ORCID Profile
0000-0002-6100-537X
Current Organisation
Swinburne University of Technology
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Stellar Astronomy and Planetary Systems | Astronomical and Space Sciences | General Relativity and Gravitational Waves
Publisher: Oxford University Press (OUP)
Date: 10-02-2016
DOI: 10.1093/MNRAS/STW233
Publisher: American Physical Society (APS)
Date: 20-08-2020
Publisher: Oxford University Press (OUP)
Date: 14-07-2017
Publisher: American Astronomical Society
Date: 19-03-2020
Abstract: On 2019 April 25, the LIGO Livingston detector observed a compact binary coalescence with signal-to-noise ratio 12.9. The Virgo detector was also taking data that did not contribute to detection due to a low signal-to-noise ratio, but were used for subsequent parameter estimation. The 90% credible intervals for the component masses range from to ( – if we restrict the dimensionless component spin magnitudes to be smaller than 0.05). These mass parameters are consistent with the in idual binary components being neutron stars. However, both the source-frame chirp mass and the total mass of this system are significantly larger than those of any other known binary neutron star (BNS) system. The possibility that one or both binary components of the system are black holes cannot be ruled out from gravitational-wave data. We discuss possible origins of the system based on its inconsistency with the known Galactic BNS population. Under the assumption that the signal was produced by a BNS coalescence, the local rate of neutron star mergers is updated to 250–2810 .
Publisher: Zenodo
Date: 2021
Publisher: Oxford University Press (OUP)
Date: 06-08-2020
Abstract: In the era of advanced electromagnetic and gravitational wave detectors, it has become increasingly important to effectively combine and study the impact of stellar evolution on binaries and dynamical systems of stars. Systematic studies dedicated to exploring uncertain parameters in stellar evolution are required to account for the recent observations of the stellar populations. We present a new approach to the commonly used single-star evolution (sse) fitting formulae, one that is more adaptable: method of interpolation for single star evolution (metisse). It makes use of interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. We have used metisse with detailed stellar tracks computed by the modules for experiments in stellar astrophysics (mesa), the bonn evolutionary code (bec), and the Cambridge stars code. metisse better reproduces stellar tracks computed using the stars code compared to sse, and is on average three times faster. Using stellar tracks computed with mesa and bec, we apply metisse to explore the differences in the remnant masses, the maximum radial expansion, and the main-sequence lifetime of massive stars. We find that different physical ingredients used in the evolution of stars, such as the treatment of radiation-dominated envelopes, can impact their evolutionary outcome. For stars in the mass range 9–100 M⊙, the predictions of remnant masses can vary by up to 20 M⊙, while the maximum radial expansion achieved by a star can differ by an order of magnitude between different stellar models.
Publisher: American Physical Society (APS)
Date: 11-08-2015
Publisher: American Physical Society (APS)
Date: 15-03-2023
Publisher: American Physical Society (APS)
Date: 04-09-2019
Publisher: American Astronomical Society
Date: 03-2021
Abstract: This paper presents the gravitational-wave measurement of the Hubble constant ( H 0 ) using the detections from the first and second observing runs of the Advanced LIGO and Virgo detector network. The presence of the transient electromagnetic counterpart of the binary neutron star GW170817 led to the first standard-siren measurement of H 0 . Here we additionally use binary black hole detections in conjunction with galaxy catalogs and report a joint measurement. Our updated measurement is H 0 = 69 − 8 + 16 km s −1 Mpc −1 (68.3% of the highest density posterior interval with a flat-in-log prior) which is an improvement by a factor of 1.04 (about 4%) over the GW170817-only value of 69 − 8 + 17 km s −1 Mpc −1 . A significant additional contribution currently comes from GW170814, a loud and well-localized detection from a part of the sky thoroughly covered by the Dark Energy Survey. With numerous detections anticipated over the upcoming years, an exhaustive understanding of other systematic effects are also going to become increasingly important. These results establish the path to cosmology using gravitational-wave observations with and without transient electromagnetic counterparts.
Publisher: American Physical Society (APS)
Date: 30-09-2019
Publisher: IOP Publishing
Date: 17-03-2017
Publisher: Oxford University Press (OUP)
Date: 12-07-2019
Abstract: The mass and spin distributions of compact binary gravitational-wave sources are currently uncertain due to complicated astrophysics involved in their formation. Multiple sub-populations of compact binaries representing different evolutionary scenarios may be present amongst sources detected by Advanced LIGO and Advanced Virgo. In addition to hierarchical modelling, unmodelled methods can aid in determining the number of sub-populations and their properties. In this paper, we apply Gaussian mixture model clustering to 1000 simulated gravitational-wave compact binary sources from a mixture of five sub-populations. Using both mass and spin as input parameters, we determine how many binary detections are needed to accurately determine the number of sub-populations and their mass and spin distributions. In the most difficult case that we consider, where two sub-populations have identical mass distributions but differ in their spin, which is poorly constrained by gravitational-wave detections, we find that ∼400 detections are needed before we can identify the correct number of sub-populations.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 20-05-2022
Abstract: Vast numbers of qubits will be needed for large-scale quantum computing because of the overheads associated with error correction. We present a scheme for low-overhead fault-tolerant quantum computation based on quantum low-density parity-check (LDPC) codes, where long-range interactions enable many logical qubits to be encoded with a modest number of physical qubits. In our approach, logic gates operate via logical Pauli measurements that preserve both the protection of the LDPC codes and the low overheads in terms of the required number of additional qubits. Compared with surface codes with the same code distance, we estimate order-of-magnitude improvements in the overheads for processing around 100 logical qubits using this approach. Given the high thresholds demonstrated by LDPC codes, our estimates suggest that fault-tolerant quantum computation at this scale may be achievable with a few thousand physical qubits at comparable error rates to what is needed for current approaches.
Publisher: American Astronomical Society
Date: 30-09-2019
Abstract: When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits ( e 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ≳100 Gpc −3 yr −1 for e 0.1, assuming a black hole mass spectrum with a power-law index ≲2.
Publisher: American Physical Society (APS)
Date: 10-08-2015
Publisher: Springer Science and Business Media LLC
Date: 21-12-2010
DOI: 10.1038/NCOMMS1147
Abstract: Quantum state tomography--deducing quantum states from measured data--is the gold standard for verification and benchmarking of quantum devices. It has been realized in systems with few components, but for larger systems it becomes unfeasible because the number of measurements and the amount of computation required to process them grows exponentially in the system size. Here, we present two tomography schemes that scale much more favourably than direct tomography with system size. One of them requires unitary operations on a constant number of subsystems, whereas the other requires only local measurements together with more elaborate post-processing. Both rely only on a linear number of experimental operations and post-processing that is polynomial in the system size. These schemes can be applied to a wide range of quantum states, in particular those that are well approximated by matrix product states. The accuracy of the reconstructed states can be rigorously certified without any a priori assumptions.
