There is 28 billion sun-like stars in the Milky Way, but ours is really special (at least for us). its severity holds the solar system together and his energy allows life on earth. It influences us in many other ways as well, as it is responsible for the weather and the passing of the seasons, ocean currents, and the beautiful phenomenon of the auroras.
But, like everything in the universe, sooner or later the Sun will cease to exist. What would happen if the sun went out? What if the Sun disappeared right now?
How and when will the sun rise?
Stars like the Sun are made up of very large amounts of gas, especially hydrogen and helium. The very strong pressure that derives from these immense masses produces temperatures so high that the electrons are torn from the atoms and the gases thus ionized take the name of plasma.
Under these conditions it produces nuclear fusion: as its name indicates, in this reaction the nuclei of atoms are fused. Thus, from two cations hydrogen (each made up of a proton) a nucleus is formed helium (containing two protons). This process releases a lot of energy, in the form of light and heat (our Sun has a temperature of 15 million °C, about 6 thousand times that of a light bulb!). By releasing this energy, in a perpetual explosion, a star manages not to be crushed by the weight of the gas that composes it. It is said that not collapses.
Inside stars like the Sun, hydrogen will run out after a few billion years. Once this "fuel" is exhausted, nuclear fusion is no longer able to prevent the collapse of the star, which releases even more heat and light due to the helium compression that is inside it (because the increase in pressure corresponds to an increase in temperature).
However, due to this increase in energy, the star expands until it becomes a red giant, a star up to hundreds of times larger than our Sun and considerably cooler on the surface.
Cold stars?
At this point, the hydrogen on the outer part of the star is also used up. It is a new collapse of the celestial body, unleashing another cycle of nuclear fusion which, however, involves helium, forming nuclei of heavier elements such as carbon (with six protons) and oxygen (with eight protons). The resulting energy is insufficient to counteract the high pressure due to the weight of these elements, so the size of the core is reduced. So we are talking about a White dwarf, a "cold" star with dimensions similar to those of the Earth. Around it leaves the outermost layers, which create a nebula: a very bright cloud of gas and dust that lives for about 10 thousand years.
It is estimated that the sun will go out in about 8.000 billion years: as many as the human beings that inhabit the Earth today. Our planet, along with Mercury and Venus, will probably vaporize much earlier, when the Sun becomes a red giant 5.000 billion years from now. But we won't have to worry about that. Since the Sun expands by 10% every billion years, by then Earth will be so hot that its oceans will have evaporated, along with life on land.
But let's imagine that the Sun just suddenly goes out, like a light bulb. What would happen?
How long would life on Earth last if the sun went out?
If the Sun suddenly stopped emitting light and heat, life on Earth would last much longer than we might expect. But let's see in detail what would happen.
The first weeks without sunlight
If the Sun went out after how long would we realize it? At first, nothing would happen. for a few eight minutes and twenty seconds everything would be normal: in that period of time, the last rays of the sun would reach the earth's surface. Then all of a sudden darkness would fall all over; our satellite, the Moon, would also darken.
Since our Milky Way galaxy is about 1/300th as bright as the Moon, we would basically see only in artificial light. But, due to sun rays delay At great distances, looking at the sky, we would observe other planets of the Solar System as if they were not affected by the problem: for example, Jupiter would continue to be illuminated for approximately half an hour after the disappearance of the Sun.
And what would happen to the temperature?
A few minutes after sunrise, temperatures would drop between 4 and 5 degrees in lighted areas. Meanwhile, strange behaviors would begin to be observed on the part of animals whose life cycles depend on the passing of days: for example, some birds would stop singing. The day and night activities of the fauna would continue quite synchronized with the 24 hours, thanks to the endogenous clocks, which regulate the daily functions of the organisms even independently of the presence of the stars. But many animals need the sun to know where to go, so they would start to move in a disorderly manner.
As soon as the light disappeared, photosynthesis would stop. Almost all of the oxygen synthesis in the atmosphere is derived from this process, but it would take a long time to run out: it would take thousands of years for it to be consumed by living things that depend on it. But most plants, unable to photosynthesize, would die within a few weeks, and the animals that eat them would begin to starve. This would cause many Physiological changes in animals: it would increase energy storage, to the detriment of growth and other functions not strictly related to survival. But not only.
