Radio telescope observations
of Sagittarius A*, the luminous radio source at the center of
the Milky Way, confirm a cosmic ray theory proposed in 1983 by
Dr. Paul LaViolette. Speaking on January 13th at the 195th meeting
of the American Astronomical Society, Dr. G. Bower, and his coworkers
H. Falcke and D. Backer, reported finding that the synchrotron
radio emission from Sagittarius A* was primarily circularly polarized,
rather than linearly polarized like most other sources.
Synchrotron
radiation is a broadband radio wave emission that is produced
when cosmic ray electrons spiral around magnetic field lines
perpendicular to the field line direction. If these magnetic
field lines are oriented transverse to our line of sight, the
electron orbits will be seen edge-on and their synchrotron radio
emission will be seen as linearly polarized. On the other hand,
if these field lines point towards us so that we look down their
field axis, the orbiting electrons would now be observed circling
in the plane of the sky, and their radio emission would be seen
by us as being circularly polarized.
Dr.
Bower did not offer an explanation for the reported polarization
finding, calling it "mysterious." However, during the
question period, Dr. LaViolette pointed out that circular polarization
would be produced if this synchrotron radiation were emitted
by cosmic ray electrons that were traveling radially outward
from the Galactic core.
Previously,
astronomers had assumed that cosmic ray electrons radiating out
from the core would be trapped by nearby magnetic field lines
oriented cross-wise to the particles' outward trajectories, thereby
impeding their escape. LaViolette's model predicted that these
fields are instead oriented primarily parallel to the particle
flight trajectories and radial with respect to the Galactic core.
He maintained that these electrons escape from the core at close
to the speed of light, spiraling outward along radial trajectories.
Due to their high speed flight, these particles would beam their
synchrotron radiation forward, confined to a very narrow angle
cone. Consequently, if LaViolette's theory of radial cosmic ray
flight is correct, we should only see radiation coming to us
from cosmic ray particles that are traveling almost directly
towards us and shining their radio emission cones in our direction.
Since we would be sighting down their flight axis, at a low pitch
angle to that axis, we would have a face-on view of their orbital
trajectories about this flight axis and be seeing their beamed
radiation as circularly polarized.
Dr.
LaViolette noted that these newly announced results support the
"Galactic superwave" model he had proposed in 1983.
This postulates that intense cosmic rays emitted from the Galactic
core during its explosive activity phase travel radially outward
at relativistic speeds and penetrate tens of thousands of light
years through the Galactic disk to ultimately bombard our solar
system. His proposal of long-range radial propagation was validated
several years later by observations that our planet is being
showered by pulses of cosmic rays emitted from X-ray pulsars
Cygnus X-3 and Hercules X-1. LaViolette's theory predicted that
galactic core cosmic rays radiate out from the centers of other
galaxies in a similar fashion.
Others present at the session, such as astrophysicist
Dr. Roger Blandford, concurred with LaViolette's interpretation
that the observed circular polarization was evidence of low pitch
angle synchrotron radiation emitted from electrons following
radial trajectories.