I'm a 1st year PhD student studying the evolution of massive stars in binary systems. I also have a keen interest in gravitational waves from colliding black holes and neutron stars, as well as in exoplanetary science. Address: Birmingham, Birmingham, United Kingdom
Neutron stars receive velocity kicks at birth in supernovae. Those formed in electron-capture sup... more Neutron stars receive velocity kicks at birth in supernovae. Those formed in electron-capture supernovae from superasymptotic giant branch stars – the lowest mass stars to end their lives in supernovae – may receive significantly lower kicks than typical neutron stars. Given that many massive stars are members of wide binaries, this suggests the existence of a population of low-mass (1.25 < Mpsr/M⊙ < 1.3), wide (Porb ≳ 104 d), eccentric (e ∼ 0.7), unrecycled (Pspin ∼ 1 s) binary pulsars. The formation rate of such binaries is sensitive to the mass range of (effectively) single stars leading to electron capture supernovae, the amount of mass lost prior to the supernova, and the magnitude of any natal kick imparted on the neutron star. We estimate that one such binary pulsar should be observable in the Milky Way for every 10 000 isolated pulsars, assuming that the width of the mass range of single stars leading to electron-capture supernovae is ≲0.2 M⊙, and that neutron stars fo...
Monthly Notices of the Royal Astronomical Society, 2021
Binaries comprised of a neutron star (NS) and a black hole (BH) have so far eluded observations a... more Binaries comprised of a neutron star (NS) and a black hole (BH) have so far eluded observations as pulsars and with gravitational waves (GWs). We model the formation and evolution of these NS+BH binaries – including pulsar evolution – using the binary population synthesis code COMPAS. We predict the presence of a total of 50–2000 binaries containing a pulsar and a BH (PSR+BHs) in the Galactic field. We find the population observable by the next generation of radio telescopes, represented by the SKA and MeerKAT, current (LIGO/Virgo) and future (LISA) GW detectors. We conclude that the SKA will observe 1–80 PSR+BHs, with 0–4 binaries containing millisecond pulsars. MeerKAT is expected to observe 0–40 PSR+BH systems. Future radio detections of NS+BHs will constrain uncertain binary evolution processes such as BH natal kicks. We show that systems in which the NS formed first (NSBH) can be distinguished from those where the BH formed first (BHNS) by their pulsar and binary properties. We...
Context. After years of scientific progress, the origin of stellar binary black holes is still a ... more Context. After years of scientific progress, the origin of stellar binary black holes is still a great mystery. Several formation channels for merging black holes have been proposed in the literature. As more merger detections are expected with future gravitational-wave observations, population synthesis studies can help to distinguish between them. Aims. We study the formation of coalescing binary black holes via the evolution of isolated field binaries that go through the common envelope phase in order to obtain the combined distributions of observables such as black-hole spins, masses and cosmological redshifts of mergers. Methods. To achieve this aim, we used a hybrid technique that combines the parametric binary population synthesis code COMPAS with detailed binary evolution simulations performed with the MESA code. We then convolved our binary evolution calculations with the redshift- and metallicity-dependent star-formation rate and the selection effects of gravitational-wave...
COMPAS (Compact Object Mergers: Population Astrophysics and Statistics) is a public rapid binary ... more COMPAS (Compact Object Mergers: Population Astrophysics and Statistics) is a public rapid binary population synthesis code. COMPAS generates populations of isolated stellar binaries under a set of parametrised assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. It includes a number of tools for population processing in addition to the core binary evolution components. COMPAS is publicly available via the github repository https://github.com/TeamCOMPAS/COMPAS/, and is designed to allow for flexible modifications as evolutionary models improve. This paper describes the methodology and implementation of COMPAS. It is a living document which will be updated as new features are added to COMPAS; the current document describes COMPAS v02.21.00.
During its first four months of taking data, Advanced LIGO has detected gravitational waves from ... more During its first four months of taking data, Advanced LIGO has detected gravitational waves from two binary black hole mergers, GW150914 and GW151226, along with the statistically less significant binary black hole merger candidate LVT151012. Here we use the rapid binary population synthesis code COMPAS to show that all three events can be explained by a single evolutionary channel-classical isolated binary evolution via mass transfer including a common envelope phase. We show all three events could have formed in low-metallicity environments (Z=0.001) from progenitor binaries with typical total masses ≳160M⊙, ≳60M⊙ and ≳90M⊙, for GW150914, GW151226 and LVT151012, respectively.
The coalescence of compact binaries containing neutron stars or black holes is one of the most pr... more The coalescence of compact binaries containing neutron stars or black holes is one of the most promising signals for advanced ground-based laser interferometer gravitational-wave detectors, with the first direct detections expected over the next few years. The rate of binary coalescences and the distribution of component masses is highly uncertain, and population synthesis models predict a wide range of plausible values. Poorly constrained parameters in population synthesis models correspond to poorly understood astrophysics at various stages in the evolution of massive binary stars, the progenitors of binary neutron star and binary black hole systems. These include effects such as supernova kick velocities, parameters governing the energetics of common envelope evolution and the strength of stellar winds. Observing multiple binary black hole systems through gravitational waves will allow us to infer details of the astrophysical mechanisms that lead to their formation. We simulate g...
