Young super-hot white dwarfs do not have dust disks. In other words, they should have more worldlets falling toward the star to be ripped into dust.Īlso, younger white dwarfs are hotter – and therefore brighter – and should be better at making dusty discs out of the debris of shredded planetesimals.īut that, Steckloff says, is not what astronomers have seen. One would expect younger white dwarfs to have less stable planetary systems, thanks to the gravitational mayhem that accompanied the effect of the red giant destroying all of the inner planets.
These shreds would then be dispersed into a “nice tight dusty debris disc” by the pressure of the light emitted by the star.īut there was a big problem with that theory. Previously, he says, it was assumed that these discs were formed from planetesimals or asteroids that were far enough out to survive immolation in the red giant phase, but then fell inward, winding up so deep in the white dwarf’s gravity that they got ripped to shreds-something that occurs at a distance often referred to as the Roche limit. “This begs the question, if white dwarfs should have cleared out all of this debris during the red giant phase, then why do some of them seem to have closely orbiting dusty debris discs,” Jordan Steckloff, of the Planetary Science Institute, US, told this week’s virtual meeting of the American Astronomical Society’s Division for Planetary Sciences. But astronomers have found that about 4% of them appear to be accompanied by clouds of dust. It then implodes, leaving the white dwarf, which can initially be as hot as 50,000 degrees Celsius, until it gradually cools into obscurity. The initial, swollen size is called a red giant – and is large enough to consume planets as far out as Earth, and even Mars. Scientists studying how comets and asteroids break up and vaporize if they get too close to their suns have resolved a conundrum about a class of stars known as white dwarf stars.Įmbers of dying suns, white dwarfs form when a star, having run out of its nuclear fuel, first expands to enormous size then collapses into a dense, Earth-sized remnant. Spinning star hurtling out of the Milky Way.Life after death for planets orbiting white dwarfs.