For longer versions of these and other
atom & Cosmos stories, visit www.sciencenews.org
Origin of cosmic rays questioned
By Devin Powell
The confirmed origin of ordinary cosmic rays may need to be unconfirmed.
New data gathered by an instrument
aboard a Russian spacecraft challenge
the theory that most cosmic rays are
fueled by supernovas, the explosions
created by dying stars.
“The mechanism for the acceleration
of cosmic rays needs to be completely
revised,” says Piergiorgio Picozza, a physicist at the University of Rome Tor Vergata
in Italy. Picozza is a coauthor of a paper
posted online March 3 in Science detailing new observations from PAMELA, the
Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics.
Cosmic rays aren’t actually rays.
They’re fast-moving particles that carry
an extraordinary amount of energy and
continuously bombard the Earth from
every direction. The most popular explanation for the origin of these particles
points to shock waves created by far-off
supernovas, one of the few phenomena
powerful enough to impart such energy.
According to that explanation, clouds
of charged gas rush outward during a
supernova and generate strong magnetic
fields. These magnetic fields could accelerate charged particles to tremendous
speeds and eject them into space.
Orbiting hundreds of kilometers
above Earth, PAMELA spent three years
collecting cosmic ray particles — mostly
hydrogen and helium nuclei with energies ranging from a billion to a trillion
electron volts, comparable to the energy
of particles collided in the biggest particle accelerator in the United States.
A supernova should accelerate both
hydrogen and helium in the same way.
But in the PAMELA data, Picozza found
differences between measurements of
the hydrogen and helium particles that
a single shock wave can’t explain.
“The two particles seem to be accelerated by different mechanisms,” he says.
Scientists should investigate other
astronomical objects as
possible sources of cosmic rays, Picozza says.
One place proposed by
Russian physicists is in
the novas, or smaller
when white dwarf
stars belch out energy.
Another option could
be giant superbubbles
of gas blown around
the universe by stellar
winds, he says.
But Mikhail Malkov, a plasma physicist
at the University of California, San Diego
who studies supernova shock waves,
isn’t ready to toss out the existing cosmic
ray theory. “The data look statistically
significant, but it’s too early to say that the
supernova acceleration model is in trou-
ble. This statement is too strong,” he says.
Telescopes peering into supernova
remnants have found lots of evidence
over the years to support the super-
nova shock wave theory. Observations
of gamma rays reveal
the structure of mag-
netic fields and missing
energy that could have
been spent making
Malkov says the
hydrogen and helium
is small and could be
accounted for simply
by tweaking the existing supernova model.
He suspects that PAMELA may be seeing cosmic rays created by a shock wave
that wasn’t completely uniform, or a
mishmash of particles released by two
Exploding stars (one above)
have been thought to be the
origin of most of the cosmic
rays arriving at Earth.
Spacetime tunnels may exist
with aid of ‘phantom matter’
suggest that pairs of stars could be joined
by wormholes built from an exotic material known as “phantom matter.”
a wormhole star
“I am pretty sure that once you admit
exotic matter of some suitable kind, you
can mathematically construct a star with
a wormhole inside,” comments relativity
theorist Dieter Brill of the University of
Maryland in College Park.
Actually seeing one is another issue.
In general, an ordinary star and one containing a wormhole would look the same
to a distant observer. But the wormhole
might alter properties such as the mass
or size of a star in a nonstandard way.
And if the wormhole is short, so that
the two stars it links don’t lie far apart,
an observer might see another unusual
signpost — two closely spaced objects
with nearly identical properties.
For now, says Folomeev, this is just an
idea that still must be confirmed by further calculations.
Some stars may contain wormholes,
throatlike tunnels connecting distant
points in spacetime, a team of physicists
proposes. But other researchers are having a hard time swallowing the idea.
“It’s a nice piece of speculative work,
but it is speculation,” says theoretical
physicist Matt Visser of Victoria University of Wellington in New Zealand.
In a paper posted online February 25
at arXiv.org, physicist Vladimir Folomeev
of the Institute of Physicotechnical Problems and Material Science of the NAS of
the Kyrgyz Republic and his colleagues