What is a galaxy? How many stars in a galaxy? How many stars/galaxies in the Universe?
What is a galaxy?
Galaxies are large systems of stars, dust and gas bound together by gravitational force. They are elliptical, spiral or irregular in shape. Our Sun is part of a spiral galaxy called the Milky Way, and lies about two-thirds of the way out from the centre to the edge.
How many stars in a galaxy?
The best estimates suggest that the Milky Way contains about 500 thousand million stars and a total mass equivalent to 1.9 million million Suns.
Galaxies vary in size considerably. For example, giant elliptical galaxies may have up to 100 times the mass of the Milky Way (or the equivalent of 1900 million million Suns) whereas the recently discovered Ultra-Compact Dwarf galaxies may have just a few tens of millions of stars.
How many stars and galaxies in the universe?
The best estimates suggest that there are at least 70 thousand million million million (70 sextillion or 7 × 1022) stars in the Universe. The Universe probably contains more than 100 thousand million (100 billion or 1011) galaxies.
Find out more:
Stars (index of fact files about stars)
Galaxies (fact file)
For more information:
- There may be 3 times as many stars in the universe as we thought NEW!
- Imperfect Estimate Claims Universe Has 70 Sextillion Stars
- How many stars are there? More than you thought NEW!
- How many stars are there in the Universe?
- Trillions of Planets Could Have Life
- Star survey reaches 70 sextillion
- Study predicts trillions of planets
- First Super-Earths Discovered Orbiting Sun-Like Stars
- First Picture of Likely Planet Around a Sun-Like Star
- Possible First Photo of Planet Around Sun-Like Star
- Young Planet Orbits Sun-Like Star
- Astronomers Discover Sun's Twin at McDonald Observatory
- Many planets may have double suns
- Sun's Baby Twin Spotted
- Habitable Planet Possible Around Nearby Star System
- Scientists find planet with 3 suns
- Nasa finds sun-like star
- 2,000 Sun-like stars out to 150 light-years
- Planets Around Sun-Like Stars
- Planets with Two Suns Likely Common
- Newfound Star Smaller than Some Planets
- Space telescopes discover more of sun's sisters NEW!
- Astronomers Find Sun's Twin NEW!
- Sun-like star's 'oddball' planet NEW!
Where in the Universe do we live?Our place in the universe. This figure illustrates our cosmic address. The Earth is one of the nine planets in our solar systems, our solar system is one among more than 400 billion star systems in the Milky Way Galaxy; the Milky Way is one of the two largest of about 30 galaxies in the Local Group; the Local Group lies near the outskirts of the Local Supercluster; and the local Supercluster fades into the background of structure throughout the universe.