"Gamma-ray astronomy is the astronomical observation of gamma rays, the most energetic form of electromagnetic radiation, with photon energies above 100 keV."
The study of gamma rays emitted by celestial objects to understand their properties and behavior.
Electromagnetic Spectrum: The electromagnetic spectrum ranges from radio waves to gamma rays. Gamma rays are at the highest end of the energy spectrum.
Radiation and Radioactivity: Gamma rays are a form of ionizing radiation, which means they have enough energy to knock electrons off of atoms, causing them to become ionized.
Gamma-ray Sources: Gamma rays can be emitted by a wide variety of astronomical objects, including supernovae, pulsars, active galactic nuclei, and gamma-ray bursts.
Gamma-Ray Detectors: There are several types of detectors used to observe gamma rays. These include Geiger-Muller tubes, scintillation detectors, and Cherenkov counters.
Gamma-Ray Telescopes: Gamma-ray telescopes are typically satellite-based observatories that use a combination of detectors and focusing instruments to observe gamma rays.
Gamma-Ray Astronomy Studies: Gamma-ray astronomy studies the emission of gamma rays from astronomical objects to gain insights into their properties, structure, and evolution.
Astroparticle Physics: Astroparticle physics is a field that studies the interactions between astrophysical objects and particles, including gamma rays.
Dark Matter: Gamma-ray astronomy can also contribute to the study of dark matter, which is thought to make up a large portion of the universe's mass and interacts only weakly with normal matter.
Neutrinos: Gamma-ray astronomy can also study the interactions of high-energy neutrinos which are subatomic particles with almost no mass.
Cosmic Rays: Cosmic rays are high-energy particles that originate from outside the solar system, and gamma-ray studies help to understand their origin and acceleration mechanisms.
Gamma-ray bursts: These are brief, intense bursts of gamma radiation that can last from a few milliseconds to several minutes. They are thought to be produced by the collapse of massive stars or the merging of two neutron stars. Gamma-ray bursts are some of the most energetic events in the universe and can be detected from billions of light-years away.
Active galactic nuclei (AGN): These are galaxies with supermassive black holes at their centers that are accreting matter. As matter falls toward the black hole, it produces intense radiation, including gamma rays. AGN can be observed across the entire electromagnetic spectrum and provide insights into the structure and evolution of galaxies.
Supernova remnants: When a massive star explodes as a supernova, it produces a shock wave that can accelerate particles to very high energies. These particles can produce gamma rays through various mechanisms, including the interaction with magnetic fields or the ambient gas. Studying the gamma-ray emission from supernova remnants can help us understand the origin of cosmic rays, which are high-energy particles that permeate the universe.
Pulsars: These are rapidly rotating neutron stars that emit beams of radiation from their magnetic poles. If the beam intersects with the Earth, we observe periodic pulses of radiation, hence the name pulsar. Pulsars can emit gamma rays through a process called inverse Compton scattering, where the radiation from the pulsar interacts with high-energy electrons in the vicinity.
Gamma-ray background: This is the diffuse, isotropic gamma-ray radiation that permeates the universe and is thought to be produced by a combination of sources, including extragalactic AGN, star-forming galaxies, and the annihilation of dark matter particles. Measuring the gamma-ray background can provide important constraints on the cosmic evolution of these sources and the nature of dark matter.
Gamma-ray telescopes: To observe gamma rays from space, specialized telescopes are necessary since gamma rays are absorbed by the Earth's atmosphere. The most well-known gamma-ray telescopes are the Fermi Gamma-ray Space Telescope and the High Energy Stereoscopic System (H.E.S.S.). These telescopes use different techniques to detect gamma rays, including pair production, where a gamma ray interacts with matter to produce an electron-positron pair, and Compton scattering, where a gamma ray interacts with an electron to produce a lower-energy photon.
"Radiation below 100 keV is classified as X-rays and is the subject of X-ray astronomy."
"In most known cases, gamma rays from solar flares and Earth's atmosphere are generated in the MeV range."
"It had been believed that gamma rays in the GeV range do not originate in the Solar System."
"GeV gamma rays are important in the study of extra-solar, and especially extra-galactic, astronomy."
"The mechanisms emitting gamma rays are diverse, mostly identical with those emitting X-rays but at higher energies, including electron–positron annihilation, the inverse Compton effect, and in some cases also the decay of radioactive material (gamma decay) in space reflecting extreme events."
"Extreme events such as supernovae and hypernovae, and the behavior of matter under extreme conditions, as in pulsars and blazars."
"In a 18 May 2021 press release, China's Large High Altitude Air Shower Observatory (LHAASO) reported the detection of a dozen ultra-high-energy gamma rays with energies exceeding 1 peta-electron-volt (quadrillion electron-volts or PeV)."
"The authors of the report have named the sources of these PeV gamma rays PeVatrons."
"...including one at 1.4 PeV, the highest energy photon ever observed."
"The authors of the report have named the sources of these PeV gamma rays PeVatrons."
"The detection of a dozen ultra-high-energy gamma rays with energies exceeding 1 peta-electron-volt (quadrillion electron-volts or PeV)."
"To observe and study gamma rays, the most energetic form of electromagnetic radiation."
"Sources of GeV gamma rays include extreme events such as supernovae and hypernovae, as well as the behavior of matter under extreme conditions."
"Radiation below 100 keV is classified as X-rays and is the subject of X-ray astronomy."
"GeV gamma rays are important in the study of extra-solar, and especially extra-galactic, astronomy."
"Extreme events such as supernovae and hypernovae, as well as the behavior of matter under extreme conditions, can generate gamma rays."
"To report the detection of a dozen ultra-high-energy gamma rays with energies exceeding 1 peta-electron-volt (quadrillion electron-volts or PeV)."
"The authors of the report have named the sources of these PeV gamma rays PeVatrons."
"Gamma rays are observed with photon energies above 100 keV, making them the most energetic form of electromagnetic radiation."