The face-on spiral galaxy M101, or the Pinwheel Galaxy, is seen at ultraviolet and optical wavelengths in this image taken by ESA’s XMM-Newton space telescope. The picture is composed of images taken by XMM-Newton’s Optical Monitor telescope using different filters: red (200–400 nm), green (200–300 nm) and blue (175–275 nm). Credit: ESA/XMM & R. Willatt Enlarge

(Phys.org) —The face-on Pinwheel spiral galaxy is seen at ultraviolet wavelengths in this image taken by ESA's XMM-Newton space telescope.

Also known as M101, the galaxy lies 21 million light-years away in the constellation Ursa Major. It measures 170 000 light-years across – nearly twice the diameter of our own  – and contains at least a trillion stars. About a billion of these stars could be similar to our own Sun.

More often seen in visible light, here the  glows at . Massive, hot young stars streaming with ultraviolet radiation mark out the galaxy's spiral arms with bright pockets of forming stars.

Since the largest stars are the shortest lived, with a maximum lifespan of a few million years, studying the ultraviolet radiation being emitted by a distant galaxy is a good way to measure how much star formation is taking place within it – and it is clear that M101 is still very active.

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