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Star birth occurs in a nebula. A star's initial mass determines the star’s temperature, luminosity, and diameter that ultimately decides which life stages and type of death it will experience. The larger the star, the shorter its life will be! Hydrostatic Equilibrium a star must be very hot and dense inside to balance its own GRAVITY TEMPERATURE inside a star governs the rate of nuclear reactions WHICH determines its LUMINOSITY (energy radiated by astronomical object seen by us as light) The balance between gravity pushing inward and outward pressure is maintained by heat due to nuclear reactions and compression is called HYDROSTATIC EQUILIBRIUM SO…..If a star expands or contracts, hydrostatic equilibrium Is not in place. NEBULA • Large clouds of gas and dust that contract due to gravitational force as it becomes hotter st 1 Stage of Life Protostar: hot condensed object of gas and dust that is pulled together by gravity at the center of a nebula it generates energy and shines but is NOT hot enough to ignite nuclear fusion Nuclear Fusion hydrogen atoms fuse into helium creating the intense energy found in stars 2nd Stage • Main Sequence (the Sun) –Longest stage, stable star –Hydrogen changes into helium which creates enormous amounts of energy –The size of the star does not change much –90% of all stars A Star of a Joke… A woman at a gas station noticed a spaceship landing in front of her. An alien stepped out of the spaceship and started to pump gas into it. The woman noticed the letters ''U.F.O.'' printed on the side of the ship. She turned to the alien and asked ''Does U.F.O. stand for Unidentified Flying Object?'' The alien answered, ''No, it stands for Unleaded Fuel Only!'' rd 3 stage Giants and Supergiants – Main Sequence star becomes a red giant • Red giant star that expands 50x their normal size and cools (giving it a reddish color) it loses all its hydrogen; appears brighter • Supergiant Large star with high mass that become even hotter and expanding even more It is 100’s of times hotter and more luminous than a red giant Supernova • gigantic explosion in which a massive star collapses – Occurs after a massive star uses up its fuel source Supernova Remnant White Dwarf • small hot star • Fuel is used up –Final stage for some stars –Can shine for billions of years before they completely cool and extinguish Black Dwarf • The remains of a white dwarf after it has completely cooled. • Scientists do not think universe is old enough to have any black dwarfs yet ? Neutron Star A neutron star is a type of remnant that can result from the gravitational collapse of a massive star during a supernova event. Small dense starone teaspoon would weigh a billion tons on Earth! What is a Black Hole? ??????????????????????????????????????????????????????? • an object that is so massive that light cannot escape its gravity Did you know….? Astronomers can detect black holes by using X-ray telescopes Pulsars A neutron star that spins and sends out beams of radiation is called a pulsar Hertzprung-Russell Diagram Shows the relationship between a star’s surface temperature and absolute magnitude – Used to study the lives of stars – Most stars lie along the main sequence portion of the diagram Our Place in Our Galaxy Be careful about wishing on stars…. What’s the Difference? Solar System Universe Galaxy Image credits: NASA, STScI Where is our Solar System? Visible stars, gas, dust in the Milky Way Galaxy Solar System here Image credits: NASA, STScI What Are Galaxies? • A galaxy is a system of stars, dust, and gas held together by gravity. • Galaxies are large collections of stars….. millions and billions of stars • There are hundreds of billions of galaxies in the Universe • Millions to hundreds of billions of stars in each galaxy Galaxy Facts • • • The most distant galaxies ever photographed are as far as 10 billion to 13 billion light-years away. Large galaxies have more than a trillion stars. Only three galaxies outside the Milky Way are visible with the unaided eye. People in the Northern Hemisphere can see the Andromeda Galaxy, which is about 2 million light-years away. People in the Southern Hemisphere can see the Large Magellanic Cloud, which is about 160,000 light-years from Earth, and the Small Magellanic Cloud, which is about 180,000 light-years away. Remember…. A light-year is the distance that light travels in a vacuum in a year -- about 5.88 trillion miles (9.46 trillion kilometers). An astronomical unit is 93 million miles or 150 million km (average distance between Sun and the Earth) The speed (velocity) of light is 300,000 km/sec. Three Main Types of Galaxies Galaxies are classified based on shape 1. Spiral--rotating disk (with arms) 2. Elliptical—spheroid or oval disk of stars with more chaotic motion 3. Irregular--none of the above Examples of Three Main Galaxy Types Elliptical Spiral Irregular Looking at the Milky Way A Spiral Galaxy Viewed as a bright band of stars across the sky There are about 200-400 billion stars in the Milky Way. Much of the Milky Way is blocked by dust seen as a dark band through the middle of the Milky Way The Milky Way is… • Gigantic! Its disk spans 100,000 light-years • it’s about 14 billion years old, give or take a few billion. – Astronomers arrived at this age by measuring the age of a single star. The galaxy can’t be any YOUNGER than its oldest stars, so this technique yields a MINIMUM age for the Milky Way. – Astronomers determined the star’s age by measuring its chemistry. They found that it contains only minute traces of anything heavier than hydrogen and helium, the two lightest elements. One of the most important tracers of the star’s age is a radioactive element called thorium.The star contains only about half as much thorium as expected.Thorium has a half-life of 14 billion years. In other words, in 14 billion years, half the star’s thorium should have turned into other elements. Since half of the thorium has disappeared, astronomers deduce that the star is about 14 billion years old — and so is the Milky Way. Spiral arms are a natural consequence of some rotations. If gas/dust in a disk are rotating with the same speed, stuff further out will take longer to go around and will lag behind Elliptical Galaxies lack spiral arms and dust and contain stars that are generally identified as being old Irregular Galaxies Irregular galaxies lack any specific form and contain stars, gas and dust