Shulou(Shulou.com)11/24 Report--

When the universe approaches the maximum entropy, the universe ends in heat death, and its eternal exponential expansion pushes it into effective complete emptiness and absolute cold. In the past, it was thought that the last moment of the thermal death of the universe would be the final explosion of the last black hole when it evaporated. But new calculations show that the last source of astrophysical disasters is a new type of supernova at the end of the universe.

In about 1032, 000 years, the last iron star will be teetering on the brink of disaster. The quantum bizarre high-density sphere supports itself against gravitational collapse by exerting pressure only on its electrons. But its electrons are also slowly disappearing, and when too many electrons disappear, the entire star will collapse catastrophically and then bounce back as a spectacular supernova, the last fireworks to celebrate the end of time.

This calculation update is due to a paper by astrophysicist Matt Kaplan, which I will describe in detail. But first, there are still many questions to know, such as how stars, including our sun, become "iron stars". What happened to their electrons?

In 1930, the scientific community was in the midst of a revolution. The new science of quantum mechanics has broken our classical understanding of the world in many ways. For example, Fowler discovered a new theoretical state of super-dense matter-degenerate matter-in which atoms are stripped of electrons, and then these electrons are squeezed so tightly that all possible quantum states are occupied.

Because they can no longer get close, electrons in degenerate matter exert a strong outward pressure-electronic degeneracy pressure. Fowler's discovery solved one of the great mysteries of the time, and a new type of star was discovered-white dwarfs. These faint but hot stars seem to have such a high density that their one cubic centimeter of material weighs a ton. Fowler realized that they could be made up of degenerate matter, and that degenerate pressure alone was enough to prevent them from collapsing under their own strong gravitational field.

Obviously, this must be the ultimate fate of the sun. Once its nuclear fuel supply is exhausted, there will be no energy flowing out to resist gravitational compression. Its core will collapse until it is stopped by electronic degeneracy pressure. At the same time, the outer layer will be ejected, and its exposed core will become a white dwarf.

The most outstanding physicists of that era began to believe that white dwarfs should be the fate of all stars. In thinking about this, Chandra Seka realized that the best physicists were wrong. He realized that while Fowler's calculations of degenerate plasma states were excellent, they were incomplete, and they did not take into account the influence of Einstein's theory of relativity. At the extreme density of white dwarfs, electrons do move fast enough for relativity to begin to intervene.

Chandra recalculated Fowler's calculations and found something crazy. Although this degenerate pressure can support a death star to some extent, if the residual mass of that star is too high, a new process will take over. In a process called electron capture, the star's own electrons are driven into its nucleus. The reduction of electrons produces less electron degeneracy pressure, which means that stars begin to collapse and more electrons are driven into the nucleus, so the whole process is out of control.

We now know that with a powerful supernova explosion, the end result is either a neutron star or a black hole. But at the time, Chandra only knew that no white dwarf could exist above this mass limit, which is now called the Chandra Seka limit. For the core left by an ordinary star, this limit should be 1.44 times the mass of the sun.

Under the Chandra Seka limit, white dwarfs begin to be hot and bright, but do not have the ability to generate new energy, and they slowly exude the heat of youth. As they cool, the once-glowing plasma changes its state, and it begins to freeze: star crystals. In conventional crystals, atoms or molecules combine to form a lattice by sharing electrons. In white dwarfs, nuclei can never recapture their electrons to become atoms again. Electrons are still hot degenerate plasmas and continue to work to keep the star from collapsing.

At the same time, the nucleus stops interacting with electrons and slows down as they cool. They barely move inside the star and slide into a regular grid. Eventually, all white dwarfs must be cooled to the temperature of the surrounding space. The current space temperature is 3 Kelvin, but with the expansion of the universe and the dissipation of cosmic background radiation, it will be even colder in the future. Eventually, all white dwarfs must fade into almost invisible spheres, which we call black dwarfs.

In the depths of a crystalline black dwarf, a carbon or oxygen core is arranged neatly in its designated columns and rows. All of a sudden, it will find that it has been sent to another location-because of the basic quantum uncertainty of its location. This quantum tunneling effect makes the nucleus close enough to its neighbor that the two merge into a heavier element. This process, called nuclear fusion, converts the core very slowly from carbon to the most stable form of matter, iron, which takes about 10 ^ 1500 years. The end result is an iron star or iron black dwarf, which is the hypothetical fate of all stars whose core is below the Chandrasica limit.

In a paper published by astrophysicist Matt Kaplan, he found a way to get these iron stars to end with brighter results-as black dwarf supernovae. Keep in mind that the Chandra Seka limit gives the maximum possible mass of stellar remnants supported by electronic degenerate pressure. But Kaplan conducted a detailed analysis of the nuclear reaction that led to Iron Star and found that the delicate balance was threatened.

In the final stage of the nuclear fusion process, two silicon nuclei are fused to produce nickel, and then one of the protons of nickel emits positrons into neutrons, resulting in iron 56 Mel, the most stable element in the universe. But the emitted positron is the antimatter counterpart that supports the star's anti-collapse electrons, which immediately annihilates with one of the electrons, exhausting the star's supply. By the time the iron star was fully formed, its Chandesica mass had dropped from about 1.44 to less than 1.16.

This means that if the mass is greater than 1.16 solar masses, white dwarfs (or today's iron black dwarfs) that initially had masses below the original Chandraseca limit may become unstable. When this happens, a catastrophic collapse should lead to a new type of supernova that will only occur in the distant future-black dwarf supernovae, which leave smaller cores or neutron stars. For the largest such stars, the first explosion is expected to begin around 101100, while those at the lower limit will take 1032,000 years to explode, the last moment of the thermal death of the universe.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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