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Galactic structure 4- Star-forming nebula O Pulsar or supernova remnant (edge-on view) 1 = 500 LIGHT-YEARS 0 GALACTIC LONGITUDE pa Crucis r6C 4755 5235 $ Or GALACTIC PLANE ^ RCW 38 INA ARM „ ? "■ÆÊIJHHp Ye/a supernova Q: NGC 3372 remnant and pulsar mÚWRM NGC 5281 fhusj mmmm supernova remnant Coordinate system centered on Earth Cygrius Loop supernova remnant NATIONAL GEOGRAPHIC GUIDE TO THE GALAXY A TURBULENT HEART • Far beyond the galactic disk, yet drawn by its gravity, lone stars and globular clusters wander the galaxy's halo. Regions of dark matter—unseen but felt through its gravitational effects— extend beyond that. ~ Vast clouds of interstellar ^ dust block much of our night sky view of the Milky Way, which from our position in the flat galactic disk appears as a fuzzy band of light. Infrared satellites can see through the dust to reveal the galaxy's structure. ^ Earth's orbit around the sun ^ lies at a severe angle to the galactic plane. - A graph based on a radio * survey reveals the whirlpool motion of molecular gas in the inner part of our galaxy: gas moving away from Earth (top half) and toward Earth (bottom half). The densest gas appears white; least dense, blue. _ Massive amounts of energy ® are released near the center of the Milky Way, producing electrons that race along magnetic field lines, illuminating remnants of stellar explosions. Probing even deeper into the ® core, a radio image details a spiral of hot gas that is falling toward what may be a black hole some 2.6 million times as massive as the sun. NGC 5272 Globular clusters Home galaxy of Earth, the Milky Way is a spiral-shaped system of a few hundred billion stars. Bright regions of recently formed stars highlight its arms, while older stars explode or expel their outer layers as beautiful planetary nebulae, then fade away and die. A thick swarm of orange and red stars marks the galactic bulge, encapsulating the star-packed galactic center. At its core may lie a black hole, a region so dense that not even light can escape its gravitational pull. All objects in the Milky Way orbit the galactic center, much like planets in Earth’s solar system revolve around the sun. But the scale is staggering: Light from a star at one edge of the galaxy takes about 100,000 years to reach the opposite side. Galactic 7 plane /A/ Ecliptic 1?°0 / SU|4 p,ane J 10 light-years wide_____________ NEH KILLEEN. AUSTRALIA TELESCOPE NATIONAL FACILITY (ATNF); K. Y. LO. UNIVERSITY OF ILLINOIS 960 light-years wide____________I___________________________________ Ç. S. BRIGGS. J. IMAMURA. N. E. KASSIM. T. J. W. LAZIO. NAVAL RESEARCH LABORATORY «F*"’ |_______| Galactic | longitude |_______ THOMAS M. DAME. OAP HARTMANN. PATRlCK*THADD€US. HARVARO-SMITHSONIAN CENTER FOR ASTROPHYSICS M80 HUBBLE HERITAGE TEAM Omega' Centauri NGC 5139* Kappa Crucis NGC 4755 Keyfiole NGC i$24 o NGC 6391 WE ARE HERE This computer-generated image of the Milky Way—one perspective of a 3-D model newly compiled for National Geographic—incorporates the actdal positions of hundreds of thousands of stars and nebulae. Ros'etfe NGC 223*1 Globular star cluster Interstellar gas and dust Primary consultants: Bruce G. Elmegreen, IBM Corporation; Debra Meloy Elmegreen, Vassar College; David Leisawitz, NASA Goddard Space Flight Center Milky Way consultants: John M. Dickey, University of Minnesota; Jayanne English. Space Telescope Science Institute; Jay Friedlander, Ted Gull, Philip Plait, NASA Goddard Space Flight Center; Roger Fux, Geneva Observatory; Jeff Goldstein, Challenger Center for Space> Science Education; Paul W. Hodge, University of Washington; T. Joseph W. Lazio, Naval Research Laboratory; Jay Lockman, Morton S. Roberts, National Radio Astronomy Observatory Milky Way souices: Hector Alvarez, Jorge May, Leonardo Bronfman, University of Chile; JohA Bally, University of Colorado; John H. Bieging, University of Arizona; Richard $. Cohen, David A. Grabelsky, Columbia University; Thomas M. Dame, Sctf/ W. Digel, Patrick Thaddeus, Harvard-Smithsonian Center for Astrophysics; Eugene A. De Geus, Kluwer Academic Publishers; Dennis Downes, Thomas L. Wilson,Joern E. Wink, Max-Planck-lnstitut fur Radioastronomie; Yvon P. Georgelin.Qbservatoire de Marseille; A. Peter Henderson, Manhattan College; Peter D. Jackson, Frank J. Kerr, University of Maryland; Richard X. McGee, Janice A. Milton, Commonwealth Scientific and Industrial Research Organisation Nebula Younger star region (OB stars) Molecular cloud Galactic bulge or center (older star region) Reference numbers for galaxies, nebulae, and star clusters 1C (Index Catalog) M (Messier) NGC (New General Catalog) Coordinate system centered on galactic center LAGOON NEBULA PLANETARY NEBULA M2-9 Palomar I galaxy, including dark nebulae rich in microscopic dust that blocks our view of stars beyond. When a star adjoins a dark nebula, the dust particles reflect starlight and the black than the sun. They