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美国国家航空航天局NASA每日一图-2017年8月11日(具有重力波前景的Starburst)

A Starburst with the Prospect of Gravitational Waves

In 1887, American astronomer Lewis Swift discovered a glowing cloud, or nebula, that turned out to be a small galaxy about 2.2 billion light years from Earth. Today, it is known as the “starburst” galaxy IC 10, referring to the intense star formation activity occurring there.

More than a hundred years after Swift’s discovery, astronomers are studying IC 10 with the most powerful telescopes of the 21st century. New observations with NASA’s Chandra X-ray Observatory reveal many pairs of stars that may one day become sources of perhaps the most exciting cosmic phenomenon observed in recent years: gravitational waves.

By analyzing Chandra observations of IC 10 spanning a decade, astronomers found over a dozen black holes and neutron stars feeding off gas from young, massive stellar companions. Such double star systems are known as “X-ray binaries” because they emit large amounts of X-ray light. As a massive star orbits around its compact companion, either a black hole or neutron star, material can be pulled away from the giant star to form a disk of material around the compact object. Frictional forces heat the infalling material to millions of degrees, producing a bright X-ray source.

When the massive companion star runs out fuel, it will undergo a catastrophic collapse that will produce a supernova explosion, and leave behind a black hole or neutron star. The end result is two compact objects: either a pair of black holes, a pair of neutron stars, or a black hole and neutron star. If the separation between the compact objects becomes small enough as time passes, they will produce gravitational waves. Over time, the size of their orbit will shrink until they merge. LIGO has found three examples of black hole pairs merging in this way in the past two years.

Starburst galaxies like IC 10 are excellent places to search for X-ray binaries because they are churning out stars rapidly. Many of these newly born stars will be pairs of young and massive stars. The most massive of the pair will evolve more quickly and leave behind a black hole or a neutron star partnered with the remaining massive star. If the separation of the stars is small enough, an X-ray binary system will be produced.

This new composite image of IC 10 combines X-ray data from Chandra (blue) with an optical image (red, green, blue) taken by amateur astronomer Bill Snyder from the Heavens Mirror Observatory in Sierra Nevada, California. The X-ray sources detected by Chandra appear as a darker blue than the stars detected in optical light.

The young stars in IC 10 appear to be just the right age to give a maximum amount of interaction between the massive stars and their compact companions, producing the most X-ray sources. If the systems were younger, then the massive stars would not have had time to go supernova and produce a neutron star or black hole, or the orbit of the massive star and the compact object would not have had time to shrink enough for mass transfer to begin. If the star system were much older, then both compact objects would probably have already formed. In this case transfer of matter between the compact objects is unlikely, preventing the formation of an X-ray emitting disk.

Chandra detected 110 X-ray sources in IC 10. Of these, over forty are also seen in optical light and 16 of these contain “blue supergiants”, which are the type of young, massive, hot stars described earlier. Most of the other sources are X-ray binaries containing less massive stars. Several of the objects show strong variability in their X-ray output, indicative of violent interactions between the compact stars and their companions.

A pair of papers describing these results were published in the February 10th, 2017 issue of The Astrophysical Journal and is available online here and here. The authors of the study are Silas Laycock from the UMass Lowell’s Center for Space Science and Technology (UML); Rigel Capallo, a graduate student at UML; Dimitris Christodoulou from UML; Benjamin Williams from the University of Washington in Seattle; Breanna Binder from the California State Polytechnic University in Pomona; and, Andrea Prestwich from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Image credit: X-ray: NASA/CXC/UMass Lowell/S. Laycock et al.; Optical: Bill Snyder Astrophotography

Read More from NASA's Chandra X-ray Observatory.

