Debris hints at rocky planets around dead stars
Published 20 April, 2009, 20:20
Astronomers say 1% to 3% of white dwarves have evidence of asteroids and rocky planets orbiting around them. This suggests that in the distant past they used to be like our own solar system.
White dwarves are what stars like the Sun become at the end of their lives. Their surface consists mostly of hydrogen and helium with a small addition of heavier elements like calcium.
The observation by an international team via NASA’s Spitzer Space Telescope revealed that some of the dwarves are polluted by a gradual rain of orbiting dust, reports the British Royal Astronomical Society. It radiates in the infrared range of the spectrum, which can be picked up by the telescope.
The team believes the dust is produced by asteroids similar to the dwarf planet Ceres in the Sun’s asteroid belt that was ripped apart by tidal forces. To come close enough to the star for it to happen, they must be perturbed from regular orbits by some external force. The force is likely to be the gravitation of bigger planets not observed by the instruments the scientists have now.
At least one to three small stars are contaminated in this way, the data suggests. A white dwarf is the final destination of the main sequence of star evolution, and the Sun will eventually become one. This is good news for those eager to find Earth-like planets around other stars. There can be as many as five million in our own galaxy.
“In the quest for Earth-like planets, we have now identified numerous systems which are excellent candidates to harbor them. Where they persist at white dwarfs, any terrestrial planets will likely not be habitable, but there may have been sites where life developed during a previous epoch,” said Dr Jay Farihi of the University of Leicester, who worked with the team.
What makes the scientists excited about their discovery is that optical and ultraviolet observation can determine the composition of the crushed asteroids.
Dr Farihi said: “We can then address the question, ‘Are the rocky extra-solar planets we find similar to the terrestrial planets of our Solar System?’”
discuss it
