Recent photographs of an active galaxy offer new confirmation
for the idea that supernova explosions are the creators of surprisingly
energetic particles called cosmic rays.
Cosmic rays are protons that whiz
through space at almost the speed of light. They originate far beyond the
solar system, but when some make it past Earth's atmosphere they can carry such
an energetic punch that they knock out electronics systems. Scientists have
long been unsure of the process that ramps the particles up to such great
speeds, though gathering evidence suggests that these super-fast protons
originate during the death
of a star
When a very large star dies, it implodes into a black hole
while expelling its outer layers in a powerful explosion called a supernova. Scientists
think that some of the energy released during these blasts acts as a sort of
supercharger, accelerating
particles to extremely fast speeds and creating cosmic rays.
New proof of this idea has come from recent observations of
the Cigar Galaxy (M82) by the VERITAS gamma ray telescope array in Amado, Ariz.
The galaxy sits about 12 million light-years from Earth in the direction of the
constellation Ursa Major (also known as the Big Dipper). It is a starburst
galaxy, meaning it has exceptionally high levels of star formation.
With so many stars forming in M82, there are also high
numbers of massive stars and supernovas, making the galaxy a perfect testing
ground for the cosmic ray explanation. If supernovas are responsible for cosmic
rays, scientists figured, then a place with more
of the stellar explosions will also have higher concentrations of the
energetic particles.
Indeed, researchers found that the density of cosmic rays in
M82 was 500 times that of the Milky Way, confirming the hypothesis.
"This discovery provides fundamental insight into the
origin of cosmic rays," said Rene Ong, a professor of physics at the
University of California, Los Angeles, and the spokesperson for the VERITAS
collaboration.
Though the telescope couldn't image cosmic rays directly in
the distant galaxy, the researchers looked for gamma rays, a very energetic
form of light produced when cosmic rays interact with gas and radiation within
the galaxy. They used this measurement to extrapolate how many cosmic rays lie
within M82.
The findings are detailed in the Nov. 1 online issue of the
journal Nature.
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