The largest stars die first. A star's mass determines how quickly it uses up its nuclear fuel: massive stars may live for only millions of years, the Sun about ten billion years, while small red dwarfs can shine for trillions of years – far beyond the current age of the universe.
We are used to thinking about theכוכבים As a symbol of permanence. Civilizations have risen and fallen, continents have moved, and even entire species have appeared and gone extinct, while the stars continue to shine in the sky.
But stars also have lifespans. And the differences between them are enormous.
An extremely massive star can be born, evolve, and die in a period of just millions of years. The sun is expected to live for a total of about ten billion years. In contrast, the smallest stars that are capable of sustaining nuclear fusion Can continue to shine for trillions of years.
In fact, the universe is still too young for even one of the longest-lived red dwarfs to have time to die of old age.
The paradox: more fuel – shorter life
On the surface, we would expect a large star to live longer. After all, it has much more hydrogen that can be used as fuel for nuclear fusion.
But stars are not cars with a bigger gas tank.
The greater the mass of a star, the stronger the gravitational force that presses its materials inward. To prevent collapse, the star must generate greater outward pressure in its core. It does this through nuclear fusion at a higher rate.
The result is that massive stars begin their lives with much more fuel, but consume it at an enormous rate.
Small stars do exactly the opposite: they have a smaller fuel reserve, but use it extremely sparingly.
Therefore, one of the most important rules inAstrophysics It is also one of the most surprising: The more massive a star, the shorter its life is generally.
The Sun: About ten billion years old
The Sun was born about 4.6 billion years ago and is currently about halfway through the longest and most stable phase of its life – the main sequence.
In its core, hydrogen nuclei fuse, ultimately forming helium nuclei. A tiny fraction of the mass is converted into energy according to Einstein's famous equation, E=mc², and it is this energy that ultimately reaches us as light and heat.
The Sun is expected to remain on the main sequence for about five billion more years.
As the hydrogen in the core depletes, the balance will change. The core will contract and the outer layers will expand. The Sun will become a red giant.
At the end of the process, it will shed its outer layers, leaving behind a dense, hot core – a white dwarf.
In previous articles on the Hayden website, we discussedWhite dwarfs, the remnants left behind by sun-like stars after their fusion phases are complete.
But it is important to distinguish between the life of an active star and the existence of a remnant. A white dwarf can continue to exist and cool for infinitely long periods of time, but is no longer a star that produces energy through nuclear fusion.
The giants who are in a hurry to die
At the other end are the massive stars.
NASA notes that extremely massive stars can live for only a few million years. In an illustration prepared for the James Webb Space Telescope observations, the lifespan of the Sun—about ten billion years—was compared to a star about 60 solar masses, which might live less than a million years.
These stars consume the hydrogen in their cores at a tremendous rate. When it runs out, they can switch to fusing heavier elements in increasingly shorter stages.
Eventually, a massive star can no longer produce enough energy to support its layers against gravity. The core collapses, and in the right cases, a supernova explosion occurs.
After the explosion may remain Neutron star – Or, if the core is massive enough, a black hole.
The short lives of massive stars are also important for the evolution of galaxies. They produce and scatter heavy elements into their surroundings, thereby enriching the material from which new generations of stars and planets are formed.
The stars who almost never age
Then come the red dwarfs.
These are small, cold, and much dimmer stars than the Sun. They are also the most common stars in the Milky Way.
A red dwarf consumes its hydrogen very slowly. In the smallest stars, the material can undergo extensive mixing, so that hydrogen from different regions of the star can reach the region where fusion occurs. Therefore, the star is able to utilize a much larger portion of its hydrogen supply than a star like the Sun.
The result is almost unimaginable in human terms.
NASA estimates that some low-mass red dwarfs can live up to about 14 trillion years.
The universe, by comparison, has only existed for about 13.8 billion years.
That is, if we take the age of the universe to date and multiply it by about a thousand times, we will arrive at the order of magnitude of the lifetime of some of the small red dwarfs.
There is no truly old red dwarf yet.
This has an interesting consequence: astronomers can observe massive stars at all stages of their lives, because many generations of them have already been born and died since the Big Bang.
They can also observe sun-like stars that are in the late stages of their development.
But no truly small red dwarf has ever lived to complete its life.
The universe is simply not old enough.
