50光年远的飞马51星
50 Light-years to 51 Pegasi
Image Credit & Copyright: Josselin Desmars
Explanation: It’s only 50 light-years to 51 Pegasi. That star’s position is indicated in this snapshot from August, taken on a hazy night with mostly brighter stars visible above the dome at Observatoire de Haute-Provence in France. Twenty-six years ago, in October of 1995, astronomers Michel Mayor and Didier Queloz announced a profound discovery made at the observatory. Using a precise spectrograph they had detected a planet orbiting 51 Peg, the first known exoplanet orbiting a sun-like star. Mayor and Queloz had used the spectrograph to measure changes in the star’s radial velocity, a regular wobble caused by the gravitational tug of the orbiting planet. Designated 51 Pegasi b, the planet was determined to have a mass at least half of Jupiter’s mass and an orbital period of 4.2 days, making it much closer to its parent star than Mercury is to the Sun. Their discovery was quickly confirmed and Mayor and Queloz were ultimately awarded the Nobel Prize in physics in 2019. Now recognized as the prototype for the class of exoplanets fondly known as hot Jupiters, 51 Pegasi b was formally named Dimidium, latin for half, in 2015. Since its discovery, over 4,000 exoplanets have been found.
Tomorrow’s picture: full moon silhouettes
50光年远的飞马51星
影像提供与版权: Josselin Desmars
说明: 飞马51星的距离只有50光年。在这幅摄于某雾蒙夜晚、法国上普罗旺斯天文台的圆顶上空仅见亮星的影像里，这颗星位于标示圈的中心。在26年前的1995年10月，天文学家梅尔和奎洛兹发布了在此天文台取得的重大发现。他们使用精确的分光仪，在飞马51星的周围找到一颗行星，成为人类在类太阳恒星附近记录到的第一颗系外行星。梅尔和奎洛兹用分光仪量测这颗恒星的径向速度变化，一种因为周围行星的重力牵引，所造成的恒星规律晃动。这颗编录号为飞马51b的行星，测定的质量至少是木星质量的一半以上，轨道周期则为4.2天，因此它和母星的距离，远小于水星和太阳。他们的发现很快得到证实，后来梅尔和奎洛兹更获颁2019年诺贝尔物理奖。这颗目前公认是系外行星家族原型的飞马51b，除了有热木星的昵称之外，在2015年更正式令名为“半木星（Dimidium）”，因为在拉丁语Dimidium之义为“半”。自从发现它之后，科学家又陆续找到4,000颗以上的系外行星。 （Dimidium = 51 Pegasi b 飞马51b、半木星、 室宿增一b）
明日的图片: full moon silhouettes
