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The Life Cycle of Stars: Chapter 8, Section 2 What we are going to learn today about the life cycle of Stars • The different types of stars • How to read an H-R diagram • How stars appear at different stages in their life cycle on the H-R diagram. The Beginning and End of Stars • The Beginning A star enters the first stage of its life cycle as a ball of gas and dust. Gravity pulls the gas and dust together, and hydrogen changes to helium in a processes called nuclear fusion. • The End Stars usually lose material slowly, but sometimes they can lose material in a big explosion. Much of a star’s material returns to space, where it sometimes forms new stars.. • How many stars are estimated to be in our Milky Way Galaxy? 200,000,000,000 Different Types of Stars • Stars can be classified by their size, mass, brightness, color, temperature, spectrum, and age. A star’s classification can change as it ages. • Main-Sequence Stars After a star forms, it enters the second and longest stage of its life cycle known as the main sequence. Energy is generated in the core as hydrogen atoms fuse into helium atoms. • What kind of star is our sun?? Main Sequence Star System: Alpha Centauri, 25 trillion miles away Red Giants • A red giant is a large, reddish (usually main sequence) star late in its life cycle, or third stage. • As the center of the star shrinks, the atmosphere of the star grows very large and cools to form a red giant or a red supergiant. • This is Betelgeuse, a red giant star in the Milky Way. Who has seen it through a telescope? In what Constellation is it located? Orion Constellation White Dwarf Stars • In the final stage of its life cycle, a star that has the same mass as the sun (main sequence star) or smaller can be classified as a white dwarf. • A white dwarf is a small, hot dim star that is the leftover center of an old star. • It has no hydrogen left and cannot generate energy any more by nuclear fusion, but it can shine for billions of years before cooling completely. In what constellation is there a white dwarf in our galaxy? White Dwarf Stars White Dwarf : Sirius Blue Supergiant: Rigel H-R Diagram: A graph for studying the stars • The H-R Diagram (Hertzprung-Russell diagram) is a graph that shows the relationship between a star’s surface temperature and its absolute magnitude. • Reading the H-R Diagram The diagonal pattern on the H-R diagram where most stars lie, is called the main sequence. • Where is our sun? The main sequence is the location on the diagram where most stars lie H-R Diagram • How hot is the surface of the sun? 5,000 – 6,000 C or 10,000 F According to the H-R diagram, what types of stars have very low temperatures and high absolute magnitudes? • A blue stars • B red giants • C white dwarfs • D main sequence stars When stars get old • When main sequence stars get old (such as our sun) they become red giants and then white dwarfs at the end of their life cycle. • Massive stars, however, generate much more energy and also don’t last as long. • Massive stars may explode with such intensity that they may become supernovas, neutron stars, pulsars, or black holes. • What will our sun probably become in its next stage? Supernovas • A supernova is a gigantic explosion in which a massive star collapses and throws its outer layers into space. • Supernova NGC 6826 Its green gas is almost half of its mass. Neutron Star • After the supernova explosion, the center of the collapsed star contracts to form a new star. It has been smashed together so forcefully that all of its particles have become neutrons. Pulsars • When a neutron star is rapidly spinning, it is called PULSAR. It emits rapid pulses of radio waves and optical energy. • This is Pulsar B1509. It is spinning so rapidly(7 rotations/sec), 12 miles wide, it creates a hand-shaped nebula • Black Holes • Sometimes the leftovers of a supernova are so massive that they collapse to form a black hole. A black hole is an object that is so massive that even light cannot escape its gravity. • Black Holes are invisible: their extreme gravity can cause light to stretch ; their spinning can drag the very fabric of space around with it Who took these pictures? • These images were taken from the ALMA telescope, CHANDRA satellite and the Hubble Space telescope. • ALMA is a radio telescope in Chile • CHANDRA is a satellite launched by NASA in 1999 • The Hubble is an orbiting observatory that was launched by the Space Shuttle Discovery in 1990 Let’s see how much you know about Stars now! • What are some different types of stars? • What does an H-R diagram tell us? • What can main sequence stars (like our sun) turn into as they get old? • What are some things massive stars become?