The initial cloud composition is the key to success

Oct 7, 2009 10:22 GMT  ·  By
The Sun is a "dirty star," and hence it hosts a large number of celestial bodies in orbits around it
   The Sun is a "dirty star," and hence it hosts a large number of celestial bodies in orbits around it

Experts have oftentimes wondered how it is that some stars circle their galaxies all alone, without planets or asteroid around them, while others, like our Sun, are perfectly capable of creating a host of accompanying celestial bodies, ranging from planets and meteors, to moons, comets and asteroid belts. In a new scientific study, published in the latest issue of The Astrophysical Journal Letters, astronomers finally explain this oddity once and for all. Apparently, “dirty stars” are best at keeping a cohort of “followers” around them.

The team behind the new study, led by American Museum of Natural History expert Mordecai-Mark Mac Low, says that the original cosmic dust and gas clouds from which the star appears “decide” whether there will be a solar system or not. When these clouds collapse under their own weight, they ignite and form a new star. If they had a lot of heavy elements in them before the collapse, chances are high that a new solar system will appear alongside the star as well. Conversely, if little to no heavy elements are present, then the star will move through the galaxy alone.

“When you observe stars, the ones with more heavy elements have more planets. In other words, what's in the disk reflects what's in the star. This is a common sense result,” Low explains. For the new study, he collaborated with Anders Johansen, of the Leiden Observatory in the Netherlands, and Andrew Youdin, from the University of Toronto Canadian Institute of Theoretical Astrophysics. The computer simulations were performed on the Huygens cluster, in Amsterdam, and the PIA cluster of the Max Planck Institute for Astronomy, in Germany.

“There is an extremely steep transition from not being able to make planets at all to easily making planets, by increasing the abundance of heavy elements just a little. The probability of having planets almost explodes,” Johansen, who is also the lead author of the new study, adds. “There's an inherent advantage in being born rich, in terms of solid rocks. But less advantaged systems, like our own Solar System, can still make planets if they work to marshal their resources and hang onto their solids as the gas evaporates away. So the Sun is middle-class, rather than rich,” Youdin concludes.

Caption: This clip shows the pebble density as it evolves in the computer simulation. The black regions have no pebbles, blue regions have a moderate density, and bright regions have a high density of pebbles. The square represents a small part of the disk of gas and dust that surrounds the star before the planets form, referred to as the protoplanetary disk, seen from above.

Credits: Anders Johansen / Leiden Observatory