How can 'HD 140283' be older than the universe?
Scientists have known about the star HD 140283, informally nicknamed the Methuselah star, for more than 100 years, since it cruises across the sky at a relatively rapid clip. The star moves at about 800,000 mph (1.3 million km/h) and travels the width of the full moon in the sky every 1,500 years or so, researchers said. Its apparent magnitude is 7.223.
Previous research had estimated that the Milky Way galaxy's so-called
"Methuselah star" is up to 16 billion years old. That's a problem,
since most researchers agree that the Big Bang that created the
universe occurred about 13.8 billion years ago.
Later estimates show that the star could be as old as 14.5 billion years (± 0.8 billion years), which is still it older than the universe's calculated age of about 13.8 billion years. This is an obvious dilemma.
How can a star be older than the universe itself?
Just to clarify, it's obviously not older than the universe. Rather, one or both of our estimates are off, as is discussed in the answers below.
A very good question. If you look at the "age of universe" entry in wikipedia, it also mentions that those "older than universe" stars were a real bad problem for the finite age universe models. If further refinements in either the star/universe age occur in future, it is very possible that this problem is resurrecting again and the current models are invalidated.
It seems to me (though I'm not an expert on how stellar age is determined), but if a star loses mass, perhaps by orbiting a white dwarf that star would appear older than it is, and the opposite, if a star accrues mass, it will appear younger than it really is. A star that orbits a white dwarf, loses mass to it and, that white dwarf goes nova, might explain a star that appears older than the universe, but, just speculating.
It's not - the current age is an estimate. The discrepancy comes from astronomer's attempts to fully and correctly measure aspects of the star, particularly its distance. From the NASA page:
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.
Currently, if you take the uncertainty into account, the current estimate for the star's age is 14.5 +/- 0.8 billion years or between 15.3 and 13.7 billion years - the latter end of the estimate overlaps with the current model of the age of the Universe - so a more correct way of describing this age is that HD 140283 is at least 13.7 billion years old by this estimation.
Another paper based on this star in Nature - "Nearby star is almost as old as the Universe", a team has narrowed down the age to 13.9 +/- 0.7 billion years, stating that:
Taking into account that experimental error, the age does not conflict with the age of the Universe, 13.77 billion years.
more concisely stating that
The star's age is therefore at least 13.2 billion years
No doubt further work is being performed to further refine the age of the star.
An interesting follow up question would be how the star formed so early. As far as I know dust is necessary for smaller stars to be formed. And that must have been rare to say the least.
In this case I'd say it's important to note that the "14.5 +/- 0.8" billion year and "13.9 +/- 0.7 billion years" estimates stated are (usually, I'm finding it hard to find the specifics in these papers) the 95% confidence intervals, i.e. the bounds between which it is 95% likely that the true value lies. This means that there is a 5% chance it lies outside these. which is small but non-negligible. (Maybe this isn't how it works in astronomy?? Correct me if I'm wrong!)
@HughNolan that occurred to me as well - that's why I put emphasis on 'in this estimation' - but the articles speak with a significant degree of confidence - as David Hammen says in his excellent answer, the astronomers tend to use at least 3 sigma - 99.7% certainty.
Ah doh that's what you get for commenting on one answer before you read them all! Thanks Doc.
And no doubt we can hope to see improvements in research methodology come out of this star, given that current research estimates place it outside the lifetime of the universe.
What is the maximum possible age of a star? The age of the universe is 13.799±0.021 Gy. The first stars formed at roughly t₀ + 0.2Gy, so we're down to about 13.58Gy. HD140283 is 13.9±0.7 Gy. So yes, it fits, but still with a *rather significant* overlap between those two intervals. This is certainly not enough to just dismiss the null hypothesis like that, in any field. The authors' conclusion that the star's age "does not conflict with the age of the universe" is therefore non sequitur. In any case, that star is quite possibly a first generation star; extremely interesting, that's for sure!
@RodyOldenhuis Given that it has some iron and other metals in its spectra, it is not a first generation star. More metal-poor objects have been found. The first metal-producing stars were likely very massive, extremely short-lived and formed about 200 Myr after the big bang.
Later estimates shows that the star could be as old as 14.5 billion years (± 0.8 billion years), which is still it older than the universe's calculated age of about 13.8 billion years, an obvious dilemma.
There is no dilemma. That ± 0.8 billion years is important. Subtract 0.8 billion years from that 14.5 billion year figure (later revised to 14.27 billion years) and you get 13.7 billion years, less than the age of the universe. Also note that that 0.8 billion years uncertainty is the standard error, or roughly one standard deviation. That revised age of 14.27 billion years makes the dilemma essentially non-existent. That's older than the estimate age of the universe by 0.4 to 0.5 million years, and this is not significant even at the one sigma level.
Particle physicists generally use the five sigma level as distinguishing between "almost certain" and "maybe" (and particle physicists are reluctant to publish "maybes"). Astronomers generally use a three sigma level. Even social scientists would balk at a deviation that is less than one sigma as being significant.
You say that "astronomers generally use a three sigma level" but also say that the "0.8 billion years uncertainty is ... roughly one standard deviation". That 0.8 Gyr number comes from this paper, so ... is that one standard deviation or three?
Usually astronomers quote 1 sigma errors, so David is saying a 2 or 3 sigma deviation is not uncommon. Also, astronomers often leave off systematic errors because they usually do not know just how big they are. Are all stellar ages off because we have left out something in the theory of stars? For instance, effects of high rotation or strong internal magnetic fields, etc. Same for the age of the universe.