"The older you get, the more you realize that the way you look is a reflection of how you treat yourself." -Hope Davis

Age may be just a number, but in cosmic terms, there are some rules it’s pretty important to obey. It should be impossible to have a complex creature that’s older than the planets; a rocky planet that predates the stars; or a star that’s older than the Universe itself. With a figure of 13.8 billion years, we’ve arrived at an incredibly accurate estimate for the age of the Universe since the Big Bang from a slew of different sources, and so nothing should be older than that.

Looking back a variety of distances corresponds to a variety of times since the Big Bang. However, if the Big Bang occurred 13.8 billion years ago, then the oldest stars must be no older than that figure. Image credit: NASA, ESA, and A. Feild (STScI).

When we survey the stars in the Milky Way, however, we find not only many that are older than 12 billion years, but a few that may predate the galaxy itself, hailing from just 300 million years after the Big Bang. In one alarming find, though, there’s a particular star, HD 140283, that appears to be 14.5 billion years old. A star older than the Universe itself is impossible, of course, but there’s got to be a reason for this discrepancy.

This is a Digitized Sky Survey image of the oldest star with a well-determined age in our galaxy. The ageing star, catalogued as HD 140283, lies over 190 light-years away. The NASA/ESA Hubble Space Telescope was used to narrow the measurement uncertainty on the star's distance, and this helped to refine the calculation of a more precise age of 14.5 billion years (plus or minus 800 million years). Image credit: Digitized Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO.

Is the age of the star wrong? Our estimate for the age of the Universe? Or is something else afoot? Regardless, there’s more to learn, and a compelling cosmic puzzle to investigate here.