Watch for falling rocks. Those are words to keep in mind when you're driving a mountain road. Or, it seems, when you're cruising past a white dwarf star.
小心坠落的岩石 。如果你在山路上开车，请把这句话记在心上吧 。或者可以说在你缓慢驶过一颗白矮星时 。
White dwarfs are small, dense remnants of normal stars that have expended their fuel. Now researchers have identified rocky, asteroidlike material raining down on two white dwarfs. The rocky material is akin to the building blocks of planets—and its presence suggests that the two stars formed planetary systems before they expired and became white dwarfs. That's the conclusion of a study in the Monthly Notices of the Royal Astronomical Society.
Astronomers identified the silicon-rich rocky material by training the Hubble Space Telescope on the nearby Hyades star cluster. Finding rocky material means the stars once had the raw ingredients to make exoplanets—although almost no known planets orbit stars inside of clusters.
天文学家通过培训哈勃望太空远镜观测附近的毕宿星团来确认富含硅元素的岩石物质 。岩石物质的发现意味着恒星内有制造行星的原材料——尽管几乎没有已知的行星围绕星团里的恒星转动 。
The discovery of planetary material thus raises more questions. Are star clusters indeed inhospitable to planets? Or are planets around stars in clusters for some reason just harder to spot? In the Hyades cluster, at least, it looks like there may be planets that have so far escaped our notice.
行星物质发现也因此产生了许多问题 。星团确实不适合行星吗？还是说出于某种原因，围绕星团的行星很难被发现？至少在毕宿星团，看起来似乎有行星逃离了我们的关注的目光 。