- 2825 - GAMMA RAYS - mystery covering years of research? Gamma Rays are essentially high energy light. They started out with the Big Bang and have been loosing energy as they travel though an expanding Universe. But, they also include processes created by cosmic ray interactions with interstellar gas, supernova explosions and interactions of energetic electrons with magnetic fields.
--------------- 2825 - GAMMA RAYS - mystery covering years of research?
- Long before experiments could detect gamma rays emitted by cosmic sources, scientists had known that the universe should be producing these photons. Work by Feenberg and Primakoff in 1948, Hayakawa and Hutchinson in 1952, and Morrison in 1958 had led scientists to believe that a number of different processes occurring in the universe would result in gamma-ray emission.
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- It was not until the 1960s that scientists were actually able to detect these emissions.
Gamma rays coming from space are mostly absorbed by Earth's atmosphere. So gamma-ray astronomy could not develop until it was possible to get the detectors above all or most of the atmosphere, using balloons or spacecraft.
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- The first gamma-ray telescope was carried into orbit on the Explorer-XI satellite in 1961, and picked up fewer than 100 cosmic gamma-ray photons. These appeared to come from all directions in the universe, implying some sort of uniform "gamma-ray background“. This background would be expected from the interaction of cosmic rays, very energetic charged particles, with gas found between the stars.
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- Significant gamma-ray emission from our Galaxy was first detected in 1967 by the gamma-ray detector aboard the OSO-3 satellite. It detected 621 events attributable to cosmic gamma rays.
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- Gamma-ray astronomy took great leaps forward with the SAS-2 (1972) and the COS-B (1975-1982) satellites. These two satellites provided an exciting view into the high-energy universe, sometimes called the "violent" universe, because the type of events in space that produce gamma rays tend to be explosions and high-speed collisions.
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- The data from the satellites confirmed the earlier findings of the gamma-ray background, produced the first detailed map of the sky at gamma-ray wavelengths, and detected a number of point sources, where the sources of radiation were very concentrated and emanated from a small area.
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- However, the poor resolution of the instruments made it impossible to identify most of these point sources with individual stars or stellar systems.
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- The most spectacular discovery in gamma-ray astronomy came in the late 1960s and early 1970s from a collection of defense satellites that were put into orbit for a reason completely unrelated to astronomy research. Detectors on board the Vela satellite series were designed to detect flashes of gamma rays from nuclear bomb blasts.
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- They began to record bursts of gamma rays, not from the vicinity of Earth, but from deep space. These gamma-ray bursts, called GRBs, can last for fractions of a second to minutes, popping off like cosmic flashbulbs from unexpected directions, flickering, and then fading after briefly dominating the gamma-ray sky.
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- They were studied for over 25 years with instruments on board a variety of satellites and space probes, including Soviet Venera spacecraft and the Pioneer Venus Orbiter, the sources of these enigmatic high-energy flashes for a while remained a mystery.
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- In one of the most intense debates in modern astrophysics, some scientists claimed that the bursts originate in a halo of neutron stars which surround our Galaxy while others argued that their origins are far beyond the Galaxy, at cosmological distances. This was settled in 1996 when the BeppoSax satellite and the Hubble Space Telescope pinpointed the location of a gamma-ray burst in distant galaxy.
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- In 1977, NASA announced plans to build a "great observatory" for gamma-ray astronomy. The Compton Gamma-Ray Observatory (CGRO) was designed to take advantage of the major advances in detector technology during the 1980s, and was launched in 1991.
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- The satellite carried four major experiments which greatly improved the spatial and temporal resolution of gamma-ray observations. The CGRO provided large amounts of data which have been used to improve our understanding of the high-energy processes in our Universe. CGRO was de-orbited in June 2000 as a result of the failure of one of its stabilizing gyroscopes.
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- In November 2004, NASA launched the Swift satellite. Its primary mission is to detect and locate GRBs as quickly as possible, report the position of the burst, then follow up with other observations of that location in the X-ray, UV and visual spectra. On April 13, 2010, NASA's Swift satellite recorded its 500th GRB.
