“三体”星系，有新发现！

地球附近“三体”星系中观测到宜居带候选行星

英国《自然》杂志网站近日刊文说，一个国际研究团队借助美国航天局的詹姆斯·韦布空间望远镜，在距离地球最近的“三体”星系——半人马座阿尔法星系，观测到一颗位于恒星宜居带的候选行星。

It turns out that, in real life, a gas giant planet actually seems to be orbiting Alpha Centauri A, according to astronomers who peered at it with the James Webb Space Telescope's (JWST) Mid-Infrared Instrument (MIRI).

What's more, the planet apparently orbits at a distance from the star where temperatures might be cozy enough for life, according to a pair of reports accepted by The Astrophysical Journal Letters.

图源：外媒

半人马座阿尔法星系是一个距离地球大约4光年的三恒星系统，其最亮的恒星A星与太阳非常相似。本次观测到的候选行星是一颗围绕A星运转的气态行星，且位于A星的宜居带内，即与恒星距离适中，温度适宜生命繁衍的区域。

Alpha Centauri A is part of a triple-star system, and has close companions known as Alpha Centauri B and Proxima Centauri. Together, they appear to be one of the brightest objects in the night sky.

迄今绝大多数系外行星是通过间接线索而非直接成像发现的，比如通过观测恒星受行星引力作用产生的摆动现象来锁定行星。而这次，研究团队利用韦布空间望远镜的中红外仪器，将焦点对准了半人马座阿尔法星系的A星。由于该星系距离地球较近，研究团队尽力排除恒星的眩光干扰，成功获得了足以分辨出行星的高分辨率图像。

When a planet orbits close to its host star, astronomers struggle to see it against the star's glare. That makes it especially difficult to spot a planet that is in the habitable zone.

But because the Alpha Centauri system is so close to Earth, JWST managed to get a high enough resolution glimpse of it to pick out the planet — although the team still had to use MIRI's "coronograph" mode to filter out some of the glare.

图源：外媒

文章介绍，研究团队还将通过更多观测来复核发现，若最终得到证实，这将是首次通过直接成像技术观测到位于恒星宜居带内的系外行星。不过研究团队表示，这颗气态行星本身不太可能存在生命，但它为评估其卫星的宜居性提供了令人兴奋的可能性。

Aniket Sanghi, an astronomer at the California Institute of Technology in Pasadena, says his team wants to double-check the detection by conducting more observations with JWST. If the findings hold true, this would be the first ever planet to be imaged in its star's habitable zone.

The discovery doesn't promise any signs of life, which a gas planet like this one isn't likely to host. "But it does open the exciting possibility of evaluating the moons around this planet for habitability," Sanghi says.

据介绍，相关论文已发表在美国《天体物理学杂志通讯》上。

来源：新华社 《自然》杂志 NPR

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