A Unusual White Dwarf with a Chaotic Previous – Sky & Telescope

What’s stranger than stones raining down onto a scorching white dwarf star? Including chunks of ice to the combination.

G238-44, a puny white dwarf at a distance of 86 light-years, is accreting two very totally different sort of objects concurrently, Ted Johnson (College of California, Los Angeles) advised the 240th assembly of the American Astronomical Society in Pasadena, California, on Wednesday. “This has by no means been noticed earlier than,” he says.

White dwarfs are the compact stays of low-mass stars that first balloon into purple giants — a destiny that awaits our personal Solar some 5 billion years from now. The purple large part wreaks havoc with orderly planetary techniques. Shut-in planets could also be devoured, whereas the orbits of extra distant worlds grow to be jumbled.

After the enormous star blows away its outer layers right into a planetary nebula, a roughly Earth-size (however nonetheless photo voltaic mass) white dwarf stays. Observations of many white dwarfs present indicators of atmospheric “air pollution”: sudden quantities of components heavier than helium. Their existence signifies that when collisions disrupt the orbits of asteroid-like our bodies within the white dwarf system, their rocky particles rains down onto the star.

So what’s so unusual about G238-44? It’s the chemical composition of the air pollution on its floor, as measured by NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE), the Keck Telescope in Hawai’i, and the Hubble Area Telescope. The relative abundances of 10 heavy components (carbon, nitrogen, oxygen, magnesium, aluminum, silicon, phosphorus, sulfur, calcium, and iron) don’t match the composition of any identified photo voltaic system object.

In keeping with Johnson, the fabric falling down onto the white dwarf is greatest described as nearly two components Mercury-like particles — typical rocky stuff — and one half materials that is just like the icy Kuiper Belt objects within the outskirts of the photo voltaic system. The findings counsel that the star’s planetary system skilled an enormous quantity of orbital chaos, which might have flung distant icy our bodies inward.

Dennis Bodewits (Auburn College), who was not concerned within the examine, is intrigued by the outcome. “That is the one technique to examine the inside composition of small our bodies in different photo voltaic techniques, so that’s cool,” he says. “Nevertheless, I don’t like sophisticated options – perhaps the observations may be defined by one disintegrated object in spite of everything, containing each steel, rock, and ice, just like the dwarf planet Ceres.”

In an identical vein, Nick Cowan (McGill College) wonders whether or not the article might have been a water-rich super-Earth or a gaseous mini-Neptune. These two planet varieties are absent in our personal photo voltaic system however plentiful elsewhere within the universe.

However Johnson claims there’s simply no technique to find yourself with the noticed relative quantities of iron, oxygen, carbon and nitrogen in a single physique.

Furthermore, UCLA astronomer and staff member Ben Zuckerman explains that the quantity of air pollution is just too small to return from the disruption of a planet. The overall mass of measured heavy components is method lower than Earth’s mass, Zuckerman says, and the shortage of an extra of infrared radiation across the white dwarf signifies that there’s not an enormous quantity of circumstellar materials left.

With only one white dwarf displaying “unusual abundances,” as Johnson calls it, it’s tough to attract definitive conclusions. Future observations could yield extra instances. “It’s an fascinating discover,” says Bodewits, “however I want there have been extra.”

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