Formation of large structures, such as Concentration of 106 to 1012 stars, dust and gas, that are gravitationally bound. Our galaxy contains ~2 × 1011 stars. There are four main types of galaxies: • Elliptical • Lenticular • Spiral • Irregular Click on Term to Read More superclusters or perhaps even the vast filaments and voids, prior to the formation of smaller structures such as individual galaxies. Top-down Development of organized structures in the universe, ranging from galaxies to clusters to superclusters, and possibly beyond to huge filaments and voids. occurs in cosmological models with Hot Form of matter that does not emit light, absorb light, or otherwise interact with electromagnetic radiation. Its only interactions are gravitational and dark matter particles can clump under the force of gravity (unlike "dark energy" which is evenly distributed throughout space). The existence of dark matter has been inferred from Click on Term to Read More.