Image: Fermi two-year all-sky map
NASA/DOE/Fermi LAT Collaboration)
This all-sky image, constructed from two years of observations by NASA's Fermi Gamma-ray Space Telescope, shows how the sky appears in gamma-ray light. Brighter colors indicate brighter gamma-ray sources. A diffuse glow fills the sky and is brightest along the plane of our galaxy (middle). Discrete gamma-ray sources include pulsars and supernova remnants within our galaxy as well as distant galaxies powered by supermassive black holes.
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updated 4/1/2012 5:28:27 PM ET 2012-04-01T21:28:27

The universe is filled with high-energy radiation, much of which is made of gamma rays belched out by strange pulsing stars and the remnants of supernova explosions. But a new study of some of most extreme objects has turned up a mystery: nearly one-third of all gamma-ray emitting objects seen to date defy identification.

The objects were spotted by NASA's Fermi Gamma-ray Space Telescope, which scans the entire sky over the course of three hours, mapping the powerful spectrum. When stacked together, the surveys create an extremely precise view of the gamma-ray universe.

Scientists then match these images to other observations to identify each source. But the identities of some gamma-ray sources in space still continue to elude the astronomers.

"There's some that, despite all our efforts, we really do not know what they are," David Thompson, Fermi's deputy project scientist, told SPACE.com.  "They do not seem to be any of the usual suspects." [ Video: Mystery of Fermi's Gamma-Ray Objects ]

The cosmic detective
The Fermi space telescope has spotted nearly 500 powerful gamma-ray sources in deep space over the last three years. Before its launch in 2008, scientists only knew of four such objects.

"We're not looking for the ordinary things," Thompson said. "We're looking for the extraordinary; powerful things that might produce gamma rays."

Of the newly discovered bodies, more than half are active galaxies. Pulsars and supernova remnants each make up about 5 percent of the sources, with high-mass binary stars and other galaxies contributing just a smidge more, the researchers said.

Yet a large collection of objects remains unidentified, they added.

In some cases, the readings themselves helped scientists to classify the sources. By looking for changes in energy levels or studying the objects' shapes, astronomers could identify pulsars and galaxies.

But gamma-ray targets without these distinctions remain a mystery. In many cases, the problem may simply be one of not enough data.

"Deeper observations at other wavelengths could find counterparts to some Fermi sources in the future," Pascal Fortin, at the Ecole Polytechnique's Laboratoire Leprince-Ringuet in France, told SPACE.com in an email. Fortin was one of the leaders of the international team that produced Fermi's hard-source list.

A tantalizing mystery
Despite their mysterious origins, the sheer number of unidentified sources is promising.

"The fact that there are so many of these suggests to us — maybe this is wishful thinking — that there may indeed be something new out there," Thompson said. "What we'd really like to find is something new and exotic."

One potential cause of the baffling readings could be black holes that are interacting in a new and unexpected way, he added.

If the strange objects reveal nothing else, they highlight how much of space is still a mystery.

"We still have a lot to learn about high-energy processes in the universe," Fortin said.

Over its decade-long mission, Fermi will continue to gather information about the gamma-ray emitters, and may help answer some of the questions it is creating.

"It's an exciting field to work in," Thompson said. "The fact that we have so many of these, I think is very promising in terms of future discoveries."

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Photos: Month in Space: March 2012

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  1. Partners in space

    A Russian Proton rocket carrying a US Intelsat-22 satellite blasts off from Kazakhstan's Russian-leased Baikonur cosmodrome on March 25. Intelsat 22 is a new satellite built by Boeing Space Systems for the Intelsat Corp. (AFP - Getty Images) Back to slideshow navigation
  2. Weightless winners

    Winners of the annual Red Bull Flugtag competition experience zero-gravity conditions during a flight in a cosmonaut training plane above the Moscow region on March 1. The flight was a prize awarded to the winners of last summer's competition, which required contestants to design, build and fly home-built aircraft. (Sergei Remezov / Reuters) Back to slideshow navigation
  3. Hello, world

