Showing 1 - 2 of 2 Items
Accretion Onto a Black Hole at the Center of a Neutron Star: Nuclear Equations of State
Date: 2022-01-01
Creator: Sophia Christina Schnauck
Access: Open access
- A recent re-examination of Bondi accretion (see Richards, Baumgarte and Shapiro (2021)) revealed that, for stiff equations of state (EOSs), steady-state accretion can only occur for accretion rates exceeding a certain minimum. To date, this result has been explored only for gamma-law equations of state. Instead, we consider accretion onto a small black hole residing at the center of a neutron star governed by a more realistic nuclear EOS. We generalize the relativistic Bondi solution for such EOSs, approximated by piecewise polytropes, and thereby obtain analytical expressions for the accretion rates which were reflected in our numerical simulations. After taking several different piecewise EOSs at different neutron star densities into account, the accretion rates of the different EOSs were only slightly larger than the previously observed minimum. In other words there appears to be evidence for a nearly universal accretion rate that depends only on the black hole mass. However, we also observed that for certain densities the fluid profiles of several EOSs exhibited superluminal sound speeds outside the horizon of the black hole, suggesting that the EOSs are not appropriate at these densities.
Accretion onto endoparasitic black holes at the center of neutron stars
Date: 2021-01-01
Creator: Chloe B Richards
Access: Open access
- We revisit the system consisting of a neutron star that harbors a small, possibly primordial, black hole at its center, focusing on a nonspinning black hole embedded in a nonrotating neutron star. Extending earlier treatments, we provide an analytical treatment describing the rate of secular accretion of the neutron star matter onto the black hole, adopting the relativistic Bondi accretion formalism for stiff equations of state that we presented elsewhere. We use these accretion rates to sketch the evolution of the system analytically until the neutron star is completely consumed. We also perform numerical simulations in full general relativity for black holes with masses up to nine orders of magnitude smaller than the neutron star mass, including a simulation of the entire evolution through collapse for the largest black hole mass. We construct relativistic initial data for these simulations by generalizing the black hole puncture method to allow for the presence of matter, and evolve these data with a code that is optimally designed to resolve the vastly different length scales present in this problem. We compare our analytic and numerical results, and provide expressions for the lifetime of neutron stars harboring such endoparasitic black holes.