Publisher: American Astronomical Society
Date: 11-09-2019
Publisher: American Physical Society (APS)
Date: 29-03-2023
Publisher: Springer Science and Business Media LLC
Date: 08-2017
DOI: 10.1038/NATURE23453
Abstract: The direct detection of gravitational waves from merging binary black holes opens up a window into the environments in which binary black holes form. One signature of such environments is the angular distribution of the black hole spins. Binary systems that formed through dynamical interactions between already-compact objects are expected to have isotropic spin orientations (that is, the spins of the black holes are randomly oriented with respect to the orbit of the binary system), whereas those that formed from pairs of stars born together are more likely to have spins that are preferentially aligned with the orbit. The best-measured combination of spin parameters for each of the four likely binary black hole detections GW150914, LVT151012, GW151226 and GW170104 is the 'effective' spin. Here we report that, if the magnitudes of the black hole spins are allowed to extend to high values, the effective spins for these systems indicate a 0.015 odds ratio against an aligned angular distribution compared to an isotropic one. When considering the effect of ten additional detections, this odds ratio decreases to 2.9 × 10
Publisher: American Physical Society (APS)
Date: 14-12-2017
Publisher: Springer Science and Business Media LLC
Date: 08-10-2014
DOI: 10.1038/NCOMMS6156
Abstract: Unwanted interaction between a quantum system and its fluctuating environment leads to decoherence and is the primary obstacle to establishing a scalable quantum information processing architecture. Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity. Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation. Using a rapidly converging Bayesian approach, we precisely measure the splitting in a singlet-triplet spin qubit faster than the surrounding nuclear bath fluctuates. We continuously adjust qubit control parameters based on this information, thereby improving the inhomogenously broadened coherence time "Equation missing" from tens of nanoseconds to μs. Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.
Publisher: American Physical Society (APS)
Date: 23-11-2021
Publisher: Oxford University Press (OUP)
Date: 07-01-2020
Abstract: A class of optical transients known as Luminous Red Novae (LRNe) have recently been associated with mass ejections from binary stars undergoing common-envelope evolution. We use the population synthesis code COMPAS to explore the impact of a range of assumptions about the physics of common-envelope evolution on the properties of LRNe. In particular, we investigate the influence of various models for the energetics of LRNe on the expected event rate and light curve characteristics, and compare with the existing s le. We find that the Galactic rate of LRNe is ∼0.2 yr−1, in agreement with the observed rate. In our models, the luminosity function of Galactic LRNe covers multiple decades in luminosity and is dominated by signals from stellar mergers, consistent with observational constraints from iPTF and the Galactic s le of LRNe. We discuss how observations of the brightest LRNe may provide indirect evidence for the existence of massive (& M⊙) red supergiants. Such LRNe could be markers along the evolutionary pathway leading to the formation of double compact objects. We make predictions for the population of LRNe observable in future transient surveys with the Large Synoptic Survey Telescope and the Zwicky Transient Facility. In all plausible circumstances, we predict a selection-limited observable population dominated by bright, long-duration events caused by common envelope ejections. We show that the Large Synoptic Survey Telescope will observe 20–750 LRNe per year, quickly constraining the luminosity function of LRNe and probing the physics of common-envelope events.
Publisher: American Physical Society (APS)
Date: 24-08-2020
Publisher: American Astronomical Society
Date: 10-2021
Publisher: Oxford University Press (OUP)
Date: 16-10-2022
Abstract: Gravitational waves from merging binary black holes can be used to shed light on poorly understood aspects of massive binary stellar evolution, such as the evolution of massive stars (including their mass-loss rates), the common envelope phase, and the rate at which massive stars form throughout the cosmic history of the Universe. In this paper, we explore the correlated impact of these phases on predictions for the merger rate and chirp mass distribution of merging binary black holes, aiming to identify possible degeneracies between model parameters. In many of our models, a large fraction (more than 70 per cent of detectable binary black holes) arise from the chemically homogeneous evolution scenario these models tend to overpredict the binary black hole merger rate and produce systems that are on average too massive. Our preferred models favour enhanced mass-loss rates for helium rich Wolf–Rayet stars, in tension with recent theoretical and observational developments. We identify correlations between the impact of the mass-loss rates of Wolf–Rayet stars and the metallicity evolution of the Universe on the rates and properties of merging binary black holes. Based on the observed mass distribution, we argue that the $\\sim 10{{\\ \\rm per\\ cent}}$ of binary black holes with chirp masses greater than 40 M⊙ (the maximum predicted by our models) are unlikely to have formed through isolated binary evolution, implying a significant contribution (& per cent) from other formation channels such as dense star clusters or active galactic nuclei. Our models will enable inference on the uncertain parameters governing binary evolution in the near future.
Publisher: American Astronomical Society
Date: 10-09-2019
Publisher: American Physical Society (APS)
Date: 04-02-2022
Publisher: American Physical Society (APS)
Date: 24-04-2015
Publisher: American Astronomical Society
Date: 07-04-2017
Publisher: Oxford University Press (OUP)
Date: 16-10-2019
Abstract: We investigate the impact of uncertainty in the metallicity-specific star formation rate over cosmic time on predictions of the rates and masses of double compact object mergers observable through gravitational waves. We find that this uncertainty can change the predicted detectable merger rate by more than an order of magnitude, comparable to contributions from uncertain physical assumptions regarding binary evolution, such as mass transfer efficiency or supernova kicks. We statistically compare the results produced by the COMPAS population synthesis suite against a catalogue of gravitational-wave detections from the first two Advanced LIGO and Virgo observing runs. We find that the rate and chirp mass of observed binary black hole mergers can be well matched under our default evolutionary model with a star formation metallicity spread of 0.39 dex around a mean metallicity 〈Z〉 that scales with redshift z as 〈Z〉 = 0.035 × 10−0.23z, assuming a star formation rate of $0.01 \\times (1+z)^{2.77} / (1+((1+z)/2.9)^{4.7}) \\, \\rm {M}_\\odot$ Mpc−3 yr−1. Intriguingly, this default model predicts that 80 per cent of the approximately one binary black hole merger per day that will be detectable at design sensitivity will have formed through isolated binary evolution with only dynamically stable mass transfer, i.e. without experiencing a common-envelope event.
Publisher: Springer Science and Business Media LLC
Date: 28-09-2020
DOI: 10.1007/S41114-020-00026-9
Abstract: We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron star–black hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. During O3, the median localization volume (90% credible region) is expected to be on the order of $$10^{5}, 10^{6}, 10^{7}\\mathrm {\\ Mpc}^3$$ 10 5 , 10 6 , 10 7 Mpc 3 for binary neutron star, neutron star–black hole, and binary black hole systems, respectively. The localization volume in O4 is expected to be about a factor two smaller than in O3. We predict a detection count of $$1^{+12}_{-1}$$ 1 - 1 + 12 ( $$10^{+52}_{-10}$$ 10 - 10 + 52 ) for binary neutron star mergers, of $$0^{+19}_{-0}$$ 0 - 0 + 19 ( $$1^{+91}_{-1}$$ 1 - 1 + 91 ) for neutron star–black hole mergers, and $$17^{+22}_{-11}$$ 17 - 11 + 22 ( $$79^{+89}_{-44}$$ 79 - 44 + 89 ) for binary black hole mergers in a one-calendar-year observing run of the HLV network during O3 (HLVK network during O4). We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers.