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Last Updated: Aug. 11, 2017
Editor: Lee Mohon

具有重力波前景的Starburst

1887年,美国天文学家刘易斯·斯威夫特(Lewis Swift)发现了一个发光的云层或星云,原来是距离地球大约22亿光年的小星系。今天,它被称为“星暴”星系IC 10,指的是在那里发生的强烈的星形成活动。

Swift发现一百多年后,天文学家正在用21世纪最强大的望远镜研究IC10。与NASA的Chandra X射线观测台的新观察显示,许多星星可能有一天成为近年来观察到的最激动人心的宇宙现象的来源:引力波。

天文学家通过分析十年来的“十年十一号”的钱德拉观测资料,发现十几个黑洞和中子星从年轻,巨大的恒星伴侣中抽出气体。这种双星系统被称为“X射线二进制”,因为它们发射大量的X射线光。随着巨大的星星围绕其紧凑的伴侣,无论是黑洞还是中子星,材料都可以从巨星上拉出来,以形成紧凑物体周围的材料盘。摩擦力将命中的材料加热到数百万度,产生明亮的X射线源。

当巨大的伴侣明星耗尽燃料时,会发生灾难性的崩溃,这将导致超新星爆炸,并留下黑洞或中子星。最终的结果是两个紧凑的物体:一对黑洞,一对中子星,或一个黑洞和中子星。如果紧凑物体之间的距离随着时间的推移变得足够小,它们将产生引力波。随着时间的推移,他们的轨道的大小将缩小直到它们合并。在过去两年里,LIGO发现了三个黑洞对合并的例子。

像IC 10这样的Starburst星系是搜索X射线二进制文件的好地方,因为它们正在快速搅拌出来。这些新出生的星星中的许多人将成为一对年轻和巨大的明星。最大的一对将会更快地演变,留下一个黑洞或中子星与其余的巨星合作。如果星星的分离足够小,则会产生X射线二进制系统。

IC 10的这个新的复合图像将来自Chandra(蓝色)的X射线数据与来自加利福尼亚内华达山脉天堂镜天文台的业余天文学家Bill Snyder拍摄的光学图像(红,绿,蓝)组合。Chandra检测到的X射线源比在光学中检测到的星星显得更暗。

IC 10中的年轻人似乎只是在巨大的星星和他们紧凑的同伴之间发挥最大限度的互动的合适年龄,产生了最多的X射线源。如果系统更年轻,那么巨大的星星将不会有时间去超新星并产生一个中子星或黑洞,或者这颗巨星的轨道,紧凑的物体不会有足够的时间来缩小到大量传播开始。如果明星系统年龄较大,那么两个紧凑的物体可能已经形成。在这种情况下,物体在紧凑物体之间的转移是不可能的,从而防止X射线发射盘的形成。

钱德拉在IC 10中检测到110个X射线源。其中,在光学中还有四十个X光源,其中16个包含“蓝色超能量”,它们是前面描述的年轻,大规模的热星。大多数其他来源是包含较少质量的星星的X射线二进制文件。几个对象在X射线输出中显示出很强的变异性,表明紧凑恒星与其同伴之间的暴力相互作用。

描述这些结果的一篇论文发表在2017年2月10日的“天体物理学杂志”上,可以在这里和这里找到。该研究的作者是马萨诸塞州洛厄尔空间科学和技术中心(UML)的Silas Laycock; UML研究生Rigel Capallo; 来自UML的Dimitris Christodoulou 来自西雅图华盛顿大学的本杰明·威廉姆斯 来自加州州立理工大学波莫纳的Breanna Binder; 和来自马萨诸塞州剑桥的哈佛史密森天文物理中心的Andrea Prestwich。

美国航空航天局在阿拉巴马州亨茨维尔的马歇尔太空飞行中心管理美国宇航局在华盛顿的科学任务局的Chandra计划。马萨诸塞州剑桥的史密森天体物理天文台控制了钱德拉的科学和飞行运行。

图片来源:X光片:NASA / CXC / UMass Lowell / S。Laycock等人 光学:比尔·斯奈德天文摄影

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最后更新:2017年8月11日
编辑:李莫亨

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