- 3237 - NEUTRON STAR - first detected merger? When the large star burns all of its fuel it can no longer resist gravity. The immense gravity at the center collapses the individual atoms themselves. The entire enormous star collapses into the center and then rebounds in a giant “supernova” explosion. What is left behind at the core is the collapsed star of neutrons. A Neutron Star is just 10 miles in diameter.
------------------ 3237 - NEUTRON STAR - first detected merger?
- All the 96 elements in the Periodic Table of Elements, which were not synthesized during the big bang are heavy elements, and we call them “metals“. Only Hydrogen and Helium were directly produced in the initial moments of the big bang. All other elements are made in some processes in the atmosphere of planets or the cores of stars.
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- For example, elements like Lithium are produced during interactions of cosmic rays with our atmosphere. “Element” means the nucleus of that element. Because we are talking about highly energetic processes, and at such high energies, the elements get ionized, meaning they lose all their electrons leaving behind the protons in the nucleus.
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- In the periodic table, there are nuclei whose origin we know. Like, Li, Be, B, C, N, O, up to Fe, Co, and Ni. All of them are a product of some nuclear process in a planet or a star.
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- The heaviest ones, Iron, Nickel, etc., are created during the violent deaths of stars, “supernovae“. Above that, we do not have observational proof about how nuclei heavier than Iron are created. Until now, we thought that they might be a product of supernovae, too, because the formation process is similar.
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- To understand how these processes for the heaviest elements occur, we need to understand a little bit of Nuclear Physics. We know that the nucleus is made up of two particles, protons and neutrons. Protons, being positively charged, neutrons being neutral. We know that two positively charged particles would repel each other.
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- To make stable or semi-stable nuclei, we need something more inside the nucleus to hold it together against the repulsive force. As we go from lighter nuclei towards heavier ones, the number of neutrons become much larger than protons.
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- From theory and experiments on radioactivity if a nucleus is bombarded with neutrons, it will absorb a neutron and eventually decay in such a way that it becomes stable. To gain stability a neutron in the nucleus splits into a proton and an electron (called beta radiation), hence maintaining the charge neutrality, and also emitting a neutrino.
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- In this process, we created an element whose proton number increased by 1 due to a neutron splitting into a proton and an electron. This way, we made a higher atomic numbered nucleus. The actual process is significantly more complicated. To synthesize much heavier nuclei, we need to imagine this process on a dramatically larger scale. We need to have access to an enormous amount of neutrons in an extreme environment.
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- Neutron Stars are extremely dense, super-heavy, small objects, which are just remains of dead stars. These objects can be about 10 miles in diameter yet have masses up to 1.5 times the mass of our Sun.
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- The gravitational force in this dead star is so overwhelming that it collapsed into a state where the atoms’ electrons are captured by the nuclei and fused with the protons to make neutrons.
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- The star is mostly made of neutrons. But, it is a dead star. How can it make heavy nuclei? It is already dead! Nuclear fusion is no longer going on. Right?
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- It turns out that when we set our telescopes onto the night sky and see it, we observe that a vast majority of stars exist in pairs. Is it possible that there might be a pair of neutron stars?
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- In 2015, a pair was detected with the gravitational waves coming from a merger of the binary blackhole pair.
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- Because neutron stars are only about 10 miles in diameter they hardly emit any visible radiation. How do you see something which does not emit light but is immensely heavy?
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- We use gravitational wave detection! We detect gravitational waves coming from a binary neutron star merger. Once we detect this, we point all the telescopes available to us towards the gravitational wave signal’s direction.
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- Theory suggests that there will be a lot of heavy nuclear production, and in that process, there will also be a lot of nuclear radiation! Hence electromagnetic radiation should be abundant to actually “see” the event!
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- On August 17, 2017 one such gravitational wave signal is detected in LIGO detectors from merging neutron star. All the telescopes on earth as well as in space were pointed towards the direction of the signal calculated from the signals in the LIGO and VIRGO detectors. We have visual confirmation of light coming from the “Neutron Star merger“!
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- Multiple electromagnetic spectra were taken in all available frequency bands, and it was confirmed that the heavy elements were indeed produced there! Just to put this into perspective, a rough estimate suggests that Gold was one of the products in this nucleosynthesis, and the amount of Gold produced was equal to 5 to 6 times the entire mass of the Earth!
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- This is the first time we saw an electromagnetic signal along with a gravitational wave signal. This was experimental confirmation that heavy elements are produced in “neutron star - neutron star” mergers.
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- The only process which produces elements like Gold, Platinum, Uranium, and so on is binary neutron star mergers. We have all of these elements on Earth. This implies that we may be the product of one such process, and we owe our existence to it!
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- We have developed special telescopes to observe these optical signals and study them in much more depth. These three telescopes, the BlackGEM array of telescopes, in Chile, in South America, detected these optical light signals coming from colliding Neutron Stars. Amazing science in action.
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- July 28, 2021 NEUTRON STAR - first detected merger? 3237
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--------------------- --- Thursday, July 29, 2021 ---------------------------
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