告知你一个肮脏的宇宙

星际尘埃或许能助天文学家弄清恒星与行星的构造。

By Katie Peek Posted 09.15.2010 at 2:28 pm

Riding in a car through space, if you were to hang your white-gloved hand out the window, it would come back dirty. The space between the Milky Way’s stars is filled with gas and dust—lots of dust.

坐在车里穿越太空，如果你要把你戴着白色手套的手悬在窗外的话，抽回手时手会变脏。银河中天体之间的空隙满是毒气与尘埃－大量的尘埃。

This summer, the European Space Agency’s Planck satellite produced a high-resolution dust map. The ultimate goal of the project is to map the cosmic microwave background, the electromagnetic leftovers of the universe’s violent beginning. Since warm dust grains emit microwaves, Planck made its map simply to see what’s behind the dust. Cosmologists usually consider the dust-emitted microwaves to be “noise” that obscures their data, worth analyzing only to erase from their measurements of the cosmic microwave background. But for other astronomers, interstellar dust is useful in its own right. Some of them plan to use the interstellar-dust data to study the Milky Way’s magnetic field, the origins and behavior of which are not well understood. Others, like Bruce Draine of Princeton University, will study the size distribution and composition of the grains themselves. “The universe is beautiful,” Draine says, “and one of the things that makes it beautiful is the dust.”

今年夏天，欧洲太空总署发射的普朗克卫星绘制出一张高清尘埃地图。此项目的终极目标就是绘制出宇宙微波背景图，宇宙剧烈起源的电磁残留物。因为激烈的尘埃颗粒使然，普朗克简单地绘图只为一看尘埃背后的究竟。宇宙学家常把尘埃排放微波当作是影响他们数据的“噪音”，只有从他们对宇宙微波背景的测量中抹去才具有分析价值。但对于其他天文学家而言，星际尘埃自身确是有用的。这些天文学家中有一些人计划利用星际尘埃数据来研究银河磁场这一起源与变化都没有得到充分了解的事物。另外一些天文学家，比如普林斯顿大学的布鲁斯.德雷恩，他将会研究颗粒本身的大小分布及组成。“宇宙很美，”德雷恩说，“让其美好的物质之一就是尘埃。”

The Life of a Dust Grain

尘埃颗粒的生命

1. INSIDE THE STAR

1，蕴含在恒星之中

Astronomers don’t know the identity of all the interstellar dust factories, but they do know that red giants—stars of up to eight solar-masses in the final stages of their life—generate quite a bit of dust. Dust components, such as carbon and oxygen, are made deep in the star’s core when helium atoms fuse together.

天文学家们不了解星际尘埃工厂的身分，但他们却知道红巨星－达到八大太阳能群众的恒星们生命的最后阶段－都产生大量的尘埃。尘埃的构成要素，有碳与氧，氦原子一起熔化之时，碳与氧就产生自恒星的核心深处。

2. ON THE STAR’S SURFACE

2，在恒星表面

Convection within the red giant dredges the new proto-dust atoms from the core up to the surface. The conditions and elements present in the stellar atmosphere will dictate the chemical composition of the dust. Then the star’s pulsations and winds fling those atoms into space.

红巨星内部的对流碰撞出新的原始尘埃原子会从其核心撞到表面。尘埃的化学成分受恒星大气呈现的状态与成分支配。然后这些恒星的震动及风会把这些尘埃原子投到宇宙中。

3. IN INTERSTELLAR SPACE

3，星际空间里

As the atoms continue to drift through space, they cool and condense into dust grains. From there, new dust grains will float out into the cosmos, where they may collect into very small rocks, then asteroids, then planets. In July, planetary scientists announced two candidate dust particles from the Stardust spacecraft, which returned to Earth in 2006 after seven years of collecting dust samples in space. This will bring the total number of dust grains currently in human possession to three. Finding even one requires a painstaking search of Stardust’s particle trap using a microscope. The first dust particle, also captured by the Stardust experiment, was announced in March. Of the three, two of the particles are magnesium-rich, while the third is carbon-based.

原子继续在太空里漂移，冷却压缩成尘埃颗粒。新的尘埃颗粒这样开始，飘浮到宇宙，为小岩石所聚集，之后这些小岩石又聚集于小行星，然后再为星球聚集。行星科学家在七月宣称两颗来自星团航天器的备选尘埃粒子，在宇宙收集了7年尘埃样本后于2006年回到地面。如此一来，将使人类已掌握的尘埃颗料的现有总数增加到三个。哪怕只有一个发现，也需陷入使用显微镜对星团颗粒的辛勤研究。第一个尘埃颗粒于三月被公诸于世，也于星团实验中被捕捉到。三个颗粒中，有两个富含镁元素，而第三个则是碳基元素为主。

FAQs

常见问题

IS INTERSTELLAR DUST VISIBLE FROM EARTH?

在地球上可以看到星际尘埃吗？

Yes! On a clear night far from city lights, stargazers can see dark patches within the smooth band of the Milky Way near the constellation Cygnus. Those patches are ribbons of dust that block the stars behind them.

可以！远离城市灯火的晴朗的夜晚，观星者能看到黑斑出现在银河平滑的环带里，天鹅座的附近。

HOW DOES IT AFFECT THE GALACTIC ENVIRONMENT?

它如何影响银河系环境？

Dust grains are the building blocks of planets. They also shield gas clouds from starlight and, by keeping those clouds cool, allow that gas to condense and make new stars. “It’s like an ecosystem,” says Gillian Knapp, an astronomer at Princeton. “It’s the little stuff that matters, and how it evolves together.”

尘埃颗粒是构成星球的要素。它们能使毒云免遭星光且让这些毒云保持冷冻状态，使这些气体可压缩成为新的恒星。“它就像是一个生态系统，”，普林斯顿的天文学家吉莉安.那普说道，“这些小东西很有用，事关如何共同进化。”　

Essential Jargon

须知

Interstellar Medium: What astronomers call all that stuff between the stars. Dust grains are only about 1 percent of its mass, with hydrogen accounting for 80 percent and helium providing most of the rest.

星际介质：即天文学家所称的恒星间的物质。尘埃颗粒只约占组成介质群的百分之一，氢占百分之八十，其余的全是氦。

Interstellar Dust: Dust grains are agglomerations of atoms, including carbon, silicon, oxygen, magnesium and aluminum. Silicon-rich grains make up about 70 percent of the dust inventory, and carbon-rich grains constitute the remainder.

星际尘埃：尘埃颗粒为原子构成部分，其中包括碳，硅，氧，镁及铝元素。富含硅元素的颗粒占了尘埃总成的约百分之七十，其余部分由富含碳元素的颗粒构成。