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SN1987A - One of The Mysterious Supernova

                    The main driving force of every star in the universe is the atomic fusion reaction. In this reaction, two atoms of the same element combine with each other to form atoms of other element of completely different properties. With this, some amount of energy is released. In the case of a star, billions of atoms move in one place under the influence of a gravitational force, and this process begins in the inner centre of the clump of atoms under increasing pressure, and once this process begins, this effect also occurs in the surrounding atoms in chain system and releases energy. This reaction is initiated by the transformation of hydrogen atoms into helium atoms. Subsequently, these atoms combine to form carbon, neon, oxygen, silicon, and finally iron. There is also a huge amount of energy released, in the form of heat and light, from the large number of atoms that participate in this fusion process. But when the star runs out of fuel and the atomic fusion reaction stops, the balance between the two opposite forces inside the star is affected. As a result, the core of the star is collapsed and star has blown up into a massive explosion with massive amounts of heat and light, which we identify as Supernovae. This supernova is an inevitable phenomenon of every star. Today we will try to know such a supernova, visible from the earth.

                    The time was the 24th day of February 1987. Ian Shelton and Oscar Duhalde, two astronauts from the Las Campanas Observatory in the Atacama Desert in Chile, the southernmost country in South America, discovered a supernova in space. Within 24 hours of this discovery, Albert Jones, a typical employee of an oat mill and car factory in Christchurch, New Zealand, and owner of a grocery store, discovered the same supernova. It should be noted here that Albert Jones is an amateur astronomer. This supernova was the brightest supernova ever seen with the naked eye since 1604. Since this supernova was the first supernova to be discovered in 1987, it was SN1987A. From a distance, this supernova is located in a tiny galaxy called the Large Magellanic Cloud, approximately 51.4 kilo parsec or 1,68,000 light-years from Earth. (Links to details about large Magellanic cloud is provided: https://spacejagat.blogspot.com/2021/06/large-magellanic-cloud-one-of-our.html)

                    Shortly after the discovery of this supernova, Astron, the largest telescope with the most powerful ultraviolet rays of the time, began to observe it. After some more observations, it became clear that the original star of the supernova was a blue supergiant star, named Sanduleak-69.202. In the month of May of that year, the brightness of the supernova reached its peak. Later, as its brightness diminished a little, the blue super giant star was more clearly identified. This phenomenon was somewhat unexpected at the time the discovery was made because the then-evolutionary models of the star did not detect the possibility of a supernova emerging from a blue supergiant star. Subsequent revisions to the related models, added more importance to the presence of matter inside the star with the evolution of the star.

                     Several hours before light from a supernova reaches Earth, neutrinos explode in a specific part of the sky and it was detected by three earth observatories (Neutrino: The tiny, almost mass less particle that travels in almost the same velocity with light). It is possible that the emission of neutrinos and the collapse of the core of the star occurred simultaneously, but certainly before the emission of visible light. After the core of the star has collapsed, the shock wave reaches the surface of the star, and then the visible light from the star's surface suddenly emits very strongly (Shock wave: A wave that occurs when there is a drastic change of pressure between an elastic object such as air, water, or a star) This is the first time in the history of astronomy that the emission of neutrinos from a supernova was directly observed which initiated Neutrino-Astronomy. The supernova-related models here have previously indicated that most of the energy emitted from a star's core after it collapses is emitted in the form of neutrinos. Observations showed that 1058 neutrinos were released for the release of 1046 Joule of total energy, meaning that each neutrino released dozens of mega-electron volt of energy.

                    By observing these supernova, scientists have speculated that the star, from which this supernova origins, may turn into a neutron star due to its size and volume. (Neutron star: A very dense, highly dynamic, and electromagnetic wave-generating cosmic object rich in neutron particles after a supernova explosion when a super massive star runs out of fuel) Since then, scientists have been using sophisticated instruments, such as the Hubble Space Telescope, to find that neutron star, but so far they have not been able to do so. Scientists have cited a number of reasons for this failure. For example, the neutron star may not have been visible yet due to its thick dust cover, or the pulsar of the neutron star may have been formed, but we do not fully understand it because of its abnormalities. Some have suggested that some more mass may have been added to the neutron star and converted it into a black hole, or that the neutron star may have turned into a quark star (Quark star: An intermediate phase when neutron star turns into a black hole) It is also said that if the core of a neutron star is composed of dense matter and the mass is not attached to it from the outside, then the brightness of the neutron star is very dim. This is probably the reason why we cannot identify the neutron star. There are many possibilities, but scientists are still trying to figure out the exact reason behind this mystery.

