Thursday, September 30, 2021

How has this collision between neutron stars impacted the history of astronomy?

 In October 2017, astronomers announced something historic: the first detection of a collision between two neutron stars.  The only 100-second event created something known as a kilonova, but the impact this record has had on astronomy is perhaps not yet fully understood.

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 Neutron stars are the result of the collapse of massive stars when they end their nuclear fusion cycles.  For a "dead" star to become a neutron star, it must have between 10 and 29 solar masses.  If this requirement is met, the result of the collapse will be one of the densest objects known — 10 km in diameter, kilometers, they can be twice the mass of the Sun. space-time structures.

 Like it or not, Einstein was right again

 When very massive objects (such as neutron stars or even black holes) collide with each other, they leave a mark known as gravitational waves, a phenomenon predicted by Einstein's General Relativity and first detected in 2016.

 These waves in space are similar to ripples in air generated by the impact of a hammer on a surface, creating what we call "sound".  We cannot hear gravitational waves, but we can detect them through instruments like LIGO and Virgo.

 It was through gravitational waves that scientists detected the kilonova in 2017, and it was also with them that they recreated the "sound" of the collision.  The event was designated GW170817 and not only provided further confirmation of Einstein's theories, but also demonstrated that theoretical predictions about the role of neutron stars in the universe were correct.

 However, there were also mysteries to be solved, such as the mysterious emission of gamma rays.  The collision continued to radiate X-rays for much longer than current models predicted.  Scientists have followed the event since the detection of gravitational waves, confused by this unexpected behavior.

 On the other hand, gamma rays played an important role in making this kilonova important to Einstein's ideas.  That's because the radiation was discovered, through an automatic alert from the Fermi telescope, just 14 seconds after the detection of gravitational waves.  This would only be possible if both signals—gravitational waves and electromagnetic waves—traveled at virtually the same speed.

 When scientists finished analyzing these detections, concluding that the difference of just 14 seconds confirms General Relativity, several other ideas that try to modify Einstein's theory could be eliminated.  These proposals to change the currently accepted gravitational theory often arise as theoretical physicists are looking for a way to reconcile physics with quantum mechanics.  It wasn't this time that they found a loophole for that.

 Spreading precious metals in the cosmos

 Another consequence of collisions between neutron stars is the material they scatter across the universe.  As the name suggests, these objects are made of neutrons, one of the two components of atomic nuclei.  When these particles fly and recombine with the energy of kilonovas, new heavy elements are created, including gold, silver and xenon.

 If you're wondering how many kilos or tons the kilonova detected in 2017 produced, here's the answer: alone, it formed more than 100 Earths in solid, pure precious metals.  This confirms the evolution model of stars and the elements they generate in each of their stages.

 In other words, all the gold and silver on our planet was forged many billions of years ago, before the birth of our sun, when two anonymous neutron stars collided.  The material scattered by the kilonova ended up in some dense cloud of gas and dust that began to collapse to form a protostar.  Therefore, all these elements were present in the protoplanetary disk where Earth was born.

 For all these reasons, the 2017 kilonova was so important to the scientific community, prompting countless telescopes, antennas and space observatories to point to the GW170817 event.  About a third of the entire community around the planet participated in the endeavor that resulted in more than 100 articles on the subject published in the first two months alone.

 Altogether, 70 observatories, on 7 continents and in space, observed the event across the electromagnetic spectrum.

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