KILONOVA


When a star dies it would go into a supernova and depending on its mass its core either collapses into a black hole or a neutron star or a white dwarf. A kilonova is 1000 times brighter than nova (but not much brighter than a supernova). It is usually produced when two massive stellar core collapses. In this case, the core is a neutron star. Neutron stars are small but extremely dense objects. To give a figure of that, 1 teaspoonful of neutron star would weigh 1 billion tons.

Below is a gif that shows what would happen if an object gets too close to a neutron star.


First, it shreds apart the joints and connections of that body and piece by piece rip of the whole body into atoms. It doesn’t end there. Those pieces form a stream of particles and collide onto the surface of the neutron star with a speed which is approximately 100,000 m/s.( More about the neutron star will be discussed later in another blog. )

On 17 August 2017, a galaxy named NGC 4993, 130 light-years away, baffled the scientists. A unique explosion that puzzled them. The one which they have never witnessed. A KILONOVA. 

It was one of a kind. No one has ever observed this kind of event before. A whole new level of talks about what this event might be and what might have caused this event was raised among the scientific community during that time.

Until that moment, LIGO was observing gravitational waves from colliding black holes which are billions of miles away. But this was the first time that scientists were able to witness both the electromagnetic radiation and gravitational waves during a single event. GW170817 was the fifth detection by the LIGO.

Hubble picture of NGC 4993 with inset showing GRB 170817A over 6 days. Credit: NASA and ESA



“There are rare occasions when a scientist has the chance to witness a new era at its beginning,” said Elena Pian, an astronomer with INAF, Italy, and lead author of one of the Nature papers. “This is one such time!”


Taking this opportunity into the hand, 70 observatories from all around the world observed that event. It was also releasing Short GRBs or Gamma-Ray Burst (which was first thought to be “little green man”) which scientists then thought would be only emitted by objects like black holes.

The ripples in spacetime known as gravitational waves are created by moving masses, but only the most intense, created by rapid changes in the speed of very massive objects, can currently be detected. One such event is the merging of neutron stars, the extremely dense, collapsed cores of high-mass stars left behind after supernovae. These mergers have so far been the leading hypothesis to explain short gamma-ray bursts. An explosive event 1000 times brighter than a typical nova — known as a kilonova — is expected to follow this type of event. And this event produced Gamma-Ray Bursts just after 1.7 seconds after the detection of gravitational waves. GRBs are some of the most energetic events observed in the universe. They typically release as much energy in just a few seconds as our Sun will throughout its 10 billion-year life


 Two neutron stars spiraling into a dance of death, each of mass varying from 1.36 to 1.60 solar masses for the bigger one and 1.17 to 1.36 solar masses for the other. They spiraled into each other until they collided in the most violent way sending out gravitational waves, electromagnetic waves all across space which lasted for over 100 seconds before fading along with short GRBs. This phenomenal event and its observation achieved the breakthrough of the year award in the year 2017. This was one of the loudest gravitational wave detection to date.

The merging of two neutron stars produces a violent explosion known as a kilonova. Such an event is expected to expel heavy chemical elements into space. This picture shows some of these elements, along with their atomic numbers.


The gravitational wave signal lasted for approximately 100 seconds starting from a frequency of 24 hertz. It covered approximately 3,000 cycles, increasing in amplitude and frequency to a few hundred hertz in the typical in spiral chirp pattern.


The neutron star merger event is thought to result in a kilonova, characterized by a short gamma-ray burst followed by a longer optical “afterglow” powered by the radioactive decay of heavy r-process nuclei. Kilonovae are candidates for the production of half the chemical elements heavier than iron in the Universe. A total of 16,000 times the mass of the Earth in heavy elements is believed to have formed, including approximately 10 Earth masses just of the two elements gold and platinum. This was a multi-messenger observation.

 The scientific interest in this event was enormous! The scientific papers were released with more than over 4000 astronomy co-authors from more than over 900 institutions. 

THIS WAS ONE HELL OF A COLLISION. THE MOST SPECTACULAR AND VIOLENT ONE, BY THE NEUTRON STARS.

REFERENCES:
1) https://science.howstuffworks.com/kilonovas-are-biggest-baddest-stellar-blasts-in-space.html
2) https://www.eso.org/public/news/eso1733/
3) https://www.space.com/colliding-neutron-stars-caued-massive-kilonova-explosion.html
4) https://www.universetoday.com/103940/whats-a-kilonova-youre-looking-at-it/
5) https://en.wikipedia.org/wiki/GW170817

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