Cosmic rays are the only sample
of matter from distant regions of the galaxy, and possibly elsewhere in
the Universe, that can be directly observed by space experiments in the
Solar System. This high energy matter consists of atomic nuclei
that travel at speeds very close to the speed of light. In fact,
the highest energy cosmic rays observed are more that 10,000,000 times
more energetic than those that can be produced in the largest particle
accelerators on Earth. The cosmic ray matter includes electrons,
the natural elements from Hydrogen and Helium to Iron and beyond as well
as anti-matter in the form of positrons and anti-protons. The
cosmic rays play an important part in galactic dynamics and can be used
to probe astrophysical conditions throughout our galaxy. Cosmic
rays appear to gain their very high energy as the result of supernova
explosion shock waves traveling through interstellar gas. The
supernova shock wave acceleration model makes specific predictions about the cosmic ray energy spectrum as
a function of elemental charge. ATIC is designed to measure the
energy spectrum of individual cosmic ray elements in order to study the
validity of this model.
The Crab Nebula
The Crab Nebula is a supernova explosion remnant.
The nebula is 6000 light years from Earth and ancient Chinese
astronomers observed the explosion in 1054 AD. In the center of
the nebula is what is left of the star that exploded. This neutron
star or pulsar is spinning so fast that it emits pulses of radiation 30 times a second.
We know that particles like electrons are being accelerated to high
energies in supernova remnants like this one because we can see their
effect in the form of x-rays, gamma-rays and synchrotron light.
Cosmic Rays are a part of galactic
Our galaxy is a dynamic, turbulent place; Gas clouds
condense under the force of gravity and form stars; During the
life of these stars fusion reactions form complex, heavy elements;
Massive stars generate strong stellar winds that, along with supernova
explosions, distribute matter back to interstellar space and generate
turbulence; Eventually massive star use up their fusion "fuel"
and collapse leading to supernove explosions; The shock waves driven by
these explosions accelerate matter to speeds very close to the speed of
light resulting in what we call cosmic rays.
How do cosmic
rays gain their enormous energies?
Are Supernova Remnants the site of particle acceleration?
Is there evidence for more than one cosmic accelerator?
How do high energy particles move through the galaxy?
spectra for individual elements of a broad energy range with a single
Discover “breaks” or “bends” in the spectra.
Measure the energy dependence of the H/He ratio.
Determine the spectral differences between elements.
Obtain the composition of the cosmic ray matter.