Astronomers Just saw the Most Powerful Gamma-ray Burst Ever Recorded

Artist’s impression of a gamma-ray burst. Credit: ESO/A. Roquette

Gamma-ray bursts (GRBs) are one of the most mysterious transient phenomena facing astronomers today. These incredibly energetic bursts are the most powerful electromagnetic events observed since the Big Bang and can last from a few milliseconds to many hours. Whereas longer bursts are thought to occur during supernovae, when massive stars undergo gravitational collapse and shed their outer layer to become black holes, shorter events have also been recorded when massive binary objects (black holes and neutron stars) merge.

These bursts are characterized by an initial flash of gamma rays and a longer-lived “afterglow” typically emitted in X-ray, ultraviolet, radio, and other longer wavelengths. In the early-morning hours on October 14th, 2022, two independent teams of astronomers using the Gemini South telescope observed the aftermath of a GRB designated GRB221009A. Located 2.4 billion light-years away in the Sagitta constellation, this event was perhaps the closes and most powerful explosion ever recorded and was likely triggered by a supernova that gave birth to a black hole.

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The Expanding Debris Cloud From the Kilonova Tells the Story of What Happens When Neutron Stars Collide

This artist’s conception illustrates the aftermath of a "kilonova," a powerful event that happens when two neutron stars merge. The object is called GW170817 and is the only cosmic event where both gravitational waves and electromagnetic radiation were detected. Image Credit: X-ray: NASA/CXC/Northwestern Univ./A. Hajela et al.; Illustration: NASA/CXC/M.Weiss

When two neutron stars collide, it creates a kilonova. The event causes both gravitational waves and emissions of electromagnetic energy. In 2017 the LIGO-Virgo gravitational-wave observatories detected a merger of two neutron stars about 130 million light-years away in the galaxy NGC 4993. The merger is called GW170817, and it remains the only cosmic event observed in both gravitational waves and electromagnetic radiation.

Astronomers have watched the expanding debris cloud from the kilonova for years. A clearer picture of what happens in the aftermath is emerging.

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