scholarly journals Exploring the Parameter Space of Compact Binary Population Synthesis

2016 ◽  
Vol 12 (S325) ◽  
pp. 46-50 ◽  
Author(s):  
Jim W. Barrett ◽  
Ilya Mandel ◽  
Coenraad J. Neijssel ◽  
Simon Stevenson ◽  
Alejandro Vigna-Gómez
Keyword(s):  
Gravitational Wave ◽  
Gaussian Process ◽  
Parameter Space ◽  
Gaussian Process Regression ◽  
Compact Object ◽  
Population Synthesis ◽  
Preliminary Results ◽  
Compact Binary ◽  
Binary Evolution

AbstractAs we enter the era of gravitational wave astronomy, we are beginning to collect observations which will enable us to explore aspects of astrophysics of massive stellar binaries which were previously beyond reach. In this paper we describe COMPAS (Compact Object Mergers: Population Astrophysics and Statistics), a new platform to allow us to deepen our understanding of isolated binary evolution and the formation of gravitational-wave sources. We describe the computational challenges associated with their exploration, and present preliminary results on overcoming them using Gaussian process regression as a simulation emulation technique.

scholarly journals stroopwafel: simulating rare outcomes from astrophysical populations, with application to gravitational-wave sources★

2019 ◽  
Vol 490 (4) ◽  
pp. 5228-5248 ◽  
Author(s):  
Floor S Broekgaarden ◽  
Stephen Justham ◽  
Selma E de Mink ◽  
Jonathan Gair ◽  
Ilya Mandel ◽  
...  
Keyword(s):  
Gravitational Wave ◽  
Parameter Space ◽  
Binary Systems ◽  
Probability Distributions ◽  
Compact Object ◽  
Monte Carlo Sampling ◽  
Distribution Functions ◽  
Population Synthesis ◽  
Standard Sampling ◽  
Near Future

ABSTRACT Gravitational-wave observations of double compact object (DCO) mergers are providing new insights into the physics of massive stars and the evolution of binary systems. Making the most of expected near-future observations for understanding stellar physics will rely on comparisons with binary population synthesis models. However, the vast majority of simulated binaries never produce DCOs, which makes calculating such populations computationally inefficient. We present an importance sampling algorithm, stroopwafel, that improves the computational efficiency of population studies of rare events, by focusing the simulation around regions of the initial parameter space found to produce outputs of interest. We implement the algorithm in the binary population synthesis code compas, and compare the efficiency of our implementation to the standard method of Monte Carlo sampling from the birth probability distributions. stroopwafel finds ∼25–200 times more DCO mergers than the standard sampling method with the same simulation size, and so speeds up simulations by up to two orders of magnitude. Finding more DCO mergers automatically maps the parameter space with far higher resolution than when using the traditional sampling. This increase in efficiency also leads to a decrease of a factor of ∼3–10 in statistical sampling uncertainty for the predictions from the simulations. This is particularly notable for the distribution functions of observable quantities such as the black hole and neutron star chirp mass distribution, including in the tails of the distribution functions where predictions using standard sampling can be dominated by sampling noise.

scholarly journals Masses of double neutron star mergers

2020 ◽  
Vol 639 ◽  
pp. A123 ◽  
Author(s):  
Matthias U. Kruckow
Keyword(s):  
Neutron Star ◽  
Gravitational Wave ◽  
Milky Way ◽  
Radio Pulsar ◽  
Population Synthesis ◽  
Radio Pulsars ◽  
Wave Observation ◽  
Binary Evolution ◽  
Star Binary

Aims. I aim to explain the mass discrepancy between the observed double neutron-star binary population by radio pulsar observations and gravitational-wave observation. Methods. I performed binary population synthesis calculations and compared their results with the radio and the gravitational-wave observations simultaneously. Results. Simulations of binary evolution were used to link different observations of double neutron star binaries with each other. I investigated the progenitor of GW190425 in more detail. A distribution of masses and merger times of the possible progenitors is presented. Conclusions. A mass discrepancy between the radio pulsars in the Milky Way with another neutron star companion and the inferred masses from gravitational-wave observations of those kind of merging systems is naturally found in binary evolution.

scholarly journals Impact of inter-correlated initial binary parameters on double black hole and neutron star mergers

2018 ◽  
Vol 619 ◽  
pp. A77 ◽  
Author(s):  
J. Klencki ◽  
M. Moe ◽  
W. Gladysz ◽  
M. Chruslinska ◽  
D. E. Holz ◽  
...  
Keyword(s):  
Uv Light ◽  
Formation Rate ◽  
Compact Object ◽  
Mass Function ◽  
Initial Mass Function ◽  
Compact Binary ◽  
Orbital Periods ◽  
Binary Evolution ◽  
The Impact ◽  
The Imf

