Just the words themselves oldest star in the Milky Way Galaxy might evoke images of ancient cosmic phenomena, remnants of the universe’s infancy as managing to linger close to our own celestial neighborhood.
Earendel: The Farthest Star Ever Observed
Often, when we hear about the discovery of stars born soon after the Big Bang, they appear to be very far away in the far reaches of the universe. Take, for example, the Earendel star, which was seen by the Hubble Space Telescope in the year 2022, about 12.9 billion light years away from us towards the constellation Cetus. This is the farthest star known in the universe and also one of the first stars born.
Due to the expansion of the universe, If this star were alive, it would be 28 billion light years away from us today. It was a B-type star, known for its relatively short lifespan. This star was 50 to 100 times more massive than our Sun and millions of times brighter. Today’s Obviously, it no longer exists.
J1808−5104 – The Oldest Star In The Milky Way Galaxy
On 5 November 2018, scientists from Johns Hopkins University discovered a star that was not only one of the oldest stars found in the universe but also present in our Milky Way galaxy and very close to us. How is this star improving our understanding of the early universe, and what clues does it give us about the first stars born in the universe?
A team of scientists discovered a binary system about 1,950 light years away from Earth toward the southern constellation Ara. It was named 2MASS J18082002–5104378, or J1808−5104 in short. Scientists believe that this secondary star among the primary and secondary stars present in this binary system could be one of the oldest stars in the universe.
Stars Population: What It Is?
The real reason scientists believe this is because of its metal content. In our very early universe, there were no heavy metals present. Population III stars were the first generation of stars in our universe. They were made of pure hydrogen and a small amount of helium. Only when hydrogen fusion began in their cores did some of the heavier metals from hydrogen and helium begin to form. When these huge, massive first-generation stars exploded in supernovae, these few heavy metals spread throughout the universe.
After which, the material in which these heavy metals were present got mixed with the new stars the birth of which were Population II stars. Some more heavy metals were produced in their core and every subsequent generation got enriched with these more heavy metals. The younger the star is today, the higher will be its metal content or metallicity. All the stars that we can observe today are Population I stars.
Our Sun is also a Population I star in which these heavy metals or metallicity are present in higher quantity as compared to Population II stars. Let us also tell you that regarding the Sun, it is believed that after the Big Bang, our Sun is the star of the 100th generation.
J1808−5104 And The Companion
Now coming back to this binary system, the primary and bigger star in it is a subgiant star. It is cooler than the Sun but is 5.3 times brighter. It is also slightly bigger than our Sun. Its solar radius is up to 2.44 times.
Now, the second star of this system, which is a red dwarf star according to astronomers, has a mass of only 10 percent of our Sun. It is right on the edge of the lower limit of hydrogen burning in its core. If its mass were even a little less, then it would not have been able to support hydrogen burning in its core.
The age of this star has been estimated to be a freaking 13.53 billion years, according to the very low metallicity found in it. Our universe is 13.8 billion years old; this star is one of those very early stars that our modern telescopes were searching for in the depths of the universe. That is, Population III stars!
This can be a star made of pure hydrogen that spread in the universe after the Big Bang. The discovery could also mean that our galaxy’s star-dense disc is much older than previously thought, at 8 to 10 billion years.
“We’ve never discovered a star with such a low mass and so few grams of metals before,” said Andrew Casey, an astrophysicist at Monash University in Australia.
Big Bang Relation With J1808−5104
After the Big Bang and Population III star’s material containing heavy elements mixed with newly formed stars, known as Population II stars, these stars became increasingly rich in heavy elements over generations. Today, the younger a star is, the higher its metal content or metallicity. All the stars we can observe today are classified as Population I stars. Our Sun is also a Population I star and contains more heavy metals than Population II stars.
It is believed that our Sun formed as a star of the 100th generation after the Big Bang. This star’s incredibly small size is why 2MASS J18082002–5104378 B has remained invisible to us for so long, even though it is right here in the Milky Way and relatively close to us. It is incredibly faint.
It could only be seen because it has a larger binary companion. When astronomers studied the larger primary star, they noticed the faint motion of the smaller star. More detailed spectroscopic analysis revealed its record-breaking low metallicity, and analysis of its orbit in the Milky Way’s thin disk of rotation, the star-dense plane, showed it to be a native of the Milky Way.
Its existence alone challenges popular notions of what a very old star might look like. They are massive, extremely distant, and probably not long dead and gone, as scientists had believed since the 1990s. In reality, calculations suggest a small star like this could live for trillions of years.
Live Quickly And Die Quickly
Very massive and heavy stars tend to live quickly and die quickly, but smaller, less massive stars – say 20 percent lighter than our Sun – could easily live for 13 billion years or more, according to Andrew Casey. The problem is that astronomers have long believed that the first stars born in the universe were very large and extremely heavy, which ended their lives very quickly, and hence, none of them should have survived till today.
This discovery will help change all those theories: it shows that ancient stars can be very low-mass, meaning that some of the oldest stars in the universe could still exist today.”
Several ancient stars are orbiting the Milky Way, including a red giant known as HE 1523-0901. This star is located 9,900 light-years away in the galactic halo of the Milky Way galaxy, and scientists estimate its age to be around 13.2 billion years. Another well-known and intriguing star, the Methuselah star (HD 140283), was initially estimated to be a remarkable 14.5 billion years old, which would exceed the universe’s age.
However, more recent models of stellar evolution have adjusted its age to align with the universe’s age, placing it between 12 and 13.7 billion years.
Hide and Seek
Due to its small size and low metallicity, 2MASS J18082002–5104378 B stands out among its peers. Its composition closely resembles the material that filled the universe after the Big Bang. Over time, this material has evolved through several generations of stars, eventually becoming mixed with heavier elements.
Because this star is so small and faint and difficult to see, it is also possible that there are many more small and faint metal-free stars. According to Casey, the discovery rate is currently “extremely low.” Still, 2MASS J18082002–5104378 B provides a very good theoretical and observational reason to believe that if this rare star exists, others must be like it.
Conclusion
“We need to keep searching for stars that seem as old as this system. These stars are very rare, like looking for a needle in a haystack. But with all the data we’ve accumulated from ground-based and space-based telescopes, we’re optimistic. We are closer than ever to knowing how stars formed in the early universe.” James Webb is doing this work very well, discovering record-breaking objects like these. What do you think about this star please let me know in the comment section.
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FAQ’s About Exomoons
Q.1 What is the significance of studying the oldest stars?
Ans. The oldest stars provide a look into the early universe. The chemical composition and ages of these stars help deduce the conditions in the universe soon after the Big Bang and how the first stars and galaxies formed, leading to the enrichment of the universe in the chemical sense. Ancient stars are time capsules that provide crucial clues in cosmic history.
Q.2 How do scientists determine the age of a star?
Ans. The age of a star is obtained from its stellar astrochronology. The abundance of elements with an atomic number higher than hydrogen and helium is deduced from the composition of the star.
In general, older stars have lower metallicities. From the comparisons between the current properties of the star and the theoretical stellar evolution models, scientists may obtain an approximate age.
Q.3 What are some challenges in measuring a star’s age?
Ans. Challenges are uncertainties in distance measurements, variations in stellar models, and complexities inherent in the processes of stellar evolution. These factors can lead to small errors but large differences in calculated ages.
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