The phenomenon of seeing something "break through" the sound barrier is not related to the actual breaking of the sound barrier itself. Rather, it is an effect caused by the interaction of an object with the surrounding air as it travels at or near the speed of sound.
When an object, such as an aircraft, approaches the speed of sound (which is approximately 343 meters per second or 1,235 kilometers per hour at sea level), it experiences various aerodynamic effects. As it gets closer to the speed of sound, the air molecules in front of the object start to compress and build up, creating a region of high pressure. This region is often called a shock wave or a sonic boom.
When the shock wave passes over an observer on the ground, they may perceive a loud noise or a sonic boom. The sonic boom is caused by the rapid change in air pressure as the shock wave moves past, creating a sudden and intense sound wave.
While the shock wave itself is not visible, you may observe visual effects coinciding with the passage of an object through the sound barrier. These effects can include condensation clouds or vapor cones. When an object moves at high speeds, the change in pressure and temperature can cause the moisture in the air to condense, forming visible cloud-like structures. These clouds, often seen around the wings or other surfaces of aircraft, are known as vapor cones or shock diamonds.
So, when you see something "break through" the sound barrier, it is not the act of breaking the sound barrier that is visible but rather the visual effects caused by the interaction of the object with the air at high speeds. The actual breaking of the sound barrier itself is an event that occurs without any visible indication.