Neutron stars receive velocity kicks at birth in supernovae. Those formed in electron-capture sup... more Neutron stars receive velocity kicks at birth in supernovae. Those formed in electron-capture supernovae from superasymptotic giant branch stars – the lowest mass stars to end their lives in supernovae – may receive significantly lower kicks than typical neutron stars. Given that many massive stars are members of wide binaries, this suggests the existence of a population of low-mass (1.25 < Mpsr/M⊙ < 1.3), wide (Porb ≳ 104 d), eccentric (e ∼ 0.7), unrecycled (Pspin ∼ 1 s) binary pulsars. The formation rate of such binaries is sensitive to the mass range of (effectively) single stars leading to electron capture supernovae, the amount of mass lost prior to the supernova, and the magnitude of any natal kick imparted on the neutron star. We estimate that one such binary pulsar should be observable in the Milky Way for every 10 000 isolated pulsars, assuming that the width of the mass range of single stars leading to electron-capture supernovae is ≲0.2 M⊙, and that neutron stars fo...
Monthly Notices of the Royal Astronomical Society, 2021
Binaries comprised of a neutron star (NS) and a black hole (BH) have so far eluded observations a... more Binaries comprised of a neutron star (NS) and a black hole (BH) have so far eluded observations as pulsars and with gravitational waves (GWs). We model the formation and evolution of these NS+BH binaries – including pulsar evolution – using the binary population synthesis code COMPAS. We predict the presence of a total of 50–2000 binaries containing a pulsar and a BH (PSR+BHs) in the Galactic field. We find the population observable by the next generation of radio telescopes, represented by the SKA and MeerKAT, current (LIGO/Virgo) and future (LISA) GW detectors. We conclude that the SKA will observe 1–80 PSR+BHs, with 0–4 binaries containing millisecond pulsars. MeerKAT is expected to observe 0–40 PSR+BH systems. Future radio detections of NS+BHs will constrain uncertain binary evolution processes such as BH natal kicks. We show that systems in which the NS formed first (NSBH) can be distinguished from those where the BH formed first (BHNS) by their pulsar and binary properties. We...
Context. After years of scientific progress, the origin of stellar binary black holes is still a ... more Context. After years of scientific progress, the origin of stellar binary black holes is still a great mystery. Several formation channels for merging black holes have been proposed in the literature. As more merger detections are expected with future gravitational-wave observations, population synthesis studies can help to distinguish between them. Aims. We study the formation of coalescing binary black holes via the evolution of isolated field binaries that go through the common envelope phase in order to obtain the combined distributions of observables such as black-hole spins, masses and cosmological redshifts of mergers. Methods. To achieve this aim, we used a hybrid technique that combines the parametric binary population synthesis code COMPAS with detailed binary evolution simulations performed with the MESA code. We then convolved our binary evolution calculations with the redshift- and metallicity-dependent star-formation rate and the selection effects of gravitational-wave...
COMPAS (Compact Object Mergers: Population Astrophysics and Statistics) is a public rapid binary ... more COMPAS (Compact Object Mergers: Population Astrophysics and Statistics) is a public rapid binary population synthesis code. COMPAS generates populations of isolated stellar binaries under a set of parametrised assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. It includes a number of tools for population processing in addition to the core binary evolution components. COMPAS is publicly available via the github repository https://github.com/TeamCOMPAS/COMPAS/, and is designed to allow for flexible modifications as evolutionary models improve. This paper describes the methodology and implementation of COMPAS. It is a living document which will be updated as new features are added to COMPAS; the current document describes COMPAS v02.21.00.
During its first four months of taking data, Advanced LIGO has detected gravitational waves from ... more During its first four months of taking data, Advanced LIGO has detected gravitational waves from two binary black hole mergers, GW150914 and GW151226, along with the statistically less significant binary black hole merger candidate LVT151012. Here we use the rapid binary population synthesis code COMPAS to show that all three events can be explained by a single evolutionary channel-classical isolated binary evolution via mass transfer including a common envelope phase. We show all three events could have formed in low-metallicity environments (Z=0.001) from progenitor binaries with typical total masses ≳160M⊙, ≳60M⊙ and ≳90M⊙, for GW150914, GW151226 and LVT151012, respectively.
The coalescence of compact binaries containing neutron stars or black holes is one of the most pr... more The coalescence of compact binaries containing neutron stars or black holes is one of the most promising signals for advanced ground-based laser interferometer gravitational-wave detectors, with the first direct detections expected over the next few years. The rate of binary coalescences and the distribution of component masses is highly uncertain, and population synthesis models predict a wide range of plausible values. Poorly constrained parameters in population synthesis models correspond to poorly understood astrophysics at various stages in the evolution of massive binary stars, the progenitors of binary neutron star and binary black hole systems. These include effects such as supernova kick velocities, parameters governing the energetics of common envelope evolution and the strength of stellar winds. Observing multiple binary black hole systems through gravitational waves will allow us to infer details of the astrophysical mechanisms that lead to their formation. We simulate g...
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