US 708
US 708是一顆位於銀河系的超高速運動次矮星,位於大熊座。該恆星是銀河系中運動最快的恆星之一,發現於1982年[1][2][3]。
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e2/US_708.jpg/270px-US_708.jpg)
發現
編輯1982年,賓夕法尼亞州立大學的天文學家彼得·烏舍爾(Peter Usher)於銀河系的銀暈中發現了 US 708這個藍色黯淡天體。史隆數位巡天於 2005年再次對它進行觀測[4][5]。
研究
編輯2015年,歐洲南方天文台的天文學家史蒂芬·蓋爾(Stephan Geier)領導的團隊在《科學》期刊發表US 708在銀河系中速度達到每秒1200公里,為至今銀河系中運動速度最快者的論文[1][6][7]。使它如此高速的原因最初被懷疑跟銀河系中心的超大質量黑洞有關。但最新研究發現它曾經在1400萬年前穿過銀河系盤面,因此它並不是來自銀河系中心區域;這代表它的高速運動原因也許不是因為黑洞[8]。最新研究則認為US 708可能曾經是一對密近聯星的其中一顆成員星[9]。
當US 708仍為紅巨星時,它的伴星已經成為白矮星。當白矮星從US 708的外層吸積氣體時,兩者的相對軌道將會改變。接著,白矮星的質量到達錢德拉塞卡極限,成為Ia超新星,使US 708被高速彈射;而不是星系中心的黑洞使它達到如此高速[10]。對US 708進行最新觀測的團隊推論US 708環繞的白矮星質量與太陽相當,並且軌道週期小於10分鐘[6][7]。
結構
編輯US 708是一顆高速自轉,且擁有被認為來自原先和伴星交互作用而生成的厚層氦層恆星。這類主要組成成分為氦的恆星一般被認為是巨大恆星失去以氫為主的外層後所殘留。蓋爾的團隊描述US 708是「銀河系中最快的不受約束恆星」。並且使用位於夏威夷的口徑10米望遠鏡凱克Ⅱ的階梯式攝譜儀與成像儀觀測[11],發現它的速度已經超過了銀河系的逃逸速度[12]。
參考資料
編輯- ^ 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]. (原始內容存檔於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]. (原始內容存檔於2021-06-08).
- ^ Thermonuclear supernova ejects galaxy’s fastest star. Astronomy magazine. 2015-03-09 [2015-03-11]. (原始內容存檔於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]. (原始內容存檔於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]. (原始內容存檔於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]. (原始內容存檔於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]. (原始內容存檔於2015-03-10).
- ^ Douglas Quenqua. Fastest Star in the Galaxy Got an Unusual Start. New York Times. 2015-03-10: D4 [2015-03-10]. (原始內容存檔於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]. (原始內容存檔於2020-11-08).
- ^ TechTimes. [March 11, 2015]. (原始內容存檔於2016-06-24).
- ^ DNews. [March 11, 2015]. (原始內容存檔於2015-05-12).
- ^ Thermonuclear Supernova Ejects Galaxy’s Fastest Star. KeK. [March 11, 2015]. (原始內容存檔於2015-03-17).