<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>

Christmas Day Burst

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 NASA's Swift satellite last December 25.

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.

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 comet Shoemaker-Levy 9 (picture) broke up when it got too close to Jupiter.

Pieces of the broken object falling onto the neutron star sparked the flash of gamma rays, the team theorizes. (Read more about the Christmas Day burst.)

Illustration courtesy A. Simonnet, NASA/EPO/SSU

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