Each of us is stardust

  The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, and the carbon in the things we eat are all composed of thousands of stars in the Big Bang, so we Everyone is stardust.
  - Carl Sagan
  in the universe has been discovered 118 kinds of chemical elements, which constitute the substance we know almost everything – including our own. Although the matter composed of these elements is ever-changing and the source is also different, the basic atoms in these matter have almost the same source-the stars that shine in the night sky.
  Big Bang
  Most modern scientists believe our universe originated in a infinite density and infinitesimal volume point – a singularity. About 13.8 billion years ago, this point suddenly began to expand violently, and in less than one second, various elementary particles that constitute the universe today were formed. Within a few minutes, the temperature dropped rapidly, and some protons and neutrons were combined by nuclear force, forming a helium nucleus, a few lithium nuclei, and hydrogen isotopes (deuterium and tritium), but after that, the elements cannot be The universe came into being at the beginning of its creation. The remaining protons and electrons form the simplest hydrogen atom (there is only 1 proton in the hydrogen nucleus). Among the elements produced during the Big Bang, hydrogen accounts for about 75% of the mass, and helium accounts for about 25%. This proportion has remained basically unchanged until today.
  In the next more than 10 billion years, the universe has experienced the formation of galaxies, and the birth and death of various stars. It is in such bright changes of stars that the rest of the universe was born. An element that is extremely important to us.
  The evolution of stars
  In the hundreds of thousands of years after the Big Bang, the denser areas of the universe gradually contracted together through the action of gravity, forming the most primitive galaxies. There are nebulae of different sizes in these galaxies. They revolve around the center and gradually collapse toward the center, causing the temperature of the core to increase. When the core temperature of the nebula increased to about 10 million degrees Celsius, it triggered hydrogen nuclear fusion and began to spread light and energy outward-a star was born. Hydrogen nuclear fusion is the main source of energy for all stars. The stable and long-lasting hydrogen nuclear fusion created our sun, as well as the light and life on our planet. It has also been used to manufacture the most powerful “weapon of destruction” in human history-hydrogen bomb.
  In stars, the most common form of hydrogen nuclear fusion reaction is the proton-proton chain reaction. The four protons (hydrogen nuclei) fuse into helium nuclei through this reaction. For 90% of the star’s life, it is undergoing such a reaction until the hydrogen fuel in its core is exhausted. However, in fact, only 1% of the total mass of a star will fuse into helium in its lifetime (this also shows that 25% of the helium content in the current universe cannot come from stars, but from the Big Bang).
  In the young age when the star undergoes hydrogen nuclear fusion, the external radiation produced by fusion opposes the gravitational force of the star itself, so that the star will not further collapse due to the gravitational force. However, after the core’s hydrogen fuel is exhausted, the core’s energy can no longer resist gravity, so the outer layer of the star collapses toward the center, and the temperature continues to rise. Subsequently, the hydrogen in the outer layer of the star is also ignited for fusion, which makes the outer layer of the star produce huge energy and expand rapidly, becoming a red giant star. The radius of a red giant can reach hundreds of times the original radius of the star-when the sun becomes a red giant, its radius can be large enough to swallow the earth! After the hydrogen in the outer layer of the red giant starts to fuse, the helium in the inner core will continue to collapse for a period of time, until the temperature reaches about 100 million ℃, the fusion of helium will ignite.
  For a star as big as the sun, after the helium has burned out, the core no longer has enough temperature for the next step of fusion. At this time, the hydrogen in the outer layer of the star is thrown into the interstellar space after several collapses and expansions, forming a planetary nebula, and the inner core will form a dense white dwarf.
  However, for a more massive star, the core fusion will continue until the final product of nuclear fusion-iron is formed. Why is it iron? This involves the specific binding energy of the nucleus. Einstein’s mass-energy equation tells us that mass can be transformed into huge energy. During the formation of the nucleus, protons and neutrons lose part of their mass, and the energy converted from these masses is combined together. This energy that combines protons and neutrons is called binding energy, and the value of binding energy divided by the total number of protons and neutrons is called specific binding energy. The specific binding energy reflects the binding force of protons and neutrons in different nuclei. The greater the specific binding energy, the greater the binding force they receive, and the more stable the nucleus. In the process of nuclear fusion, the atomic nucleus continuously loses mass and releases energy, and the specific binding energy continues to rise. However, when iron is formed, the specific binding energy also reaches the maximum-the fusion of iron and above elements not only releases energy, but also To absorb energy! This is why the nuclear reaction inside the star stops after iron is produced.
  Supernovae and neutron stars merge
  since nuclear fusion can only produce iron, then, after the element iron is how did this happen? In fact, most of them come from the brightest light in the universe-supernova explosions.
  When the massive star reaches the end of its life, the iron in the core can no longer undergo nuclear fusion reactions, and the entire star begins to collapse violently. In the process of collapse, the core releases a lot of energy, exploding the unstable outer shell, and generating huge energy-the brightness of the supernova when it bursts can even exceed the total brightness of the galaxy in which it is located! During this process, the core releases a large number of high-energy neutrons. These extremely high-energy neutrons will combine with the nucleus of the outer shell to form elements with higher atomic numbers. The sparkle of gold and silver we see comes from the tempering of the brightest fireworks in the universe.
  After a supernova explodes, a denser neutron star will form in its core, and a more massive star will even form a black hole that swallows everything. Sometimes, when two neutron stars or black holes approach, they will attract each other until they merge. In the process of merging, they can even release more energy than supernova explosions (it is through the energy released by them that people have observed gravitational waves). At the same time, a large amount of matter will be ejected into the universe, which contains a lot of weight. element. In fact, people have observed that neutron star mergers have produced gold several times the mass of the earth.
  From the stars of our
  universe elements are conceived in the light of the stars, and after millions of years of wandering, the formation of our solar system, the formation of our planet. And in this small and great homeland, it was billions of years of vicissitudes of life that gave birth to a magical life, and we humans were born. It is a rare miracle that such a simple atom and molecule can create a complex creature like ours! I think we are extremely lucky. I think people should look up at the starry sky with gratitude, because the stars are the creator gods of all things and the mothers of each of us. Every atom in our body has spanned countless epochs, and has a destiny that is incomparable, before they are united together, creating a miracle that belongs to us—each of us is stardust.
  Some people say that all encounters in the world are reunions after a long absence. I think, billions of years ago, we might have really met in the stars.