夜空中的艺术家与炼金士Artists and Alchemists of the Sky
灰尘，生活中再普通不过了，但你知道吗？
Dust – what would be more common in our daily life, but did you know?
在大气中，由风从土壤中扬起的、火山爆发的和工业污染的小颗粒组成。
In Earth’s atmosphere, they consist of particles lifted from the soil by wind, volcanic eruptions, and pollution.
在家中，大约50%由死皮细胞组成。
At homes，~ 50% of them are from dead skin cells.
在太空中，掌握了星星的历史和未来。
In space, stars’ history and future are in their hands.
尽管尘埃渺小，乍一看并不是最吸引人瞩目的话题，但它是天文学中最不受重视却最重要的课题之一。它们不仅能告诉我们星系的磁场和温度的温情故事，还能描绘出星系结构的3D形态，是夜空中最渊博的一群。
Even though small and aren’t the most enthralling subject upon first glance, dust is one of the most underappreciated topics in astronomy. Not only do they tell the tales about the magnetic fields and temperatures of our galaxy, but they can also even paint out the 3D morphology of galaxy structures.
据预测，在未来十年里，我们将通过对太空尘埃的观测，第一次有机会充分了解银河系中的气体结构。例如，最近在拉德克利夫波（Radcliffe Wave）的发现中，尘埃就提供了大量不可或缺的关键信息。拉德克利夫波是一种巨大的，能够定义了银河系中太阳附近区域形状的气体结构。
It is predicted that over the next decade, by using observation of space dust, it will our first chance of fully understanding the structure of gases in our Milky Way. For example, the recent discovery of the Radcliffe Wave, which is a gigantic structure that defines the shape of the Sun's local neighbourhood in the galaxy, used a great deal of information provided by the dust.
图为由斯皮策望远镜拍摄的仙女座星系的24微米辐射(追踪尘埃)照片。可以清晰的看到星系的旋臂，且有强烈尘埃发射的区域为活跃恒星形成的区域。
24-micron emission (tracing the dust) in the Andromeda galaxy. Image taken with Spitzer. Clear spiral arms are seen, and the regions with intense dust emission correspond to regions of active star formation.
灰尘不仅是建筑师和艺术家，还是渊博的炼金术士。他们手握各种创造恒星、行星的化学物质信息，以及复杂的，组成你我的分子的来源故事。如此珍贵，可惜的是尘埃并不能在太空中永存，他们也是脆弱的。在太空平凡的超新星剧烈爆炸中，这些星际尘埃很容易就能被摧毁。
Apart from being architects and artists, dusts are also great alchemists. Knowledgeable about the chemistry that created stars, planets and origins of the complex molecules, like those that make up you and me. However, dusts do not last forever in space, they are delicate and precious as they can get destroyed by the frequent violent explosions in space – the supernovae.
图为一个大质量恒星在我们附近的小麦哲伦星云爆炸时产生的超新星残留物。来自NASA的钱德拉天文台（蓝色和紫色）的x射线数据有效的帮助了天文学家确认宇宙中的大部分氧气是在大质量恒星中合成的，来自NASA哈勃望远镜和智利甚大望远镜的光学数据显示为在这里以红色和绿色显示。 The supernova remnant produced by a massive star that exploded in the nearby Small Magellanic Cloud. X-rays from Chandra (blue and purple) have helped astronomers confirm that most of the oxygen in the universe is synthesised in massive stars, while the optical data from NASA's Hubble Telescope and the Very Large Telescope in Chile are shown here in red and green.
💍 璀璨夺目的指环 💍
The Dazzling Rings
为了了解这些物质和能量的巨大爆炸将会怎样摧毁我们探究外太空的“窗口”，一组来自英国和比利时的科学家开始了对附近的3个超新星遗迹的研究：G11.2-0.3、G27.4+0.0和G29.7-0.3。(这里的“附近”指的是4-6千秒差距：约1.3万到2万光年远。)
To understand how these massive explosions of matter and energy may destroy our ‘windows’ to the outer space, a group of scientists from the UK and Belgium began the study by first examining three nearby supernova remnants: G11.2-0.3, G27.4+0.0, and G29.7-0.3., (‘nearby’ here means 4-6 kiloparsecs: ~13,000 to 20,000 light years away.)
