Fallback and Black Hole Production in Massive Stars

Abstract

The compact remnants of core collapse supernovae - neutron stars and black holes - have properties that reflect both the structure of their stellar progenitors and the physics of the explosion. In particular, the masses of these remnants are sensitive to the density structure of the presupernova star and to the explosion energy. To a considerable extent, the final mass is determined by the ``fallback'', during the explosion, of matter that initially moves outwards, yet ultimately fails to escape. We consider here the simulated explosion of a large number of massive stars (10 to 100 \Msun) of Population I (solar metallicity) and III (zero metallicity), and find systematic differences in the remnant mass distributions. As pointed out by Chevalier(1989), supernovae in more compact progenitor stars have stronger reverse shocks and experience more fallback. For Population III stars above about 25 \Msun and explosion energies less than $1.5 \times 10^{51}$ erg, black holes are a common outcome, with masses that increase monotonically with increasing main sequence mass up to a maximum hole mass of about 35 \Msun. If such stars produce primary nitrogen, however, their black holes are systematically smaller. For modern supernovae with nearly solar metallicity, black hole production is much less frequent and the typical masses, which depend sensitively on explosion energy, are smaller. We explore the neutron star initial mass function for both populations and, for reasonable assumptions about the initial mass cut of the explosion, find good agreement with the average of observed masses of neutron stars in binaries. We also find evidence for a bimodal distribution of neutron star masses with a spike around 1.2 \Msun (gravitational mass) and a broader distribution peaked around 1.4 \Msun.Comment: Accepted for publication in Ap

On the Mass Distribution and Birth Masses of Neutron Stars

“…(Note that in Figure 16, we plot the corresponding gravitational mass for the neutron stars.) This simple analytical estimate is in agreement with the detailed numerical calculations of Zhang et al (2008), which are also shown in the figure. The green hatched region outlines the results for different compositions, explosion energies, and locations of the pistons for an assumed maximum neutron star mass of 2 M .…”

“…Fallback of stellar matter onto the collapsing core during the supernova explosion allows for the remnant to increase. However, this is also expected to increase the dispersion of masses by a comparable amount (see Zhang et al 2008), which is inconsistent with the narrowness of the inferred mass distribution of double neutron star masses. Considering a bimodal underlying distribution in the population of double neutron stars, as in Schwab et al (2010), makes the width of each distribution even narrower: 0.008 M and 0.025 M for the two components.…”

On the Sensitivity of Massive Star Nucleosynthesis and Evolution to Solar Abundances and to Uncertainties in Helium‐Burning Reaction Rates

“…The remnant masses are the gravitational masses of the resulting neutron stars or black holes. They are based on the baryonic mass below the piston (i.e., the mass enclosed within a radius reaching out to the base of the oxygen shell at the presupernova stage) corrected for the binding energy ( Zhang et al 2007) according to the approximation given by Lattimer & Prakash (2001). In our study, none of the stars had any significant fallback after explosion.…”

Are pulsars born with a hidden magnetic field?

“…The total mass accreted during this phase is more uncertain. Detailed 1D numerical simulations of the shock propagation and fallback estimate that typical values range from 10 −4 M to a few solar masses (Woosley et al 1995;Zhang et al 2008;Ugliano et al 2012). If more than a solar mass is accreted, the final outcome would be the delayed formation of a black hole, hours to days after core bounce.…”

“…If more than a solar mass is accreted, the final outcome would be the delayed formation of a black hole, hours to days after core bounce. Chevalier (1989) and Zhang et al (2008) showed that the accretion rate is expected to be maximum when the reverse shock reaches the NS and decreases as t −5/3 at later times. Therefore, the total amount of accreted mass is dominated by the fallback during the first few hours.…”