# shift the cluster to an orbit around Galactic center
acc, _, _ = galaxy.get_gravity_at_point(0 | units.kpc, Rinit,
0 | units.kpc, 0 | units.kpc)
vcirc = (-acc * Rinit)**0.5
print("Vcirc=%f km/s" % vcirc.value_in(units.kms))
particles.x += Rinit
particles.vy += vcirc
cluster.particles.add_particles(particles)
# set up bridge; cluster is evolved under influence of the galaxy
sys = bridge(verbose=False)
sys.add_system(cluster, (galaxy, ), False)
# evolve and make plots
times = units.Myr([0., 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4])
f = pyplot.figure(figsize=(16, 8))
for i, t in enumerate(times):
sys.evolve_model(t, timestep=timestep)
print("Evolved the system to time %f" % t)
x = sys.particles.x.value_in(units.parsec)
y = sys.particles.y.value_in(units.parsec)
subplot = f.add_subplot(2, 4, i + 1)
subplot.plot(x, y, 'r .')
subplot.plot([0.], [0.], 'b +')
subplot.set_xlim(-60, 60)
subplot.set_ylim(-60, 60)
subplot.set_title(t)
# shift the cluster to an orbit around GC
# (note the systems share the same coordinate frame, although units may
# differ)
vcirc = circular_velocity_for_stable_orbit(Rinit, central_mass)
shift_particles(cluster, Rinit, 0 | units.parsec, 0. | units.parsec,
0 | units.kms, 0.8 * vcirc, 0 | units.kms)
code.particles.add_particles(cluster)
# add galactic center to the code
code.particles.add_particle(galactic_center)
print("Start evolution")
# evolve and make plots
times = units.Myr([0., 0.2, 0.4, 0.6])
f = pyplot.figure(figsize=(8, 8))
for i, time in enumerate(times):
code.evolve_model(time)
print("Evolved to time:", time)
x = code.particles.x.value_in(units.parsec)
y = code.particles.y.value_in(units.parsec)
subplot = f.add_subplot(2, 2, i + 1)
subplot.plot(x, y, 'r .')
subplot.plot([0.], [0.], 'b +')
subplot.set_xlim(-60, 60)
subplot.set_ylim(-60, 60)
subplot.set_title(time)
if i == 7:
