For more than 100 years astronomers have been observing a strange star in the constellation Libra about 190 light-years from Earth. It moves fast at 1.3 million kilometers per hour across the sky. More interestingly, however, HD 140283 – or Methuselah, as is well known – is also one of the universe's oldest known stars.
In 2000, scientists attempted to date the star based on observations from the European Space Agency's (ESA) Hipparcos satellite, which is estimated to be 16 billion years old. Such a figure was quite stunning and also quite confusing. Astronomer Howard Bond of Pennsylvania State University pointed out that the age of the universe ̵
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Measured by par, the predicted age of the star increased a major problem. How can a star be older than the universe? Or vice versa, how could the universe be younger? It was certainly clear that Methuselah, named after a biblical patriarch who died at the age of 969, making him the most enduring of all figures in the Bible, was old, since the metal-poor subgiant is predominantly hydrogen and contains helium and very little iron. Its composition meant that the star must have arisen before iron became commonplace.
But more than two billion years older than its environment? Certainly that is not possible.
A Closer Look at the Age of Methuselah
Bond and his colleagues set out to find out if this original figure of 16 billion was true or not. They studied eleven series of observations recorded between 2003 and 2011 by the fine steering sensors of the Hubble Space Telescope, which noted the positions, distances and energy discharges of stars. With parallax, spectroscopy and photometry measurements a better sense of age could be determined.
"One of the uncertainties of the age of HD 140283 was the exact distance of the star," Bond told All About Space. "It was important to do this correctly because we can better determine its luminosity and from that age – the brighter the intrinsic luminosity, the younger the star." We looked for the parallax effect, which meant we observed the star for six months Apart from the positional shift due to the Earth 's orbit, which indicates to us the distance core and the meaning of elements that exist in the outer Sliding layers down, he said, they worked on the idea that leftover helium diffuses deeper into the nucleus and burns less hydrogen through nuclear fusion, as the fuel consumes faster, the age drops.
"Another important factor was the amount of oxygen in the star," Bond said. HD 140283 had a higher than predicted oxygen-to-iron ratio, and since oxygen in the Universe was not abundant for several million years, this again indicated a lower age for the star.
Bond and his associates estimated the age of HD 140283 to be 14.46 billion years – a significant reduction from the previously claimed 16 billion. However, that was still more than the age of the universe itself, but the scientists created a residual uncertainty of 800 million years, which, according to Bond, made the age of the star compatible with the age of the universe, though it was not quite perfect.
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"Like all measured estimates, it is subject to both random and systematic errors," said physicist Robert Matthews of Aston University, Birmingham, United Kingdom, which was not involved in the study. "The overlap in the error bars gives an indication of the likelihood of a conflict with cosmological age determinations," said Matthews. "In other words, the best-supported age of the star conflicts with that for the inferred age of the universe [as determined by the cosmic microwave background] and the conflict can only be resolved by bringing the error bars to their utmost limits."
Refinements caused the age of HD 140283 to drop slightly more. A follow-up study in 2014 updated the age of the star to 14.27 billion years. "The conclusion was that age is about 14 billion years and, if one includes all sources of uncertainty – in both observational and theoretical modeling – the error is about 700 or 800 million years, so there is no conflict because 13.8 billion years lie in the star's fault bar, "Bond said.
Closer Look at the Age of the Universe
For Bond, the similarities between the age of the Universe and that of the ancient near The Star – both were determined by different methods of analysis – is "an amazing scientific achievement that provides very strong evidence for the big bang of the universe. " He said that the problem with the age of the oldest stars was far less severe than in the 1990s, when the age of the stars approached 18 billion, or 20 billion years in one case. "Times are now in tune with the uncertainty of the regulations," Bond said.
Matthews believes, however, that the problem has not yet been solved. Astronomers at an international conference of top cosmologists at the Kavli Institute of Theoretical Physics in Santa Barbara, California in July 2019 puzzled over studies that suggested different ages for the universe. They looked at measurements of galaxies that are relatively close together, indicating that the universe is hundreds of millions of years younger than the age determined by the cosmic microwave background.
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According to the 2013 European Planck Space Telescope, the universe is far from being 13.8 billion years old, and it can even be 11.4 Billions of years old. One of the behind-the-scenes researchers is Nobel laureate Adam Riess of the Space Telescope Science Institute of Baltimore, Maryland.
The conclusions are based on the idea of an expanding universe as shown in 1929 by Edwin Hubble. This is fundamental to the Big Bang – the understanding that once there was a state of hot density that exploded and stretched the room. There is a starting point that should be measurable, but new evidence suggests that the rate of expansion is actually 10% higher than that proposed by Planck.
In fact, the Planck team determined an expansion rate of 67.4 km per second per megaparsec, but recent measurements of the universe's expansion rate indicate values of 73 or 74. This means that there is a difference between measuring today's expansion of the universe and predicting how fast it should expand based on the physics of the early universe, said Riess. This leads to a reassessment of accepted theories, but also shows that there is still much to be learned about dark matter and dark energy, which are probably behind this puzzle.
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A higher value for the Hubble constant means a shorter age for the Universe. A constant of 67.74 km / s per megaparsec would lead to an age of 13.8 billion years, whereas one out of 73 or even 77, as some studies have shown, would indicate a universe age of no more than 12.7 billion years , This is a mismatch that reiterates that HD 140283 is older than the universe. Since then, it has also been superseded by a study published in the journal Science in 2019 that proposed a Hubble constant of 82.4 – indicating that the age of the universe is only 11.4 billion years. "I suspect that the observing cosmologists overlooked something that evokes this paradox, not the stellar astrophysicists," he said, suggesting that the measurements of the stars might be more accurate. "That's not because the cosmologists are in any way more slippery, but because the age determination of the universe is subject to more and possibly more difficult observational and theoretical uncertainties than that of stars."
How will scientists find out?
What could possibly make the universe look younger than this particular star?
"There are two possibilities, and the history of science suggests that in such cases, reality is a mixture of both," said Matthews. "In this case, those would be sources of observation errors that were not fully understood, as well as some gaps in the theory of the dynamics of the universe, such as the power of dark energy, which has been the main driver of cosmic expansion for many billions of years."  Related: Dark Matter and Dark Energy: The Secret Explained (Infographic)
He suggests the possibility that the current "Altersparadox" reflects the time variation of dark energy and therefore a change the rate of acceleration – a possibility found by theoreticians might be consistent with ideas about the fundamental nature of gravity, such as the so-called causal theory. New research into gravitational waves may help to resolve the paradox, Matthews said.
To do this, scientists would study the waves in the structure of space and time created by pairs of dead stars instead of relying on the cosmic microwave background or monitoring neighboring objects such as Cepheid variables and supernovae, to measure the waves Hubble constant – the former gave a speed of 67 km / s per megaparsec and the latter of 73.
The problem is that the measurement of gravitational waves is not an easy task since they were recorded directly in 2015 Stephen Feeney, astrophysicist at the Flatiron Institute in New York, could make a breakthrough over the next decade. The idea is to collect data from collisions between pairs of neutron stars using the visible light that these events send out to find out at what speed they are moving relative to Earth. This includes analyzing the resulting gravitational waves for an idea of distance – both can be combined to give a Hubble constant measurement that should be the most accurate.
The Age of HD 140283 mystery leads to something bigger and more scientifically complex, changing the way the universe works.
"The most likely explanations for the paradox are an overlooked observation effect and / or something that is lacking in our understanding of the dynamics of cosmic expansion," said Matthews. Exactly what this "something" is will certainly challenge astronomers for a while.