Friday, August 10, 2012

*****A journey through our Solar system*****
Part 2 - Birth of our Solar System

The nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. According to this theory it all 4.568 billion years ago when an interstellar cloud of gas and dust, approximately 50,000 AU in diameter, began to collapse gravitationally. Its mass may have been a few thousand solar masses. The cloud fragmented and one area with at least 1.1 to 2.0 solar masses, continued to collapse. Several mechanisms could have initiated such an event.

A shock wave from a supernova may have triggered the formation of the Sun by creating regions of over-density within the cloud, causing these regions to collapse. Because only massive, short-lived stars produce supernovae, the Sun must have formed in a large star-forming region that produced massive stars.

The cloud formed a disk about 60 AU across and about one AU thick. Temperatures rose more rapidly near the center where the density and opacity were greatest. The center of the cloud may have been about 2000 K (3000 °F), while the edge remained cold at about 100 K (-300 °F). Dust vaporized near the center, and atoms became ionized creating a magnetic field which permeated the contracting mass.

Because of the conservation of angular momentum, the nebula spun faster as it collapsed. As the material within the nebula condensed, the atoms within it began to collide with increasing frequency, converting their kinetic energy into heat. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc. Over about 100,000 years, the competing forces of gravity, gas pressure, magnetic fields, and rotation caused the contracting nebula to flatten into a spinning Protoplanetary disc with a diameter of ~200 AU and form a hot, dense protostar (a star in which hydrogen fusion has not yet begun) at the center.

In next part we will explain the evolution of our Solar System. hope you will enjoy.