Final answer:
Objects within the ISCO that are perturbed inwards fall into the black hole due to its strong gravitational pull. Matter orbiting in the accretion disk releases energy, primarily as radiation, as it falls into the black hole.
Step-by-step explanation:
The ISCO, or Innermost Stable Circular Orbit, is a concept in astrophysics related to black holes. If an object within the ISCO is perturbed inwards, it cannot remain in a stable orbit and will fall into the black hole. This is due to the strong gravitational pull that dominates within the threshold of the ISCO, not allowing for stable orbits at a smaller radius. Matter spiraling into a black hole often forms an accretion disk, and as it moves inward, the material becomes compressed and heated up to extreme temperatures. Energy is released in the form of radiation, such as X-rays, as the matter falls toward the event horizon. Eventually, matter crossing the event horizon will disappear into the black hole.
In the broader context of conservation of angular momentum, if the moment of inertia of an isolated system such as an accretion disk increases, then its angular velocity must decrease to conserve the total angular momentum, according to the principle of conservation of angular momentum.