Spectral Sirens: Cosmology from the Full Mass Distribution of Compact Binaries.

We explore the use of the mass spectrum of neutron stars and black holes in gravitational-wave compact binary sources as a cosmological probe. These standard siren sources provide direct measurements of luminosity distance. In addition, features in the mass distribution, such as mass gaps or peaks, will redshift and thus provide independent constraints on their redshift distribution. We argue that the entire mass spectrum should be utilized to provide cosmological constraints. For example, we find that the mass spectrum of LIGO-Virgo-KAGRA events introduces at least five independent mass "features": the upper and lower edges of the pair instability supernova (PISN) gap, the upper and lower edges of the neutron star-black hole gap, and the minimum neutron star mass. We find that although the PISN gap dominates the cosmological inference with current detectors (second generation, 2G), as shown in previous work, it is the lower mass gap that will provide the most powerful constraints in the era of Cosmic Explorer and Einstein Telescope (third generation, 3G). By using the full mass distribution, we demonstrate that degeneracies between mass evolution and cosmological evolution can be broken, unless an astrophysical conspiracy shifts all features of the full mass distribution simultaneously following the (nontrivial) Hubble diagram evolution. We find that this self-calibrating "spectral siren" method has the potential to provide precision constraints of both cosmology and the evolution of the mass distribution, with 2G achieving better than 10% precision on H(z) at z≲1 within a year and 3G reaching ≲1% at z≳2 within one month.

A two per cent Hubble constant measurement from standard sirens within five years.

Gravitational-wave detections provide a novel way to determine the Hubble constant1-3, which is the current rate of expansion of the Universe. This 'standard siren' method, with the absolute distance calibration provided by the general theory of relativity, was used to measure the Hubble constant using the gravitational-wave detection of the binary neutron-star merger, GW170817, by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo4, combined with optical identification of the host galaxy5,6 NGC 4993. This independent measurement is of particular interest given the discrepancy between the value of the Hubble constant determined using type Ia supernovae via the local distance ladder (73.24 ± 1.74 kilometres per second per megaparsec) and the value determined from cosmic microwave background observations (67.4 ± 0.5 kilometres per second per megaparsec): these values differ7,8 by about 3σ. Local distance ladder observations may achieve a precision of one per cent within five years, but at present there are no indications that further observations will substantially reduce the existing discrepancies9. Here we show that additional gravitational-wave detections by LIGO and Virgo can be expected to constrain the Hubble constant to a precision of approximately two per cent within five years and approximately one per cent within a decade. This is because observing gravitational waves from the merger of two neutron stars, together with the identification of a host galaxy, enables a direct measurement of the Hubble constant independent of the systematics associated with other available methods. In addition to clarifying the discrepancy between existing low-redshift (local ladder) and high-redshift (cosmic microwave background) measurements, a precision measurement of the Hubble constant is of crucial value in elucidating the nature of dark energy10,11.

The first gravitational-wave source from the isolated evolution of two stars in the 40-100 solar mass range.

The merger of two massive (about 30 solar masses) black holes has been detected in gravitational waves. This discovery validates recent predictions that massive binary black holes would constitute the first detection. Previous calculations, however, have not sampled the relevant binary-black-hole progenitors--massive, low-metallicity binary stars--with sufficient accuracy nor included sufficiently realistic physics to enable robust predictions to better than several orders of magnitude. Here we report high-precision numerical simulations of the formation of binary black holes via the evolution of isolated binary stars, providing a framework within which to interpret the first gravitational-wave source, GW150914, and to predict the properties of subsequent binary-black-hole gravitational-wave events. Our models imply that these events form in an environment in which the metallicity is less than ten per cent of solar metallicity, and involve stars with initial masses of 40-100 solar masses that interact through mass transfer and a common-envelope phase. These progenitor stars probably formed either about 2 billion years or, with a smaller probability, 11 billion years after the Big Bang. Most binary black holes form without supernova explosions, and their spins are nearly unchanged since birth, but do not have to be parallel. The classical field formation of binary black holes we propose, with low natal kicks (the velocity of the black hole at birth) and restricted common-envelope evolution, produces approximately 40 times more binary-black-holes mergers than do dynamical formation channels involving globular clusters; our predicted detection rate of these mergers is comparable to that from homogeneous evolution channels. Our calculations predict detections of about 1,000 black-hole mergers per year with total masses of 20-80 solar masses once second-generation ground-based gravitational-wave observatories reach full sensitivity.

Reasons for mild parkinsonian signs - which constellation may indicate neurodegeneration?

INTRODUCTION: Mild parkinsonian signs (MPS) are common in the elderly population. Several factors including physical decline and comorbidities in addition to neurodegeneration may be possible sources for MPS. The objective was to examine whether MPS are associated with a history of orthopedic disturbances, vascular diseases or prodromal markers for neurodegeneration. METHODS: The TREND study is a prospective longitudinal cohort study in individuals >50 years with biennial assessments designed to identify prodromal markers for neurodegeneration. In this substudy, 1091 elderly individuals were evaluated for a possible association of MPS with prodromal markers for neurodegeneration, orthopedic disturbances, vascular diseases, as well as cerebral abnormalities. These factors were assessed by self-administered questionnaires, with a structured health interview, a neurological examination and by transcranial sonography. RESULTS: 82 participants showed MPS. They were found to have more often hyposmia and RBD, had a higher autonomic dysfunction score and they more frequently showed hyperechogenicity of the substantia nigra compared to controls. Neither orthopedic disturbances nor vascular diseases were significantly associated with the prevalence of MPS. CONCLUSION: MPS might be a sign of early neurodegeneration rather than caused by other motor influencing diseases.

