The jet appeared to be moving at seven times the speed of light, according to Hubble’s measurements. Radio observations later revealed that the jet had decelerated to speeds four times faster than light. This, however, is a “cosmic illusion,” because nothing travels faster than light.

A collision between two neutron stars propelled a jet through space at 99.97% the speed of light. This is according to Hubble Space Telescope measurements from NASA. The explosive event, designated GW170817, occurred in August 2017. The blast was estimated to have the same energy as a supernova explosion.

The first gravitational wave and gamma-ray signals were detected simultaneously as a result of the binary neutron star merger. These extraordinary collisions were a watershed moment in the investigation. Seventy observatories on Earth and in space observed the aftermath of this merger. They discovered gravitational waves as well as a wide range of electromagnetic radiation. This event occurred in 2017.

A historical remark

This was a monumental achievement in time domain and multi-messenger astrophysics. The study of the universe as it evolves over time through the use of various “messengers” such as light and gravitational waves. Within two days of the explosion, scientists directed Hubble’s attention to the site. When neutron stars collided, they created a black hole whose gravity drew matter toward it. Jets emerged from a rapidly spinning disc from those poles. The roaring jet smashed into the expanding debris cloud and swept it up during the explosion. Finally, an emergent jet appeared through a material blob.

Scientists have spent years analyzing Hubble data and data from other telescopes to create this complete image. For very long baseline interferometry, Hubble observations were combined with observations from multiple National Science Foundation radio telescopes (VLBI). Data was gathered 75 and 230 days after the explosion.

“I’m astounded that Hubble could provide us with such a precise measurement, which rivals the precision achieved by powerful radio VLBI telescopes scattered around the world,” said Kunal P. Mooley of Caltech in Pasadena, California. He is the lead author of a paper that will be published in Nature magazine on October 13th.

Extensive precision

Furthermore, to achieve extreme precision, the authors combined Hubble data with data from the Gaia satellite and VLBI. According to Jay Anderson of the Space Telescope Science Institute in Baltimore, Maryland, this measurement was made after months of careful data analysis. Their collective observations assisted them in locating the explosion site. The jet appeared to be moving at seven times the speed of light, according to Hubble’s measurements. Radio observations later revealed that the jet had decelerated to speeds four times faster than light.

This “superluminal” movement is an illusion because nothing can move faster than light. Because the jet is approaching Earth at nearly the speed of light, the light it emits later will travel a shorter distance. The jet essentially chases its own light. As a result, the light from the jet was emitted much later than the observer expected. As a result, the object’s speed is overestimated and exceeds the speed of light.

At the time of launch, the jet was travelling at 99.97% of the speed of light, according to Wenbin Lu of the University of California, Berkeley. A 2018 announcement of a combination of Hubble and VLBI measurements supports the theory that neutron star mergers are related to short-duration gamma-ray bursts. This connection requires an emerging fast-moving jet, as measured in GW170817.

Hubble’s constant

Furthermore, this research enables more in-depth studies of neutron star mergers detected by the gravitational wave observatories LIGO, Virgo, and KAGRA. Over the next few years, a large enough sample of relativistic jets may provide another method for measuring the Hubble constant. This constant represents an estimate of the rate of expansion of the universe.

The Hubble constant values for the early universe and the nearby universe differ. This is one of astrophysics’ greatest mysteries. Differences in values are based on extremely precise measurements of Type Ia supernovae by Hubble and other observatories, as well as measurements of the Cosmic Microwave Background by the Planck satellite. A better understanding of relativistic jets could help astronomers solve the puzzle.