The distributions of the initial main-sequence binary parameters are one of the key ingredients in obtaining evolutionary predictions for compact binary (BH–BH/BH–NS/NS–NS) merger rates. Until now, such calculations were done under the assumption that initial binary parameter distributions were independent. For the first time, we implement empirically derived inter-correlated distributions of initial binary parameters primary mass (M1), mass ratio (q), orbital period (P), and eccentricity (e). Unexpectedly, the introduction of inter-correlated initial binary parameters leads to only a small decrease in the predicted merger rates by a factor of ≲2–3 relative to the previously used non-correlated initial distributions. The formation of compact object mergers in the isolated classical binary evolution favours initial binaries with stars of comparable masses (q ≈ 0.5–1) at intermediate orbital periods (log P (days) = 2–4). New distributions slightly shift the mass ratios towards lower values with respect to the previously used flat q distribution, which is the dominant effect decreasing the rates. New orbital periods (∼1.3 more initial systems within log P (days) = 2–4), together with new eccentricities (higher), only negligibly increase the number of progenitors of compact binary mergers. Additionally, we discuss the uncertainty of merger rate predictions associated with possible variations of the massive-star initial mass function (IMF). We argue that evolutionary calculations should be normalized to a star formation rate (SFR) that is obtained from the observed amount of UV light at wavelength 1500 Å (an SFR indicator). In this case, contrary to recent reports, the uncertainty of the IMF does not affect the rates by more than a factor of ∼2. Any change to the IMF slope for massive stars requires a change of SFR in a way that counteracts the impact of IMF variations on compact object merger rates. In contrast, we suggest that the uncertainty in cosmic SFR at low metallicity can be a significant factor at play.

scholarly journals The origin of spin in binary black holes

2020 ◽  
Vol 635 ◽  
pp. A97 ◽  
Author(s):  
Simone S. Bavera ◽  
Tassos Fragos ◽  
Ying Qin ◽  
Emmanouil Zapartas ◽  
Coenraad J. Neijssel ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Wave ◽  
Scientific Progress ◽  
Hybrid Technique ◽  
Population Synthesis ◽  
Binary Black Holes ◽  
Common Envelope ◽  
The Common ◽  
Binary Evolution

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 detectors to obtain predictions of observable properties. Results. By assuming efficient angular momentum transport, we are able to present a model that is capable of simultaneously predicting the following three main gravitational-wave observables: the effective inspiral spin parameter χeff, the chirp mass Mchirp and the cosmological redshift of merger zmerger. We find an excellent agreement between our model and the ten events from the first two advanced detector observing runs. We make predictions for the third observing run O3 and for Advanced LIGO design sensitivity. We expect approximately 80% of events with χeff <  0.1, while the remaining 20% of events with χeff ≥ 0.1 are split into ∼10% with Mchirp <  15 M⊙ and ∼10% with Mchirp ≥ 15 M⊙. Moreover, we find that Mchirp and χeff distributions are very weakly dependent on the detector sensitivity. Conclusions. The favorable comparison of the existing LIGO/Virgo observations with our model predictions gives support to the idea that the majority, if not all of the observed mergers, originate from the evolution of isolated binaries. The first-born black hole has negligible spin because it lost its envelope after it expanded to become a giant star, while the spin of the second-born black hole is determined by the tidal spin up of its naked helium star progenitor by the first-born black hole companion after the binary finished the common-envelope phase.

scholarly journals Improving gravitational-wave parameter estimation using Gaussian process regression

2016 ◽  
Vol 93 (6) ◽  
Author(s):  
Christopher J. Moore ◽  
Christopher P. L. Berry ◽  
Alvin J. K. Chua ◽  
Jonathan R. Gair
Keyword(s):  
Parameter Estimation ◽  
Gravitational Wave ◽  
Gaussian Process ◽  
Gaussian Process Regression ◽  
Wave Parameter

scholarly journals Thermal Timescale Mass Transfer in Binary Population Synthesis

2004 ◽  
Vol 194 ◽  
pp. 243-243
Author(s):  
Stephen Justham ◽  
Ulrich Kolb
Keyword(s):  
Mass Transfer ◽  
Stellar Evolution ◽  
State Of The Art ◽  
Nonlinear Behaviour ◽  
Population Synthesis ◽  
Intermediate Mass ◽  
Transfer Rates ◽  
Compact Binary ◽  
Binary Evolution ◽  
Evolution Algorithms

