Merging of Two Neutron Stars

When any star with mass above 8 Solar masses experiences Supernova, it ends up as a Neutron Star. Once the neutron star has formed, in another millions of years, the star gradually loses its latent heat and cools down from its initial temperature i.e. 1 million degree Fahrenheit. The star will end up as a cold, dead remnant star of which once was the most densest stellar object in the universe.   

But, the matter remains in Space. When two neutron stars (Binary neutron stars) of the same condition or a different condition meets, a remarkable event occurs. Normally, when a star explodes it will be called a “Supernova“. But, when two dense stars combine, the explosion caused is termed as “Kilonova”. A kilonova is a type of explosion which is even stronger (1000 times brighter) than a typical supernova. Perhaps, this could be one of the most ferocious events that can occur in the universe. When Binary Neutron Stars (BNS) collide they form a Black Hole.   

The below animation shows two neutron stars weighing 1.4 and 1.7 solar masses. When they meet, they start to whirl towards each other. The immense tidal force starts to wrap the crusts of the stars. This causes the smaller star to explode. But, its hot and dense matter then begins to spiral around the system. The larger star starts to collapse when it’s own overwhelming mass begins to merge with the matter and thus resulting in a black hole which will be much more denser than the neutron star where not even light can escape!   

Scientist consider this event to be amazing because after the kilonova, it does not just emit the highly radioactive elements (like Gold, Platinum, Uranium, Selenium, Erbium, Barium, Technetium, Neodymium) in one-fifth speed of the light but, it also emits Short gamma-ray bursts (GRBs). In only 2 seconds, these GRBs could emit the equal amount of energy as the other stars in the entire galaxy could produce in a year! This energy produced could be that immense. Since, these events occur in a blink of an eye, it is quite a challenge observing and detecting them.

Yet for the first time, on 17th August 2017, using LIGO and VIRGO, scientists were able to detect the gravitational waves ripping through the fabric of space-time at frequencies of tens of cycles per second that was caused due to collision of two neutron stars in the Galaxy NGC 4993, 130 million light-years away from Earth. Just two seconds later, ESO detected the Gamma Ray Burst (GRB) in the same region of space.

This event started a new era in astronomy and Gravitational physics for the first time in Earthling’s history. We can now explain the universe by combining light signals with gravitational waves.