Graveyards of solar systems around dead suns

DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 20 April, 2009

Leicester University astronomer Jay Farihi speaks to Astronomy Now web editor Emily Baldwin on his discovery of the dusty remains of ancient solar systems around white dwarf stars.

Using NASA's Spitzer Space Telescope to study white dwarf stars, astronomers have found the dusty remains of ancient solar systems.

White dwarfs are the dense glowing embers of Sunlike stars. While their atmospheres should consist entirely of hydrogen and helium, they are sometimes contaminated with heavier elements like calcium and magnesium. "These metals really shouldn't be there," Jay Farihi of Leicester University tells Astronomy Now. "That means they are external pollutants." Although heavy elements can be swept up from interstellar clouds, Farihi says there are none located near the stars his team studied, therefore they must come from the remnants of planetary systems.

Rocky debris around white dwarf stars could be the remains of solar systems like our own. Image: NASA/JPL-Caltech.

"We looked at 50 stars with Spitzer and 14 have dust discs," he says. This dust is thought to originate from rocky bodies like asteroids or even rocky planets. "The observations are consistent with asteroids torn about by a star's gravity, just like how Saturn's rings were created."

Farihi says that the rocky debris imaged by Spitzer probably represents the innermost planets of a solar system that were ripped apart by the gravitational forces of their host star at the end of its life. Extrapolating our own Sun's life into the white dwarf phase, simulations show that the Earth may not survive, but that Mars and asteroid belt would probably lie outside of the Sun's grasp. "So we could be seeing the fate of our Solar System [in the systems seen by Spitzer]," adds Farihi, who also comments that this means there is also the possibility of some planets in these systems remaining intact.

Perhaps the most exciting and important aspect of this research is that the composition of these crushed asteroids can be measured using the heavy elements seen in the white dwarf. In one case 17 heavy elements were found in one star, yielding a composition that closely matches the equivalent of a combined Earth and Moon. The next step will be to search for those ingredients that may suggest that life-bearing planets may once have existed in these systems. "In the quest for Earthlike planets, we have now identified numerous systems which are excellent candidates to harbour them," says Farihi. "Where they persist at white dwarfs, any terrestrial planets will likely not be habitable, but may have been sites where life developed during a previous epoch."