We know that, when travelling through a medium, particles can move faster than light does. Now, back to those waves travelling faster than light. That black hole is then surrounded by a cloud of accretion material around its equator if it's rotating quickly enough, the fallback of the initially exploded material will result in relativistic jets shooting from the polar regions, blasting through the outer envelope of the progenitor star before producing gamma-ray bursts. Astronomers also think such bursts are produced when a massive, rapidly spinning star collapses into a black hole, violently ejecting material into the surrounding space in a colossal hypernova.

We know from the 2017 observations of colliding neutron stars that these smash-ups can create gamma-ray bursts. They can last from a few milliseconds to several hours, they're extraordinarily bright, and we don't yet have a comprehensive list of what causes them. Gamma-ray bursts are the most energetic explosions in the Universe. But to understand this, we need to back up a little to look at the source of those jets. Therefore, a wave could travel through a gamma-ray burst jet at superluminal speeds without breaking relativity. We know that when light is travelling through a medium (such as gas or plasma), its phase velocity is slightly slower than c - the speed of light in a vacuum, and, as far as we know, the ultimate speed limit of the Universe. Such speeding waves could actually be possible.

If waves within the relativistic jets that produce gamma-ray bursts travel faster than light - at 'superluminal' speeds - one of the effects could be time reversibility. Now, new research suggests a potential answer for what might be causing this time reversibility effect.

Are gamma rays faster than light