In August 2017, astrophysicists observed a powerful explosion called GW170817, the first recorded gravitational wave that resulted from the merger of two neutron stars, releasing energy comparable to that of a supernova explosion.
Just two days later, scientists set up the Hubble Space Telescope to observe the effects of the explosion. The neutron stars collapsed into a black hole whose powerful gravity began to attract matter. This material formed a fast-rotating disc that generated jets coming out of its poles. These jeets encountered an expanding shell of explosive debris and captured particles of material.
By combining the various observations, scientists were able to determine the exact location of the explosion. Hubble's measurements showed that the jet was moving at a visible rate of seven times the speed of light. Radio observation shows that after a while the jet slowed to a seemingly four times the speed of light.
In fact, nothing can exceed the speed of light, scientists explain. "Superlight" traffic is a visual illusion associated with the specifics of observation. Since the jet approaches the Earth at almost the speed of light, the light it emits later requires a shorter distance. This is like a situation in which particles of the matter of the jets catch up with their own light, always releasing new light.
However, the real speed of the jet calculated by scientists is also striking. The particles emitted during the explosion are removed from the black hole at a speed of at least 99.97 per cent of the speed of light.