Star-forming galaxies are responsible for generating gamma rays that have not yet been attributed to a known source. The discovery may lead astrophysicists to decipher dark matter
Star-forming galaxies are responsible for generating gamma rays that have so far not been attributed to a known source, researchers from the Australian National University (ANU) have now confirmed.
Lead author Dr Matt Roth from ANU's Research School of Astronomy and Astrophysics said until now it was not clear what creates gamma radiation - one of the most energetic forms of light in the universe - that appears in patches of apparent "empty sky".
The discovery could provide clues that will help astronomers solve other mysteries of the universe, such as what kind of particles dark matter is made of - one of the holy grails of astrophysics.
"It is a significant milestone to finally discover the source of this gamma ray emission, and to solve a mystery of the universe that astronomers have been trying to decipher since the sixties," said Dr. Roth.
"There are two clear sources that produce large amounts of gamma rays that are visible in the universe. One when gas falls into the supermassive black holes found at the centers of all galaxies—called the nucleus of an active galaxy—and the other is related to star formation in the disks of galaxies.
"We modeled the gamma ray emission from all the galaxies in the universe and compared our results to the predictions of other sources and found that it is the star-forming galaxies that produce most of this diffuse gamma ray radiation and not the nuclear process."
The ANU researchers were able to pinpoint what produced these mysterious gamma rays after better understanding how cosmic rays - particles traveling at speeds very close to the speed of light - move through the interstellar gas. Cosmic rays are important because they create large amounts of gamma ray emission in star-forming galaxies as they collide with the interstellar gas.
Data from the Hubble Space Telescope and the Fermi Gamma-ray Space Telescope, both of NASA, were an important source used to discover the unknown source of the gamma rays. The researchers analyzed information about many galaxies such as their star formation rates, total masses, physical size and distances from Earth.
"Our model can also be used to make predictions about radio emission - the electromagnetic radiation that has a frequency similar to a car radio - from star-forming galaxies, and this could help researchers better understand the internal structure of galaxies," said Dr. Roth.
"We are now looking at creating maps of the gamma-ray sky that could be used to inform nearby gamma-ray observations from next-generation telescopes. This includes the Cherenkov Telescope Array, which Australia is involved in.
"We hope that this new technology will allow us to observe many more gamma-ray star-forming galaxies that we can detect with the current gamma-ray telescopes."
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Every look from inside the disc to the center of a galaxy shows a band of gamma radiation in the center - what's the innovation?