Answer – A galaxy is a vast expanse of outer space comprising stars, dark matter, and interstellar matter (such as gas, dust, and stellar remnants) held together by gravity. The universe, on the other hand, encompasses everything in space—several billion galaxies, matter, and energy.

Explanation: 

Most galaxies contain billions of stars and can be spread over thousands of light years. They differ in size and shape due to the varying patterns of formation and evolution. The Milky Way, the galaxy in which the Earth occurs, is home to 100–400 billion stars across 100,000 light years; its neighboring galaxy, Andromeda, is 220,000 light years wide.

Galaxies may also differ based on the activities observed within. While some continue to be sites of rapid star formation, others have been dormant for a long time and have stopped forming new stars.

The universe, on the other hand, comprises all galaxies and everything in between. It is said to have resulted from a high temperature and density state that resulted in a “big bang” 13.8 billion years ago. Since then, it has cooled and continued to expand, allowing for the formation of everything from subatomic particles to galaxies.

Scientists initially believed that gravity would eventually slow the expansion of the universe. However, recent research has revealed that the universe is expanding at a rapid pace. An unknown driving force called dark energy is said to be at play for this.

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