The Impact of Initial–Final Mass Relations on Black Hole Microlensing

Abstract

Uncertainty in the initial–final mass relation (IFMR) has long been a problem in understanding the final stages of massive star evolution. One of the major challenges of constraining the IFMR is the difficulty of measuring the mass of nonluminous remnant objects (i.e., neutron stars and black holes). Gravitational-wave detectors have opened the possibility of finding large numbers of compact objects in other galaxies, but all in merging binary systems. Gravitational lensing experiments using astrometry and photometry are capable of finding compact objects, both isolated and in binaries, in the Milky Way. In this work we improve the Population Synthesis for Compact object Lensing Events (PopSyCLE) microlensing simulation code in order to explore the possibility of constraining the IFMR using the Milky Way microlensing population. We predict that the Roman Space Telescope’s microlensing survey will likely be able to distinguish different IFMRs based on the differences at the long end of the Einstein crossing time distribution and the small end of the microlensing parallax distribution, assuming the small (π E ≲ 0.02) microlensing parallaxes characteristic of black hole lenses are able to be measured accurately. We emphasize that future microlensing surveys need to be capable of characterizing events with small microlensing parallaxes in order to place the most meaningful constraints on the IFMR.

Primordial Black Hole Dark Matter Simulations Using PopSyCLE

“…Note that our results use a higher cadence than the Lam et al (2020) "v3" results, catching more events with long duration. However, when running our simulations without PBHs using the exact same simulation parameters as Lam et al (2020), we find identical results to those reported in Lam et al (2020, Appendix A.1) and by Rose et al (2022).…”

“…The Stellar Population Interface for Stellar Evolution and Atmospheres, or SPISEA, is a Python package used to generate star clusters (single-age and single-metallicity populations) using various input parameters, including age, mass, metallicity, extinction, atmospheric models, and initial mass functions (Hosek et al 2020). SPISEA allows for compact object generation by supporting user control of the initial-final mass relation (IFMR; Rose et al 2022). We follow the SPISEA modifications outlined in Lam et al (2020) Section 2.2, which uses the Raithel18 (Raithel et al 2018) IFMR from recent simulations, along with the zero-age mainsequence (ZAMS) mass of each star, in order to build a population of stellar evolved BHs, neutron stars (NSs), and white dwarfs (WDs).…”

The Star Formation History of the Milky Way’s Nuclear Star Cluster

“…One important outcome of the star formation history of the NSC is that it allows us to predict the type and number of compact objects including SBHs, NSs, and WDs. We calculate the predicted number of compact objects via SPISEA with our derived star formation history, the first metallicity constraints on the NSC, realistic multiplicity properties (Lu et al 2013), and the metallicity-dependent initial-final mass relation (IFMR) implemented by Rose et al (2022; the Spera15 IFMR object within SPISEA).…”

Astrometric Microlensing by Primordial Black Holes with the Roman Space Telescope

“…SPISEA generates SOBHs, NSs, and WDs by evolving clusters matching each subpopulation of stars generated by Galaxia (thin and thick disk, bulge, stellar halo), assuming they are single-age, and single-metallicity populations and then injects the resulting compact objects into the simulation. SPISEA uses an initial mass function, stellar multiplicity, extinction law, metallicity-dependent stellar evolution, and an initial final mass relation (IFMR; see, e.g., Rose et al 2022). Separate IMFRs are used for NSs and SOBHs (see Appendix C of Lam et al 2020) and WDs (Kalirai et al 2008).…”