Binary Origin Research Articles

New results on the gamma-ray burst variability--luminosity relation

At the dawn of the gamma--ray burst (GRB) afterglow era, a Cepheid-like correlation was discovered between the time variability $V$ and the isotropic-equivalent peak luminosity $L_ iso $ of the prompt emission of about a dozen long GRBs with measured redshift available at that time. Soon afterwards, the correlation was confirmed in a sample of about 30 GRBs, even though it was affected by significant scatter. Unlike the minimum variability timescale (MVT), $V$ measures the relative power of short-to-intermediate timescales. We aim to test the correlation using about 200 long GRBs with spectroscopically measured redshift, detected by Swift Fermi and Konus/ WIND for which both observables can be accurately estimated. The variability for all selected GRBs was calculated according to the original definition using the 64 ms background-subtracted light curves of Swift /BAT ( Fermi /GBM) in the 15--150 (8--900) keV energy passband. Peak luminosities were either taken from the literature or derived from modelling broad-band spectra acquired with either Konus/ WIND or Fermi /GBM. The statistical significance of the correlation has weakened to $ 2$<!PCT!>, mostly due to the appearance of a number of smooth and luminous GRBs that are characterised by a relatively small $V$. At odds with most long GRBs, three out of four long-duration merger candidates have high $V$ and low iso The luminosity is more tightly connected with shortest timescales measured by MVT than the short to intermediate timescales measured by $V$. We discuss the implications for internal dissipation models and the role of the $e^ pm $ photosphere. We identified a few smooth GRBs with a single broad pulse and low $V$ that might have an external shock origin, in contrast with most GRBs. The combination of high variability $(V 0.1)$, low luminosity iso $ erg s$^ $, and short MVT ($ 0.1$ s) could be a good indicator for a compact binary merger origin.

Eccentricity Estimation for Five Binary Black Hole Mergers with Higher-order Gravitational-wave Modes

The detection of orbital eccentricity for a binary black hole system via gravitational waves is a key signature to distinguish between the possible binary origins. The identification of eccentricity has been difficult so far due to the limited availability of eccentric gravitational waveforms over the full range of black hole masses and eccentricities. Here we evaluate the eccentricity of five black hole mergers detected by the LIGO and Virgo observatories using the TEOBResumS-DALI, TEOBResumS-GIOTTO, and TEOBResumSP models. This analysis studies eccentricities up to 0.6 at the reference frequency of 5 Hz and incorporates higher-order gravitational-wave modes critical to model emission from highly eccentric orbits. The binaries have been selected due to previous hints of eccentricity or due to their unusual mass and spin. While other studies found marginal evidence for eccentricity for some of these events, our analyses do not favor the incorporation of eccentricity compared to the quasi-circular case. While lacking the eccentric evidence of other analyses, we find our analyses marginally shifts the posterior in multiple parameters for several events when allowing eccentricity to be nonzero.

Missing metals in DQ stars: a compelling clue to their origin

ABSTRACT White dwarf stars frequently experience external pollution by heavy elements, and yet the intrinsically carbon-enriched DQ spectral class members fail to exhibit this phenomenon, representing a decades-old conundrum. This study reports a high-resolution spectroscopic search for Ca ii in classical DQ white dwarfs, finding that these stars are stunted both in pollution frequency and heavy element mass fractions, relative to the wider population. Compared to other white dwarf spectral classes, the average external accretion rate is found to be at least three orders of magnitude lower in the DQ stars. Several hypotheses are considered which need to simultaneously account for (i) an apparent lack of accreted metals, (ii) a dearth of circumstellar planetary material, (iii) an observed deficit of unevolved companions in post-common envelope binaries, (iv) relatively low helium mass fractions, and remnant masses that appear smaller than for other spectral classes, (v) a high incidence of strong magnetism, and (vi) modestly older disc kinematics. Only one hypothesis is consistent with all these constraints, suggesting DQ white dwarfs are the progeny of binary evolution that altered both their stellar structures and their circumstellar environments. A binary origin is already suspected for the warmer and more massive DQ stars, and is proposed here as an inclusive mechanism to expose core carbon material, in a potential evolutionary unification for the entire DQ spectral class. In this picture, DQ stars are not descended from DA or DB white dwarfs that commonly host dynamically active planetary systems.

