الفهرس | Only 14 pages are availabe for public view |
Abstract The study of bars in spiral galaxies is an important area of research that has led to significant progress in our understanding of galaxy evolution. By identifying and characterizing bars in different types of galaxies, we can gain insights into the physical processes that shape the structure and dynamics of these systems. Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters. Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure, extending from the central bulge, at the ends of which the spiral arms begin. The proportion of barred spirals relative to barless spirals has likely changed over the history of the universe, with only about 10% containing bars about 8 billion years ago, to roughly a quarter 2.5 billion years ago, until present, where over two-thirds of the galaxies in the visible universe (Hubble volume) have bars. Bars are important for the evolution of galaxies as they provide a way to move material in and out in the disk and possibly help to spark star formation in the central regions. They may even help feed the central massive black hole that seems to be present in almost all galaxies. But bars provide us with a great puzzle because we still don’t understand why some galaxies have bars and others do not. |