10. New Stars

    • According to the nebular hypothesis, the Sun and planets originated at the same time during the gravitational collapse of a rotating interstellar cloud of gas and dust.

    • The nebular hypothesis does not by itself explain the current slow rotation of the Sun or the division of the major planets into the rocky, dense terrestrial planets close to the Sun and the gaseous, low density, giant planets located in more distant regions from the Sun. Magnetic braking or intense solar winds might have slowed the Sunís rotation. The high temperature and intense activity of the young Sun may explain the differences between the terrestrial and giant planets.

    • Star birth is now occurring in giant molecular clouds.

    • Interstellar clouds of atomic hydrogen are normally in equilibrium, but their collapse can be triggered by intense radiation from a nearby hot and massive star or by the supernova explosion of a nearby star.

    • Rotating proto-planetary disks have been observed around many newborn stars, demonstrating the nebular hypothesis in action around these stars.

    • Hundreds of exoplanets have been discovered orbiting nearby stars. These exoplanets are about as massive as Jupiter but often closer to the star than Mercury is to the Sun. They are known as hot Jupiters.

    • The Kepler mission has discovered exoplanets with about the mass of the Earth orbiting their planet in the habitable zone in which liquid water can be found.

Copyright 2010, Professor Kenneth R. Lang, Tufts University