So when astrophysicists describe what the final stages of these stars' lives will look like, they don't rely on observing a red dwarf that has ended its life. They use models of structure andStellar evolution To calculate what is likely to happen in the distant future.
As early as 1997, astrophysicists Fred Adams and Gregory Laughlin examined the long-term evolution of the universe and its stellar populations. Such calculations take us to times when the stars we know today will no longer exist.
What is happening at the lower limit?
There is also a limit to how small a star can be.
If a body is not massive enough, the temperature and pressure in its core do not reach the values necessary for stable hydrogen fusion to occur.
Such bodies are called Brown dwarfs.
They are sometimes called “failed stars,” although this is a somewhat misleading description: they are a type of astronomical object in their own right, located in terms of mass between giant planets and the lightest stars.
A brown dwarf can't simply conserve fuel for trillions of years like a red dwarf. It doesn't have enough mass to sustain normal, stable hydrogen fusion like a star in the first place.
Could life around a red dwarf enjoy trillions of years?
Here a tantalizing question arises: if a star can shine for trillions of years, do planets around it have almost unlimited time to develop life?
Not necessarily.
Red dwarfs Young ones can be very active and emit strong bursts of ultraviolet and X-rays. Because the habitable zone—the region where temperatures might allow liquid water on a planet's surface—is very close to a small, cold star, planets there may be particularly exposed to this activity.
Therefore, the lifespan of the star is only one of the factors that determines the chance of life developing.
Interestingly, K stars – orange dwarfs, slightly smaller and cooler than the Sun but larger than red dwarfs – are considered by some researchers to be particularly promising candidates for the search for habitable worlds. They may live for about 15–45 billion years, while also being calmer than many red dwarfs.
The future universe will be very different.
We live in a special time in the history of the universe.
There are stars today in almost every mass range: from massive, bright stars that live quickly and die young to tiny red dwarfs that will continue to exist into a future that is hard to even imagine.
But this situation will not last forever.
Over vast periods of time, the gas reserves available for the formation of new stars will run out. The massive stars will disappear first. After them, sun-like stars will gradually disappear.
Red dwarfs will be among the last stars to continue to shine.
In this sense, if any intelligent beings were to look up at the sky trillions of years from now, their universe would be very different from ours. Many of the bright stars we see today would no longer be there.
And what will remain for the longest time will be the stars that are currently very easy to ignore: the small, cold, and dim.
It is not always the one with the most fuel who lives the longest. In the universe, as in many other cases, the crucial question is At what rate is it used?.
This process is already happening. As we recently reported in the article “The rate of star formation in the universe has plummeted—but the main fuel pool has hardly disappeared."In the past 4.5 billion years, the rate of star formation in the universe has declined sharply, even as the pool of atomic hydrogen has been depleted at a much more moderate rate. This means that not only does the universe contain stars with very different lifespans—the rate at which new stars are joining the population is also decreasing."
Questions and Answers
How long will the sun live?
The Sun's total lifespan as a star is about ten billion years. It is about 4.6 billion years old and is expected to remain on the main sequence for about another five billion years before evolving into a red giant.
What type of star lives the longest?
The longest-lived stars are low-mass red dwarfs. Models of stellar evolution suggest that they can live for trillions of years, and in some cases, up to 14 trillion years.
Why do large stars live shorter than small stars?
Although they have more material that can be used as fuel, the pressure and temperature in their cores are much higher and they undergo nuclear fusion at a very rapid rate. Therefore, they consume their fuel quickly.
Have we ever seen a red dwarf die of old age?
No. The age of the universe is about 13.8 billion years, while the lives of small red dwarfs can last hundreds of billions or even trillions of years. Not enough time has passed since the Big Bang for one of these long-lived stars to end its life naturally.
More on the subject on the science website
- Stellar Evolution – Articles and Research on the Hidan website
- Red dwarfs – articles on the science website
- White dwarfs – the final stage in the lives of sun-like stars
- Supernovae – the violent deaths of massive stars
- Neutron stars – the compressed remains of massive stars
For the original publication: Opening the original publication
2 תגובות
Because it is a basic law of nature
And why on earth do you think that behind all this wonderful thing there isn't some incomprehensible and inexplicable higher power that is very difficult for us to define physically because it is spiritual and invisible to the human eye. Could it be that the entire universe just came out of nowhere without a planning and responsible entity?