M2-9:蝴蝶星云的翅膀

M2-9:蝴蝶星云的翅膀

ByNASA中文

2020年9月13日 M2-9: Wings of a Butterfly Nebula Image Credit: Hubble Legacy Archive, NASA, ESA – Processing: Judy Schmidt Explanation: Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays as they die. In the case of low-mass stars like our Sun and M2-9 pictured here, the stars transform themselves from normal stars to white dwarfs by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula that fades gradually over thousands of years. M2-9, a butterfly planetary nebula 2100 light-years away shown in representative colors, has wings that tell a strange but incomplete tale. In the center, two stars orbit inside a gaseous disk 10 times the orbit of…

哈勃发现了参宿四神秘变暗事件背后的秘密

哈勃发现了参宿四神秘变暗事件背后的秘密

ByNASA中文

美国航空航天局（NASA）哈勃空间望远镜的观测结果表明，红超巨星（red supergiant）参宿四（Betelgeuse，又称猎户座α星，α Orionis）的意外变暗很可能是由于大量热物质喷射到太空中，形成的尘埃云阻挡了参宿四表面的星光而造成的。 哈勃的研究团队认为，从恒星表面大型对流单元的上升流中释放出的超高温等离子体，在穿过高温大气到达温度较低的外层大气时，降温冷却形成了尘埃颗粒，进而产生了尘埃云。从2019年末开始，这些尘埃云阻挡了大约四分之一从恒星表面射出的光线，直到2020年4月，恒星才恢复了正常亮度。 参宿四是一颗年迈的红超巨星，由于它的内核中复杂而变化多端的核聚变反应，参宿四的大小已经发生了膨胀。现在的参宿四是如此之大，如果把它放在我们太阳系中心太阳的位置上，它的外表面将延伸到超过木星轨道的地方。 参宿四此次变暗的现象可以说是史无前例的，甚至达到了在地球上肉眼可见的程度，变暗开始于2019年10月，到2020年2月中旬的时候，这颗怪物巨星已经失去了它三分之二还要多的光彩。 这幅四分图描绘了快速演化的明亮红超巨星参宿四的南部区域，在2019年末到2020年初可能突然变暗了几个月。在前两个分图中，也就是哈勃望远镜在紫外线中所见的样子，从恒星表面上出现的巨大对流单元中喷出了明亮而高温的等离子体团。在第三个分图中，喷射而出的气体迅速向外膨胀，冷却后形成了巨大的尘埃云。最后一个分图显示出在巨大尘埃云的遮挡下，从地球的角度看来有四分之一恒星表面的光都被围堵了。 图片来源：NASA、欧洲空间局（ES）和空间望远镜研究所（Space Telescope Science Institute，STScI）的E•惠特利（E. Wheatley） 这种突然的变暗让天文学家感到满头问号，他们争先恐后地提出了许多或能解释这种突发变化的理论。其中有一种理论是：一个面积巨大而低温暗淡的“星点”覆盖了参宿四可见表面的一片宽阔区域。但是，领导哈勃观测研究的安德烈亚•杜普雷（Andrea Dupree）则提出，是尘埃云遮挡了参宿四的一部分。杜普雷是位于马萨诸塞州剑桥市哈佛-史密森天体物理学中心（Center for Astrophysics | Harvard & Smithsonian，CfA）的副主任。 从2019年1月开始，哈勃对参宿四进行了好几个月的紫外线光谱观察，得出了导致光度变暗的时间线。这些观测数据为参宿四变暗的背后机理提供了重要的新线索。 在2019年9月、10月和2019年11月，哈勃望远镜拍下了密集的被加热的物质在恒星大气中移动的迹象；在之后的12月，多台地面望远镜观测到参宿四南半球的亮度下降。 “有了哈勃望远镜，我们就可以看到离开恒星可见表面并穿过并逃逸出大气层的物质，这一过程发生在让恒星看起来变暗的尘埃形成之前，”杜普雷说道，“我们可以看到恒星东南部一处高密度且高温的区域向外移动的影响。” “这种材料的发光量比恒星的正常亮度还要高出两到四倍，”她继续说道，“然后，大约一个月之后，随着参宿四逐渐变暗，它的南部亮度下降得非常显著。