National Geographic : 2011 Dec
100,000 LY 100,000 LY 100,000 LY* DWARF GALAXY ABOVE PLANE OF THE MILKY WAY DWARF GALAXY BELOW PLANE OF THE MILKY WAY Boötes I Hercules Boötes II Segue 1 Sextans Sculptor Fornax Segue 2 Draco Ursa Major I Ursa Minor Ursa Major II Willman 1 Carina Sagittarius Milky Way Small Magellanic Cloud Large Magellanic Cloud Coma Berenices new stars in bursts, some within just the past few hundred million years. e Large Cloud, for its part, is a star-making factory, full of freshly minted star clusters and the soap-bubble skins shed by hot young stars that have exploded. Conspicuous in the Large Cloud is the glowing red Tarantula Nebula, a gigantic star-forming region that lies 160,000 light-years from Earth but shines so brightly that when observed through a big observa- tory telescope, its light pours out of the eyepiece like a ashlight beam. e Tarantula's ruddy glow comes from what astronomers call excited hydrogen gas. e gas is excited by powerful light from giant stars burn- ing furiously enough to deplete their nuclear fuel within only millions of years, rather than the billions of years it takes more modest stars like our sun. ey then explode, as supernovae. When a blue giant star in the Tarantula region went supernova, seen on the night of February 23, 1987, it captured the attention of astronomers worldwide. ey've been observing its remnants ever since. e Milky Way and the Magellanic Clouds appear destined to see a lot more of one another in the eons ahead. Will their dynamic dance even- tually result in a merger? Or will the clouds just come and go, spending their careers as a quiet, composed couple that comes downtown for a star- making binge every couple of billion years? Nobody will live long enough to witness the fate of these galaxies, but sooner or later scientists should be able to learn their dance steps, and to catch faint echoes of the music. j Galactic Suburbia The Magellanic Clouds are the largest and brightest of the galaxies orbiting our own. The others (those within 500,000 light-years of the sun are shown) are star-poor dwarfs that have orbited the Milky Way multiple times. The clouds may have yet to complete a single orbit. GRAPHICS: LAWSON PARKER, NGM STAFF SOURCE: SHOKO JIN, UNIVERSITY OF HEIDELBERG, GERMANY; GURTINA BESLA, COLUMBIA UNIVERSITY *A light-year (LY) is the distance light travels in a year at the speed of light: 186,000 miles per second.