Why Did the Nebula Start to Collapse?

The dust and gases in a nebula are very spread out, but gravity can slowly begin to pull together clumps of dust and gas. ... Eventually, the clump of dust and gas gets so big that it collapses from its own gravity.

What caused the nebula to collapse and start spinning?

Shock waves from the explosion compressed the cloud of gas and dust. Compression made the cloud collapse, as gravity pulled the gas and dust together, forming a solar nebula. Just like a dancer that spins faster as she pulls in her arms, the cloud began to spin as it collapsed.

What caused the nebula to flatten as it contracted?

HEATING: The temperature of the solar nebula increases as it collapses. As the cloud shrinks, its gravitational potential energy is converted to the kinetic energy of individual gas particles falling inward. ... This flattening is a natural consequence of collisions between particles in a spinning cloud.