Wikipedia Commons

 Einstein views Gravity NOT as a force, but as a bending of spacetime  It still affects how things move, but not as an attractive force  It is pictured as a bent surface that the objects move along

 Around very massive objects, this bending of spacetime is very str0ng, so objects still move together  And it bends in all three dimensions, not just two!

 However it is imaged, or however it is explained, gravity is what drives the formation of stars  And their eventual destruction!

 Space is not just empty, even between celestial objects  Gas and dust exist (very, very sparse)  Some areas have denser masses of dust/gas  Very cold, so they do not emit radiation NASA Image

 Gravity causes gas/dust clouds to contract  With enough mass, becomes densely packed  With enough pressure, nuclear fusion begins  A star is born….  Many times, groups are stars are formed

 Hydrogen is fused together to make Helium  Energy is released as visible light and other EM radiations

 During most of a stars life, a balance of gravity and energy production creates a stable dynamic  Sizes – Red dwarf to Blue Giant

 As fuel dwindles, stars become unstable  Swell to Red Giant stage  Final fate depends on mass

 Small mass –“Planetary nebula” to white dwarf to black dwarf (0.4 to 8 times our Sun’s mass)  Massive –Supernova to neutron star (8 to 25 M)  Supermassive –Supernova to Black Hole (25+M)

Has 5 to 10 times the mass of our Sun Can be found throughout a galaxy Remnants of single stars at the end of their cycle

Thought to be at the center of every galaxy Has the mass of hundreds of millions of Sun sized stars Can sometimes create jets of hot gas shooting out from near the event horizon

Evolution of Stars Large Stars Smaller Stars Stellar Nursery Supernova Planetary Nebula Red Giant Star Red Supergiant Star White Dwarf Black Dwarf Sun-like Star Blue Giant Star Neutron Star Black Hole