The merger of Binary Neutron Star produces a burst of Gamma Radiations

The merger of Binary Neutron Star produces a burst of Gamma Radiations

Researchers are quite happy about a discovery as they are hopeful that it will help the Astrophysicists to understand the links between Gravitational Waves, Neutron Stars Merger, and Short Gamma-ray Bursts.

The gravitationally collapsed core of a large star is called a ‘Neutron Star’. They are the smallest as well as the densest stars that are known to humanity. The fact that a sugar-cube-sized neutron star weighs billions of tons is the proof of their compactness as the matter is packed very tightly inside them. The merger of binary neutron stars is quite common but a recent study suggested that a Gamma-ray Burst (GRB) accompanied it. Narrow beams of gamma rays constitute these bursts and they are regarded as the most powerful electromagnetic event of the universe. It releases as much energy in a matter of seconds as the Sun will in its entire lifetime and it takes place at a distance of billions of light years from the Earth.

We have two different types of GRBs which differ on the basis of their duration. This is the reason why they are called Short Duration GRB and Long Duration GRB. According to scientists, the shorter GRBs are initiated when two neutron stars merge. This usually gives birth to a new black hole and the time frame of a short GRB is up to 2 seconds. On the other hand, a long GRB occurs when a huge star dies. Its core turns itself into a massive black hole which absorbs anything and everything including light. The duration of this kind of a GRB is several minutes but it may last for a couple of seconds as well.

A collaboration of the American and European scientists told the world about the detection of a gamma-ray flash in November 2017. As it coincided with a blast of gravitational waves, further research was performed in order to extract maximum information about that incident. Davide Lazzati, a Theoretical Astrophysicist at the OSU College of Science, described their findings to the world by saying,

A simultaneous detection of gamma rays and gravitational waves from the same place in the sky was a major milestone in our understanding of the universe. The gamma rays allowed for a precise localization of where the gravitational waves were coming from, and the combined information from gravitational and electromagnetic radiation allows scientists to probe the binary neutron star system that’s responsible in unprecedented ways.”

A new cosmic explosion called ‘Kilonova’ was also observed, in the form of visible light, following the blast of gravitational waves.

An intriguing question which circulated the scientific world before the research of Lazzati was whether the detected electromagnetic waves were a short burst of gamma rays or were it a short gamma-ray burst. It could be interesting for you to know that these two things are different from each other as the first one is much weaker than the latter. He published a paper in summer 2017 which contradicted the common belief of astrophysicists as he claimed that the short gamma-ray bursts can be observed even if they are not directed towards our planet. He said,

X and gamma rays are collimated, like the light of a lighthouse, and can be easily detected only if the beam points toward Earth. Gravitational waves, on the other hand, are almost isotropic and can always be detected.

He elaborated his point by referring to the interaction of the short gamma-ray burst with its surroundings. According to his views, it creates a secondary source of emission called ‘Cocoon’. He mentioned that this emission is undetectable if the beam is pointing towards Earth. However, if the beams of these bursts are moving away from us, Cocoon is very much detectable.

The team of researchers continued to observe the location of these gravitational waves after their discovery in November 2017 and their findings are summed up by Lazzati in the following words:

“It was different from the typical short GRB afterglow. Usually, there’s a short burst, a bright pulse, bright X-ray radiation, then it decays with time. This one had a weak gamma-ray pulse, and the afterglow was faint, brightened very quickly, kept brightening, and then turned off. But that behavior is expected when you’re seeing it from an off-axis observation point, when you’re not staring down the barrel of the jet. This is doing exactly what we expected an off-axis jet would do and is convincing proof that binary neutron star mergers and short gamma-ray bursts are indeed related to each other.”

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