Binary origin of blue straggler stars in Galactic star clusters

Building on the recent release of a new Gaia -based blue straggler star catalog in Galactic open star clusters (OCs), we explored the properties of these stars in a cluster sample spanning a wide range in fundamental parameters. We employed Gaia EDR3 to assess the membership of any individual blue or yellow straggler to their parent cluster. We then made use of the ASteCA code to estimate the fundamental parameters of the selected clusters, in particular, the binary fraction. With all this at hand, we critically revisited the relation of the blue straggler population and the latter. For the first time, we found a correlation between the number of blue stragglers and the host cluster binary fraction and binaries. This supports the hypothesis that binary evolution is the most viable scenario of straggler formation in Galactic star clusters. The distribution of blue stragglers in the Gaia color-magnitude diagram was then compared with a suite of composite evolutionary sequences derived from binary evolutionary models that were run by exploring a range of binary parameters: age, mass ratio, period, and so forth. The excellent comparison between the bulk distribution of blue stragglers and the composite evolutionary sequences loci further supports the binary origin of most stragglers in OCs and paves the way for a detailed study of individual blue stragglers.

Considering the Single and Binary Origins of the Type IIP SN 2017eaw

Current population synthesis modeling suggests that 30%–50% of Type II supernovae originate from binary progenitors; however, the identification of a binary progenitor is challenging. One indicator of a binary progenitor is that the surrounding stellar population is too old to contain a massive single star. Measurements of the progenitor mass of SN 2017eaw are starkly divided between observations made temporally close to core collapse, which show a progenitor mass of 13–15 M ⊙ (final helium-core mass MHe,core=4.4–6.0M⊙ —which is a more informative property than initial mass) and those from the stellar population surrounding the SN, which find M ≤ 10.8 M ⊙ ( MHe,core≤3.4M⊙ ). In this paper, we reanalyze the surrounding stellar population with improved astrometry and photometry, finding a median age of 16.8−1.0+3.2 Myr for all stars younger than 50 Myr ( MHe,core=4.7M⊙ ) and 85.9−6.5+3.2 Myr for stars younger than 150 Myr. 16.8 Myr is now consistent with the helium-core mass range derived from the temporally near-explosion observations for single stars. Applying the combined constraints to population synthesis models, we determine that the probability of the progenitor of SN 2017eaw being an initially single star is 65% compared to 35% for prior binary interaction. 85.9 Myr is inconsistent with any formation scenarios. We demonstrate that combining progenitor age constraints with helium-core mass estimates from red supergiant SED modeling, late-time spectra, and indirectly from light-curve modeling can help to differentiate single and binary progenitor scenarios and provide a framework for the application of this technique to future observations.

A comparative study of three modes of s-process nucleosynthesis in extremely metal-poor AGB stars

Abstract Carbon-enhanced metal-poor (CEMP) stars in the Galactic halo have a wide range of neutron-capture element abundance patterns. To identify their origin, we investigate three modes of s-process nucleosynthesis that have been proposed to operate in extremely metal-poor asymptotic giant branch (AGB) stars: convective 13C burning, which occurs when hydrogen is engulfed by helium-flash convection in low-mass AGB stars; convective 22Ne burning, which occurs in helium-flash convection of intermediate-mass AGB stars; and radiative 13C burning, which occurs in the 13C pocket that is formed during inter-pulse periods. We show that the production of s-process elements per iron seed (s-process efficiency) does not depend on metallicity below [Fe$/$H] = −2, because 16O in the helium zone dominates the neutron poison. The convective 13C mode can produce a variety of s-process efficiencies for Sr, Ba, and Pb, including the maxima observed among CEMP stars. The 22Ne mode only produces the lowest end of s-process efficiencies among CEMP models. We show that the combination of these two modes can explain the full range of observed enrichment of s-process elements in CEMP stars. In contrast, the 13C pocket mode can hardly explain the high level of enrichment observed in some CEMP stars, even if considering star-to-star variations of the mass of the 13C pocket. These results provide a basis for discussing the binary mass transfer origin of CEMP stars and their subgroups.

