Galaxies can range in size from a dwarf with as few as ten million stars to massive giant galaxies with a hundred trillion stars. Each star orbits its galaxies own centre of mass and it is estimated that there are more than 170 billion galaxies in the observable universe.
Galaxy facts and information
- There are over 170 billion galaxies in the observable universe yet there is also a “future visibility limit”. Objects beyond this limit will never enter our observable universe at any time in the infinite future. The reason for this is that light emitted by objects outside that limit would never reach us.
- Tens of thousands of galaxies have been catalogued but only a few have been given well-established name like the Andromeda galaxy, The Milky Way, the Magellanic clouds, the Whirlpool Galaxy and the Sombrero Galaxy.
- The word galaxy is derived from the Greek word galaxias which literally means “milky”. This is a reference to the Milky Way galaxy which contains our solar system.
- Galaxies are historically categorized by their apparent shape, of which there are three:
- Spiral galaxies are disk-shaped with dusty, curving arms.
- Irregular galaxies have an unusual or irregular shape.
- An elliptical galaxy, has an ellipse-shaped light profile.
- Most galaxies are between 1,000 and 10,000 parsecs in diameter. A parsec is a astronimcal unit of length. To put the number into perspective, one parsec is equivalent to approximately 31 trillion kilometres or 19 trillion miles.
- In astronomical literature, the capitalized word “Galaxy” is used to refer to our galaxy, the Milky Way. This is to differentiate it from the billions of other galaxies in the universe.
- Most galaxies in the universe are actually dwarf galaxies. These are relatively small when compared to other galaxies – roughly one hundredth the size of the Milky Way with only a few billion stars.
- The most distant and primordial galaxy ever discovered is the catchy z8 GND 5296, which is approximately 13.1 billion light years away. It was discovered in October 2013 by a team of astronomers from the University of Texas at Austin led by Steven Finkelstein.
