Explanation: How far do magnetic fields extend up and out of spiral galaxies? For decades astronomers knew only that some spiral galaxies had magnetic fields. However, after NRAO’s Very Large Array (VLA) radio telescope (popularized in the movie Contact) was upgraded in 2011, it was unexpectedly discovered that these fields could extend vertically away from the disk by several thousand light-years. The featured image of edge-on spiral galaxy NGC 5775, observed in the CHANG-ES (Continuum Halos in Nearby Galaxies) survey, also reveals spurs of magnetic field lines that may be common in spirals. Analogous to iron filings around a bar magnet, radiation from electrons trace galactic magnetic field lines by spiraling around these lines at almost the speed of light. The filaments in this image are constructed from those tracks in VLA data. The visible light image, constructed from Hubble Space Telescope data, shows pink gaseous regions where stars are born. It seems that winds from these regions help form the magnificently extended galactic magnetic fields.
Tomorrow’s picture: Messier 66 Close Up
说明: 螺旋星系的磁场能延伸多远？数十年来，天文学家只知道有些螺旋星系有磁场。不过，在2011年美国国家电波天文台（NRAO）的极大阵列（VLA的天线碟曾在电影「接触未来」里大出风头）设备升级之后，意外发现这类星系的磁场，可从盘面垂直向外伸展数千光年。这幅来自CHANG-ES巡天计画的侧向螺旋星系NGC 5775之主题影像，显示在螺旋星系里，针状磁力线或许很常见的景观。而类似棒磁铁周围的铁屑，星系磁力线的周围，也有电子以光速旋绕磁力线所发出的辐射。影像中的丝状物，即是建构自极大阵列数据的磁力线。而建构自哈伯太空望远镜据的可见光影像，则呈现恒星诞生所在的粉红云气区。源自恒星形成区的恒星风，看似协力造就了这些延伸极远的壮观星系磁场。
明日的图片: Messier 66 Close Up