Exploring the Observability of Surviving Companions of Stripped-envelope Supernovae: A Case Study of Type Ic SN 2020oi

Stripped-envelope (SE) supernovae (SNe) were considered as the explosions of single massive stars with strong stellar winds, while later observations favor binary origins. One direct piece of evidence to support the binary origins is to find the surviving companions of SE SNe because previous numerical studies suggested that the binary companion should survive the SN impact and could be detectable. Recently, Gagliano et al. reported that the nearby Type Ic SN 2020oi in M100 (∼17.1 Mpc) resulted from a binary system based on the Hubble Space Telescope photometric and spectroscopic observation. Based on the suggested binary properties of SN 2020oi, we conduct 2D hydrodynamics simulations of SN–companion interactions and the subsequent post-impact evolution of the companion. Our results suggest that a surviving companion becomes brighter in 2 orders of magnitude and temporarily redder after the SN impact. The companion might be detectable with the JWST NIRCam short-wavelength channel in a few years. Furthermore, the predicted magnitudes of surviving companions show a significant magnitude gradient around the peak. This could be another indicator to identify the surviving companion from an SE SN.

Expectations for fast radio bursts in neutron star–massive star binaries

Context. Recent observations of a small sample of repeating fast radio bursts (FRBs) have revealed a periodicity in their bursting activity that suggests a binary origin for the modulation. Aims. We set out to explore the scenario where a subset of repeating FRBs originates in binary systems that host a highly energetic neutron star and a massive companion star, akin to γ-ray binaries and young high-mass X-ray binaries. Methods. In this scenario, we infer observables, compare them with current observational constraints, and make predictions for future observations. Firstly, we specifically focused on the host galaxy properties and binary formation rates. Subsequently, we investigated the expected evolution of the rotation and dispersion measure in this scenario, the predicted birth site offsets, and the origin of the persistent radio emission observed in a subset of these systems. Results. The host galaxies for repeating FRBs favour the formation of neutron star–massive star binary systems, but any conclusive evidence will require future discoveries and localisations of FRBs. The birth rate of high-mass X-ray binaries, used as a proxy for all considered binaries, significantly exceeds the estimated rate of FRBs, which can be explained if only a small subset of these systems produce FRBs. We show that, under simple assumptions, we can reproduce the dispersion measure and rotation measure evolution that is seen in a subset of repeating FRBs. We also discuss the possibility of detecting a persistent radio source associated with the FRB due to an intra-binary shock between the companion star wind and either the pulsar wind or giant magnetar flares. The observed long-term luminosity stability of the persistent radio sources is most consistent with a giant flare-powered scenario. However, this explanation is highly dependent on the magnetic field properties of the neutron star. Conclusions. With these explorations, we provide a framework to discuss future FRB observations in the context of neutron star–massive star binary scenarios. We conclude that more localisations and observations of repeaters will be necessary to conclusively determine or rule out a connection between (repeating) FRBs and such binaries.

Radio jet precession in M 81*

We report four novel position angle measurements of the core region M 81* at 5 GHz and 8 GHz, which confirm the presence of sinusoidal jet precession in the M 81 jet region, as suggested by Martí-Vidal et al. (2011, A&A, 533, A111). The model makes three testable predictions regarding the evolution of the jet precession, which we test in our data with observations from 2017, 2018, and 2019. Our data confirm a precession period of ∼7 yr on top of a small linear drift. We further show that two 8 GHz observation are consistent with a precession period of ∼7 yr but show a different time lag with respect to the 5 GHz and 1.7 GHz observations. We do not find a periodic modulation of the light curve with the jet precession and therefore rule out a Doppler nature for the historic 1998–2002 flare. Our observations are consistent with either a binary black hole origin for the precession or the Lense-Thirring effect.