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- To continue the study of the universe in the gamma-ray spectrum, Swift operated in conjunction with the Fermi Gamma-Ray Space Telescope, launched in 2008. Fermi, originally called GLAST (Gamma-ray Large Area Space Telescope), also studies GRBs, as well as blazars, neutron stars, gamma-ray background radiation, supernova remnants, dark matter and more.
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- A pair of distant explosions discovered by NASA’s Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory have produced the highest-energy light yet seen from these events, called gamma-ray bursts (GRBs). The record-setting detections, made by two different ground-based observatories, provide new insights into the mechanisms driving gamma-ray bursts.
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- The most common type of GRB occurs when a star much more massive than the Sun runs out of fuel. Its core collapses and forms a black hole, which then blasts jets of particles outward at nearly the speed of light. These jets pierce the star and continue into space. They produce an initial pulse of gamma rays, the most energetic form of light, that typically lasts about a minute.
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- As the jets race outward, they interact with surrounding gas and emit light across the spectrum, from radio to gamma rays. These so-called afterglows can be detected up to months, and, rarely, even years after the burst at longer wavelengths.
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- Much of what we’ve learned about GRBs over the past couple of decades has come from observing their afterglows at lower energies. On January 14, 2019, just before 4 p.m. EST, both the Fermi and Swift satellites detected a spike of gamma rays from the constellation Fornax. The missions alerted the astronomical community to the location of the burst, dubbed GRB 190114C.
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- One facility receiving the alerts was the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observatory, located on La Palma in the Canary Islands, Spain. Both of its 17-meter telescopes automatically turned to the site of the fading burst. They began observing the GRB just 50 seconds after it was discovered and captured the most energetic gamma rays yet seen from these events.
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- The energy of visible light ranges from about 2 to 3 electron volts. In 2013, Fermi’s Large Area Telescope (LAT) detected light reaching an energy of 95,000,000,000 electron volts (GeV), then the highest seen from a burst.
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- This falls just shy of 100 GeV, the threshold for so-called very high-energy (VHE) gamma rays. With GRB 190114C, MAGIC became the first facility to report unambiguous VHE emission, with energies up to a trillion electron volts (1 TeV). That’s 10 times the peak energy Fermi has seen to date.
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- The discovery of TeV gamma rays shows that these explosions are even more powerful than thought before. More importantly, this detection facilitated an extensive follow-up campaign involving more than two dozen observatories, offering important clues to the physical processes at work in GRBs.
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- These included NASA’s NuSTAR mission, the European Space Agency’s XMM-Newton X-ray satellite, the NASA/ESA Hubble Space Telescope, in addition to Fermi and Swift, along with many ground-based observatories.
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- Hubble images captured the burst’s optical afterglow. They show that the blast originated in a spiral galaxy about 4.5 billion light-years away. This means the light from this GRB began traveling to us when the universe was two-thirds of its current age.
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- The High Energy Stereoscopic System (H.E.S.S.) pointed its large, 28-meter gamma-ray telescope to the location of the burst, called GRB 180720B. A careful analysis carried out during the weeks following the event revealed that H.E.S.S. clearly detected VHE gamma rays with energies up to 440 GeV. Even more remarkable, the glow continued for two hours following the start of the observation. Catching this emission so long after the GRB’s detection is both a surprise and an important new discovery.
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- Scientists suspect that most of the gamma rays from GRB afterglows originate in magnetic fields at the jet’s leading edge. High-energy electrons spiraling in the fields directly emit gamma rays through a mechanism called synchrotron emission.
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- The core of a massive star collapsed and formed a black hole. This “engine” drives a jet of particles that moves through the collapsing star and out into space at nearly the speed of light. The prompt emission, which typically lasts a minute or less, may arise from the jet’s interaction with gas near the newborn black hole and from collisions between shells of fast-moving gas within the jet (internal shock waves).
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- The afterglow emission occurs as the leading edge of the jet sweeps up its surroundings (creating an external shock wave) and emits radiation across the spectrum for some time, months to years, in the case of radio and visible light, and many hours at the highest gamma-ray energies yet observed. These far exceed 100 billion electron volts (GeV) for two recent GRBs.
