Galaxy
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.
A galaxy is a massive, gravity-bound system of stars, gas, dust, and dark matter. Galaxies range from dwarf systems with few stars to giants containing trillions.
What it is
A galaxy is a gravitationally bound system composed of stars, stellar remnants, interstellar gas, dust, and dark matter. Dark matter accounts for most of the mass, though it is not directly visible. The term comes from the Greek *galaxias*, meaning 'milky'.
Types of galaxies
Astronomers classify galaxies by shape into spiral, elliptical, and irregular types. Spiral galaxies have distinct arms rich in gas and dust, while elliptical galaxies are more rounded and contain older stars. Irregular galaxies lack a defined shape.
Key details
Galaxies vary widely in size and often contain a central bulge, disk, and halo. Many large galaxies, including the Milky Way, have supermassive black holes at their centres. Galaxies are commonly found in groups and clusters, such as the Local Group.
In short
- Galaxies are gravity-bound systems of stars, gas, dust, and dark matter.
- Main types: spiral, elliptical, and irregular.
- Many large galaxies host supermassive black holes at their centres.
- The Milky Way is the galaxy containing Earth.
Canadian astronomy institutions and observatories study galaxies as part of broader research into the universe, including work connected to the Milky Way and nearby galaxies.
Quick questions
What is a galaxy?
What galaxy is Earth in?
What are the main types of galaxies?
Sources
- Wikipedia — https://en.wikipedia.org/wiki/GalaxySupports: Definition, composition, Greek etymology, broad size range, common galaxy types
- Encyclopaedia Britannica — https://www.britannica.com/science/galaxySupports: Definition, galaxy types, clusters, structural features, Hubble classification
- National Geographic — https://www.nationalgeographic.com/science/article/galaxiesSupports: Composition, supermassive black holes, estimated number of galaxies, classification overview
- NASA Space Place — https://spaceplace.nasa.gov/galaxy/Supports: Simple definition, gravity, Milky Way context
- Encyclopaedia Britannica — https://www.britannica.com/summary/galaxySupports: Summary definition, sizes, clusters, structural components, types
- Encyclopedia.com — https://www.encyclopedia.com/science-and-technology/astronomy-and-space-exploration/astronomy-general/galaxySupports: Classification, estimated number of galaxies, size range, active galaxies