发现环双星系统

May the Fourth Be With You!

When the first Star Wars movie was released in 1977, it featured the now-iconic two-sun, “circumbinary” planet Tatooine. At that time astronomers didn’t really know if such solar systems existed. Indeed, the first extra-solar planet wasn’t detected until the early 1990s. And, the first actual circumbinary planet was detected in 2005, and it was a Jupiter-size planet orbiting a system composed of a sun-like star and a brown dwarf.

Fast forward a few decades and researchers working with data from the Transiting Exoplanet Survey Satellite (TESS) discovered the mission’s first circumbinary planet, a world orbiting two stars, as shown in this image from January 2020. The planet, called TOI 1338 b, is around 6.9 times larger than Earth, or between the sizes of Neptune and Saturn. It lies in a system 1,300 light-years away in the constellation Pictor.

The stars in the system make an eclipsing binary, which occurs when the stellar companions circle each other in our plane of view. One is about 10% more massive than our Sun, while the other is cooler, dimmer and only one-third the Sun’s mass. TOI 1338 b’s transits are irregular, between every 93 and 95 days, and vary in depth and duration thanks to the orbital motion of its stars. TESS only sees the transits crossing the larger star — the transits of the smaller star are too faint to detect. Its orbit is stable for at least the next 10 million years. The orbit’s angle to us, however, changes enough that the planet transit will cease after November 2023 and resume eight years later.

Image Credit: NASA/Goddard Space Flight Center

May the Fourth Be With You!（愿原力与你同在！五四青年节快乐！）

当第一部《星球大战》电影在1977年上映时，它出现了现在具有代表性的双太阳、环双子星塔图因。当时，天文学家并不知道是否真的存在这样的太阳系。事实上，第一颗太阳系外行星直到20世纪90年代初才被发现。而且，第一颗真正的环状行星是在2005年发现的，它是一颗木星大小的行星，围绕着一个由类太阳恒星和一颗褐矮星组成的系统运行。

快进几十年，研究人员利用凌日系外行星探测卫星(TESS)的数据发现了该任务的第一颗环双子星，这是一个围绕两颗恒星运行的世界，如2020年1月的这张图片所示。这颗行星名为TOI 1338b，大约是地球的6.9倍，大小介于海王星和土星之间。它位于距我们1300光年的绘架星座的一个星系中。

该系统中的恒星形成了日食双星，当伴星在我们的视线范围内相互环绕时，就会发生日食现象。其中一颗的质量比我们的太阳大10%，而另一颗则更冷、更暗，质量只有太阳的三分之一。TOI 1338b的凌日是不规则的，每93到95天一次，由于其恒星的轨道运动，凌日的深度和持续时间也不同。TESS只能看到大恒星的凌日现象——小恒星的凌日太过微弱，无法探测。至少在接下来的1000万年里，它的轨道是稳定的。然而，该轨道与我们的角度发生了很大的变化，2023年11月之后，行星凌日将停止，并在8年后恢复。

图片来源：美国航空航天局/戈达德太空飞行中心