Synopsis: Tantalizing cosmic-ray electrons

A report from the PAMELA satellite says the electron flux in cosmic rays is consistent with the existence of new sources, such as dark matter particles or other astrophysical phenomena, but the results are still inconclusive.
Synopsis figure
Credit: Courtesy PAMELA space mission

In 2009, the satellite-borne instrument PAMELA reported that high-energy cosmic rays contained an unexpectedly large ratio of positrons to electrons. The excess flux of positrons suggested that perhaps the propagation of cosmic rays through space was different than had been assumed, or models needed to account for additional astrophysical sources, such as supernova remnants or dark matter particles—the latter being a particularly exciting possibility.

If additional sources are indeed at play, they should contribute roughly equally to positrons and to electrons, but in comparison to the larger electron flux, the contribution from extra sources would be more difficult to see than with positrons.

Now a new report from the PAMELA Collaboration appearing in Physical Review Letters contributes data on the absolute spectrum of electrons, for the first time at energies above 50GeV. Although the new data can be fit reasonably well with a standard-model calculation of cosmic-ray propagation, a somewhat better fit can be obtained by including additional sources of electrons in the calculation. (These same additional sources provide a good fit to the excess positron fraction that PAMELA observed earlier.) The data are also consistent (within errors) with results from the Fermi Large Area Telescope, which measured the combined contribution from positrons and electrons and provided some support for the new sources hypothesis.

Although the new PAMELA results support the earlier tantalizing indications of additional sources of cosmic rays, the field is not yet at the point of confirming their existence or nature. – Stanley Brown


More Features »


More Announcements »

Subject Areas


Previous Synopsis

Quantum Information

Photosynthesis disentangled?

Read More »

Next Synopsis

Fluid Dynamics

Reluctant swimmers

Read More »

Related Articles

Synopsis: Neutrino Flashes from Exploding Stars

Synopsis: Neutrino Flashes from Exploding Stars

Calculations indicate that neutrino emission from a supernova could be detected on Earth, possibly revealing how the star explodes. Read More »

Synopsis: Cosmic Test of Quantum Mechanics
Quantum Physics

Synopsis: Cosmic Test of Quantum Mechanics

Light from two stars in the Milky Way has been used to test an open loophole of quantum physics. Read More »

Focus: Photons Brake the Sun
Plasma Physics

Focus: Photons Brake the Sun

Detailed solar observations and theory suggest that photons remove angular momentum from the Sun, explaining why the Sun’s surface spins more slowly than its core. Read More »

More Articles