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原图片作者：C. Heinke et al. 文字：NASA/CXO/SAO
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New Chandra observations give the best information yet on why such neutron stars, called millisecond pulsars, are rotating so fast. The key, as in real estate, is location, location, location - in this case the crowded confines of the globular star cluster 47 Tucanae, where stars are less than a tenth of a light year apart. Almost two dozen millisecond pulsars are located there. This large sample is a bonanza for astronomers seeking to test theories for the origin of millisecond pulsars, and increases the chances that they will find a critical transitional object such 47 Tuc W.
Chandra 新近的观测，对毫秒脉冲星为何自传如此之快的问题，提供了迄今为止最有用的信息。关键的事情，正如在房地产行业中一样，是地段，地段，还是地段，也就是脉冲星所处的环境！就本例来说，在球状星团杜鹃座47的范围内，成员星之间距离不足十分之一光年，这就是有利于毫秒脉冲星形成的地段条件。在杜鹃座47中蕴含着将近两打毫秒脉冲星，这样巨大的样本，对于寻求毫秒脉冲星起源的天文学家来说，是一座富矿。它增大了我们找到像杜鹃座47W这样一个临界的过渡天体的机会。
47 Tuc W stands out from the crowd because it produces more high-energy X-rays than the others. This anomaly points to a different origin of the X-rays, namely a shock wave due to a collision between matter flowing from a companion star and particles racing away from the pulsar at near the speed of light. Regular variations in the optical and X-ray light corresponding to the 3.2-hour orbital period of the stars support this interpretation.
杜鹃座47W从星团中脱颖而出，因为它产生的高能X射线比其它成员都要强。这一异乎寻常的特征表明了X射线的另一种来源，即，因一颗伴星涌出的物质与从脉冲星逸散的微粒（？）以接近光速相撞而产生的冲击波。与该星3.2小时轨道周期相对应的规则光学和X射线光变从侧面支持了这一阐述。
A team of astronomers from the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA pointed out that the X-ray signature and variability of the light from 47 Tuc W are nearly identical to those observed from an X-ray binary source known as J1808. They suggest that these similarities between a known millisecond pulsar and a known X-ray binary provide the long-sought link between these types of objects.
来自哈佛-史密松天体物理中心的一个天文学家小组指出，来自杜鹃座47W的X射线信号及光变特征与观测X射线双星J1808所得到的几乎完全相同。他们认为，一个已知的毫秒脉冲星与一个已知的X射线双星之间的这种相似性，为我们提示了这两类天体间长期未知的内在联系。
In theory, the first step toward producing a millisecond pulsar is the formation of a neutron star when a massive star goes supernova. If the neutron star is in a globular cluster, it will perform an erratic dance around the center of the cluster, picking up a companion star which it may later swap for another.
理论上，形成一颗毫秒脉冲星的第一步，是一个大质量恒星在成为超新星而爆发后留下的中子星。如果这个中子星处于球状星团中，它就会围绕星团中心作不规则的“舞蹈”运动，俘获一个“舞伴”（伴星），而且将来还可能更换它的伴侣。
As on a crowded dance floor, the congestion in a globular cluster can cause the neutron star to move closer to its companion, or to swap partners to form an even tighter pair. When the pairing becomes close enough, the neutron star begins to pull matter away from its partner. As matter falls onto the neutron star, it gives off X-rays. An X-ray binary system has been formed, and the neutron star has made the crucial second step toward becoming a millisecond pulsar.
如同在一个拥挤的舞厅里一样，球状星团里的壅塞局面会让中子星和它的伴星靠得更近，或者彼此交换舞伴，结合成更牢固的组合。当这样的一对双星距离足够近时，中子星就开始从伴星夺取物质。当伴星物质陷落到中子星上时，它就发射出X射线。X射线双星就这样形成了，于是这颗中子星就向成为毫秒脉冲星迈出了关键的第二步。
The matter falling onto the neutron star slowly spins it up, in the same way that a child's carousel can be spun up by pushing it every time it comes around. After 10 to 100 million years of pushing, the neutron star is rotating once every few milliseconds. Finally, due to the rapid rotation of the neutron star, or the evolution of the companion, the infall of matter stops, the X-ray emission declines, and the neutron star emerges as a radio-emitting millisecond pulsar.
向中子星奔去的物质缓缓地加快着中子星的旋转，如同小孩玩的旋转木马，每当转过来时就推它一把，它就会越转越快。经过了几千万到上亿年的加速，中子星开始以几毫秒为周期高速自转。最后，由于中子星疾速的自转，或是伴星自身的演化，物质的流入停止，X射线辐射减弱，这颗中子星就呈现出了毫秒脉冲星的面目。
It is likely that the companion star in 47 Tuc W - a normal star with a mass greater than about an eighth that of the Sun - is a new partner, rather than the companion that spun up the pulsar. The new partner, acquired fairly recently in an exchange that ejected the previous companion, is trying to dump on the already spun-up pulsar, creating the observed shock wave. In contrast, the X-ray binary J1808 is not in a globular cluster, and is very likely making do with its original companion, which has been depleted to a brown dwarf size with a mass less than 5% that of the Sun.
杜鹃座47W的伴星——一颗质量略大于太阳质量八分之一的普通恒星——是新获得的，而非原来为脉冲星加速的那颗。这颗伴星是在新近的一次更换中，原来的伴星被抛出后被捕获的。这颗新伴星正全力向高速自转的脉冲星上扑去，造成了观测到的冲击波。与之相对照，X射线双星J1808并非在球状星团里，很可能正靠着它原配的伴星苟延残喘。它的伴星已经被剥削得只剩下一颗褐矮星般大小，质量不到太阳的5%.
Most astronomers accept the binary spin-up scenario for creating millisecond pulsars because they have observed neutron stars speeding up in X-ray binary systems, and almost all radio millisecond pulsars are observed to be in binary systems. Until now, definitive proof has been lacking, because very little is known about transitional objects between the second and final steps.
多数天文家接受这个假想的模式，因为他们已经在X射线双星系统中观测到了中子星的加速现象，而且几乎所有的毫秒脉冲星都被发现时处于双星系统中。然而直到目前，决定性的证据还未获得，因为介于第一和第二步之间的过渡天体还几乎不为人所知。
That is why 47 Tuc W is hot. It links a millisecond pulsar with many of the properties of an X-ray binary, to J1808, an X-ray binary that behaves in many ways like a millisecond pulsar, thus providing a strong chain of evidence to support the theory.
这就是杜鹃座47W成为大热门的原因。它使具有X射线双星多方面性质的毫秒脉冲星，与表现得类似毫秒脉冲星的X射线双星——J1808——联系在了一起。这样，就为支持上述理论提供了强有力的证据链条。
Observation Dates 16-17 Mar 2000; 29 Sep-03 Oct 2002; 11 Oct 2002
Observation Time 47 hours
References Slavko Bogdanov, Jonathan Grindlay, and Maureen Van Den Berg, "An X-ray Variable Millisecond Pulsar in the Globular Cluster 47 Tucanae: Closing the Link to Low Mass X-ray Binaries", 2005 Astrophys. J. (In press) see also astro-ph/0506031
Release Date July 19, 2005 |
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