The glow from the explosion resulting from the collision of two neutron stars. Image: NASA/ESA.
In an event known as GRB 200522A, a research team led by Wen-fai Fong, an astrophysicist at Northwestern University in the United States, observed two neutron stars colliding far from Earth. The energy released from the collision illuminated a portion of the sky with a brilliant gamma-ray burst, followed by an extended afterglow in the electromagnetic spectrum. As the faint light gradually dimmed, the research team discovered an unusual infrared signal, the first-ever recorded signal from a newly formed neutron star.
A neutron star is a peculiar type of star with an exceptionally strong magnetic field. While astronomers have detected neutron stars in various locations throughout the universe, witnessing the birth of one has never been possible before. This time, they suspected the birth of a young neutron star due to the unconventional flash of light. Initially, there was an extremely bright and rapid gamma-ray burst, followed by a prolonged afterglow, indicating the collision of neutron stars. This afterglow was much brighter than usual, demonstrating an astronomical phenomenon never witnessed before.
To detect the neutron star collision event, Fong and her team examined both short-duration gamma-ray bursts (GRBs) and long-lasting sources of light resulting from the collision. Under normal circumstances, the remnants of a neutron star collision are divided into two parts: a long-lasting afterglow, which persists for several days due to material ejected from the collision, impacting dust and gas between the stars at high speeds, and a kilonova afterglow, composed of rapidly rotating particles around the collision area.
Based on their models and previous observations, the research team found that GRB 200522A was ten times brighter than any previously recorded kilonova events. They believe that this explosion gave birth to a rapidly spinning, massive neutron star, and its magnetic field acted like a grinder, energizing particles and making them emit more intense light. The research findings were published in the Astrophysical Journal on November 12.
An alternative explanation is the “reverse shock.” Two streams of high-speed particles following the afterglow may collide with each other. Under suitable conditions, such a collision could resemble the birth of a neutron star. Similarly, the decay of radioactive particles in the kilonova explosion could have caused GRB 200522A to shine brighter. However, Fong suggests that both scenarios are highly unlikely.