26 research outputs found
The correlation of field binary black hole mergers and how 3G gravitational-wave detectors can constrain it
Understanding the origin of merging binary black holes is currently one of
the most pressing quests in astrophysics. We show that if isolated binary
evolution dominates the formation mechanism of merging binary black holes, one
should expect a correlation between the effective spin parameter,
, and the redshift of the merger, , of binary black
holes. This correlation comes from tidal spin-up systems preferentially forming
and merging at higher redshifts due to the combination of weaker orbital
expansion from low metallicity stars given their reduced wind mass loss rate,
delayed expansion and have smaller maximal radii during the supergiant phase
compared to stars at higher metallicity. As a result, these tightly bound
systems merge with short inspiral times. Given our fiducial model of isolated
binary evolution, we show that the origin of a
correlation in the detectable LIGO--Virgo binary black hole population is
different from the intrinsic population, which will become accessible only in
the future by third-generation gravitational-wave detectors such as Einstein
Telescope and Cosmic Explorer. Finally, we compare our model predictions with
population predictions based on the current catalog of binary black hole
mergers and find that current data favor a positive correlation of
as predicted by our model of isolated binary evolution.Comment: 14 pages, 10 figures, submitted to A&
One Channel to Rule Them All? Constraining the Origins of Binary Black Holes using Multiple Formation Pathways
The second LIGO-Virgo catalog of gravitational wave transients has more than
quadrupled the observational sample of binary black holes. We analyze this
catalog using a suite of five state-of-the-art binary black hole population
models covering a range of isolated and dynamical formation channels and infer
branching fractions between channels as well as constraints on uncertain
physical processes that impact the observational properties of mergers. Given
our set of formation models, we find significant differences between the
branching fractions of the underlying and detectable populations, and that the
diversity of detections suggests that multiple formation channels are at play.
A mixture of channels is strongly preferred over any single channel dominating
the detected population: an individual channel does not contribute to more than
of the observational sample of binary black holes. We calculate
the preference between the natal spin assumptions and common envelope
efficiencies in our models, favoring natal spins of isolated black holes of
, and marginally preferring common envelope efficiencies of
while strongly disfavoring highly inefficient common envelopes.
We show that it is essential to consider multiple channels when interpreting
gravitational wave catalogs, as inference on branching fractions and physical
prescriptions becomes biased when contributing formation scenarios are not
considered or incorrect physical prescriptions are assumed. Although our
quantitative results can be affected by uncertain assumptions in model
predictions, our methodology is capable of including models with updated
theoretical considerations and additional formation channels.Comment: 27 pages (14 pages main text + 13 pages appendices/references), 8
figures, 1 table, published in Ap
Active Learning for Computationally Efficient Distribution of Binary Evolution Simulations
Binary stars undergo a variety of interactions and evolutionary phases,
critical for predicting and explaining observed properties. Binary population
synthesis with full stellar-structure and evolution simulations are
computationally expensive requiring a large number of mass-transfer sequences.
