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The Life Cycle of a star By Ramunė Stabingytė and Kotryna Bieliauskaitė Kaunas “Vyturys” cathalic secondary school What is a Star? • A star is a huge sphere of very hot glowing gas. • When stars are grouped together we call them constellations. • The big dipper is constellation that we see often. http://en.wikipedia.org/wiki/File:Big_dipper_from_the_kalalau_lookout_ at_the_kokee_state_park_in_hawaii.jpg The Sun • The Sun is the only star in our solar system – All eight planets, comets, and an asteroid belt, revolve around the Sun. • The Sun is a yellow, medium sized star. http://en.wikipedia.org/wiki/File:Yohkohimage.gif Classifying Stars • Stars are classified according to their temperature and brightness. • Hot Stars are Blue or White • Cooler Stars are Red or Orange Classifying Stars Cont… • A young star is called a dwarf star –They can be colored red, yellow, or white. • Our Sun is a yellow dwarf • Older Stars are called Supergiants –They can be colored red or blue. The Timeline of a Star • Our Sun is an average star. The chart below shows the lifecycle of our sun over billions of years. http://en.wikipedia.org/wiki/File:Solar_Life_Cycle.svg Birth of a star • In space, there are huge clouds of gas and dust called nebulas. • These clouds are made up of hydrogen and helium and are the birthplace of new stars. • Gravity pulls the hydrogen gas in the nebula together and it begins to spin, • As the gas spins faster and faster, it heats up and is known as a protostar. Protostar • The second stage of star creation. • At this point the temperature eventually reaches 15,000,000 °C. • The cloud begins to glow brightly. • At this stage, it contracts a little and becomes stable and is called a main sequence star. Main sequence star • A star will remain in this stage, shining for millions or billions of years to come. • As the main sequence star glows, hydrogen in the core is converted into helium by nuclear reactions. • Our sun is a main sequence star. Red giant phase • When the hydrogen supply in the core begin to run out, the core becomes unstable and contracts. • The outer shell of the star starts to expand. • As it expands, it cools and glows red. • The star has now reached the red giant phase. White dwarfs • Gravity causes the last of the star’s matter to collapse inward and compact, this is the white dwarf stage. • At this stage the star’s matter is extremely dense. • White dwarfs shine with a white hot light. • The star has now reached the black dwarf phase in which it will forever remain. Massive stars • Once massive stars reach the red giant phase, the core temperature increases. • Gravity continues to pull carbon atoms together as the temperature increases forming oxygen, nitrogen, and eventually iron. • At this point, fusion stops and the iron atoms start to absorb energy. • This energy is eventually released in a powerful explosion called a supernova. Supernova • A supernova can light up the sky for weeks. • The temperature in one can reach 1,000,000,000 °C. • The supernova then either becomes a neutron star or a black hole. Neutron star • Neutron stars spin rapidly giving of radio waves. • If the radio waves are emitted in pulses, the neutron star is called a pulsar. Black hole • The core of a massive star that has 8 or more times the mass of our Sun remains massive after the supernova. • It has now become a black hole which readily attracts any matter and energy that comes near it. • Black holes are not visible, they are detected by the Xrays which are given off as matter falls into the hole. How do the sizes of the stars compare?