The unassuming little speck in the centre of this sky survey image may not look like anything particularly special. But there’s something rather special about it indeed. Because this star is HE1327-2326, and it may just be the oldest known star in our galaxy.
The very first stars in the Universe are practically mythological beasts to modern astronomy. Hypothesised to contain nothing more then the hydrogen, helium and trace amounts of lithium created in the big bang, these stars were what created the very first elements. And they created them rapidly. Known as “Population III”, the very first stars would have grown to titanic sizes, only burning for a few million years, before exploding as supernovae and scattering their ashes far and wide. The Universe itself was essentially a pan full of stellar popcorn waiting to burst. Once those first stars enriched the Universe with the first chemical elements heavier than lithium, they paved the way for the second generation of stars, “Population II” to coalesce from the darkness.
Around 4000 light years away, in the constellation of Hydra, HE1327-2326 is believed to be just such a population II star. With 300000 times less iron than the Sun, HE1327-2326 fits the description of an early population II star very nicely; in the earlier days of the Universe, heavier elements were much scarcer. From the low amount of iron in this star, it’s estimated to be a venerable 13.6 billion years old, nearly as old as the Universe.
HE1327-2326 is only a small star, with a mass a bit lower than that of the Sun. Probably the reason why it’s still burning. There’s a possibility it was once the smaller member of a binary system, which it was likely ejected from long ago. What events this star has seen in its lifetime, we’ll likely never know. While it’s unlikely to have any planets in tow (given that planets need more heavy elements to form than would have been around back when HE1327-2326 was born), but it’s still interesting to wonder…