Spiral galaxy
galaxy having a number of arms of younger stars that spiral out from the centre containing older ones / From Wikipedia, the free encyclopedia
A spiral galaxy is a kind of galaxy that looks like a flat, slowly rotating disk with a bulge in the centre, and spiral patterns extending outward from the bulge. It contains stars, gas, dust, dark matter and a supermassive black hole at its centre.[1]
Galaxies were long thought to be nebulae. The spiral nebula as a type was first described by Edwin Hubble in his 1936 work The Realm of the Nebulae.[2] They are now listed as galaxies, and are named after their shape.
The barred spiral galaxy is an important and common type of spiral galaxy. There are three other kinds of spiral galaxies. Grand-design spiral galaxies have two well-shaped and well-defined arms. Multiple-arm spiral galaxies have more arms. In flocculent spiral galaxies, it is hard to see the arms at all, as they are choppy and are ill-defined.[3]
About 60% of galaxies in the universe near us (the 'local universe') are spiral and irregular galaxies.[4] They are mostly found in low-density parts of the universe,[5] and are rare in the centers of galaxy clusters.[6]