Studies of binary evolution have, until recently, neglected thermal timescale mass transfer (TTMT). Recent work has suggested that this previously poorly studied area is crucial in the understanding of systems across the compact binary spectrum. We use the state-of-the-art binary population synthesis code BiSEPS (Willems and Kolb, 2002, MNRAS 337 1004-1016). However, the present treatment of TTMT is incomplete due to the nonlinear behaviour of stars in their departure from gravothermal ‘equilibrium’. Here we show work that should update the ultrafast stellar evolution algorithms within BiSEPS to make it the first pseudo-analytic code that can follow TTMT properly. We have generated fits to a set of over 300 Case B TTMT sequences with a range of intermediate-mass donors. These fits produce very good first approximations to both HR diagrams and mass-transfer rates (see figures 1 and 2), which we later hope to improve and extend. They are already a significant improvement over the previous fits.

scholarly journals The expansion of stripped-envelope stars: Consequences for supernovae and gravitational-wave progenitors

2020 ◽  
Vol 637 ◽  
pp. A6 ◽  
Author(s):  
E. Laplace ◽  
Y. Götberg ◽  
S. E. de Mink ◽  
S. Justham ◽  
R. Farmer
Keyword(s):  
Mass Transfer ◽  
Neutron Star ◽  
Gravitational Wave ◽  
Compact Objects ◽  
Population Synthesis ◽  
Outer Envelope ◽  
Low Metallicity ◽  
Binary Evolution ◽  
Ultimate Fate ◽  
High Metallicity

Massive binaries that merge as compact objects are the progenitors of gravitational-wave sources. Most of these binaries experience one or more phases of mass transfer, during which one of the stars loses all or part of its outer envelope and becomes a stripped-envelope star. The evolution of the size of these stripped stars is crucial in determining whether they experience further interactions and understanding their ultimate fate. We present new calculations of stripped-envelope stars based on binary evolution models computed with MESA. We use these to investigate their radius evolution as a function of mass and metallicity. We further discuss their pre-supernova observable characteristics and potential consequences of their evolution on the properties of supernovae from stripped stars. At high metallicity, we find that practically all of the hydrogen-rich envelope is removed, which is in agreement with earlier findings. Only progenitors with initial masses below 10 M⊙ expand to large radii (up to 100 R⊙), while more massive progenitors remain compact. At low metallicity, a substantial amount of hydrogen remains and the progenitors can, in principle, expand to giant sizes (> 400 R⊙) for all masses we consider. This implies that they can fill their Roche lobe anew. We show that the prescriptions commonly used in population synthesis models underestimate the stellar radii by up to two orders of magnitude. We expect that this has consequences for the predictions for gravitational-wave sources from double neutron star mergers, particularly with regard to their metallicity dependence.

scholarly journals Optimization of closed-loop electrical stimulation enables robust cerebellar-directed seizure control

2021 ◽  
Author(s):  
Bethany Stieve ◽  
Thomas Richner ◽  
Chris Krook-Magnuson ◽  
Theoden Netoff ◽  
Esther Krook-Magnuson
Keyword(s):  
Electrical Stimulation ◽  
Temporal Lobe Epilepsy ◽  
Gaussian Process ◽  
Parameter Space ◽  
Seizure Control ◽  
Gaussian Process Regression ◽  
Bayesian Optimization ◽  
On Demand ◽  
Stimulation Parameters ◽  
Stimulation Of

Additional treatment options for temporal lobe epilepsy are needed, and potential interventions targeting the cerebellum are of interest. Previous animal work has shown strong inhibition of hippocampal seizures through on-demand optogenetic manipulation of the cerebellum. However, decades of work examining electrical stimulation - a more immediately translatable approach - targeting the cerebellum has produced very mixed results. We were therefore interested in exploring the impact that stimulation parameters may have on seizure outcomes. Using a mouse model of temporal lobe epilepsy, we conducted on-demand electrical stimulation of the cerebellar cortex, and varied stimulation charge, frequency, and pulse width, resulting in over a thousand different potential combinations of settings. To explore this parameter space in an efficient, data-driven, manner, we utilized Bayesian optimization with Gaussian process regression, implemented in Matlab with an Expected Improvement Plus acquisition function. We examined two different fitting conditions and two different electrode orientations. Following the optimization process, we conducted additional on-demand experiments to test the effectiveness of selected settings. Across all animals, we found that Bayesian optimization allowed identification of effective intervention settings. Additionally, generally similar optimal settings were identified across animals, suggesting that personalized optimization may not always be necessary. While optimal settings were consistently effective, stimulation with settings predicted from the Gaussian process regression to be ineffective failed to provide seizure control. Taken together, our results provide a blueprint for exploration of a large parameter space for seizure control, and illustrate that robust inhibition of seizures can be achieved with electrical stimulation of the cerebellum, but only if the correct stimulation parameters are used.

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