<p>A comet-like body gets torn apart by a neutron star in an illustration of what might have caused an unusual gamma-ray burst spotted by <a href="http://www.nasa.gov/mission_pages/swift/main/index.html">NASA's Swift satellite</a> last December 25.</p><p>It's thought so-called long gamma-ray bursts happen when massive stars collapse and explode as supernovae. But last year's flash, dubbed the Christmas Day burst, was unlike any other gamma-ray burst yet seen, prompting researchers to consider alternate explanations.</p><p>One team proposes that an object about half the mass of the dwarf planet Ceres got within about a million kilometers of a neutron star that's 1.4 times the mass of the sun. As the comet approached the star, it got ripped apart by gravitational forces—just as the <a href="http://news.nationalgeographic.com/news/2009/04/photogalleries/hubble-top-discoveries/photo4.html">comet Shoemaker-Levy 9 (picture)</a> broke up when it got too close to Jupiter.</p><p>Pieces of the broken object falling onto the neutron star sparked the flash of gamma rays, the team theorizes. (Read <a href="http://newswatch.nationalgeographic.com/2011/11/30/mysterious-christmas-day-starburst-explained/">more about the Christmas Day burst</a>.)</p>