sparkle like an assortment of gems on a jeweler's velvet pad. .Jlkjn some dark clouds lurk strange obfects-like_G339JS8-T26, detected by a European Southern OBse~rvatory-tele— scope in Chile and mapped in infrared light (right). A star ------------------------ 20 times as massive as the sun and 10,000 times brighter, it sports a disk of circum-stellar dust, shown here in false color, about 20,000 times wider than Earth's visible light from the Hubble Space Telescope. ,________ —Oou'ds'oflnter-stellar dust (right), strewn over huge regions along the central plane of the Milky Way, are not thick and smooth but seem as frothy as the head on a glass of beer. Supernova shock waves and stellar wind from evolving stars may have shaped this surprising pattern. When a massive star comes to the end of its nuclear fuel supply, it collapses and then rebounds in a brief, powerful explosion, or super- :-------------------------------- nova. The Chinese ** . • called these celes- •• tial fireworks guest stars and i ‘ ’ recorded one such event in the con- stellation Taurus in July 1054 that "~V v ' was visible in broad daylight. . JEFF HESTER. PAUL SCOWEN, ARIZONA STATE UNIVERSITY; NASA In that location ™ today astronomers find the fast-expanding Crab Nebula (left), a supernova remnant. At its heart lies a pulsar—a collapsed star—whirling 30 * times a second. Satellite galaxies of the Milky Way host equally remarkable celestial phenomena. In the Large Magellanic Cloud (above right), 180,000 light-years from Earth, clumpy, filamentary clouds of hydrogen gas reveal their stately march in a radio m^p from the Australia Telescope Compact AMi^^uirEuROPEANsw^GENc^Ai^7 Array. The loVyer half of the cloud (blue) is rotating toward the Earth the skyman does the full moon. Where while the topside-ired) turns away. thtere was once only a vast dark cloud. Glistening along the spiral arms of ^^radiation from the brightest and most w the galaxy, brighTomission nebulaemassive young star in the nebula, Her-mark regions where nevy stars are forjjk schel 36, heats and ionizes the gas across mg. The Lagoon Nebula (above), abtfut a wide region. Despite the brilliance of the 5,000 light-years distant, is^a>tfydetected Lagoon Nebula and similar objects like with the naked eye as a fy*zyspot in the the famous Orion Nebula, such areas are southern constellatiop'Sagittanus. Wide- usually little more than hot blisters on the field images shoyvTfiat it covers more of flanks of giant interstellar clouds. retirees, however, •> v. every sta r in the S% ¿¿V cluster is about the same age, billions i%-$*'.f of years older than our 4.6-billion- year-old sun. q Peering a between dust foypjjg %• v V;« clouds toward the central bulge of the Milky Way, the HUBBLE H€R,TAGE TEAM Hubble Space Telescope focused on a rare clear region in the Sagittarius star cloud (above right). These Sagittarius stars formed at different times; most are older longitude BRUCE BALKX UNIVERSITY Of WASHINGTON; VINCENT ICKE. LEIDEN UNIVERSlTY^6ARfi£LT MELLEMA. STOCKHOLM UNIVERSITY; NASA Exotic kaleidoscopes of the Milky w^y, colorful nebulae and star clusters are \ found throughout Earth's galaxy. Even a run-of-the-mill star may eventually produce a nebula of surpassing beauty. _ Just as our sun will do in its death ' throes some five billion years from now, a dying star expanded into a red giant and was transformed into the nebula M2-9 (above). At its center shines a small, hot core, which will cool and fade over eons to come. Its stellar wind, streams of charged particles, rushes outward in opposite directions, like exhaust ^rom back-to-back jet engines. This biRolarism, revealed by the Hubble Space Tele'spope, is common among planetary nebulaOvUltraviolet light from the star heats M2^9î§ gases and makes them glow. Other typesqf nebulae exist in our cloud seems to have a silver lining, o The million-plus stars packed into a globular cluster such as Omega Centauri (right) are senior citizens of the Milky Way. Unlike human With new tools, astronomers are unraveling the nature of the Milky Way and measuring distances to stars and nebulae with greater accuracy. Still, they ask, how did the Milky Way form in the first place? How and when did the arms form? How many more planets circle nearby stars besides the 102 already discovered? And the biggest question of all: Do any of them harbor life? SUNGEUN KIM. UNIVERSITY OF ILLINOIS; LISTER STAVELEY SMfTH. ATNF --20 V 1,000 light-years wide FRANK VAROSI. WILLIAM H WALLER. NASA; INFRARED ASTRONOMICAL SATELLITE; SKYV1EW EUROPEAN SOUTHERN OBSERVATORY PATRICK SEITZER. UNIVERSITY OF MICHIGAN Copyright © 2002 National Geographic Society. Washington. D.C. Reprinted August 2005 22040 For information regarding available maps call 1-800-962-1643 or write to National Geographic Maps. PO Box 4357. Evergreen. CO 80437-4357 You can find us on the Internet at nationalgeographic.com/maps
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