Final answer:
The heating of an interstellar cloud by radiation from embedded young stars is NOT a trigger for star formation, as it causes expansion rather than compression of the gas. Star formation mechanisms include cloud collisions, compression by supernova shock waves, and radiation pressure.
Step-by-step explanation:
The mechanism that is NOT considered to be a way in which star formation is triggered or started is B) heating of an interstellar cloud by radiation from embedded young stars. This process can cause the surrounding gas to expand rather than compress, making it less likely to trigger star formation. Instead, triggers for star formation include:
- A) collisions between interstellar clouds, which can lead to starbursts in the involved galaxies, significantly increasing the rate at which stars are formed.
- C) compression of an interstellar cloud by the shock waves from a supernova explosion, where the energy and material ejected from a dying massive star compress nearby gas, increasing its density and potentially leading to star formation.
- D) compression of an interstellar cloud by the pressure of light from nearby stars, known as radiation pressure, which can contribute to the compression of gas and dust needed to begin the star formation process.
Conversely, star formation is more likely in cold molecular clouds because the lower temperatures allow gas and dust to clump together under gravity without high thermal pressure opposing the process.