Astronomers have made the most detailed map ever of our galaxy’s overall shape, showing that its spiral arms extend much further than expected. Evan Levine, Leo Blitz and Carl Heiles of the University of California at Berkeley analysed the distribution of atomic hydrogen in the Milky Way at radio wavelengths to reveal hitherto unseen features of our galactic backyard. The map shows that our galaxy’s spiral structure is not symmetrical around its centre but contains more arms in some areas than others. Contrary to theoretical predictions, the arms also continue well beyond the distance at which stars should be found.
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