Ultra-rare star reveals traces of Universe's first light

In the distant past, spanning billions of years, the Universe lingered in complete darkness. Not until the first celestial bodies emerged did space become clear and light began to spread.

Interestingly, none of those initial stars, called Population III, has ever been observed.

Currently, astronomers have discovered the next best thing: A star so deficient in chemical elements that it must have formed following closely behind the generation that altered the Universe.

These stars are classified as Population II stars, and they are extremely uncommon. This particular star, known as PicII-503, is notably intriguing – it's the star with the lowest iron content ever detected beyond the edges of the Milky Way, residing in an ancient dwarf galaxy over 10 billion years in age.

"Identifying a star that unmistakably contains the heavy elements from the first stars was something we thought might be just within reach, given how rare these objects are," explains astrophysicist Anirudh Chiti from Stanford University.

"With the most minimal iron content ever found in any ultra-faint dwarf galaxy, PicII-503 offers insight into the original element creation within a primordial system that is without equal."

The Universe lacks a central point, so if the earliest stars were still around, they'd likely be evenly scattered throughout space-time.

However, researchers believe that Population III stars were significantly larger than any of today's stars, leading to very short existences for them.

In the early days of the Universe, choices for star-forming materials were minimal, essentially just hydrogen and helium.

But once stars came into existence, they began fusing atoms together at their cores to generate elements up to the weight of iron.

When stars exhausted their fusion materials, they detonated dramatically, spreading those fused elements into the cosmos. Supernova eruptions are ferocious kilns where elements beyond iron in weight are created.

These heavier elements—termed 'metals' by astronomers—then blend into the gas that will birth the subsequent generation of stars, and this cycle continues. 

The younger a star, the richer its metal composition. Conversely, the older a star is, the fewer metals it tends to contain.

PicII-503 resides roughly 150,000 light-years from us, in a diminutive, faint dwarf galaxy known as Pictor II, which circles the Milky Way. 

Pictor II is identified as a fossil galaxy—its stars are ancient, and it hasn't experienced star formation or absorbed new stars for billions of years.