Galaxies next door Mysteries of the Magellanic Clouds They produced the nearest supernova in 300 years, are connected by a giant stream of matter, and may collide with the Milky Way. by Bill Andrews he Milky Way has a bit of a enous peoples of the South Seas, but problem with its neighbors. their first recorded mention dates back Two smaller galaxies, the to a.d. 964, in Persian astronomer Abd Large Magellanic Cloud Al-Rahman Al Sufi’s Book of Fixed Stars. (LMC) and the Small Magel- Al Sufi, later known in Europe as Azo- lanic Cloud (SMC), have phi, identified the LMC as Al Bakr, or Tbuzzed around us for eons, giving no “The White Ox,” and noted that it is vis- clear indication of their intentions. ible only from southern latitudes. They may end up colliding with our The Clouds’ first recorded European galaxy, or they may leave one day, never mention occurred more than 500 years to return. The LMC alone also has been later, in a letter from explorer and car- host to a variety of explosions, both tographer Amerigo Vespucci. During real (the closest observed supernova in his third voyage from 1503 to 1504, he 300 years) and fictional (Battlestar wrote of “three Canopes, two bright and Galactica skirmishes). one obscure” in the southern skies, with Despite these potentially off-putting the former referring to the Magellanic characteristics, astronomers can’t get Clouds and the latter likely referring to enough of the Magellanic Clouds. After the Coalsack Dark Nebula. all, they’re fascinating and beautiful The big break for the Clouds came objects, and they might even hold the just decades later, after Ferdinand keys to understanding the biggest mys- Magellan’s circumnavigation of Earth teries in the universe. from 1519 to 1522. Of the initial crew of 237 men, only 18 finished the journey The road to fame and returned to Spain. One of the lucky The Magellanic Clouds, as one might few was Venetian scholar Antonio expect, appear as illuminated clouds, Pigafetta. His description of the Clouds like pieces of the Milky Way that wan- as dim clusters of stars became widely dered off in the sky — but only to known to Western astronomers, and it’s observers in the Southern Hemisphere. because of his reports that the galaxies The Tarantula Nebula, a They were surely known to the indig- are now named for Magellan. prominent feature of the The Clouds’ final push toward Large Magellanic Cloud, is considered the most active Bill Andrews is an assistant editor of superstar status had to wait another star-forming region in the Astronomy. He’s read about the (fictional) four centuries. In 1987, the region near Local Group of galaxies. Both planet Tralfamadore, located in the Small the Tarantula Nebula in the LMC was Magellanic Clouds are full of Magellanic Cloud, for more than half his life. host to a fantastic sight: the closest celestial treasures like this one. John P. Gleason 30 Astronomy • June© 2010 2011 Kalmbach Publishing Co. This material may not be reproduced in any form without permission from the publisher. www.Astronomy.com Magellanic Timeline Prehistory — The Magellanic Clouds are easily visible in the Southern Hemisphere to the naked eye. Milky Way Galactic Plane A.D. 964 — Persian astronomer Abd Al-Rahman Al Sufi makes the first Large Magellanic Cloud recorded mention of the Small Magellanic Cloud Large Magellanic Cloud, calling it Al Bakr, or “The White Ox.” This combined radio/optical image outlines the interaction of the Magellanic 1503 — Explorer and mapmaker Clouds with each other and the Milky Way (shown horizontally centered). Some Amerigo Vespucci provides the first Euro- theories predict the Clouds will ultimately end up in our galaxy, “cannibalized” pean recorded mention of the Clouds in a by its larger gravity. The blue and white represents the Milky Way and Magel- letter from his third voyage. lanic Clouds, red is the hydrogen gas of the Magellanic Stream and the disks of the Magellanic Clouds, and brown is dust clouding the Milky Way. Nidever, et al./NRAO/ 1522 — Venetian AUI/NSF and Mellinger/Leiden-Argentine-Bonn Survey/Parkes Observatory/Westerbork Observatory/Arecibo Observatory scholar Antonio Pigafetta’s description of the Clouds, about 10 times smaller than its com- galaxies, according to Knödlseder. “It’s seen during his time on panion. The two seem to be embed- not a blanket, universal phenomenon.” Magellan’s round-the- ded in an “envelope” of hydrogen gas world voyage, circulate of much lower density than either Spying on the neighbors throughout Western countries. Cloud called the Magellanic Bridge. Despite their unusual makeup, the Their low metal contents and Magellanic Clouds serve as extraordi- 1970s — Astronomers discover the higher gas concentrations mean the narily valuable tools for understanding Magellanic