Publisher: Springer Science and Business Media LLC
Date: 26-04-2018
DOI: 10.1007/S41114-018-0012-9
Abstract: We present possible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron star systems, which are the most promising targets for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and $$90\\%$$ 90 % credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5– $$20~\\mathrm {deg}^2$$ 20 deg 2 requires at least three detectors of sensitivity within a factor of $$\\sim 2$$ ∼ 2 of each other and with a broad frequency bandwidth. When all detectors, including KAGRA and the third LIGO detector in India, reach design sensitivity, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.
Publisher: IOP Publishing
Date: 12-04-2017
Publisher: American Physical Society (APS)
Date: 12-04-2022
Publisher: Verein zur Forderung des Open Access Publizierens in den Quantenwissenschaften
Date: 13-01-2020
DOI: 10.22331/Q-2020-01-13-223
Abstract: Investigating the classical simulability of quantum circuits provides a promising avenue towards understanding the computational power of quantum systems. Whether a class of quantum circuits can be efficiently simulated with a probabilistic classical computer, or is provably hard to simulate, depends quite critically on the precise notion of ``classical simulation'' and in particular on the required accuracy. We argue that a notion of classical simulation, which we call EPSILON-simulation (or ϵ -simulation for short), captures the essence of possessing ``equivalent computational power'' as the quantum system it simulates: It is statistically impossible to distinguish an agent with access to an ϵ -simulator from one possessing the simulated quantum system. We relate ϵ -simulation to various alternative notions of simulation predominantly focusing on a simulator we call a poly-box . A poly-box outputs 1 / p o l y precision additive estimates of Born probabilities and marginals. This notion of simulation has gained prominence through a number of recent simulability results. Accepting some plausible computational theoretic assumptions, we show that ϵ -simulation is strictly stronger than a poly-box by showing that IQP circuits and unconditioned magic-state injected Clifford circuits are both hard to ϵ -simulate and yet admit a poly-box. In contrast, we also show that these two notions are equivalent under an additional assumption on the sparsity of the output distribution ( poly-sparsity ).
Publisher: IOP Publishing
Date: 16-01-2020
Abstract: GW170817 is the very first observation of gravitational waves originating from the coalescence of two compact objects in the mass range of neutron stars, accompanied by electromagnetic counterparts, and offers an opportunity to directly probe the internal structure of neutron stars. We perform Bayesian model selection on a wide range of theoretical predictions for the neutron star equation of state. For the binary neutron star hypothesis, we find that we cannot rule out the majority of theoretical models considered. In addition, the gravitational-wave data alone does not rule out the possibility that one or both objects were low-mass black holes. We discuss the possible outcomes in the case of a binary neutron star merger, finding that all scenarios from prompt collapse to long-lived or even stable remnants are possible. For long-lived remnants, we place an upper limit of 1.9 kHz on the rotation rate. If a black hole was formed any time after merger and the coalescing stars were slowly rotating, then the maximum baryonic mass of non-rotating neutron stars is at most , and three equations of state considered here can be ruled out. We obtain a tighter limit of for the case that the merger results in a hypermassive neutron star.
Publisher: Springer Science and Business Media LLC
Date: 05-07-2021
DOI: 10.1038/S41467-021-24371-7
Abstract: A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.
Publisher: American Astronomical Society
Date: 04-09-2019
Publisher: American Physical Society (APS)
Date: 26-07-2010
Publisher: American Astronomical Society
Date: 29-06-2021
Abstract: We report the observation of gravitational waves from two compact binary coalescences in LIGO’s and Virgo’s third observing run with properties consistent with neutron star–black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115 the first was observed by LIGO Livingston and Virgo and the second by all three LIGO–Virgo detectors. The source of GW200105 has component masses 8 . 9 − 1 . 5 + 1. 2 and 1. 9 − 0. 2 + 0. 3 M ⊙ , whereas the source of GW200115 has component masses 5. 7 − 2 . 1 + 1. 8 and 1. 5 − 0. 3 + 0. 7 M ⊙ (all measurements quoted at the 90% credible level). The probability that the secondary’s mass is below the maximal mass of a neutron star is 89%–96% and 87%–98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are 280 − 110 + 110 and 300 − 100 + 150 Mpc , respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of 45 − 33 + 75 Gpc − 3 yr − 1 when assuming that GW200105 and GW200115 are representative of the NSBH population or 130 − 69 + 112 Gpc − 3 yr − 1 under the assumption of a broader distribution of component masses.
Publisher: Oxford University Press (OUP)
Date: 08-11-2017
Publisher: Oxford University Press (OUP)
Date: 27-09-2019
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 s ling 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 s ling from the birth probability distributions. stroopwafel finds ∼25–200 times more DCO mergers than the standard s ling 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 s ling. This increase in efficiency also leads to a decrease of a factor of ∼3–10 in statistical s ling 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 s ling can be dominated by s ling noise.
Publisher: American Physical Society (APS)
Date: 04-09-2019
Publisher: Oxford University Press (OUP)
Date: 28-02-2023
Abstract: We describe a search for gravitational waves from compact binaries with at least one component with mass $0.2$–$1.0 \\, \\mathrm{M}_\\odot$ and mass ratio q ≥ 0.1 in Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo data collected between 2019 November 1, 15:00 utc and 2020 March 27, 17:00 utc. No signals were detected. The most significant candidate has a false alarm rate of $0.2 \\, \\rm {yr}^{-1}$. We estimate the sensitivity of our search over the entirety of Advanced LIGO’s and Advanced Virgo’s third observing run, and present the most stringent limits to date on the merger rate of binary black holes with at least one subsolar-mass component. We use the upper limits to constrain two fiducial scenarios that could produce subsolar-mass black holes: primordial black holes (PBH) and a model of dissipative dark matter. The PBH model uses recent prescriptions for the merger rate of PBH binaries that include a rate suppression factor to effectively account for PBH early binary disruptions. If the PBHs are monochromatically distributed, we can exclude a dark matter fraction in PBHs $f_\\mathrm{PBH} \\gtrsim \\, 0.6$ (at 90 per cent confidence) in the probed subsolar-mass range. However, if we allow for broad PBH mass distributions, we are unable to rule out fPBH = 1. For the dissipative model, where the dark matter has chemistry that allows a small fraction to cool and collapse into black holes, we find an upper bound fDBH & 10−5 on the fraction of atomic dark matter collapsed into black holes.
