This new discovery is centered around a star in our very own Milky Way. It’s called SMSS J160540.18-144323.1 (but we’re just going to call it ‘Bob’ for the purposes of this article.) Bob is about 35,000 light years away. Bob bears the marks of its very early ancestor, one of the Universe’s first generation of stars that was extremely low in metal and that lived in the Universe’s early days.

Astronomers talk about stars in terms of metallicity. In astronomical terms, a metal is any element heavier than hydrogen, helium, and lithium, all of which were created in the Big Bang. Early stars contained only those three light elements because the other heavier elements hadn’t been created yet. Elements heavier than the first three were created in successive generations of stars.

This first generation of metal-free stars is called Population III. They are largely hypothetical, but our knowledge of astrophysics says they have to have existed. Population III stars were extremely massive, hot stars that didn’t last long. The only way we can learn anything about them is to study the stars that formed out of the material they ejected when they died. It’s kind of like forensic astrophysics.