Astronomy
The Chemical Evolution of Galaxies Over Cosmic Time
Quick fact
The first generations of stars were almost pure hydrogen and helium; today's galaxies are so enriched that the Sun contains more than 70 elements heavier than helium, all synthesized by earlier stars.
Why this is interesting
Every atom of gold in your jewellery was forged inside a long-dead star and then spread across the galaxy. But how did those metals get there, and why does the galaxy's chemistry change over time?