Gamma-ray burst
Most observed events last longer than two seconds and are classified as long gamma-ray bursts. They have been studied in much greater detail than their short counterparts. Almost every well-studied long gamma-ray burst has been associated with a rapidly star-forming galaxy and in many cases a core-collapse supernova as well. This links long GRBs with the deaths of massive stars. Long GRB afterglow observations at high redshift (great distances) also suggest GRBs originate in star-forming regions. This is because observing distant galaxies is to look back in time to galaxies at an earlier stage.