© Lick ObservatoryHalley's Comet becomes visible to the unaided eye about every 76 years as it nears the sun.
It certainly captures the imagination: a star passing silently by our solar system knocks a deadly barrage of comets towards Earth. However, recent simulations by one group of researchers has shown that these star-induced comet showers may not be as dramatic as once thought.
The idea of nearby stars influencing comets goes back to 1950, when the astronomer Jan Hendrik Oort hypothesized an invisible repository of comets - the so-called Oort cloud - swarming around the solar system out to a distance of 100,000 AU (one AU is the distance between the sun and the Earth).
Oort assumed that stars passing through the cloud would cause a fresh batch of comets to fall in towards the sun, where they become visible to astronomers. Such a disturbance could have long term effects.
"The comets we see now could be from a stellar passage hundreds of millions of years ago," said Hans Rickman of the Uppsala Astronomical Observatory in Sweden.
However, Rickman and his colleagues have confirmed that star encounters alone cannot explain comet behavior. Using a computer model of the Oort cloud, they show that gravity effects from the galaxy are equally important. The results are reported in a recent article in the journal
Celestial Mechanics and Dynamical Astronomy.
Comment: Have you read Cosmic Turkey Shoot?