A rapidly changing jet orientation in the stellar-mass black-hole system V404 Cygni.

Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers them are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession1 due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star2. Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow3, although the interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood. Here we report a rapidly changing jet orientation-on a time scale of minutes to hours-in the black-hole X-ray binary V404 Cygni, detected with very-long-baseline interferometry during the peak of its 2015 outburst. We show that this changing jet orientation can be modelled as the Lense-Thirring precession of a vertically extended slim disk that arises from the super-Eddington accretion rate4. Our findings suggest that the dynamics of the precessing inner accretion disk could play a role in either directly launching or redirecting the jets within the inner few hundred gravitational radii. Similar dynamics should be expected in any strongly accreting black hole whose spin is misaligned with the inflowing gas, both affecting the observational characteristics of the jets and distributing the black-hole feedback more uniformly over the surrounding environment5,6.

A wide star-black-hole binary system from radial-velocity measurements.

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun1-4. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries5,6. When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of [Formula: see text] solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories.

The SiTian Project.

SiTian is an ambitious ground-based all-sky optical monitoring project, developed by the Chinese Academy of Sciences. The concept is an integrated network of dozens of 1-m-class telescopes deployed partly in China and partly at various other sites around the world. The main science goals are the detection, identification and monitoring of optical transients (such as gravitational wave events, fast radio bursts, supernovae) on the largely unknown timescales of less than 1 day; SiTian will also provide a treasure trove of data for studies of AGN, quasars, variable stars, planets, asteroids, and microlensing events. To achieve those goals, SiTian will scan at least 10,000 square deg of sky every 30 min, down to a detection limit of $V \approx 21$ mag. The scans will produce simultaneous light-curves in 3 optical bands. In addition, SiTian will include at least three 4-m telescopes specifically allocated for follow-up spectroscopy of the most interesting targets. We plan to complete the installation of 72 telescopes by 2030 and start full scientific operations in 2032.

Towards a BRICS Optical Transient Network (BRICS-OTN).

This paper is based on a proposal submitted for a BRICS astronomy flagship program, which was presented at the 2019 meeting of the BRICS Astronomy Working Group, held in Rio de Janeiro from 29 September to 2 October 2019. The future prospects for the detection and study of transient phenomena in the Universe heralds a new era in time domain astronomy. The case is presented for a dedicated BRICS-wide flagship program to develop a network of ground-based optical telescopes for an all-sky survey to detect short lived optical transients and to allow follow-up of multi-wavelength and multi-messenger transient objects. This will leverage existing and planned new facilities within the BRICS countries and will also draw on the opportunities presented by other multi-wavelength space- and ground-based facilities that exist within the BRICS group. The proposed optical network would initially perform followup observations on new transients using existing telescopes. This would later expand to include a new global network of \sim ∼ 70 wide-field 1-m telescopes which will cover the entire sky, simultaneously, with a cadence of less than a few hours. This realization would represent a ground-breaking and unique global capability, presenting many scientific opportunities and associated spin-off benefits to all BRICS countries.

A 300-parsec-long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793.

Black-hole accretion states near or above the Eddington luminosity (the point at which radiation force outwards overcomes gravity) are still poorly known because of the rarity of such sources. Ultraluminous X-ray sources are the most luminous class of black hole (L(X) approximately 10(40) erg s(-1)) located outside the nuclei of active galaxies. They are likely to be accreting at super-Eddington rates, if they are powered by black holes with masses less than 100 solar masses. They are often associated with shock-ionized nebulae, though with no evidence of collimated jets. Microquasars with steady jets are much less luminous. Here we report that the large nebula S26 (ref. 4) in the nearby galaxy NGC 7793 is powered by a black hole with a pair of collimated jets. It is similar to the famous Galactic source SS433 (ref. 5), but twice as large and a few times more powerful. We determine a mechanical power of around a few 10(40) erg s(-1). The jets therefore seem 10(4) times more energetic than the X-ray emission from the core. S26 has the structure of a Fanaroff-Riley type II (FRII-type) active galaxy: X-ray and optical core, X-ray hot spots, radio lobes and an optical and X-ray cocoon. It is a microquasar where most of the jet power is dissipated in thermal particles in the lobes rather than relativistic electrons.

Ventajas del abordaje externo para la artroplastia de rodilla por genu valgo severo / Advantages of the lateral approach in severe genu valgus knee arthroplasty

Introducción: El tratamiento del valgo severo es complejo. El abordaje externo descrito por Keblish es ventajoso para tratar estas deformidades. Evaluamos nuestros resultados utilizando un abordaje externo en artroplastias de rodilla con genu valgo severo. Materiales y Métodos: De 795 artroplastias primarias realizadas entre enero de 2012 y marzo de 2020, analizamos 40 que tenían un abordaje externo. Todos los pacientes tenían una deformidad en valgo >20° y un ligamento colateral medial suficiente. Se incluyó a 33 mujeres (3 bilaterales) y 4 hombres, el promedio de edad era de 71 años. La causa fue fundamentalmente osteoartrosis (82%). La deformidad prequirúrgica era de 27°. Las mediciones preoperatorias eran: KSS 15 (rango 5-42) y KFS 17 (rango 0-40). El tiempo promedio de cirugía fue de 91 minutos y el seguimiento, de 37 meses. Resultados: El ángulo femorotibial posoperatorio fue de 6,2° (rango 4-40), el KSS posoperatorio fue de 79 (rango 46-95) y el KFS, de 82 (rango 60-100). Hubo tres complicaciones (7%): una infección, un mal posicionamiento de componentes y uno de neuropraxia peronea. Conclusiones: En la artroplastia de rodilla por genu valgo, este abordaje permite restituir el eje femorotibial, lograr una adecuada estabilidad de la prótesis, aun con implantes sin mayor grado de constreñimiento, con una tasa de complicaciones equiparable a la de otras técnicas. Nivel de Evidencia: IV

Introduction: The treatment of severe valgus is complex. The lateral approach described by Keblish is advantageous for the treatment of these deformities. We decided to evaluate our outcomes using a lateral approach in severe genu valgus knee arthroplasty. Materials and Methods: Of 795 primary arthroplasties from January 2012 to March 2020, we analyzed 40 performed by lateral approach. All had a valgus deformity greater than 20° and a sufficient medial collateral ligament. 33 women (3 bilateral) and 4 men were included. Average age was 71 years (59-79). The main cause was osteoarthrosis (82%). The presurgical deformity was 27° (21-39). The preoperative measurements were: Knee Society Score (KSS) 15 (5 to 42). Preoperative functional score (KFS): 17 (0 to 40). Average surgical time: 91 minutes. The average postoperative follow-up was 37 months. Results: Postoperative femorotibial angle 6.2° (range 4° to 10°). Postoperative KSS 79 (46-95). KFS 82 (60-100). Complications: 3 cases (7%), one infection, one case with poor positioning of components, and one case of peroneal neuropraxia. Conclusion: In knee arthroplasty due to genu valgus, this approach allows restoring the femoro-tibial axis and achieving adequate prosthetic stability, even with implants without a greater degree of constraint, with a complication rate comparable to other techniques. Level of Evidence: IV