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天文学家们早就知道在银河系的中心存在着一个超级质量的黑洞，这就是Sagittarius A(简称为Sgr A)，它是一个非常可怜的食客。

英文原文：

Astronomers have long known that the supermassive black hole at the center of the Milky Way Galaxy, known as Sagittarius A (or Sgr A for short), is a particularly poor eater. The fuel for this black hole comes from powerful winds blown off dozens of massive young stars that are concentrated nearby. These stars are located a relatively large distance away from Sgr A, where the gravity of the black hole is weak, and so their high-velocity winds are difficult for the black hole to capture and swallow. Scientists have previously calculated that Sgr A should consume only about 1 percent of the fuel carried in the winds.www.Ｅxamda.CoM However, it now appears that Sgr A consumes even less than expected -- ingesting only about one percent of that one percent. Why does it consume so little? The answer may be found in a new theoretical model developed using data from a very deep exposure made by NASA’s Chandra X-ray Observatory. This model considers the flow of energy between two regions around the black hole: an inner region that is close to the so-called event horizon (the boundary beyond which even light cannot escape), and an outer region that includes the black hole’s fuel source -- the young stars -- extending up to a million times farther out. Collisions between particles in the hot inner region transfer energy to particles in the cooler outer region via a process called conduction. This, in turn, provides additional outward pressure that makes nearly all of the gas in the outer region flow away from the black hole. The model appears to explain well the extended shape of hot gas detected around Sgr A in X-rays as well as features seen in other wavelengths.

This Chandra image of Sgr A and the surrounding region is based on data from a series of observations lasting a total of about one million seconds, or almost two weeks. Such a deep observation has given scientists an unprecedented view of the supernova remnant near Sgr A (known as Sgr A East) and the lobes of hot gas extending for a dozen light years on either side of the black hole. These lobes provide evidence for powerful eruptions occurring several times over the last ten thousand years.

The image also contains several mysterious X-ray filaments, some of which may be huge magnetic structures interacting with streams of energetic electrons produced by rapidly spinning neutron stars. Such features are known as pulsar wind nebulas.

This new model of Sgr A was presented at the 215th meeting of the American Astronomical Society in January 2009 by Roman Shcherbakov and Robert Penna of Harvard University and Frederick K. Baganoff of the Massachusetts Institute of Technology.

译文：

天文学家们早就知道在银河系的中心存在着一个超级质量的黑洞，这就是Sagittarius A(简称为Sgr A)，它是一个非常可怜的食客。这个黑洞的食物来自于它周围十几个大质量的年青恒星所吹出的强风。这些恒星的位置距Sgr A相对较远，黑洞的引力较弱，所以黑洞很难捕捉并吞食它们发出的高速强风。科学家过去曾经计算出Sgr A仅能吃掉这些强风所携带的燃料的1%。

然而，最近发现Sgr A甚至比先前估计的还要吃的少——它仅消化了原来估算的1% 的1%。为什么它吸收的如此之少呢？答案可能会从新的理论模型中找到，而这个新的理论模型是从NASA 钱德拉 X-射线观测站所获得的超深空数据中发展起来的。此模型分析围绕在黑洞周边的两个区域间的能量流：内部的区域接近于视界（一个理论上的边界，超过此边界甚至光都无法逃脱黑洞的吞噬），外部区域包括黑洞的燃料源——年青的恒星——并继续扩展数百万倍。在较热的内部区域，粒子间的相互撞击将能量传递给了较冷的外部区域中的粒子，这一过程被称为传导。而这个过程的就提供了额外的外向压力使几乎所有外部区域中的气体被吹离黑洞。这个模型看来很好的解释了X-射线探测到的Sgr A周围扩张的热气体形态与其它波长射线所探测的特征相一致。

这幅钱德拉观测站制作的Sgr A及其周边区域的图像是基于一系列观测所得的数据，这一系列观测持续了整整1百万秒，或者说是几乎两周的时间。如此深度的观察使科学家前所未有的看到了Sgr A附近一个超新星的残余部分（称之为Sgr A East）以及黑洞两边延续十几光年的热气体团。这些气体团证实了在过去一万年里曾发生过数次猛烈的喷发。

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