A jet of charged particles moving at nearly the speed of light smashed its way out of debris left behind in the aftermath of the neutron-star merger that produced the gravitational waves detected by the LIGO–Virgo collaboration on 17 August 2017.
The event, catalogued as GW170817, has been a Rosetta Stone for astronomers because it allowed them for to observe the same event using gravitational waves and electromagnetic radiation ranging from a gamma ray burst (GRB) to a radio afterglow. This was a first for the new and exciting field of multimessenger astronomy.
The collision of two neutron stars is called a kilonova and is thought to produce either a black hole or a ‘hypermassive’ neutron star. Some of the neutron-rich debris forms a shell, or cocoon, around the black hole or neutron star. The rest spirals onto the remnant object, producing a jet of charged particles that blasts out into space at nearly the speed of light.
As the jet slams into the cocoon, it causes it to glow, a phenomenon that astronomers call the afterglow. However, it had been unclear whether the jet is able to penetrate through the cocoon and emerge on the other side.