Chapter 31 Vocabulary

2. Dwarf- Giant star that has lost its outer layers, leaving behind a hot, dense core that continues to contract under gravity.
3. Sequence- Section of the H-R diagram that is plotted from the upper left to the lower right and contains 90 percent of all known stars.
7. The space that contains all known matter and energy.
10. Hole- A region in space that is so dense that nothing can escape its inward pull of gravity.
11. Fusion- A nuclear reaction in which atomic nuclei join together.
13. Interstellar cloud of gas, ice and dust also where stars are born.
16. Layer of the sun that emits light into space.
17. Background Radiation- Residual radiation from the formation of the universe; predicted by the big bang theory and later detected in 1956.
19. Large group of stars, dust, and gas held together by gravity.

1. Late stage in a star's life cycle that occurs when its hydrogen fuel is depleted, its core contracts, and its outer layers expand and cool.
4. Group- Group of about 50 galaxies including the Milky Way.
5. Gigantic explosion of a star in which the temperature within the collapsing star reaches 10 billion K, can evolve into a neutron.
6. Bang Theory- Theory that about 13.7 billion years ago, the entire universe was contained in a single point that began expanding outward.
8. Oval-shaped, closed curve.
9. Darker, cooler areas of the Sun's photosphere.
12. Way- Spiral galaxy that is about 100,000 light-years in diameter and contains from 200 to 400 billion stars, including the sun.
14. Study of how the universe began, what it is made of, and how it continues to evolve.
15. Electrically neutral particle inside the nucleus of an atom.
18. Energy- Energy that might be causing the accelerating expansion of the universe.