Galaxy

A galaxy is a massive system made up of billions of stars, along with gas, dust, and dark matter. All of these parts are held together by the force of gravity. Galaxies come in many different sizes and shapes. Some are large and bright, while others are small and faint. Our own home, the Milky Way Galaxy, is one of billions of galaxies in the universe.

Galaxies are the main building blocks of the universe. They can be found alone or grouped together in clusters. Astronomers have classified galaxies into three main types based on their shapes. Spiral galaxies have arms that wind outward from a center, like the Milky Way. Elliptical galaxies are round or oval and often contain older stars. Irregular galaxies do not have a clear shape and may look uneven or scattered.

At the center of most galaxies, scientists believe there is a supermassive black hole. This is a region in space with gravity so strong that not even light can escape. The black hole helps hold the galaxy together. In the Milky Way, the central black hole is called Sagittarius A*. Stars and gas orbit around it, just as the planets in our solar-system orbit the sun.

Galaxies can vary greatly in size. Some dwarf galaxies have only a few billion stars, while giant galaxies can have more than a trillion. The Milky Way is a medium-sized spiral galaxy with more than 100 billion stars. Many of those stars have their own planets and moons. New stars form from clouds of gas and dust inside galaxies, while old stars eventually die and release material that forms new ones.

Galaxies are often grouped together by gravity. A small group of galaxies is called a group, and larger gatherings are called clusters. These clusters can combine into even larger structures known as superclusters. The Milky Way belongs to the Local Group, which includes about 50 galaxies, such as the Andromeda Galaxy and the Magellanic Clouds.

Astronomers use telescopes to study galaxies and learn about their formation and movement. light from distant galaxies takes millions or even billions of years to reach earth, so when scientists observe them, they are actually seeing what those galaxies looked like in the past. Studying galaxies helps people understand how the universe began, how it changes over time, and how stars and planets form within it.