Gamma-ray bursts were discovered in the late 1960s by the U.S. Vela nuclear test detection satellites. The Velas were built to detect gamma radiation pulses emitted by nuclear weapon tests in space. The United States suspected that the USSR might attempt to conduct secret nuclear tests after signing the Nuclear Test Ban Treaty in 1963. While most satellites orbited at about 500 miles above Earth’s surface, the Vela satellites orbited at an altitude of 65,000 miles. At this height, the satellites orbited above the Van Allen radiation belt, which reduced the noise in the sensors. The extra height also meant that the satellites could detect explosions behind the moon, a location where the United States government suspected the Soviet Union would try to conceal nuclear weapon tests. The Vela system generally had four satellites operational at any given time such that a gamma-ray signal could be detected at multiple locations. This made it possible to localize the source of the signal to a relatively compact region of space. While these characteristics were incorporated into the Vela system to improve the detection of nuclear weapons, these same characteristics were what made the satellites capable of detecting gamma-ray bursts.
Gamma-ray bursts (GRBs) are flashes of gamma rays emanating from seemingly random places in deep space at random times. The duration of a gamma-ray burst is typically a few seconds, but can range from a few milliseconds to several minutes, and the initial burst is usually followed by a longer-lived “afterglow” emitting at longer wavelengths (X-ray, ultraviolet, optical, infrared, and radio). Gamma-ray bursts are detected by orbiting satellites about two to three times per week.
Most observed GRBs appear to be collimated emissions caused by the collapse of the core of a rapidly rotating, high-mass star into a black hole. A subclass of GRBs (the “short” bursts) appear to originate from a different process, the leading theory being the merger of neutron stars orbiting in a binary system. All observed GRBs have originated from outside the Milky Way galaxy, though a related class of phenomena, soft gamma repeater flares, are associated with galactic magnetars. The sources of most GRBs have been billions of light years away.
A nearby gamma-ray burst could possibly cause mass extinctions on Earth.[The short duration of a gamma-ray burst would limit the immediate damage to life. However, a nearby burst might alter atmospheric chemistry by reducing the ozone layer and generating acidic nitrogen oxides ultimately causing severe damage to the biosphere. Since GRBs in metal-rich galaxies like the Milky Way are rare, mass extinctions due to GRBs may only happen once per billion years.
A Ticking Time Bomb?
According to some researches the side of Earth facing the concentrated beam of an incoming gamma burst from a nearby source would suffer atmospheric shock waves which ignited everything in the air and on the surface of the planet. The immense heating of the atmosphere would begin causing catastrophic weather changes worldwide within only minutes. Everything which could burn would do so. However, taking refuge in sturdy shelters would offer some momentary protection. Following this brief (under one second) blast of gamma rays would be days of cosmic rays raining down upon Earth, and passing with killing energies through everything as deep as half a kilometer. It’s unlikely even humanity’s elite in the best and deepest underground shelters available could survive. Life in the depths of the oceans will be killed. Everything on the surface will be dead.Fortunately these death rays consist of beams likely only one degree wide, and so will usually miss a particular world like Earth. Unfortunately, the stats still put us at risk about once every hundred million years.
Current missions
Swift Spacecraft
INTEGRAL, the European Space Agency’s International Gamma-Ray Astrophysics Laboratory Announcements, was launched on March 16 2006. It is the first observatory capable simultaneously observing objects at gamma ray, X-ray, and visible wavelengths.[39]
NASA’s Swift satellite launched in November 2004. It combines a sensitive gamma-ray detector with the ability to point on-board X-ray and optical telescopes towards the direction of a new burst in less than one minute after the burst is detected.[40] Swift’s discoveries include the first observations of short burst afterglows and vast amounts of data on the behavior of GRB afterglows at early stages during their evolution, even before the GRB’s gamma-ray emission has stopped. The mission has also discovered large X-ray flares appearing within minutes to days after the end of the GRB.
On June 11, 2008 NASA’s Gamma-ray Large Area Space Telescope (GLAST), later renamed the Fermi Gamma-ray Space Telescope, was launched. The mission objectives include “crack[ing] the mysteries of the stupendously powerful explosions known as gamma-ray bursts.
Other gamma-ray burst observation missions include and AGILE. Discoveries of GRBs are made as they are detected via the Gamma-ray Burst Coordinates Network so that researchers may promptly focus their instruments on the source of the burst to observe the afterglows.
Links:
Rashid's Blog: A Place for Inquisitive Learners 