A supermassive black hole Sagittarius A* (SgrA*) with the mass M SgrA * 4 × 10 6 M resides at the centre of our galaxy [1,2]. A large reservoir of hot (10 7 K) and cooler (10 2 − 10 4 K) gas surrounds it within few pc [3]. Building up such a massive black hole within the ∼ 10 10 year lifetime of our galaxy would require a mean accretion rate of ∼ 4 × 10 −4 M yr −1 . At present, X-ray observations constrain the rate of hot gas accretion at the Bondi radius (10 5 R Sch = 0.04 pc at 8 kpc) tȯ M Bondi ∼ 3 × 10 −6 M yr −1 [4,5,6], and polarization measurements [7] constrain it near the event horizon toṀ horizon ∼ 10 −8 M yr −1 . A range of models was developed to describe the accretion gas onto an underfed black hole [8,9,10]. However, the exact physics still remains to be understood. One challenge with the radiation inefficient accretion flows (RIAFs) is that even if one understands the dynamics there is no accepted prescription for associating emissivity (and absorption) with the flow. The other issue is the lack of model-independent probes of accretion flow at intermediate radii (between few and ∼ 10 5 R s ), i.e. the constraints that do not assume a model of accretion flow as an input parameter. Here we report a detection and imaging of the 10 4 K ionized gas disk within 2×10 4 R Sch in a millimetre hydrogen recombination line H30α : n = 31 → 30 at 231.9 GHz [11,12] using the Atacama Large Millimeter/submillimeter Array (ALMA). The emission was detected with a double-peaked line profile spanning full width of 2, 200 km s −1 with the approaching and the receding components straddling Sgr A*, each offset from it by 0.11 arcsec = 0.004 pc. The red-shifted side is displaced to the north-east, while the blue-shifted side is displaced to the south-west. The limit on the total mass of ionized gas estimated from the emission is 10 −4 − 10 −5 M at a mean hydrogen density 10 5 − 10 6 cm −3 , depending upon whether or not we assume the presence of a uniform density disk or an ensemble of orbiting clouds, and the amplification factor of the mm radiation due to the strong background source which is Sgr A* continuum.Black hole accretion and feedback are crucial to understanding the evolution of galaxies, the origin of relativistic jets, and to study physics near black hole horizons. Sgr A* is our nearest supermassive black hole. As such it offers an excellent opportunity to study accretion and outflow processes close to a black hole. X-ray measurements of gas density and temperature at the outer edge of the accretion flow, together with the assumptions of spherical adiabatic and constant in time accretion [13], can be used to estimate the mass supply to the black hole aṡ M Bondi ∼ 3×10 −6 M yr −1 [4,5,6]. If the radiative efficiency were ∼ 10% [14,15], the luminosity would be roughly 30,000 times the bolometric luminosity of ∼ 3 × 10 36 erg s −1 [16]. Extensive

Carefully accounting for neutrino transport is an essential component of many astrophysical studies. Solving the full transport equation is too expensive for most realistic applications, especially those involving multiple spatial dimensions. For such cases, resorting to approximations is often the only viable option for obtaining solutions. One such approximation, which recently became popular, is the M1 method. It utilizes the system of the lowest two moments of the transport equation and closes the system with an ad hoc closure relation. The accuracy of the M1 solution depends on the quality of the closure. Several closures have been proposed in the literature and have been used in various studies. We carry out an extensive study of these closures by comparing the results of M1 calculations with precise Monte Carlo calculations of the radiation field around spherically-symmetric protoneutron star models. We find that no closure performs consistently better or worse than others in all cases. The level of accuracy a given closure yields depends on the matter configuration, neutrino type, and neutrino energy. Given this limitation, the maximum entropy closure by Minerbo (1978) on average yields relatively accurate results in the broadest set of cases considered in this work.

In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark-gluon plasma, liquid helium 3 He-A, neutron stars and the Early Universe. We study first-order hydrodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiral magnetic waves) and transverse velocity (chiral Alfvén wave). We demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.

One-dimensional anisotropic photonic crystals and microcavities based on birefringent porous silicon are fabricated. The reflectance spectra demonstrate the presence of photonic band gap and microcavity modes with spectral positions tunable upon the sample azimuthal rotation around its normal and/or rotation of polarization plane of incident light. Simultaneous enhancement of second- and third-harmonic generation at the photonic band-gap edge due to the phase matching is observed. The angular positions of the second- and third-harmonic peaks are controllable via the anisotropy of the refractive indices of porous silicon layers.