Is This Star Older Than the Universe? | Unveiled

Is This Star Older than the Universe?

The biblical figure Methuselah is said to have lived for 969 years; a feat which would comfortably make him the oldest ever human being. It’s not all that surprising, then, that the oldest known star in the universe should go by the same name… But what is surprising is just how old Methuselah the astronomical object could be….

This is Unveiled and today we’re answering the extraordinary question; Is this star older than the universe?

Despite having a fairly reliable estimate, we still don’t know (and may never know) the exact age of the universe. According to NASA’s Wilkinson Microwave Anisotropy Probe (or WMAP), it’s 13.772 billion years’ old with an uncertainty of 59 million years… According to the European Space Agency’s Planck spacecraft, it’s been around for more like 13.82 billion years… And then there are plenty of other estimates, in and around those figures.

We generally try to work out the age of the universe using two different methods: 1) we track the rate of expansion that the universe is undergoing and trace it all the way back to the Big Bang, and 2) we search out the oldest stars in the sky. That second one works well, but only assuming we have accurate data on the stars…. So, how do we really know how old they are?

Estimating the age of a star is different from guessing the age of a person. Quite significantly different! We can usually see and track the physical changes in most people when they age, for example. It’s the same with most other creatures and plants; the same with most things we know to have a lifespan. Stars don’t throw out the same clues, however. From our vantage point on Earth, they tend to look similar for most of their lives, which makes determining their age more difficult. But it is still possible.

Scientists mostly focus on clusters of stars to discern the age of each of them. By knowing that a close cluster was made out of the same material at around the same time, they can compare each star’s differing masses and luminosities to come to an accurate estimate. This is the simplest scenario, but when a star isn’t in a cluster, it’s not quite so easy. Expert astronomers can garner some indication with main-sequence stars - again by analysing mass and luminosity - but otherwise there’s gyrochronology, which entails working out a star’s age by its colour and spin. Inaccuracies are common with this particular method, however, as even slight uncertainties can translate to billions of miscalculated years. We are, at least, reasonably clear on our own star, mostly because it’s so close to us (comparatively speaking). Among other ways, we’ve learned the age of the sun - which is some 4.6 billion years’ old - by closely analysing radioactive elements found in meteorites elsewhere in the solar system.

The oldest known star with a reliably accurate age is officially known as HD 140283, but has also been dubbed “The Methuselah Star.” Astronomers have known about Methuselah for more than a century, with it thought that it was born into a smaller dwarf galaxy that, billions of years ago, was consumed by the Milky Way. Currently, it’s “only” 190 light-years away from us - an unreachable distance, but relatively close in a universe which is more than 90 billion lightyears across.

But here’s the weird part. Research originally aged the Methuselah Star at around 16 billion years’ old - far older than the universe itself. Clearly, then, this star presents a problem… especially as even recent research aiming to solve the problem eventually revised the estimated age to around 14.5 billion years old - 1.5 billion years younger, but still older than the universe as a whole. The current accepted figure does have a margin of error of around 800 million years, meaning the lowest boundary puts Methuselah at roughly 13.7 billion years’ old… but that still only just gets it within the general estimates for the age of literally everything else. So, is it possible that this star, of all the stars, actually is older than the universe itself?

The shortest and most conventional answer is; no! It’s impossible for a star or anything else to be older than the universe it’s part of. According to most popular theories, the Big Bang was responsible for the creation of matter in the first place; and nothing physical can have existed without matter, before this event. The universe is thought to have been completely empty before the Big Bang happened, with all mass and energy concentrated into one point. But this means that there surely has to be an error somewhere - either we’re wrong about the age of the star, or we’re wrong about the age of the universe. But we are fairly certain about the 13.8 billion-year age of the universe… No, we don’t know the precise age, but we do have a solid and accepted ballpark figure. So, we must be wrong about the star’s age?

Unfortunately, though, in this case we are also fairly certain about the age of Methuselah. It, in particular, has been measured as precisely as currently possible, combining data on its luminosity, composition, and spin. The relatively manageable 190-light-year distance between us and it is what makes scientists especially sure about its age… as we have a clear and detailed view of Methuselah as it orbits. Ultimately, we can reliably predict that it’s very close to ending its main sequence life, and that it will soon transition into a red giant.

Despite how difficult it is to discern the age of stars, we can’t immediately find anything wrong with our aging techniques here. Instead, it could be that some strange occurrence in the past is only making it seem as though this star is especially ancient. Theories abound on how or why it should look older than it actually is. Theoretical astrophysicist Ethan Siegel argues that Methuselah could have been born as a higher-mass star to begin with, before quickly losing mass somehow… theoretically leaving it with the appearance and composition of a much older star. Or it could have in some way absorbed material at some time in its history… again causing Methuselah to appear more developed (and older) than it is.

Our best guess is that there are (or were) a variety of conditions like these which, combined, serve to lower this particular star’s age to less than what it impossibly appears to be. Newer theories about stellar evolution also suggest that helium can diffuse deeper into the core, for example; a cosmological tweak which would potentially shorten a star’s lifespan - making it younger than what we’d currently predict. Perhaps this is what’s happening in Methuselah?

According to Penn State University’s Howard Bond, who worked with NASA in 2013 to revise Methuselah’s age, the star has a higher than first thought oxygen-to-iron ratio, too, which could also effectively shorten the time it’s been around. In fact, it’s thought that further observations of the oxygen abundance in Methuselah could lower its age even further… because higher levels of oxygen would imply that it was actually born in an even later era of the universe; a time comfortably after the Big Bang when the universe itself was also richer in oxygen.

So, we do have the beginnings of potential answers, although we’re still some distance away from a conclusive solution. For now, we have to assume that our margin of error - the 800 million-year uncertainty on Methuselah’s current accepted age of 14.5 billion years - is correct, and that the star just so happens to be younger than it seems. If that’s true, then it’s old, yes, but not quite as old as the universe itself. If not, then our understanding of the universe could be fundamentally wrong; which would be a much larger problem to encompass more than just the life of one star!

Although paradoxes like these cause cosmological headaches, problems like the age of Methuselah aren’t necessarily a bad thing. Instead, they force scientists to reconsider past assumptions and to refine the methods used to make sense of the world around us. Whatever the cause for this particular anomaly, Methuselah is something which simply refuses to conform! And that’s why this star could be older than the universe.