Publisher: Springer Science and Business Media LLC
Date: 12-04-2021
DOI: 10.1038/S41467-021-22274-1
Abstract: Performing large calculations with a quantum computer will likely require a fault-tolerant architecture based on quantum error-correcting codes. The challenge is to design practical quantum error-correcting codes that perform well against realistic noise using modest resources. Here we show that a variant of the surface code—the XZZX code—offers remarkable performance for fault-tolerant quantum computation. The error threshold of this code matches what can be achieved with random codes (hashing) for every single-qubit Pauli noise channel it is the first explicit code shown to have this universal property. We present numerical evidence that the threshold even exceeds this hashing bound for an experimentally relevant range of noise parameters. Focusing on the common situation where qubit dephasing is the dominant noise, we show that this code has a practical, high-performance decoder and surpasses all previously known thresholds in the realistic setting where syndrome measurements are unreliable. We go on to demonstrate the favourable sub-threshold resource scaling that can be obtained by specialising a code to exploit structure in the noise. We show that it is possible to maintain all of these advantages when we perform fault-tolerant quantum computation.
Publisher: SAGE Publications
Date: 18-06-0015
Abstract: Pain can elevate stress in people with dementia. Although salivary cortisol is used as a biomarker of stress in people with dementia, few studies have reported the feasibility of collection methods to assess salivary cortisol in nursing home residents with both dementia and chronic pain. To explore the feasibility of collecting cortisol via salivary swab as an indicator of stress in people with dementia and chronic pain. Participants ( N = 43) aged ≥ 65 years and living with dementia and chronic pain were randomly assigned to the PARO (in idual, nonfacilitated, 30-min sessions with the robotic seal PARO, 5 days per week for 6 weeks) or usual-care group using computer-generated random numbers. Salivary cortisol was collected in the early morning before the intervention (Week 0) and at the completion of the intervention (Week 6) for comparison. There were multiple challenges associated with saliva collection and analysis, including cognitive impairment of participants, ability to obtain repeated s les with saliva volume adequate for assay, and overall cost. Ultimately, adequate saliva was collected from only 8 participants (both pre- and post-intervention) for assay and quantitative analysis. Considering the multiple challenges involved in obtaining valid saliva s les in this population, salivary cortisol may not be a feasible biomarker of physiological stress in people with dementia and chronic pain.
Publisher: Oxford University Press (OUP)
Date: 21-09-2020
Abstract: Gravitational waves provide a unique tool for observational astronomy. While the first LIGO–Virgo catalogue of gravitational-wave transients (GWTC-1) contains 11 signals from black hole and neutron star binaries, the number of observations is increasing rapidly as detector sensitivity improves. To extract information from the observed signals, it is imperative to have fast, flexible, and scalable inference techniques. In a previous paper, we introduced bilby: a modular and user-friendly Bayesian inference library adapted to address the needs of gravitational-wave inference. In this work, we demonstrate that bilby produces reliable results for simulated gravitational-wave signals from compact binary mergers, and verify that it accurately reproduces results reported for the 11 GWTC-1 signals. Additionally, we provide configuration and output files for all analyses to allow for easy reproduction, modification, and future use. This work establishes that bilby is primed and ready to analyse the rapidly growing population of compact binary coalescence gravitational-wave signals.
Publisher: American Physical Society (APS)
Date: 04-12-2019
Publisher: American Physical Society (APS)
Date: 20-11-2019
Publisher: American Physical Society (APS)
Date: 23-06-2022
Publisher: American Astronomical Society
Date: 26-06-2019
Publisher: American Astronomical Society
Date: 03-2021
Abstract: Radio pulsar observations probe the lives of Galactic double neutron star (DNS) systems while gravitational waves enable us to study extragalactic DNS in their final moments. By combining measurements from radio and gravitational-wave astronomy, we seek to gain a more complete understanding of DNS from formation to merger. We analyze the recent gravitational-wave binary neutron star mergers GW170817 and GW190425 in the context of other DNS known from radio astronomy. By employing a model for the birth and evolution of DNS, we measure the mass distribution of DNS at birth, at midlife (in the radio), and at death (in gravitational waves). We consider the hypothesis that the high-mass gravitational-wave event GW190425 is part of a subpopulation formed through unstable case BB mass transfer, which quickly merge in ∼10–100 Myr. We find only mild evidence to support this hypothesis and that GW190425 is not a clear outlier from the radio population as previously claimed. If there are fast-merging binaries, we estimate that they constitute 8%–79% of DNS at birth (90% credibility). We estimate the typical delay time between the birth and death of fast-merging binaries to be ≈5–401 Myr (90% credibility). We discuss the implications for radio and gravitational-wave astronomy.
Publisher: American Physical Society (APS)
Date: 17-05-2011
Publisher: American Astronomical Society
Date: 13-12-2017
Publisher: American Physical Society (APS)
Date: 18-10-2019
Publisher: American Physical Society (APS)
Date: 08-10-2024
Publisher: American Astronomical Society
Date: 18-12-2017
Publisher: Springer Science and Business Media LLC
Date: 16-10-2017
DOI: 10.1038/NATURE24471
Abstract: On 17 August 2017, the Advanced LIGO and Virgo detectors observed the gravitational-wave event GW170817-a strong signal from the merger of a binary neutron-star system. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO-Virgo-derived location of the gravitational-wave source. This sky region was subsequently observed by optical astronomy facilities, resulting in the identification of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first 'multi-messenger' astronomical observation. Such observations enable GW170817 to be used as a 'standard siren' (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic 'distance ladder': the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.
Publisher: American Astronomical Society
Date: 10-2022
Abstract: The spins of merging binary black holes offer insights into their formation history. Recently it has been argued that in the isolated binary evolution of two massive stars the firstborn black hole is slowly rotating, while the progenitor of the second-born black hole can be tidally spun up if the binary is tight enough. Naively, one might therefore expect that only the less massive black hole in merging binaries exhibits nonnegligible spin. However, if the mass ratio of the binary is “reversed” (typically during the first mass transfer episode), it is possible for the tidally spun up second-born to become the more massive black hole. We study the properties of such mass ratio reversed binary black hole mergers using a large set of 560 population synthesis models. We find that the more massive black hole is formed second in ≳70% of binary black holes observable by LIGO, Virgo, and KAGRA for most model variations we consider, with typical total masses ≳20 M ⊙ and mass ratios q = m 2 / m 1 ∼ 0.7 (where m 1 m 2 ). The formation history of these systems typically involves only stable mass transfer episodes. The second-born black hole has nonnegligible spin ( χ 0.05) in up to 25% of binary black holes, with among those the more (less) massive black hole is spinning in 0%–80% (20%–100%) of the cases, varying greatly in our models. We discuss our models in the context of several observed gravitational-wave events and the observed mass ratio—effective spin correlation.
