The Galaxy

A galaxy is a massive system of stars gas dust and dark matter bound by gravity often with a black hole at its center. Black holes are regions of extreme gravity where not even light escapes. Stars are glowing spheres of gas powered by fusion while planets orbit stars reflecting light. The universe is all of space time matter and energy. Earth the third planet from the Sun supports life. The Sun is our star. Asteroids are rocky objects orbiting the Sun. Astronauts explore space.