Gamma rays are an extremely energetic form of electromagnetic radiation and they are invisible.
In the 1960s, satellites designed to detect nuclear bomb explosions on Earth picked up short bursts of gamma rays coming from random points in the distant Universe. Since this discovery, the cause of gamma ray bursts (sometimes called GRBs) has been debated.
Image: An illustration of a gamma ray burst (credit: NASA/D.Berry)
Bursts of powerful radiation come from the distant Universe.
Gamma rays may provide a clue.
Professor Brian Boyle from the Anglo-Australian Observatory explains how observations of a gamma ray burst helped his team discover that it resulted from a supernova and the possible formation of a black hole.
Star death takes place alongside the birth of new stars.
The source of gamma ray bursts, high intensity flashes of gamma ray radiation from the distant Universe, puzzled scientists for many years. However, intense study tracked down the source of these explosions to the formation of black holes.
Gamma ray bursts may help scientists see the earliest days of the Universe.
Gamma ray bursts may allow astronomers to see the first stars form in the early Universe.
Patrick Moore and his guests discuss gamma ray bursts.
Sir Patrick Moore and his guests discuss gamma ray bursts, which are thought to be caused by exploding massive stars. Could the star Eta Carinae emit a gamma ray burst one day?
BBC News reports on the Swift gamma ray burst mission.
Prior to launch, Fergus Walsh reports on the Swift mission to investigate gamma ray bursts.
Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several hours. The initial burst is usually followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, microwave and radio).
Most observed GRBs are believed to consist of a narrow beam of intense radiation released during a supernova or hypernova as a rapidly rotating, high-mass star collapses to form a neutron star, quark star, or black hole. A subclass of GRBs (the "short" bursts) appear to originate from a different process – this may be due to the merger of binary neutron stars. The cause of the precursor burst observed in some of these short events may be due to the development of a resonance between the crust and core of such stars as a result of the massive tidal forces experienced in the seconds leading up to their collision, causing the entire crust of the star to shatter.
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) and extremely rare (a few per galaxy per million years). All observed GRBs have originated from outside the Milky Way galaxy, although a related class of phenomena, soft gamma repeater flares, are associated with magnetars within the Milky Way. It has been hypothesized that a gamma-ray burst in the Milky Way, pointing directly towards the Earth, could cause a mass extinction event.
GRBs were first detected in 1967 by the Vela satellites, a series of satellites designed to detect covert nuclear weapons tests. Hundreds of theoretical models were proposed to explain these bursts in the years following their discovery, such as collisions between comets and neutron stars. Little information was available to verify these models until the 1997 detection of the first X-ray and optical afterglows and direct measurement of their redshifts using optical spectroscopy, and thus their distances and energy outputs. These discoveries, and subsequent studies of the galaxies and supernovae associated with the bursts, clarified the distance and luminosity of GRBs. These facts definitively placed them in distant galaxies and also connected long GRBs with the explosion of massive stars, the only possible source for the energy outputs observed.