文章掠影：
　　天文學家們早就知道在銀河系的中心存在著一個超級質(zhì)量的黑洞，這就是Sagittarius A*(簡稱為Sgr A*)，它是一個非常可憐的食客。
　　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.
　　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.
　　參考譯文：
　　天文學家們早就知道在銀河系的中心存在著一個超級質(zhì)量的黑洞，這就是Sagittarius A*(簡稱為Sgr A*)，它是一個非�？蓱z的食客。這個黑洞的食物來自于它周圍十幾個大質(zhì)量的年青恒星所吹出的強風。這些恒星的位置距Sgr A*相對較遠，黑洞的引力較弱，所以黑洞很難捕捉并吞食它們發(fā)出的高速強風�？茖W家過去曾經(jīng)計算出Sgr A*僅能吃掉這些強風所攜帶的燃料的1%。
　　然而，最近發(fā)現(xiàn)Sgr A*甚至比先前估計的還要吃的少——它僅消化了原來估算的1% 的1%。為什么它吸收的如此之少呢？答案可能會從新的理論模型中找到，而這個新的理論模型是從NASA 錢德拉 X-射線觀測站所獲得的超深空數(shù)據(jù)中發(fā)展起來的。此模型分析圍繞在黑洞周邊的兩個區(qū)域間的能量流：內(nèi)部的區(qū)域接近于視界（一個理論上的邊界，超過此邊界甚至光都無法逃脫黑洞的吞噬），外部區(qū)域包括黑洞的燃料源——年青的恒星——并繼續(xù)擴展數(shù)百萬倍。在較熱的內(nèi)部區(qū)域，粒子間的相互撞擊將能量傳遞給了較冷的外部區(qū)域中的粒子，這一過程被稱為傳導。而這個過程的就提供了額外的外向壓力使幾乎所有外部區(qū)域中的氣體被吹離黑洞。這個模型看來很好的解釋了X-射線探測到的Sgr A*周圍擴張的熱氣體形態(tài)與其它波長射線所探測的特征相一致。
　　這幅錢德拉觀測站制作的Sgr A*及其周邊區(qū)域的圖像是基于一系列觀測所得的數(shù)據(jù)，這一系列觀測持續(xù)了整整1百萬秒，或者說是幾乎兩周的時間。如此深度的觀察使科學家前所未有的看到了Sgr A*附近一個超新星的殘余部分（稱之為Sgr A East）以及黑洞兩邊延續(xù)十幾光年的熱氣體團。這些氣體團證實了在過去一萬年里曾發(fā)生過數(shù)次猛烈的噴發(fā)。
　　這幅圖像中還包含了幾個神秘的X-射線片斷，它們中的一些可能是因為巨大的磁場結(jié)構(gòu)和強電子流相互作用而產(chǎn)生了快速旋轉(zhuǎn)的中子星。這種特征被稱為脈沖星云。
　　這一新的關(guān)于Sgr A*的模型是在2009年1月召開的215屆美國天文協(xié)會會議中，由哈佛大學的Roman Shcherbakov和Robert Penna，以及馬薩諸塞技術(shù)學院的Frederick K. Baganoff提出來的。