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arXiv 1502.04655astro-ph.SRastro-ph.EP
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已知最接近太阳系的恒星

The Closest Known Flyby of a Star to the Solar System

Eric E. Mamajek, Scott A. Barenfeld, Valentin D. Ivanov, Alexei Y. Kniazev, Petri Vaisanen, Yuri Beletsky, Henri M. J. Boffin

备注：
4 pages, 1 figure
发表信息：
2015, Astrophysical Journal Letters 800, L17
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摘要：

经过的恒星会扰动奥尔特云，引发彗星雨和地球上潜在的灭绝事件。我们结合最近发现的，附近的，低质量的双星系统WISE J072003.20-084651.2（“Scholz星”）的速度测量，以计算其过去的轨迹。将这个0.15 M $\sim$双星系统的银河轨道与太阳积分，我们发现该双星系统只在太阳70 $^{+15}_{-10}$ kya（1 $σ$不确定度）的52 $^{+23}_{-14}$ kAU（0.25 $^{+0.11}_{-0.07}$秒差距）范围内通过，即在外奥尔特云内。这是已知的距离和速度受到严格限制的恒星与我们太阳系最近的相遇。先前的工作表明，0.25 pc范围内的飞越很少发生（$\sim$ 0.1 Myr $^{-1}$）。我们发现，由于低质量和高速度的二进制系统，遇到动力学弱。使用最好的天体测量，我们的模拟表明，该恒星穿透外奥尔特云的概率为$\sim$ 98%，但穿透动态活跃的内奥尔特云（$<$ 20 kAU）的概率为$\sim$ 10 $^{-4}$。虽然这个系统的飞越可能对长周期彗星的通量造成微不足道的影响，但最近发现的这一双星突出表明，动态重要的奥尔特云扰动可能潜伏在附近的恒星中。

英文摘要：

Passing stars can perturb the Oort Cloud, triggering comet showers and potentially extinction events on Earth. We combine velocity measurements for the recently discovered, nearby, low-mass binary system WISE J072003.20-084651.2 ("Scholz's star") to calculate its past trajectory. Integrating the Galactic orbits of this $\sim$0.15 M$_{\odot}$ binary system and the Sun, we find that the binary passed within only 52$^{+23}_{-14}$ kAU (0.25$^{+0.11}_{-0.07}$ parsec) of the Sun 70$^{+15}_{-10}$ kya (1$σ$ uncertainties), i.e. within the outer Oort Cloud. This is the closest known encounter of a star to our solar system with a well-constrained distance and velocity. Previous work suggests that flybys within 0.25 pc occur infrequently ($\sim$0.1 Myr$^{-1}$). We show that given the low mass and high velocity of the binary system, the encounter was dynamically weak. Using the best available astrometry, our simulations suggest that the probability that the star penetrated the outer Oort Cloud is $\sim$98%, but the probability of penetrating the dynamically active inner Oort Cloud ($<$20 kAU) is $\sim$10$^{-4}$. While the flyby of this system likely caused negligible impact on the flux of long-period comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.

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