A Binary Origin for the First Isolated Stellar-mass Black Hole Detected with Astrometric Microlensing

The Milky Way is believed to host hundreds of millions of quiescent stellar-mass black holes (BHs). In the last decade, some of these objects have been potentially uncovered via gravitational microlensing events. All these detections resulted in a degeneracy between the velocity and the mass of the lens. This degeneracy has been lifted, for the first time, with the recent astrometric microlensing detection of OB110462. However, two independent studies reported very different lens masses for this event. Sahu et al. inferred a lens mass of 7.1 ± 1.3 M ⊙, consistent with a BH, while Lam et al. inferred 1.6–4.2 M ⊙, consistent with either a neutron star or a BH. Here, we study the landscape of isolated BHs formed in the field. In particular, we focus on the mass and center-of-mass speed of four subpopulations: isolated BHs from single-star origin, disrupted BHs of binary-star origin, main-sequence stars with a compact object companion, and double compact object mergers. Our model predicts that most (≳70%) isolated BHs in the Milky Way are of binary origin. However, noninteractions lead to most massive BHs (≳15–20 M ⊙) being predominantly of single origin. Under the assumption that OB110462 is a free-floating compact object, we conclude that it is more likely to be a BH originally belonging to a binary system. Our results suggest that low-mass BH microlensing events can be useful to understand binary evolution of massive stars in the Milky Way, while high-mass BH lenses can be useful to probe single stellar evolution.

On the Jacobi capture origin of binaries with applications to the Earth-Moon system and black holes in galactic nuclei

ABSTRACT Close encounters between two bodies in a disc often result in a single orbital deflection. However, within their Jacobi volumes, where the gravitational forces between the two bodies and the central body become competitive, temporary captures with multiple close encounters become possible outcomes: a Jacobi capture. We perform three-body simulations in order to characterize the dynamics of Jacobi captures in the plane. We find that the phase space structure resembles a Cantor-like set with a fractal dimension of about 0.4. The lifetime distribution decreases exponentially, while the distribution of the closest separation follows a power law with index 0.5. In our first application, we consider the Jacobi capture of the Moon. We demonstrate that both tidal captures and giant impacts are possible outcomes. The impact speed is well approximated by a parabolic encounter, while the impact angles follow that of a uniform beam on a circular target. Jacobi captures at larger heliocentric distances are more likely to result in tidal captures. In our second application, we find that Jacobi captures with gravitational wave dissipation can result in the formation of binary black holes in galactic nuclei. The eccentricity distribution is approximately superthermal and includes both prograde and retrograde orientations. We conclude that dissipative Jacobi captures form an efficient channel for binary formation, which motivates further research into establishing the universality of Jacobi captures across multiple astrophysical scales.

Outliers in the Ep,z – Eγ relation of Fermi-GBM long-duration gamma-ray bursts

ABSTRACT Long gamma-ray bursts (GRBs) are typically associated with massive star core collapse, while the short GRBs are associated with compact binary mergers. However, recent evidence indicates that some peculiar long-duration bursts may correspond to compact binary mergers origins. In this paper, we use the data of the Fermi Gamma-ray Burst Monitor to search for peculiar long-duration bursts which may be from compact binary mergers based on outlier events in the $E_{p,z}\!-\!E_{\gamma ,\rm iso}$ relation. We obtained 10 outlier events by systematically analysing bursts with $T_{90}\gt 4.2 \rm \ s$ from 2008 August to 2021 July. In order to determine whether these outlier events were from compact binary mergers, we analysed their properties, including spectral lag, hardness ratio, and energy-hardness parameter. Based on the distributions of T90 − HR and T90 − Ep, we calculated the probability of outlier events belonging to the short GRBs. Our analysis indicates that GRB 120304B is likely to arise from the merger of a neutron star and a massive white dwarf. GRB 150210A is likely to arise from massive star core collapse. The other eight GRBs are fuzzy bursts that have both long and short GRBs properties. Additionally, we find that outlier samples have relatively high Ep and low fluences.

