In gamma-ray astronomy , gamma-ray bursts ( GRBs ) are immensely energetic explosions that have been observed in distant galaxies . They are the most energetic and luminous electromagnetic events since the Big Bang . [1] Bursts can last from ten milliseconds to several hours. [2] [3] After an initial flash of gamma rays , a longer-lived "afterglow" is usually emitted at longer wavelengths ( X-ray , ultraviolet , optical , infrared , microwave and radio ). [4]
The intense radiation of most observed GRBs is thought to be released during a supernova or superluminous supernova as a high-mass star implodes to form a neutron star or a black hole . A subclass of GRBs appear to originate from the merger of binary neutron stars . [5]
The sources of most GRBs are billions of light years away from Earth , implying that the explosions are both extremely energetic (a typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime) [6] and extremely rare (a few per galaxy per million years [7] ). All observed GRBs have originated from outside the Milky Way galaxy , although a related class of phenomena, soft gamma repeaters , are associated with magnetars within the Milky Way. It has been hypothe