This NASA/ESA Hubble Space Telescope image features the galaxy NGC 4388, a member of the Virgo galaxy cluster.
ESA/Hubble & NASA, S. Veilleux, J. Wang, J. Greene
A sideways spiral galaxy shines in this NASA/ESA Hubble Space Telescope image. Located about 60 million light-years away in the constellation Virgo (the Maiden), NGC 4388 is a resident of the Virgo galaxy cluster. This enormous cluster of galaxies contains more than a thousand members and is the nearest large galaxy cluster to the Milky Way.
NGC 4388 appears to tilt at an extreme angle relative to our point of view, giving us a nearly edge-on prospect of the galaxy. This perspective reveals a curious feature that wasn’t visible in a previous Hubble image of this galaxy released in 2016: a plume of gas from the galaxy’s nucleus, here seen billowing out from the galaxy’s disk toward the lower-right corner of the image. But where did this outflow come from, and why does it glow?
The answer likely lies in the vast stretches of space that separate the galaxies of the Virgo cluster. Though the space between galaxies appears empty, this space is occupied by hot wisps of gas called the intracluster medium. As NGC 4388 moves within the Virgo cluster, it plunges through the intracluster medium. Pressure from hot intracluster gas whisks away gas from within NGC 4388’s disk, causing it to trail behind as NGC 4388 moves.
The source of the ionizing energy that causes this gas cloud to glow is more uncertain. Researchers suspect that some of the energy comes from the center of the galaxy, where a supermassive black hole spins gas around it into a superheated disk. The blazing radiation from this disk might ionize the gas closest to the galaxy, while shock waves might be responsible for ionizing filaments of gas farther out.
This image incorporates new data, including several additional wavelengths of light, that bring the ionized gas cloud into view. The image holds data from several observing programs that aim to illuminate galaxies with active black holes at their centers.
Image credit: ESA/Hubble & NASA, S. Veilleux, J. Wang, J. Greene
这张NASA/ESA哈勃太空望远镜图像展示了星系NGC4388，它是室女座星系团的成员之一。
ESA/Hubble & NASA, S. Veilleux, J. Wang, J. Greene
在这张NASA/ESA哈勃太空望远镜图像中，一座侧向的旋涡星系熠熠生辉。NGC4388位于室女座，距离地球约6000万光年，是室女座星系团的一员。这个规模庞大的星系团拥有超过1000个成员，也是距离银河系最近的大型星系团。
NGC4388相对于我们的视线呈现出极端倾角，使我们几乎以侧视、近乎边缘朝向的角度观测到该星系。这样的视角揭示了一个耐人寻味的特征：在2016年发布的早期哈勃图像中并未显现的核区气体羽流。在本图中，这股气体从星系盘面翻涌而出，向画面右下方延展。但这股外流从何而来？又为何会发光？
答案很可能藏在室女座星系团成员之间那片广袤的空间之中。尽管星系间看似空无一物，实际上充满了被称为星系团内介质的高温稀薄气体。当NGC4388在室女座星系团内部运动时，它会穿行并“俯冲”穿过这层星系团内介质。来自高温团内气体的压力会剥离NGC4388盘面中的气体，使其在星系运动方向的后方形成拖曳尾迹。
然而，使这团气体云发生电离并发光的能量来源仍不够确定。研究人员推测，部分能量来自星系中心：那里的一颗超大质量黑洞会使周围气体高速旋转并形成炽热的吸积盘。该吸积盘释放的强烈辐射可能会电离更靠近星系本体的气体；而更远处的细丝状气体则可能由激波引发电离。
这张图像整合了新的观测数据，包括若干额外的观测波段，从而将电离气体云呈现出来。图像包含多个观测项目的数据，这些项目旨在揭示那些中心存在活动黑洞的星系。
图片来源: ESA/Hubble & NASA, S. Veilleux, J. Wang, J. Greene
