August 17, 2017 was a historic day for astrophysics: that day, for the first time, the light and gravitational waves caused by the merger of two neutron stars were captured, a collision (or kilonova) that theoretical physics had described 30 years earlier but never observed.
Months later, an international team of researchers analyzed the images of the collision and today Science publishes the details.
The collision occurred in a galaxy 130 million light years from Earth and was recorded by gravitational wave observatories (LIGO and Virgo), which captured unpublished images of the exceptional event, which remains unique.
At the moment of the collision between the two stars, a gamma ray burst was produced and a jet of materials was released that were thrown almost at the speed of light.
In the weeks and months after the collision, scientists saw the burst of light evolve across the entire electromagnetic spectrum, from X and gamma rays to visible light and radio waves, which was interpreted as the “afterglow” of fusion.
Two hypotheses (or models) tried to explain the increase in light: it could come from a bubble originated after the collision, “which was expanding and growing”, or it could be a jet of matter, “a more united, smaller element and that it moves faster in a single direction “, explains to Efe the researcher from the JIVE Institute (Netherlands) and co-author of the study, Benito Marcote.
However, with the images available until then, it was not possible to determine which was the correct model. More resolution was needed to determine the font size.
With this premise, an international team of scientists led by astrophysicist Giancarlo Ghirlanda from the National Institute of Astrophysics (INAF, Italy) observed the glow 207 days after the merger with the help of a network of 33 radio telescopes spread over the five continents.
The images were sent to the JIVE Institute, where they were combined and analyzed using a technique known as Very Long Baseline Interferometry (VLBI), which allows reaching a level of detail so great as to distinguish a person walking on the surface. of the moon.
would allow to measure the size of the object
Such a level of resolution of the images “would allow to measure the size of the object and determine what hypothesis it was, since a bubble should appear as a moderately large object, and a jet should appear as something small and compact”, points out to Efe the Cantabrian astrophysicist.
The data confirmed that the collision (named GW170817) produced a structured jet that expanded almost at the speed of light and was able to pass through the kilonova (ball of materials emitted after the explosion) and spread through interstellar space.