Scene1-part1.mov(2.8 Mb)
A rotating neutron star appears at the center of the screen, colored red.
Surrounding the star is an accretion disk--a disk of slowly inspiraling
gas, here colored blue. The brightness of the disk indicates the
density of the gas; high density is bright blue, low density is dark
blue. Notice that at one radius in the disk, the density changes
suddenly. This is the sonic radius--when matter gets this close to the
star it plunges inward and hits the surface. Hence matter is sparse
this close to the star or closer. The viewer's perspective rotates so
that it looks straight down on the disk, and then we zoom in on the
star.
Scene1-part2.mov(6.9 Mb)
The second part of scene one demonstrates the motion of particles after
they reach the sonic radius. White dots are used to represent the
motion of individual gas molecules. First, two consecutive gas particles
(white dots) are released from the sonic radius. To make their trail
clear, a
white tracer will remain in the trail of the particles' paths. Next,
batches of particles are released without trails.
Scene 2: Generation of the Sonic-Point Keplerian Frequency
QPO
Scene2-part1.mov(8.5 Mb)
The neutron star and accretion disk appear again. This time, a clump of
matter, colored white, appears just outside the sonic radius. As the
clump rotates around the star, some of its gas passes the sonic point
and plunges onto the star. We show this with white test particles being
dropped from the clump's rotation. Where the particles hit the star, a
(yellow) beam appears, representing the beam of X-rays emitted where the
gas collides with the star. After a couple rotations, the picture
freezes, and the stream of
particles is replaced by a continuous blue swath, still representing the
same gas.
Scene2-part2.mov(11.1 Mb)
The star continues to rotate, and the swath continues to rotate about
the star. At two points, tracers appear showing the path of an
individual test particle. The viewer notes that it is exactly the same
as in Part 1.
Scene 3: Generation of the Sonic-Point Keplerian and Beat
Frequency QPOs
Scene3-part1.mov(5.1 Mb)
The neutron star, accretion disk, and swath reappear. The motion freezes
as the final complication to this model is added--the neutron star has a
weak magnetic field which channels infalling particles, creating a
second beam (pink). This beam is weaker and is not directly observable;
hence, we truncate it partway into the accretion disk.
Scene3-part2.mov(14.3 Mb)
The system is once more set in motion. The pink (pulsar) beam rotates
at the same rate as the star, which is appreciably slower than the
angular speed of the clump and swath. Therefore, the clump repeatedly
overtakes the pink beam. When the clump passes through the pink beam,
it is excited and the rate of emission of particles from the clump to
the star increases. So the density of the swath increases, as
represented by a brightening in its shade of blue. When the high
density regions of the swath hit the neutron star, the intensity of
x-rays increases, shown by a brightening in the yellow beam.