Stream and realize it’s con- Magellanic Clouds are “much closer to the rest of the universe. “Many of the nected to the Magellanic Clouds. A supernova near the LMC’s Tarantula Nebula burned what galaxies in the early universe processes are basically the same” brightly in 1987, giving used to have,” says Snezana Stani- among the Clouds and other galaxies, 1987 — In February, Southern Hemisphere mirovic, assistant professor of astron- says Knödlseder, “so they provide a the closest supernova in observers the closest look omy at the University of Wisconsin- much deeper view of what’s going on almost 300 years appears at these stellar explosions Madison. “By studying the physical in other galaxies, and how their differ- in southern skies near the since 1604. This Hubble LMC’s Tarantula Nebula. photo depicts the super- processes in the Magellanic Clouds … ent components interact.” nova remnant centered in we can learn about galaxy evolution Further, due to our position in our 2007 — New Hubble rings of cast-off material, in and how it depends on dust, gas, and own galaxy, it’s hard to know exactly observations show that the midst of diffuse clouds metal content.” what we’re seeing when we look at the Magellanic Clouds of gas. NASA/HST For example, the Magellanic Clouds Milky Way phenomena, explains travel much faster than helped explain the unknown origin of Knödlseder. For example, is this super- previously thought, likely observed supernova, or stellar explo- Magellanic Clouds. As Knödlseder than helium), that make the LMC a cosmic rays, particles that bombard nova remnant interacting with that implying a parabolic path sion, since 1604 (before the invention says, “It was famous all over.” focus of galactic study. Earth from anywhere beyond its atmo- molecular cloud, or is one just in front around the Milky Way of the telescope). Despite being an irregular galaxy sphere. “For a long time,” Knödlseder of the other? Studying the Magellanic instead of an elliptical orbit. “The most spectacular thing that a Galactic profiles (one with no obvious shape, like a says, “the question was: Are the cos- Clouds, Knödlseder says, is a “little bit February 2008 — Astronomers human ever could see would be an Of course, for astronomers, whose job spiral or elliptical), the LMC has a mic rays generated in our own galaxy, like if you could fly out of our own gal- discover a giant strand of the Magellanic explosion of a star,” says Jürgen it is to look at and understand the prominent central bar and a spiral or are they just a kind of bath [spread] axy and look at it from the top.” Stream poking through the Milky Way’s Knödlseder of the Center for the heavens, the Magellanic Clouds had arm. The central bar is so warped that throughout the universe?” And it’s not just the nice view that disk, possibly implying that our galaxy is Study of Radiation in Space in Tou- been well-known for some time. The its ends are nearer to the Milky Way Either theory could explain the cos- makes the Magellanic Clouds a useful “cannibalizing” its two smaller companions. louse, France. “I think that garnered Tarantula Nebula in particular has than its middle. The galaxy lies mic rays we see almost uniformly on target. “The Magellanic Clouds are [a lot of interest] for normal people, long been considered the most active approximately 160,000 light-years Earth, but if the second theory was basically our neighbors,” says Anna- January 2010 — The Magellanic just to witness the fact that a star star-forming region in the Local from Earth and is about one-tenth as right and they blanketed the entire purni Subramaniam of the Indian Insti- Stream turns out to be much longer and exploded, by naked eye, because it’s Group of galaxies. It’s just one of the large as the Milky Way. universe, astronomers should be able tute of Astrophysics. Scientists study older than previously thought. such a rare phenomenon.” fantastic objects and phenomena, About 22° away from the LMC in to detect cosmic ray interactions in them for the same reason they study Book: University of California, Irvine; Magellan: Naval Museum of Even more unusual than a solar from globular clusters to planetary the sky (75,000 light-years away in other galaxies. When they didn’t see the Sun: They’re so close, they can give Madrid; Supernova 1987A: NASA/CXC/PSU/S.Park & D.Burrows/STScI/ CfA/P. Challis; Clusters: ESA & NASA/Davide de Martin and Edward W. eclipse, the dazzling new “star” with an nebulae to an environment with reality) and 200,000 light-years dis- any interactions in the SMC, astrono- us more details than something farther Olszewski (University of Arizona, USA) apparent magnitude of 3 brought an unusually low metallicity (meaning a tant from Earth, the SMC is also an mers could conclude that the source of away.