US 708
US 708是一颗位于银河系的超高速运动次矮星，位于大熊座。该恒星是银河系中运动最快的恒星之一，发现于1982年[1][2][3]。
发现
1982年，宾夕法尼亚州立大学的天文学家彼得·乌舍尔（Peter Usher）于银河系的银晕中发现了 US 708这个蓝色黯淡天体。史隆数位巡天于 2005年再次对它进行观测[4][5]。
研究
2015年，欧洲南方天文台的天文学家史蒂芬·盖尔（Stephan Geier）领导的团队在《科学》期刊发表US 708在银河系中速度达到每秒1200公里，为至今银河系中运动速度最快者的论文[1][6][7]。使它如此高速的原因最初被怀疑跟银河系中心的超大质量黑洞有关。但最新研究发现它曾经在1400万年前穿过银河系盘面，因此它并不是来自银河系中心区域；这代表它的高速运动原因也许不是因为黑洞[8]。最新研究则认为US 708可能曾经是一对密近联星的其中一颗成员星[9]。
当US 708仍为红巨星时，它的伴星已经成为白矮星。当白矮星从US 708的外层吸积气体时，两者的相对轨道将会改变。接着，白矮星的质量到达钱德拉塞卡极限，成为Ia超新星，使US 708被高速弹射；而不是星系中心的黑洞使它达到如此高速[10]。对US 708进行最新观测的团队推论US 708环绕的白矮星质量与太阳相当，并且轨道周期小于10分钟[6][7]。
结构
US 708是一颗高速自转，且拥有被认为来自原先和伴星交互作用而生成的厚层氦层恒星。这类主要组成成分为氦的恒星一般被认为是巨大恒星失去以氢为主的外层后所残留。盖尔的团队描述US 708是“银河系中最快的不受约束恒星”。并且使用位于夏威夷的口径10米望远镜凯克Ⅱ的阶梯式摄谱仪与成像仪观测[11]，发现它的速度已经超过了银河系的逃逸速度[12]。
参考资料
- ^ 1.0 1.1 Stephan Geier, F. Fürst, E. Ziegerer, T. Kupfer, U. Heber, A. Irrgang, B. Wang, Z. Liu, Z. Han, B. Sesar, D. Levitan, R. Kotak, E. Magnier, K. Smith, W. S. Burgett, K. Chambers, H. Flewelling, N. Kaiser, R. Wainscoat, C. Waters. The fastest unbound star in our Galaxy ejected by a thermonuclear supernova. Science magazine. 2015-03-06 [2015-03-10]. （原始内容存档于2015-09-24）.
Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy.
- ^ Eric Mack. 'Shrapnel' Star Sets Milky Way Speed Record. Forbes magazine. 2015-03-08 [March 11, 2015]. （原始内容存档于2021-06-08）.
- ^ Thermonuclear supernova ejects galaxy’s fastest star. Astronomy magazine. 2015-03-09 [2015-03-11]. （原始内容存档于2020-11-09）.
Scientists using the W. M. Keck Observatory and Pan-STARRS1 telescopes on Hawaii have discovered a star that breaks the galactic speed record, traveling with a velocity of about 2.7 million mph (1,200 km/s). This velocity is so high, the star will escape the gravity of our galaxy. In contrast to the other known unbound stars, the team showed that this compact star was ejected from an extremely tight binary by a thermonuclear supernova explosion.
- ^ US 708: Hypervelocity Star Ejected by Supernova Breaks Galactic Speed Record. Science News. 2015-03-06 [2015-03-10]. （原始内容存档于2020-11-08）.
A multinational team of astronomers led by Dr Stephan Geier from the European Southern Observatory in Garching, Germany, has determined that a hypervelocity star known as US 708 is traveling at about 1,200 km per second.
- ^ RT. RT. [March 11, 2015]. （原始内容存档于2020-11-08）.
- ^ 6.0 6.1 Fastest Star in Our Galaxy Propelled by a Thermonuclear Supernova. Institute for Astronomy, University of Hawaii. [March 11, 2015]. （原始内容存档于2021-08-28）.
- ^ 7.0 7.1 John Timmer. Fastest star leaving our galaxy was blasted out by a supernova: A double-detonation supernova spits out a hypervelocity hot dwarf. Ars Technica. March 5, 2015 [March 11, 2015]. （原始内容存档于2015-03-10）.
- ^ Douglas Quenqua. Fastest Star in the Galaxy Got an Unusual Start. New York Times. 2015-03-10: D4 [2015-03-10]. （原始内容存档于2020-11-08）.
By measuring the velocity, trajectory and rotation of the star, known as US 708, researchers at the European Southern Observatory determined that it started life as one half of a close binary pair — two stars that closely orbited one other.
- ^ IflScience. [March 11, 2015]. （原始内容存档于2020-11-08）.
- ^ TechTimes. [March 11, 2015]. （原始内容存档于2016-06-24）.
- ^ DNews. [March 11, 2015]. （原始内容存档于2015-05-12）.
- ^ Thermonuclear Supernova Ejects Galaxy’s Fastest Star. KeK. [March 11, 2015]. （原始内容存档于2015-03-17）.
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