Publisher: Oxford University Press (OUP)
Date: 10-01-2020
Abstract: We estimate the properties of the double neutron star (DNS) population that will be observable by the planned space-based interferometer Laser Interferometer Space Antenna (LISA). By following the gravitational radiation-driven evolution of DNSs generated from rapid population synthesis of massive binary stars, we estimate that around 35 DNSs will accumulate a signal-to-noise ratio above 8 over a 4-yr LISA mission. The observed population mainly comprises Galactic DNSs (94 per cent), but detections in the LMC (5 per cent) and SMC (1 per cent) may also be expected. The median orbital frequency of detected DNSs is expected to be 0.8 mHz, and many of them will be eccentric (median eccentricity of 0.11). LISA is expected to localize these DNSs to a typical angular resolution of 2°. We expect the best-constrained DNSs to have eccentricities known to a few parts in a thousand, chirp masses measured to better than 1 per cent fractional uncertainty, and sky localization at the level of a few arcminutes. The orbital properties will provide insights into DNS progenitors and formation channels. The localizations may allow neutron star natal kick magnitudes to be constrained through the Galactic distribution of DNSs, and make it possible to follow up the sources with radio pulsar searches. LISA is also expected to resolve ∼104 Galactic double white dwarfs, many of which may have binary parameters that resemble DNSs we discuss how the combined measurement of binary eccentricity, chirp mass, and sky location may aid the identification of a DNS.
Publisher: Springer Science and Business Media LLC
Date: 27-08-2019
DOI: 10.1038/S41524-019-0224-X
Abstract: Topologically ordered materials may serve as a platform for new quantum technologies, such as fault-tolerant quantum computers. To fulfil this promise, efficient and general methods are needed to discover and classify new topological phases of matter. We demonstrate that deep neural networks augmented with external memory can use the density profiles formed in quantum walks to efficiently identify properties of a topological phase as well as phase transitions. On a trial topological ordered model, our method’s accuracy of topological phase identification reaches 97.4%, and is shown to be robust to noise on the data. Furthermore, we demonstrate that our trained DNN is able to identify topological phases of a perturbed model, and predict the corresponding shift of topological phase transitions without learning any information about the perturbations in advance. These results demonstrate that our approach is generally applicable and may be used to identify a variety of quantum topological materials.
Publisher: Oxford University Press (OUP)
Date: 07-04-2022
Abstract: The evolution of massive stars is the basis of several astrophysical investigations, from predicting gravitational-wave event rates to studying star formation and stellar populations in clusters. However, uncertainties in massive star evolution present a significant challenge when accounting for these models’ behaviour in stellar population studies. In this work, we present a comparison between five published sets of stellar models from the BPASS (Binary Population and Spectral Synthesis), BoOST (Bonn Optimized Stellar Tracks), Geneva, MIST (MESA Isochrones and Stellar Tracks), and PARSEC (PAdova and TRieste Stellar Evolution Code) simulations at near-solar metallicity. The different sets of stellar models have been computed using slightly different physical inputs in terms of mass-loss rates and internal mixing properties. Moreover, these models also employ various pragmatic methods to overcome the numerical difficulties that arise due to the presence of density inversions in the outer layers of stars more massive than 40 M⊙. These density inversions result from the combination of inefficient convection in the low-density envelopes of massive stars and the excess of radiative luminosity to the Eddington luminosity. We find that the ionizing radiation released by the stellar populations can change by up to 18 per cent, the maximum radial expansion of a star can differ between 100 and 1600 R⊙, and the mass of the stellar remnant can vary up to 20 M⊙ between the five sets of simulations. We conclude that any attempts to explain observations that rely on the use of models of stars more massive than 40 M⊙ should be made with caution.
Publisher: Oxford University Press (OUP)
Date: 17-02-2023
Abstract: We present the discovery of 37 pulsars from ∼ 20 yr old archival data of the Parkes Multibeam Pulsar Survey using a new FFT-based search pipeline optimized for discovering narrow-duty cycle pulsars. When developing our pulsar search pipeline, we noticed that the signal-to-noise ratios of folded and optimized pulsars often exceeded that achieved in the spectral domain by a factor of two or greater, in particular for narrow duty cycle ones. Based on simulations, we verified that this is a feature of search codes that sum harmonics incoherently and found that many promising pulsar candidates are revealed when hundreds of candidates per beam even with modest spectral signal-to-noise ratios of S/N∼5–6 in higher-harmonic folds (up to 32 harmonics) are folded. Of these candidates, 37 were confirmed as new pulsars and a further 37 would have been new discoveries if our search strategies had been used at the time of their initial analysis. While 19 of these newly discovered pulsars have also been independently discovered in more recent pulsar surveys, 18 are exclusive to only the Parkes Multibeam Pulsar Survey data. Some of the notable discoveries include: PSRs J1635−47 and J1739−31, which show pronounced high-frequency emission PSRs J1655−40 and J1843−08 belong to the nulling/intermittent class of pulsars and PSR J1636−51 is an interesting binary system in a ∼0.75 d orbit and shows hints of eclipsing behaviour – unusual given the 340 ms rotation period of the pulsar. Our results highlight the importance of reprocessing archival pulsar surveys and using refined search techniques to increase the normal pulsar population.
Publisher: Oxford University Press (OUP)
Date: 19-03-2020
Abstract: We have implemented prescriptions for modelling pulsars in the rapid binary population synthesis code Compact Object Mergers: Population Astrophysics and Statistics. We perform a detailed analysis of the double neutron star (DNS) population, accounting for radio survey selection effects. The surface magnetic field decay time-scale (∼1000 Myr) and mass-scale (∼0.02 M⊙) are the dominant uncertainties in our model. Mass accretion during common envelope evolution plays a non-trivial role in recycling pulsars. We find a best-fitting model that is in broad agreement with the observed Galactic DNS population. Though the pulsar parameters (period and period derivative) are strongly biased by radio selection effects, the observed orbital parameters (orbital period and eccentricity) closely represent the intrinsic distributions. The number of radio observable DNSs in the Milky Way at present is about 2500 in our model, corresponding to approximately 10 per cent of the predicted total number of DNSs in the Galaxy. Using our model calibrated to the Galactic DNS population, we make predictions for DNS mergers observed in gravitational waves. The DNS chirp mass distribution varies from 1.1 to 2.1 M⊙ and the median is found to be 1.14 M⊙. The expected effective spin χeff for isolated DNSs is ≲0.03 from our model. We predict that 34 per cent of the current Galactic isolated DNSs will merge within a Hubble time, and have a median total mass of 2.7 M⊙. Finally, we discuss implications for fast radio bursts and post-merger remnant gravitational waves.
