Galaxies - NASA Science
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.
Stars and Galaxies - NASA Jet Propulsion Laboratory (JPL)
2021年1月12日 · Our universe includes a variety of astonishing and sometimes bizarre objects. Massive black holes so powerful, they swallow nearby objects. Galaxies that merge into giant swirls. Enormous stars that eventually explode and become supernovas. Neutron stars — objects so dense, one tablespoon of their material would weigh about 1 billion tons on ...
Stars - NASA Science
Stars are giant balls of hot gas – mostly hydrogen, with some helium and small amounts of other elements. Every star has its own life cycle, ranging from a few million to trillions of years, and its properties change as it ages. Stars form in large clouds of gas and dust called molecular clouds.
Galaxy | Definition, Formation, Types, Properties, & Facts | Britannica
2024年11月19日 · A galaxy is 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. Galaxies usually exist in clusters, some of which measure hundreds of …
Galaxies - HubbleSite
2024年10月28日 · Galaxies are vast cosmic islands of stars, gas, dust, and dark matter held together by gravity. Hubble’s keen eye has revealed intricate details of the shapes, structures, and histories of galaxies — whether alone, as part of small groups, or within immense clusters.
What Is a Galaxy? | NASA Space Place – NASA Science for Kids
2024年11月8日 · A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle. When you look up at stars in the night sky, you’re seeing other stars in the Milky Way.
Universe - NASA Science
Galaxies. Collections of stars, planets, and vast clouds of gas and dust bound together by gravity.
Galaxies—facts and information - National Geographic
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...
Galaxy Formation and Evolution - Center for Astrophysics
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.
How galaxies form: Theories, variants and growth | Space
2022年7月13日 · Here are some of the most promising theories of how galaxies form, how and why they merge, as well as the different varieties of galaxies that have been observed. As the universe expanded in...