Astrophysics is the sub-discipline of physics that studies the behavior of astronomical objects such as stars and planets. In their studies, astrophysicists use theories like General Relativity, chemistry, and thermodynamics.
From both theoretical expertise and observations, we have the following theories:
- the Big Bang (estimated to be about billion years ago), from which the entirety of the universe originated;
- the existence of dark matter (otherwise unknown outside of gravitational interactions) and dark energy (otherwise unknown outside of speeding up inflation), thought to comprise 95% of the universe's total energy.
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