Approximately 60% of all galaxies are thought to be spiral galaxies, making spiral galaxies the home of the majority of the stars in the Universe. The Milky Way is thought to be a barred spiral galaxy. The most challenging to identify are fully ‘side-on’, meaning that only the outer edge of one side of the galaxy’s arms is visible. The most visually spectacular spiral galaxies are ‘face-on’, meaning that their bulge and all their spiral arms are clearly visible.
Classifying spiral galaxies is not always straightforward, as their appearance varies considerably depending on their orientation relative to Earth. Approximately two-thirds of all spiral galaxies are thought to be barred spiral galaxies. Barred spirals differ from normal spiral galaxies in that the arms of the galaxy do not lead all the way into the centre, but are connected to the two ends of a straight bar of stars which contains the nucleus at its centre. Spiral galaxies are surrounded by sparsely populated halos - roughly spherical regions above and below the plane of the discs.
Spiral galaxies have a complex structure: a dense central bulge lies at the centre of a rotating disc, which features a spiral structure that originates at the bulge. The Milky Way is a spiral galaxy.įour classes are used to classify galaxies: spiral barred spiral elliptical and irregular. A spiral galaxy typically has a rotating disc with spiral ‘arms’ that curve out from a dense central region.
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