Star-forming galaxies are responsible for creating gamma-rays that until now
had not been associated with a known origin, researchers from The Australian
National University (ANU) have confirmed.
Lead author Dr. Matt Roth, from the ANU Research School of Astronomy and
Astrophysics, said until now it has been unclear what created gamma-rays—one
of the most energetic forms of light in the Universe—that appear in patches
of seemingly "empty sky."
The discovery could offer clues to help astronomers solve other mysteries of
the Universe, such as what kind of particles make up Dark Matter—one of the
holy grails of astrophysics.
"It's a significant milestone to finally discover the origins of this
gamma-ray emission, solving a mystery of the Universe astronomers have been
trying to decipher since the 1960s," Dr. Roth said.
"There are two obvious sources that produce large amounts of gamma-rays seen
in the Universe. One when gas falls into the supermassive black holes which
are found at the centers of all galaxies—called an active galactic nucleus
(AGN)—and the other associated with star formation in the disks of galaxies.
"We modeled the gamma-ray emission from all the galaxies in the Universe and
compared our results with the predictions for other sources and found that
it is star-forming galaxies that produce the majority of this diffuse
gamma-ray radiation and not the AGN process."
ANU researchers were able to pinpoint what created these mysterious
gamma-rays after obtaining a better understanding of how cosmic
rays—particles that travel at speeds very close to the speed of light—move
through the gas between the stars. Cosmic rays are important because they
create large amounts of gamma-ray emission in star-forming galaxies when
they collide with the interstellar gas.
Data from NASA's Hubble Space Telescope and Fermi Gamma-Ray Space Telescope
was a key resource used to uncover the unknown origins of the gamma-rays.
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 for radio emission—the
electromagnetic radiation that has a frequency similar to a car radio—from
star-forming galaxies, which could help researchers understand more about
the internal structure of galaxies," Dr. Roth said.
"We are currently looking at producing maps of the gamma-ray sky that can be
used to inform upcoming gamma-ray observations from next-generation
telescopes. This includes the Cherenkov Telescope Array, which Australia is
involved in.
"This new technology will hopefully allow us to observe many more
star-forming galaxies in gamma-rays than we can detect with current
gamma-ray telescopes."
This research, published today in Nature, features authors from Australia
and Italy.
Reference:
Matt A. Roth et al, The diffuse γ-ray background is dominated by
star-forming galaxies, Nature (2021).
DOI: 10.1038/s41586-021-03802-x
Tags:
Space & Astrophysics