Final answer:
When gravity increases while mass remains constant, the distance or diameter between the objects decreases, according to Newton's inverse square law of gravitation.
Step-by-step explanation:
According to Newton's law of universal gravitation, if the force of gravity increases while the mass remains unchanged, the distance between the two objects must be decreasing. Since the force of gravity is inversely proportional to the square of the distance between the centers of two objects (the diameter in case of a spherical object), a decrease in distance (or diameter) would result in an increase in the gravitational force. This is due to the inverse square law, which can be seen clearly in celestial bodies; for instance, as a planet's mass increases, its gravity compresses the materials, potentially decreasing its diameter if the added mass significantly enhances the gravitation.