First observations of a possible kilonova afterglow

(ORDO NEWS) — For the first time, astronomers have been able to observe what is possibly the afterglow of a kilonova.

A kilonova occurs when two neutron stars—one of the densest objects in the universe—combine with an accompanying explosion about 1,000 times as powerful as a classical nova. In this case, the formation of a narrow off-axis jet of high-energy particles accompanied the flare, which was named GW170817.

Three and a half years after the collision, the jet gradually dissipated, and in its place a mysterious X-ray source was discovered.

Astrophysicists believe that the main explanation for this new X-ray source is the occurrence of a shock wave in a cloud of fragments left at the site of the collision – similar to the sonic boom created by a supersonic aircraft. This shock wave then heats up the surrounding material, generating X-rays known as kilonova afterglow.

An alternative explanation suggests that materials fall into a black hole – which was formed from the merger of two neutron stars – accompanied by the emission of X-rays.

This afterglow was recorded by a team led by Aprajita Hajela of Northwestern University, USA, using NASA‘s Chandra X-ray Space Observatory.

A collision between two neutron holes called GW170817 was recorded on August 17, 2017 and entered the history of astronomy as the first event of its kind, recorded simultaneously using gravitational wave and electromagnetic (or light) signals.

Observing this source for several years, Hazhela’s team noticed that the gradual decrease in X-ray brightness attributed to the jets ceased and a relatively stable radiation flux formed. The constancy of the flux became a clue to astronomers indicating the presence of material afterglow.

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