Final answer:
The Sun's core would expand and cool down due to increased thermal energy, then contract and heat up due to compression, re-establishing hydrostatic equilibrium without becoming a black hole or a red giant.
Step-by-step explanation:
If the Sun's core were suddenly heated slightly above its current temperature of approximately 15 million K, we would expect a few things to take place based on the principles of star mechanics and hydrostatic equilibrium. The increased temperature would cause the core to expand slightly due to increased pressure from the higher thermal energy. However, this expansion would reduce the core's density and thus the temperature would lower somewhat, resulting in a decrease in the rate of nuclear fusion reactions. The core would then cool down and contract until hydrostatic equilibrium was re-established. As the core contracts, it would heat up due to compression until the fusion rate returns to its original state. This process posits a self-correcting mechanism, where the core would stabilize itself without becoming a black hole or reaching the stage of a red giant.