Publisher: American Physical Society (APS)
Date: 06-12-2017
Publisher: IOP Publishing
Date: 14-02-2013
Publisher: American Astronomical Society
Date: 16-10-2017
Publisher: Oxford University Press (OUP)
Date: 23-09-2021
Abstract: Mergers of black hole–neutron star (BHNS) binaries have now been observed by gravitational wave (GW) detectors with the recent announcement of GW200105 and GW200115. Such observations not only provide confirmation that these systems exist but will also give unique insights into the death of massive stars, the evolution of binary systems and their possible association with gamma-ray bursts, r-process enrichment, and kilonovae. Here, we perform binary population synthesis of isolated BHNS systems in order to present their merger rate and characteristics for ground-based GW observatories. We present the results for 420 different model permutations that explore key uncertainties in our assumptions about massive binary star evolution (e.g. mass transfer, common-envelope evolution, supernovae), and the metallicity-specific star formation rate density, and characterize their relative impacts on our predictions. We find intrinsic local BHNS merger rates spanning $\\mathcal {R}_{\\rm {m}}^0 \\approx$ 4–830 $\\, \\rm {Gpc}^{-3}$$\\, \\rm {yr}^{-1}$ for our full range of assumptions. This encompasses the rate inferred from recent BHNS GW detections and would yield detection rates of $\\mathcal {R}_{\\rm {det}} \\approx 1$–180$\\, \\rm {yr}^{-1}$ for a GW network consisting of LIGO, Virgo, and KAGRA at design sensitivity. We find that the binary evolution and metallicity-specific star formation rate density each impacts the predicted merger rates by order $\\mathcal {O}(10)$. We also present predictions for the GW-detected BHNS merger properties and find that all 420 model variations predict that $\\lesssim 5{{\\ \\rm per\\ cent}}$ of the BHNS mergers have BH masses $m_{\\rm {BH}} \\gtrsim 18\\, \\rm {M}_{\\odot }$, total masses $m_{\\rm {tot}} \\gtrsim 20\\, \\rm {M}_{\\odot }$, chirp masses ${\\mathcal {M}}_{\\rm {c}} \\gtrsim 5.5\\, \\rm {M}_{\\odot }$, and mass ratios qf ≳ 12 or qf ≲ 2. Moreover, we find that massive NSs with $m_{\\rm {NS}} \\gt 2\\, \\rm {M}_{\\odot }$ are expected to be commonly detected in BHNS mergers in almost all our model variations. Finally, a wide range of $\\sim 0{{\\ \\rm per\\ cent}}$ to $70{{\\ \\rm per\\ cent}}$ of the BHNS mergers are predicted to eject mass during the merger. Our results highlight the importance of considering variations in binary evolution and cosmological models when predicting, and eventually evaluating, populations of BHNS mergers.
Publisher: Cambridge University Press (CUP)
Date: 10-2016
DOI: 10.1017/S1743921317000059
Abstract: As 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.
Publisher: EDP Sciences
Date: 12-2022
DOI: 10.1051/0004-6361/202244044
Abstract: Context. The proximity to the Eddington luminosity has been attributed as the cause of several observed effects in massive stars. Computationally, if the luminosity carried through radiation exceeds the local Eddington luminosity in the low-density envelopes of massive stars, it can result in numerical difficulties, inhibiting further computation of stellar models. This problem is exacerbated by the fact that very few massive stars are observed beyond the Humphreys-Davidson limit, the same region in the Hertzsprung-Russell diagram where the aforementioned numerical issues relating to the Eddington luminosity occur in stellar models. Aims. One-dimensional stellar evolution codes have to use pragmatic solutions to evolve massive stars through this computationally difficult phase. In this work, we quantify the impact of these solutions on the evolutionary properties of massive stars. Methods. We used the stellar evolution code MESA with commonly used input parameters for massive stellar models to compute the evolution of stars in the initial mass range of 10–110 M ⊙ at one-tenth of solar metallicity. Results. We find that numerical difficulties in stellar models with initial masses greater than or equal to 30 M ⊙ cause these models to fail before the end of core helium burning. Recomputing these models using the same physical inputs but three different pragmatic solutions to treat the numerical instability, we find that the maximum radial expansion achieved by stars can vary by up to 2000 R ⊙ , while the remnant mass of the stars can vary by up to 14 M ⊙ between the sets. These differences can have implications on studies such as binary population synthesis.
Publisher: Springer Science and Business Media LLC
Date: 03-03-2012
Publisher: American Physical Society (APS)
Date: 10-11-2020
Publisher: American Physical Society (APS)
Date: 26-06-2012
Publisher: Springer Science and Business Media LLC
Date: 15-04-2019
Publisher: Oxford University Press (OUP)
Date: 11-05-2020
Abstract: The LIGO/Virgo collaborations recently announced the detection of a binary neutron star merger, GW190425. The mass of GW190425 is significantly larger than the masses of Galactic double neutron stars known through radio astronomy. We hypothesize that GW190425 formed differently from Galactic double neutron stars, via unstable ‘case BB’ mass transfer. According to this hypothesis, the progenitor of GW190425 was a binary consisting of a neutron star and a ∼4–$5\\, {\\mathrm{ M}_\\odot }$ helium star, which underwent common-envelope evolution. Following the supernova of the helium star, an eccentric double neutron star was formed, which merged in ${\\lesssim }10\\, {\\rm Myr}$. The helium star progenitor may explain the unusually large mass of GW190425, while the short time to merger may explain why similar systems are not observed in radio. To test this hypothesis, we measure the eccentricity of GW190425 using publicly available LIGO/Virgo data. We constrain the eccentricity at $10\\, {\\rm Hz}$ to be e ≤ 0.007 with $90{{\\ \\rm per\\ cent}}$ confidence. This provides no evidence for or against the unstable mass transfer scenario, because the binary is likely to have circularized to e ≲ 10−4 by the time it was detected. Future detectors will help to reveal the formation channel of mergers similar to GW190425 using eccentricity measurements.
Publisher: American Physical Society (APS)
Date: 21-01-2016
Publisher: Oxford University Press (OUP)
Date: 12-04-2018
DOI: 10.1093/MNRAS/STY908
Publisher: Oxford University Press (OUP)
Date: 14-04-2021
Abstract: 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 find 40 per cent of the LIGO/Virgo observed NS+BHs from a Milky Way like field population will have a chirp mass ≥3.0 M⊙. We estimate the spin distributions of NS+BHs with two models for the spins of BHs. The remnants of BHNS mergers will have a spin of ∼0.4, whilst NSBH merger remnants can have a spin of ∼0.6 or ∼0.9 depending on the model for BH spins. We estimate that approximately 25–1400 PSR+BHs will be radio alive whilst emitting GWs in the LISA frequency band, raising the possibility of joint observation by the SKA and LISA.
Publisher: Oxford University Press (OUP)
Date: 24-03-2022
Abstract: The observable population of double neutron star (DNS) systems in the Milky Way allow us to understand the nature of supernovae and binary stellar evolution. Until now, all DNS systems in wide orbits (Porb & 1 d) have been found to have orbital eccentricities, e & 0.1. In this paper, we report the discovery of pulsar PSR J1325−6253: a DNS system in a 1.81-d orbit with a surprisingly low eccentricity of just e = 0.064. Through, 1.4 yr of dedicated timing with the Parkes radio telescope we have been able to measure its rate of advance of periastron, $\\dot{\\omega }=0{_{.}^{\\circ}}138\\pm 0{_{.}^{\\circ}}002\\, \\mathrm{yr}^{-1}$. If this induced $\\dot{\\omega }$ is solely due to general relativity then the total mass of the system is, Msys = 2.57 ± 0.06 M⊙. Assuming an edge-on orbit the minimum companion mass is constrained to be Mc, min & 0.98 M⊙ which implies the pulsar mass is Mp, max & 1.59 M⊙. Its location in the P–$\\dot{P}$ diagram suggests that, like other DNS systems, PSR J1325−6253 is a recycled pulsar and if its mass is similar to the known ex les (& .3 M⊙), then the companion neutron star is probably less than ∼1.25 M⊙ and the system is inclined at about 50°–60°. The low eccentricity along with the wide orbit of the system strongly favours a formation scenario involving an ultra-stripped supernova explosion.
