How long can humans survive if the sun suddenly turns into a neutron star?

? The sun has been burning for 4.5 billion years and will eventually burn out. Modern science believes that the sun can burn for another 6.5 billion years. After 6.5 billion years, the hydrogen in the middle of the sun will burn out and begin to collapse under the influence of gravity. As the temperature rises, the outside of the sun will expand and the sun will enter the red giant phase.

In this process, the sun will lose 30%-40% of its mass, Mercury and Venus will be engulfed by the sun, and the earth is likely to avoid being engulfed by the sun due to its orbit moving outward. But then the earth will no longer be habitable, and all the water will evaporate. Eventually, the sun gradually loses light and its outer layers begin to shrink, cooling into a dense white dwarf. The solar system will also be dark and dead.

? White dwarfs have extremely high density and temperature, but their brightness is very low. This is the final destination of low- to medium-mass stars. There are no fusion reactions or energy production in white dwarfs. After billions of years of cooling, the white dwarf will be so close to absolute zero that no one will remember its past glory. Stars more than ten times more massive than the sun will eventually become neutron stars. Neutron stars are very dense objects between white dwarfs and black holes. Some of them will become pulsars, which emit continuous electromagnetic pulses.

In about a week, the Earth's surface temperature will drop to zero degrees Celsius and ice will begin to form on the Earth's surface. Many plants and animals will die during this period due to low temperatures and bursts of cosmic rays. Humans can only rely on burning fossil fuels to maintain the temperature of their homes. Constrained by factors such as uneven distribution of fossil fuels and high transportation costs, human society is on the verge of collapse and collapse, and has begun to snatch the necessities of life. One year later, the earth's surface temperature will drop to -100 degrees Celsius. From a cosmic perspective, the earth will no longer be a blue planet, but a frozen planet. All large animals and plants have become extinct, and only a few simple organisms survive on geothermal energy. The number of humans will also be reduced to hundreds or even tens of millions. They have moved underground to survive, relying on previously stored fuel and food to survive, and mankind's moral bottom line gradually began to collapse. Finally, when the energy dissipated by the earth and the energy generated by geothermal energy reach a balance, the earth's temperature will stabilize at around -200°C. In this process, the fate of mankind will depend on the level of science and technology. The Earth's surface is no longer hospitable to life. Unless the underground city systems in "The Wandering Earth" are built or immigrated to other planets, humankind will perish and all traces of human civilization will be permanently frozen under thick ice, waiting for exploration by other civilizations.