GALAXIES A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site Galaxy, The Our home galaxy, also known as the Milky Way Galaxy, a large type Sb or Sbc spiral galaxy containing some 200 to 400 billion stars (or possibly many more if brown dwarfs are included). Comprised of a disk, a bulge, and a halo, it has a total mass, including an uncertain but large amount of dark matter in the halo, of 750 billion to 1 trillion solar masses. The galactic disk is home to the various spiral arms of the Galaxy, including the Orion Arm in which the Sun is located (27,700 light-years from the center), the Outer Arm and Perseus Arm (both outside our own), the Sagittarius-Carina Arm (immediately inward of the Sun), and the Scutum Arm, Crux Arm, and three-kiloparsec Arm (all even closer to the center). Within these arms are many ordinary, intermediate-age disk stars, such as the Sun, together with the more showy Population I objects, in the form of young, hot stars, stellar associations, open clusters, diffuse nebulae, and the bulk of the interstellar matter from which future stars will form. The galactic bulge and the much larger galactic halo contain Population II objects – mostly old stars and roughly 200 globular clusters, of which about 150 are known. These globulars are strongly concentrated toward the galactic nucleus. The nucleus of the Milky Way contains a complex of gas, dust, stars, supernova remnants, magnetic filaments, and, almost certainly, a massive black hole at the very center; it lies in the direction of Sagittarius, around R.A. 17h 46m and Dec. -28° 56'. Lying dead center in the Galaxy is the Sagittarius A Complex, which is believed to be associated with a black hole, material in orbit around this object, and a nearby supernova remnant. Surrounding the galactic center are narrow threads known as nonthermal filaments (NTFs), the most prominent of which are called the Arc, the Pelican, and the Snake. These seem to consist of magnetic flux tubes filled with relativistic electrons, beaming synchrotron radiation, that have been swept up from adjacent molecular clouds and hurled along the field lines at incredible speeds. Another unusual structure in the nucleus is catalogued as 359.1-00.5 and appears to be a superbubble with a cluster of as many as 200 newborn stars at its heart. The Milky Way Galaxy has about 20 known satellite galaxies, some of which are identified in the table below (also see individual entries for these galaxies) and is the second largest (after the Andromeda Galaxy), but possibly most massive, member of the Local Group. Vital statistics Diameter of disk ~ 100,000 light-years Thickness of disk 2,300 to 2,600 light-years Thickness of bulge 16,000 light-years Mass 200 to 400 billion Msun Proportion of gas and dust 5 to 10% Mean density 0.1 Msun per cubic parsec Total luminosity ~ 1044 erg/s Magnetic field 3 - 5 × 10-6 gauss Satellite galaxies of the Milky Way Galaxy Distance (light-years) Discovered Absolute magnitude Diameter (light-years) Sagittarius Dwarf Elliptical 78,000 1994 -13.4 >10,000 ? Large Magellanic Cloud 160,000 prehistoric -18.1 20,000 Small Magellanic Cloud 180,000 prehistoric -16.2 15,000 Ursa Minor Dwarf 220,000 1954 -8.9 1,000 Draco Dwarf 270,000 1954 -8.8 500 Sculptor Dwarf 285,000 1938 -11.1 1,000 Sextans Dwarf 290,000 1990 -9.5 3,000 Carina Dwarf 330,000 1977 -9.3 500 Fornax Dwarf 450,000 1938 -13.2 3,000 Leo I 670,000 1950 -9.6 500 Leo II 830,000 1950 -11.9 1,000 Related category    • GALAXIES Archived news Stars spotted on the edge of a massive black hole (May 16 2005) Strange space burst could be new object (Mar 3, 2005) Milky Way's supermassive black hole was active (Jan 31, 2005) Stars reveal the Milky Way's age (Aug 18, 2004) Runaway stars may solve black hole riddle (Apr 15, 2004) Recommended books   Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP