Composition and structure of Milky Way

Tweet

The overall shape of the Milky Way is believed to be a barred spiral galaxy. It consists of a bar-shaped core region surrounded by a disk of gas, dust and stars. Within the disk region are several arm structures that spiral outward in a logarithmic spiral shape. The mass distribution within the Milky Way closely resembles the Sbc Hubble classification, which is a spiral-galaxy with relatively loosely-wound arms.[10] It was only in the 1980s that astronomers began to suspect that the Milky Way is a barred spiral[11] rather than an ordinary spiral, which observations in 2005 with the Spitzer Space Telescope have since confirmed, showing that the galaxy's central bar is larger than previously suspected.[12] This argues for a classification of type SBbc (loosely wound barred spiral). In 1970 Gérard de Vaucouleurs predicted that the Milky Way was of type SAB(rs)bc, where the "rs" indicates a broken ring structure around the core region.[13] As of 2006, the Milky Way's mass is thought to be about 5.8×1011 M?[14][15][16] comprising 200 to 400 billion stars. Its integrated absolute visual magnitude has been estimated to be -20.9. Most of the mass of the Milky Way is thought to be dark matter, forming a dark matter halo of an estimated 600–3000 billion solar masses (M?) which is relatively spread out evenly.