What mechanism causes particles to spiral toward the central star when they reach about one meter in diameter?
Answer
Gas drag within the disk
Once dust particles aggregate to approximately one meter in size, they become highly susceptible to the surrounding environment within the protoplanetary disk. This specific hurdle, known as the meter-size barrier, occurs because the gas component of the disk exerts a frictional drag force on these objects. This drag causes the particles to rapidly lose angular momentum, forcing them into a decaying orbit that spirals them inward toward the nascent star, effectively removing them from the material available for building larger planetary bodies further out.
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