We present results from high-resolution semi-global simulations of
neutrino-driven convection in core-collapse supernovae. We employ an idealized
setup with parametrized neutrino heating/cooling and nuclear dissociation at
the shock front. We study the internal dynamics of neutrino-driven convection
and its role in re-distributing energy and momentum through the gain region. We
find that even if buoyant plumes are able to locally transfer heat up to the
shock, convection is not able to create a net positive energy flux and overcome
the downwards transport of energy from the accretion flow. Turbulent convection
does, however, provide a significant effective pressure support to the
accretion flow as it favors the accumulation of energy, mass and momentum in
the gain region. We derive an approximate equation that is able to explain and
predict the shock evolution in terms of integrals of quantities such as the
turbulent pressure in the gain region or the effects of non-radial motion of
the fluid. We use this relation as a way to quantify the role of turbulence in
the dynamics of the accretion shock. Finally, we investigate the effects of
grid resolution, which we change by a factor 20 between the lowest and highest
resolution. Our results show that the shallow slopes of the turbulent kinetic
energy spectra reported in previous studies are a numerical artefact.
Kolmogorov scaling is progressively recovered as the resolution is increased.

文章对超新星中微子驱动对流进行了高分辨率的半全局模拟，发现该对流虽然不能产生净正能量通量，但对加聚流的动力学有着显著的支撑作用，同时探究了分辨率对动力学性质的影响。

中心塌缩超新星中的中微子驱动对流：高分辨率模拟

Neutrino-Driven Convection in Core-Collapse Supernovae: High-Resolution  Simulations

The cores of most galaxies are thought to harbour supermassive black holes,
which power galactic nuclei by converting the gravitational energy of accreting
matter into radiation (ref 1). Sagittarius A*, the compact source of radio,
infrared and X-ray emission at the centre of the Milky Way, is the closest
example of this phenomenon, with an estimated black hole mass that is 4 million
times that of the Sun (refs. 2,3). A long-standing astronomical goal is to
resolve structures in the innermost accretion flow surrounding Sgr A* where
strong gravitational fields will distort the appearance of radiation emitted
near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have
detected intrinsic structure in Sgr A*, but the spatial resolution of
observations at these wavelengths is limited by interstellar scattering (refs.
4-7). Here we report observations at a wavelength of 1.3 mm that set a size of
37 (+16, -10; 3-sigma) microarcseconds on the intrinsic diameter of Sgr A*.
This is less than the expected apparent size of the event horizon of the
presumed black hole, suggesting that the bulk of SgrA* emission may not be not
centred on the black hole, but arises in the surrounding accretion flow.

研究了通过 1.3mm 波长射电观测所得到最近的银河系中心黑洞 Sagittarius A * 固有尺度大小并据此推断黑洞中心放射可能不是局部的、主要源自于其周围的吸积流，这可能挑战了我们对黑洞工作原理的认识。

银河系中心超大质量黑洞候选体的事件视界尺度结构

Event-horizon-scale structure in the supermassive black hole candidate  at the Galactic Centre

Images from the vicinity of the black hole horizon at the Galactic centre
(Sgr A*) could be obtained in the near future with a Very Large Baseline Array
of sub-millimetre telescopes. The recently observed short-term infrared and
X-ray variability of the emission from Sgr A* implies that the accretion flow
near the black hole is clumpy or unsteady. We calculate the appearance of a
compact emission region (bright spot) in a circular orbit around a spinning
black hole as a function of orbital radius and orientation. We find that the
mass and spin of the black hole can be extracted from their generic signatures
on the spot image as well as on the lightcurves of its observed flux and
polarisation. The strong-field distortion remains noticeable even when the spot
image is smoothed over the expected ~20 microarcsecond resolution of future
sub-millimetre observations.

通过朝向银河系中央的超大质量黑洞视界附近拍摄短波射电，红外以及 X 射线照片，发现了一个环绕旋转黑洞圆形轨道上存在流致密区域，其质量和自旋能够通过区域的视图特征以及其观测流量和极化特征曲线推出。