Unveiled in the 1960s by American military satellites on the lookout for undisclosed nuclear detonations, gamma-ray bursts (GRBs) represent swift, intense explosions of gamma rays - the most potent form of light. These ephemeral phenomena, lasting anywhere from milliseconds up to several hours, outshine a regular supernova by hundreds of times and are about a quintillion times as luminous as the Sun. They are spotted in remote galaxies and are the most radiant electromagnetic occurrences known in the cosmos. A standard burst emits as much energy in a matter of seconds as the Sun will over its entire 10-billion-year lifespan.
Usually, an enduring afterglow of X-ray, ultraviolet, optical, infrared, microwave, and radio emissions succeed the initial gamma-ray flash. Current data from advanced satellites, such as NASA's Swift and Fermi observatories, suggest these luminous bursts result from the implosion of matter into black holes. On average, about one GRB is detected each day.
GRBs are not sourced from any specific direction in space, though they are linked to extremely faint galaxies at tremendous distances. These explosions are believed to be highly concentrated, with the majority of the energy directed into a narrow jet moving nearly at light speed. Only the jets pointed directly at us can be detected as GRBs.
Astronomers categorize GRBs into long-duration and short-duration events. Despite the different processes likely behind their creation, both result in the formation of a new black hole. Long-duration bursts can last from 2 seconds to several hours. While these are tied to the death of massive stars in supernovas, not all supernovas lead to a GRB. Short-duration bursts, lasting less than 2 seconds, seem to result from the collision of two neutron stars into a new black hole, or the merger of a neutron star and a black hole to form a larger one.
Hubble's precise resolution aids in studying the environments of GRBs. Hubble imagery revealed one type of GRB originates from distant galaxies undergoing high rates of star formation. This validated the theory that the light bursts stemmed from the collapse of massive stars. Hubble’s unique ultraviolet spectroscopy will be crucial in understanding how elements are created in these massive explosions.
In 2017, NASA's Fermi telescope recorded a short-duration GRB linked to gravitational waves detected by the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO). A collision of two neutron stars is believed to have spawned an extraordinarily explosive kilonova, along with the GRB and the gravitational waves. Hubble embarked on observing the kilonova and capturing its near-infrared spectrum, which unveiled the motion and chemical composition of the expanding debris. The spectrum matched precisely what theoretical physicists had predicted for the outcome of the merging of two neutron stars.
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