Superman's ability to hear in space is often attributed to his superhuman powers, specifically his super-hearing or enhanced auditory senses. In various portrayals, Superman's powers go beyond the capabilities of a regular human and allow him to hear sounds from great distances, even in the vacuum of space.
While sound indeed does not travel through the vacuum of space due to the absence of a medium to carry sound waves, comic book writers and creators often take creative liberties with the laws of physics to make superheroes like Superman more exciting and versatile.
Superman's super-hearing ability is typically explained as an extension of his enhanced senses, which also include super-vision and other heightened senses. He might be able to pick up on various vibrations or energies, allowing him to perceive sounds and communication in space. Remember, superheroes are fictional characters, and their abilities often transcend the limitations of real-world physics to make their stories more captivating and entertaining.