Andromeda Galaxy in the Ultraviolet

This is an ultraviolet image of Andromeda from NASA's Galaxy Evolution Explorer. Image credit: Galex, NASA/JPL-Caltech

The Andromeda Galaxy, M31, is the nearest major galaxy to our own Milky Way. It is about 780 kiloparsecs or 2.5 million light years away, as measured by it's brightest Cepheid variable stars. It is rather similar to our own galaxy in structure. It shows spiral arms and is about 80 kiloparsecs or 260000 light years across. This image is a composite of 11 image segments. This view is two-color composite, where blue represents far-ultraviolet light, and orange is near-ultraviolet light. The individual stars in the image are foreground stars in our own galaxy.

仙女座星系，M31，是我们银河系最近的大型星系。它距离我们大约780千秒差距或250万光年，这是通过它最亮的造父变星测量得到的。它在结构上与我们的银河系相当。它有螺旋臂，直径约为80千秒差距或260000光年。这张图片是11个图像片段的合成图。这个视图是双色合成图，其中蓝色代表远紫外光，橙色代表近紫外光。图片中的个体恒星是我们银河系中的前景恒星。

这是来自NASA的银河系演化探测器的紫外图像，展示的是仙女座星系。图片版权：Galex，NASA/JPL-Caltech

From NASA's description: "The bands of blue-white making up the galaxy's striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. Eventually, these dusty lanes will be blown away by strong stellar winds, as the forming stars ignite nuclear fusion in their cores. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago."

从NASA的描述来看：‘构成银河系鲜明环带的蓝白色区域，是孕育着高温、年轻、大质量恒星的区域。较冷的尘埃暗蓝色灰色条带在这些明亮的环带中显得格外突出，显示出当前在密集的云团中发生恒星形成的区域。最终，这些尘埃条带将被强烈的恒星风吹走，因为正在形成中的恒星会在核心中点燃核融合。与此同时，中心的橙白色球体显示出一群较冷、年老的恒星，这些恒星是在很久以前形成的。

"When observed in visible light, Andromeda's rings look more like spiral arms. The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA's Spitzer Space Telescope. Astronomers using Spitzer interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago."

当用可见光观测时，仙女座星系的环状结构看起来更像螺旋臂。紫外视图显示，这些臂更接近之前用NASA的斯皮策空间望远镜在红外波段观测到的环状结构。天文学家利用斯皮策望远镜解释这些环状结构为证据，表明该星系在2亿年前曾与邻近星系M32发生直接碰撞。

"Andromeda is so bright and close to us that it is one of only ten galaxies that can be spotted from Earth with the naked eye. "

仙女座是如此明亮且离我们很近，以至于它是仅有的十个可以用肉眼从地球看到的星系之一。