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They Produced the Nearest Supernova in 300 Years, Are Connected by a Giant Stream of Matter, and May Collide with the Milky Way

They Produced the Nearest Supernova in 300 Years, Are Connected by a Giant Stream of Matter, and May Collide with the Milky Way

Galaxies next door Mysteries of the They produced the nearest in 300 years, are connected by a giant stream of matter, and may collide with the . 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 , the to a.d. 964, in Persian Abd Al-Rahman Al Sufi’s Book of Fixed . (LMC) and the Small Magel- Al Sufi, later known in 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 , 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, can’t get Clouds and the latter likely referring to enough of the Magellanic Clouds. After the Coalsack Dark . 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 teries in the . 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 . because of his reports that the galaxies The , 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 -forming region in the . He’s read about the (fictional) four centuries. In 1987, the region near 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 A.D. 964 — Persian astronomer Abd Al-Rahman Al Sufi makes the first Large Magellanic Cloud recorded mention of the 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 . The blue and white represents the Milky Way and Magel- letter from his third voyage. lanic Clouds, red is the gas of the 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//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 . 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.” 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 ), that make the LMC a cosmic rays, 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 sphere. “For a long time,” Knödlseder of the other? Studying the Magellanic instead of an elliptical . “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 . 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) of 3 brought an unusually low (meaning a tant from Earth, the SMC is also an mers could conclude that the source of away. “And probably we are assuming a unprecedented level of attention to the place with fewer elements heavier irregular galaxy low in metals, but cosmic rays must lay within individual lot of things for other galaxies, so we

