Lesson Objectives The students will be able to. . . Identify the conditions necessary for fusion to occur inside a star. Relate the color of a star to its temperature. Discuss the importance of the H-R diagram to astronomers. Describe the phases in the life cycle of a sun like star Discus how the deaths of super massive stars are responsible for the creation of the heavier elements. 1 Index What is a star? Nuclear Fusion Types of stars Classifying stars Stars are like people A star is born Stars get old too Silent death Out with a bang Remains Deaths of super massive stars Exceptional deaths Black holes 2 Introduction Today’s topic What stars really are How stars are classified Star life cycles 3 What is a star? A giant ball of gas They emit light and heat through nuclear reactions They are powered by fusing Hydrogen into Helium 4 Nuclear Fusion Certain conditions must be met for fusion to occur Extremely high values for density, temperature, and mass. For example, the density at the sun’s core is 158.0g/cm. That is 18 times the density of copper The sun’s core reaches a temperature of 15 million degrees The sun has a mass of 330,000 Earths 5 Fusion occurs in a star’s core Hydrogen is fused into Helium Some mass is lost and converted to energy The energy is given off as heat and light E=MC2 6 Types of Stars Main sequence stars Sun sized stars Giants Have Super a diameter of 250 times the size of the sun Giants Have a diameter of 1000 times that of the sun. The largest known is 2700 times the sun’ size. White Dwarfs Are the size of small planets ex. Sirius the largest white dwarf has a diameter of 10,400km. Neutron Have stars a diameter of only 20 – 30km 7 Types of Stars Stars are classified by their characteristics Size Temperature Brightness 8 Classifying Stars Stars are also classified based on temperature and brightness using the H-R diagram 9 Stars are like people They have life cycles of their own. They are born They live a life They grow old They die and have remains 10 A Star is born All stars begin their lives as a cloud of gas The cloud is mainly hydrogen Gravity causes the denser portion to collapse This forms a proto star The gasses continue to collapse pressure and temperature increase. Nuclear fusion begins 11 A star isn’t born Sometimes there is not enough mass Fusion never starts Gravity holds gases around a core These are the brown dwarfs 12 Stars live on the main sequence While on the main sequence stars consume their hydrogen fuel source. Most stars spend 10 billion years here Larger stars die faster because they use up thier fuel Smaller stars can last up to 50 billion years 13 Stars get old too The stars run out of Hydrogen fuel Gravity contracts the core The temperature gets hot enough to ignite the Helium The star expands and the outer layers cool The star becomes a red giant 14 Silent death The nuclear reactions stop Gravity crushes the matter together as close as possible The core glows brightly becoming a white dwarf 15 Out with a bang Sometimes the outer layers are blown away in an enormous explosion called a super nova 16 Remains When a white dwarf stops glowing it becomes a black dwarf. The black dwarf is usually surrounded by a planetary nebula. 17 Deaths of super massive stars Some stars are so massive that they create neutron stars Their explosions are so violent that all that is left behind are the neutrons of the atoms 18 Star Power It is in the incredible power of neutron stars and white dwarfs that the heavier elements are formed Temperature exceeds 7 million degrees The density is so great that a thimble of matter weighs more than an elephant. All of the elements are born from hydrogen 19 Exceptional deaths Some super novas create a phenomena called a black hole. The gravity is so strong that light is pulled in Black holes occur at the center of galaxies 20 Black Hole at Galactic Center 21 Black Hole Flash 22 The End? Some scientists believe that black holes will devour the entire universe. They Some could recreate the big bang believe the universe will expand forever. There is not enough mass to pull it back together 23 Credits Slide show by Nick Delciappo Cleveland public schools Reference Hsu, Tom. Foundations of Physical Science with Earth and Space Science, Delta Education LLC, New Hampshire, Second edition, 2007 pp.639-646. 24