An unusual gamma-ray burst has puzzled the astronomical community. Four groups of astronomers hailing from various countries, including the United States, United Kingdom, Denmark and Italy, investigated a gamma-ray burst that seems to shed doubt on some widely held assumptions (see pages 1044–1055).

Generally, astronomers divide the bursts into two types, short and long. Long bursts (of the order of tens of seconds) are thought to be produced by the core collapse of a massive star; short bursts (less than about 2 seconds) by the merging of two neutron stars. But in analysing data from NASA's Swift satellite, the Hubble telescope and ground-based telescopes, these four groups identified a long-lasting burst not associated with a stellar explosion that showed some features of short bursts.

“These results have stimulated a great deal of discussion,” says Neil Gehrels, lead author of one of the papers and head of the astroparticle physics laboratory at NASA's Goddard Space Flight Center in Greenbelt, Maryland. He and others speculate that such a burst might be produced either by the involvement of a black hole in a neutron-star merger or by the collapse of a massive star into a black hole. He and his colleagues plan to use Swift and ground-telescope data to search for similar phenomena.