On Earth, recycling signs are everywhere, urging us to save our planet while we still can. In space, some galaxies apparently recycle without any signs to remind them.
At least one galaxy isn’t letting materials that could form potential stars go to waste. An international team of scientists led by astronomers Shiwu Zhang and Zheng Cai of Tsinghua University in China has found evidence that an enormous galaxy within an even larger nebula called MAMMOTH-1 is drawing in material from its surroundings to spawn new stars.
However, that material contains elements formed by past supernovae that are thought to have happened within galaxies, with the elements they created being flung into the nebula by the galaxy’s central black hole. This means that the galaxy, which the research team refers to as G-2, is now forming stars from material that had previously been hurled out into intergalactic space by a galaxy—either itself or another nearby.
“Simulations have shown that recycling of gas—the re-accretion of gas that was previously ejected from a galaxy—could sustain star formation in the early Universe,” the researchers said in a study recently published in Science.
Recycling, stellar style
Stars fuel themselves with the energy that comes out of nuclear fusion, smashing atoms of hydrogen together into helium. Only massive stars (8 solar masses or more) go supernova, after they have fused all their hydrogen into helium. Gravity then causes the collapse of a massive star, which soon bursts into an extremely luminous explosion that blows away its outer layers. Supernovas cause shockwaves that can generate enough power to fuse new atomic nuclei—even metals such as iron.
But one star’s afterlife can mean another’s birth. After the explosion, the remains of the dead star scatter into space, swirling into the interstellar medium. While some of this material is forever lost to space, stars can still potentially incorporate some of the material created in the supernova.