On September 18, Beijing time, according to foreign media reports, when mankind finally detected the collision between two neutron stars in 2017, we finally confirmed the theory that heavier elements than iron were formed in the high-energy flames of these big explosions. And therefore, we believe that this also explains how these heavy elements, including gold, travel throughout the universe. However, the new study raises a question. According to the new chemical evolution model of galaxies, the abundances of heavy elements produced by neutron star collisions are even equal to those observed in today’s Galaxy. < / P > < p > “at the beginning of the universe, neutron star merging did not produce enough heavy elements. And, 14 billion years from now, they still won’t, “said Amanda Karakas, an astrophysicist at Monash University.” the universe is not making these heavy elements fast enough to explain the presence of heavy elements in ancient stars, and in general, there are not enough collisions to explain the abundance of heavy elements in today’s universe. ” < / P > < p > stars are the melting pot of most elements in the universe. In the early universe, when the initial quark soup cooled enough to accumulate material, hydrogen and helium, still the most abundant elements in the universe, were formed. < / P > < p > the first stars are formed when these blocks of matter are brought together by gravity. The core of a star is a fusion furnace. They polymerize hydrogen into helium; they polymerize helium into carbon; and so on, when the lighter elements are depleted, they continue to polymerize heavier elements with heavier elements until iron is formed. Iron itself can polymerize, but the process consumes too much energy – more than the polymerization itself can produce. Therefore, the iron core is the end point. “We can think of a star as a giant pressure cooker that creates new elements,” Karakas said. The reactions that make these elements also provide energy for stars to glow and heat for billions of years. As stars age, the temperature inside them will gradually rise, producing heavier elements < / P > < p > to produce elements heavier than iron (such as gold, silver, thorium and uranium), it is necessary to rely on the fast neutron capture process, also known as the r-process. The r-process may occur in a real high-energy explosion, which produces a series of nuclear reactions in which the nucleus collides with neutrons to synthesize elements heavier than iron. As we have known, the kilonova explosion produced by neutron star collision is a high energy environment which can produce r-process. This is not controversial. However, to produce such multiple elements as we observe, we need to find a minimum frequency of neutron star collisions. < / P > < p > to understand the sources of these elements, the researchers used the latest astrophysical observations and chemical abundances in the Milky way to construct a galactic chemical evolution model for all stable elements, from carbon to uranium, including theoretical nuclear production and event rates. < / P > < p > they list their work in a periodic table that shows the sources of all modeling elements. In addition, they found that from the beginning of the universe to the present, the frequency of neutron star annexation is insufficient. Instead, they think, the possible explanation may be another supernova. < / P > < p > these supernovae are called magnetorotational supernovae, and they occur when the core of a large fast spinning star with a strong magnetic field collapses. These supernova explosions are also thought to have enough energy to produce r-processes. If only a small fraction of the supernova explosions in stars with masses between 25 and 50 Suns are magnetorotational, the results can compensate for this difference. < / P > < p > “even the most optimistic estimate of the frequency of neutron star annexation cannot account for the abundance of these elements in the universe,” Karacas said. Because it seems like a fast spinning supernova with a strong magnetic field is the real source of most of these elements < p > < p > previous studies have also found that a supernova called a “collapse star supernova” can also produce heavy elements, that is, a fast spinning star with a mass of more than 30 suns becomes a supernova before collapsing into a black hole. Such supernova explosions are thought to be more rare than neutron star collisions, but they may also be a factor in the production of heavy elements – and are in good agreement with other findings of the team. < / P > < p > the team found that stars less than eight suns produce carbon, nitrogen, fluorine, and nearly half of all elements heavier than iron. Stars weighing more than eight suns produce most of the oxygen and carbon needed for life, as well as most of the remaining elements between carbon and iron. < / P > < p > “no element other than hydrogen can be produced by only one type of star,” explains astrophysicist Qian Qiu Kobayashi of the University of Hertfordshire, UK. “Half of the carbon comes from dying low mass stars and the other half comes from supernovae. Half of the iron comes from normal supernova explosions of massive stars, while the other half comes from supernovae IA. Ia supernovae are produced in the conjoint system of low mass stars < / P > < p > about 0.3% of gold and platinum on earth can be traced back to the neutron star collision about 4.6 billion years ago. But the new discovery does not necessarily mean that the history of the origin of these gold and platinum will have to be rewritten. And we’ve only been detecting gravitational waves for five years. With the improvement of our equipment and technology, we may discover more frequent neutron star collisions in the future than we observe now. < / P > < p > another strange result is that the researchers’ model produces more silver than is actually observed, while gold is less than actually observed. This shows that the model needs to be adjusted and improved. It may be a matter of calculation, or our understanding of stellar nuclear synthesis is not comprehensive enough. 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