Natal Kicks of Compact Binaries: I. Population Synthesis Framework and Illustrative Examples
6 affiliations
- 1School of Physics & Astronomy, University of Southampton , Highfield, Southampton SO17 1BJ ,
- 2University of Oxford Astrophysics, Department of Physics, , Keble Road, Oxford OX1 3RH ,
- 3University of the Free State Department of Physics, , PO Box 339, Bloemfontein 9300 ,
- 4McWilliams Center for Cosmology & Astrophysics , Department of Physics Carnegie Mellon University, Pittsburgh, PA 15213 ,
- 5University of Oxford Department of Physics, , Keble Road, Oxford OX1 3RH ,
- 6AI Center of Excellence, Shiv Nadar Institution of Eminence , NCR Delhi ,
Abstract
The natal kicks imparted to neutron stars and black holes at birth are critical for understanding massive-star evolution, compact-object formation, and compact binary merger rates. However, constraining these kicks is challenging, since they cannot be directly observed. Here, we outline a framework for inferring natal kick probability distributions for compact binaries. Our method embeds the rapid binary-population code COSMIC in a Monte-Carlo workflow that evolves ensembles of simulated binaries. From those which host compact objects, we can select subsets that match the observational characteristics of any given system (e.g. component masses, orbital period, mass-transfer status, systemic velocity). As a proof-of-concept, we apply this framework to six compact binaries spanning a wide range of companion masses and compact-object types. For each system, we identify the evolutionary channel(s) that could have led to the current observational characteristics, and isolate regions of allowed natal kicks and progenitor parameter space. We reconfirm that at least one black hole system, XTE J1118+480, must have received a natal kick υNK > 100 km s−1. The neutron-star system, GX 301–2, is also inferred to have received an impulsive kick exceeding 280 km s−1. We discuss the strengths and limitations associated with population-synthesis-based inference methods and explore the effects of adopting different prescriptions for critical binary evolution phases. We provide a detailed demonstration of the non-linear relationship between υNK and υsys, highlighting the shortcomings of relying on observations alone to measure natal kicks. The inferred kick velocity distributions across our benchmark sample are generally consistent with previous constraints.
Related
- Population synthesis of low-mass binaries with wind-accreting neutron stars
- The scarcity of white dwarf-brown dwarf binaries in the solar neighbourhood: A population synthesis study
- Evolution of Massive Main-Sequence Stars in Binary Population Synthesis. II. Consequences for Black Hole High-Mass X-ray Binaries and Binary Black Holes
- Type Ia supernova population machine – I. A unified cosmological simulation–binary synthesis framework establishing non-universal delay-time distributions and cosmic progenitor-channel dominance crossover
- Population-level correlations in Bayesian statistics: an illustrative model for gravitational-wave astronomy
BibTeX
@article{brown2026natal,
title = {{Natal Kicks of Compact Binaries: I. Population Synthesis Framework and Illustrative Examples}},
author = {Cordelia Dashwood Brown and Poshak Gandhi and Christian Knigge and Yue Zhao and Phil Charles and Pornisara Nuchvanichakul and Katelyn Breivik and Akarsh Sahay and Siddharth Malu},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1878},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1878/8865330},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Natal Kicks of Compact Binaries: I. Population Synthesis Framework and Illustrative Examples
AU - Cordelia Dashwood Brown
AU - Poshak Gandhi
AU - Christian Knigge
AU - Yue Zhao
AU - Phil Charles
AU - Pornisara Nuchvanichakul
AU - Katelyn Breivik
AU - Akarsh Sahay
AU - Siddharth Malu
PY - 2026
DA - 2026/10/05
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1878
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1878/8865330
AB - The natal kicks imparted to neutron stars and black holes at birth are critical for understanding massive-star evolution, compact-object formation, and compact binary merger rates. However, constraining these kicks is challenging, since they cannot be directly observed. Here, we outline a framework for inferring natal kick probability distributions for compact binaries. Our method embeds the rapid binary-population code COSMIC in a Monte-Carlo workflow that evolves ensembles of simulated binaries. From those which host compact objects, we can select subsets that match the observational characteristics of any given system (e.g. component masses, orbital period, mass-transfer status, systemic velocity). As a proof-of-concept, we apply this framework to six compact binaries spanning a wide range of companion masses and compact-object types. For each system, we identify the evolutionary channel(s) that could have led to the current observational characteristics, and isolate regions of allowed natal kicks and progenitor parameter space. We reconfirm that at least one black hole system, XTE J1118+480, must have received a natal kick υNK > 100 km s−1. The neutron-star system, GX 301–2, is also inferred to have received an impulsive kick exceeding 280 km s−1. We discuss the strengths and limitations associated with population-synthesis-based inference methods and explore the effects of adopting different prescriptions for critical binary evolution phases. We provide a detailed demonstration of the non-linear relationship between υNK and υsys, highlighting the shortcomings of relying on observations alone to measure natal kicks. The inferred kick velocity distributions across our benchmark sample are generally consistent with previous constraints.
SN - 0035-8711
SN - 1365-2966
ER -