    This image of the far side of the lunar surface, with Earth peeking up from the horizon, was taken by the MoonKAM system onboard the NASA GRAIL mission's Ebb spacecraft on March 17 and released on March 23. A little more than halfway up and on the left side of the image is the crater De Forest. The image is one of a set of pictures requested by students at Emily Dickinson Elementary School in Montana as part of the MoonKAM educational program. (NASA / SRS via Reuters) Back to slideshow navigation
  4. Aurora from above

    The southern lights glow green in a picture taken by Dutch astronaut Andre Kuipers on board the International Space Station between Antarctica and Australia on March 10. The station's lab modules and solar panels can be seen along the upper and right edges of the image. (NASA / Reuters) Back to slideshow navigation
  5. Heavenly lights

    Jonina Oskarsdottir captured this picture of the northern lights on March 8 over Faskrudsfjordur, Iceland. "No words can describe the experience of the northern lights tonight," Oskarsdottir told SpaceWeather.com. She used a Canon EOS 5D Mark II camera to take the shot, with a Canon 14mm f/2.8L USM II lens set for ISO 1600 ... and a 1-second exposure. (Jonina Oskarsdottir) Back to slideshow navigation
  6. Spirals in the sea

    Spectacular spirals of ice form in the sea surrounding Russia's Kamchatka Peninsula, in a picture taken by Dutch astronaut Andre Kuipers from the International Space Station on March 15. (André Kuipers / ESA/NASA) Back to slideshow navigation
  7. One giant leap

    Austrian skydiver Felix Baumgartner stands at the threshold of a balloon-borne capsule just before a test jump from a height of 71,500 feet. The successful test was conducted on March 15 over Roswell, N.M., in preparation for Baumgartner's planned supersonic jump from 120,000 feet. That feat would break a 52-year-old record for the highest parachute jump. (Jay Nemeth / Red Bull via Getty Images) Back to slideshow navigation
  8. Five-rocket fireworks

    A time-lapse photo shows the ascent of five suborbital sounding rockets from NASA's Wallops Flight Facility in Virginia on March 27. The launches were part of the Anomalous Transport Rocket Experiment, or ATREX, which was aimed at tracking high-altitude winds in the jet stream. The fiery display was visible along the East Coast from upstate New York and Massachusetts to North Carolina. (NASA) Back to slideshow navigation
  9. Infrared rainbow

    A false-color infrared image, released March 12, shows fledgling stars hidden among the gas and clouds of the Orion Nebula. The colors indicate different infrared wavelengths as detected by NASA's Spitzer Space Telescope and the European Space Agency's Herschel telescope. (NASA/ESA/JPL-Caltech/IRAM / EPA) Back to slideshow navigation
  10. Enter the Dragon

    NASA astronauts and industry experts check out the crew accommodations in SpaceX's Dragon spacecraft. On top, from left, are NASA Crew Survival Engineering Team Lead Dustin Gohmert, NASA astronauts Tony Antonelli and Lee Archambault, and SpaceX Mission Operations Engineer Laura Crabtree. On bottom, from left, are SpaceX Thermal Engineer Brenda Hernandez and NASA astronauts Rex Walheim and Tim Kopra. The Dragon is being developed for NASA's use as a cargo carrier as well as a crew vehicle. (SpaceX) Back to slideshow navigation
  11. Looking down at Luna

    This picture from NASA's Lunar Reconnaissance Orbiter, released March 14, shows Luna 17, the Soviet lander that carried the Lunokhod 1 rover to the surface in 1970. The debarking ramps for the rover are visible extending down to the surface to the right. Many rover tracks are visible around the lander. The inset picture provides a closeup look at Luna 17. (NASA/GSFC/ASU) Back to slideshow navigation
  12. The eye of Mars

    Radially oriented slope streaks paint stripes on the sides of this Martian crater in Arabia Terra. Slope streaks are common features on steep slopes in Mars' dusty terrain, but this crater is a particularly dramatic example. The picture was taken by the HiRISE camera on NASA's Mars Reconnaissance Orbiter and released on March 7. (NASA/JPL/University of Arizona) Back to slideshow navigation
  13. Eclipse in space