32 Astronomy • June 2010 www.Astronomy.com 33 The Extremely Finally, a parabolic orbit likely means the Clouds would just pass by Local Group and keep on going into space. “They would never get close to us again,” says Stanimirovic. “Their fate would be Milky Way Previous, totally unknown.” Well, maybe. elliptical orbit LMC Previous, elliptical orbit Now streaming For more than 30 years, astronomers SMC have known about a huge tail that Current, 500,000 stretches away from the Magellanic parabolic orbit light-years Clouds, spanning more than 100° in Milky Way the sky. Consisting mainly of hydro- gen, it’s dubbed the Magellanic Stream and has been the subject of much recent scientific revision. And in Feb- ruary 2008, ’s Common- wealth Scientific and Industrial Research Organisation found that a Large pointy “finger” of gas opposite the Magellanic 100,000 light-years Both of the Magellanic Stream appears to puncture the Milky Cloud Clouds possess a lighter- Way’s disk about 70,000 light-years The Small Magellanic density fog of hydrogen sur- Cloud, about 200,000 light- Magellanic Bridge rounding them called the from Earth, near the Southern Cross years distant, is an irregular Magellanic Bridge, as well as from our perspective. The researchers galaxy about 10 times Small Magellanic a long tail of similar material expect the rest of the Magellanic smaller than the LMC and Cloud that trails out behind them, Clouds to sort of “fall” into the Milky 100 times smaller than the known as the Magellanic Way, eventually leading to a galactic Milky Way. NASA/ESA/HST Stream. This illustration dis- Magellanic Current, parabolic orbit plays their positions relative merger between it and the Magellanic Stream to each other and the Milky Clouds powered mostly by gravity. Of the first tendrils of the Stream. This nent of the Way, as well as their recently course, this isn’t a certainty yet either. discovery is welcome news because it within galaxies. And the Australian recalculated parabolic path. In January, David Nidever of the provides a new, plausible explanation Square Kilometer Array Pathfinder Astronomy: Roen Kelly, Gurtina Besla University of Virginia found that the for the Stream that doesn’t involve will map the Magellanic system with Magellanic Stream is more than 40 orbiting the Milky Way. 10 times higher resolution than ever must check it out with the nearby ones posed several theories as to why not, bolic orbit that takes them near the percent longer than previously before in 2013, providing some first,” says Subramaniam. That’s par- but it’s still a mystery. Milky Way just once. thought, and thus almost certainly To the future answers about its composition, but, ticularly prudent advice, given how Another, more fundamental mis- “Those were really shaking results older. The newer estimate makes the Naturally, we haven’t seen the last of most likely, also new questions. many times the Magellanic Clouds have understanding involves the galaxies’ in the community,” Stanimirovic says, Stream around 2.5 billion years old, the Magellanic Clouds, our galactic “The future is bright for the Magel- proven scientists wrong. very natures. “For a long, long time, “because for decades astronomers placing its birth at about the same neighbors as Subramaniam put it. lanic Clouds,” says Stanimirovic, and scientists thought that the Magellanic have been working with the assump- time as when scientists suspect the “You can live without talking to them thus far so is galactic research in gen- Magellanic missteps Clouds were gravitationally bound to tion that the Clouds are orbiting two Magellanic Clouds passed near or making any contact with them,” she eral. As Magellan himself proved Supernova 1987A surprised everyone the Milky Way,” says Stanimirovic. around the Milky Way.” Now, every- each other. The brush likely caused says. “But talking to a neighbor prob- (albeit posthumously), everything is with its unexpectedly close and glitter- They believed the Clouds moved in an thing is different. “This destroys and supernova explo- ably can give you a little more info, or connected — there are no edges to ing show, but it particularly surprised elliptical orbit, periodically nearing decades of numerical modeling of sions turbulent enough to blow out new insight, or new depths. Under- our understanding. astronomers. The star that exploded and departing the Milky Way over interactions between the Magellanic standing the Magellanic Clouds is Whether looming large after 1987’s into SN 1987A turned out to have billions of years. Clouds and the Milky Way Galaxy.” important from that point of view: It supernova, being all but forgotten for been a blue supergiant, a class then Then, in 2007, Harvard astrono- For example, astronomers had long gives new direction to understanding.” centuries, or rewriting the rules of our considered unable to “go” supernova. mers used data from the Hubble Space theorized that the Milky Way’s warped And a number of facilities will lead galactic neighborhood, the Magellanic While it’s still not completely under- Telescope to determine that the Mag- disk resulted from the gravitational the charge. The Atacama Large Mil- Clouds have plotted a complex course stood, astronomers now suspect the ellanic Clouds actually moved much pull of the Clouds’ occasional passes. limeter/submillimeter Array will pro- with our imagination. object was once a binary system whose faster than previously thought. “When But, if they’re really on a one-way trip vide a high-resolution view of many “The Magellanic Clouds are an stars had merged, producing the blue they tried to use new data and go back by the Milky Way, astronomers will of the molecular species residing in eye-opener,” says Subramaniam. “It’s supergiant thousands of years later. into [original calculations], they real- have to come up with another explana- the Clouds starting in 2012, helping good to explore and find out what SN 1987A was a core-collapse ized that it was getting really, really tion. Another new puzzle involves try- us better understand star formation things are possible.” supernova, which should have left hard to reproduce this bound, ellipti- ing to make sense of the intermittent The Magellanic Clouds, visible in the in such galaxies. The European Space Surely Ferdinand would agree. Southern Hemisphere, appear as glow- behind a . Despite more cal orbit,” says Stanimirovic. So instead star-forming activity in the Magellanic ing clouds in the night sky. The Large Agency’s Herschel Space Observatory than 20 years of searching, however, of being regulars in the Milky Way’s Clouds without counting on the occa- Magellanic Cloud, seen here, lies about is mapping the distribution of cold Read Senior Editor Richard Talcott’s no evidence of a neutron star has neighborhood, it turns out the Magel- sional gravitational effects of the Milky 160,000 light-years away and is classi- dust across the Clouds, teaching us story, “The First Days of SN 1987A” online at www.Astronomy.com/toc. turned up. Astronomers have pro- lanic Clouds are more likely on a para- Way present in an elliptical orbit. fied as an irregular galaxy, despite its about this virtually unknown compo- central bar and spiral arm. NASA

34 Astronomy • June 2010 www.Astronomy.com 35

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