Hua Feng understands that unlike the Sun, the original star of a type Ia supernova is dense and much smaller than the Sun (but still much more massive), so that the dense star needs to expand (and cool) dramatically if it is to become transparent.

Although the world of supernova is very far away from the world that Hua Feng is in at the moment, sometimes any subtle changes that are overlooked may affect the future development and change of the entire galaxy region, perhaps a slow process, or a sudden one that does not give people time to react.

The heat from the explosion is consumed during the expansion of the star, making it impossible to produce photons. In fact, the energy emitted by type Ia supernovae comes entirely from the decay of radioactive isotopes produced in the explosion, which mainly consists of nickel-56 (half-life 6.1 days) and its decay product cobalt-56 (half-life 77 days). The gamma rays radiated from the radioactive decay are absorbed by the ejected substances, which are thus heated to an incandescent state.

In nuclear collapse supernovae, radioactive decay eventually becomes the main source of energy for optical radiation as the ejected material expands and cools. A bright Type Ia supernova can release 0.5 to 1 solar mass of nickel-56, but a nuclear collapse supernova typically releases only about 0.1 times the mass of the Sun.

Supernovae are a key source for the generation of elements heavier than oxygen. Of these elements, iron-56 and lighter elements come from nuclear fusion, while heavier than iron comes from nuclear synthesis that occurs during supernova explosions. Despite the controversy, supernova is indeed the most likely to proceed

- candidate sites for the process,

- The process is a rapid form of nucleosynthesis that takes place at high temperatures as well as at high high molecular densities. A large number of highly unstable nuclei are produced in the reaction, and these nuclei all contain a surplus number of neutrons. These states are unstable and undergo rapid β decay to reach a more stable state.

- The process may occur in the explosion of a type II supernova, in which about half of the abundant elements heavier than iron are produced, including plutonium, uranium, californium, etc. The only other process that can be compared to the heavy element is the S-process that occurs within the aging red giant, but this process proceeds much more slowly and does not produce elements heavier than lead.

The remnants of the supernova N 63A supernova in the Large Magellanic Cloud, which are located in swarms of gas and dust, include a central dense star and material that spreads rapidly outward due to shock waves. The matter swept over the surrounding interstellar matter in a state of rapid expansion, a state that could last up to two centuries.

They then undergo a process of adiabatic expansion, which will then take another 10,000 years or so to gradually cool and mix with the surrounding interstellar matter.

According to standard theories in astronomy, the Big Bang produced hydrogen and helium, and possibly a small amount of lithium, while all other elements were synthesized in stars and supernovae. A supernova explosion fills the interstellar matter around it with metal (for astronomers, metal is all elements heavier than helium, unlike what is known in chemistry).

These synthesized metals enrich the elemental composition of the molecular clouds that form stars, so that each generation of stars (and planetary systems) has a different composition, ranging from pure hydrogen and helium to metal-filled compositions. Supernovae are the main mechanism of redistribution of the heavier elements generated in the fusion of star nuclei in the universe, and all the components of the different elements have a great impact on the life of a star and the existence of the planets around it.

The kinetic energy of an expanding supernova remnant is able to compress the condensed nearby molecular cloud, which initiates the formation of a star. If the gas cloud is unable to release too much energy, the increased turbulence pressure can also prevent star formation.

In a supernova explosion near the solar system, evidence from the decay products of a radioactive isotope with a short half-life can provide an understanding of the elemental composition of the solar system 4.5 billion years ago, and these evidence even suggests that the formation of the solar system may have been initiated by this supernova explosion. The heavy elements produced by supernovae have passed an astronomical amount of time, and these chemical components have finally made the birth of life on Earth possible.

In addition to the supernova remnants observed in the visible region, the Einstein Observatory, an artificial satellite designed to observe X-rays from space, has discovered many X-ray sources in the sky, and more than 30 of them are X-ray supernova remnants. The appearance of the comet Longqing, the first ancient nova, in 1572 left X-ray remains. Supernova shock waves make the interstellar medium warm for millions of degrees and emit intense X-rays. This is a typical type I supernova.

Using radio telescopes, supernova remnants made of only the raretest gases can be discovered. For example, radio astronomers were the first to discover the supernova remnants of Cassiopeia A, and later discovered its extremely faint counterpart in the optical band.

Supernova explosions are also related to the production of cosmic rays. The speed of particles in the interstellar medium is generally in the range of tens of kilometers per second, but there are some special cases - some particles can move at speeds close to the speed of light, which are cosmic rays. Cosmic rays are made up of some material particles such as electrons, protons, etc., which are completely different from electromagnetic waves in nature. Generally speaking, due to the absorption of cosmic rays by the Earth's atmosphere, it is necessary to go beyond the atmosphere to detect cosmic rays.

