GMOS Perfect Spiral

Galaxies – the starry sky and Andromeda

M31 Andromeda Galaxy Image: NASA

The Andromeda Galaxy is estimated to contain in the region of one trillion stars, and is on a collision course with the Milky Way – we have a few billion years to go yet!

Galaxies can be named by various methods – our own is named for it’s appearance in a clear dark sky, where it looks like a milky river, or milk spilled across the sky by ancient gods. Other galaxies like this include the whirlpool galaxy, a fantastic spiral galaxy. They can be named by names and numbers, often in conjunction with a full name. One main numerical system is the Messier Catalogue, compiled by Charles Messier in the late 1700s. His goal was to compile a list of things which weren’t comets, the resulting list of Messier objects being catalogued as M1, M2 etc. The Andromeda Galaxy, as well as having a Messier Number, can be found in the constellation of Andromeda as can be seen in the starchart.

Eliptical Galaxy ESO 325-G004 Image: NasaGalaxies come in a few types, defined by shape, the main ones being spiral and eleptical. The Milky Way and Andromeda are examples of spiral galaxies, have a flattened, disk-like appearance with a central bulge, a bit like two fried eggs stuck back to back. Eleptical galaxies tend to form after the merging of two or more spiral galaxies, and are fuzzy blobs of stars. The colour of a galaxy can tell us if it is forming stars or not – galaxies containing many star-forming regions tend to be blueish, while the reddish ones contain few if any young stars. Spiral galaxies tend to contain more blue, while elipticals are ‘dead’ and form very few new stars. When two spirals collide, the resulting turbulence within the galaxies triggers a massive burst of star formation, after which new stars stop forming, and the eleptical contains an aging population.

On an even larger scale, galaxies can form clumps, or clusters, which can contain a mixture ofGalaxy cluster Abel 1689 Image: NASA all different types of galaxies, like the one on the right. These galaxy clusters can contain enough mass that their gravity effects light, bending the path of light as it passes. This gravitational lensing effect can sometimes be used as a giant magnifying glass, and some of the most distant galaxies have been discovered due to this effect.

Large scale structure from 6DF Survey Image: 6DFGS ConsortiumFinally, at the extreme end of the scale, galaxies and clusters tend to form into filaments rather than being evenly distributed across the universe. This is known as large-scale structure.