Discovery of a Binary-origin Classical Cepheid in a Binary System with a 59 day Orbital Period* *Based on observations collected at the European Southern Observatory, Chile. † †This Letter includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

We report the discovery of a surprising binary configuration of the double-mode Cepheid OGLE-LMC-CEP-1347 pulsating in the first (P 1 = 0.690 days) and second-overtone (P 2 = 0.556 days) modes. The orbital period (P orb = 59 days) of the system is five times shorter than the shortest known to date (310 days) for a binary Cepheid. The Cepheid itself is also the shortest-period one ever found in a binary system and the first double-mode Cepheid in a spectroscopically double-lined binary. OGLE-LMC-CEP-1347 is most probably on its first crossing through the instability strip, as inferred from both its short period and fast period increase, consistent with evolutionary models, and from the short orbital period (not expected for binary Cepheids whose components have passed through the red giant phase). Our evolutionary analysis yielded a first-crossing Cepheid with a mass in a range of 2.9–3.4 M ⊙ (lower than any measured Cepheid mass), consistent with observations. The companion is a stable star, at least two times fainter and less massive than the Cepheid (preliminary mass ratio q = 0.55), while also redder and thus at the subgiant or more advanced evolutionary stage. To match these characteristics, the Cepheid has to be a product of binary interaction, most likely a merger of two less massive stars, which makes it the second known classical Cepheid of binary origin. Moreover, further evolution of the components may lead to another binary interaction.

The white dwarf binary pathways survey – VIII. A post-common envelope binary with a massive white dwarf and an active G-type secondary star

ABSTRACT The white dwarf binary pathways survey is dedicated to studying the origin and evolution of binaries containing a white dwarf and an intermediate-mass secondary star of the spectral type A, F, G, or K (WD + AFGK). Here, we present CPD-65 264, a new post-common envelope binary with an orbital period of 1.37 d that contains a massive white dwarf ($0.86\pm 0.06\, \mathrm{M}_{\odot }$) and an intermediate-mass ($1.00\pm 0.05\, \mathrm{M}_{\odot }$) main-sequence secondary star. We characterized the secondary star and measured the orbital period using high-resolution optical spectroscopy. The white dwarf parameters are determined from HST spectroscopy. In addition, TESS observations revealed that up to 19 per cent of the surface of the secondary is covered with starspots. Small period changes found in the light curve indicate that the secondary is the second example of a G-type secondary star in a post-common envelope binary with latitudinal differential rotation. Given the relatively large mass of the white dwarf and the short orbital period, future mass transfer will be dynamically and thermally stable and the system will evolve into a cataclysmic variable. The formation of the system can be understood assuming common envelope evolution without contributions from energy sources besides orbital energy. CPD-65 264 is the seventh post-common envelope binaries with intermediate-mass secondaries that can be understood assuming a small efficiency in the common envelope energy equation, in agreement with findings for post-common envelope binaries with M-dwarf or substellar companions.

Tossing Black Hole Spin Axes

The detection of double black hole (BH+BH) mergers provides a unique possibility to understand their physical properties and origin. To date, the LIGO–Virgo–KAGRA network of high-frequency gravitational-wave observatories has announced the detection of more than 85 BH+BH merger events. An important diagnostic feature that can be extracted from the data is the distribution of effective inspiral spins of the BHs. This distribution is in clear tension with theoretical expectations from both an isolated binary star origin, which traditionally predicts close-to-aligned BH component spins, and formation via dynamical interactions in dense stellar environments that predicts a symmetric distribution of effective inspiral spins. Here it is demonstrated that isolated binary evolution can convincingly explain the observed data if BHs have their spin axis tossed during their formation process in the core collapse of a massive star, similarly to the process evidently acting in newborn neutron stars. BH formation without spin-axis tossing, however, has difficulties reproducing the observed data—even if alignment of spins prior to the second core collapse is disregarded. Based on simulations with only a minimum of assumptions, constraints from empirical data can be made on the spin magnitudes of the first- and second-born BHs, thereby serving to better understand massive binary star evolution prior to the formation of BHs.