If you ascend to an altitude of 50 kilometers in a balloon, you can use the negatives to photograph the traces of cosmic rays. Only a very small number of extremely energetic cosmic rays can reach the Earth's surface. However, when high-energy cosmic rays interact with the Earth's atmosphere, a flash effect is triggered, and secondary cosmic rays are produced at the same time, and it is relatively easy to detect secondary cosmic rays on the Earth's surface.

Experiments have shown that some of the lower energy cosmic rays are affected by solar activity. For example, solar activity has an 11-year cycle, and the observed low-energy cosmic rays vary with this cycle.

In addition, when solar activity increases, the magnetic field around the Earth increases, which weakens the activity of cosmic rays observed on Earth.

Conversely, the maximum value of cosmic ray flow tends to occur at the moment when solar flares and activity are minimal. Observations have also shown that the vast majority of cosmic rays are supernova explosions from the distant depths of the universe.

Because cosmic rays often change direction due to the action of interstellar magnetic fields, it is difficult to determine where their radiation sources are.

However, when cosmic rays interact with the interstellar medium, they emit G-rays, which are electromagnetic waves whose direction of motion is no longer affected by the magnetic field.

NASA has launched artificial satellites that specialize in observing cosmic G-rays. The observations show that there is a good correlation between the distribution of cosmic G-rays and the distribution of the discovered supernovae. This largely supports the idea that cosmic rays come from supernova explosions.

There is also an essential difference between a supernova event and a nova event, that is, a nova explosion occurs only on the surface of the star, while a supernova explosion occurs in the deep layers of the star, so the scale of the supernova explosion is much larger. The material scattered into space during the explosion of supernovae has an important contribution to the formation of new interstellar medium and even new stars, but this material comes from the shell of a dead star.

Supernovae are at the intersection of many different branches of astronomical research. Supernovae, as the final destination of many species of stellar life, can be used to test the current theory of stellar evolution.

The phenomena observed at the moment of the explosion and after the explosion involve a variety of physical mechanisms, such as neutrino and gravitational wave emission, combustion propagation and explosion nucleosynthesis, radioactive decay and the interaction of shock waves with periplanetary matter. The remnants of explosions, such as neutron stars or black holes, and clouds of expanding gas, serve as heating the interstellar medium.

Supernovae play an important role in producing the heavy elements in the universe. The Big Bang produced only hydrogen, helium, and a small amount of lithium. Nuclear fusion in the red giant stage produces a variety of medium-mass elements (heavier than carbon but lighter than iron).

Elements heavier than iron are almost always synthesized when supernova explodes, and they are thrown into interstellar space at great speeds. In addition, supernovae are the main "spokesmen" for the chemical evolution of galaxies. In the evolution of early galaxies, supernovae played an important feedback role. The loss of galaxy material and star formation may be closely related to supernovae.

Because they are very bright, supernovae are also used to determine distances. Combining the distance with the expansion rate of the supernova's parent galaxy can determine the Hubble constant and the age of the universe. In this regard, Type Ia supernovae have proven to be strong distance indicators. Initially, it was assumed by standard candles, and later it was calibrated using parameters such as the shape of the light curve.

As the best distance indicator outside of the Virgo, it has a calibrated peak luminosity dispersion of only 8% and extends to a distance of V> 30,000 km s-1.

The Hubble diagram of the Ia supernova (more precisely, the magnitude-redshift relation) is now the most powerful tool for studying the history of the expansion of the universe: its linear part is used to determine the Hubble constant, and the curved part is used to study the evolution of expansion, such as acceleration, and even the different material and energy components that make up the universe.

The nature of Ia supernovae, which can be used as a "standard candle", can also be used to study the nature of its parent galaxy. The light curves of high-redshift Ia supernovae can also be used to test the theory of the expansion of the universe.

It can be expected that the time dilation effect caused by the expansion of the universe will be manifested in the light curve of the high-redshift supernova. The observational data show that the Ia supernova light curve at the redshift z is (1+z) times wider than that at z= 0.

This provides another strong support for the theory of the expanding universe. Certain type II supernovae can also be used to determine distances. The expansion rate of projectiles of type II-P supernovae in the plateau phase correlates with their thermoluminoscopy, which is also used for distance determination.

As a result of these corrections, the dispersion of magnitude -1 in the V-band of the original type II-P supernova can be reduced to a magnitude of -0.3, which provides another means of measuring distances independent of SN Ia.

In addition, the radio emission of type II supernovae also appears to have quantifiable properties, such as the correlation between the 6 cm light curve peak and the time of occurrence of the 6 cm peak after the explosion, which can also be used for distance estimation.