The recently developed binary population synthesis code POSYDON incorporates
grids of MESA binary star simulations which are then interpolated to model
large-scale populations of massive binaries. The traditional method of
computing a high-density rectilinear grid of simulations is not scalable for
higher-dimension grids, accounting for a range of metallicities, rotation, and
eccentricity. We present a new active learning algorithm, psy-cris, which uses
machine learning in the data-gathering process to adaptively and iteratively
select targeted simulations to run, resulting in a custom, high-performance
training set. We test psy-cris on a toy problem and find the resulting training
sets require fewer simulations for accurate classification and regression than
either regular or randomly sampled grids. We further apply psy-cris to the
target problem of building a dynamic grid of MESA simulations, and we
demonstrate that, even without fine tuning, a simulation set of only
the size of a rectilinear grid is sufficient to achieve the same classification
accuracy. We anticipate further gains when algorithmic parameters are optimized
for the targeted application. We find that optimizing for classification only
may lead to performance losses in regression, and vice versa. Lowering the
computational cost of producing grids will enable future versions of POSYDON to
cover more input parameters while preserving interpolation accuracies.Comment: 20 pages (16 main text), 10 figures, submitted to Ap
X-ray luminosity function of high-mass X-ray binaries: Studying the signatures of different physical processes using detailed binary evolution calculations
The ever-expanding observational sample of X-ray binaries (XRBs) makes them
excellent laboratories for constraining binary evolution theory. Such
constraints can be obtained by studying the effects of various physical
assumptions on synthetic X-ray luminosity functions (XLFs) and comparing to
observed XLFs. In this work, we focus on high-mass XRBs (HMXBs) and study the
effects on the XLF of various, poorly-constrained assumptions regarding
physical processes such as the common-envelope phase, the core-collapse, and
wind-fed accretion. We use the new binary population synthesis code POSYDON,
which employs extensive pre-computed grids of detailed stellar structure and
binary evolution models, to simulate the evolution of binaries. We generate 96
synthetic XRB populations corresponding to different combinations of model
assumptions. The generated HMXB XLFs are feature-rich, deviating from the
commonly assumed single-power law. We find a break in our synthetic XLF at
luminosity erg s, similar to observed XLFs. However, we
find also a general overabundance of XRBs (up to a factor of 10 for
certain model parameter combinations) driven primarily by XRBs with black hole
accretors. Assumptions about the transient behavior of Be-XRBs, asymmetric
supernova kicks, and common-envelope physics can significantly affect the shape
and normalization of our synthetic XLFs. We find that less well-studied
assumptions regarding the circularization of the orbit at the onset of
Roche-lobe overflow and criteria for the formation of an X-ray emitting
accretion disk around wind-accreting black holes can also impact our synthetic
XLFs. Our study reveals the importance of large-scale parameter studies,
highlighting the power of XRBs in constraining binary evolution theory.Comment: 31 pages, 32 figures, Accepted by A&A. Fixed typos and updated
references. Referee's comments were addresse
A Black Hole Kicked At Birth: MAXI J1305-704
When a compact object is formed in a binary, any mass lost during core
collapse will impart a kick on the binary's center of mass. Asymmetries in this
mass loss would impart an additional natal kick on the remnant black hole or
neutron star, whether it was formed in a binary or in isolation. While it is
well established that neutron stars receive natal kicks upon formation, it is
unclear whether black holes do as well. Here, we consider the low-mass X-ray
binary MAXI J1305-704, which has been reported to have a space velocity
200 km/s. In addition to integrating its trajectory to infer its
velocity upon formation of its black hole, we reconstruct its evolutionary
history, accounting for recent estimates of its period, black hole mass, mass
ratio, and donor effective temperature from photometric and spectroscopic
observations. We find that if MAXI J1305-704 formed via isolated binary
evolution in the thick Galactic disk, then its black hole received a natal kick
of at least 70 km/s with 95\% confidence.Comment: To be submitted; 9 pages, 5 figure
Searching for candidates of coalescing binary black holes formed through chemically homogeneous evolution in GWTC-3
The LIGO, Virgo, and KAGRA (LVK) collaboration has announced 90 coalescing
binary black holes (BBHs) with to date, however, the
origin of their formation channels is still an open scientific question. Given
various properties of BBHs (BH component masses and individual spins) inferred
using the default priors by the LVK, independent groups have been trying to
explain the formation of the BBHs with different formation channels. Of all
formation scenarios, the chemically homogeneous evolution (CHE) channel has
stood out with distinguishing features, namely, nearly-equal component masses
and preferentially high individual spins aligned with the orbital angular
momentum. We perform Bayesian inference on the BBH events officially reported
in GWTC-3 with astrophysically-predicted priors representing different
formation channels of the isolated binary evolution (CEE: common-envelope
evolution channel; CHE; SMT: stable mass transfer). Given assumed models, we
report strong evidence for GW190517\_055101 being most likely to have formed
through the CHE channel. Assuming the BBH events in the subsample are all
formed through one of the isolated binary evolution channels, we obtain the
