Red giant stars that eat planets might shine less brightly
When giant stars eat giant planets, their starlight may shine a bit less brightly. That dimming could affect how astronomers measure distances across the universe — and possibly even put past measurements in doubt. “You would think the planet would be a small perturbation to the star,” says astrophysicist Licia Verde. “It turns out that it’s not.” Those perturbations may even help explain why estimates for how fast the universe is expanding disagree, Verde and her colleagues argue in a paper posted March 25 at arXiv.org. When stars similar in mass to the sun burn through most of the hydrogen in their cores, their outer layers puff up until the stars are hundreds of times their original sizes, becoming red giants. At a certain core density, red giants were all thought to reach the same peak brightness. That uniform brightness has helped astronomers estimate cosmic distances. It’s hard to know how far away a star is without knowing its intrinsic brightness — a star may...