Astronomical models already showed that galaxies recycle their gases to produce stars with increasingly rich chemistry, but now this process has gained good observational evidence. It’s just that a team of scientists detected for the first time the gas “falling” back into their galaxy after being expelled through supernova explosions.
Galaxies are surrounded by hard-to-detect material like dark matter and gas clouds that help fuel the formation of the next generations of stars. These gases are formed by massive stars that explode in violent supernovae, hurling stellar material with such force that it escapes the galactic disk.
These clouds are rich in heavy metals (i.e., chemical elements other than hydrogen and helium) due to the nuclear fusion of stars — as they live, they fuse elements like carbon and heavier things, until the hydrogen fuel runs out inside, causing explosions.
After the explosion of a supernova, a good part of the gas turns into nebulae, but there are also good amounts that are ejected out of the galaxies, reaching the region known as the galactic halo. Other processes may also contribute, such as the ejection of matter by active supermassive black holes.
The process proposed by the most accepted astronomical models is that these clouds end up falling back into the galactic disks through gravity. Then they compress to form the new generation of stars. In turn, the clouds that produced these stars are chemically richer—and that’s how the chemical composition of galaxies evolves.
Located 11 billion light-years away — three billion years after the Big Bang — within a cluster of young galaxies, a giant nebula called MAMMOTH-1 was found by astronomers accumulating these “recycling” gases. The nebula spans 300,000 light-years and may explain how galaxies manage to form so many new stars despite not having enough material inside.
With the Keck and Subaru telescopes in Hawaii, astronomers collected records of how the nebula feeds on material from the galaxy cluster via at least three outflows of gas. Two of these streams come from a quasar — a galaxy with an active nucleus, that is, emitting radiation formed by the activity of a central supermassive black hole.
The study was published in the journal Science.
