In 2013, the Hubble Space Telescope found the birth certificate of oldest known star in the universe, cataloged as HD 140283, aptly named “methuselah”. The star, located in the constellation Libra, which is at the very first stages of expanding into a red giant, could be as old as 14.5 billion years (plus or minus 0.8 billion years), which at first glance would make it older than the universe’s calculated age of about 13.8 billion years, creating what we commonly call a dilemma.
The strange star, said NASA’s Hubble team, which has an anemic 1/250th as much of the heavy element content of our sun and other stars in our solar neighborhood.)has been known about for more than a century because of its fast motion across the sky. The high rate of motion is evidence that the star is simply a visitor to our stellar neighborhood. Its orbit carries it down through the plane of our galaxy from the ancient halo of stars that encircle the Milky Way, and will eventually slingshot back to the galactic halo.
Born in a Primeval Dwarf Galaxy
This Methuselah star has seen many changes over its long life. It was likely born in a primeval dwarf galaxy, suggests the Hubble team. that was eventually was gravitationally shredded and sucked in by the emerging Milky Way over 12 billion years ago. The star, which retains its elongated orbit from that event, is passing through the solar neighborhood at 800,000 miles per hour, taking just 1,500 years to traverse a section of sky with the angular width of the full Moon. The star’s proper motion angular rate is so fast (0.13 milliarcseconds an hour) that Hubble could actually photograph its movement in literally a few hours.
The image above is a Digitized Sky Survey image of the oldest star with a well-determined age in our galaxy. The aging star, cataloged as HD 140283, lies 190.1 light-years away. The Anglo-Australian Observatory (AAO) UK Schmidt telescope photographed the star in blue light. Credit: Digitized Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO
“We have found that this is the oldest known star with a well-determined age,” said Howard Bond of Penn State University , and the Space Telescope Science Institute in 2013.
Earlier Estimates Pegged the Star at 16 Billion Years
Earlier estimates from observations dating back to 2000 placed the star as old as 16 billion years. And this age range presented a potential gum ball for cosmologists. “Maybe the cosmology is wrong, stellar physics is wrong, or the star’s distance is wrong,” Bond said. “So we set out to refine the distance.”
The new Hubble age estimates reduce the range of measurement uncertainty, so that the star’s age overlaps with the universe’s age — as independently determined by the rate of expansion of space, an analysis of the microwave background from the big bang, and measurements of radioactive decay, says the Hubble Space Telescope astronomers.
Atacama Cosmology Telescope to the Rescue
Fast forward to 2021: Astronomers using new data collected by the Atacama Cosmology Telescope (ACT), a six-meter diameter telescope on Cerro Toco in the Atacama Desert of northern Chile, evaluated the oldest light in the universe and came up with a new conclusion that the universe is 13.77 billion years old – give or take 40 million years. The findings, suggests Cornell University Astro team, add a fresh twist to an ongoing debate in the astrophysics community.
The new estimate, using data gathered by the ACT, matches the one provided by the standard model of the universe, as well as measurements of the same light made by the European Space Agency’s Planck satellite, which measured remnants of the Big Bang from 2009 to ’13. ACT data revealed that the universe expands at a rate of 67.6km per megasecond. This finding also matches that of the Hubble discovery provided by ESA’s Planck satellite that is 67.4km. Other observations suggest that it runs at 74km per second.
Planck and ACT in Sync
“Now we’ve come up with an answer where Planck and ACT agree,” observed Simone Aiola, a cosmologistat the Flatiron Institute’s Center for Computational Astrophysics who focuses on data-driven analyses with the goal of testing physics on cosmologcal scales with Cosmic Microwave Backgorund (CMB) data
A conclusion echoed by Steven Choi, the lead author of the new study on the age of the universe d published in the Journal of Cosmology and Astroparticle Physics –The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectra at 98 and 150 GHz”. “We find an expansion rate that is right on the estimate by the Planck satellite team. This gives us more confidence in measurements of the universe’s oldest light” in sync with accepted Big Bang’s theory,” said Choi, an NSF Astronomy and Astrophysics Postdoctoral Fellow at the Cornell Center for Astrophysics and Planetary Science.
In 2019, a research team measuring the movements of galaxies calculated that the universe is hundreds of millions of years younger than the Planck team predicted. That discrepancy suggested a new model for the universe might be needed and sparked concerns that one of the sets of measurements might be incorrect.
The CMB a faint glow of light—very long wavelength microwave radiation—that fills the universes is a snapshot of the oldest light in our cosmos, when the Universe was just 380 000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure, the stars and galaxies we observe in the night sky.
By resolving the CMB .in a higher resolution than ever, the astronomers were able to carefully study variations in the polarization of its light. They used the spacing between these variations to calculate how far light from the CMB traveled to reach Earth—and thus to calculate the new estimate for the Universe’s age.
Hubble Constant Points to a Younger Universe
The study’s figure for the Hubble Constant suggest that an object 1 megaparsec (around 3.26 million light-years) from Earth is moving away from us at 67.6 kilometers per second. Planck found the Hubble Constant to be a very similar 67.4 km/s/Mpc in 2018, whereas the 2019 figure— inferred from measurements of Cepheid variable stars—was 74 km/s/Mpc. Another 2019 study using red giant stars found the Hubble Constant to be 69.8 km/s/Mpc. This larger Hubble Constant implies a faster moving, and therefore a younger, Universe.
“We find an expansion rate that is right on the estimate by the Planck satellite team. This gives us more confidence in measurements of the Universe’s oldest light,” said Choi. “It was going to be interesting one way or another,” he added.
The discrepancies between estimates for the Universe’s expansion rate—and therefore its age—suggest that astronomers may need a new interpretation of the Universe’s fundamental properties.