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Download the life cycle of stars
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THE LIFE CYCLE OF STARS This star has entered the last stage of its life cycle • The first stage of star formation is NUCLEAR FUSION • Gravity pulls clouds ofgas and dust (nebulae) together into a sphere – as it becomes denser, it gets hotter and the hydrogen changes to helium. • Stars are classified by: 1. 2. 3. 4. 5. 6. 7. Size Brightness Mass Color Temperature Spectrum Age TYPES OF STARS: • MAIN SEQUENCE STARS – this is the second phase and the longest phase • Energy is generated in the core as hydrogen atoms fuse into helium atoms • Stars are about 98% Hydrogen and Helium • The sun in this stage (10 million yrs. to become this stage – has been shining for 5 billion years ) Earth is 4.6 billion years old GIANTS AND SUPERGIANTS • Third stage – RED GIANT • RED GIANT – A large reddish star late in its life cycle - a star that expands and cools once it uses all of its hydrogen • Eventually will shrink • When shrinks – atmosphere grows large and cools to a red giant or red supergiant • In 5 billion years the sun will become a red giant • Red giants – 10 or more times bigger than the sun. • Red Supergiants – at least 100 times bigger than the sun. WHITE DWARFS AND RED DWARFS • WHITE DWARF – a small, hot, dim star that is the leftover center of an old star • No hydrogen left • Can shine for billions of years before they cool completely • RED DWARF – low-mass stars • Oldest stars in the universe BLUE STARS • BLUE STARS – very massive blue stars are not in the main sequence very long. • They quickly use up the hydrogen in their cores • Expand and turn into giants or supergiants SUPERNOVAS • A main sequence star with a mass of more than about 10 Suns experiences a spectacular end. • It swells into a red supergiant with cooling, expanding outer layers. • Eventually its core collapses, causing a huge explosion known as a supernova • A gigantic explosion in which a massive star collapses and throws its outer layers into space NEUTRON STARS and PULSARS • NEUTRON STAR – a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons • If the core of a supernova has relatively low mass, the core will be crushed into a tiny, super dense neutron star • PULSAR – a spinning neutron star BLACK HOLE • A volume of space in which gravity is SO GREAT that nothing can escape, not even light, although objects can fall in • If the core of a supernova has a mass of more than about two Suns, its own gravity will squash it further, into a black hole. HR Diagram (page 592 – 593) Shows the relationship between a star’s surface temperature and absolute magnitude . Hertzsprung-Russell Diagram • The temperature is given along the bottom of the diagram. Hertzsprung-Russell Diagram • The absolute magnitude (brightness) is given along the left side. Hertzsprung-Russell Diagram • The Hot (blue) stars are located on the LEFT • The Cool (red) stars are located on the RIGHT. Hertzsprung-Russell Diagram • The BRIGHT stars are at the TOP. • The DIM stars are at the BOTTOM. • The DIAGONAL pattern where most stars lie is the MAIN SEQUENCE. • The SUN is located in the middle of the diagram. • Average stars like the sun become giants or supergiants (Right) and then down to the left to become white dwarfs.