“The age of cosmic-ray astronomy has arrived. In the next few years, our data will permit us to identify the exact sources of these cosmic rays and how they accelerate these particles.”
~ Nobel laureate James Cronin, University Professor Emeritus in Physics at the University of Chicago.
Cosmic powerhouses pour out vast amounts of energy, and they accelerate particles to almost the speed of light. They are the most energetic objects in our galaxy, but scientists are still trying to figure out what they are, and what they’re doing. But so far, these recently discovered objects remain shrouded in mystery.
Up until this point, the history of astronomical discovery has been
dominated by the detection of light. “We are doing astronomy with
protons—charged particles,” said Joao de Mello Neto, of the University
of Rio de Janeiro in Brazil. “We are opening a new window in astronomy.”
Cosmic rays—consisting mostly of protons—fly through the universe at
nearly the speed of light. These rays contain more than one hundred
million times more energy than the particles produced in the world’s
most powerful particle accelerator. Fortunately, Earth’s atmosphere
protects us from their potentially harmful effects. Astrophycicists are
eager to unravel the mystery of what is producing these powerful rays.
"Understanding these objects [cosmic powerhouses] is one of the most
intriguing problems in astrophysics," explains Takayasu Anada of the
Institute for Space and Astronautical Science in Kanagawa, Japan.
However, working in synergy with a ground-based telescope array, the
joint Japanese Aerospace Exploration Agency (JAXA)/NASA Suzaku X-ray
observatory is beginning to shed some light on the strange celestial
objects. They were first discovered in just the last few years by an
array of four European-built telescopes named the High Energy
Stereoscopic System (H.E.S.S.), located in the African nation of
Namibia. H.E.S.S. indirectly detects very-high-energy gamma rays from
outer space. These gamma rays are the highest-energy form of light ever
detected from beyond Earth, so H.E.S.S. and other similar arrays have
opened up a new branch of astronomy.
The image above from Japan's Suzaku X-ray observatory shows RXJ1713.7-3946, a
supernova remnant -the gaseous remnant of a massive star that exploded.
The remnant is about 1,600 years old. The contour lines show where
gamma-ray intensity is highest, as measured by the High Energy
Stereoscopic System (HESS) in Namibia.
When Anada and his colleagues pointed Suzaku at a source known as HESS
J1837-069 (the name reflects it’s coordinates), the X-ray spectrum
closely pulsar wind nebulae, which are gaseous clouds that are sculpted
by winds blown off by collapsed stars known as pulsars. Pulsar wind
nebulae emit hard X-rays, and their X-ray output remains relatively
constant over long timescales. "The origin of the gamma-ray emission
from HESS J1837-069 remains unclear, but we suspect that this source is
a pulsar wind nebula from the Suzaku observation," says Anada.
A team of researchers led by Hironori Matsumoto of the University of
Kyoto in Japan, targeted Suzaku on HESS J1614-518. This source belongs
to a class of objects known as "dark particle accelerators" because
their ultrahigh energies suggest they are accelerating particles to
near-light speed, turning them into cosmic rays.
Although the nature of these objects still remains a mystery, Suzaku’s
observations did reveal some secrets, particularly what some
powerhouses are producing. When electrons are accelerated to high
speeds, they spiral around magnetic field lines that permeate space,
generating copious X-rays. Since protons are much more massive than
electrons, they emit few X-rays. Matsumoto and his colleagues reported
that HESS J1614-518 emits very weak X-rays. "This result strongly
suggests that high-energy protons are being produced in this object,"
says Matsumoto.
Suzaku also observed two other H.E.S.S. dark particle accelerators, but
found no obvious X-ray counterparts at the H.E.S.S. positions. These
sources must also be weak X-ray emitters, indicating they are also
accelerating mostly protons. Using the high sensitivity of the Suzaku
satellite, the scientists are planning on finding the strong candidates
for the origin of cosmic rays.
Posted by Rebecca Sato.
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Sources:
http://www.nasa.gov/centers/goddard/news/topstory/2007/cosmic_powerhouses.html
http://www-news.uchicago.edu/releases/07/071108.cronin.shtml