虽然这三个不是离我们最近的超新星遗迹，但被选中是因为它们有明显x射线和红外(IR)与周围星际介质的相互作用，这对下一步的研究是至关重要的。
Although not the closest to us, these three were chosen for their clear interaction with the surrounding interstellar medium in both the X-ray and infrared (IR), which is key for further investigations.
图为NASA的钱德拉天文台拍摄的x射线 G11.2-0.3 超新星遗迹图
The X-ray image from Chandra data of the supernova remnant G11.2-0.3
分析超新星遗迹第一步是确定每个遗迹的近圆形外壳，也就是围绕在中央脉冲星风星云周围，由超新星爆炸产生的冲击波扫过的物质。
The analysis began by identifying the near-circular shell for each remnant, which is the material swept up by the shock from a supernova explosion surrounding the central pulsar wind nebula.
虽然这些外壳是3D的物体，但就像我们在天空中看到的所有东西一样，都只能观察到它们的2D图像。所以在这里，我们观测到的外壳会呈现为那璀璨的‘指环’，因为从我们视线的角度来看，遗迹外部区域的热气体量会比中心区域的更多。
The shell is a 3D object, however, as with everything we see in the sky, it becomes a 2D image when observing it. So here, it will appear as a ring, since there is more hot gas in our line of sight at the outer regions than when looking through the more central parts.
左图：来自斯皮策望远镜的24微米射线的(红外追踪) G11.2-0.3 图像。图中可以清晰的看到超新星遗迹中的一层尘埃。右图：来自钱德拉的同样的超新星残骸x射线图，这里也可以清晰地看到残骸的外壳。
Left: 24-micron emission of G11.2-0.3 (tracing the dust in the infrared) from Spitzer. A clear shell of dust is seen in the SNR.Right: X-ray emission image from Chandra for the same SNR. The shell of the remnant is clearly visible in X-rays.
当x射线的外壳层边界得到确认后，下一步便是利用x射线的数据可以求出壳层内气体的温度和密度。由于x射线的高能量（数百万摄氏度），它们是超新星遗迹中高温气体的极佳示踪剂。
After the shell boundaries are determined in X-ray, the data of X-ray emission can then be used to find out the temperature and density of gases in the shell. Because of X-ray’s high energy (millions of degrees), they are great tracers for hot gases in supernova remnants.
冷气来袭
The Cold is Coming
随着x射线确定了外壳的空间结构，研究小组继续使用了红外线来了解更多关于尘埃的具体信息。将实际测量到的红外数据与之前仅用x射线作为示踪剂的预测数据进行比较后，小组发现发现两者的匹配度并不高。但当小组把相当数量的“低温星尘”加入到预测数据中后，三个超新星遗迹的实际数据与预测数据的吻合度都得到了大幅度的提高。
With spatial structure of the shell determined by X-ray, the team then moved on to using IR to find out more about the dust. After comparing the measured IR data with the predicted data of only using X-ray as the tracer, it shows there is not a great match. So, the team then included a sizable amount of ‘cold dust’ into the prediction, which made a much better fit for the real data in all three cases.
