- 3500 - PHYSICS - periodic table for astronomers? Scientists have created the Periodic Table for astronomers? How is it different? Do you remember about learning the periodic table in high school? Remember memorizing all the elements according to their atomic numbers, properties, and classifications as metals, non-metals, just to pass the chemistry test.
--------------------- 3500 - PHYSICS - periodic table for astronomers?
- Here is what the periodic table looks like for astronomers: All the 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 later made in some processes in the atmosphere of planets or the cores of stars.
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- Elements like Lithium are produced during interactions of cosmic rays with our atmosphere. These highly energetic processes and at such high energies, the elements get ionized, meaning they lose all their electrons. So it is the nuclei of the atoms we sre referring to.
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- In the periodic table, there are nuclei 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. The heaviest ones, Iron, Nickel, etc., are created during the violent deaths of stars, called supernovae.
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- 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 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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- So, to make stable or semi-stable nuclei, beyond one point, we need something more inside the nucleus to hold it together against the repulsive force. When we go from lighter nuclei towards heavier ones, the number of neutrons become much larger than protons.
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- We know from theory and experiments on radioactivity that if a nucleus is bombarded with neutrons, it will absorb a neutron and eventually decay in such a way that it becomes stable.
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- To gain stability sometimes, a neutron in the nucleus splits into a proton and an electron (this is called “beta radiation“), hence maintaining the charge neutrality, and also emit 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. We made a higher atomic numbered nucleus. This is a very crude way of explaining this process, note that this is a very, very diluted version of what actually happens.
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- 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 20 kilometers in diameter yet have masses up to 150% 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 were captured by the nuclei and fused with the protons to make neutrons, and hence the name: A neutron star.
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- We now know an object which is mostly made of neutrons. It is a dead star. How can it make heavy nuclei? It is already dead! Nuclear fusion is no longer going on. 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.
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- Is it possible that there might be a pair of neutron stars? In 2015, we detected the gravitational waves coming from a merger of a binary blackhole pair. It does not seem impossible to find a pair of neutron stars, and if we can see two of that merge, maybe we will see the birth of such heavy elements by the process described.
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- Neutron stars are only about 20 kilometers in diameter, so they are tiny. They hardly emit any visible radiation. How do you see something which does not emit light but is immensely heavy? The answer is gravitational waves!
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- We try to 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 stars, and Astrophysicists worldwide are alerted about it. Immediately, all the telescopes on Earth as well as in space were pointed towards the direction of the signal and we have visual confirmation of light coming from the neutron stars merger!
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- Multiple 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 astronmers saw an electromagnetic signal along with a gravitational wave signal. We now have access to a completely new window to look at the universe! This was also the experimental confirmation that heavy elements are produced in neutron star mergers.
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- What does this discovery mean to us? So far, the only process which produces elements like Gold, Platinum, Uranium, and so on is binary neutron star merger. 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. We have built these three telescopes, the BlackGEM array of telescopes in Chile, in South America, to detect these optical light signals coming from colliding Neutron Stars.
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- We will soon learn more with these new eyes on the sky.
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March 6, 2022 PHYSICS - periodic table for astronomers? 3494
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