38 research outputs found

    Maternal effect senescence via reduced DNA repair ability in the three‚Äźspined stickleback

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    Maternal effect senescence, a decline in offspring viability with maternal age, has been documented across diverse animals, but its mechanisms remain largely unknown. Here, we test maternal effect senescence and explore its possible molecular mechanisms in a fish. We compared the levels of maternal mRNA transcripts of DNA repair genes and mtDNA copies in eggs and the levels of DNA damage in somatic and germline tissues between young and old female sticklebacks. We also tested, in an in vitro fertilization experiment, whether maternal age and sperm DNA damage level interactively influence the expression of DNA repair genes in early embryos. Old females transferred less mRNA transcripts of DNA repair genes into their eggs than did young females, but maternal age did not influence egg mtDNA density. Despite a higher level of oxidative DNA damage in the skeletal muscle, old females had a similar level of damage in the gonad to young females, suggesting the prioritization for germline maintenance during ageing. The embryos of both old and young mothers increased the expression of DNA repair genes in response to an increased level of oxidative DNA damage in sperm used for their fertilization. The offspring of old mothers showed higher rates of hatching, morphological deformity and post‚Äźhatching mortality and had smaller body size at maturity. These results suggest that maternal effect senescence may be mediated by reduced capacity of eggs to detect and repair DNA damages, especially prior to the embryonic genomic activation.Agencia Estatal de Investigaci√≥n | Ref. PGC2018-095412-B-I00Universidade de Vigo/CISU

    First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass

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    In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching ‚ąľ100% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be 51.8 ¬Ī 2.3 őľas (68% credible intervals), with the ring thickness constrained to have an FWHM between ‚ąľ30% and 50% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be 4.8‚ąí0.7+1.4 őľas, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be 4.0‚ąí0.6+1.1√ó106 M ‚äô

    Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI

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    The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto the astrophysical phenomena unfolding on horizon scales in two known black holes, M87* and Sgr A*. However, with this leap in resolution has come a new set of practical complications. Sgr A* exhibits intraday variability that violates the assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales and data sets with very sparse (u, v) coverage. We present a new set of tools to detect and mitigate this variability. We develop a data-driven, model-agnostic procedure to detect and characterize the spatial structure of intraday variability. This method is calibrated against a large set of mock data sets, producing an empirical estimator of the spatial power spectrum of the brightness fluctuations. We present a novel Bayesian noise modeling algorithm that simultaneously reconstructs an average image and statistical measure of the fluctuations about it using a parameterized form for the excess variance in the complex visibilities not otherwise explained by the statistical errors. These methods are validated using a variety of simulated data, including general relativistic magnetohydrodynamic simulations appropriate for Sgr A* and M87*. We find that the reconstructed source structure and variability are robust to changes in the underlying image model. We apply these methods to the 2017 EHT observations of M87*, finding evidence for variability across the EHT observing campaign. The variability mitigation strategies presented are widely applicable to very long baseline interferometry observations of variable sources generally, for which they provide a data-informed averaging procedure and natural characterization of inter-epoch image consistency

    First Sagittarius A* Event Horizon Telescope Results. VI. Testing the Black Hole Metric

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    Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein‚Äôs equations and does not have pathologies outside of the event horizon. We present new constraints on potential deviations from the Kerr prediction based on 2017 EHT observations of Sagittarius A* (Sgr A*). We calibrate the relationship between the geometrically defined black hole shadow and the observed size of the ring-like images using a library that includes both Kerr and non-Kerr simulations. We use the exquisite prior constraints on the mass-to-distance ratio for Sgr A* to show that the observed image size is within ‚ąľ10% of the Kerr predictions. We use these bounds to constrain metrics that are parametrically different from Kerr, as well as the charges of several known spacetimes. To consider alternatives to the presence of an event horizon, we explore the possibility that Sgr A* is a compact object with a surface that either absorbs and thermally reemits incident radiation or partially reflects it. Using the observed image size and the broadband spectrum of Sgr A*, we conclude that a thermal surface can be ruled out and a fully reflective one is unlikely. We compare our results to the broader landscape of gravitational tests. Together with the bounds found for stellar-mass black holes and the M87 black hole, our observations provide further support that the external spacetimes of all black holes are described by the Kerr metric, independent of their mass

    The Event Horizon Telescope Image of the Quasar NRAO 530

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    We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5‚ąí7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of ‚ąľ20 őľas, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of ‚ąľ5%‚Äď8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 őľas along a position angle ‚ąľ ‚ąí28¬į. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin

    A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

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    We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT

    Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign

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    The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5‚Äď11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between ‚ąí2 and ‚ąí3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*'s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines

