High energy gamma rays may emanate in the Milky Way (Forwarded)

Public Affairs Office
Los Alamos National Laboratory

Contact:
Todd Hanson (505) 665-2085

04-197

December 14, 2005

High energy gamma rays may emanate in the Milky Way

LOS ALAMOS, N.M. -- Los Alamos scientists, in collaboration with
researchers from nine institutions across the United States, have evidence
from the Laboratory's Milagro telescope that TeV (one trillion electron
volts) gamma rays, the most energetic form of electromagnetic radiation
known, can originate in the plane of the Milky Way galaxy. The discovery
is the first evidence of such high-energy gamma rays arising from
interactions of cosmic rays with matter in our galaxy.

In a paper published in today's Physical Review Letters, the team of
scientists explain how they have been able to determine an approximate
location of the gamma rays place of origin within the Milky Way based on
observations of the secondary, or air shower, particles that are generated
when gamma rays hit Earth's atmosphere. These air shower particles are
detected as they pass through the water in the 6-million-gallon pond that
comprises the Milagro telescope and create a phenomenon called Cerenkov
radiation. This Cerenkov radiation produces visible and ultraviolet
photons that are detected by the telescope's 737 floating photon
detectors. The gamma rays that enter the atmosphere are the same as the
photons that make up visible light, but are roughly one trillion times
more energetic than visible light.

According to Gus Sinnis, the Los Alamos astrophysicist in charge of the
Milagro telescope, "The gamma rays we observed at Milagro might very well
be particle fragments that were scattered across the galaxy when even
higher energy cosmic rays struck the matter distributed throughout the
Milky Way. These cosmic rays may, in turn, have come from a collapsing
star or a supermassive black hole."

With the ability to continuously monitor the entire Northern hemisphere
sky in the 1 TeV energy range, Milagro is the largest gamma ray detector
of its kind in the United States. The latest discovery is the result of an
analysis that isolated roughly 70,000 TeV gamma-ray events emanating from
within a region of the Milky Way plane out of roughly 150 billion
TeV-level events recorded by Milagro for the three years beginning in July
2000.

In addition to researchers from Los Alamos, the Milagro Milky Way gamma
ray team includes researchers from George Mason University, New York
University, Michigan State University, the University of
California-Irvine, University of California-Santa Cruz, University of
Maryland-College Park, University of New Hampshire and the University of
Wisconsin.

The Milagro telescope has been in operation at the Laboratory's Fenton
Hill research site since 1998. The continuing operation of Milagro is made
possible by support from the National Science Foundation, the Department
of Energy's Office of Science, Los Alamos National Laboratory and the
University of California's Institute of Geophysics and Planetary Physics.

Los Alamos National Laboratory is operated by the University of California
for the National Nuclear Security Administration of the U.S. Department of
Energy and works in partnership with NNSA's Sandia and Lawrence Livermore
national laboratories to support NNSA in its mission.
Los Alamos enhances global security by ensuring the safety and reliability
of the U.S. nuclear deterrent, developing technologies to reduce threats
from weapons of mass destruction, and solving problems related to defense,
energy, environment, infrastructure, health and national security
concerns.