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Galaxies
Beginner
Collections of billions of stars.
Gravitationally bound systems of 10⁶–10¹⁴ stars, gas, dust and dark matter: spirals, ellipticals and irregulars. There are about 2 trillion in the observable universe.
Andromeda is 2.5 million light years away.
Collisions and mergers shape them.
In more detail
Galaxies are gravitationally bound systems of stars, gas, dust and dark matter, ranging from dwarf galaxies to giant ellipticals. There are hundreds of billions of galaxies in the observable universe.
Real-world uses
- Galaxy surveys map the large-scale structure of the universe.
- Astronomers study galaxy evolution to understand cosmic history.
- Astronomers classify galaxies by shape as spiral, elliptical or irregular to study how they form and evolve.
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Frequently asked questions
How many galaxies are there?
Estimates range from hundreds of billions to around two trillion in the observable universe.
What shapes are galaxies?
Spiral, elliptical, lenticular and irregular forms.
How many galaxies are there?
Estimates suggest hundreds of billions of galaxies exist in the observable universe.
Related topics in Particle Physics & Cosmology
Chandrasekhar limit · Neutron stars and pulsars · Black holes in astrophysics · Milky Way · Hubble's law · Expansion of the universe