An asteroid has been ripped to shreds and vaporized after straying too close to a hot white dwarf star, observations suggest. The asteroid was probably flung towards the white dwarf by the gravity of one or more unseen planets. The evidence comes in the form of a hot ring of metallic vapour around a white dwarf called SDSS 1228+1040. Researchers led by Boris Gänsicke of the University of Warwick, UK, found signs of the disc in light spectra from the white dwarf acquired by the Sloan Digital Sky Survey’s 2.5-metre telescope at Apache Point, New Mexico, US, the 4.2-metre William Herschel Telescope on the Canary Islands, and by Caltech’s orbiting Galaxy Evolution Explorer (GALEX). The spectra indicate that a disc containing calcium, magnesium, and iron gas is orbiting the white dwarf at a distance 100 times closer than Mercury’s orbit around the Sun. At this distance, intense radiation from the white dwarf heats the gas to 5000 K. The spectra also shows that the white dwarf’s atmosphere is enriched in magnesium. That indicates material from the disc is falling onto the star, since the star’s own surface gravity is so great that its own heavy elements should have already sunk towards its centre and out of sight.

A gaseous metal disk around a white dwarf