy • These lumps tend to condense into stars • That is why stars tend to be found in clusters Protostar • The dense cloud fragment gets hotter as it contracts • The cloud becomes denser and radiation cannot escape • The thermal pressure and gas temperature start to rise and rise • The dense cloud fragment becomes a protostar When does a protostar become a star • When the core temperatures reaches 10 million K, hydrogen fusion can start occurring Classification of Stars • Stars are classified according to luminosity and surface temperature • Luminosity is the amount of power it radiates into space • Surface temperature is the temperature of the surface Hertzsprung-Russell Diagram • Ejnar Hertzsprung and Henry Norris Russell plotted spectral type (temperature) versus stellar luminosity • Saw trends in the plots • Stars did not plot randomly OBAFGKM • Oh Be A Fine Girl/Gal Kiss Me • http://www.mtholyoke.edu/courses/tburbine/ASTR223/O BAFGKM.mp3 Hertzsprung-Russell Diagram • Most stars fall along the main sequence • Stars at the top above the main sequence are called Supergiants • Stars between the Supergiants and main sequence are called Giants • Stars below the Main Sequence are called White Dwarfs wd white dwarfs • giant – a star with a radius between 10 and 100 times that of the Sun • dwarf – any star with a radius comparable to, or smaller than, that of the Sun Classifications • Sun is a G2 V • Betelgeuse is a M2 I Main Sequence Stars • Fuse Hydrogen into Helium for energy • On main sequence, mass tends to decrease with decreasing temperature Things to remember • 90% of classified stars are on main sequence • Main sequence stars are “young” stars • If a star is leaving the main sequence, it is at the end of its lifespan of burning hydrogen into helium Stellar Classifications • O, B, A, F, G, K, M • A0, A1, A2, … A9 in the order from the hottest to the coolest “Deaths” of Stars • White Dwarfs • Neutron Stars • Black Holes White Dwarfs • White Dwarfs is the core left over when a star can no longer undergo fusion • Most white dwarfs are composed of carbon and oxygen • Very dense – Some have densities of 3 million grams per cubic centimeter – A teaspoon of a white dwarf would weigh as much as an elephant White Dwarfs • Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth • 200,000 times as dense as the earth White Dwarfs • Collapsing due to gravity • The collapse is stopped by electron degeneracy pressure Electron Degeneracy Pressure • No two electrons can occupy the same quantum state The Sun • Will end up as a White Dwarf Neutron Star • • • • Neutron stars are usually 10 kilometers across But more massive than the Sun Made almost entirely of neutrons Electrons and protons have fused together How do you make a neutron star? • Remnant of a Supernova Supernova • A supernova is a stellar explosion. • Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. • The last person to see and chronicle a supernova outburst in our galaxy was Johannes Kepler. • That was in 1604 rivaled Venus in brightness. Density • You could take everybody on Earth and cram them into a volume the size of sugar cube Explosion • The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron core • 1044-46 Joules • Annual energy generation of Sun is 1034 Joules Black Hole • After a supernova if all the outer mass of the star is not blown off • The mass falls back on the neutron star • The gravity causes the neutron star to keep contracting Black Hole • A black hole is a region where nothing can escape, even light. Event Horizon • Event Horizon is the boundary between the inside and outside of the Black Hole • Within the Event Horizon, the escape velocity is greater than the speed of light • Nothing can escape once it enters the Event Horizon http://www.astronomynotes.com/evolutn/remnants.gif Can you see a Black Hole? No • Black Holes do not emit any light • So you must see them indirectly • You need to see the effects of their gravity Any Questions?