Cosmic-ray ‘hot spots’ point to mystery source


The localized regions of excess cosmic rays (in red) observed by Milagro superimposed on a star map in this region. The Orion constellation is connected by white lines in the lower part of the image. (Credit: Los Alamos National Lab)

NYU (US)—Physicists have observed for the first time two distinct “hot spots” that appear to be showering Earth with an excess of cosmic rays. The discovery calls into question nearly a century of understanding about galactic magnetic fields near our solar system, and suggests the possibility that an unknown source or magnetic effect could be responsible.

For nearly seven years scientists from more than a dozen institutions, including New York University, used the Milagro Gamma Ray Observatory to peer into the sky above the northern hemisphere. The observatory, located at Los Alamos National Lab in New Mexico, is unique in that it allows around-the-clock monitoring of the entire sky above the northern hemisphere. Because of its design and field of view, Milagro was able to record more than 200 billion cosmic-ray collisions with the Earth’s atmosphere.

Cosmic rays are high-energy particles that move through our galaxy from distant sources. Cosmic rays’ origins are unknown, but scientists have theorized they might originate from supernovae, from quasars, or from less-understood or yet-to-be-discovered sources within the universe. However, because cosmic rays are charged particles, magnetic fields from the Milky Way and our solar system change the flight paths of the particles so much that researchers had not been able to pinpoint their exact origin. Consequently, traditional wisdom has held that no localized area of excess of cosmic rays should appear in the sky.

The Milagro observations have allowed researchers for the first time to see statistical peaks in the number of events originating from specific regions of the sky near the constellation Orion. Researchers say the emergence of several highly active hot spots—one near the constellation Taurus and another in a comma-shaped region near the constellation Gemini—raises the possibility that an unknown source or magnetic effect near our solar system is responsible for these observations.

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