How do we know when the Sun will die?

Illustration: Benjamin Currie

Consider the Sun: hot, massive and the reason why all this (savage movements) is possible. Our local star drives the whole life as we know it, providing energy that sustains everything from the smallest photosynthetic microorganisms to the largest animals on land and in the seas.

But one day – far, far into the future – the Sun will die. Still, things won’t just darken. Instead, they will be very, very bright. Hot, too, unbearable. The sun will become unrecognizable if there is still someone to see it.

“One of the most basic questions that every conscious person has is: how did we get here, what is the purpose, what does it all mean? Questions of our origins and our future, ”said Jackie Faherty, an astrophysicist at the American Museum of Natural History, in a telephone conversation. “If you want to understand the habitable zone of our Sun, you must know how long it will be there, how it develops and how it changes. It all comes down to that basic story. ”

What brings us to today’s riddle: How much time is left for our life-giving Sun, and how do we know that?

“Once you realize it’s a ball of gas, you know it’s not some endless machine,” Faherty said. “You just have to figure out when it’s going to expire.” Calculating that timeline is a relatively simple equation, built on complex mathematics and smaller realizations.

To know how much time the Sun has left – and, spoiler, it’s about 5 billion years – you need to know how old it is. Stars do not die unexpectedly, so knowing the age of a star is an important indicator of how fast it is growing. In the 19th century, in the context of an argument over how old the Earth was, Charles Darwin and Lord Kelvin, an astrophysicist, discussed the age of the Sun. Darwin’s assessment was eventually closer; nuclear energy had not yet been discovered, and Kelvin worked under the assumption that the sun burns coal. That kind of knocked out his numbers.

Our basis for the age of the Sun is derived from the earliest rocks still traveling through the solar system, which are basically discarded materials that were never converted to a planet or moon during the merging of the solar system. These rocks constantly give us an age of 4.6 billion years, and scientists have been able to accurately date them using them number of techniques.

The Sun, recorded by NASA’s Solar Dynamics Observatory in 2013.

It is also important to know the sunshine, because it tells us how energetic the star is. We know how bright the Sun is since we know how far we are from it, a measurement called astronomical unit, or AU. (“It’s all about distance,” Faherty explained.) The measurement was painstakingly calculated using the parallax effect and the transit of Venus across the Sun from 1769; the famous Captain Cook even made some observations in Tahiti.

One astronomical unit is now fixed at 92,955,807.3 miles and is a vital measure for considering distances within and around our solar system. With this measurement, astronomers were able to determine the Sun’s luminosity – that is, they were not sure whether the star was extremely close and incredibly dark, or extremely distant and incredibly bright.

As it turns out, the Sun is average when it comes to stars. This is clearly shown by one of the most important graphs in astronomical history, the Hertzsprung-Russell diagram, which mapped the brightness and color of the stars. The two astronomers after whom it is named alluded to the idea that stars burn hydrogen in some way, and that burning is related to star temperature and interior physics.

Things really came into focus when Cecilia Payne, then a doctoral student in astrophysics at Harvard, wrote her thesis on the idea that stars are mostly composed of hydrogen and helium. At the time, Russell (known for the diagram) and one of Payne’s supervisors called the numbers “impossible,” and Payne eventually rejected the idea in the thesis. But it was proved that she was on the spot, and only through her work could the Hertzsprung-Russell diagram really be used as a tool in astrophysics, to understand the class of the star; that is, what his physics is like and what his destiny will be. Only by placing our Sun in that stellar setup do we get a sense of what a star it is and how brilliantly it shines among its peers.


“Observing other stars has allowed us to have a comprehensive theory of stellar evolution. In particular, star clusters played a key role (stars that are at the same distance, of the same composition, and differ only in mass). It was there that it was possible to understand that stellar evolution depends strictly on stellar mass, ”said Gianluca Pizzone, an astronomer from the International Astronomical Union, in an email.

Because we know the rate of the Sun’s nuclear fusion, we also know the rate at which it burns its nuclear fuel. Albert Zijlstra, an astrophysicist from the University of Manchester, explained that this rate is extremely slow. “The sun is not a bomb, it is an extremely bad nuclear fusion reactor,” he said in a video call. “It produces less energy per kilogram than you. That takes time. ” Easy, Sun. No rush.

But these ideas are now merging. Knowing how old the Sun is and the speed of its fusion means that astrophysicists know how much the Sun has already burned. The sun burns for about 5 billion years and will burn for another 5 billion years. Here things get interesting: “You would expect nuclear fusion to slow down [over time] because there is less hydrogen. But that is not possible – it is the heat that keeps the sun stable. Hydrogen is running out a bit, and the whole Sun is convecting a bit, increasing the temperature, ”said Zijlstra. (This is already happening, but there is still a lot of hydrogen.) But in the end, the hydrogen will disappear and the Sun will collapse inside – gravity always wins.

Our Sun is not big enough to produce a supernova, a huge stellar explosion. Larger stars leave behind neutron stars or black holes; The end of the sun will be dramatic in a different way. As hydrogen burns, the Sun becomes smaller and the layers outside the core of the star become warmer. Fusion begins to occur ua should outside the nucleus. The sun becomes a red giant, a much more widespread star that burns with less energy than before. The road to the red giant takes a while, but once it becomes, decay is quick.

“At this point, it would be a very bad time to move to Mercury,” Zijlstra said. “Eventually you find yourself inside the Sun.” The new, inflated Sun took its first victim.

The sun will continue to rise and destabilize. And Venus is swallowed. (There is some debate about whether the fully inflated Red Giant Sun will reach Earth or not, but suffice it to say that things will be crunchy here; at the very least, the oceans will boil and the Earth will look like today’s Venus.) diffusely begins to evaporate.

Only 100,000 years after it became a red giant, it loses half its mass. At this point, the Sun is at its end. It is a white dwarf, a dense stellar remnant the size of our planet. At this point it is depleted of nuclear energy and will slowly cool into a solid ball of carbon – basically floating diamond in space.

And around that compact dwarf, a cloud of material ejected by the sun can fluoresce, a blinding planetary nebula. But that is not certain, said Zijlstra, who in 2019 was a co-author of the work in Natural astronomy about the probability that our Sun will illuminate the nebula. For such a nebula to occur, the Sun would have to be hot enough while the cloud was still near it, and even then the cosmic light show would be a blink of an eye in stellar time: about 10,000 years. Pizzone said the nebula might look something like the halo of Messier 57, the Nebula Ring.

Nebula Ring.

It’s worth keeping all of this in perspective. That blink of an eye at the end of our star would last about twice as long as written human history. Long before life on Earth came into being, the original planet was as inhospitable as it would be again. In other words, we are not just in the right place – we are at the right time.

“It’s really important to realize that we’re very happy to be living right now, when there is this very delicate balance with the Sun’s output energy (and the stabilizing orbit of our Moon) today,” said Adam Kowalski, a stellar astrophysicist at the National Solar Observatory. – Tell Gizmod. “We don’t want to upset this balance because so far we haven’t found any planet around another star that we know has such a delicate balance.”

Needless to say, we found ways to mess things up. This decade will define the trajectory of climate change patterns in the century to come and beyond. In evolutionary terms, “we were only here to sneeze in the life of the solar system,” Faherty said. “You shouldn’t think the Earth will be swallowed by the Sun and that’s how we’re going to go… I’d be more concerned about our own influence changing things before we even get to that stage.”

So we know how and when the Sun will die and take the Earth’s habitability with it. However, it is impossible to know if some intelligent life will still be here in 5 billion years to crash with a ship.

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Naveen Kumar

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