A new japanese research of a GRB shows that it unlike the present theory of GRBø's have a high metalicity, taht suggests that the socalled "dark" GRBs may originate from another event than normal GRB's

A research team led by astronomers from Kyoto University, Tokyo Institute of Technology, and the National Astronomical Observatory of Japan used the Subaru Telescope to observe a dark gamma-ray burst (GRB) that provides clues for understanding the origin of dark gamma-ray bursts.

Their research is a very rare case of the detection of a dark GRB's host galaxy and afterglow in the near-infrared wavelength. They not only found that the host galaxy of this GRB is one of the most massive GRB host galaxies but also that a local dusty environment around the GRB significantly suppresses its afterglow.

The observational results suggest a high metallicity environment (one that contains a majority of elements heavier than helium) around the GRB, a finding that is inconsistent with previous interpretations of GRBs, which associate their origin with a supernova explosion of a low metallicity massive star at the end of its life.

This research suggests the possibility that GRBs classified as "dark" may originate in another mechanism such as the merger of binary stars.

Further reading: The Subaru Observatory homepage