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