Abstract
The LIGO/Virgo gravitational-wave observatories have detected at least 50 double black hole (BH) coalescences. This sample 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.
All ten LIGO/Virgo binary black hole (BH-BH) coalescences reported following the O1/O2 runs have near-zero effective spins. There are only three potential explanations for this. If the BH spin ...magnitudes are large, then: (i) either both BH spin vectors must be nearly in the orbital plane or (ii) the spin angular momenta of the BHs must be oppositely directed and similar in magnitude. Then there is also the possibility that (iii) the BH spin magnitudes are small. We consider the third hypothesis within the framework of the classical isolated binary evolution scenario of the BH-BH merger formation. We test three models of angular momentum transport in massive stars: a mildly efficient transport by meridional currents (as employed in the Geneva code), an efficient transport by the Tayler-Spruit magnetic dynamo (as implemented in the MESA code), and a very-efficient transport (as proposed by Fuller et al.) to calculate natal BH spins. We allow for binary evolution to increase the BH spins through accretion and account for the potential spin-up of stars through tidal interactions. Additionally, we update the calculations of the stellar-origin BH masses, including revisions to the history of star formation and to the chemical evolution across cosmic time. We find that we can simultaneously match the observed BH-BH merger rate density and BH masses and BH-BH effective spins. Models with efficient angular momentum transport are favored. The updated stellar-mass weighted gas-phase metallicity evolution now used in our models appears to be key for obtaining an improved reproduction of the LIGO/Virgo merger rate estimate. Mass losses during the pair-instability pulsation supernova phase are likely to be overestimated if the merger GW170729 hosts a BH more massive than 50
M
⊙
. We also estimate rates of black hole-neutron star (BH-NS) mergers from recent LIGO/Virgo observations. If, in fact. angular momentum transport in massive stars is efficient, then any (electromagnetic or gravitational wave) observation of a rapidly spinning BH would indicate either a very effective tidal spin up of the progenitor star (homogeneous evolution, high-mass X-ray binary formation through case A mass transfer, or a spin- up of a Wolf-Rayet star in a close binary by a close companion), significant mass accretion by the hole, or a BH formation through the merger of two or more BHs (in a dense stellar cluster).
Extreme events are increasing globally with devastating ecological consequences, but the impacts on underlying genetic diversity and structure are often cryptic and poorly understood, hindering ...assessment of adaptive capacity and ecosystem vulnerability to future change. Using very rare "before" data we empirically demonstrate that an extreme marine heatwave caused a significant poleward shift in genetic clusters of kelp forests whereby alleles characteristic of cool water were replaced by those that predominated in warm water across 200 km of coastline. This "genetic tropicalisation" was facilitated by significant mortality of kelp and other co-occurring seaweeds within the footprint of the heatwave that opened space for rapid local proliferation of surviving kelp genotypes or dispersal and recruitment of spores from warmer waters. Genetic diversity declined and inbreeding increased in the newly tropicalised site, but these metrics were relative stable elsewhere within the footprint of the heatwave. Thus, extreme events such as marine heatwaves not only lead to significant mortality and population loss but can also drive significant genetic change in natural populations.
The phenomenological disc instability model has been successful in reproducing the observed light curves of dwarf nova outbursts by invoking an enhanced Shakura–Sunyaev α parameter ∼0.1–0.2 in ...outburst compared to a low value ∼0.01 in quiescence. Recent thermodynamically consistent simulations of magnetorotational instability (MRI) turbulence with appropriate opacities and equation of state for dwarf nova accretion discs have found that thermal convection enhances α in discs in outburst, but only near the hydrogen ionization transition. At higher temperatures, convection no longer exists and α returns to the low value comparable to that in quiescence. In order to check whether this enhancement near the hydrogen ionization transition is sufficient to reproduce observed light curves, we incorporate this MRI-based variation in α into the disc instability model, as well as simulation-based models of turbulent dissipation and convective transport. These MRI-based models can successfully reproduce observed outburst and quiescence durations, as well as outburst amplitudes, albeit with different parameters from the standard disc instability models. The MRI-based model light curves exhibit reflares in the decay from outburst, which are not generally observed in dwarf novae. However, we highlight the problematic aspects of the quiescence physics in the disc instability model and MRI simulations that are responsible for this behaviour.
This Letter presents the results from pointlike neutrino source searches using ten years of IceCube data collected between April 6, 2008 and July 10, 2018. We evaluate the significance of an ...astrophysical signal from a pointlike source looking for an excess of clustered neutrino events with energies typically above ∼1 TeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of 2.9σ after accounting for statistical trials from the entire catalog. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the northern catalog are inconsistent with background at 3.3σ significance. The southern catalog is consistent with background. These results, all based on searches for a cumulative neutrino signal integrated over the 10 years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector.
We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010–2015. Assuming standard oscillations, the astrophysical neutrinos in ...this dedicated cascade sample are dominated (∼90 %) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be γ = 2.53 ± 0.07 and a flux normalization for each neutrino flavor of ϕastro = 1.66+0.25 −0.27 at E0 = 100 TeV , in agreement with IceCube's complementary muon neutrino results and with all-neutrino flavor fit results. In the measured energy range we reject spectral indices γ ≤ 2.28 at ≥ 3 σ significance level. Because of high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below ∼100 TeV compared to previous IceCube results. Results from fits assuming more complex neutrino flux models suggest a flux softening at high energies and a flux hardening at low energies (p value ≥ 0.06). The sizable and smooth flux measured below ∼100 TeV remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi Large Area Telescope, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma rays.
