A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. [1] [2] The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System.

2024年10月22日 · Galaxies consist of stars, planets, and vast clouds of gas and dust, all bound together by gravity. The largest contain trillions of stars and can be more than a million light-years across. The smallest can contain a few thousand stars and span just a few hundred light-years.

4 天之前 · Galaxy, any of the systems of stars and interstellar matter that make up the universe. Many such assemblages are so enormous that they contain hundreds of billions of stars. Virtually all galaxies appear to have been formed soon after the universe began, and they pervade all space that is viewable by modern telescopes.

2025年3月17日 · What Is a Galaxy? The Short Answer: A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity. We live on a planet called Earth that is part of our solar system. But where is our solar system? It’s …

2024年10月22日 · Galaxy groups and clusters are collections of galaxies bound together by gravity. They are building blocks for the larger-scale structures of the universe. The Hubble Space Telescope captured this image, called the Hubble Ultra Deep Field, in 2004 by combining 800 images with a cumulative exposure of 11.3 days.

2019年1月4日 · Galaxies are composed of stars, dust and dark matter, all held together by gravity. Astronomers aren't certain exactly how galaxies formed. After the Big Bang, space was made up almost entirely...

2019年4月17日 · Galaxies are sprawling systems of dust, gas, dark matter, and anywhere from a million to a trillion stars that are held together by gravity. Nearly all large galaxies are thought to also contain...

2025年3月26日 · The galaxy JADES-GS-z13-1, observed just 330 million years after the big bang (corresponding to a redshift of z=13.05), shows bright emission from hydrogen known as Lyman-alpha emission. ... A powerful active galactic nucleus, driven by one of the first supermassive black holes, is another possibility identified by the team. This research was ...

Galactic astronomy is the study of the Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies.

Galaxies are home to most of the stars in the universe, and they form the beads of the cosmic jewelry that defines structure on the largest scales. But galaxies haven’t always been around, and they have changed over the universe’s 13.8 billion-year history.