Admin and Founder of The Secrets of the Universe and former intern at Indian Institute of Astrophysics, Bangalore, I am a science student pursuing Master’s in Physics from India. I love to study and write about Stellar Astrophysics, Relativity& Quantum Mechanics.
Stars are one of the most basic entities in our universe. Their study reveals a lot of secrets of the cosmos. However, a recent discovery has put us in a 'scientific crisis' as Astrophysicists have discovered a star that is older than the universe itself. Commonly known as Methuselah Star, the official designation of this star is HD 140283. The star was known to us since 1912.
What Type of Star is HD 140283?
Stars come in variety of sizes and surface temperatures. By studying these physical parameters, the age and evolutionary stage of the star can be easily determined. HD 140283 is a subgiant star. This means, unlike our Sun, it isn't burning hydrogen into helium in its core. So it is neither on main sequence, nor on red giant branch of Hertzsprung Russel Diagram. It has roughly the same mass and temperature as that of Sun but has twice the radius and four times the luminosity. The main spectral type of Methuselah star is G, same as that of Sun. It is 202 light years away, in the constellation of Libra.
The Surprising Age of Methuselah Star
The thing that has surprised the astronomers is not the classification of Methuselah star, but its age. The universe popped into existence 13.8 billion years ago. This number is calculated by studying the current expansion rate of the universe and reversing the entire process. This number has an uncertainty of 800 million years. HD 140283 is estimated to be 14.46 billion years, a number greater than the age of the universe.
British physicist Robert Matthews wrote for UAE-based media outlet The National: “It’s a riddle of cosmic proportions: How can the universe contain stars older than itself?
“That’s the conundrum now facing astronomers trying to establish the age of the universe — and its resolution could spark a scientific revolution.
How was the age of Methuselah Star Determined?
You may be wondering how astronomers concluded this puzzling age of this star. To understand that, let us learn a concept of stellar astrophysics. When the universe formed, the major elements that were synthesized were hydrogen and helium. The lithium was formed in trace amount. A few hundred million years after the big bang, the first stars formed. These were the so called population III stars or the metal poor stars. In Astronomy, every element other than hydrogen and helium is known as a metal. This is in contrast to what your chemistry textbook taught you. So the first stars were formed from hydrogen and helium and in their cores formed heavier elements such carbon, nitrogen, silicon, sulphur, nickel, iron etc.
When these population III stars died, they enriched the interstellar medium with these heavier elements. The new generation stars that subsequently formed, contained these heavier metals. They were higher in metallicity than the Population III stars. The next generation stars were called Population II stars. Repeating the same process, Population I stars with even more metal content started forming. Our Sun is a metal rich population I star. It has high metallicity (high proportion of heavier elements).
Studying the iron content in the star, scientists then determine its age. The iron content in Methuselah star is lower by a factor of 250 than that of the Sun. This puts the age of the star to a maximum of 14.46 billion years.
How important is this discovery?
It is important to know that the current age of universe has an uncertainty of 800 million years and the minimum age of Methuselah star is 13.6 billion years. The possibility that the star was formed after the big bang, therefore, cannot be ignored. If that is the case, then we have just discovered one of the oldest star in the universe. Studying that star will give more information about the early universe.
If the star is older than the universe, then we are in a scientific crisis. This means the big bang model isn't correct and needs improvements. Also, we may need to reconsider the expansion rate of the universe and have a better result for the age of the universe.
That's how science works! Better theories replacing the old ones...If you want to know more about Astrophysics, read our 30 articles series, Basics of Astrophysics..