The Fermi Space Telescope has detected 1,873 gamma ray sources in space, and nearly 600 are complete mysteries, NASA wrote today on its website.

NASA's Fermi team has recently released the second catalog of gamma ray sources from its satellite's Large Area Telescope and have no idea where nearly one-third of gamma rays originated.

"Fermi sees gamma rays coming from directions in the sky where there are no obvious objects likely to produce gamma rays," said David Thompson, Fermi deputy project scientist, of Goddard Space Flight Center in Maryland.



Gamma rays are a "super-energetic form of light produced by sources such as black holes and massive exploding stars," according to NASA.

Researchers say two-thirds of the gamma rays come from objects such as pulsars or blazars. The remaining third are a complete mystery right now.

Researchers are speculating on the nature of the mystery sources, including the possibility that they are made of dark matter.

"Some of the mystery sources could be clouds of dark matter, something that's never been seen before," Thompson said.

NASA explains that about “85% of the gravitational mass of the universe is dark matter,” and “the stuff we see makes up the rest.”

“Dark matter is something that pulls on things with the force of its gravity but can't be detected in any other way. It doesn't shine – doesn't emit or scatter light – hence the adjective ‘dark,’ ” NASA writes.

Astronomers cannot detect dark matter directly using optical or radio telescopes, but researchers think dark matter just might shine in gamma rays.

"We've been using Fermi to search for dark matter for a long time," said Peter Michelson of Stanford University, the principal investigator for the Large Area Telescope.

So why do researchers think the source could be dark matter?

"Some researchers believe that when two dark matter antiparticles bump into each other, they will annihilate, producing gamma rays. Concentrated clouds of dark matter could form a gamma ray source at specific wavelengths detectable by Fermi," NASA explains.

"If we see a bump in the gamma-ray spectrum – a narrow spectral line at high energies corresponding to the energy of the annihilating particles – we could be the first to 'apprehend' dark matter,” Michelson said.

Researcher point out that there are other possibilities for the mystery sources, including colliding galaxy clusters or some type of new phenomenon, such as something involving galactic black holes.

The Fermi team plans to continue observing the mystery sources.

"Of course we're hoping for something really exotic like dark matter, but we have to look first at all the other options," Thompson said. "Fermi is an ongoing mission. We'll continue to search for answers to these puzzles and perhaps turn up even more surprises."

Watch NASA's video "ScienceCasts: 600 Mysteries in the Night Sky" here: