Stardust

First Exoplanet Discovered through Astrometry Suggests Plethora of Worlds to Come
首个通过天体测量发现的太阳系外行星暗示更多世界的到来

By Amir Alexander
June 11, 2009

There are several reasons why the new exoplanet discovered last month orbiting the red dwarf VB 10 has set the planet-hunting community abuzz. For one thing the planet is a "cold Jupiter," similar to our giant neighbor and very different from the host of "Hot Jupiters" that make up the largest contingent of known exoplanets. For another the planet's home star is one of the smallest known stars, with a mass of only one twelfth that of the Sun. This makes it the smallest star known to possess a planet. But what makes this alien world truly exceptional to astronomers is the manner in which it was discovered: For the planet designated VB 10b is the first one ever discovered through astrometry.
上个月发现的绕红矮星 VB 10 转动的新太阳系外行星使得行星搜寻社区变得喧闹起来有几个原因。其中之一该行星是个同我们的巨大邻居相似的“冷木星”，与一大群“热木星”有很大的不同，这使得了解太阳系外行星的可能性提高了。另一点，该行星的主星是种已知的最小恒星，质量仅有太阳的1/12。这使其成为已知拥有一颗行星的最小恒星。不过这个外星世界对天文学家来说真正特别之处在于其发现的方法：定为 VB 10b 的这个行星是第一个通过天体测量发现的行星。

As the term suggests, "astrometry" is the measurement of stars, or more specifically their precise location in the sky. In a way, "astrometry" is precisely what astronomers have always done, measuring the exact positions of celestial objects. It is therefore not altogether surprising that astrometry was also the first method used in searching for planets around faraway stars. In fact, the earliest claim by an astronomer to have discovered an exoplanet through astrometry was made as early as 1943 – more than half a century before the discovery of the first confirmed exoplanet by Michel Mayor and his colleagues.
如同术语所说，“天体测量”是对恒星的测量，更具体的说是对它们在天空中精确位置的测量。某种程度上，“天体测量”的确是天文学家们总是在做的事，测量天上目标的准确位置。因此总的来说没啥奇怪的，天体测量也是第一种用来寻找遥远恒星周围行星的方法。实际上，最早由一位天文学家宣称通过天体测量发现一个太阳系外行星的事发生在1943年——比 Michel Mayor 及其同事所发现的第一个被确认太阳系外行星要早半个世纪。

Here's how the method works: when a planet orbits a star, it is not only the planet that moves. The star too moves in its own little orbit, circling around the system's center of gravity. In principle the star's wobble can be observed and recorded with precise astrometric measurements from Earth. From this it is then possible to deduce the distant planet's orbit and period. And since the mass of the star itself is known with considerable accuracy from its light spectrum, it is also possible to deduce the companion planet's mass.
这种方法是这样工作的：当一颗行星围绕恒星运行时并不只是行星在动，恒星同样也在它自己的小轨道上围绕系统的引力中心运动。原则上讲在地球上通过精确的天体测量可以观测并记录到恒星的这种摆动。这样就有可能推算出遥远行星的轨道和周期。同时由于可以通过恒星的光谱相当准确的知道恒星自身的质量，就有可能推算出伙伴行星的质量。

Astrometry is not the only planet-hunting method to look for a star's motion as it is orbited by a planet. The radial velocity technique, responsible for detecting most of the known exoplanets, also looks for the telltale signs of a star's wobble that indicate the presence of a planet. But radial velocity can detect only the motion of a star towards or away from Earth, and works best when the star's motion along this axis is most pronounced – i.e. when the planetary system is "edge on" when viewed from the Earth. Conversely, astrometry works best when a planetary system is "face-on" when seen from Earth, because then the star's movements in the orbital plane are most pronounced. In this sense the astrometry and radial velocity planet-hunting methods complement each other, each excelling in the other method's blind spot.
当恒星附近有一颗行星的时候天体测量并不是唯一的一种通过观察恒星运动搜寻行星的办法。视向速度技术，绝大多数已知太阳系外行星所用的探测技术，同样是观察表明有行星存在的恒星的摆动。不过视向速度仅能探测到恒星朝向或远离我们的速度，并且在恒星运动沿着一轴线最显著的时候最有效。举例来说就是从地球上看去行星系统是“侧向”的时候。与之相反，从地球看去行星系统是“面向”的时候天体测量最有效，因为此时恒星在轨道面上的运动最显著。从这一意义上说天体测量和视向速度行星搜索法是互为补充的，各自在彼此方法的盲区表现出色。

Astrometry has other advantages as well. The leading exoplanet detection methods, radial velocity and transit photometry, are both most sensitive to planets orbiting very close to their star. Astrometry, in contrast, works best with planets that orbit at a considerable distance from their star, because such planets induce a greater displacement in the position of their stars. As a result astrometry is ideally suited for detecting solar systems where planets take months or years to complete an orbit, rather than "hot Jupiter" systems, where gas giants complete each revolution in a matter of days. In other words, astrometry is ideally suited for detecting planetary systems like our own.
天体测量也有其他优势。视向速度和食测光法是处于领导地位的太阳系外行星探测法，都对行星轨道非常靠近其主星的情况最敏感。天体测量正相反，对行星轨道距主星有相当距离的情况最有效，因为这样的行星诱导其主星位置位移的量较大。因此天体测量十分适合探测那些行星公转周期在数月到数年的恒星系统，而不是那些公转周期大约数天的“热木星”系统。换句话说，天体测量很适合探测像我们这样的行星系统。

The main drawback of the astrometric method, as its long history of discredited claims attests, is that it is very hard to do. One major difficulty is that regardless of whether they possess planets or not, all stars do move through the sky in a slight but measurable movement known as "proper motion." This is the stars' real motion relative to the Sun and around the center of the galaxy. In addition, all stars appear to move in the sky due to "stellar parallax" – the slight displacement caused by the motion of the Earth around the Sun. Now although proper motion and parallax produce only a very tiny displacement in a star's position in the sky, it is still far greater than the displacement that would indicate the presence of a planetary companion.
天体测量的主要缺点在于其很难操作。一个主要的难题是不考虑恒星是否拥有行星，所有的恒星都以一种很微小但可以测量的速度在天空中移动，这就是所谓的“自行”。这是恒星围绕银河中心相对于太阳的真实运动。此外，所有的恒星由于“恒星视差”——由于地球绕太阳运行所产生的微小运动，的缘故会在空中表现出移动。虽然自行和视差仅是恒星位置在天空中非常微小的移动，它仍然比能表明有行星伙伴存在的移动要大的多。

In order to detect a planet orbiting a distant star with astrometry, one must first take into account the change in the star's position caused by parallax and proper motion. Only the residue left (if one is found) after these larger factors have been deducted from the total motion can potentially be evidence of an orbiting planet. Detecting this miniscule residual motion requires an extraordinary degree of astrometric precision, which has never been conclusively achieved. Until now, that is.
要用天体测量法探测绕遥远恒星转动的行星，人们首先必须考虑由自行和视差产生的恒星位置的改变。只有这些大的因子从总体运动中扣除后剩余的量能潜在的证实有一颗行星。要探测这一微小的剩余运动需要一种异常精确的角度测量，以前还未能完全获得这一方法，直到现在。

In a paper that will be published in the July issue of The Astrophysical Journal, astronomers Steven Pravdo and Stuart Shaklan of the Jet Propulsion Laboratory in Pasadena announce the discovery of a giant planet orbiting the red dwarf star VB 10. With the exception of largely discredited claims made decades ago, the planet, designated VB 10b, is the first planet every detected through astrometry.
一篇将于七月在《天体物理学》上发表的论文中，来自帕萨迪纳喷气推进实验室的天文学家Steven Pravdo 和 Stuart Shaklan 宣布发现一颗巨行星正绕红矮星 VB 10 运行。与几十年前大量不足信的声明不同，该行星被命名为 VB 10b，是第一颗通过天体测量发现的行星。

Pravdo and Shaklan made their discovery with the Stellar Planets Survey (STEPS) – an astrometric search for exoplanets and other low-mass objects that they have been running since 1998. Several times a year the two astronomers attach the STEPS CCD camera to the Hale Telescope at the Palomar Observatory in California. Each time they pointed their instrument at their selected target stars, and looking for any change in their position relative to background stars. The precision of their observations was mind-boggling, equivalent to measuring the width of a human hair from a distance of 3 kilometers.
自1998年以来 Pravdo 和 Shaklan 使用一种用于搜索太阳系外行星和其他低质量物体叫做 Stellar Planets Survey(STEPS) 的天体测量法完成其发现的。两位天文学家一年有数次将STEPS CCD相机附加到加利福尼亚帕洛玛天文台的 Hale 望远镜上。每一次他们都将其设备指向选定的目标星，观察它们的位置相对于背景星的任何变化。他们观测的精度是难以置信的，相当于在3千米外测量一根发丝的宽度。

After 9 years of observations Pravdo and Shaklin noticed that on of the targets of STEPS, VB 10, moves through the sky in a way that cannot be fully explained by the usual factors. They measured the star's proper motion and calculated its stellar parallax. They considered apparent motion due to rotating star-spots, and aberrations due to the possible presence of a disk of gas and dust around the star. And still the residual motion persisted. Once they introduced the possibility of a low-mass companion orbiting the star, however, the unexplained residual motion all but disappeared. The conclusion seemed inescapable: the star VB 10 is home to a planet.
经过9年的观测 Pravdo 和 Shaklin 注意到 STEPS 的一个目标 VB 10 在空中移动的方式无法完全用常规的因数解释。他们测量了该恒星的自行并计算了其视差。他们考虑所呈现出的这种运动是由于转动的星斑，以及可能存在一个围绕恒星的气体、尘埃盘产生的像差造成的。然而剩余的运动依然顽固的存在。一旦他们引入一个低质量伙伴围绕恒星转动的可能性后这无法解释的剩余运动差不多消失了。结论似乎是不可避免的：VB 10 有一颗行星。

By carefully analyzing the motion of the star, Pravdo and Shaklin were able to learn a great deal about its planetary companion. The planet, designated VB 10b, is a gas giant, 6.4 times the mass of Jupiter. It orbits its star at a distance similar that of Mercury from the Sun, and completes each orbit in 271 days. Being so close to its star, one might expect the planet to be a scorching "hot Jupiter" like many other exoplanets discovered in the past 14 years. This, however, is not the case: VB 10 is a tiny star, so small that until quite recently it held the distinction of being the smallest known star. Its mass is only one twelfth that of the Sun, and it is barely massive enough to initiate the fusion reaction in its core that makes stars shine. As a result, although VB 10b is much closer to its star than Jupiter is to the Sun, the two planets are in fact heated to about the same degree.
通过仔细的分析该恒星的运动，Pravdo 和 Shaklin 能了解到它的类行星伙伴很多情况。被命名为 VB 10b 的这颗行星是一个6.4倍木星质量的气体巨行星。它围绕其主星轨道的距离与水星到太阳的距离相近，公转一周需要271天。由于同主星靠得很近，有人可能会认为该行星如同这14年中发现的其他太阳系外行星一样是一颗极热的“热木星”。不过情况并不是这样：VB 10 是一颗很小的恒星，以至于直到最近它都保有已知最小恒星的殊荣。它的质量仅有太阳的1/12，刚刚达到能在其核心点燃核聚变成为恒星的界限。因此，虽然VB 10b距其主星比木星到太阳要近的多，实际上两颗行星被加热的程度一样。

"We found a Jupiter-like planet at around the same relative place as our Jupiter, only around a much smaller star" explained Pravdo. "It's possible this star also has inner rocky planets" he added, which would create a miniature version of our own solar system. Such a possibility is particularly intriguing because Pravdo's and Shaklin's calculations show that the habitable zone around VB 10 – the band in space in which liquid water is stable – largely overlaps with the region in which rocky planets could move in stable orbits. In other words, it is possible that an Earth-like planet with liquid water is circling the star well inside the orbit of VB 10b.
Pravdo 解释说：“我们在一个相当于木星位置的地方发现了一个木星状的行星，只不过它围绕的恒星是如此的小。这个恒星有可能还有岩石的内行星。”可以看作是我们太阳系的微缩版。这种可能性尤其吸引人，因为根据 Pravdo 和 Shaklin 的计算表明 VB 10 周围的宜居区——液态水可以稳定存在的空间地带——与岩石行星可以稳定运行的地带有很大的重合。换句话说，有可能一颗有水的地球型行星正在 VB 10b 的轨道内绕该恒星运行。



The VB 10 System and the Solar System.
The planetary system around the red dwarf VB 10 may be a miniature version of our solar system. The star is only one twelfth the mass of the Sun, and it is orbited by a Jupiter like gas giant, VB 10b, at a distance similar to that of Mercury from the Sun. This leaves room for small rocky planets orbiting even closer to VB 10, just as the small rocky planets in the solar system are inside Jupiter's orbit. Credit: NASA/JPL-Caltech
VB 10 和太阳系系统
环绕红矮星 VB 10 的行星系统有可能是太阳系的缩小版。该恒星只有太阳质量的十二分之一，并被一颗类木星的气体巨行星VB 10b 环绕，距离与水星到太阳相仿。这给更靠近 VB 10 的小型岩石行星留出了位置，就像太阳系中小的岩石行星位于木星轨道之内一样。


All this remains highly speculative at this point, and VB 10b will no doubt revolve many times around its star before scientists find out if a distant Earth is orbiting nearby. What is undeniable is that the astrometric detection of a planet around a red dwarf raises the possibility that planets are more common around these small stars than was previously suspected. Only 9 other red dwarfs are known to have planetary companions, and these were all discovered through the radial velocity technique. As Pravdo and Shaklin point out, however, this method is far less sensitive for these dim stars than it is for the larger and brighter Sun-like stars. Astrometry, in contrast, is exceptionally well-suited to detect planets around small stars, since such stars move more when they are orbited by a planet.
剩下的就是这一观点是带有高度推测性的，不用怀疑，在科学家找出是否有有一个遥远的“地球”在其主星附近运行之前，VB 10b 要绕主星转上好多圈。不可否认的是通过天体测量探测到红矮星附近的一颗行星较之以往提升了在这种小恒星周围更普遍存在行星的可能性。只有其他9个红矮星已知拥有行星伙伴，并且都是通过视向速度技术发现的。然而正如 Pravdo 和 Shaklin 指出的，这一方法的灵敏度对于这些微小的恒星来说远不及那些大的、更明亮的太阳型恒星。天体测量正好相反，由于被行星围绕时这样的恒星移动的较多，尤其适合探测小恒星附近的行星。

Now that astrometry has proven its value in detecting planets around red dwarfs, it is likely that many more such worlds will be discovered in the coming years. And since red dwarfs make up 70% of all stars, this could significantly alter astronomers' estimates of how common planets are in our galaxy. It could mean, explained Pravdo, that planets are more common than we thought. Wesley Traub, chief scientists for NASA's Exoplanet Exploration Program at JPL agreed: This discovery, he said, "shows that planets can be found around extremely low-mass stars. This is a hint that nature likes to form planets, even around stars very different from our Sun."
现在天体测量法已经证实了其在探测红矮星附近行星的价值，很有可能在接下来的几年里更多这样的世界将被发现。并由于红矮星占全部恒星数量的70%，这将显著的改变天文学家对我们的银河系中行星的普遍程度的估计。Pravdo 解释道，这可能意味着行星比我们想象的要常见。NASA 太阳系外行星探索计划的首席科学家 Wesley Traub 表示肯定：“这一发现表明能在质量如此小的恒星附近发现行星。这是一个提示，即使在那些与我们的太阳大不相同的恒星周围大自然也喜欢形成行星。”


Original:http://www.planetary.org/news/2009/0611_First_Exoplanet_Discovered_through.html

囧....囧
于是，翻吧....

In celebration of the 17th anniversary of the launch and deployment of the Hubble Space Telescope, a team of astronomers is released one of the largest panoramic images ever taken with Hubble's cameras -- a 50-light-year-wide view of the central region of the Carina Nebula where a maelstrom of star birth is taking place.
为庆祝“哈勃”空间望远镜发射及部署17周年，一组天文学家发布了“哈勃”曾拍摄的最大的一幅全景图——船底座星云中心跨越50光年的一片大规模恒星诞生处。


恒星诞生在船底座星云
该图片是由“哈勃”空间望远镜的高级巡天相机拍摄的48幅拼接而成。“哈勃”图像采自中性氢的光。加入的色彩信息来自智利的塞洛托洛洛中美洲天文台。红色对应硫，绿色是氢，蓝色是氧发出的。
感谢：NASA, ESA, N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA)



The fantasy-like landscape of the nebula is sculpted by the action of outflowing winds and scorching ultraviolet radiation from the monster stars that inhabit this inferno. In the process, these stars are shredding the surrounding material that is the last vestige of the giant cloud from which the stars were born.
这犹如梦幻般的景象是来自栖身于这片地狱的巨星涌出的星风和炽热的紫外线辐射所雕刻出。在这一过程中，这些恒星撕扯着在其诞生处周围剩余的星云物质。

Hubble's view of the nebula shows star birth in a new level of detail. The immense nebula contains at least a dozen brilliant stars that are roughly estimated to be at least 50 to 100 times the mass of our Sun.
“哈勃”对该星云的观察将恒星的诞生细节提到了新的水平。这片巨大的星云包含了至少十几个明亮的恒星，粗略估计它们的质量都至少是50-100倍太阳质量。

The most unique and opulent inhabitant is the star Eta Carinae, at far left. Eta Carinae is in the final stages of its brief and eruptive lifespan, as evidenced by two billowing lobes of gas and dust that presage its upcoming explosion as a titanic supernova.
最特别、最华丽的居民就是船底座 Eta 星，靠近左边。船底座 Eta 处在其短暂而爆发性生命的末期，，正如两处翻滚的气体和尘埃圆形凸起所预示它即将爆发成为超新星。

The fireworks in the Carina region started three million years ago when the nebula's first generation of newborn stars condensed and ignited in the middle of a huge cloud of cold molecular hydrogen. Radiation from these stars carved out an expanding bubble of hot gas. The island-like clumps of dark clouds scattered across the nebula are nodules of dust and gas that are resisting being eaten away by photoionization.
船底座区域中的焰火起始于300万年前星云首批诞生的新生恒星在一片寒冷巨大的氢分子云中受压缩并被点燃。从这些恒星发出的辐射雕刻出了一个膨胀的热汽泡。散布在星云中孤岛样的块状冷云是正在经受光电离吞噬的气体和尘埃节。

The hurricane blast of stellar winds and blistering ultraviolet radiation within the cavity is now compressing the surrounding walls of cold hydrogen. This is triggering a second stage of new star formation.
空穴中星风的击波和炽热的紫外线辐射正在压缩周围冷氢气形成的墙。由此触发了第二阶段新恒星的形成。

Our Sun and our solar system may have been born inside such a cosmic crucible 4.6 billion years ago. In looking at the Carina Nebula we are seeing the genesis of star making as it commonly occurs along the dense spiral arms of a galaxy.
我们的太阳和太阳系或许就是46亿年前在这样的宇宙熔炉中诞生的。通过对船底座星云的观察，我们看到了通常沿银河密集的旋臂所诞生恒星的起源。

The immense nebula is an estimated 7,500 light-years away in the southern constellation Carina the Keel (of the old southern constellation Argo Navis, the ship of Jason and the Argonauts, from Greek mythology).
这片巨大的星云位于南天星座船底座的龙骨处，估计距离7500光年。

Original:
http://www.planetary.org/news/2007/0424_New_Image_Hubble_Celebrates_17th.html

ABOUT THIS IMAGE:
This Hubble Space Telescope view of the central region of the Carina Nebula reveals a violent maelstrom of star birth. The fantasy-like landscape of the nebula is sculpted by the intense pressure of starlight from monster stars and their accompanying star clusters, as well as the hydrodynamics of their stellar winds of charged particles.
关于该图：
此次“哈勃”空间望远镜对船底座星云中心区域的观察展现了一场狂暴的恒星诞生风潮。这梦幻般的景象是由巨星及其伴生星协发出的强烈光压，以及其带电粒子的星风产生的流体力学所塑造出的。

[Top] — An approximately one-light-year tall "pillar" of cold hydrogen towers above the wall of the molecular cloud. The 2.5-million-year-old star cluster called Trumpler 14 appears at the right side of the image. A small nugget of cold molecular hydrogen, called a Bok globule, is silhouetted against the star cluster.
顶部——一个大约一光年高的冷氢“塔柱”处在分子云墙的上面。年龄为250万年的星团 Trumple 14 处在图像的右边。一种叫“博克球状体”（Bok globule）的冷分子氢“小金块儿”形成逆着星团的剪影。

[Center] — A Bok globule nicknamed the "caterpillar" appears at the right. Its glowing edge indicates that it is being photoionized by the hottest stars in the cluster. It has been hypothesized that stars may form inside such dusty cocoons. The top of the Keyhole Nebula, the most prominent feature embedded inside Carina, is on the left. Another Bok globule is in the foreground.
中间——一个叫“毛虫”的博克球状体在右边。它增长中的边缘预示其正被星群中最炽热的恒星光致电离。据猜测恒星可能形成在这样充满尘埃的茧中。深植在船底座星云内部最显著的特征“锁眼”星云的顶端位于图像左侧。另一个博克球状体在它的前面。

[Bottom] — These great clouds of cold hydrogen resemble summer afternoon thunderheads. They tower above the surface of a molecular cloud on the edge of the nebula. So-called "elephant trunk" pillars resist being heated and eaten away by blistering ultraviolet radiation from the nebula's brightest stars.
底部——这些壮丽的冷氢气云颇似夏日午后的积雨云。它们耸立在星云边缘一块分子云的表面上，被称为“象鼻”的柱状体承受着来自星云最明亮恒星的炽热紫外线辐射的加热和吞噬。



[Left] — A towering "mountain" of cold hydrogen gas laced with dust is the site of new star formation in the Carina Nebula. The great gas pillar is being eroded by the ultraviolet radiation from the hottest newborn stars in the nebula.
左图——一个饰有尘埃花边高耸的冷氢气“山脉”正是船底座星云中新恒星诞生地。壮丽的气体柱正被星云中新生的炽热恒星发出的紫外线所侵蚀。

[Right] — A close-up look at the peak of one of these "pillars of creation" reveals unequivocal evidence that stars are being born inside the columns. A pencil-like streamer of gas shoots out in both directions from the pillar and plows into surrounding gas like a fire hose hitting a wall of sand. The jet is being launched from a newly forming star hidden inside the column. A similar jet appears near the bottom of the image. These stellar jets are a common signature of the birth of a new star.
其中一个“创生柱”的特写，展示了恒星正在该拄体内诞生毫无疑问的证据。一个铅笔状的气体流从柱体两端射出一头扎入周围的气体中，就像用消防水龙喷一堵沙墙。喷流是从隐藏在柱状体内部的一颗新生恒星射出的，在图片靠近底部处有一个相似的喷流。这种恒星喷流是新恒星诞生共同的信号。



The tadpole-looking feature in the center of this image is a nodule of cold hydrogen gas laced with dust. The image offers circumstantial evidence that a young star is being born inside the placental cloud. The diagonal feature may be caused by twin jets of gas blasting away from the hidden star. They are slamming into neighboring gas to create a pair of bow shocks on either side of the globule. The twisted "tail" on the back of the globule may be evidence for a wobbling jet of material being blasted from the suspected star.
在图像中心蝌蚪状的结构是一个混和尘埃的冷氢云。该图片提供了一颗年轻恒星正从胚胎云中诞生的旁证。对角线状的结构可能是从隐藏恒星吹出的孪生气体喷流造成的。它们撞进周围的气体在球状体两边制造了一对弓形击波。在球状体身后那条扭曲的“尾巴”可能是从被怀疑的恒星刮出的一条物质摆动喷流的证明。



An approximately one-light-year tall "pillar" of cold hydrogen towers above the wall of the molecular cloud. The 2.5-million-year-old star cluster called Trumpler 14 appears at the right side of the image. A small nugget of cold molecular hydrogen, called a Bok globule, is silhouetted against the star cluster.
从分子云墙上耸立出来的一个大约1光年高的冷氢气柱。被称作 Trumpler 14 的年龄为250万年的星团位于图像的右边。一个叫“博克球状体”的冷氢“小金块”逆着该星团形成剪影。



A Bok globule nicknamed the "caterpillar" appears at the right. Its glowing edge indicates that it is being photoionized by the hottest stars in the cluster. It has been hypothesized that stars may form inside such dusty cocoons. The top of the Keyhole Nebula, the most prominent feature embedded inside Carina, is on the left. Another Bok globule is in the foreground.
一个绰号“毛虫”的博克球状体在右边。它增长中的边界显示其正被星团中的热星光致电离。根据假设恒星可能正是从这种充满灰尘的茧中形成的。深植于船底座中最显著的结构“锁眼”星云的顶部处在左边。另一个博克球状体位于其前方。



These great clouds of cold hydrogen resemble summer afternoon thunderheads. They tower above the surface of a molecular cloud on the edge of the nebula. So-called "elephant trunk" pillars resist being heated and eaten away by blistering ultraviolet radiation from the nebula's brightest stars.
这些壮丽的冷氢云颇似夏日午后的积雨云。它们从星云底部的一片分子云表面耸立而出。称作“象鼻”的柱状体正承受着来自星云明亮恒星所发出的炽热紫外线的加热和侵蚀。







This labeled image identifies some of the significant features in the Carina Nebula region. The rectangles outline the details in the accompanying photographs. Several of the brightest stars are identified by their catalog numbers (CPD=Cape Observatory Photographic Durchmusterung, HD, HDE=Henry Draper Catalog), among the hottest, heaviest stars known. The brighter stars outside of the compact cluster Trumpler 14 belong to another larger cluster, Trumpler 16, which also includes the peculiar star Eta Carinae. Several of these are multiple systems: HD 93129 includes three stars. HD 93160 and HD 39161 are a binary system and HD 93161 is itelf binary.
这张有标注的图片标明了船底座星云区域内的一些主要结构。长方框勾出了细节照片的位置。一些最明亮的恒星被标出了目录号(CPD=Cape Observatory Photographic Durchmusterung, HD, HDE=Henry Draper Catalog)，跻身于已知最热、最重的恒星之列。在紧凑的 Trumler 14 星团之外比较明亮的恒星属于另一个较大的星团 Trumpler 16，罕见的船底座 Eta 星也在其中。它们中的一些是多重系统：HD 93129 包含3颗恒星， HD 93160 和 HD 93161（貌似作者把93161写成39161了） 一对二重系统，并且 HD 93161 自身也是双星。

天文学家认为在大多数星系的中都存在巨大的黑洞。这些黑洞的质量能达到太阳的几百万倍甚至数十亿倍，对星系及其周围环境产生巨大影响。黑洞塑造其周围环境的手段之一是产生强大的高能粒子喷射。这些喷射，在射电波段明亮，摆布着包裹星系的热气体。当这一情况发生时天文学家便能观察到巨大的空腔以及在热的X线发射气体前面的强力冲击。

然而，相反的情节明显出现在星系 3C442A。来自“钱德拉”X线望远镜的X射线数据和来自“甚大阵”的射电数据显示在3C442A中间的热气体（蓝色）正在推动射电明亮的气体（橙色）分开。射电结构内部的部分锐利且凹陷，与X射线明亮的气体正在往边上清除射电发射气体的观点相符合。这是首个像这样的角色互换有说服力的证据。

Chandra X射线图像 3C442A

VLA 的射电图像 3C442A

光学图像

由英国布里斯托大学的 Diana Worrall 领导的科学家小组研究该系统并确定了为什么3C442A中的动力学看上去是颠倒的。起先，在3C442A靠近中间的地方有两个正在合并的星系。这两个星系在第二次碰撞的途中，对近距遭遇已经富有经验了。迫近中的合并所产生的能量不断加热来自两星系的混合大气，导致其闪耀出明亮的X射线并膨胀。

研究人员确定产生射电发射气体突出瓣的喷射已不再活动。喷射可能在星系碰撞时期停止了，并有可能是碰撞的结果。由于射电发射气体失去了能量源，便任由膨胀中的热气体摆布并被推到一边。

Original：http://chandra.harvard.edu/photo/2007/3c442a/

Astronomers think that there are enormous black holes at the centers of most, if not all, galaxies. These black holes, which can be millions or even billions of times more massive than the Sun, can greatly affect the galaxy and the environments around them. One way such black holes shape their surroundings is by generating powerful jets of high-energy particles. The jets, which are bright in radio waves, have been seen to push around the hot gas that envelops the galaxy. When this happens, astronomers can detect huge cavities and powerful shock fronts in the hot, X-ray emitting gas.

However, the opposite scenario is apparently unfolding in the galaxy known as 3C442A. X-ray data from NASA's Chandra X-ray Observatory and radio observations from the NSF's Very Large Array show that the hot gas (blue) in the middle of 3C442A is pushing apart the radio-bright gas (orange). The inner sections of the radio structure are sharp and concave, which is consistent with the idea that the X-ray bright gas is sweeping the radio-emitting gas aside. This is the first convincing evidence for such a role reversal.

A team of scientists, led by Diana Worrall of University of Bristol, UK, has studied this system and determined why the dynamics in 3C442A seem to be topsy-turvy. First, there are two galaxies near the middle of 3C442A which are in the process of merging. These two galaxies are on their second pass toward a collision, having already experienced a close encounter. The energy generated from this impending merger is heating the combined atmospheres from these two galaxies, causing them to shine brightly in X-rays and expand.

The researchers determined that the jets that had produced the lobes of radio-emitting gas are no longer active. The jets may have ceased at the time of, and possibly as a result of, the galaxy collision. Since the radio-emitting gas no longer has a power source, it is then at the mercy of the expanding hot gas and has been pushed aside.

Cassini Spacecraft Images Seas on Saturn's Moon Titan
03.13.07
“卡西尼”飞船图像——土星卫星“泰坦”上的海洋
03.13.07

Instruments on NASA's Cassini spacecraft have found evidence for seas, likely filled with liquid methane or ethane, in the high northern latitudes of Saturn's moon Titan. One such feature is larger than any of the Great Lakes of North America and is about the same size as several seas on Earth.
“卡西尼”飞船上的设备在土星卫星“泰坦”的高北纬度地区发现了似乎是填充着甲烷或乙烷的海洋的证据。一个这样的结构就比北美五大湖中的任意一个都大，与地球上的一些海洋大小相仿。

