The pressures in the relaxation zone behind a shock front for gas-particle flow were measured in the vertical shock tube with a system of injecting and collecting particles.
This interstellar "bullet," traveling over three million miles per hour (5 million km), is just catching up with the shock front, which has been slowed by plowing into interstellar material.
Indeed, Cheng expects that the energy of the shock front at the galactic centre is nearly 100 times greater than that created by a supernova explosion.