    The moon came between NASA's Solar Dynamics Observatory satellite and the sun, seen here in extreme ultraviolet light, on Feb. 28. SDO observed the partial solar eclipse for 1 hour and 41 minutes. (NASA/GSFC/SDO) Back to slideshow navigation
  14. Greetings from Robonaut

    This fisheye-lens image, provided by NASA on March 13, shows the Robonaut 2 humanoid robot during a system checkout in the Destiny laboratory of the International Space Station. Teams on the ground commanded Robonaut through a series of dexterity tests as it spelled out "Hello World" in sign language. (NASA via AFP - Getty Images) Back to slideshow navigation
  15. Big and small moons

    Ice-covered Enceladus, a 300-mile-wide Saturnian moon, is dwarfed by 3,200-mile-wide Titan as well as the giant planet's rings in this March 12 picture from the Cassini orbiter. Titan, Saturn's largest moon, is covered by a brownish hydrocarbon-rich haze. (NASA/JPL/SSI/J. Major) Back to slideshow navigation
  16. Fruits ... in ... space!

    Dutch astronaut Andre Kuipers clowns around with some zero-gravity fruit in the International Space Station's Unity node on Feb. 3. (NASA) Back to slideshow navigation
  17. Ghostly nebula

    Wispy tendrils of hot dust and gas are aglow in this ultraviolet image of the Cygnus Loop Nebula, taken by NASA's Galaxy Evolution Explorer and released March 22. The nebula, which lies about 1,500 light-years from Earth, is a supernova remnant left over from a massive stellar explosion that occurred 5,000 to 8,000 years earlier. The Cygnus Loop extends more than three times the size of the full moon in the night sky, and is tucked next to one of the wings of the "swan" in the constellation of Cygnus. (NASA/JPL-Caltech / AFP - Getty Images) Back to slideshow navigation
  18. Mercury in perspective

    This color-coded perspective view shows elevations in the ancient volcanic plains that lie the northern high latitudes of Mercury, as revealed by NASA's Messenger spacecraft. Purple colors are low and white is high, spanning a vertical range of about 1.4 miles (2.3 kilometers). (NASA / JHUAPL / CIW-DTM / GSFC) Back to slideshow navigation
  19. Stirring sight

    After a nearly ice-free winter, Lake Erie was filled with swirls of suspended sediment and algae on March 21. This view from NASA's Terra satellite shows swirls of sediment-rich water in the lake. As the shallowest of the Great Lakes, Erie’s bottom can be stirred up by strong spring winds and the currents they generate. (Jeff Schmaltz / NASA) Back to slideshow navigation
  20. Dust devil caught on camera

    A towering dust devil casts a serpentine shadow on the Martian surface in this image, acquired by the HiRISE camera on NASA's Mars Reconnaissance Orbiter and released on March 7. Such whirlwinds often spin through the Martian landscape - but they're not often caught on camera. (NASA/JPL-Caltech/Univ. of Arizona) Back to slideshow navigation
  21. Dubai's lights at night

    The city lights of Dubai sparkle at night in this photograph taken from the International Space Station on Feb. 22. Dubai is a popular photographic target for the space station's astronauts because of the artificial archipelagos that are located just offshore in the Persian Gulf. The palm-tree-shaped cluster of lights at bottom right is the Palm Jumeira complex, which is still under development. Isolated areas of blurred city lights are due to patchy clouds. (NASA via AP) Back to slideshow navigation
  22. Celestial lanterns

    Two of the brightest planets in the night sky went through a series of conjunctions during late February and March. Jupiter is on the left and Venus is on the right in this picture, taken by Marek Nikodem of Szubin, Poland, at nightfall on March 12. "They are like two lanterns illuminating the darkness," Nikodem told SpaceWeather.com. "It's a wonderful sight." (Marek Nikodem) Back to slideshow navigation
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