Astronomers have discovered one of the oldest and most primitive stars ever found, offering a rare glimpse into the early universe.
The star, named PicII-503, lies in a tiny, faint galaxy called Pictor II, more than 10 billion years old.
What makes this discovery remarkable is that the star still carries the chemical “fingerprints” of the very first stars that formed after the Big Bang.
PicII-503 is extremely poor in iron—containing less than one forty-thousandth of the amount found in our Sun.
At the same time, it has an unusually high amount of carbon.
This unusual combination makes it one of the clearest examples of a second-generation star, formed shortly after the very first stars in the universe exploded.
The first stars were made mostly of hydrogen and helium. Inside their cores, they created heavier elements such as carbon and iron.
When these stars ended their lives in powerful explosions called supernovae, they released these elements into space. New stars then formed from this enriched material.
Second-generation stars like PicII-503 act like time capsules, preserving information about those earliest cosmic events.
The discovery was led by astronomer Anirudh Chiti of Stanford University and published in Nature Astronomy.
The team used data from several powerful telescopes, including the Dark Energy Camera in Chile, as part of a survey designed to find the oldest stars in our galaxy and nearby dwarf galaxies.
Finding such a star is extremely difficult because these ancient objects are incredibly rare. Among hundreds of stars in the Pictor II galaxy, PicII-503 stood out as unusually low in heavy elements. Follow-up observations confirmed that it has the lowest iron levels ever measured in a star outside the Milky Way.
One of the most exciting aspects of this discovery is the star’s high carbon content. Its carbon-to-iron ratio is more than 1,500 times higher than that of the Sun. This matches a mysterious group of stars found in the outer regions of the Milky Way, known as carbon-enhanced metal-poor stars. Until now, scientists were unsure where these stars came from.
PicII-503 provides a strong clue. It supports the idea that such stars formed from low-energy supernova explosions. In these events, heavier elements like iron fall back into the collapsed core, while lighter elements like carbon are released into space. This material then forms new stars with high carbon but very little iron.
Because Pictor II is such a small galaxy, only low-energy explosions could have kept these elements from escaping into space. This makes PicII-503 a perfect example of how early stars enriched their surroundings.
This discovery helps connect the history of small ancient galaxies with the stars we see today in the Milky Way. It also offers valuable insight into how the first elements were created, setting the stage for planets, chemistry, and eventually life.
