Key Points
- The Sun is a 4.5 billion years old yellow dwarf star, and it is considered middle-aged.
- Scientists determined the Sun’s age through radiometric dating, comparing it to the age of rocks on Earth and meteorites.
- The Sun has an estimated lifespan of around 10 billion years, and it is expected to burn bright for another 5.4 billion years.
- As the Sun dies, it will expand into a red giant, potentially engulfing Mercury, Venus, and the Earth, before becoming a white dwarf.
The Sun is only one of more than 100 billion stars in the Milky Way, but it’s the beating heart of our Solar System. Not only do the Earth and the other planets revolve around this star, but the Sun actually holds 99.8 percent of our Solar System’s mass and could roughly fit inside it around one million planets the size of Earth.
According to NASA, its core reaches temperatures of more than 27 million degrees Fahrenheit, while the surface is about 10,000°F. Some of this heat supports life on Earth, and without it, we likely wouldn’t be around.
Like anything else out there, we know that the Sun will die. This begs the question, how old is the Sun exactly, and what is its lifespan?
Let’s find it out!
How Did the Sun Form?
The history of our Sun — much like the history of our Solar System — started with a massive molecular cloud. This cloud, or solar nebula, contained a perfect cocktail of hydrogen, helium, and dust particles that began to spin and collapse onto itself under the force of its own gravity.
The gravitational forces concentrated in the middle of the solar cloud drew in most of the dust and gas inside the nebula, which ultimately led to an increase in pressure. This increased pressure led to the fusion of hydrogen atoms with a consequential increment in the production of helium and the output of energy, heat, and light.
The process of nuclear fusion inside the solar nebula is what ultimately led to the formation of the Sun. Most of the dust and gas gathered around the Sun’s core into one giant sphere that maintains its nuclear fusion process to this day — in fact, this is why this star continues outputting energy and heat.
As for the remaining dust and gas from the solar nebula, some of these particles collided with each other and sometimes got stuck together, giving birth to the planets, moons, and the other objects in the Solar System.
©42videography/Shutterstock.com
How Old Is the Sun?
According to NASA, the Sun is a 4.5 billion years old yellow dwarf star. A yellow dwarf is a term scientists use to describe a medium-sized star that primarily emits light in the yellow range, and based on gathered data, approximately 20 percent of the stars in the Milky Way are yellow dwarfs.
The estimated solar age provided by NASA refers to the age of the Sun from its adulthood until now. Calculated from the initial collapse, the Sun is around 4.6 billion years old.
Even though 4.6 billion years seems like a lot, the Sun isn’t actually old. As far as the yellow dwarfs go, our Solar System’s star is only middle-aged. It is therefore is expected to continue its nuclear fusion for a long time before it eventually turns into a red giant.
How Did Scientists Determine the Sun’s Age?
Scientists managed to determine the Sun’s age with pinpoint accuracy through radiometric dating. This is a method that calculates the age of geologic materials in Earth years. In calculating the age of the Sun, the scientists considered the age of some of the oldest rocks on Earth. They also considered the age of some meteorites, as well as the age of materials brought from the Moon.
As the entire Solar System was formed at the same time, and the radiometric dating determined the age of all these rocks to be around 4.6 billion years old (surprise, surprise), it wasn’t difficult to conclude that the Sun is about the same age.
What Is the Sun’s Lifespan?
As explained, our Sun is a yellow dwarf, and these stars have an average lifespan of around 10 billion years. Considering that the Sun is already 4.6 billion years old, we can expect it to burn bright for another 5.4 billion years, give or take.
What Will Happen When the Sun Dies?
Like most stars, the Sun is mostly made up of hydrogen and helium, alongside a bunch of other elements, including carbon, oxygen, nitrogen, iron, magnesium, and silicon. All these chemical elements constitute the star’s nuclear fuel, but hydrogen is the most important element in this reaction.
As the hydrogen supply starts to run low near the end of the yellow dwarf stage, the Sun’s core will begin to shrink. This shrinkage of the Sun’s core will lead to an increment in the volume of gas that makes up the rest of the star. This will expand the Sun’s diameter while its temperature will gradually rise.
Slowly, the yellow dwarf will swell into a red giant, gobbling up Mercury, Venus, and, possibly, the Earth in the process. During this stage, the Sun will continue to shed its outer layers, which will eventually turn into a planetary nebula. At the same time, the shrinking core, now cooled down, will be compressed into a tiny white dwarf. Then, the white dwarf will eventually fade away into a theoretical object known as a black dwarf.
Black dwarfs don’t actually exist at the moment. It is believed that all stars in the universe we know today are too young to have evolved into black dwarfs. However, scientists consider these theoretical objects the end of stellar evolution. Similar to black holes, black dwarfs will emit no heat or light, but they should retain their mass. Scientists will therefore theoretically be able to detect them through the effects produced by their gravitational fields.
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This will briefly become a planetary nebula.©iStock.com/mik38
Importance of the Sun in the Solar System
The Sun is the core of our Solar System, and not just theoretically. Its gravity is what holds everything together. Its evolution into a red giant first and white dwarf after will irreversibly alter the entire Solar System.
The planets closest to the Sun will be the first to suffer a scorching death. The forming red giant will eat them. Mars won’t be swallowed up, but its orbit will be affected. The Earth may or may not be swallowed by the Sun. However, the temperature will become too hot to support life.
While the inner planets will be the first to suffer, the outer planets may also see their orbits become unstable due to the weaker gravitational hold of the Sun. Scientists expect the orbits to drift outward and settle twice as far as they are today.
As the red giant dims into a white dwarf and loses even more mass, the orbit of the outer planets will drift even further out. They will still remain in orbit around the Sun but in a mostly dark and icy world.
Wrap Up
The Sun is a middle-aged star and is about 4.6 billion years old. Due to its size and light range, it is classified as a yellow dwarf. Yellow dwarf stars have a lifespan of about 10 billion years. This means that around 5.4 billion years from now, the Sun will deplete its hydrogen supply and turn into a red giant.
Most of the inner planets will die along with the Sun, while the exoplanets will eventually remain in orbit around a white dwarf that won’t be able to provide sufficient heat or light to sustain life.
The image featured at the top of this post is ©solarseven/Shutterstock.com.
