Big bang theory

3. the average density of matter required for the Universe to just halt its expansion, but only after an infinite time
5. a place in space where gravity pulls so much that even light can not get out
6. the study of the nature and evolution of the universe.
8. type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude
15. the radiation era in the Big Bang theory
16. the era that started when the gravitational effect of matter began to dominate the effect of radiation pressure

1. any of the systems of stars and interstellar matter that make up the universe
2. refers to its surface and that is what determines its color
4. the explosively rapid expansion of space-time that occurred a tiny fraction of a second after the Big Bang
7. the distance light travels in one year
9. change in observed wavelength, or frequency
10. the angle between the Earth at one time of year, and the Earth six months later, as measured from a nearby star
11. any of the four basic forces that govern how objects or particles interact and how certain particles decay
12. unit of temperature
13. a component of the universe whose presence is discerned from its gravitational attraction rather than its luminosity
14. the physical interaction among electric charges, magnetic moments, and the electromagnetic field