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]
def form_stars_from_group_older_version(
group_index,
sink_particles,
newly_removed_gas,
lower_mass_limit=settings.stars_lower_mass_limit,
upper_mass_limit=settings.stars_upper_mass_limit,
local_sound_speed=0.2 | units.kms,
minimum_sink_mass=0.01 | units.MSun,
logger=None,
randomseed=None,
shrink_sinks=True,
**keyword_arguments):
"""
Form stars from specific group of sinks.
NOTE: This is the older version where removed gas is
considered as star-forming region. This is now being
updated to the above latest version.
"""
logger = logger or logging.getLogger(__name__)
logger.info("Using form_stars_from_group on group %i", group_index)
if randomseed is not None:
logger.info("Setting random seed to %i", randomseed)
numpy.random.seed(randomseed)
# Sanity check: each sink particle must be in a group.
ungrouped_sinks = sink_particles.select_array(lambda x: x <= 0,
['in_group'])
if not ungrouped_sinks.is_empty():
logger.info(
"WARNING: There exist ungrouped sinks. Something is wrong!")
return None
# Consider only group with input group index from here onwards.
group = sink_particles[sink_particles.in_group == group_index]
# Sanity check: group must have at least a sink
if group.is_empty():
logger.info(
"WARNING: There is no sink in the group: Something is wrong!")
return None
number_of_sinks = len(group)
logger.info("%i sinks found in group #%i: %s", number_of_sinks,
group_index, group.key)
group_mass = group.total_mass()
logger.info("Group mass: %s", group_mass.in_(units.MSun))
next_mass = generate_next_mass(
initial_mass_function=initial_mass_function,
lower_mass_limit=lower_mass_limit,
upper_mass_limit=upper_mass_limit,
)[0][0]
try:
# Within a group, group_next_primary_mass values are either
# a mass, or 0 MSun. If all values are 0 MSun, this is a
# new group. Else, only interested on the non-zero value. The
# non-zero values are the same.
logger.info('SANITY CHECK: group_next_primary_mass %s',
group.group_next_primary_mass)
if group.group_next_primary_mass.max() == 0 | units.MSun:
logger.info('Initiate group #%i for star formation', group_index)
group.group_next_primary_mass = next_mass
else:
next_mass = group.group_next_primary_mass.max()
# This happens for the first ever assignment of this attribute
except AttributeError:
logger.info(
'AttributeError exception: Initiate group #%i for star formation',
group_index)
group.group_next_primary_mass = next_mass
logger.info("Next mass is %s", next_mass)
if group_mass < next_mass:
logger.info("Group #%i is not massive enough for the next star",
group_index)
return None
# Form stars from the leftover group sink mass
mass_left = group_mass - next_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)
logger.info("%i stars created in group #%i with %i sinks", number_of_stars,
group_index, number_of_sinks)
new_stars = Particles(number_of_stars)
new_stars.age = 0 | units.Myr
new_stars[0].mass = next_mass
new_stars[1:].mass = masses[:-1]
group.group_next_primary_mass = masses[-1]
new_stars = new_stars.sorted_by_attribute("mass").reversed()
logger.info("Group's next primary mass is %s",
group.group_next_primary_mass[0])
# Create placeholders for attributes of new_stars
new_stars.position = [0, 0, 0] | units.pc
new_stars.velocity = [0, 0, 0] | units.kms
new_stars.origin_cloud = group[0].key
new_stars.star_forming_radius = 0 | units.pc
new_stars.star_forming_u = local_sound_speed**2
# Find the newly removed gas in the group
removed_gas = Particles()
if not newly_removed_gas.is_empty():
for s in group:
removed_gas_by_this_sink = (
newly_removed_gas[newly_removed_gas.accreted_by_sink == s.key])
removed_gas.add_particles(removed_gas_by_this_sink)
logger.info("%i removed gas found in this group", len(removed_gas))
# Star forming regions that contain the removed gas and the group
# of sinks
if not removed_gas.is_empty():
removed_gas.radius = removed_gas.h_smooth
star_forming_regions = group.copy()
star_forming_regions.density = (
star_forming_regions.initial_density / 1000
) # /1000 to reduce likelihood of forming stars in sinks
star_forming_regions.accreted_by_sink = star_forming_regions.key