Bruton agammaglobulinemia tyrosine kinase (BTK), a cytoplasmic protein tyrosine kinase, is a component of the B-cell receptor signaling pathway. Ibrutinib, a BTK inhibitor, has demonstrated a ...significant clinical activity against chronic lymphocytic leukemia (CLL) in early clinical trials. Understanding the molecular mechanisms of action would shed light on CLL pathophysiology and provide additional opportunities for the development of new therapies. In this study, we have chosen an in vivo approach by employing an ongoing phase 1b trial of ibrutinib. We prospectively collected and analyzed serial samples from the CLL patients before and after the initiation of ibrutinib. We found that the blockage of cell proliferation was one of the primary effects of ibrutinib against leukemic CLL cells in vivo. Using a co-culture system that induces CLL proliferation in vitro, analysis of several parameters, including Ki-67 expression and bromodeoxyuridine (BrdU) incorporation, revealed that the proliferation of CLL cells was directly inhibited by ibrutinib. Furthermore, activities of BTK and phospholipase Cγ2 as well as downstream signaling molecules, AKT and ERK, were all coordinately downregulated over time in ibrutinib-treated patients. Our findings suggest that the cell proliferation is one of the essential properties of CLL. Blocking cell proliferation via inhibition of BTK-mediated signaling may contribute to clinical responses in ibrutinib-treated patients.
To assess the variation in risk-adjusted 30-day postoperative mortality for patients with colorectal cancer between hospital trusts within the English NHS.
Retrospective cross-sectional ...population-based study of data extracted from the National Cancer Data Repository.
All providers of major colorectal cancer surgery within the English NHS.
All 160,920 individuals who underwent major resection for colorectal cancer diagnosed between 1998 and 2006 in the English NHS. Main outcome measures National patterns of 30-day postoperative mortality were examined and logistic binary regression was used to study factors associated with death within 30 days of surgery. Funnel plots were used to show variation between trusts in risk-adjusted mortality.
Overall 30-day mortality was 6.7% but decreased over time from 6.8% in 1998 to 5.8% in 2006. The largest reduction in mortality was seen in 2005 and 2006. Postoperative mortality increased with age (15.0% (95% CI 14.1% to 15.9%) for those aged >80 years), comorbidity (24.2% (95% CI 22.0% to 26.5%) for those with a Charlson comorbidity score ≥ 3), stage of disease (9.9% (95% CI 9.3% to 10.6%) for patients with Dukes' D disease), socioeconomic deprivation (7.8% (95% CI 7.2% to 8.4%) for residents of the most deprived quintile) and operative urgency (14.9% (95% CI 14.2% to 15.7%) for patients undergoing emergency resection). Risk-adjusted control charts showed that one trust had consistently significantly better outcomes and three had significantly worse outcomes than the population mean.
Significant variation in 30-day postoperative mortality following major colorectal cancer surgery existed between NHS hospitals in England throughout the period 1998-2006. Understanding the underlying causes of this variation between surgical providers will make it possible to identify and spread best practice, improve outcomes and, ultimately, reduce 30-day postoperative mortality following colorectal cancer surgery.
ABSTRACT
Small low-mass stars are favourable targets for the detection of rocky habitable planets. In particular, planetary systems in the solar neighbourhood are interesting and suitable for precise ...characterization. The RedDots campaigns seek to discover rocky planets orbiting nearby low-mass stars. The 2018 campaign targeted GJ 1061, which is the 20th nearest star to the Sun. For three consecutive months we obtained nightly, high-precision radial velocity measurements with the HARPS spectrograph. We analysed these data together with archival HARPS data. We report the detection of three planet candidates with periods of 3.204 ± 0.001, 6.689 ± 0.005, and 13.03 ± 0.03 d, which are close to 1:2:4 period commensurability. After several considerations related to the properties of the noise and sampling, we conclude that a fourth signal is most likely explained by stellar rotation, although it may be due to a planet. The proposed three-planet system (and the potential four-planet solution) is long-term dynamically stable. Planet–planet gravitational interactions are below our current detection threshold. The minimum masses of the three planets range from 1.4 ± 0.2 to 1.8 ± 0.3 M⊕. Planet d, with msin i = 1.64 ± 0.24 M⊕, receives a similar amount of energy as Earth receives from the Sun. Consequently it lies within the liquid-water habitable zone of the star and has a similar equilibrium temperature to Earth. GJ 1061 has very similar properties to Proxima Centauri but activity indices point to lower levels of stellar activity.
Methylmercury (MeHg) is a bioaccumulative neurotoxin that is produced by certain anaerobic microorganisms, but the abundance and importance of different methylating populations in the environment is ...not well understood. We combined mercury geochemistry, hgcA gene cloning, rRNA methods, and metagenomics to compare microbial communities associated with MeHg production in two sulfate-impacted lakes on Minnesota's Mesabi Iron Range. The two lakes represent regional endmembers among sulfate-impacted sites in terms of their dissolved sulfide concentrations and MeHg production potential. rRNA amplicon sequencing indicates that sediments and anoxic bottom waters from both lakes contained diverse communities with multiple clades of sulfate reducing Deltaproteobacteria and Clostridia. In hgcA gene clone libraries, however, hgcA sequences were from taxa associated with methanogenesis and iron reduction in addition to sulfate reduction, and the most abundant clones were from unknown groups. We therefore applied metagenomics to identify the unknown populations in the lakes with the capability to methylate mercury, and reconstructed 27 genomic bins with hgcA. Some of the most abundant potential methylating populations were from phyla that are not typically associated with MeHg production, including a relative of the Aminicenantes (formerly candidate phylum OP8) and members of the Kiritimatiellaeota (PVC superphylum) and Spirochaetes that, together, were more than 50% of the potential methylators in some samples. These populations do not have genes for sulfate reduction, and likely degrade organic compounds by fermentation or other anaerobic processes. Our results indicate that previously unrecognized populations with hgcAB are abundant and may be important for MeHg production in some freshwater ecosystems.
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