标题： 银河系中心黑洞人马座A*的固有大小：72个史瓦西半径 显示英文标题

标题： Intrinsic Size OF Sgr A*: 72 Schwarzschild Radii

摘要： 银河系中心恒星的最新自行研究表明，银河系中心紧凑的非热无线电波源人马座（Sgr）A*是一个质量为250万个太阳质量的黑洞。 通过近同时的多波长甚长基线阵列测量，我们首次确定了Sgr A*的固有大小和形状为72 Rsc乘以小于20 Rsc，其中长轴基本上指向南北方向，其中 Rsc（= 7.5 x 10^{11} 厘米）是质量为250万个太阳质量的黑洞的史瓦西半径。 与之前预期的Sgr A*的固有结构只能在波长小于1毫米的情况下观测到相反，我们可以分辨出7毫米波长下的固有源大小，因为（1）沿短轴的散射尺寸是长轴的一半，以及（2）使用相同的干涉仪对Sgr A*进行的近同时多波长测绘使得精确推断7毫米波长下的短轴散射角度成为可能。 固有的大小和形状直接限制了Sgr A*的各种发射模型。 特别是，为了解释Sgr A*的结构，吸积流的辐射主导模型可能需要包含一个无线电喷流。 显示英文摘要

摘要： Recent proper motion studies of stars at the very center of the Galaxy strongly suggest that Sagittarius (Sgr) A*, the compact nonthermal radio source at the Galactic Center, is a 2.5 million solar mass black hole. By means of near-simultaneous multi-wavelength Very Long Baseline Array measurements, we determine for the first time the intrinsic size and shape of Sgr A* to be 72 Rsc by < 20 Rsc, with the major axis oriented essentially north-south, where Rsc (= 7.5 x 10^{11} cm) is the Schwarzschild radius for a 2.5 million solar mass black hole. Contrary to previous expectation that the intrinsic structure of Sgr A* is observable only at wavelengths shorter than 1 mm, we can discern the intrinsic source size at 7 mm because (1) the scattering size along the minor axis is half that along the major axis, and (2) the near simultaneous multi-wavelength mapping of Sgr A* with the same interferometer makes it possible to extrapolate precisely the minor axis scattering angle at 7 mm. The intrinsic size and shape place direct constraints on the various emission models for Sgr A*. In particular, the advection dominated accretion flow model may have to incorporate a radio jet in order to account for the structure of Sgr A*.