publish date 2022-03-06 09:33:47
Astronomers may have ‘first’ observed the afterglow of an epic cosmic event known as a kilonova.
Kilonova are defined as massive explosions caused by the collision of neutron stars with each other, sending an intense jet of high-energy particles through space.
It produces a luminous flash of radioactive light that produces large amounts of important elements such as silver, gold, platinum and uranium.
Researchers believe they detected the “afterglow” from the 2017 kilonova event, in the form of X-rays captured by NASA’s Chandra X-ray Observatory. The new study was led by experts at the Northwestern Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) in Evanston, Illinois.
“We have entered uncharted territory here to study the effects of a neutron star merger. We are looking for something new and unusual for the first time. This gives us an opportunity to study and understand new physical processes, which have not been observed before,” said Abragita Hajela of Northwestern, who led the study.
Neutron stars – the collapsed cores of giant stars – have a very small radius (usually 18.6 miles, or 30 km) and very high densities, consisting mostly of compact neutrons. It is among the densest things in the universe.
When the two neutron stars meet, their merger leads to the formation of a more massive neutron star, or black hole, depending on the mass.
A kilonova is basically the explosion from the fusion event, which is 1,000 times brighter than a classic nova.
And in 2017, scientists discovered the merger of two neutron stars in a galaxy called NGC 4993, thanks to a gravitational wave signal called GW170817.
In this case, a narrow off-axis jet of high-energy particles accompanied the GW170817 fusion event.
Now, three and a half years after the merger, the radiation has faded, revealing a new source of mysterious X-rays.
As the main explanation for the new X-ray source, astrophysicists believe the expanding debris from the merger generated a shock – similar to the sonic boom of a hypersonic aircraft.
This shock then heated the surrounding material, emitting X-rays, known as kilonova auroras.
An alternative explanation is that material falling into a black hole – formed as a result of merging neutron stars – is causing the X-rays to appear. Either scenario would be the first of its kind in this field.
To distinguish between the two interpretations, astronomers will continue to observe GW170817 in X-rays and radio waves.
If the afterglow is a kilonova, the X-ray and radio emissions are expected to get brighter over the next few months or years.
But if it comes to matter falling on a newly formed black hole, the X-ray output must either remain constant or decrease rapidly, and no radio emission will be detected over time.
The study was published in The Astrophysical Letters.
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