Fermi data offer new clues to dark matter in our universe

April 07, 2014

Fermi data offer new clues to dark matter in our universe

Dark matter makes up about 27 percent of the universe.

According to a report from NASA’s Goddard Space Flight Center in Greenbelt, Md., a new study of gamma ray light from the center of the Milky Way galaxy makes the strongest case to date that some of this emission may arise from dark matter.  The study’s most recent results appeared February 11 in the journal Physical Review D.

NASA researchers estimate that approximately 68 percent of the universe is dark energy.  Dark matter makes up about 27 percent of the universe’s total mass and energy, and the rest – everything on Earth, everything ever observed with all of our instruments, all normal matter – totals to less than five percent of the universe.

Using publicly available data from NASA’s Fermi Gamma-ray Space Telescope, independent scientists from multiple institutions have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources.  In addition, the researchers say that this surplus emission is consistent with some forms of dark matter.

“The new maps allow us to analyze the excess and test whether more conventional explanations, such as the presence of undiscovered pulsars or cosmic-ray collisions on gas clouds, can account for it,” said Dan Hooper, an astrophysicist at Fermilab in Batavia, Ill., and a lead author of the study.  “The signal we find cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models.”

The galactic center is full of gamma-ray sources, from interacting binary systems and isolated pulsars, to supernova remnants and particles colliding with interstellar gas.  It is also where astronomers anticipate finding the galaxy’s highest density of dark matter.

Although the true nature of dark matter is unknown, WIMPs, or Weakly Interacting Massive Particles, represent a top class of candidates.  Theorists have pictured a wide range of WIMP types – some of which may either reciprocally annihilate or produce an intermediate, quickly decaying particle when they collide.  These pathways end with the production of gamma rays – the most energetic form of light – at energies within the detection range of Fermi’s Large Area Telescope (LAT).

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