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给星系中心称重(zhuan)  

2013-02-04 02:13:54|  分类: 天文学习 |  标签: |举报 |字号 订阅

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为远方的黑洞称重(图) - 月亮飞船 - 欢迎光临月亮飞船的博客

by Sid Perkins    胡德良 
 Give astronomers a few hours, and they can tell you the mass of any black hole within 244 million light-years. That's possible with a new technique that involves measuring the impacts of the light-sucking objects on clouds of molecular gas circling the centers of their home galaxies. In a paper published online today in Nature, researchers report that they have used the method to weigh the supermassive black hole at the heart of NGC 4526, which lies 53 million light-years away. Previously, researchers have estimated black hole masses by modeling their gravitational effects on individual stars or on clouds of electrically charged gases, but the motions of those objects are typically much more random than the motions of clouds containing uncharged gases. In the new work, scientists training their radio telescopes on NGC 4526 specifically measured the motions of gas clouds (depicted in purple, and superimposed on a Hubble Space Telescope image) containing carbon monoxide, a gas commonly found in such clouds. The motions of those clouds, as observed at a particular wavelength of microwave radiation, indicate that the black hole that resides there is about 450 million times the mass of our sun. Using the new technique with radio-telescope arrays poised to come on line soon, scientists should—working at the same resolution and sensitivity of today's instruments—be able to readily estimate in a matter of hours the masses of black holes inhabiting the centers of galaxies up to 244 million light-years away from ours. That's a volume of space that contains tens of thousands of galaxies, including hundreds that host substantial clouds of molecular gas, the researchers note.   给天文学家们几个小时的时间,他们就能够告诉你2.44亿光年范围之内任何黑洞的质量。利用一项新技术有可能做到这些,这项新技术涉及测量这种吸光物体(黑洞)对星系周围分子气体云的影响度。今天,研究人员在《自然》杂志在线版上报道说,他们利用这个方法测量了星系NGC 4526中心的超级黑洞,该黑洞位于5300万光年之外。以前,研究人员通过模拟黑洞对个别恒星或带电云团的引力影响来估计黑洞质量,但是相对于非带电云团来讲,恒星及带电云团的运动表现出极大的不规则性。在这项新研究中,科学家们将他们的射电望远镜对准NGC 4526,特别测量了气体云的运动(在哈勃太空望远镜获取的图片中显示为紫色而且层次分明),其中含有一氧化碳,而一氧化碳通常存在于这样的云团中。在微波辐射的特定波长下对这些气体云的观测表明,位于中心的黑洞大约是太阳质量的4.5亿倍。利用这项新技术以及很快准备投入运行的射电望远镜阵列,凭着当今仪器的辨率和敏感度,科学家们应该能够在几个小时的时间里,轻而易举地估计出距离我们2.44亿光年范围内星系中心的黑洞质量。研究人员指出,这个空间范围包括数以万计的星系,而且包括几百个拥有分子气体云的星系。
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