universe

6. The sum of all the space, matter, and energy that exists.
8. small, hot, dim star that is the leftover center of an old star.
10. large celestial body that is composed of gas and that emits light.
11. the gas and dust of the arms that sits between the stars.
13. do not have a particular shape.
17. have little gas or dust and have a round shape.
19. an observed change in the frequency of a wave when the source or observer is moving.
20. hot, blue, stable for millions of years.
22. very luminous object that produces energy at a high rate.
23. If the mass of leftover supernova is greater than 3 solar masses then it will collapse and form a

1. announced the universe was expanding.
2. group of stars or galaxies held together by gravity.
3. a tiny particle
4. beginning stage of star
5. spinning neutron stars that are the source of pulsating radio waves
7. cool, red, stable for billions of years.
9. combines the nuclei of Hydrogen atoms into the nuclei of Helium.
10. have spiral arms made of gas, dust, and stars.
12. year 9.5*10^12 km
14. collection of stars, dust, and gas held together by gravity.
15. theory that the universe started with a cataclysmic explosion.
16. large reddish star late in its life cycle.
18. If the leftover core of a supernova that remains is 1.4-3 solar masses it can become a
21. a gigantic explosion in which a massive star collapses and throws its outer layers into space.