Is the “Methuselah star” actually older than the Cosmos?

For as long as humans have envisioned the Universe, we’ve gaped at the vastness of it all. Was our Cosmos infinite? Was it eternal? Or did it come into being a finite amount of time ago? Over the 20th and 21st centuries, these existential questions one-by-one fell into the realm of science, and now have the best answers we’ve ever been able to get. As of today, we can assertively state that we in fact know how old the Universe is: 13.8 billion years old, marking time at the start of the Big Bang. If we were able to step back through time, we’d find that the cosmos as we know it was a very different place early on. Modern stars and galaxies formed from a series of gravitational mergers of smaller-mass objects, which themselves comprised of younger, more pristine stars. At the earliest times, no stars or galaxies were present. Even neutral atoms or stable atomic nuclei were not present once upon a time. Today, astrophysicists and astronomers who study the early cosmos assertively state its age with an uncertainty of no more than ~1%: a remarkable achievement.

The oldest stars that we’ve discovered to date are almost pristine, made up of nearly 100% hydrogen and helium, where their ages can above 13 billion years. Oddly enough, the star which currently has the oldest age determination, the so-called Methuselah star, has an estimated age of 14.5 billion. How can a star be older than the age of the Cosmos itself? It can’t be. Here’s what must be what’s going on.

Methuselah star is a confusing star. It is just 190 light years away and we can measure many of its observed properties quite well, including its:

• surface temperature,
• luminosity,
• and composition.

We can also observe that it’s no longer a main sequence star but rather is just starting to evolve into the subgiant phase on its certain journey toward becoming a red giant. These pieces of info, combined, let us to get a well-constrained value for the star’s age, and the result is unsettling, to say the least: 14.46 billion years. Yet some of the other properties it shows, like an iron content of 0.4% the Sun’s, suggest that it’s quite old, but not very pristine. What we fail to discuss, however, when it comes to the age of this star is a crucial piece of information: there is a huge uncertainty on its age of around 800 million years, and that’s merely at the one-sigma (i.e., 68% confidence) level.

This value still places the age of this star as awkwardly early, and hints at a potential clash between how old the stars are and how old the Cosmos is. Nevertheless, there’s nearly a 20% chance that the star’s true age is younger than the age of the Cosmos, and that would mean that there’s no discrepancy at all.