In observations obtained at the William Herschel Telescope using ISIS spectrograph, the Warwick astronomers detected a large quantity of hydrogen and oxygen in the atmosphere of a white dwarf (known as SDSS J1242+5226), the compact remnant of a Sun-like star at the end of its life.
This is direct evidence that a water-rich exo-asteroid was disrupted and eventually delivered the water it contained onto the star. This world, the researchers discovered, was comparable in size to Ceres – at 900km across, the largest asteroid in the Solar System.
The impact of water-rich asteroids or comets onto a planet or white dwarf results in the mixing of hydrogen and oxygen into their atmospheres. Both elements were detected in large amounts in SDSS J1242+5226. "The amount of water found in SDSS J1242+5226 is equivalent to 30-35% of the oceans on Earth", explained Dr Raddi.
Research co-author Professor Boris Gänsicke, also of the University of Warwick, explained: "Oxygen, which is a relatively heavy element, will sink deep down into the white dwarf over time, and hence a while after the disruption event is over, it will no longer be visible.
"In contrast, hydrogen is the lightest element; it will always remain floating near the surface of the white dwarf where it can easily be detected. There are many white dwarfs that hold large amounts of hydrogen in their atmospheres, and this new study suggests that this is evidence that water-rich asteroids or comets are common around other stars."
Raddi, R.; Gänsicke, B. T.; Koester, D.; Farihi, J.; Hermes, J. J.;
Scaringi, S.; Breedt, E.; Girven, J., 2015, "Likely detection of
water-rich asteroid debris in a metal-polluted white dwarf", MNRAS, 450, 2083. Paper.
"Fresh evidence for how water reached earth found in asteroid debris", RAS Press Release, 7th May, 2015.