Cassini's radar instrument imaged several very dark features near Titan's north pole. Much larger than similar features seen before on Titan, the largest dark feature measures at least 100,000 square kilometers (39,000 square miles). Since the radar has caught only a portion of each of these features, only their minimum size is known. Titan is the second largest moon in the solar system and is about 50 percent larger than Earth's moon.
“卡西尼”的雷达设备描绘了“泰坦”北极附近的一些非常暗的特征。比之前在“泰坦”上看到的类似结构要大得多，最大的暗轮廓估计至少有100000平方千米。鉴于雷达仅捕获到每个这样轮廓的一部分，目前只知道它们的最小尺寸。“泰坦”是太阳系中第二大的卫星，比地球的月亮大约50%。


"泰坦“上的一个湖与苏必利尔湖的比较。感谢：NASA/JPL/GSFC

"We've long hypothesized about oceans on Titan and now with multiple instruments we have a first indication of seas that dwarf the lakes seen previously," said Dr. Jonathan Lunine, Cassini interdisciplinary scientist at the University of Arizona, Tucson.
亚利桑那大学的 Jonathan Lunine 博士说到：“长期以来人们猜测‘泰坦’上有海洋，如今依靠多种设备我们第一次有了令先前看到的湖泊相形见绌的海洋存在的迹象。

While there is no definitive proof yet that these seas contain liquid, their shape, their dark appearance in radar that indicates smoothness, and their other properties point to the presence of liquids. The liquids are probably a combination of methane and ethane, given the conditions on Titan and the abundance of methane and ethane gases and clouds in Titan's atmosphere.
虽然还没有最终的证明这些海洋里面是液体，但它们的外形、在雷达中呈现出暗色暗示着光滑，以及其他的特性表明存在液体。按“泰坦”大气中丰富的甲烷和乙烷气体以及“泰坦”上的情形，液体可能是甲烷和乙烷的混合物。

Cassini's visual and infrared mapping spectrometer also captured a view of the region, and the team is working to determine the composition of the material contained within these features to test the hypothesis that they are liquid-filled.
“卡西尼”的光学和红外分光计也拍到了该区域，小组目前正在确定这些特征中混合物质的成分以检验它们填充着液体的假设。

The imaging cameras, which provide a global view of Titan, have imaged a much larger, irregular dark feature. The northern end of their image corresponds to one of the radar-imaged seas. The dark area stretches for more than 1,000 kilometers (620 miles) in the image, down to 55 degrees north latitude. If the entire dark area is liquid-filled, it would be only slightly smaller than Earth's Caspian Sea. The radar data show details at the northern end of the dark feature similar to those seen in earlier radar observations of much smaller, liquid-filled lakes. However, to determine if the entire dark feature is a liquid-filled basin will require investigation through additional radar flyovers later in the mission.
提供“泰坦”全景影像的成像相机已描绘出一个更大的不规则阴暗结构。图像的北端同雷达描绘出的海洋中的一个相符。黑暗的地区在图像中延伸超过1000千米，直到北纬55度。如果整个阴暗地区充满液体它将比地球的里海稍小一点。雷达数据在阴暗结构的北端展示出的细节同稍早雷达观测到的小得多的液体湖类似。然而要确定整个阴暗结构是否是一个充满液体的盆地还需要在随后的飞跃中通过雷达更多的调查。


上图是一幅较大“泰坦”图像的一部分，显示出曾见过的最大液态实体之一。在最右端的湖比地球上最大的湖还要大，可以比较恰当的称其为海。图片感谢： NASA/JPL

The presence of these seas reinforces current thinking that Titan's surface must be re-supplying methane to its atmosphere, the original motivation almost a quarter century ago for the theoretical speculation of a global ocean on Titan.
这些海洋的存在支持了当前的观点——“泰坦”的表面在向其大气再补充甲烷。

Cassini's instruments are peeling back the haze that shrouds Titan, showing high northern latitudes dotted with seas hundreds of miles across, and hundreds of smaller lakes that vary from several to tens of miles.
“卡西尼”的设备正在剥离围绕着“泰坦”的阴霾，展示出高北纬地区散布着数百英里宽的海洋，以及数百个几英里到十几英里不等的小湖泊。

Due to the new discoveries, team members are re-pointing Cassini's radar instrument during a May flyby so it can pass directly over the dark areas imaged by the cameras.
由于这些新的发现，小组成员正在调整在5月的飞越过程中雷达设备的指向，让它能直接从照片上的阴暗地区上方经过。

Original：
http://www.nasa.gov/mission_pages/cassini/media/cassini-20070313.html