Investigations in Theoretical Astrophysics

摘要：Narayan， Ramesh这项拨款将研究两个课题。第一种是引力透镜，这是一种来自遥远光源的光线受到介入星系的引力影响而偏转的现象。在某些情况下，这会导致观察者看到一个源的多个图像。从观测到的图像中可以推断出介入质量的引力分布，并提出了一种新的算法，该算法基于最大熵法，这是一种著名的图像处理技术。此外，当一个光源是多重图像时，光通过不同的路径到达观察者需要不同的时间长度。通过将透镜模型与图像中相关变化之间测量的时间差相结合，可以估计到光源的距离，从而得到哈勃常数Ho的值。第二个主题是吸积流，粘性的螺旋状气体进入致密的重力质量，如中子星或黑洞。PI建议对靠近吸积质量的内部区域进行建模，大部分观测到的辐射来自那里。中子星和黑洞的情况将得到不同的处理，因为气体在中子星上的吸积最终会减慢并停留在恒星表面，而黑洞周围的气流在穿过视界之前会加速到超音速径向速度。＊＊＊

ABSTRACT AST- 9423209 Narayan, Ramesh This grant will pursue two topics. The first is Gravitational Lensing, the phenomenon by which light rays from a distant source are deflected by the gravitational influence of intervening galaxies. In some cases, this results in an observer seeing multiple images of a source. It is possible to deduce the gravitational distribution of the intervening mass from the observed images, and it is proposed to develop a new algorithm for this, based on the Maximum Entropy Method, a well-known image processing technique. Furthermore, when a source is multiply-images, light takes different lengths of time to reach the observer by different paths. By combining a model of the lens with the measured time difference between correlated variations in the image, the distance to the source can be estimated, which gives a value for Ho, the Hubble constant. The second topic is Accretion Flows, viscous spiraling in of gas onto a compact gravitating mass, such as a neutron star or a black hole. The PI proposes to model the inner regions close to the accreting mass, whence most of the observed radiation derives. The neutron star and black hole cases will be treated differently, since gas accreting onto a neutron star ultimately slows down and settles on the stellar surface, whereas flow around a black hole accelerates to supersonic radial speeds before falling through the horizon. ***