They developed a graph, called the H-R diagram, that relates the temperature of a star to its absolute magnitude.

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2 Ejnar Hertzsprung and Henry Russell noticed that stars with higher temperatures and large sizes also have brighter absolute magnitudes the actual amount of light given off by a star. (also referred to as luminosity) Apparent magnitude the perceived amount of light given off by a star as seen by Earthlings. They developed a graph, called the H-R diagram, that relates the temperature of a star to its absolute magnitude. The stars on the diagram are classified by size, temperature, and brightness.

3 Graph that relates Temperature and Absolute Magnitude (Brightness) of Stars.

4 Spectral Class indicates temperature classification More negative Brighter Larger sizes More positive Dimmer Smaller sizes hotter cooler

5 A red star with a magnitude of 3 would be (choose all that apply) cool hot large small.

6 The color and spectral class on the H-R diagram indicate the star s. temperature The coolest stars on this diagram are red in color.

7 About 90% of stars, including our sun, are part of the Main Sequence, in which the hottest stars are the brightest and brightness decreases as temperature decreases.

8 Main Sequence most stars fall into this category (broad range of sizes, brightness & temperatures); this group represents the main stage of a star s life Dwarfs small stars in the lower part of the diagram, and are not bright Giants large stars in the upper part of the diagram, and are bright Supergiants extremely massive, bright stars in the very top part of the diagram

9 A star begins as large clouds of hydrogen gas and dust, called a nebula. The particles exert gravitational force on each other and the nebula begins to contract toward the center and build up heat. Temperatures increase to 10 million K (10,000,000 Kelvin = degree Celsius = degree Fahrenheit Fusion begins as hydrogen changes to helium releasing energy into space and a

10 Nuclear Fusion

11 As long as a star s gravity (pulling inward) balances its force from fusion (pushing outward), a star is a star (a normal part of the star s life). When most of the hydrogen is used up and changed to helium, there is no longer a balance of gravity and pressure, the core contracts and the temperature increases. The outer layers expand and cool becoming a In about 5 billion years our sun will become a giant. (as Helium fuses into Carbon)

12 When the helium supply begins to be used up, the core contracts even more and its outer layers escape into space. Left behind is the hot, dense core, where helium changes to carbon. The core contracts due to gravity, heats up again, and becomes a White Dwarfs are about the size of Earth.

13 In stars that are at least 10 times as massive as our sun, the life cycle is short and violent. In massive stars the core heats up to much higher temperatures, creating heavier elements, and it becomes a Eventually Iron forms and begins absorbing the energy like a ticking time bomb. Finally, the outer portion of the star explodes into a

14 If the collapsed core of the Supernova is about 2 times as massive as the Sun, it may shrink approximately 20 km in diameter. Only neutrons can exist in this dense core. The core is prevented from collapsing completely because Neutrons resist the pull inward. Neutron stars are so dense, a teaspoonful would weigh about 100 million metric tons.

15 If the supernova leaves behind a core that is 30 times or more massive than our Sun, probably nothing can stop the core from collapsing inward on itself. All the core s mass collapses to a point that has no volume. Nothing can escape its gravity pull, not even light. Because light cannot escape, it is called a

16 Black holes do not pull objects in, stars and planets can orbit around black holes. Astronomers sometimes use bursts of X-rays from stars entering black holes to locate the black holes.

17 Back to the beginning of the life cycle - nebula are created from matter given off by stars. It is believed that during a supernova explosion, the force is so strong and the temperatures so hot (100,000,000,000 o C) that the other elements on the Periodic Table are created.

18 The Life Cycle of a Star depends on the Original MASS!!!!!