Abstract
Mass measurements from low-mass black hole X-ray binaries (LMXBs) and radio pulsars have been used to identify a gap between the most massive neutron stars (NSs) and the least massive black holes (BHs). BH mass measurements in LMXBs are typically only possible for transient systems: outburst periods enable detection via all-sky X-ray monitors, while quiescent periods enable radial velocity measurements of the low-mass donor. We quantitatively study selection biases due to the requirement of transient behavior for BH mass measurements. Using rapid population synthesis simulations (COSMIC), detailed binary stellar-evolution models (MESA), and the disk instability model of transient behavior, we demonstrate that transient LMXB selection effects introduce observational biases, and can suppress mass-gap BHs in the observed sample. However, we find a population of transient LMXBs with mass-gap BHs form through accretion-induced collapse of an NS during the LMXB phase, which is inconsistent with observations. These results are robust against variations of binary evolution prescriptions. The significance of this accretion-induced collapse population depends upon the maximum NS birth mass M NS , birth − max . To reflect the observed dearth of low-mass BHs, COSMIC and MESA models favor M NS , birth − max ≲ 2 M ⊙ . In the absence of further observational biases against LMXBs with mass-gap BHs, our results indicate the need for additional physics connected to the modeling of LMXB formation and evolution.
| Original language | English (US) |
|---|---|
| Article number | 212 |
| Journal | Astrophysical Journal |
| Volume | 954 |
| Issue number | 2 |
| DOIs | |
| State | Published - Sep 1 2023 |
Funding
The authors thank Michael Zevin and Simon Stevenson for useful discussions, and the referee for useful suggestions. J.S. and I.K. were supported as CIERA REU students by the National Science Foundation (NSF) under grant No. 1757792. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF. J.S. was also partially supported by CIFAR (through V.K.\u2019s Senior Fellowship). V.K. was partially supported through a CIFAR Senior Fellowship, a Guggenheim Fellowship, and the Gordon and Betty Moore Foundation (grant award GBMF8477). C.P.L.B. was supported by the CIERA Board of Visitors Research Professorship. J.J.A. was supported by Northwestern University through a CIERA Postdoctoral Fellowship. K.R. was supported by the Gordon and Betty Moore Foundation (PI Kalogera, grant award GBMF8477) and the Riedel Family Graduate Fellowship in CIERA. A.D., P.S., and M.S. were supported by the Gordon and Betty Moore Foundation (grant award GBMF8477). S.B.B., T.F., K.K., D.M., and Z.X. were supported by a Swiss National Science Foundation Professorship grant (PP00P2_176868; PI Fragos). K.K. acknowledges support from the Federal Commission for Scholarships for Foreign Students for the Swiss Government Excellence Scholarship (ESKAS No. 2021.0277). Z.X. acknowledges support from the Chinese Scholarship Council (CSC). E.Z. acknowledges funding support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 772086). The Flatiron Institute is funded by the Simons Foundation. This research was supported in part through the computational resources and staff contributions provided for the Quest High-Performance Computing Cluster at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology.
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science