The stars that we usually observe in the sky, including the sun, are known to have ages that can reach billions of years. Then why did the star age this long? What’s the fuel so that it keeps burning?
Actually, the length of a star’s life period depends on how fast it uses its nuclear fuel.
Our sun is a dwarf star that has been forming for nearly 5 billion years. And it has enough fuel to keep it burning for the next 5 billion years.
Well, stars including the Sun can light up due to an activity known as nuclear fusion, which converts 4 hydrogen atoms into helium.
This activity occurs in the dense and hot core of the star where temperatures can reach 20 million degrees Celsius. While nuclear fusion exerts pressure towards the outside of the star’s core, there is also gravitation which generates inward pressure.
And these two forces are in perfect balance, which is called hydrostatic balance.
This hydrostatic balance will continue throughout the life of the star. Until a star runs out of fuel, the exit pressure will decrease.
The point is that if the fuel of the Star has been depleted and is about to reach its expiration date, the outlet pressure will decrease. The bigger a star, the greater its gravitational influence.
Thus the bigger the star, the more hydrogen is needed to combine, to generate enough pressure to hold its gravity.
Star Activity Affects Age
Large, massive stars use their fuel at a much higher rate than low-mass stars, such as the Sun. So that their lifespan will be much shorter.
They glow with a much greater luminosity. Just like the analogy of a truck with a private car. The bigger the car, the more fuel it uses, and the bigger it is.
Meanwhile, the energy or luminosity emitted by a star like the Sun is about 3.8 × 10 to the power of 26 joules per second.
For those who don’t know the joule, a joule is a unit of energy. Like kilograms, it is for weight, for energy it uses joules. With units of kilograms per mass of gravity.
To make it easier, 3.8 × 10 to the power of 26 is equal to 38 followed by the number 0 as much as 26 backward, which is quite big too. That way the calculation of nuclear fusion reactions in the sun can last for 10 billion years.
In contrast to its more massive stars, which are vulnerable to a life of 10 million years, because they produce too much energy, and usually just waste their energy.
Then, how do astronomers know that the sun is already 5 billion years old?
To answer that is simple. The current age of the sun is determined from radioactive calculations on objects in the solar system that is known to have formed around the same time as the sun. Can be calculated from the value of carbon or atoms.