Publisher: IOP Publishing
Date: 13-01-2012
Publisher: Oxford University Press (OUP)
Date: 07-09-2018
Publisher: American Astronomical Society
Date: 02-2022
Abstract: Compact Object Mergers: Population Astrophysics and Statistics (COMPAS compas.science ) is a public rapid binary population synthesis code. COMPAS generates populations of isolated stellar binaries under a set of parameterized 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 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 that will be updated as new features are added to COMPAS the current document describes COMPAS v02.21.00.
Publisher: Oxford University Press (OUP)
Date: 08-2023
Abstract: Massive binaries are vital sources of various transient processes, including gravitational-wave mergers. However, large uncertainties in the evolution of massive stars, both physical and numerical, present a major challenge to the understanding of their binary evolution. In this paper, we upgrade our interpolation-based stellar evolution code metisse to include the effects of mass changes, such as binary mass transfer or wind-driven mass loss, not already included within the input stellar tracks. metisse’s implementation of mass loss (applied to tracks without mass loss) shows excellent agreement with the sse fitting formulae and with detailed mesa tracks, except in cases where the mass transfer is too rapid for the star to maintain equilibrium. We use this updated version of metisse within the binary population synthesis code bse to demonstrate the impact of varying stellar evolution parameters, particularly core overshooting, on the evolution of a massive (25 and 15 M⊙) binary system with an orbital period of 1800 d. Depending on the input tracks, we find that the binary system can form a binary black hole or a black hole–neutron star system, with primary (secondary) remnant masses ranging between 4.47 (1.36) and 12.30 (10.89) M⊙, and orbital periods ranging from 6 d to the binary becoming unbound. Extending this analysis to a population of isolated binaries uniformly distributed in mass and orbital period, we show that the input stellar models play an important role in determining which regions of the binary parameter space can produce compact binary mergers, paving the way for predictions for current and future gravitational-wave observatories.
Publisher: American Physical Society (APS)
Date: 07-08-2017
Publisher: American Physical Society (APS)
Date: 06-02-2012
Publisher: Springer Science and Business Media LLC
Date: 14-11-2022
Publisher: Oxford University Press (OUP)
Date: 29-04-2022
Abstract: We investigate the relationship between the global properties of star clusters and their double black hole (DBH) populations. We use the code NBODY6 to evolve a suite of star cluster models with an initial mass of $\\mathcal {O}(10^4)$M⊙ and varying initial parameters. We conclude that cluster metallicity plays the most significant role in determining the lifespan of a cluster, while the initial half-mass radius is dominant in setting the rate of BH exchange interactions in the central cluster regions. We find that the mass of interacting BHs, rather than how frequently their interactions with other BHs occur, is more crucial in the thermal expansion and eventual evaporation of the cluster. We formulate a novel approach to easily quantify the degree of BH-BH dynamical activity in each model. We report 12 in-cluster and three out-of-cluster (after ejection from the cluster) DBH mergers, of different types (inspiral, eccentric, and hierarchical) across the 10 N-body models presented. Our DBH merger efficiency is 3–4 × 10−5 mergers per M⊙. We note the cluster initial density plays the most crucial role in determining the number of DBH mergers, with the potential presence of a transitional density point (between 1.2 and 3.8 × 103 M⊙ pc−3) below which the number of in-cluster mergers increases with cluster density and above which the increased stellar density acts to prevent in-cluster BH mergers. The importance of the history of dynamical interactions within the cluster in setting up the pathways to ejected DBH mergers is also discussed.
Publisher: Oxford University Press (OUP)
Date: 10-05-2022
Abstract: The two neutron star–black hole mergers (GW200105 and GW200115) observed in gravitational waves by advanced LIGO and Virgo, mark the first ever discovery of such binaries in nature. We study these two neutron star–black hole systems through isolated binary evolution, using a grid of population synthesis models. Using both mass and spin observations (chirp mass, effective spin, and remnant spin) of the binaries, we probe their different possible formation channels in different metallicity environments. Our models only support LIGO data when assuming the black hole is non-spinning. Our results show a strong preference that GW200105 and GW200115 formed from stars with sub-solar metallicities Z ≲ 0.005. Only two metal-rich (Z = 0.02) models are in agreement with GW200115. We also find that chirp mass and remnant spins jointly aid in constraining the models, while the effective spin parameter does not add any further information. We also present the observable (i.e. post-selection effects) median values of spin and mass distribution from all our models, which may be used as a reference for future mergers. Further, we show that the remnant spin parameter distribution exhibits distinguishable features in different neutron star–black hole sub-populations. We find that non-spinning, first born black holes dominate significantly the merging neutron star–black hole population, ensuring electromagnetic counterparts to such mergers a rare affair.
Publisher: American Physical Society (APS)
Date: 02-04-2020
Publisher: American Association of Physics Teachers (AAPT)
Date: 07-2021
DOI: 10.1119/10.0003534
Abstract: In 2015, the first observation of gravitational waves marked a breakthrough in astrophysics and in technological research and development. The discovery of a gravitational-wave signal from the collision of two black holes, a billion light-years away, received considerable interest from the media and public. We describe the development of a purpose-built exhibit explaining this new area of research to a general audience. The core element of the exhibit is a working Michelson interferometer: a scaled-down version of the key technology used in gravitational-wave detectors. The Michelson interferometer is integrated into a hands-on exhibit, which allows for user interaction and simulated gravitational-wave observations. An interactive display provides a self-guided explanation of gravitational-wave related topics through video, animation, images, and text. We detail the hardware and software used to create the exhibit, and discuss two installation variants: An independent learning experience in a museum setting (the Thinktank Birmingham Science Museum) and a science-festival with the presence of expert guides (the 2017 Royal Society Summer Science Exhibition). We assess audience reception in these two settings, describe the improvements we have made given this information, and discuss future public-engagement projects resulting from this work. The exhibit is found to be effective in communicating the new and unfamiliar field of gravitational-wave research to general audiences. An accompanying website provides parts lists and information for others to build their own version of this exhibit.
Publisher: Oxford University Press (OUP)
Date: 17-05-2022
Abstract: 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 formed in electron-capture supernovae receive typical kicks less than 10 km s−1. We have searched the catalogue of observed binary pulsars, but find no convincing candidates that could be formed through this channel, consistent with this low predicted rate. Future observations with the Square Kilometre Array may detect this rare sub-class of binary pulsar and provide strong constraints on the properties of electron-capture supernovae and their progenitors.
