Using NASA’s Hubble Space Telescope, astronomers spotted a jet-propelled by the titanic collision between two neutron stars. The measurements suggest that the jet was traveling through space at speeds greater than 99.97% of the speed of light.
In August 2017, the explosive event known as GW170817 was detected. Similar to a supernova explosion, the blast generated energy. It was the first instance where both gravitational waves and gamma radiation from merging two neutron stars were detected.
This marked a significant milestone in the research into these unusual collisions. In addition to the gravitational wave detection, the aftermath of this merger was collectively observed by 70 observatories in space and throughout the world over a wide range of the electromagnetic spectrum. This marked a significant development in the field of Time Domain and Multi-Messenger Astrophysics, which uses a variety of “messengers” like gravitational waves and light to study the universe’s evolution through time.
Two days later, scientists immediately directed Hubble to the explosion’s site. The neutron stars disintegrated into a black hole, whose strong gravity started to attract matter toward it. The resulting material spun quickly and produced jets that shot forth from its poles. The roaring jet crashed into the expanding shell of explosion debris and swept up junk there. There was a material blob through which a jet came.
Despite the fact that the event took place in 2017, scientists took several years to analyze the Hubble data and data from other telescopes to paint this full picture.
Kunal P. Mooley of Caltech in Pasadena, California, said, “I’m amazed that Hubble could give us such a precise measurement, which rivals the precision achieved by powerful radio VLBI telescopes spread across the globe.”
Jay Anderson of the Space Telescope Science Institute in Baltimore, Maryland, said, “It took months of careful analysis of the data to make this measurement.”
The authors used Hubble data and data from ESA’s (the European Space Agency) Gaia satellite and VLBI to achieve extreme precision. Combining different data allowed scientists to pinpoint the explosion site.
The Hubble measurement showed the jet was moving at an apparent velocity of seven times the speed of light. The radio observations show the jet later decelerated to an apparent speed four times faster than the speed of light.
Because the jet is approaching Earth at nearly the speed of light, the light it emits at a later time has a shorter distance to go. In essence, the jet is chasing its light. In actuality, more time has passed between the jet’s emission of the light than the observer thinks. This causes the object’s velocity to be overestimated – in this case, seemingly exceeding the speed of light.