Gamma-ray-burst beaming and gravitational-wave observations.

Using the observed rate of short-duration gamma-ray bursts (GRBs) it is possible to make predictions for the detectable rate of compact binary coalescences in gravitational-wave detectors. We show that the nondetection of mergers in the existing LIGO/Virgo data constrains the beaming angles and progenitor masses of gamma-ray bursts, although these limits are fully consistent with existing expectations. We make predictions for the rate of events in future networks of gravitational-wave observatories, finding that the first detection of a neutron-star-neutron-star binary coalescence associated with the progenitors of short GRBs is likely to happen within the first 16 months of observation, even in the case of only two observatories (e.g., LIGO-Hanford and LIGO-Livingston) operating at intermediate sensitivities (e.g., advanced LIGO design sensitivity, but without signal recycling mirrors), and assuming a conservative distribution of beaming angles (e.g., all GRBs beamed within θ(j) = 30°). Less conservative assumptions reduce the waiting time until first detection to a period of weeks to months, with an event detection rate of >/~10/yr. Alternatively, the compact binary coalescence model of short GRBs can be ruled out if a binary is not seen within the first two years of operation of a LIGO-Hanford, LIGO-Livingston, and Virgo network at advanced design sensitivity. We also demonstrate that the gravitational wave detection rate of GRB triggered sources (i.e., those seen first in gamma rays) is lower than the rate of untriggered events (i.e., those seen only in gravitational waves) if θ(j)≲30°, independent of the noise curve, network configuration, and observed GRB rate. The first detection in gravitational waves of a binary GRB progenitor is therefore unlikely to be associated with the observation of a GRB.

Growth differentiation factor 15: a novel risk marker adjunct to the EuroSCORE for risk stratification in cardiac surgery patients.

OBJECTIVES: This study sought to determine the usefulness of plasma growth differentiation factor 15 (GDF-15) for risk stratification in patients undergoing cardiac surgery in comparison with the additive European System of Cardiac Operative Risk Evaluation (EuroSCORE), N-terminal pro-B-type natriuretic peptide (NTproBNP), and high-sensitive troponin T (hsTNT). BACKGROUND: GDF-15 is emerging as a humoral marker for risk stratification in cardiovascular disease. No data are available if this marker may also be used for risk stratification in cardiac surgery. METHODS: In total, 1,458 consecutive patients were prospectively studied. Pre-operative plasma GDF-15, NTproBNP, hsTNT, clinical outcomes, and 30-day and 1-year mortality were recorded. GDF-15 was determined with a pre-commercial electrochemiluminescence immunoassay. RESULTS: Median additive EuroSCORE (addES) was 5 (interquartile range: 3 to 8); 30-day and 1-year mortality were 3.4% and 7.6%, respectively. Median GDF-15 levels were 1.04 ng/ml (95% confidence interval [CI]: 1.0 to 1.07 ng/ml) in 30-day survivors and 2.62 ng/ml (95% CI: 1.88 to 3.88) in 30-day nonsurvivors (p < 0.0001). C-statistics showed that the area under the curve of a combined model of GDF-15 and addES for 30-day mortality was significantly greater (0.85 vs. 0.81; p = 0.0091) than of the addES alone. For the EuroSCORE categories (0 to 2, 3 to 5, 6 to 10, >10) the presence of GDF-15 ≥1.8 ng/ml resulted in a significant 41.4% (95% CI: 19.2 to 63.7%; p < 0.001) net reclassification improvement and an integrated discrimination improvement of 0.038 (95% CI: 0.022 to 0.0547; p < 0.0001) compared to the model including only the addES, whereas the presence of NTproBNP (cutoff ≥2,000 pg/ml) or hsTNT (cutoff 14 pg/ml) did not result in significant reclassification. CONCLUSIONS: The pre-operative plasma GDF-15 level is an independent predictor of post-operative mortality and morbidity in cardiac surgery patients, can further stratify beyond established risk scores and cardiovascular markers, and thus adds important additional information for risk stratification in these patients. (The Usefulness of Growth Differentiation Factor 15 [GDF-15] for Risk Stratification in Cardiac Surgery; NCT01166360).

Beyond two dark energy parameters.

Our ignorance of dark energy is generally described by a two-parameter equation of state. In these approaches, a particular ad hoc functional form is assumed, and only two independent parameters are incorporated. We propose a model-independent, multiparameter approach to fitting dark energy and show that next-generation surveys will constrain the equation of state in three or more independent redshift bins to better than 10%. Future knowledge of dark energy will surpass two numbers (e.g., [w{0},w{1}] or [w{0},w{a}]), and we propose a more flexible approach to the analysis of present and future data.

Problems with small area surveys: lensing covariance of supernova distance measurements.

While luminosity distances from type Ia supernovae (SNe) are a powerful probe of cosmology, the accuracy with which these distances can be measured is limited by cosmic magnification due to gravitational lensing by the intervening large-scale structure. Spatial clustering of foreground mass leads to correlated errors in SNe distances. By including the full covariance matrix of SNe, we show that future wide-field surveys will remain largely unaffected by lensing correlations. However, "pencil beam" surveys, and those with narrow (but possibly long) fields of view, can be strongly affected. For a survey with 30 arcmin mean separation between SNe, lensing covariance leads to a approximately 45% increase in the expected errors in dark energy parameters.