Galaxy

A galaxy is a huge group of stars.

It also has dust and gas.

These groups stay together in space. A force called gravity holds them in place.

Some groups are very small. Other groups are giant. Some have many stars.

Our home is in one called the Milky Way. It is a spiral shape.

Space is very big! Can you look at the stars tonight?

A galaxy is a huge group of things in space. It holds stars, gas, and dust together. Gravity, a pulling force, keeps them all in one place.

Most of a galaxy is made of dark matter. We cannot see this matter, but it is there. Most galaxies have a supermassive black hole at their center. This is a very large, heavy object.

Galaxies come in many shapes. Some are shaped like a spiral. Our home, the Milky Way, is a spiral galaxy.

Other galaxies look like round blobs. We call these elliptical galaxies. Some have no clear shape at all. Scientists call these irregular galaxies.

Galaxies can be very different in size. Small dwarf galaxies have less than a thousand stars. Giant galaxies can have one hundred trillion stars!

Galaxies often live in large groups. They can even bump into each other. There are billions of galaxies in the universe. The Andromeda Galaxy is our nearest large neighbor. It is 2.4 million light years away.

A galaxy is a huge system of many things in space. It holds stars, gas, and dust together in one place. Gravity is the pulling force that keeps everything bound together.

Most of a galaxy's mass is actually made of dark matter. We cannot see this dark matter, but it is there. Only a few percent of a galaxy is visible as stars or nebulae. Many galaxies also have a supermassive black hole at their center. These huge objects are a common feature in most galaxies.

Galaxies come in many different shapes. Some look like spinning pinwheels, which we call spiral galaxies. Our own home, the Milky Way, is a spiral galaxy.

Other galaxies look like smooth, round blobs called elliptical galaxies.

Some galaxies have no clear shape and are called irregular galaxies. Galaxies can even change by interacting with a neighbor. Sometimes they even collide during their lifetime.

People have studied the sky for a very long time. Long ago, astronomers called these objects spiral nebulae. They thought they might just be clouds of gas.

In 1610, Galileo Galilei used a telescope to see many stars in the Milky Way. Later, Thomas Wright thought galaxies might be large rotating disks.

In 1922, Ernst Öpik helped find the distance to the Andromeda Galaxy. Finally, Edwin Hubble proved that these objects were far beyond our own galaxy.

Galaxies vary greatly in their size and numbers. A small dwarf galaxy might have less than a thousand stars. A supergiant galaxy can have one hundred trillion stars!

The Milky Way is at least 26,800 parsecs wide. Our nearest large neighbor is the Andromeda Galaxy. It is about 2.4 million light years away.

Scientists think there are between 200 billion and 2 trillion galaxies in the universe. Most galaxies are between 3,000 and 300,000 light years across.

Galaxies do not live alone in the dark. They usually organize into groups, clusters, and superclusters.

The Milky Way is part of a group called the Local Group. This group is inside the even larger Virgo Supercluster. At the largest scale, these groups form long sheets and filaments. Between these structures are huge, empty areas called voids. This structure is how the whole universe is arranged. It is like a giant web stretching across space.

A galaxy is a massive system of stars and other celestial materials. These systems are held together by the force of gravity. A galaxy contains stars, stellar remnants, interstellar gas, and dust. It also contains dark matter, which is a substance we cannot see. Most of the mass in a typical galaxy is actually dark matter. Only a few percent of that mass is visible as stars or nebulae.

Galaxies vary significantly in their scale and composition. They range from dwarf galaxies with fewer than 1,000 stars to supergiants. These giants can contain as many as 100 trillion stars. Each star or object orbits the galaxy's center of mass. Many galaxies also feature a supermassive black hole at their center. These enormous objects are a common characteristic of galactic cores.

Astronomers categorize galaxies by their visual characteristics. One common type is the spiral galaxy, which looks like a spinning disk. Our own Milky Way is a spiral galaxy. Another type is the elliptical galaxy, which appears as a smooth, rounded shape.

Some galaxies are classified as irregular because they lack a clear structure.

Galaxies can also be notable for special properties. They might interact with a neighbor or produce stars at unusual rates. Some even possess an active galactic nucleus.

Our understanding of galaxies has changed through centuries of observation. In the 17th century, Galileo Galilei used a telescope to see many faint stars in the Milky Way. In 1750, Thomas Wright speculated that the Milky Way was a rotating disk of stars. He suggested that other nebulae might be separate galaxies. Later, in 1845, Lord Rosse observed the spiral structure of the Whirlpool Galaxy.

For a long time, astronomers called these objects "spiral nebulae." They were not sure if these were clouds or independent systems.

The debate over the nature of galaxies became very famous. In 1920, Harlow Shapley and Heber Curtis held the "Great Debate." They argued about whether spiral nebulae were part of the Milky Way or separate universes. Heber Curtis believed they were independent "island universes." In 1922, Ernst Öpik provided a distance estimate for the Andromeda Galaxy. Finally, Edwin Hubble used a large telescope to resolve individual stars in distant nebulae. He proved they were far beyond our own galaxy.

The scale of the universe is truly immense. There are between 200 billion and 2 trillion galaxies in the observable universe. Most galaxies are between 3,000 and 300,000 light years in diameter. For example, the Milky Way is at least 26,800 parsecs wide. Our nearest large neighbor is the Andromeda Galaxy. It is located 2.4 million light years away.

Galaxies are not scattered randomly through space. They are organized into large structures. Most galaxies belong to groups, clusters, or superclusters. The Milky Way is part of the Local Group. This group is part of the larger Virgo Supercluster.

At the largest scale, these associations form sheets and filaments. These structures surround immense, empty areas called voids. This creates a massive web-like pattern across the cosmos.