    First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization

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    Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at the center of the M87 galaxy. EHT images in linear polarization have further identified a coherent spiral pattern around the black hole, produced from ordered magnetic fields threading the emitting plasma. Here we present the first analysis of circular polarization using EHT data, acquired in 2017, which can potentially provide additional insights into the magnetic fields and plasma composition near the black hole. Interferometric closure quantities provide convincing evidence for the presence of circularly polarized emission on event-horizon scales. We produce images of the circular polarization using both traditional and newly developed methods. All methods find a moderate level of resolved circular polarization across the image („Äą‚ą£v‚ą£„ÄČ < 3.7%), consistent with the low image-integrated circular polarization fraction measured by the Atacama Large Millimeter/submillimeter Array (‚ą£v int‚ą£ < 1%). Despite this broad agreement, the methods show substantial variation in the morphology of the circularly polarized emission, indicating that our conclusions are strongly dependent on the imaging assumptions because of the limited baseline coverage, uncertain telescope gain calibration, and weakly polarized signal. We include this upper limit in an updated comparison to general relativistic magnetohydrodynamic simulation models. This analysis reinforces the previously reported preference for magnetically arrested accretion flow models. We find that most simulations naturally produce a low level of circular polarization consistent with our upper limit and that Faraday conversion is likely the dominant production mechanism for circular polarization at 230 GHz in M87*

    First Sagittarius A* Event Horizon Telescope results. II. EHT and multiwavelength observations, data processing, and calibration

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    We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5‚Äď11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ‚ąľ50 őľas, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.http://iopscience.iop.org/2041-8205Physic

    Ontogenèse et socialité chez les araignées

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    Among the major evolutionary transitions, the transition from a solitary lifestyle to sociality has occurred independently in many taxa. Spiders offer a wide range of social organizations, differing in the complexity and duration of interactions between congeners. Among the 48,000 species of spiders, less than 30 have developed an elaborate social life characterized by the construction of a common web, the existence of cooperative brood care and the presence of collective hunting. However, even in solitary spiders, a gregarious phase is observed during the juvenile stage following the emergence of the cocoon. This gregarious phase is then followed by the development of agonistic interactions and the initiation of dispersal. This thesis integrates behavioural approaches, chemical analyses and computer modelling to address two questions of sociality in spiders. The first two chapters aim to provide information on the mechanisms inhibiting the expression of agonistic behaviours and dispersal in juveniles of the solitary species Agelena labyrinthica. In the last part we discuss the issue of cooperative hunting among social spiders. This cooperative hunt is considered one of the major advantages of social life because it allows the capture of prey unreachable to solitary species. The third chapter of this thesis aims to understand the mechanisms allowing the synchronization of the movements of individuals during collective hunt in the social spider Anelosimus eximius. Our results provide arguments in favour of a social transition induced by a retention of the cohesion of juveniles. They also point out that juveniles of solitary species already have all the prerequisites for social behaviours, even for behaviours that seems to require a high level of coordination such as synchronized hunting.La transition entre vie solitaire et vie sociale est une transition √©volutive majeure, apparue ind√©pendamment dans de nombreux taxons. Les araign√©es offrent une gamme √©tendue d'organisations sociales, diff√©rant par la complexit√© et la dur√©e des interactions entre cong√©n√®res. Parmi les 48 000 esp√®ces d'araign√©es, une trentaine a d√©velopp√© une vie sociale √©labor√©e caract√©ris√©e par la construction d'une toile commune, l'existence de soins coop√©ratifs aux juv√©niles et la pr√©sence de chasses collectives. Cependant, les juv√©niles de toutes les esp√®ces d'araign√©es solitaires pr√©sentent une phase gr√©gaire temporaire suite √† leur √©mergence du cocon maternel. Cette phase gr√©gaire, dont la dur√©e est variable entre les esp√®ces, aboutit √† la dispersion des juv√©niles et l'initiation d'interactions agonistiques. La caract√©risation de cette transition est cruciale pour identifier les m√©canismes ayant pr√©sid√© au d√©veloppement d'une vie sociale permanente chez les araign√©es. Une premi√®re partie est consacr√©e √† la caract√©risation des m√©canismes impliqu√©s dans l'initiation de la dispersion chez les juv√©niles de l'esp√®ce solitaire Agelena labyrinthica. Nos r√©sultats indiquent que l'agressivit√© est une cons√©quence, non la cause, de la dispersion. Dans une seconde partie, nous montrons l'influence du contexte social sur les comportements de pr√©dation des juv√©niles au cours de leur phase gr√©gaire. Finalement, la troisi√®me partie de cette th√®se aborde les chasses collectives chez l'araign√©e sociale Anelosimus eximius. Nos r√©sultats montrent que l'√©mergence d'une synchronisation dans les d√©placements des araign√©es repose sur une modulation des comportements individuels d√©pendante de l'activit√© des cong√©n√®res. En combinant approches exp√©rimentales et th√©oriques, cette th√®se sugg√®re que la communication joue un r√īle d√©terminant dans le maintien de la coh√©sion sociale et l'expression de formes sophistiqu√©es de coop√©ration chez les araign√©es
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