Publisher: American Physical Society (APS)
Date: 02-09-2020
Publisher: American Physical Society (APS)
Date: 09-06-2021
Publisher: American Physical Society (APS)
Date: 23-08-2013
Publisher: Verein zur Forderung des Open Access Publizierens in den Quantenwissenschaften
Date: 22-09-2022
DOI: 10.22331/Q-2022-09-22-815
Abstract: We propose an extension to the Pauli stabiliser formalism that includes fractional 2 & #x03C0 / N rotations around the Z axis for some integer N . The resulting generalised stabiliser formalism – denoted the XP stabiliser formalism – allows for a wider range of states and codespaces to be represented. We describe the states which arise in the formalism, and demonstrate an equivalence between XP stabiliser states and 'weighted hypergraph states' – a generalisation of both hypergraph and weighted graph states. Given an arbitrary set of XP operators, we present algorithms for determining the codespace and logical operators for an XP code. Finally, we consider whether measurements of XP operators on XP codes can be classically simulated.
Publisher: American Astronomical Society
Date: 28-08-2015
Publisher: Springer Science and Business Media LLC
Date: 15-08-2022
DOI: 10.1038/S41467-022-32236-W
Abstract: Coupling qubits to a superconducting resonator provides a mechanism to enable long-distance entangling operations in a quantum computer based on spins in semiconducting materials. Here, we demonstrate a controllable spin-photon coupling based on a longitudinal interaction between a spin qubit and a resonator. We show that coupling a singlet-triplet qubit to a high-impedance superconducting resonator can produce the desired longitudinal coupling when the qubit is driven near the resonator’s frequency. We measure the energy splitting of the qubit as a function of the drive litude and frequency of a microwave signal applied near the resonator antinode, revealing pronounced effects close to the resonator frequency due to longitudinal coupling. By tuning the litude of the drive, we reach a regime with longitudinal coupling exceeding 1 MHz. This mechanism for qubit-resonator coupling represents a stepping stone towards producing high-fidelity two-qubit gates mediated by a superconducting resonator.
Publisher: Springer Science and Business Media LLC
Date: 05-04-2017
DOI: 10.1038/NCOMMS14906
Abstract: 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 ≳160 M ⊙ , ≳60 M ⊙ and ≳90 M ⊙ , for GW150914, GW151226 and LVT151012, respectively.
Publisher: American Physical Society (APS)
Date: 11-07-2019
Publisher: American Physical Society (APS)
Date: 09-04-2018
Publisher: Oxford University Press (OUP)
Date: 04-07-2022
Abstract: Making the most of the rapidly increasing population of gravitational-wave detections of black hole (BH) and neutron star (NS) mergers requires comparing observations with population synthesis predictions. In this work, we investigate the combined impact from the key uncertainties in population synthesis modelling of the isolated binary evolution channel: the physical processes in massive binary-star evolution and the star formation history as a function of metallicity, Z, and redshift z, $\\mathcal {S}(Z,z)$. Considering these uncertainties, we create 560 different publicly available model realizations and calculate the rate and distribution characteristics of detectable BHBH, BHNS, and NSNS mergers. We find that our stellar evolution and $\\mathcal {S}(Z,z)$ variations can combined impact the predicted intrinsic and detectable merger rates by factors in the range 102–104. We find that BHBH rates are dominantly impacted by $\\mathcal {S}(Z,z)$ variations, NSNS rates by stellar evolution variations and BHNS rates by both. We then consider the combined impact from all uncertainties considered in this work on the detectable mass distribution shapes (chirp mass, in idual masses, and mass ratio). We find that the BHNS mass distributions are predominantly impacted by massive binary-star evolution changes. For BHBH and NSNS, we find that both uncertainties are important. We also find that the shape of the delay time and birth metallicity distributions are typically dominated by the choice of $\\mathcal {S}(Z,z)$ for BHBH, BHNS, and NSNS. We identify several ex les of robust features in the mass distributions predicted by all 560 models, such that we expect more than 95 per cent of BHBH detections to contain a BH $\\gtrsim 8\\, \\rm {M}_{\\odot }$ and have mass ratios ≲ 4. Our work demonstrates that it is essential to consider a wide range of allowed models to study double compact object merger rates and properties. Conversely, larger observed s les could allow us to decipher currently unconstrained stages of stellar and binary evolution.
Publisher: IOP Publishing
Date: 22-12-2014
Publisher: American Physical Society (APS)
Date: 05-08-2022
Publisher: American Physical Society (APS)
Date: 27-12-2022
Publisher: EDP Sciences
Date: 03-2020
DOI: 10.1051/0004-6361/201936204
Abstract: 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 χ eff , the chirp mass M chirp and the cosmological redshift of merger z merger . 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 χ eff 0.1, while the remaining 20% of events with χ eff ≥ 0.1 are split into ∼10% with M chirp 15 M ⊙ and ∼10% with M chirp ≥ 15 M ⊙ . Moreover, we find that M chirp and χ eff 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.
Publisher: American Astronomical Society
Date: 2022
Abstract: The LIGO/Virgo gravitational-wave observatories have detected at least 50 double black hole (BH) coalescences. This s le is large enough to have allowed several recent studies to draw conclusions about the implied branching ratios between isolated binaries versus dense stellar clusters as the origin of double BHs. It has also led to the exciting suggestion that the population is highly likely to contain primordial BHs. Here we demonstrate that such conclusions cannot yet be robust because of the large current uncertainties in several key aspects of binary stellar evolution. These include the development and survival of a common envelope, the mass and angular-momentum loss during binary interactions, mixing in stellar interiors, pair-instability mass loss, and supernova outbursts. Using standard tools such as the rapid population synthesis codes StarTrack and COMPAS and the detailed stellar evolution code MESA , we examine as a case study the possible future evolution of Melnick 34, the most massive known binary star system (with initial component masses of 144 M ⊙ and 131 M ⊙ ). We show that, despite its fairly well-known orbital architecture, various assumptions regarding stellar and binary physics predict a wide variety of outcomes: from a close BH–BH binary (which would lead to a potentially detectable coalescence), through a wide BH–BH binary (which might be seen in microlensing observations), or a Thorne–Żytkow object, to a complete disruption of both objects by a pair-instability supernova. Thus, because the future of massive binaries is inherently uncertain, sound predictions about the properties of BH–BH systems formed in the isolated binary evolution scenario are highly challenging at this time. Consequently, it is premature to draw conclusions about the formation channel branching ratios that involve isolated binary evolution for the LIGO/Virgo BH–BH merger population.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2016
End Date: 2017
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2022
End Date: 2025
Funder: Australian Research Council
View Funded ActivityStart Date: 03-2022
End Date: 02-2025
Amount: $421,540.00
Funder: Australian Research Council
View Funded Activity