SMSS J031300.36−670839.3 is a star in the Milky Way at a distance of 6,000 ly (1,800 pc) from Earth. With an age of approximately 13.6 billion years, it is one of the oldest stars known. Another star, HD 140283, was considered to be older, but there is uncertainty in values of its age. This makes SM0313 the oldest known star with an accurate determination of its age. The star formed only about 100 million years after the Big Bang and has been shining for 13.6 billion years. The star's very low upper limit of iron of less than one ten-millionth the iron level of the Sun, suggests that it is one of the first Population II stars, formed from a gas cloud enriched by some of the first stars. SMSS J031300.36-670839.3 also has a much higher carbon supply compared to iron, more than a thousand times greater. Apart from hydrogen, which appeared in the Big Bang, the star also contains carbon, magnesium, and calcium, which could have been formed in a low-energy supernova. Methylidyne (CH) is also detected by its absorption line. No oxygen or nitrogen has been detected. The star is a K-class red giant.
NASA/STScI
In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations.
In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926.
Artist's conception of the spiral structure of the Milky Way showing Baade's general population categories. The blue regions in the spiral arms are composed of the younger population I stars, while the yellow stars in the central bulge are the older population II stars. In reality, many population I stars are also found mixed in with the older population II stars.
Population I star Rigel with reflection nebula IC 2118
Artist’s impression of a field of population III stars 100 million years after the Big Bang.
Possible glow of population III stars imaged by NASA's Spitzer Space Telescope
