冲压力剥离 Ram Pressure Stripping

冲压压力其实是我们生活中经常会经历的一种影响。当一个物体穿过一个介质时，比如空气，物体运动越快，介质中越多的粒子就会与那个物体发生碰撞。就像我们跑得越快，我们的脸上就会感受到更大的压力一样。

Ram-pressure is an effect we experience every day. It’s just the idea when an object moves through a medium, such as air, the faster the motion the more particles in that medium will hit the object. Like as we run faster, we would feel a stronger pressure on our face.

所以，如果冲压压力作用于星系，就会产生剥离的效果。当一个星系穿过一个介质时，就是星系团之间的等离子体，由于介质的阻力，星系里松散的气体会被落下，通常留下一条长长的尾巴。就像主文章中的水母星系一样。        

So, if ram-pressure applied to galaxies, it would cause a stripping effect. As a galaxy move through a medium, in this case the intra-cluster plasma, its loosely bounded gas would be fall behind due to the drag forces from the medium, often leaving a long tail behind.

图为星系与水母的形态对比图：左边为哈勃望远镜所拍到的合成图像，D100正在从左到右移动，身后留下了被遗弃的气体；右边是用来比较的水母图片

The comparison between the galaxy and jellyfish: the left shows the composition image from HST, where D100 is moving from left to right leaving the gas behind as a tail; the right is an image of a jellyfish for comparison

一下，把一袋面粉倒在一个人的头上，然后把头探出行驶汽车的窗外，冲压力剥离对星系的影响就是这样。(示范目的，千万不要尝试哦！)

Imagine pouring a bag of flour over someone's head and sticking it out of the window of moving car. (Demonstration purpose, DO NOT TRY!)

星系图片来自美国、日本、捷克和英国学者合作， 由 W.J. Cramer 带领的团队的 “Spectacular HST observations of the Coma galaxy D100 and star formation in its ram pressure stripped tail" 论文

水母图片来自 Alexander Semenov

中英文内容为原创

Galaxy picture from “Spectacular HST observations of the Coma galaxy D100 and star formation in its ram pressure stripped tail" by the scientist team lead by W.J. Cramer from USA, Japan, Czech Republic and UK

Jellyfish image from Alexander Semenov

All Chinese and English contents are original