為什么太陽風比預(yù)期的要熱

新的研究有助于解釋為什么太陽風比預(yù)期的要熱

When a fire extinguisher is opened, the compressed carbon dioxide forms ice crystals around the nozzle, providing a visual example of the physics principle that gases and plasmas cool as they expand. When our sun expels plasma in the form of solar wind, the wind also cools as it expands through space—but not nearly as much as the laws of physics would predict.

當滅火器打開時，壓縮的二氧化碳在噴嘴周圍形成冰晶，這為氣體和等離子體膨脹時冷卻的物理原理提供了一個直觀的例子。 當我們的太陽以太陽風的形式排出等離子體時，風也會隨著它在空間中的膨脹而冷卻下來——但冷卻程度遠不及物理定律所預(yù)測的那樣。

In a study published April 14 in the Proceedings of the National Academy of Sciences, University of Wisconsin-Madison physicists provide an explanation for the discrepancy in solar wind temperature. Their findings suggest ways to study solar wind phenomena in research labs and learn about solar wind properties in other star systems.

在4月14日發(fā)表在《美國國家科學院院刊》的一項研究中，威斯康星大學麥迪遜分校的物理學家為太陽風溫度的差異提供了一個解釋。 他們的發(fā)現(xiàn)為在研究實驗室研究太陽風現(xiàn)象，和了解其他恒星系統(tǒng)的太陽風特性提供了方法。

"People have been studying the solar wind since its discovery in 1959, but there are many important properties of this plasma which are still not well understood," says Stas Boldyrev, professor of physics and lead author of the study. "Initially, researchers thought the solar wind has to cool down very rapidly as it expands from the sun, but satellite measurements show that as it reaches the Earth, its temperature is 10 times larger than expected. So, a fundamental question is: Why doesn't it cool down?"

“自1959年發(fā)現(xiàn)太陽風以來，人們一直在研究它，但是這種等離子體的許多重要性質(zhì)仍然沒有得到很好的理解，”物理學教授兼該研究的主要作者 Stas Boldyrev 說。 “最初，研究人員認為太陽風從太陽擴散時必須迅速降溫，但衛(wèi)星測量顯示，當太陽風到達地球時，它的溫度是預(yù)期的10倍。所以，一個基本的問題是:為什么它沒有冷卻下來?”

Solar plasma is a molten mix of negatively charged electrons and positively charged ions. Because of this charge, solar plasma is influenced by magnetic fields that extend into space, generated underneath the solar surface. As the hot plasma escapes from the sun's outermost atmosphere, its corona, it flows through space as solar wind. The electrons in the plasma are much lighter particles than the ions, so they move about 40 times faster.

太陽等離子體是帶負電荷的電子和帶正電荷的離子的熔融混合物。 由于這種電荷，太陽等離子體受到延伸到太空的磁場的影響，磁場產(chǎn)生于太陽表面之下。 當熾熱的等離子體從太陽最外層的大氣層---- 日冕中逃逸時，它會以太陽風的形式在太空中流動。等離子體中的電子比離子輕得多，所以它們的移動速度是離子的40倍。

With more negatively charged electrons streaming away, the sun takes on a positive charge. This makes it harder for the electrons to escape the sun's pull. Some electrons have a lot of energy and keep traveling for infinite distances. Those with less energy can't escape the sun's positive charge and are attracted back to the sun. As they do, some of those electrons can be knocked off their tracks ever-so-slightly by collisions with surrounding plasma.

隨著更多帶負電荷的電子流離開，太陽帶上了正電荷。 這使得電子更難逃離太陽的引力。 有些電子具有很大的能量，可以無限地運動。那些能量少的不能逃脫太陽的正電荷，被吸引回太陽。當它們這樣做的時候，其中的一些電子會因為與周圍等離子體的碰撞而稍稍偏離軌道。

In an effort to explain the temperature observations in the solar wind, Boldyrev and his colleagues, UW-Madison physics professors Cary Forest and Jan Egedal looked to a related, but distinct, field of plasma physics for a possible explanation.

為了解釋太陽風中的溫度觀測結(jié)果，博爾迪列夫和他的同事，威斯康辛大學麥迪遜分校的物理學教授卡里 · 福瑞斯特和簡 · 艾格達爾，從等離子體物理學的一個相關(guān)但不同的領(lǐng)域中尋找一個可能的解釋。

Around the time scientists discovered solar wind, plasma fusion researchers were thinking of ways to confine plasma. They developed "mirror machines," or plasma-filled magnetic field lines shaped as tubes with pinched ends, like bottles with open necks on either end.

大約在科學家發(fā)現(xiàn)太陽風的時候，等離子體聚變研究人員正在想方設(shè)法限制等離子體。 他們發(fā)明了“鏡子機器” ，即等離子體填充磁場線，形狀像管子，兩端捏緊，就像兩端都有開口的瓶子。

As charged particles in the plasma travel along the field lines, they reach the bottleneck and the magnetic field lines are pinched. The pinch acts as a mirror, reflecting particles back into the machine.

當?shù)入x子體中的帶電粒子沿著磁力線運動時，它們到達瓶頸，磁力線被壓縮。 壓力就像一面鏡子，把粒子反射回機器。

The accuracy with which mirror machine theory predicts solar wind temperature opens the door for using them to study solar wind in laboratory settings.

鏡像機理論預(yù)測太陽風溫度的準確性，為在實驗室環(huán)境中使用它們來研究太陽風打開了大門。