两个图标均为 G11.2-03 的最佳拟合光谱能量分布，图中红线为已经被模型计入的暖尘，蓝线为冷尘成分的最佳拟合，黑线为是两者之和
左图：使用了碳尘颗粒但不包括额外冷灰尘成分
右图：使用碳粉尘颗粒，并添加额外的冷组分灰尘
Best-fit spectral energy distribution (SED) for G11.2-03 with red as the warm dust already accounted for by the model, the blue as the best fit to the cold dust component, and the black as the sum of the two
Left: using carbon dust grains in the model without including the extra cold component of dust Right: using carbon dust grains with the extra cold component of dust added on
这一结果表明，在之前对超新星遗迹的预测中，科学家们大大低估了其中的尘埃含量，遗迹中一定残留着相当高比例的尘埃。换句话说，我们可能大大高估了超新星摧毁尘埃的能力。计算中大量额外的冷尘埃实际可能是未被发现的冷气体区域，这些冷气体已经穿过超新星冲击波，所以在x射线追踪中没有显示出来。
This result suggests that previous predictions on the remnants has significantly underestimated the amount of dust in supernova remnant, there must be a relatively high proportion of it in there. In another words, we have probably vastly overestimated the ability of supernovae to destroy dust. This large additional quantity of cold dust could be the undetected regions of cold gases that have already passed through the supernova shockwave, which doesn’t show up in X-rays.
世纪合体
The Centenary Cooperation
除了告诉我们更多关于太空中星系的秘密，尘埃在宇宙本身的生命周期中也极其重要。它是星际介质中的关键成分，在星际介质中起到冷却、收缩，创造新行星、恒星和其他星球的作用。
As well as telling us more secrets about the galaxies in space, dust is also extremely important in the life cycle of the universe itself. It is the key ingredient in the interstellar medium, where star-forming materials cool, contract and bring life to new planets, stars and others.
在时间轴另一端的超新星，虽然发生在恒星生命的最末期，但也是星系演化中里程碑式的存在，掌握着恒星形成的速率和星系的发展。
On the other side, supernovae happening at the end of the stars’ lifetime, are the critical milestones in the galaxy evolution as they regulate the rate of star formation.
图为来自NASA钱德拉的仙后座A (Cas A)的图像：一个大质量恒星爆炸后留下的碎片场。这场爆炸大约出现在300多年前的星空中。
An image from Chandra of Cassiopeia A (Cas A) - the debris field left behind after a massive star exploded. This explosion would have appeared in Earth's sky over 300 years ago.
我们今天的发现，正是因为结合了这两种重要事件而变得特别重要。如果先前的模型和模拟（那些由超新星尘埃被破坏的数据形成的模型和模拟）在很大程度上高估了超新星摧毁尘埃的能力，那么这些先前的结果可能并不像我们当初认为的那样可靠了。
With these two important features in space combined to form our discovery today. If previous models and simulations, that were formed from data on dust destruction of supernovae, have largely overestimated the power of supernovae to destroy dust, then those previous results may not be as solid ground as we first thought.
因此，当今那些代表了我们现在对恒星形成最好理解的高分辨率的星际介质模型很有可能是一场严重的误解。
Hence the high-resolution simulations models for the interstellar medium, that represent our best understanding of star formation now, could be very much misunderstanding.
新的物理可能正默默的
在那浩瀚的夜空中，
等待我们的发现和理解!
New physics may be lurking in the dark sky,
to be seen and understood!
图为太空中最冷、最暗却最明亮的尘埃的红外光芒，来自ESA和NASA合作的赫歇尔天文台。图中展现了一个寒冷而混乱的区域，物质在这里刚刚开始凝结成新的恒星：蓝色为温度较高的物质，红色为温度较低的物质，绿色则是中间温度的物质。
Some of the coldest and darkest dust in space shines brightly in this infrared image from the Herschel Observatory of ESA and NASA. The image shows a cold and turbulent region where material is just beginning to condense into new stars: blue the warmer material, red the coolest, and green as the intermediate temperatures.
图片来自 NASA, Chandra 官网以及以下文章
文中部分英文信息参考来自 F. D. Priestley, H. Chawner, M. Matsuura, I. De Looze, M. J. Barlow, H. L. Gomez 的 ‘Revisiting the dust destruction efficiency of supernovae' 文章
其余中英文内容为原创
Images from official website of NASA, Chandra and the below articles
Parts are sited from ‘Revisiting the dust destruction efficiency of supernovae' from F. D. Priestley, H. Chawner, M. Matsuura, I. De Looze, M. J. Barlow, H. L. Gomez
The rest of the Chinese and English content are original
