This composite satellite image shows gamma rays (magenta), blasting out of Cassiopeia A remnant supernova. New research suggests that the most mysterious gamma ray bursts of the universe could form in a similar fashion.
Gamma-ray blasts (GRBs), which are the most intense, brightest and most energetic bursts of light in all of the universe, are the strongest. A single GRB can shine about one million trillion times brighter that the sun on Earth. It is produced by a massive cosmic explosion. Scientists are unable to explain why.
One problem is that all known GRBs originate from faraway galaxies, often billions of light years from Earth. Sometimes, the GRB's home galaxie is so far away that the burst's flashes of light appear to be coming from nowhere. They briefly disappear into the black sky, then return. These "empty sky" gammaray bursts have been a mystery for over 60 years. A new study published in Nature on Sept. 15 offers a convincing mathematical explanation for these powerful bursts.
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Researchers from the University of California, Berkeley, modeled the interactions of gamma radiations with other powerful energy sources such as cosmic rays. They concluded that all those nebulous and empty-sky bursts could result in massive stellar explosions in distant galaxies.
Matt Roth, an Australian National University astrophysicist, stated in a statement that "We modelled the gamma radiation from all the galaxies and found that it's star-forming galaxies which produce the majority [empty-sky] Gamma-ray radiation."
The Fermi telescope of NASA captured a map of the gamma ray sky. The so-called empty sky GRBs are far above and below that of the map's centre, which shows our galaxy's center. Image credit: NASA Goddard
Explosions from the Past
Two main explanations are offered by astronomers for the mystery of empty-sky gamma rays. One explanation is that the rays are caused by gas falling into supermassive blackholes, which sit at the center of all galaxies in our universe. This scenario is where gas particles are sucked into the black holes. A small fraction of these gas particles escape and instead emit large, near-light speed jets matter. These powerful jets are believed to be responsible for gamma ray bursts.
Another explanation is stellar explosions known as supernovas. These supernovas can cause large stars to run out of fuel, erupting in violent supernovas that send nearby particles flying at near-light speed. These extremely energetic particles are called cosmic rays and can collide with other particles in the gassy hinterland, generating gamma rays.
The researchers focused their study on the second explanation. They modelled the interactions of cosmic rays with interstellar gases in different types of star-forming galaxies. The researchers found that the rate at which gamma-ray emission occurs was affected by several factors including the size of the galaxies, star formation rate (which influences the rate supernovas), and the initial energy of each cosmic ray created by each supernova.
The team developed a model that predicted GRBs for all sizes of galaxies. They then compared the model to real data from NASA's Fermi Gamma-ray Space Telescope. Their calculations were consistent with observations, and supernovas in star-forming galaxyes could account for most empty-sky GRBs.
Roth stated, "It's an important milestone to finally uncover the origins this gammaray emission. Solving a mystery in the universe that astronomers had been trying to unravel since the 1960s."
Researchers concluded that some of the gamma radiation picked up by satellites is still caused by black holes. The mysterious empty-sky GRBs are not explained by hungry holes. Exploding stars in distant corners of the universe can explain it.
Original publication on Live Science
