Humans have been observing HD 140283 in the constellation Libra for over a century. Moving at a speed of 1.3 million kilometers per hour, this star is the oldest known star in the universe, and scientists even believe it may be older than the universe itself.
In 2000, based on data measured by the Hipparcos satellite of the European Space Agency, star HD 140283 was calculated to be up to 16 billion years old.
This figure poses a significant problem for astronomers because the age of the universe, calculated from the cosmic microwave background radiation, is 13.8 billion years.
This is referred to as the “age paradox” in astronomy. Consequently, this star has been named after Methuselah, the longest-lived man in the Bible, who lived to be 969 years old.
Essentially, this star is composed of hydrogen and helium, with almost no iron inside, which is consistent with its long lifespan; when this star formed, iron was still a rare material in the universe. But how can a star exist for more than 2 billion years longer than the entire universe?
Star HD 140283 is calculated to be up to 16 billion years old.
Astronomer Howard Bond from Penn State University and his research team explored this issue further. They examined data collected by the Hubble Space Telescope from 2003 to 2011, recording the positions, distances, and energies of many stars.
By analyzing various scientific measurements, they hoped to more accurately determine the age of Methuselah. One potential cause of this discrepancy is the accurate distance of the star.
Astronomers used the distance and apparent brightness of the star to calculate its actual brightness and thus estimate its age.
The brighter the actual brightness, the younger the star. The distance to the stars is measured by parallax, which is the slight positional change of observed stars over a six-month period as Earth moves from one side of its orbit to the other.
The second cause of miscalculated star age arises from theoretical models of stars, such as accurately understanding the rate of nuclear reactions in the core and the diffusion of various elements in the outer layers of the star.
Bond’s team suggested that helium in the outer layers of the star diffuses deeper into the inner core than previously estimated, allowing the nuclear fusion reactions to consume less hydrogen than estimated, indicating that this star may be younger than previously calculated.
The third cause relates to the abundance of oxygen. The ratio of oxygen to iron in Methuselah may be higher than predicted. In the first few million years after the universe formed, oxygen was also a rare element, which may mean that Methuselah is younger than previously thought.
After extensive observations and analyses, Bond’s research team ultimately estimated the age of this star at 14.46 billion years, a significant reduction from the previously estimated 16 billion years. However, with this number, it is still older than the age of the universe. Nevertheless, this estimate could have an error margin of about 800 million years, so Bond believes this does not contradict the evolutionary history of the universe.
After recalculating, scientists narrowed the estimated age of Methuselah to 14.27 billion years.
Bond’s team later published further research in 2014, narrowing the estimated age of Methuselah to 14.27 billion plus or minus 700 to 800 million years.
However, Robert Matthews, a physicist at Aston University in Birmingham, UK, feels that the issue with this star is not as simple as that.
In fact, in July 2019, at the International Conference of Cosmologists in Santa Barbara, California, the question of how old the universe is arose once again.
Astronomers, including 2011 Nobel Prize winner Adam Ries, discovered that the universe could be hundreds of millions of years younger than predicted based on the cosmic microwave background radiation while observing relatively nearby galaxies.
The essence of the concept of the universe’s age stems from the phenomenon of cosmic expansion, and this new research suggests that the expansion of the universe is occurring about 10% faster than previously estimated.
In 2013, through observations of the cosmic microwave background by the European Space Agency’s Planck telescope, scientists calculated the age of the universe to be 13.8 billion years with an expansion rate of 67.4 km/s per megaparsec. However, recent measurements suggest that this value should be approximately 74 km/s per megaparsec.
This means that current measurements of the universe’s expansion rate do not align with predictions based on the physics of the early universe.
With an expansion rate of 74 km/s per megaparsec, the corresponding age of the universe would be 12.7 billion years. After 2019, the latest estimates by the New York Times even raised this constant to as high as 82.4, suggesting the universe would be approximately 11.4 billion years old, thus leaving the actual age of Methuselah unresolved.
Matthews believes: “Among outstanding cosmologists and astrophysicists, I tend to think that cosmologists are misunderstanding the issue. Not because they are careless, but because the observations and theories necessary to estimate the age of the universe are more complex than estimating the age of stars.”
He believes that there are two potential sources of error in estimating the age of the universe: one is the existence of observational errors not fully understood, and the other is errors in the evolutionary models of the universe.
Based on the experience of scientific history, the truth is often both. He suggests that dark energy may change over time, a possibility that physicists have previously proposed, and indicates that this could align with the theory of causal sets in quantum gravity.
If so, the latest gravitational wave research could resolve the “age paradox.” The first direct measurement of gravitational waves was in 2015, and there are still many challenges ahead. However, astrophysicists believe that we will see a breakthrough in the next decade. One current idea is to collect visible light emitted from colliding neutron star pairs to measure how long it takes to reach Earth while simultaneously calculating their gravitational waves. The accuracy of this method will certainly surpass calculations based on cosmic microwave background radiation.
Ultimately, the mystery of Methuselah’s age could help us better understand how the universe operates. This mystery might assist us in understanding some overlooked gravitational effects or enhance our comprehension of the mechanism of cosmic expansion. This is a challenge that astronomers will tackle in the coming years.
