Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany.
Nature. 2013 Sep 19;501(7467):391-4. doi: 10.1038/nature12499. Epub 2013 Aug 14.
Earth's nearest candidate supermassive black hole lies at the centre of the Milky Way. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to synchrotron emission such as that previously observed. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre and show that the pulsar's unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission--from radio to X-ray wavelengths--from the black hole.
地球最近的候选超大质量黑洞位于银河系中心。它的电磁发射被认为是由其环境中的气体的辐射低效吸积提供能量，这是大多数星系核的标准能量供应模式。X 射线测量已经解析出一种稀薄的热气体成分，黑洞可以从中获得物质。然而，气体的磁化率是决定吸积流结构的关键参数，目前仍不清楚。强磁场可以影响吸积的动力学，从下落的气体中带走角动量，通过相对论喷流将物质排出，并导致以前观察到的同步辐射等现象。在这里，我们报告了对银河系中心附近一个新发现的脉冲星的多频率射电测量结果，并表明脉冲星异常大的法拉第旋转（在存在外加磁场时，辐射的偏振面的旋转）表明在黑洞附近存在一个动态上重要的磁场。如果这个磁场被吸积到事件视界，它就提供了足够的磁通量来解释从无线电到 X 射线波长的观测到的黑洞发射。
