The gas that surrounds a planet or star. The Earth's atmosphere is made up of mostly nitrogen, while the Sun's atmosphere consists of mostly hydrogen. The Advanced X-ray Astrophysics Facility. AXAF was renamed Chandra X-ray Observatory, CXO , and launched in July 1999. They were discovered by Swiss physicist J. J. Balmer.
Binary stars are two stars that orbit around a common center of mass.
A non-radiating ball of gas resulting from either a white dwarf that has radiated all its energy or gas which has contracted but contains too little mass to begin nuclear fusion. An object whose gravity is so strong that not even light can escape from it. This is analogous to the first law of thermodynamics. This is analogous to the second law of thermodynamics, with the surface areas of the black holes being a measure of the entropy of the system. Perfect absorbers must also be perfect radiators.