Spectral modelling of Type IIb supernovae

We use the new non-local-thermodynamical-equilibrium (NLTE) light curve and spectral synthesis code JEKYLL to evolve a macro-scopically mixed ejecta model of a Type IIb supernova (SN) originating from a star with an initial mass of 12 M⊙ through the photospheric and nebular phase. The ejecta model is adopted from earlier work and has a mass of 1.7 M⊙, has a kinetic energy of 0.7 foe, and contains 0.075 M⊙ of 56Ni. The macroscopic mixing is simulated through a statistical representation of ejecta fragmented into small clumps but spherically symmetric on average. We compare our model with SN 2011dh and find that both the spectra and the light curves are well reproduced in both the photospheric and nebular phase, although there are also some differences. Our work further strengthens the evidence that this SN originated from a star with an initial mass of ~12 M⊙ that had lost all but a tiny (<0.1 M⊙) fraction of its hydrogen envelope, strongly suggesting a binary origin. We also investigate the effects of the macroscopic mixing by comparing macroscopically and microscopically mixed models and by varying the clumping geometry. In the photospheric phase, we find strong effects on the effective opacity in the macroscopically mixed regions, which affects the model light curves. The diffusion peak is considerably narrower (rise time decreased by 11%) in the macroscopically mixed case and differs strongly (rise time decreased by 29%) if the radioactive material in the helium envelope is allowed to expand more than in our standard model. The effect is mainly geometrical and is driven by the expansion of the clumps that contain radioactive material, which tend to decrease the effective opacity. In the limit of optically thick clumps, the decrease is roughly given by the product of the (volume) expansion and filling factors for the radioactive material, and in our models values up to ~8 are explored. These findings have implications for light curve modelling of stripped-envelope SNe in general, and the effect would increase the estimated ejecta masses. In the nebular phase, we find strong effects on the collisional cooling rates in the macroscopically mixed regions, which affects lines driven by collisional cooling, in particular the [Ca ii] 7291, 7323 Å and [O i] 6300, 6364 Å lines. The effect is mainly related to differences in composition between macroscopically and microscopically mixed ejecta. As these lines are often used for mass determinations, this highlights the importance of how and to what extent the calcium- and oxygen-rich material is mixed. As shown in this and earlier work, both NLTE and macroscopic mixing are essential ingredients for accurately modelling the light curves and spectra of Type IIb SNe throughout their evolution.

Classical OBe Stars as Post-supernova Runaways: Confirming Binary Origins

Massive binaries play an important role in fields ranging from gravitational-wave astronomy to stellar evolution. We provide several lines of evidence that classical OBe stars in the Small Magellanic Cloud (SMC) obtain their rapid rotation from mass and angular momentum transfer in massive binaries, which predicts that the subsequent supernovae should often eject OBe stars into the field. We find that (1) OBe stars have a higher field frequency than OB stars; (2) our cumulative distribution function (CDF) of stellar distances from O stars shows that OBe stars are indeed much more isolated than ordinary OB stars of corresponding spectral types; (3) the CDFs of OBe stars approach that of high-mass X-ray binaries (HMXBs), which are confirmed post-supernova objects; and (4) Oe stars are as isolated from clusters as Be stars, implying that their final masses are relatively independent of their initial masses, consistent with major mass transfer. Lastly, we also find that the spatial distribution of supergiant OBe stars differs from that of classical OBe stars, consistent with the different mechanisms responsible for their emission-line spectra.