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- Researchers interpret the VHE emission as a distinct afterglow component, which means some additional process must be at work. The best candidate is inverse Compton scattering. High-energy electrons in the jet crash into lower-energy gamma rays and boost them to much higher energies.
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- The researchers conclude that an additional physical mechanism may indeed be needed to produce the VHE emission. Within the lower energies observed by these missions, however, the flood of synchrotron gamma rays makes uncovering a second process much more difficult. If the VHE emission arises from the synchrotron process alone, then fundamental assumptions used in estimating the peak energy produced by this mechanism will need to be revised.
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- The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.
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- Goddard manages the Swift mission in collaboration with Penn State in University Park, the Los Alamos National Laboratory in New Mexico and Northrop Grumman Innovation Systems in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy.
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- 2821 - GAMMA RAY BURSTS - how often it happens? Would you like to see the most powerful explosion that occurs in the Universe? Don’t worry you do not have to stand too close. These explosions are at least 2,000,000,000 lightyears away. They occur once a day on average and one of these occurred in the constellation Hydra. Log on to http://grb.sonoma.edu/ and see the sky map with the Gamma Ray Bursts exploding in real time.
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- 2330 - Monday, December 27, 2004, the brightest flash of light in our history passed by Earth . It came from a neutron star, a remnant of a giant star that ended its live in a supernova explosion. These giant stars start out at 30 to 40 times the mass of our Sun. They live short lives of only 10 million years before they have burned all their nuclear fuel down to an iron core.
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- 2329 - Gamma Rays and Cosmic Rays are totally different. Gamma Rays are high frequency, high power light waves. Cosmic Rays are high speed particles , atomic nuclei, mostly hydrogen protons, mostly coming from our Sun, but some from distant stars.
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-1482 - Enormous Gamma Ray bubbles and jets are shooting out from our galaxy’s Blackhole. What is going on? If you travel far out into space and look back at the Milky Way Galaxy edge-on with a camera that detects light in the Gamma Ray frequency range your image includes two enormous “ bubbles”, “tear drops” above and below the galaxy center. And, there are two jets shooting up at a 15 degree angles to the perpendicular. How to explain this ?
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- 1323 - Other Gamma Ray Sources and Mysteries? What we “see” in our Universe is very limited, extremely limited. Our eyes can detect that part of the electromagnetic spectrum from about 400 to 700 nanometers wavelength. That is the wavelengths from blue light to red light and all the colors in between. We can use our radio receivers to detect the really long wavelengths. TV receivers, Microwave receivers detect other parts of the electromagnetic spectrum.
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- 1238 - Do Thunderstorms Create Anti-Matter with Lightning? Gamma Ray telescopes were launched into space to study distance sources of Gamma Ray radiation and flares. Imagine our surprise when the Gamma Ray flares were found coming from the tops of thunderstorms in the opposite direction we were looking.
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- 1160 - What Can Astronomers See with Gamma Rays? Astronomers are just beginning to see in Gamma Rays. Visible light has energies between 2 and 3 electron volts. An electron volt is the energy of a single electron moving through a voltage about the potential of a flashlight battery. A very small amount of energy. Gamma Rays are light photons of very high energy, in the 100,000 to 100,000,000 electron volts.
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- 1158 - Where Do Gamma Rays Come From? Gamma Rays are light of the maximum possible energy. With wavelengths shorter than 10^-11 meters, each Gamma Ray photon has an energy of at least 100,000 electron volts. That is 100,000 times more energy than visible light. Some Gamma Rays have even shorter wavelengths and even more energy. The most energetic Gamma Ray recorded was 100,000,000,000 electron volts.
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- 916 - Gamma Ray Telescopes. Electromagnetic radiation starts with radio waves and goes all the way up to Gamma Rays as the frequency increases. The energy of radiation is a function of frequency. So, as the frequency increases the energy in the photons increases. When you get up to Gamma Rays they can carry so much energy that they can actually convert back to mass, according to E=mc^2.
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- September 12, 2020 2825
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