Transcript Stars Notes
Notes #2 Stars Brightness • A star’s brightness is measured by its magnitude. Brighter stars have a lower magnitude Sirius is the brightest star in our sky. It is about 9 light-years away from Earth and has a magnitude of 1.4 Stellar Classification • Stars are classified depending on the color and temperature Stellar Classification Temperature (K) O 25,000 K and higher B A 11,000 – 25,000K 7500 – 11,000 K F G K 6000 – 7500 K 5000 – 6000 K 3500 – 5000 K M Less than 3500 K A star’s energy • Luminosity is the total rate at which a star emits radiation energy. • Luminosity is not dependent on distance to the star • Hertzsprung-Russell diagrams (HR diagrams) plot a star’s luminosity and temperature A Light Year • The distance that light can travel in one year. • 5.88 trillion miles (trillion=1012) (9.46 trillion kilometers) • The light from the sun takes 8 minutes and 26 seconds to reach the Earth. The life cycle of a star - birth • Stars begin as a cloud of dust and gas called a molecular cloud or nebula • The molecular cloud is pulled in by gravity, this is called accretion • Nuclear fusion starts and the star is born The life cycle of a star “mid life” • Nuclear fusion continues in the star, releasing massive amounts of energy over time • Fusion reactions in the core balance the inward force of gravity allowing the star to reach a state of equilibrium. The life cycle of a star – late life • • • • Fusion of hydrogen slows Core starts to contract Outer layers expand Core reaches temperatures high enough to spark the fusion into carbon (200,000,000°C) • Star is now a red giant The life cycle of a star – at the end of life • Outer layers continue to expand and form a planetary nebula • Remaining core is now a white dwarf which is dense and slowly cools and no longer produces energy The life cycle of a star – alternate ending • Large stars (1.4 times larger than our sun) become super giants instead of red giants • These stars continue fusion, producing successively heavy elements until their core becomes iron (600,000,000 °C ) • When the entire core becomes iron fusion stops, signaling a violent end… Supernova – the death of a super giant • Once the core is all iron, it collapses and rebounds with an explosion that violently blows the star’s outer layers away from the core. • Temperatures reach 1,000,000,000 °C Supernova – the death of a super giant • If any of the core remains it either becomes a black hole or a neutron star – A thimbleful of matter in a neutron star would weigh more than 100 million tons on earth Supernova – the death of a super giant • If any of the core remains it either becomes a neutron star or a black hole. – A black hole is matter that is so compressed that nothing can escape its gravity pull. – chp897920_700k.asf Theoretical Black Hole