171130期:M33:三角座大星系 

M33:三角座大星系

说明:图中华丽的M33正向螺旋星系藏在三角座这个北天小星座中。人们常称它为风车星系或三角座大星系。直径达五万光年以上的M33为本星系群第三大星系,仅次于仙女座大星系(M31)和我们的银河系。在银河系的三百万光年之外,M33被认为是仙女座大星系的卫星星系,可能的话,天文学家可以在其中一个星系中观测到另一个星系宏伟壮丽的螺旋形状。至于地球上的观测结果,就是这幅清晰的合成图了,此图巧妙地呈现了M33松散的螺旋臂上的蓝色星团和带点儿粉色的恒星形成区。事实上,巨穴般的NGC 604是其中最明亮的恒星形成区,位于星系中心7点钟方向。与M31相似,M33内有大量经过仔细量测的变星,该星族使得银河系旁的这个螺旋星系成为了一把量天尺,可以用来建立宇宙的距离尺度

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M33: Triangulum Galaxy
Image Credit & CopyrightPeter Nagy

Explanation: The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other’s grand spiral star systems. As for the view from planet Earth, this sharp composite image nicely shows off M33’s blue star clusters and pinkish star forming regions along the galaxy’s loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 7 o’clock position from the galaxy center. Like M31, M33’s population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

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