我们认为，哈勃探测到的外喷流可能形成了暗淡的尘埃云，只有哈勃向我们提供了这一导致参宿四变暗现象的证据。” 研究团队相应的论文已于8月13日在线发表在《天体物理学杂志》（The Astrophysical Journal）上。 像参宿四这样的大质量超巨星对我们来说非常重要，因为它们会将诸如碳这一类的重元素排放到太空中，这些元素成为了新一代恒星诞生的基础。众所周知，碳还是碳基生命的基本原料。 追踪创伤性的爆发 从2019年年初开始，杜普雷的团队就在使用哈勃分析这颗庞然大物，他们的观测是哈勃为期三年的一项研究的一部分，这项研究旨在监测参宿四外部大气的变化。参宿四是一颗变化无常的恒星，在420天的振荡周期中，它会经历体积的膨胀和收缩，以及亮度的增长和降低。 哈勃望远镜的紫外线观测敏感度极高，这让研究人员能够探测到参宿四这颗恒星表面上方温度极高（超过11 000摄氏度）的层状结构，因为这样的高温是无法在可见光波长下被探测到的。参宿四动荡的对流单元以鼓泡泡的形式，将这些层状结构的某些部分上升到表面从而得以升温。 在2019年末和2020年，哈勃拍摄下了参宿四的光谱图像，并通过测量二价镁（单个镁离子）线探测了恒星的外部大气。在2019年9月至11月期间，研究人员测量了从恒星表面进入其外层大气的物质移动速度，约为200 000英里每小时（320 000千米每小时）。 这种炽热而稠密的物质继续行进到参宿四的可见表面之外，上升到了距离这颗动荡恒星数百万千米之外的地方。研究人员表示，在这样的距离下，这些物质会冷却到足以形成尘埃的程度。 这种解释与哈勃在2020年2月的紫外线观测结果一致，观测表明，参宿四外部大气的行为恢复了正常，尽管可见光图像显示它仍在进一步变暗。 虽然杜普雷还不清楚参宿四爆发的原因，但她认为这里面有恒星振荡周期的功劳，因为可见光记录表明，恒星的振荡在整个爆发事件中一直都在如常进行。论文的共同作者、波茨坦莱布尼兹天体物理研究所（Leibniz Institute for Astrophysics Potsdam）的克劳斯•施特拉斯迈尔（Klaus Strassmeier）使用该研究所的自动望远镜恒星运动望远镜（STELLar Activity，STELLA），测量了在振荡周期内参宿四表面气体上升和下降时的气体速度变化。在对流单元上升的同时，恒星正处于周期中的膨胀阶段。从参宿四内部向外振荡产生的波动，可能帮助推动了流出的等离子体穿过大气层。 杜普雷估计，在爆发持续的三个月中，参宿四损失的物质量约为南半球正常物质量的两倍。就像所有恒星一样，参宿四的质量一直在减小，而在爆发的时候，质量损失速率比太阳的质量损失高出了3000万倍。 参宿四距离地球如此之近，而它本身又如此庞大，哈勃望远镜甚至已经能分辨出它的地表特征了，这还是除了我们的太阳之外唯一被如此“端详”的恒星，表面细节几乎一览无余。 借助哈勃，杜普雷在1995年拍摄的图像首次展示出了参宿四斑驳的表面，其中包含大量的对流单元，这些单元时而收缩时而膨胀，从而让它们看起来时而暗淡时而明亮。 超新星爆发前兆？ 红超巨星注定要在超新星爆炸中结束自己的生命，一些天文学家认为，参宿四的突然变暗可能是超新星爆发的前兆。这颗恒星离我们相对较近，大约相距725光年，这意味着它的变暗发生在公元1300年左右，只是直到现在，从它射出的光才刚刚到达地球。 “没有人知道恒星在发生超新星爆炸之前会做些什么，因为我们从没观测到过，”杜普雷解释说，“对于成为超新星的恒星，天文学家可能在它们发生超新星爆炸之前的一年里有所观测，但在爆炸前的几天或几周内进行观测的可能性非常小。” 杜普雷将在八月下旬或九月初利用哈勃再一次观测这颗恒星。目前，参宿四出在白天的天空中，非常靠近太阳，这让哈勃无法对它进行观测。但另一方面，NASA的日地关系天文台（Solar Terrestrial Relations Observatory，STEREO）已经从太空中拍摄了这颗怪物恒星的图像，相应的观察结果表明，参宿四从5月中旬到7月中旬又再次变暗了，尽管没有今年年初那么强烈。 杜普雷希望使用STEREO进行更多的后续观察，来监测参宿四的亮度变化。她的计划是，在明年参宿四在它的振荡周期内再次向外膨胀时，利用STEREO对参宿四进行第二次观测，查看它是否释放了另一个爆炸性的爆发。 参考来源： https://www.nasa.gov/feature/goddard/2020/hubble-finds-that-betelgeuses-mysterious-dimming-is-due-to-a-traumatic-outburst