                    It is thought that before the supernova was formed, its progenitor star collided with its companion star, and the two stars merged, but their core was probably separated. There is a constant flow of radioactive radiation from the core of these two stars. This radioactivity is the cause of the brightness and warmth of this supernova. The main source of energy is the continuous decay of the radioactive isotope of the element at its two cores (Isotope: When the number of protons in the centre of multiple atoms of the same element is same but the number of neutrons is different than the state of those atoms is called isotope. When the ratio of protons and neutrons in the nucleus of an atom exceeds 1:1.5, the atom becomes unstable and reveals the nature of radioactivity.) In this supernova, the decay of 56Co or Cobalt-56 is complete, so the intensity of its radioactivity has decreased a bit at present. But now the main driving force of this supernova is 44Ti or Titanium-44 which is a radioactive isotope of Titanium. In 2021, in addition to intense radioactive radiation, the effects of X-ray radiation from supernovae have also been found. From this, it can be said that there is definitely a neutron star in that region of universe. This theory supports the Magnetohydrodynamic model.

                    A few months after the discovery of this supernova, observations through the Hubble Telescope have revealed that there were three rings surrounding this supernova which is actually an ionized particle produced by the effect of ultraviolet rays emitted from a star after it has become a supernova. It is also called Stellar air. These rings are so clear that they can be observed by a spectroscopy. Observations in 2001 showed that matter emitted from the core of the star collided with the supernova's ring at a speed of 7,000 km per hour, causing the region's temperature to rise and X-ray emissions at high rate. For this reason, the intensity of X-ray emissions in the SN1987A supernova increased drastically between 2001 and 2009. Observations by Hubble and other telescopes from 1994 to 2014 led to the conclusion in 2015 that the emission of matter from the rings is decreasing due to the shock wave and it is estimated that between 2020 and 2030 it will further decrease which will lead the rings to fade. At present the speed of this shock wave is between 2,300 km to 3,600 km per hour. It is hoped that by the time this shock wave is over, more information will be available about that blue super massive star.

Long before the discovery of this supernova, the astronomical model pointed an area in universe and assumed a neutron star, covered by dust, might be present. In fact, the supernova SN1987A was discovered at that same place. After this prediction came true, three scientific groups of the world started observing and researching on this. Within a month of the discovery of the supernova, the European Southern Observatory, one of the three groups, found infrared rays in that region. However, despite the different opinions of scientists at different times about the origin of this ray, no one could say for sure.

                    Previously it was thought that dust, originated from the central part of the supernova, might be the source of the dust obtained in a galaxy. But the results of extensive research were not at all consistent with the previous concept. So the mystery about the source of the dust in the galaxy has not been solved even today. In addition to the warm dust, obtained from the SN 987A supernova, the existence of cold dust has also been reported. The Atacama Large Millimeter Array Telescope has found cold carbon monoxide, silicon monoxide, etc. in the supernova region, suggesting that at one time all of these elements must have been inside the star. The Hubble Telescope, the Chandra X-Ray Observatory, and the NuSTAR X-Ray Telescope are also trying to find new information by observing that supernova.

                    Among the various cosmic objects in the universe, this SN 1987A is a normal object. There is nothing unusual about this, but the importance of this supernova in the history of human space research is immense. This is the first supernova that modern scientists have studied in detail. This is the first opportunity to observe a radioactive source with the emission of a light from supernova. So it can be said that the evolution of stars, the transition of galaxies and the era of space exploration by human have all been marked by this type-II SN1987A supernova. This supernova has played and continues to play an important role in advancing our space research in a commendable height. There is no doubt about it and it goes without saying.

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