Calculating the Age of Stars: Hasin Shadab

Did you know that our sun is approximately 4.6 billion years old? Furthermore, scientists have estimated that it will last for another 7 billion years before reaching its final stage of the life cycle? But how do astronomers get to know all this stuff? Before knowing that, you need to know what a sun is. The sun is a star; to calculate the age of stars, astronomers have developed various types of methods, starting from calculating luminosity to calculating its rotational speed.

Not all stars in the universe live separately; some identical stars live in groups known as clusters. Meanwhile, others that are not identical live independently from each other. Calculating the age of the stars that live in groups is more straightforward than the star that lives individually.

To calculate the age, astronomers have developed a model by discovering the trend in rotation, luminosity, and temperature of stars for their life cycle. But each method depends on the type of star. If the star is in a cluster, astronomers try to discover the luminosity and color to find the temperature of stars. That means if the color of a star is blue, then the temperature is approximately 25000 kelvin (24737-degree Celcius ), which is the hottest star. The stars with the color red have a temperature of roughly 3000 kelvin (2727 degrees Celsius). That is the coldest star. As the stars start to age up, their temperatures decrease.

But, in the case of lone stars, astronomers have developed a method, called gyrochronology, based on the rotational speed of the stars. As the stars become older, they tend to lose motion. More importantly, getting accurate results, astronomers have developed a space telescope for closely monitoring the rotation of stars. To calculate the rotational speed, the astronomers search for dark spots as these dark spots work as markers of starting points for the rotation cycle of stars. The astronomers measure the time taken for the dark patches to go out of view and then come back to view. These dark spots dim the star slightly; as the dark spots move out of sight, the luminosity of the star increases.

However, these space telescopes are there to observe the life cycle of stars. As a result, astronomers have developed a model of the life cycle of stars recording the color, temperature, and luminosity of the stars at each stage of the life cycle. Astronomers used this model to figure out at which stage the star is at, which helps estimate an approximate age.

So are these methods accurate enough to calculate actual age? No, they do come with some uncertainties. Moreover, not every star abides by the theories of astrophysics since there are some exceptions. You cannot calculate the age of a star the way you would generally calculate a human’s age by subtracting the birth year from the current year. Besides, even if you do find the birth year of the stars, you still cannot calculate the age as time travels faster out in space than on Earth. So it is hard to get an accurate result as most methods include 15-25% uncertainty. The moral of the story is that stars are like humans. As we get older, our cheeks start to loosen up, wrinkles begin to form all over our faces, and muscles start to rust up, which reduces our motion. As the stars age up, dark spots commence to form over their surface instead of wrinkles, and subsequently, their rotation slows down.