The feeding frenzy
hungry animals behave differently than usual: the priority becomes the search for food, so they neglect activities such as socialization, reproduction and antipredatory behaviors (useful actions to avoid being preyed on) to explore larger territories. Therefore, if the Sun were to go out, the increasing scarcity of plants and the species that feed on them would lead the surviving animals to behave more recklessly and the dynamics between individuals and between different species would also be seen changed.
For example, the hermit crab Dardanus pedunculatus it normally harbors symbiotic anemones that allow it to blend in, protecting it from predation. However, when the crustacean is hungry, it may feed on the anemones. In war and famine, anything goes.
The first year without sunlight
If the Sun were to go out, our planet's average temperature in degrees Kelvin would halve every month: in just four weeks we would go from around 300 K (27 °C) to 150 K (-123 °C). Although the largest plants have enough sugar reserves to survive in the dark for years, the temperatures would cause them to they will freeze in a matter of weeks. Likewise, within the first few months almost all living things would become extinct due to frost.
But not all of our planet's heat depends on the Sun. Radioactive decay causes our planet's core to reach a temperature of 5°C (about twice that of a light bulb); In addition, 20% of the underground heat It comes from the high pressure to which the rocks are subjected. Some of this heat also reaches the Earth's crust, particularly in the geothermal areas, areas where geothermal energy manages to make its way. They are volcanoes, fumaroles, hot springs, hydrothermal springs, and geysers: near these areas, life would last a bit longer.
And we?
To survive, humans would have to create settlements near these areas, and as temperatures drop further, build underground or thermally insulated buildings powered by nuclear power plants. Anyone not in these areas would certainly be dead within a year. Of course, one major problem would remain: how to eat? We could save some vegetables with artificial lighting, but it would be difficult to find solutions to feed many people well and for a long time. Probably, barring exceptional inventions, our species could only survive a few years.
If the sun went out: the first twenty years
Three years after the disappearance of the Sun, the oceans would appear as totally frozen: the water would have solidified kilometers deep. But ice has a lower density than water and is a very good thermal insulator, so these layers of ice would float on top of a layer of water, protected from freezing. This would allow Water stay liquid on our planet for billions of years.
Some underwater organisms, including some deep-sea animals, do not depend on the Sun for survival. Furthermore, the sea bottom it would be warmed by the heat coming from the interior of the Earth: at depth, the ocean has an average temperature of 0-3 °C. However, most of these living things depend on decaying bodies on the surface to survive: with the extinction of other living things that depend on the sun and photosynthetic organisms, these beings would also disappear.
However, underwater ecosystems such as hydrothermal vents, underwater "chimneys" from which geothermally heated water comes out, would be preserved. And so are the chemolithotrophic microbes that inhabit them: capable of converting heat, methane and sulfur into energy, these organisms would survive as if nothing had happened.
Many other microorganisms could continue to live for millions of years even if the sun goes down. There are hundreds of species of extremophile organisms (who live only in extreme conditions) and extremely tolerant organisms (which survive even in such cases). some microorganisms psychrophilic, that is, those who love the cold, live on ice: they could represent the only form of life on the surface for the rest of the existence of planet Earth. They include, for example, some antarctic mushrooms. And then there would be some organisms capable of remaining cryopreserved, suspended waiting to return to live in the heat.
Because on the surface, meanwhile, the air would also get colder and colder. To the point that, ten years after sunrise, the gases that make it up would condense: there would be liquid air and then air snow. After another ten years, the elements that make up the atmosphere would be completely frozen.
What if the sun disappeared?
In addition to the effects observed by the absence of light, in the event that the Sun disappeared completely, there would be those that depend on the absence of gravity. Since gravitational waves travel at the speed of light, again no effects would be observed for the first eight minutes and twenty seconds. After that, our planet would begin to move almost in a straight line, tangent to its orbit, due to inertia.
At that point, it would be a lottery. Like Earth, all objects in the Solar System would begin to travel in a straight line. On its way, at a speed of 30 km per second, our planet would meet thousands of celestial bodies. It could collide with it, decreeing the end of everything, or be attracted by a new gravitational center, like one more star that would act like a Sun. In this case, the small flashes of life that our planet still harbors could give rise to new species. .