How did this collision between neutron stars impact the history of astronomy? – The clear people



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

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Neutron stars are the result of massive stars collapsing as they complete their nuclear fusion cycles. For a “dead” star to become a neutron star, it must have between and 29 solar masses. If this requirement is met, the result of the collapse will be one of the densest objects known – with 10 km in diameter, kilometers, they can be double the mass of the Sun. And sometimes they collide, shaking the structures of space-time.

Like it or not, Einstein was right again

Illustration of a collision between two neutron stars (Image: Play / NASA / Swift / Dana Berry)

When very massive objects (like 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 2017.

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

It was thanks to gravitational waves that scientists detected the kilonova in

, and it is also with them that they recreated the “sound” of the collision. The event was called GW9795 and not only provided further confirmation of Einstein’s theories, but also demonstrated that the 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 emit x-rays for much longer than current models predicted. Scientists have been following the event since detecting gravitational waves, baffled by this unexpected behavior.

On the other hand, gamma rays played an important role in making this kilonova important for Einstein’s ideas. Indeed, the radiation was discovered, thanks to an automatic alert of the Fermi telescope, only 14 seconds after the detection of the gravitational waves. This would only be possible if the two signals – gravitational waves and electromagnetic waves – were traveling at practically the same speed.

When scientists finished analyzing these detections, concluding that the difference of just 14 seconds confirms general relativity, several other ideas that attempt to change Einstein’s theory could be ruled out. These proposals to change the currently accepted gravitational theory often come as theoretical physicists seek a way to reconcile physics with quantum mechanics. It was not this time that they found a loophole for it.

Spread precious metals in the cosmos


Elements marked in dark orange are formed by the collision of neutron stars (Image: Reproduction / Jennifer Johnson / ESA / NASA / AASNOVA)

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

If you are wondering how many pounds or tons the kilonova detected in 2017 produced, here is the answer: On its own, it formed over 100 Earths of solid and pure precious metals. This confirms the pattern of evolution of stars and the elements they generate at each of their stages.

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

Gravitational waves, in artistic design (Image: Reproduction / ESA / C. Carreau)

For all these reasons, the kilonova of 2017 was so important to the scientific community, carrying many telescopes, antennas and space observatories pointing to the GW9795 event. About a third of the entire community around the planet participated in the effort which resulted in more than 68 articles on the subject published in just the first two months.

In total, 70 observatories, on 7 continents and in space, observed the event through the electromagnetic spectrum. The discovery and subsequent observations won the Breakthrough of the Year award in 2017 from Science magazine.

Source:, AAAS

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