Final answer:
The correct answer to the riddle is a hole, and while not directly related, black holes in astrophysics metaphorically grow stronger as more mass collapses into them.
Step-by-step explanation:
The answer to the riddle "The more you take away, the bigger this becomes" is a hole. When material is removed from a hole, it grows larger. The other options—debt, vacuum, and shadow—are not correct in the context of this riddle.
If we were to explore the concept of black holes, it would be relevant to mention that they are indeed related to the theme of the riddle in a metaphorical sense. As mass collapses into a smaller and denser region of space, a black hole grows in strength. Black holes are the result of gravitational collapse and have an event horizon that is proportional to their mass. They are fascinating cosmological objects that pull in matter, including light, from which nothing can escape once crossed the event horizon. The existence of black holes remains one of the most remarkable phenomena in astrophysics.