try:
star_forming_regions.u = star_forming_regions.u
except AttributeError:
star_forming_regions.u = local_sound_speed**2
star_forming_regions.add_particles(removed_gas.copy())
star_forming_regions.sorted_by_attribute("density").reversed()
# Generate a probability list of star forming region indices the
# stars should associate to
probabilities = (star_forming_regions.density /
star_forming_regions.density.sum())
probabilities /= probabilities.sum() # Ensure sum is exactly 1
logger.info("Max & min probabilities: %s, %s", probabilities.max(),
probabilities.min())
logger.info("%i star forming regions", len(star_forming_regions))
def delta_positions_and_velocities(new_stars, star_forming_regions,
probabilities):
"""
Assign positions and velocities of stars in the star forming regions
according to the probability distribution
"""
number_of_stars = len(new_stars)
# Create an index list of removed gas from probability list
sample = numpy.random.choice(len(star_forming_regions),
number_of_stars,
p=probabilities)
# Assign the stars to the removed gas according to the sample
star_forming_regions_sampled = star_forming_regions[sample]
new_stars.position = star_forming_regions_sampled.position
new_stars.velocity = star_forming_regions_sampled.velocity
new_stars.origin_cloud = star_forming_regions_sampled.accreted_by_sink
new_stars.star_forming_radius = star_forming_regions_sampled.radius
try:
new_stars.star_forming_u = star_forming_regions_sampled.u
except AttributeError:
new_stars.star_forming_u = local_sound_speed**2
# Random position of stars within the sink radius they assigned to
rho = (numpy.random.random(number_of_stars) *
new_stars.star_forming_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)).value_in(units.pc)
y = (rho * sin(phi) * sin(theta)).value_in(units.pc)
z = (rho * cos(phi)).value_in(units.pc)
X = list(zip(*[x, y, z])) | units.pc
# Random velocity, sample magnitude from gaussian with local sound
# speed like Wall et al (2019)
# temperature = 10 | units.K
# or (gamma * local_pressure / density).sqrt()
velocity_magnitude = numpy.random.normal(
# loc=0.0, # <- since we already added the velocity of the sink
scale=new_stars.star_forming_u.sqrt().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)).value_in(units.kms)
vy = (velocity_magnitude * sin(velocity_phi) *
sin(velocity_theta)).value_in(units.kms)
vz = (velocity_magnitude * cos(velocity_phi)).value_in(units.kms)
V = list(zip(*[vx, vy, vz])) | units.kms
return X, V
dX, dV = delta_positions_and_velocities(new_stars, star_forming_regions,
probabilities)
logger.info("Updating new stars...")
new_stars.position += dX
new_stars.velocity += dV
# For Pentacle, this is the PP radius
new_stars.radius = 0.05 | units.parsec
# mass_ratio = 1 - new_stars.total_mass()/group.total_mass()
# group.mass *= mass_ratio
excess_star_mass = 0 | units.MSun
for s in group:
logger.info('Sink mass before reduction: %s', s.mass.in_(units.MSun))
total_star_mass_nearby = (
new_stars[new_stars.origin_cloud == s.key]).total_mass()
# To prevent sink mass becomes negative
if s.mass > minimum_sink_mass:
if (s.mass - total_star_mass_nearby) <= minimum_sink_mass:
excess_star_mass += (total_star_mass_nearby - s.mass +
minimum_sink_mass)
logger.info('Sink mass goes below %s; excess mass is now %s',
minimum_sink_mass.in_(units.MSun),
excess_star_mass.in_(units.MSun))
s.mass = minimum_sink_mass
else:
s.mass -= total_star_mass_nearby
else:
excess_star_mass += total_star_mass_nearby
logger.info(
'Sink mass is already <= minimum mass allowed; '
'excess mass is now %s', excess_star_mass.in_(units.MSun))
logger.info('Sink mass after reduction: %s', s.mass.in_(units.MSun))
# Reduce all sinks in group equally with the excess star mass
logger.info('Reducing all sink mass equally with excess star mass...')
mass_ratio = 1 - excess_star_mass / group.total_mass()
group.mass *= mass_ratio
logger.info("Total sink mass in group: %s",
group.total_mass().in_(units.MSun))
if shrink_sinks:
group.radius = ((group.mass / group.initial_density) /
(4 / 3 * numpy.pi))**(1 / 3)
logger.info("New radii: %s", group.radius.in_(units.pc))
return new_stars
