2025年4月27日
IC 418: The Spirograph Nebula
Image Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgement: R. Sahai (JPL) et al.
Explanation: What is creating the strange texture of IC 418? Dubbed the Spirograph Nebula for its resemblance to drawings from a cyclical drawing tool, planetary nebula IC 418 shows patterns that are not well understood. Perhaps they are related to chaotic winds from the variable central star, which changes brightness unpredictably in just a few hours. By contrast, evidence indicates that only a few million years ago, IC 418 was probably a well-understood star similar to our Sun. Only a few thousand years ago, IC 418 was probably a common red giant star. Since running out of nuclear fuel, though, the outer envelope has begun expanding outward leaving a hot remnant core destined to become a white-dwarf star, visible in the image center. The light from the central core excites surrounding atoms in the nebula causing them to glow. IC 418 lies about 2000 light-years away and spans 0.3 light-years across. This false-color image taken from the Hubble Space Telescope reveals the unusual details.
Tomorrow’s picture: interstellar tadpoles
IC 418: 万花尺星云
影像提供: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgement: R. Sahai (JPL) et al.
说明: IC418奇特的纹理是如何产生的？因为行星状星云IC418很像是一幅用循环绘图盘所画出来的图案，故有万花尺星云（Spirograph Nebula）的昵称。至于IC 418特殊的纹理到底如何产生的呢，到现在为止，答案还不是很明确。很可能和它中心的变星有关，这颗中心星会辐射出很紊乱的恒星风，使它的亮度常在几小时之内就会发生不规则的变光。然而，有证据显示IC 418过去并不是这么怪异。在数百万年前，它可能和我们太阳很像，是个行为很规律的恒星。即使在数千年前，IC 418也还是一颗寻常的红巨星而已。不过，自从它核心的核燃料耗尽后，外层的气壳就开始膨胀，露出了影像中心的炽热中心星，这颗中心星将继续演化，最后成为白矮星。而来自于中心星的辐射，则激发周围云气中的各种原子，发出五颜六色的辉光。IC 418距离我们大约2000光年，它的大小约有0.3光年。这张由哈勃太空望远镜所拍摄的假色影像，异常清晰的解析了这团星云的细微结构。
明日的图片: interstellar tadpoles