The origin of close massive binaries in the M17 star-forming region

Context.Spectroscopic multiplicity surveys of O stars in young clusters and OB associations have revealed that a large portion (∼70%) of these massive stars (Mi > 15M⊙) belong to close and short-period binaries (with a physical separation of less than a few astronomical units). Follow-up VLT(I) high-angular-resolution observations led to the detection of wider companions (up tod ∼ 500 au), increasing the average companion fraction to > 2. Despite the recent and significant progress, the formation mechanisms leading to such close massive multiple systems remain to be elucidated. As a result, young massive close binaries (or higher-order multiple systems) are unique laboratories for determining the pairing mechanism of high-mass stars.Aims.We present the first VLTI/GRAVITY observations of six young O stars in the M17 star-forming region (≲1 Myr) and two additional foreground stars. VLTI/GRAVITY provides theK-band high-angular-resolution observations needed to explore the close environment of young O-type stars, and, as such, offers an excellent opportunity to characterise the multiplicity properties of the immediate outcome of the massive star formation process.Methods.From the interferometric model fitting of visibility amplitudes and closure phases, we search for companions and measure their positions and flux ratios. Combining the resulting magnitude difference with atmosphere models and evolutionary tracks, we further constrain the masses of the individual components.Results.All six high-mass stars are in multiple systems, leading to a multiplicity fraction of 100% and yielding a 68% confidence interval of 94–100%. We detect a total of nine companions with separations of up to 120 au. Including previously identified spectroscopic companions, the companion fraction of the young O stars in our sample reaches 2.3 ± 0.6. The derived masses span a wide range, from 2.5 to 50M⊙, with a great tendency towards high-mass companions. However, we do not find a significant correlation between the mass of the companions and their separation.Conclusions.While based on a modest sample, our results clearly indicate that the origin of the high degree of multiplicity is rooted in the star formation mechanism of the sample stars. No clear evidence for one of the competing concepts of massive star formation (core accretion or competitive accretion) could be found. However, given that we find all of the companions within ∼120 au, our results are compatible with migration as a scenario for the formation of close massive binaries.

Asteroseismology Across the Hertzsprung–Russell Diagram

Asteroseismology has grown from its beginnings three decades ago to a mature field teeming with discoveries and applications. This phenomenal growth has been enabled by space photometry with precision 10–100 times better than ground-based observations, with nearly continuous light curves for durations of weeks to years, and by large-scale ground-based surveys spanning years designed to detect all time-variable phenomena. The new high-precision data are full of surprises, deepening our understanding of the physics of stars. ▪ This review explores asteroseismic developments from the past decade primarily as a result of light curves from the Kepler and Transiting Exoplanet Survey Satellite space missions for massive upper main sequence OBAF stars, pre-main-sequence stars, peculiar stars, classical pulsators, white dwarfs and subdwarfs, and tidally interacting close binaries. ▪ The space missions have increased the numbers of pulsators in many classes by an order of magnitude. ▪ Asteroseismology measures fundamental stellar parameters and stellar interior physics—mass, radius, age, metallicity, luminosity, distance, magnetic fields, interior rotation, angular momentum transfer, convective overshoot, core-burning stage—supporting disparate fields such as galactic archeology, exoplanet host stars, supernovae progenitors, gamma-ray and gravitational wave precursors, close binary star origins and evolution, and standard candles. ▪ Stars are the luminous tracers of the Universe. Asteroseismology significantly improves models of stellar structure and evolution on which all inference from stars depends.

Eccentricity estimate for black hole mergers with numerical relativity simulations

The origin of black hole mergers discovered by the LIGO1 and Virgo2 gravitational-wave observatories is currently unknown. GW1905213,4 is the heaviest black hole merger detected so far. Its observed high mass and possible spin-induced orbital precession could arise from the binary having formed following a close encounter. An observational signature of close encounters is eccentric binary orbit5–7; however, this feature is currently difficult to identify due to the lack of suitable gravitational waveforms. No eccentric merger has been previously found8. Here we report 611 numerical relativity simulations covering the full eccentricity range and an estimation approach to probe the eccentricity of mergers. Our set of simulations corresponds to ~105 waveforms, comparable to the number used in gravitational-wave searches, albeit with coarser mass ratio and spin resolution. We applied our approach to GW190521 and found that it is most consistent with a highly eccentric ( $$e=0.6{9}_{-0.22}^{+0.17}$$ ; 90% credible level) merger within our set of waveforms. This interpretation is supported over a non-eccentric merger with >10 odds ratio if ≳10% of GW190521-like mergers are highly eccentric. Detectable orbital eccentricity would be evidence against an isolated binary origin, which is otherwise difficult to rule out on the basis of observed mass and spin9,10. Massive black holes that are produced dynamically by black hole mergers are thought to involve eccentric orbits, whose imprint may remain in the gravitational waveform detected by the LIGO/Virgo Collaboration.