Large Area Telescope explores high-energy particles

July 28, 2009
The Delta II rocket carrying the Fermi Gamma ray Space Telescope, known prior to launch as GLAST, lifts off from Cape Canaveral on 11 June 2008.

( -- NASA's Fermi Gamma-ray Space Telescope is making some exciting discoveries about cosmic rays and the Large Area Telescope aboard Fermi is the tool in this investigation. Scientists in the Naval Research Laboratory's (NRL's) Space Science Division were instrumental in the design and development of the Large Area Telescope (LAT).

Cosmic rays are electrons, positrons, and that move at nearly the speed of light. Astronomers believe that the high-energy originate from exotic places in the galaxy, such as the debris of exploded stars.

The LAT is a wide field-of-view imaging telescope, which consists of a tracker that determines the trajectory of the gamma ray or cosmic ray being measured, and an NRL-developed cesium-iodide calorimeter that determines the energy of the incoming ray. A charged-particle anti-coincidence shield helps filter out unwanted signals, such as those produced by background particles. LAT was developed for detecting ; however, it is also proving to be a great tool for studying the high-energy electrons in cosmic rays.

Gamma rays travel in straight lines, so scientists are able to pinpoint their sources simply by measuring the direction of each gamma ray as it arrives at the LAT. In contrast, cosmic rays diffuse through our Galaxy, scattering off and spiraling through the turbulent galactic magnetic fields. Because of their movements, scientists find it challenging to determine where the cosmic rays originated. One of Fermi's main goals is determining the sources of cosmic rays.

NRL's highly sensitive LAT measured the energies of more than four million high-energy electrons between August 2008 and January 2009, far more high-energy electrons than have ever been studied before. This extremely large data set allowed scientists to make a precise census of high-energy electrons and led to a surprising excess in the rate of electrons striking the LAT, more than expected from earlier measurements and theoretical models. The LAT data appear to be key to understanding electron measurements made from the European satellite PAMELA and the ground-based High Energy Spectroscopic System located in Namibia.

The LAT's results indicate that our understanding of the sources and propagation of high-energy particles in the galaxy is incomplete, and they seem to suggest that there is a nearby object beaming cosmic rays in the direction of Earth. Some scientists suggest that a nearby pulsar - the fast-spinning leftover of an exploded star - could be the source sending the electrons and positrons toward Earth. A more exotic possibility is that the particles are evidence of the existence of . For some time, astrophysicists have suggested that some form of matter - previously undetected and invisible, hence "dark" - exists to provide the extra gravity needed to keep galaxies from whirling apart. While researchers have never directly and conclusively observed dark matter, it could be that the excess LAT observes are the result of interactions or decays of the theorized dark matter particles. Looking ahead, Fermi researchers will be watching for changes in the cosmic ray activity in different parts of the sky. This activity might help them piece together the puzzle in finding the source for the cosmic rays.

Source: Naval Research Laboratory (news : web)

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4.7 / 5 (3) Jul 28, 2009
Great to see that ultra high energy particles studied by Fermi and H.E.S.S. are consistent with both models of gamma-ray emission (local neutron stars/pulsars and/or local annihilating DM) and may help to better understand PAMELA observation that "firmly" rejected the DM annihilation scenario recently. It seems that complete characterization of the 'positron excess' is still undecided. Just waiting for the anti-DM response to this study. Personally, I'm willing to go wherever the evidence leads (DM agnostic). What if both mechanisms contribute to the 'positron excess'? Just as likely, what if non-annihilating DM turns out to be the best candidate? Even if DM is shown not to be a contributor to the positron measurements, this certainly doesn't disprove the existence of DM in the universe.
not rated yet Jul 29, 2009
If we see something that we did not see before, will we call it dark matter or something new?
1 / 5 (2) Aug 03, 2009

yyz is right. Neutron stars are not dead nuclear embers.

Repulsive interactions between neutrons energize neutron stars, cause cosmic explosions, and produce Hydrogen - a waste product from neutron-decay product - that departs ordinary stars like the Sun and galactic centers to fill interstellar space.

See: "Neutron repulsion confirmed as energy source", J. Fusion Energy 20 (2003) 197-201;

With kind regards,
Oliver K. Manuel
5 / 5 (1) Aug 04, 2009
Repulsive interactions between neutrons energize neutron stars, cause cosmic explosions, and produce Hydrogen - a waste product from neutron-decay product - that departs ordinary stars like the Sun and galactic centers to fill interstellar space.

If that was true ALL neutron stars would have massive explosions on the surface. So far it has only been observed where the neutron star has a companion star. Gas pulled from the companion falls onto the neutron star and when there is enough accumulation of hydrogen the mass fuses right on the surface resulting in gamma ray bursts. At least that is what the evidence supports.

And only Oliver thinks he has confirmation. From a study by - wait for the big name -



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