White dwarfs polluted with planetary debris
The Hubble Space Telescope has found chemical evidence for the building blocks for rocky planets in an extremely unusual place: the atmospheres of two burned-out stars. Called white dwarfs, these stars are small, dim shadows of stars that would have once been like our sun, and they reside 150 light-years from Earth in the young star cluster of Hyades. Hubble’s spectroscopic observations identified silicon and low levels of carbon, both of which are strong indicators of a rocky material similar to that which makes up Earth. “When these stars were born, they built planets,” said Jay Farihi, lead author of the study, “and there’s a good chance they currently retain some of them… Based on the silicon-to-carbon ratio in our study, we can actually say that this material is basically Earth-like.” The material is thought to have ended up in the atmosphere of these stars after they collapsed into white dwarfs, and the larger planets in their solar system nudged asteroids into star-grazing orbits. The stars’ gravitational pull tore the asteroids apart, and the pulverised debris fell into a ring around the white dwarfs and were eventually funnelled inwards to pollute the stars themselves. The discovery suggests that rocky planets may commonly assemble around stars, and may help us to understand what will happen to our solar system in five billion years, when our own sun burns out.