哈勃望远镜看到了恒星爆炸的边缘

哈勃望远镜看到了恒星爆炸的边缘

ByNASA中文

While appearing as a delicate and light veil draped across the sky, this image from the NASA/ESA Hubble Space Telescope actually depicts a small section of the Cygnus supernova blast wave, located around 2,400 light-years away. The name of the supernova remnant comes from its position in the northern constellation of Cygnus (the Swan), where it covers an area 36 times larger than the full Moon. The original supernova explosion blasted apart a dying star about 20 times more massive than our Sun between 10,000 and 20,000 years ago. Since then, the remnant has expanded 60 light-years from its center. The shockwave marks the outer edge of the supernova remnant and continues to expand at around 220 miles per second. The interaction of the ejected…

哈勃望远镜钩住了超新星宿主星系

哈勃望远镜钩住了超新星宿主星系

ByNASA中文

This image from the NASA/ESA Hubble Space Telescope features the spectacular galaxy NGC 2442, nicknamed the Meathook galaxy owing to its extremely asymmetrical and irregular shape. This galaxy was host to a supernova explosion spotted in March 2015, known as SN 2015F, that was created by a white dwarf star. The white dwarf was part of a binary star system and siphoned mass from its companion, eventually becoming too greedy and taking on more than it could handle. This unbalanced the star and triggered runaway nuclear fusion that eventually led to an intensely violent supernova explosion. The supernova shone brightly for quite some time and was easily visible from Earth through even a small telescope until months later. Download in full resolution from ESA’s Hubble…

NGC 5189：极为复杂的行星状星云

NGC 5189：极为复杂的行星状星云

ByNASA中文

2020年8月14日 NGC 5189: An Unusually Complex Planetary Nebula Image Credit: NASA, ESA, Hubble, HLA; Reprocessing & Copyright: Jesús M. Vargas Explanation: Why is this nebula so complex? When a star like our Sun is dying, it will cast off its outer layers, usually into a simple overall shape. Sometimes this shape is a sphere, sometimes a double lobe, and sometimes a ring or a helix. In the case of planetary nebula NGC 5189, however, besides an overall “Z” shape (the featured image is flipped horizontally and so appears as an “S”), no such simple structure has emerged. To help find out why, the Earth-orbiting Hubble Space Telescope has observed NGC 5189 in great detail. Previous findings indicated the existence of multiple epochs of material outflow,…

