Gamma-ray burst

[7][8] After the initial flash of gamma rays, a longer-lived § afterglow is emitted, usually in the longer wavelengths of X-ray, ultraviolet, optical, infrared, microwave or radio frequencies.

From gravitational wave observations, short-duration (sGRB) events describe a subclass of GRB signals that are now known to originate from the cataclysmic merger of binary neutron stars.

Gamma-ray bursts were first observed in the late 1960s by the U.S. Vela satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space.

[21] Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos National Laboratory, led by Ray Klebesadel, filed the data away for investigation.

As additional Vela satellites were launched with better instruments, the Los Alamos team continued to find inexplicable gamma-ray bursts in their data.

From 1991, the Compton Gamma Ray Observatory (CGRO) and its Burst and Transient Source Explorer (BATSE) instrument, an extremely sensitive gamma-ray detector, provided data that showed the distribution of GRBs is isotropic (that is, not biased towards any particular direction in space).

[30][31] Even the most accurate positions contained numerous faint stars and galaxies, and it was widely agreed that final resolution of the origins of cosmic gamma-ray bursts would require both new satellites and faster communication.

This event was localized within four hours of its discovery, allowing research teams to begin making observations much sooner than any previous burst.

The following year, GRB 980425 was followed within a day by a bright supernova (SN 1998bw), coincident in location, indicating a clear connection between GRBs and the deaths of very massive stars.

However, the revolution in the study of gamma-ray bursts motivated the development of a number of additional instruments designed specifically to explore the nature of GRBs, especially in the earliest moments following the explosion.

[41][42] Swift is equipped with a very sensitive gamma-ray detector as well as on-board X-ray and optical telescopes, which can be rapidly and automatically slewed to observe afterglow emission following a burst.

Meanwhile, on the ground, numerous optical telescopes have been built or modified to incorporate robotic control software that responds immediately to signals sent through the Gamma-ray Burst Coordinates Network.

[67] Following this, several dozen short gamma-ray burst afterglows were detected and localized, several of them associated with regions of little or no star formation, such as large elliptical galaxies.

The observation of minutes to hours of X-ray flashes after an sGRB was seen as consistent with small particles of a precursor object like a neutron star initially being swallowed by a black hole in less than two seconds, followed by some hours of lower-energy events as remaining fragments of tidally disrupted neutron star material would remain in orbit, spiraling into the black hole over a longer period of time.

They have been proposed to form a separate class, caused by the collapse of a blue supergiant star,[86] a tidal disruption event[87][88] or a new-born magnetar.

[88] A 2013 study,[92] on the other hand, shows that the existing evidence for a separate ultra-long GRB population with a new type of progenitor is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion.

GRB 080319B, for example, was accompanied by an optical counterpart that peaked at a visible magnitude of 5.8,[93] comparable to that of the dimmest naked-eye stars despite the burst's distance of 7.5 billion light years.

The most widely accepted mechanism for the origin of long-duration GRBs is the collapsar model,[115] in which the core of an extremely massive, low-metallicity, rapidly rotating star collapses into a black hole in the final stages of its evolution.

[107] The model posits long gamma-ray bursts as occurring in binary systems with a carbon–oxygen core and a companion neutron star or a black hole.

[125][126][127][128] An alternative explanation proposed by Friedwardt Winterberg is that in the course of a gravitational collapse and in reaching the event horizon of a black hole, all matter disintegrates into a burst of gamma radiation.

[131] The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2010 there was still no generally accepted model for how this process occurs.

In this model, pre-existing low-energy photons are scattered by relativistic electrons within the explosion, augmenting their energy by a large factor and transforming them into gamma-rays.

Extremely energetic electrons within the shock wave are accelerated by strong local magnetic fields and radiate as synchrotron emission across most of the electromagnetic spectrum.

This ultraviolet radiation could potentially reach dangerous levels depending on the exact nature and distance of the burst, but it seems unlikely to be able to cause a global catastrophe for life on Earth.

Nitric acid is toxic to a variety of organisms, including amphibian life, but models predict that it would not reach levels that would cause a serious global effect.

It has proved difficult to assess a reliable evaluation of the consequences of this on the terrestrial ecosystem, because of the uncertainty in biological field and laboratory data.

[153][154] There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 billion years close enough to Earth as to significantly damage life.

There is a 50% chance that such a lethal GRB took place within two kiloparsecs of Earth during the last 500 million years, causing one of the major mass extinction events.

[15] The late Ordovician species of trilobites that spent portions of their lives in the plankton layer near the ocean surface were much harder hit than deep-water dwellers, which tended to remain within quite restricted areas.

In light of evolving understanding of gamma-ray bursts and their progenitors, the scientific literature records a growing number of local, past, and future GRB candidates.