Answer to Question 1
In cold, dense molecular clouds, gravity brings material together. As gas moves inwards it converts gravitational potential energy to thermal energy and warms up. Once the cloud becomes so dense that the thermal radiation cannot escape, the temperature rises rapidly and the dense core becomes a protostar. As the cloud has collapsed from a large size to a small size, it must spin very fast to conserve angular momentum. This results in the formation of a protostellar disk around the protostar. Planets may form in this disk as the star continues to grow. Eventually stellar winds and jets clear away the surrounding gas and a newly formed star emerges.
Answer to Question 2
The discovery of extrasolar planets shows, first and foremost, that other planets and planetary systems exist. Indeed, the statistics show that planet formation appears to be rather common. The fact that we find giant Jupiter-like planets very close to the stars demonstrates, however, that planets can move considerable distances from their birthplaces as they interact with the protostellar disk and other planets. The nebular theory of planet formation is therefore being adjusted to allow for planetary migration.
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