How Old Is Our Sun | What happens when the sun dies?


How old is our sun 

In the case of stars, their longevity is determined by their mass. The more massive the star, the shorter its lifetime, counted in millions of years, before it eventually culminates in a giant cosmic firework, a supernova. 

It would be different for our Sun. Our star is a yellow dwarf whose mass (330,000 times the size of Earth) has a total life expectancy of about 10 billion years. Where we are now The good news for life on Earth: It’s only 4.6 billion years old and, according to astronomical estimates, it should therefore shine for the next five billion years. 


Habitability of the Sun and Earth 

Still, we have to consider moving forward because Earth will be uninhabitable in less than a billion years (regardless of current global warming). Why? Because every billion years the brightness of the sun will increase by about 10%. As such, our soft blue planet is slowly turning into a steamy space, perhaps akin to the hell that currently rules our neighbor Venus. 

How Old Is Our Sun

So the habitable zone in our solar system will shift. So we can imagine that Homo sapiens may have migrated to mild Mars. But if it does, it won’t take long. It may also be necessary to take a route to other stars when the human species has the means to do so. 


What happens when the sun dies?  

Over time, the hydrogen reserves that the Sun accumulated at birth will be depleted. With its relatively low mass, the star has maintained a balance between gravity and radiation (which results from hydrogen fusion) for billions of years. But there will come a “day” when the fuel will run out. 

At the center of the star would be a core of helium (created by hydrogen fusion) that would collapse. The rising temperature releases energy when compressed, which pushes the outer layers of the Sun away. Over the next five million years, the star will grow significantly, which astrophysicists call a red giant. Red because its surface temperature will drop (up to 3,000 K). According to a 2008 study, its range will increase from about 700,000 km today to over 170 million km! In other words: Mercury, Venus and Earth will also be trapped in it, eventually shattering (unless our planet’s orbit is pushed back, depending on the mass the red giant is losing). 

How Old Is Our Sun

When compressed, the helium core heats up and reaches a temperature of 100 million degrees. Under these conditions helium can begin to form carbon. This is the “helium flash”. However, it won’t last long. And it won’t go any further because the rest of the mass of the Sun will not be enough to reach 600 million degrees at the center, the temperature required for the ignition of the carbon nucleus. The hydrogen and helium around would continue to burn for a few thousand years, tearing our star apart and expanding its outer shell. 

Ultimately, gravity will prevail because there is no radiation to counteract it. The rest of our star will shrink and become a white dwarf, an extremely dense and hot (about 30,000 °C) body the size of Earth. During this time, the outer layers, which are far apart, become room-thin. Over a period of about 10,000 years, the shell will glow from the inside out and shine in the light of the still hot central focus. 

The result would be a planetary nebula (the misleading name comes from the round shape observed by William Herschel). Will it be visible from other planetary systems like we can see through our telescopes? The most famous are the M57, the Lear Ring and the M27. Will our descendants in exile really be able to observe the rest of the Sun around which life flourished? A study published in May 2018 suggests that, using models of stellar evolution, it would be spot on. Indeed, because of its mass, the Sun would be on the verge of brightness. So the planetary nebula will be visible, but very faint. 


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