lower limits on the local merger rate density of these channels at (CEE), (CHE), and
(SMT) at credible level.Comment: 13 pages, 4 figures, 1 tabl
The impact of mass-transfer physics on the observable properties of field binary black hole populations
We study the impact of mass-transfer physics on the observable properties of
binary black hole populations formed through isolated binary evolution. We
investigate the impact of mass-accretion efficiency onto compact objects and
common-envelope efficiency on the observed distributions of ,
and . We find that low common envelope efficiency translates to
tighter orbits post common envelope and therefore more tidally spun up
second-born black holes. However, these systems have short merger timescales
and are only marginally detectable by current gravitational-waves detectors as
they form and merge at high redshifts (), outside current detector
horizons. Assuming Eddington-limited accretion efficiency and that the
first-born black hole is formed with a negligible spin, we find that all
non-zero systems in the detectable population can come only from
the common envelope channel as the stable mass-transfer channel cannot shrink
the orbits enough for efficient tidal spin-up to take place. We find the local
rate density () for the common envelope channel is in the range
considering a range of while for the stable mass transfer channel the rate density is . The latter drops by two orders of magnitude if the mass
accretion onto the black hole is not Eddington limited because conservative
mass transfer does not shrink the orbit as efficiently as non-conservative mass
transfer does. Finally, using GWTC-2 events, we constrain the lower bound of
branching fraction from other formation channels in the detected population to
be . Assuming all remaining events to be formed through either stable
mass transfer or common envelope channels, we find moderate to strong evidence
in favour of models with inefficient common envelopes.Comment: 26 pages, 13 figures, accepted for publication in A&
Investigating the Lower Mass Gap with Low Mass X-ray Binary Population Synthesis
Mass measurements from low-mass black hole X-ray binaries (LMXBs) and radio
pulsars have been used to identify a gap between the most massive neutron stars
(NSs) and the least massive black holes (BHs). BH mass measurements in LMXBs
are typically only possible for transient systems: outburst periods enable
detection via all-sky X-ray monitors, while quiescent periods enable
radial-velocity measurements of the low-mass donor. We quantitatively study
selection biases due to the requirement of transient behavior for BH mass
measurements. Using rapid population synthesis simulations (COSMIC), detailed
binary stellar-evolution models (MESA), and the disk instability model of
transient behavior, we demonstrate that transient-LMXB selection effects
introduce observational biases, and can suppress mass-gap BHs in the observed
sample. However, we find a population of transient LMXBs with mass-gap BHs form
through accretion-induced collapse of a NS during the LMXB phase, which is
inconsistent with observations. These results are robust against variations of
binary evolution prescriptions. The significance of this accretion-induced
collapse population depends upon the maximum NS birth mass . To reflect the observed dearth of low-mass BHs, COSMIC and MESA
models favor . In the absence of
further observational biases against LMXBs with mass-gap BHs, our results
indicate the need for additional physics connected to the modeling of LMXB
formation and evolution.Comment: 21 pages, accepted to Ap
POSYDON: A General-Purpose Population Synthesis Code with Detailed Binary-Evolution Simulations
Most massive stars are members of a binary or a higher-order stellar systems,
where the presence of a binary companion can decisively alter their evolution
via binary interactions. Interacting binaries are also important astrophysical
laboratories for the study of compact objects. Binary population synthesis
studies have been used extensively over the last two decades to interpret
observations of compact-object binaries and to decipher the physical processes
that lead to their formation. Here, we present POSYDON, a novel, binary
population synthesis code that incorporates full stellar-structure and
binary-evolution modeling, using the MESA code, throughout the whole evolution
of the binaries. The use of POSYDON enables the self-consistent treatment of
physical processes in stellar and binary evolution, including: realistic
mass-transfer calculations and assessment of stability, internal
angular-momentum transport and tides, stellar core sizes, mass-transfer rates
and orbital periods. This paper describes the detailed methodology and
implementation of POSYDON, including the assumed physics of stellar- and
binary-evolution, the extensive grids of detailed single- and binary-star
models, the post-processing, classification and interpolation methods we
developed for use with the grids, and the treatment of evolutionary phases that
are not based on pre-calculated grids. The first version of POSYDON targets
binaries with massive primary stars (potential progenitors of neutron stars or
black holes) at solar metallicity.Comment: 60 pages, 33 figures, 8 tables, referee's comments addressed. The
code and the accompanying documentations and data products are available at
https:\\posydon.or
Astrophysics with the Laser Interferometer Space Antenna
Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy as it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and other space-based instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed: ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or intermediate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help make progress in the different areas. New research avenues that LISA itself, or its joint exploitation with studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe