A doomed planet is being torn up by its 'zombie' white dwarf star — but astronomers don't understand why

一颗注定要失败的行星正在被它的“僵尸”白矮星撕裂——但天文学家不明白为什么

A white dwarf star has been caught in the middle of consuming a planetary relic, offering fresh clues as to what happens to planetary systems after their star dies.

一颗白矮星正在吞噬一颗行星遗迹，为恒星死亡后行星系统会发生什么提供了新的线索。

Three billion years ago, a sun-like star reached the end of its life, throwing off its outer layers following its red giant phase to leave behind its inert core, which we see today as the white dwarf called LSPM J0207+3331, located 145 light-years away. But what happened to its planets?

30亿年前，一颗类似太阳的恒星走到了生命的尽头，在红巨星阶段后脱落了外层，留下了惰性的核心，我们今天看到它是一颗名为LSPM J0207+3331的白矮星，位于145光年之外。但是它的行星发生了什么？

Spectroscopic observations of LSPM J0207+3331 by several telescopes, including the Magellan Baade 6.5-meter telescope in Chile and the 10-meter Keck I telescope on Hawaii's Mauna Kea, have revealed that fragments of planets and asteroids have survived for three billion years.

包括智利的麦哲伦巴德6.5米望远镜和夏威夷莫纳克亚山的10米凯克I望远镜在内的几台望远镜对LSPM J0207+3331进行的光谱观测显示，行星和小行星的碎片已经存活了30亿年。

For one of those fragments, however, its time is at an end. The spectroscopic observations have shown that gravitational tidal forces from the white dwarf have torn it apart, scattering debris from the planetary body onto the surface of the white dwarf. The measurements identified 13 elements from this doomed object, including aluminum, carbon, chromium, cobalt, copper, iron, magnesium, manganese, nickel, silicon, sodium, strontium and titanium, in mostly Earth-like abundances.

然而，对于其中一个片段来说，它的时间已经结束了。光谱观测表明，来自白矮星的引力潮汐力将它撕裂，将行星体的碎片散落到白矮星表面。测量结果从这个注定要毁灭的物体中确定了13种元素，包括铝、碳、铬、钴、铜、铁、镁、锰、镍、硅、钠、锶和钛，其丰度大多与地球相似。

The white dwarf features a hydrogen-rich envelope, and in general any elements deposited onto the white dwarf should sink into this hydrogen envelope and disappear from view. For so many elements to still be visible implies that their accretion onto the white dwarf must have happened relatively recently — within the past 35,000 years.

白矮星有一个富含氢的包层，一般来说，沉积在白矮星上的任何元素都应该沉入这个氢包层中并从视野中消失。如此多的元素仍然可见，这意味着它们在白矮星上的吸积一定是最近才发生的——在过去的35,000年内。

It could even be ongoing – LSPM J0207+3331 could still be dismantling this object, which is estimated to have been 120 miles (193 kilometers) across, a piece at a time as you read this.

它甚至可能正在进行中——LSPM J0207+3331可能仍在拆除这个物体，当你读到这篇文章时，它估计有120英里（193公里）宽，一次一块。

Heavy elements from destroyed planets and asteroids have been detected on white dwarfs before, but after three billion years this process of debris falling onto the white dwarf should have ended.

以前曾在白矮星上探测到来自被摧毁的行星和小行星的重元素，但30亿年后，这种碎片落到白矮星上的过程应该已经结束了。

"The amount of rocky material is unusually high for a white dwarf of this age," said Patrick Dufour of the Trottier Institute for Research on Exoplanets at Université de Montréal in a statement.

蒙特利尔大学特罗蒂尔系外行星研究所的帕特里克·杜福尔在一份声明中说：“对于这个年龄的白矮星来说，岩石物质的数量异常高。”

LSPM J0207+3331 is also ringed by a probable debris disk rich in silicates and which was discovered as an excess mid-infrared glow by NASA's Wide-field Infrared Survey Explorer (WISE). The hypothesis is that the object that has recently been ripped apart by the white dwarf could have originated from this debris disk of material that survived the death of the star. Future James Webb Space Telescope (JWST) observations of this disk could allow researchers to determine its mineralogy and constrain its total mass, which will provide further clues as to the nature of the object that the white dwarf has destroyed.

LSPM J0207+3331还被一个可能富含硅酸盐的碎片盘环绕，该碎片盘被美国宇航局的宽视场红外巡天探测器（WISE）发现为过量的中红外辉光。假设是，最近被白矮星撕裂的物体可能起源于这个恒星死亡后幸存下来的物质碎片盘。未来詹姆斯·韦伯太空望远镜（JWST）对这个圆盘的观测可以让研究人员确定它的矿物学并限制它的总质量，这将为白矮星摧毁的物体的性质提供进一步的线索。

What is not yet clear is why has this object met its doom now, and not at any time in the previous three billion years?

目前还不清楚的是，为什么这个物体现在就面临厄运，而不是在过去30亿年中的任何时候？

"This discovery challenges our understanding of planetary system evolution," added Érika Le Bourdais, also of Montréal and the lead author of the research. "Ongoing accretion at this stage suggests white dwarfs may also retain planetary remnants still undergoing dynamical changes."

“这一发现挑战了我们对行星系统演化的理解，”同样来自蒙特利尔、该研究的主要作者Érika Le Bourdais补充道。“这一阶段正在进行的吸积表明，白矮星也可能保留仍在经历动态变化的行星残余物。”

When a sun-like star begins to die and expands into a red giant, its inner planets are consumed and destroyed. However, bodies orbiting far enough away, such as asteroids, comets and gas giant planets, can survive, after a fashion. The changing gravitational field as a star sheds mass can disrupt the planets' orbits, resulting in many collisions between asteroids, comets and surviving planets and moons over billions of years that can grind solid bodies down to dust and small chunks. It's this material that fills the debris disk around LSPM J0207+3331, and what is surprising is that substantial solid bodies still exist in that disk, and that something must have happened to cause one of those solid bodies to fall towards the white dwarf.

当一颗类太阳恒星开始死亡并膨胀成红巨星时，它的内行星就会被消耗和毁灭。然而，轨道足够远的天体，如小行星、彗星和气态巨行星，可以在某种程度上幸存下来。当恒星失去质量时，引力场的变化会扰乱行星的轨道，导致小行星、彗星以及幸存的行星和卫星之间在数十亿年的时间里发生多次碰撞，这些碰撞会将固体物体磨成灰尘和小块。正是这种物质填充了LSPM J0207+3331周围的碎片盘中，令人惊讶的是，该盘中仍然存在大量的固体，并且一定发生了什么事情导致其中一个固体向白矮星坠落。

"Something clearly disturbed this system long after the star's death," said John Debes of the Space Telescope Science Institute. "There's still a reservoir of material capable of polluting the white dwarf, even after billions of years."

太空望远镜科学研究所的约翰·德贝斯说：“在恒星死后很长一段时间内，显然有什么东西扰乱了这个系统。”“即使数十亿年后，仍然有一个物质库能够污染白矮星的物质库。”

What has destabilized the debris is unclear. Any surviving gas giant planets could be responsible, with multi-planet interactions having possibly gradually destabilized orbits of smaller bodies over billions of years. "This could point to long-term dynamical processes we don’t yet fully understand," said Debes.

目前还不清楚是什么破坏了碎片的稳定。任何幸存的气态巨行星都可能是罪魁祸首，多行星相互作用可能会在数十亿年内逐渐破坏较小天体的轨道的稳定性。“这可能指向我们尚未完全了解的长期动态过程，”德贝斯说。

Proving this idea won't be easy, however.

然而，证明这个想法并不容易。

Gas giant planets would be too far from the white dwarf and likely too cool to be bright enough to be imaged, although the JWST might be able to have a go. More likely, the European Space Agency's Gaia astrometric mission may have been able to detect a wobble in the motion of the white dwarf on the sky caused by the gravity of orbiting gas giant planets pulling on it. The first batch of exoplanet data from Gaia is expected to be released in December 2026 – perhaps then the mystery might be solved?

气态巨行星离白矮星太远，而且可能太冷，亮度不足以成像，尽管JWST也许可以尝试一下。更有可能的是，欧洲航天局的盖亚天体测量任务可能已经能够探测到天空中白矮星运动的摆动，这是由轨道气态巨行星的引力拉动它造成的。盖亚的第一批系外行星数据预计将于2026年12月发布——也许到那时谜团就会解开？

The findings have been published on Oct. 22 in The Astrophysical Journal.

这些发现发表在10月22日的《天体物理学杂志》上。