Chapter 30 Section 2 Handout Stellar Evolution

1 Why are astronomers not able to observe the entire life of any star? Because a star typically exists for billions of years.

2 What is luminosity? The total amount of energy a star gives off each second.

3 What is the Hertzsprung-Russell diagram? The graph that illustrates the pattern revealed when the surface temperatures of stars are plotted against their luminosity.

4 What is plotted on the horizontal axis and the vertical axis of the Hertzsprung-Russell (H-R) diagram? Horizontal axis: The temperature of a star’s surface. Vertical axis: The luminosity of a star.

5 What is the main sequence? The band that runs diagonally through the Hertzsprung-Russell diagram and extends from cool, dim, red stars at the lower right to hot, bright, blue stars at the upper left.

6 What is a nebula? A cloud of gas and dust where a star begins.

7 What is Newton’s law of universal gravitation? All objects in the universe attract each other through gravitational force.

8 Gravitational force increases as the mass of an object: Increases or as the distance between two objects decreases.

9 What is a protostar? A shrinking, spinning region that begins to flatten into a disk with a central concentration of matter.

10 What happens as more matter is pulled into a protostar? Gravitational energy is converted into heat energy, and the temperature of the protostar increases.

11 What is important about the onset of fusion? It marks the birth of a star.

Life Cycles of Stars Stars are born (nebular theory) They all start like our sun converting hydrogen into helium by high temperature and nuclear fusion

Life Cycle of Stars by MASS White dwarf then black dwarf? Star like our sun Red giant Planetary nebula Nebula-gas and dust Protostars Neutron star and/or black hole supernova Red supergiant Massive star

12 What happens as gravity increases the pressure on the matter within a star? The rate of fusion increases.

13 What does the equilibrium between the outward pressures of radiation and the force of gravity do? It makes the star stable in size.

14 How long does a main sequence star maintain a stable size? As long as it has an ample supply of hydrogen to fuse into helium.

15 What is the second and longest stage in the life of a star? The main-sequence stage.

16 A star that has the same mass as the sun’s mass: Stays on the main sequence for about 10 million years.

17 When does a star enter its third stage? When almost all of the hydrogen atoms in its core have fused into helium atoms.

Nucleosynthesis and Fusion Reactions The main process responsible for the energy produced in most main sequence stars is the proton-proton (pp) chain.

18 What does increased temperature from contraction in the core cause the helium core to do? As the helium core becomes hotter, it transfers energy into a thin shell of hydrogen surrounding the core.

Red Giant Stars

19 Describe the stars known as giants and their place on the H-R diagram. They are large, red stars whose hot core has used most of its hydrogen. They are above the main sequence.

20 What are supergiants? Main-sequence stars that are more massive than the sun and become larger than regular giant stars.

21 What is a planetary nebula? A cloud of gas that forms around a sunlike star that is dying.

22 What is a white dwarf? A hot, extremely dense core of matter leftover from an old star.

23 What is a black dwarf? A white dwarf that no longer gives off light.

24 An explosion on a white dwarf caused by a pressure build-up is a: Nova

25 What effect may a nova have on a star? It may cause it to become many thousands of times brighter.

26 Describe a supernova and how it differs from a nova. A supernova is a star that has such a tremendous explosion that it blows itself apart. Unlike a nova, a white dwarf can sometimes accumulate so much mass on its surface that gravity overwhelms the outward pressure. The star collapses and is so dense that the outer layers rebound and explode.

27 Stars that have masses of more than 8 times the sun’s mass produce supernovas: Without needing a secondary star to fuel them.

The End?