def form_stars(sink,
initial_mass_function=settings.stars_initial_mass_function,
lower_mass_limit=settings.stars_lower_mass_limit,
upper_mass_limit=settings.stars_upper_mass_limit,
local_sound_speed=0.2 | units.kms,
logger=None,
randomseed=None,
**keyword_arguments):
"""
Let a sink form stars.
"""
logger = logger or logging.getLogger(__name__)
if randomseed is not None:
logger.info("setting random seed to %i", randomseed)
numpy.random.seed(randomseed)
# sink_initial_density = sink.mass / (4/3 * numpy.pi * sink.radius**3)
initialised = sink.initialised or False
if not initialised:
logger.debug("Initialising sink %i for star formation", sink.key)
next_mass = generate_next_mass(
initial_mass_function=initial_mass_function,
lower_mass_limit=lower_mass_limit,
upper_mass_limit=upper_mass_limit,
)
# sink.next_number_of_stars = len(next_mass)
# sink.next_total_mass = next_mass.sum()
sink.next_primary_mass = next_mass[0]
# if sink.next_number_of_stars > 1:
# sink.next_secondary_mass = next_mass[1]
# if sink.next_number_of_stars > 2:
# sink.next_tertiary_mass = next_mass[2]
sink.initialised = True
if sink.mass < sink.next_primary_mass:
logger.debug("Sink %i is not massive enough for the next star",
sink.key)
return [sink, Particles()]
# We now have the first star that will be formed.
# Next, we generate a list of stellar masses, so that the last star in the
# list is just one too many for the sink's mass.
mass_left = sink.mass - sink.next_primary_mass
masses = new_masses(
stellar_mass=mass_left,
lower_mass_limit=lower_mass_limit,
upper_mass_limit=upper_mass_limit,
initial_mass_function=settings.stars_initial_mass_function,
)
number_of_stars = len(masses)
new_stars = Particles(number_of_stars)
new_stars.age = 0 | units.Myr
new_stars[0].mass = sink.next_primary_mass
new_stars[1:].mass = masses[:-1]
sink.next_primary_mass = masses[-1]
# if sink.next_number_of_stars > 1:
# new_stars[1].mass = sink.next_secondary_mass
# if sink.next_number_of_stars > 2:
# new_stars[2].mass = sink.next_tertiary_mass
new_stars.position = sink.position
new_stars.velocity = sink.velocity
# Random position within the sink radius
radius = sink.radius
rho = numpy.random.random(number_of_stars) * radius
theta = (numpy.random.random(number_of_stars) * (2 * numpy.pi | units.rad))
phi = (numpy.random.random(number_of_stars) * numpy.pi | units.rad)
x = rho * sin(phi) * cos(theta)
y = rho * sin(phi) * sin(theta)
z = rho * cos(phi)
new_stars.x += x
new_stars.y += y
new_stars.z += z
# Random velocity, sample magnitude from gaussian with local sound speed
# like Wall et al (2019)
# temperature = 10 | units.K
try:
local_sound_speed = sink.u.sqrt()
except AttributeError:
local_sound_speed = local_sound_speed
# or (gamma * local_pressure / density).sqrt()
velocity_magnitude = numpy.random.normal(
# loc=0.0, # <- since we already added the velocity of the sink
scale=local_sound_speed.value_in(units.kms),
size=number_of_stars,
) | units.kms
velocity_theta = (numpy.random.random(number_of_stars) *
(2 * numpy.pi | units.rad))
velocity_phi = (numpy.random.random(number_of_stars) *
(numpy.pi | units.rad))
vx = velocity_magnitude * sin(velocity_phi) * cos(velocity_theta)
vy = velocity_magnitude * sin(velocity_phi) * sin(velocity_theta)
vz = velocity_magnitude * cos(velocity_phi)
new_stars.vx += vx
new_stars.vy += vy
new_stars.vz += vz
new_stars.origin_cloud = sink.key
# For Pentacle, this is the PP radius
new_stars.radius = 0.05 | units.parsec
sink.mass -= new_stars.total_mass()
# TODO: fix sink's momentum etc
# EDIT: Do not shrink the sinks at this point, but rather when finished
# forming stars.
# # Shrink the sink's (accretion) radius to prevent it from accreting
# # relatively far away gas and moving a lot
# sink.radius = (
# (sink.mass / sink_initial_density)
# / (4/3 * numpy.pi)
# )**(1/3)
# cleanup
# sink.initialised = False
new_stars.birth_mass = new_stars.mass
return [sink, new_stars]
