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Galactic Crash Leaves Clues to Milky Way's Structure
By SPACE.com Staff
posted: 06:27 am ET
17 October 2002
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For 16 October 2002 Astronomers have identified a faint arc of young stars around galaxy Centaurus A that was formed during when it merged with another smaller galaxy. The results suggest that so-called halo stars, such as those that ring our own Milky Way Galaxy, are formed through a similar process. Astronomers had previously noticed the blue arcing feature in Cen A, as the galaxy is often referred to. The structure measures 2,000 light-years across, but researchers were not able to distinguish its origin. Eric Peng, a graduate student at Johns Hopkins University in Baltimore, and his colleagues used images and spectroscopic data from the Cerro Tololo Inter-American Observatory in Chile to identify the arc and determine the age and distance of the young stars within it. They conclude that Cen A, which is 10 million light-years away, consumed a gas-rich dwarf galaxy 200 to 400 million years ago, igniting a period of star formation. Both the gaseousness of the companion galaxy and how recently the event took place are unusual, said the astronomers. "The tidal forces of the main galaxy caused a burst of star formation within the in-falling galaxy, and what we see now are these young stars spread along the remnant of the incoming orbit," Peng said. But, they add, this was not the only instance of a galactic merger involving Cen A. Its structure and shape imply that it has also merged with a spiral galaxy. Peng, who collaborated with Holland Ford, also of Johns Hopkins, Ken Freeman of the Australian National University, and Rick White of the Space Telescope Science Institute, believes the stars in the arc will eventually settle closer around the edge of Cen A as halo stars. The results will be published in the December issue of the Astronomical Journal. "This adds a nice example in the local universe to the growing evidence that galaxy halos are built up from the accretion of dwarf satellite galaxies," Peng said. "These halos are interesting partly because they're hard to study, but also because time scales for things to happen in halos are very long, which means they may preserve conditions that reveal how a galaxy formed and evolved." Peng plans on further observations of the arc and also of the region in general to try and identify other dwarf galaxy remnants. More Deep Space News | Astronotes
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