A JWST image of the supernova death of a star in the early universe that would have seeded surrounding galaxies with the building blocks for the next generation of stars

Older stars have worked their way through the hydrogen supply in their cores, having already fused it all into helium and then fusing this helium to create even heavier elements, which astronomers call "metals." This means older stars are richer in metals than younger stars, which are still dominated by hydrogen and some helium.

The study team used the JWST to detect specific elements in the older star population of Gz9p3. These target elements included silicon, carbon and iron, the latter of which is the heaviest element that can be synthesized by stars. This means these stars, when they died in supernova explosions, would have enriched the early universe with metals. Much of this metal content would have gone on to become the building blocks of the next generation of stars. 

In addition, the team discovered that the population of old stars in Gz9p3 was much larger than previously suspected. This means that, while astronomers have been aware of this cycle of stellar life and death and the increasing metal enrichment of subsequent generations of stars, the Gz9p3 observations indicate galaxies may have become "chemically mature" faster than had been suspected previously.

"These observations provide evidence of a rapid, efficient build-up of stars and metals in the immediate aftermath of the Big Bang, tied to ongoing galaxy mergers, demonstrating that massive galaxies with several billion stars existed earlier than expected," Boyett wrote. 

A history of violence

Galaxies that sit isolated from their galactic counterparts do form stars, but the process is slow and ends when that galaxy exhausts its reservoir of gas and dust, the materials that form stars.

For galaxies close to each other, the process of star formation can be sped up and even revived after it has drawn to a halt. That's because when these galaxies are drawn together by a mutual gravitational attraction, they collide. The merger then causes an inflow of fresh gas that kickstarts a period of rapid star birth called a "starburst," meaning mergers provide an excellent way for galaxies to rapidly grow their stellar populations.