Final answer:
A rapidly spinning ball of neutrons that forms from the collapse of a supernova is known as a neutron star. Neutron stars spin quickly due to the conservation of angular momentum, and when they emit regular radiation pulses, they are referred to as pulsars or millisecond pulsars. Kilonovas are energetic explosions from neutron star collisions.
Step-by-step explanation:
The stellar remnant that involves a rapidly spinning ball of neutrons is called a neutron star. These dense remnants result from the collapse of a supernova, conserving their angular momentum and therefore spinning at very high speeds. Because of their reduced size, typically about 10 to 20 kilometers in diameter, they can complete one full rotation in just a fraction of a second. This principle, known as the conservation of angular momentum, explains why these stars can spin much faster than their progenitors. Specific neutron stars that are observed to emit regular pulses of radiation, named pulsars, are found to spin even more rapidly, possibly due to acquiring additional mass from a companion star, making them millisecond pulsars.
Collisions between neutron stars can result in even more spectacular phenomena, such as kilonovas, which release massive amounts of energy and heavy elements into space. The Vela Supernova Remnant is an example of a neutron star's birthplace, visible in the night sky with rounded filaments and a sphere of X-ray radiation emanating from the site of the original explosion.