Donati Jean-François, Paletou Fréderic, Bouvier Jérome, Ferreira Jonathan
Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, F-31400 Toulouse, France.
Nature. 2005 Nov 24;438(7067):466-9. doi: 10.1038/nature04253.
Models predict that magnetic fields play a crucial role in the physics of astrophysical accretion disks and their associated winds and jets. For example, the rotation of the disk twists around the rotation axis the initially vertical magnetic field, which responds by slowing down the plasma in the disk and by causing it to fall towards the central star. The magnetic energy flux produced in this process points away from the disk, pushing the surface plasma outwards, leading to a wind from the disk and sometimes a collimated jet. But these predictions have hitherto not been supported by observations. Here we report the direct detection of the magnetic field in the core of the protostellar accretion disk FU Orionis. The surface field reaches strengths of about 1 kG close to the centre of the disk, and it includes a significant azimuthal component, in good agreement with recent models. But we find that the field is very filamentary and slows down the disk plasma much more than models predict, which may explain why FU Ori fails to collimate its wind into a jet.
模型预测，磁场在天体物理吸积盘及其相关的风与喷流的物理过程中起着至关重要的作用。例如，盘的旋转会使最初垂直的磁场围绕旋转轴扭曲，这会导致盘中等离子体减速并使其向中心恒星下落。在此过程中产生的磁能通量指向远离盘的方向，将表面等离子体向外推，从而形成来自盘的风，有时还会形成准直喷流。但迄今为止，这些预测尚未得到观测结果的支持。在此，我们报告了对原恒星吸积盘猎户座FU核心磁场的直接探测。靠近盘中心处的表面磁场强度达到约1千高斯，且包含显著的方位角分量，这与近期模型高度吻合。但我们发现该磁场非常呈丝状，且使盘等离子体减速的程度远超过模型预测，这或许可以解释为何猎户座FU无法将其风准直成喷流。