哈勃望远镜远近都能看到

哈勃望远镜远近都能看到

ByNASA中文

The barred spiral galaxy known as NGC 4907 shows its starry face from 270 million light-years away to anyone who can see it from the Northern Hemisphere. This is a new image from the NASA/ESA Hubble Space Telescope of the face-on galaxy, displaying its beautiful spiral arms, wound loosely around its central bright bar of stars. Shining brightly below the galaxy is a star that is actually within our own Milky Way galaxy. This star appears much brighter than the billions of stars in NGC 4907 as it is 100,000 times closer, residing only 2,500 light-years away. NGC 4907 is also part of the Coma Cluster, a group of over 1,000 galaxies, some of which can be seen around NGC 4907 in this image. This…

哈勃望远镜拍摄到一颗叫做HBC 672的恒星和蝙蝠的影子

哈勃望远镜拍摄到一颗叫做HBC 672的恒星和蝙蝠的影子

ByNASA中文

Astronomers using a previously captured Hubble imagery spotted a remarkable image of a young star’s unseen, planet-forming disk casting a huge shadow across a more distant cloud in a star-forming region. The star is called HBC 672, and the shadow feature was nicknamed the “Bat Shadow” because it resembles a pair of wings. The nickname turned out to be unexpectedly appropriate, because now those “wings” appear to be flapping! Image Credit: NASA, ESA, and STScI 天文学家利用之前哈勃望远镜拍摄到的照片，一颗年轻的恒星在其未被发现的形成行星的圆盘上投下了一个巨大的阴影，覆盖了恒星形成区域中较远的星云。这颗恒星被称为HBC 672，它的影子特征被称为“蝙蝠影子”，因为它像一对翅膀。原来这个绰号是出乎意料的合适，因为现在那些“翅膀”似乎在拍打! 影像来源：NASA, ESA, and STScI

明亮行星状星云NGC 7027的哈勃影像

明亮行星状星云NGC 7027的哈勃影像

ByNASA中文

2020 June 30 Bright Planetary Nebula NGC 7027 from Hubble Image Credit: NASA, ESA, Joel Kastner (RIT) et al.; Processing: Alyssa Pagan (STScI) Explanation: What created this unusual planetary nebula? NGC 7027 is one of the smallest, brightest, and most unusually shaped planetary nebulas known. Given its expansion rate, NGC 7027 first started expanding, as visible from Earth, about 600 years ago. For much of its history, the planetary nebula has been expelling shells, as seen in blue in the featured image. In modern times, though, for reasons unknown, it began ejecting gas and dust (seen in red) in specific directions that created a new pattern that seems to have four corners. These shells and patterns have been mapped in impressive detail by recent images…

哈勃望远镜拍摄到了边缘的星系

哈勃望远镜拍摄到了边缘的星系

ByNASA中文

The galaxy known as NGC 5907 stretches wide across this image. Appearing as an elongated line of stars and dark dust, the galaxy is categorized as a spiral galaxy just like our own Milky Way. In this new image from the NASA/ESA Hubble Space Telescope, we don’t see the beautiful spiral arms because we are viewing it edge-on, like looking at the rim of a plate. It is for this reason that NGC 5907 is also known as the Knife Edge galaxy. The Knife Edge galaxy is about 50 million light-years from Earth, lying in the northern constellation of Draco. Although not visible in this image, ghostly streams of stars on large arching loops extend into space, circling around the galaxy; they are believed to…

哈勃望远镜有一个明亮的发现

哈勃望远镜有一个明亮的发现

ByNASA中文

Seen here in incredible detail, thanks to the NASA/ESA Hubble Space Telescope, is the starburst galaxy formally known as PLCK G045.1+61.1. The galaxy, which appears as multiple reddish dots near the center of the image, is being gravitationally lensed by a cluster of closer galaxies, also seen in the image. Gravitational lensing occurs when a large distribution of matter, such as a galaxy cluster, sits between Earth and a distant light source. As space is warped by massive objects, the light from the distant object bends as it travels to us, creating stretched, magnified and sometimes multiple images of the lensed object. This effect was first predicted by Einstein’s general theory of relativity. From 2009 to 2013, the European Space Agency’s Planck space observatory captured…