Swirling Disks Of Stars, Gas And Rock!

A galaxy is among the biggest structures known to exist in space. They are huge collections (often disks), of stars, gas, planets etc held together by gravity. They often have a supermassive black hole at their centre and may contain over 100 billion stars and solar systems! Scientists believe there are 200 billion galaxies in the Universe! That’s a crazy big number isn’t?!


Interesting Facts About Galaxies!

  • A galaxy is a huge collection of black holes, stars, brown dwarfs, planets (and their moons), nebulae, interstellar dust and even an unknown amount of the mysterious dark energy & dark matter!
  • All objects in a galaxy are gravitationally bound to one another and are believed (in the case of spiral galaxies) to orbit at least one enormous supermassive black hole at the galaxies centre.
  • Until the early 1920’s it was thought that the Milky Way Galaxy was the entire universe before it was revealed it was only one of many galaxies!
  • It is now estimated that there are 200 billion galaxies in the universe, which means there are more galaxies than there are grains of sand on all the beaches on Earth!
  • All but three galaxies outside of our Milky Way Galaxy (Andromeda and the Large & Small Magnetic Clouds) are too faint to see with the naked eye.
  • Galaxies are not randomly distributed throughout the universe but are gravitationally bound into groups, clusters and superclusters.
  • Our Milky Way Galaxy is a member of what is known as the ‘Local Group’.
  • Galaxies range in size from ‘dwarf’ galaxies with only a few million stars to 'giants' with as many as 100 trillion stars!
  • The stars you see in the night sky are all located within our nearby region of the Milky Way Galaxy.
  • The dark patches in the Milky Way are actually enormous clouds of gas (hydrogen & helium) and dust which obstruct distant starlight. These star-forming nebulae are common in the spiral arms of other galaxies too, not just the Milky Way.
  • Earth, our home planet, is just one planet that orbits the Sun which is one of an estimated 200-400 billion stars which exist in the Milky Way Galaxy!
  • The closest galaxy to the Milky Way is the Andromeda Galaxy which scientist say we will merge within about 5 billion years time!
  • When galaxies collide, the objects within them are often so distant from one another, that there is a very small chance of a collision or close interactions. However, mergers often result in new stars being formed and the galaxy taking on a new shape!

The Different Types Of Galaxies

Astronomers divide galaxies into three main types based on their shape;

  • Spiral Galaxy – these have a flat disk shape with a huge central bulge containing old stars and spiral arms which orbit around the galaxies centre. New stars are constantly being created in these spiral arm regions.
    • Barred Spiral Galaxy – these are a sub-group of spiral galaxies but have a bar-shaped group of stars in the centre. Our Milky Way is shaped like this.
  • Elliptical Galaxy – these appear oval-shaped with no disk and are contain old stars and few young ones.
  • Irregular Galaxy – These galaxies have an irregular shape, possibly due to a collision and combining of two or more galaxies.
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