This NASA/ESA Hubble Space Telescope image features an uncommon galaxy with a striking appearance. NGC 7722 is a lenticular galaxy located about 187 million light-years away in the constellation Pegasus.
这张美国宇航局/欧洲航天局哈勃太空望远镜的图像展示了一个外观引人注目的罕见星系。 NGC 7722 是一个位于飞马座的透镜状星系，距离我们约 1.87 亿光年。
A lenticular, meaning “lens-shaped,” galaxy is a type whose classification sits between more familiar spiral galaxies and elliptical galaxies. It is also less common than spirals and ellipticals — partly because these galaxies have a somewhat ambiguous appearance, making it hard to determine if it is a spiral, an elliptical, or something in between. Many of the known lenticular galaxies sport features of both spiral and elliptical. In this case, NGC 7722 lacks the defined arms of a spiral galaxy, while it has an extended, glowing halo and a bright bulge in its center like an elliptical galaxy. Unlike elliptical galaxies, it has a visible disk — concentric rings swirl around its bright nucleus. Its most prominent feature, however, is undoubtedly the long lanes of dark red dust coiling around the outer disk and halo.
透镜状星系的意思是“透镜状”，其分类介于更熟悉的螺旋星系和椭圆星系之间。它也不像螺旋星系和椭圆星系那么常见，部分原因是这些星系的外观有些模糊，因此很难确定它是螺旋星系、椭圆星系还是介于两者之间的星系。许多已知的透镜状星系都具有螺旋星系和椭圆星系的特征。在这种情况下，NGC 7722 缺乏螺旋星系的明确旋臂，但它有一个延伸的发光晕，中心有一个明亮的凸起，就像椭圆星系一样。与椭圆星系不同，它有一个可见的圆盘——同心环围绕其明亮的核旋转。然而，它最显着的特征无疑是盘绕在外盘和光晕周围的深红色尘埃长带。
This new Hubble image, the sharpest taken of NGC 7722, brings the galaxy’s impressive dust lanes into sharp focus. Bands of dust like this are not uncommon in lenticular galaxies, and they stand out against the broad, smooth halo of light that typically surrounds lenticulars. Astronomers think NGC 7722’s distinctive dust lanes are the result of a past merger with another galaxy, similar to other lenticular galaxies . Researchers do not fully understand how lenticular galaxies form, but they think mergers and other gravitational interactions play an important part in reshaping galaxies and exhausting their supplies of gas while bringing new dust.
这张新的哈勃图像是 NGC 7722 拍摄的最清晰的图像，使银河系令人印象深刻的尘埃带成为焦点。像这样的尘埃带在透镜状星系中并不罕见，它们在透镜状星系周围宽阔、光滑的光晕的衬托下显得格外突出。天文学家认为 NGC 7722 独特的尘埃带是过去与另一个星系合并的结果，类似于其他透镜状星系。研究人员并不完全了解透镜状星系是如何形成的，但他们认为合并和其他引力相互作用在重塑星系和耗尽其气体供应同时带来新的尘埃方面发挥着重要作用。
While it doesn’t host as many new, young stars as a spiral galaxy, there’s still activity in NGC 7722: in 2020 it was host to the explosion of a star that astronomers detected from Earth. SN 2020SSF was a Type Ia supernova, an event that occurs when a white dwarf star in a binary system siphons enough mass away from its companion star that it grows unstable and explodes. These explosions output a remarkably consistent level of light: by measuring how bright they appear from Earth and comparing that to how bright they intrinsically are, astronomers can tell how far away they must be. Type Ia supernovae are one of the best ways to measure distances to galaxies, so understanding exactly how they work is of great importance for astronomy.
虽然它不像螺旋星系那样拥有那么多新的年轻恒星，但 NGC 7722 仍然存在活动：2020 年，天文学家在地球上探测到一颗恒星爆炸。 SN 2020SSF 是一颗 Ia 型超新星，当双星系统中的一颗白矮星从其伴星吸走足够的质量使其变得不稳定并爆炸时，就会发生这种事件。这些爆炸发出的光水平非常一致：通过测量它们在地球上的亮度，并将其与它们本身的亮度进行比较，天文学家可以判断它们距离地球有多远。 Ia 型超新星是测量星系距离的最佳方法之一，因此准确了解它们的工作原理对于天文学非常重要。
Taken with Hubble’s Wide Field Camera 3 , this Hubble image was obtained as part of an observing program (# 16691 , PI: R. J. Foley) that followed up on recent supernovae. SN 2020SSF, is not visible in this image. Researchers purposefully observed NGC 7722 two years after the supernova faded to witness the supernova’s aftereffects and examine its surroundings, which can only be accomplished once the intense light of the explosion is gone. With Hubble’s clear vision, astronomers can search for radioactive material created by the supernova, catalog its neighbors to help determine the original star’s age, and look for the companion star it left behind — all from almost 200 million light-years away.
这张哈勃图像是用哈勃广域相机 3 拍摄的，是作为跟踪最近超新星的观测计划（#16691，PI：R.J. Foley）的一部分获得的。 SN 2020SSF，在此图像中不可见。研究人员在NGC 7722超新星消退两年后有目的地对其进行了观测，以见证超新星的余波并检查其周围环境，而这只有在爆炸的强光消失后才能完成。借助哈勃望远镜的清晰视野，天文学家可以搜索超新星产生的放射性物质，对其邻居进行编目以帮助确定原始恒星的年龄，并寻找它留下的伴星——所有这些都在近 2 亿光年之外。
Text Credit: European Space Agency (ESA)
文字来源：欧洲航天局 (ESA)
Claire Andreoli NASA’s Goddard Space Flight Center , Greenbelt, MD claire.andreoli@nasa.gov
Claire Andreoli NASA 戈达德太空飞行中心，马里兰州格林贝尔特 claire.andreoli@nasa.gov