Gamma rays are the highest-energy form of electromagnetic (EM) radiation – about a billion times more powerful than the EM waves we see as visible light. When scientists observe intense bursts of gamma rays from space, it usually indicates the presence of a large-scale, high-energy cosmic event – like the sudden gravitational collapse of a star or matter streaming into the enormous gravitational sink of a black hole. Gamma-ray bursts are the most energetic events known in the universe, and, though scientists have been able to figure out a few things about them, gamma-ray bursts are still a bit of a mystery.

Gamma-ray bursts come from outside our Milky Way galaxy, usually from very, very far away. The initial wave of intense energy usually includes other types of electromagnetic radiation as well, which we can also “see” and image. The analysis of this data answers some questions, leaves some questions unanswered, and raises still other questions about the nature of the universe.

Scientists are very interested in the extreme events that produce gamma-ray bursts because such physical phenomena serve as “laboratories” whereby our understanding of space, time, and energy gets challenged, expanded, deepened, and sometimes even overturned. It’s interesting that, though interpretation of EM radiation, the very largest structures of the universe can tell us much about what happens at the very smallest atomic and subatomic levels of interaction. The most common explanation for what causes gamma-ray bursts is that, when a massive star runs out of fuel (meaning the internal fusion reactor that powers the star and is a force of expansion has burned up all of its fuel, leaving only heavier, less reactive elements with increasingly tremendous inward gravitational forces), it quickly collapses inward and creates a very dense body like a neutron star or a black hole. As it collapses, areas of the star’s magnetic field can intensify and align along two opposite poles, creating lines of magnetic force that act like “superhighways” for charged particles being ejected from the core. Astronomers refer to these superhighways as “jets.” The collision of that material into surrounding gas and matter produces the high-energy gamma-ray bursts. This isn’t the only way gamma-ray bursts can be produced, however. Scientists believe that two neutron stars colliding can also produce gamma-ray bursts. Both phenomena, though, involve the collapse of huge, dense masses.

All stars produce their energy from elements in their core. They fuse helium into hydrogen and then into successively heavier elements until the fusion process runs out of fuel. Stars still burning hydrogen to helium are called “main sequence” stars and they can be identified by the kinds and amounts of EM radiation the produce. When a star’s fuel burns out, the star begins to die. How a star lives – and dies – depends on its mass. If a star has a mass that’s less than about twice the mass of our Sun, then it will either expand into a red giant (during our Sun’s red giant phase, it will be so large that it would appear to take up a third of the sky) or condense slightly into a white dwarf (one teaspoon of a white dwarf would weigh as much as the moon). On a cosmic scale, neither of these outcomes is highly dramatic. More massive stars, on the other hand, can collapse in on themselves and form very dense neutron stars. Extremely massive stars – when they collapse – press their core into such extreme conditions that they produce black holes. Neutron stars are much more common than black holes – and red giants are much more common than white dwarfs.

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