NASAのインスタグラム(nasa) - 3月21日 06時43分

Glittering Frisbee Galaxy: This image from Hubble's shows a section of a spiral galaxy located about 50 million light-years from Earth. We tend to think of spiral galaxies as massive and roughly circular celestial bodies, so this glittering oval does not immediately appear to fit the visual bill. What's going on? Imagine a spiral galaxy as a circular frisbee spinning gently in space. When we see it face on, our observations reveal a spectacular amount of detail and structure. However, the galaxy frisbee is very nearly edge-on with respect to Earth, giving it an appearance that is more oval than circular. The spiral arms, which curve out from the galaxy's dense core, can just about be seen.

Although spiral galaxies might appear static with their picturesque shapes frozen in space, this is very far from the truth. The stars in these dramatic spiral configurations are constantly moving as they orbit around the galaxy's core, with those on the inside making the orbit faster than those sitting further out. This makes the formation and continued existence of a spiral galaxy's arms something of a cosmic puzzle, because the arms wrapped around the spinning core should become wound tighter and tighter as time goes on - but this is not what we see. This is known as the winding problem.

Image credit: ESA/Hubble & NASA

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