New Probe's First Gamma Ray Sky Map Unveiled

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The Large Area Telescope aboard Fermi uses 16 detector towers fitted with layers of the metal tungsten and strips of silicon to record gamma rays.

When a gamma ray hits a layer of tungsten, it sometimes becomes a pair of subatomic particles. The silicon strips then track the paths of these particles, revealing where the gamma ray came from.

Understanding gamma ray sources could be the key to unlocking mysteries such as the nature of dark matter, how black holes can accelerate matter to near the speed of light, and how solar flares generate dangerous high-energy particles.

The research can also answer fundamental questions about the composition and dynamics of our own Milky Way galaxy.

"The center of the galaxy is an incredibly busy place, a crowded place," NASA's Ritz said. "We know that there is a supermassive black hole at the core of our galaxy and quite a lot of high-energy processes going on."

In the new map created using Fermi data, the bright band across the center reveals very high-energy gamma rays coming from the core of the Milky Way.

"This radiation is due mostly to gamma rays generated by the collision of high-energy cosmic rays with dust and gases" swirling around the supermassive black hole, Michelson said.

The map, he noted, also shows the Vela pulsar, "a rotating neutron star and the brightest source in this sky."

Powerful Explosions

In addition to the full-sky map, the first data from Fermi's burst monitor include records of "a gamma ray burst about once a day … the highest rate of detection of any satellite," said Chip Meegan, principal investigator for the instrument, based at the Marshall Space Flight Center.

The bursts, which arrive from random positions all over the sky, are evidence that "all 14 of our detectors are working just beautifully," Meegan said.

Gamma ray bursts are of special interest to astronomers because they are among the brightest events ever observed. (See a related image captured in March of a gamma ray burst that was visible to the naked eye.)

The intense flashes of gamma rays can release within seconds the same amount of energy that the sun will put out over its entire ten-billion-year lifetime—but no one is sure what causes them.

The going theory is that the bursts are tied to the explosive deaths of massive stars, but exactly what types of stars and how the explosions are triggered remains a mystery.

Astronomers hope to make strides in solving gamma ray bursts and other mysteries over Fermi's planned five years in operation.

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