Gamma rays are found at one end of the electromagnetic spectrum, which also includes radio waves, infrared light, visible light, ultraviolet light, and x-rays. Gamma-rays have a shorter wavelength and more energy than any other form of electromagnetic radiation. In the late 1960s, enormous bursts of energy in the form of gamma-rays were detected in space. Distributed randomly across the sky, these intensely energetic flashes stumped researchers. What astronomical phenomenon could create such powerful bursts of energy? Not only were the origins of the energy unknown, researchers could not even pinpoint whether the bursts were located within the galaxy or at cosmological distances.
For decades, gamma-ray bursts, known as GRBs, remained one of the biggest mysteries of astronomy. However, with advances in technology, the GRB mystery has begun to be solved. Since the 1990s, missions such as the Compton Gamma Ray Observatory and the BeppoSAX and HETE-2 satellites have helped scientists begin to understand these brilliant bursts of energy. Most recently, NASA's Swift satellite, launched in 2004, carries a suite of instruments dedicated toward studying GRBs. Swift scans the sky for a GRB, and once it detects one, it maneuvers "swiftly" and aims two other telescopes at the GRB, thus enabling them to collect and record information about the burst's afterglow in multiple wavelengths.
Scientists have classified GRBs into two groups based on their duration: long bursts last more than about two seconds and short bursts last less than about two seconds. Within its first year of operation, Swift (in cooperation with other telescopes) has provided compelling observational data supporting theories for both short and long GRBs.
Long GRBs are most likely the result of the explosive death of an extremely massive star, one with a mass more 40 times that of the Sun, as it becomes a black hole. Swift has observed a long GRB at the outer edge of the universe at a distance of about 13 billion light-years. By studying distant GRBs, astronomers are able to study some of the oldest objects in the universe and learn more about the conditions of the young universe. For example, such a distant GRB confirms that massive stars existed when the Universe was young and offers insight into where and when the earliest stars formed.
Swift has also been able to collect groundbreaking observations of short GRBs. These data confirm that short GRBs are the result either of a neutron star merging with a black hole or of two neutron stars merging to create a black hole. Because such a merger creates significant gravitational effects, the discovery of the origin of short GRBs will aid in the study of gravitational waves.
To learn more about the death of high-mass stars, check out Birth of a Supernova, Type Ia and Birth of a Supernova, Type II.
To learn more about how different wavelengths are useful in astronomy, check out Astronomical Images in Different Wavelengths.
To learn more about the electromagnetic spectrum, check out The Electromagnetic Spectrum: FRONTLINE and The Electromagnetic Spectrum: NASA.
To learn more about black holes, check out Monster Black Hole in Galaxy M84.