The Galaxy was a massive, gravitationally bound assemblage of stars, an interstellar medium of gas and dust, and an unknown type of dark matter. The galaxy was the setting of the histories of the Galactic Republic, the Galactic Civil War, and the Yuuzhan Vong War.
According to some sources, the galaxy was 120,000 light years across, or 37,000 parsecs (a parsec is 3.258 light years), and approximately 13 billion years old. A black hole existed at the center of the galaxy.
While there was a hyperspace disturbance outside of the galaxy, hyperspace made it possible within the galaxy to have an enormous, and diverse, civilization. There were approximately 400 billion stars, and around 180 billion of these had planets that could support life. Ten percent of those planets developed life, while sentient life developed in 1/1,000 of those (about 20 million). Factoring in output of heat and light for advanced civilizations to form, there were 7.1 billion truly habitable stars, and 3.2 billion habitable star systems, with only 69 million systems meeting the requirements for Imperial representation, and 1.75 million planets considered full member worlds. In total, the galaxy was populated by approximately 100 quadrillion different life forms.