- Simulations reveal that up to half the material in our galaxy arrived from smaller galactic neighbours, as a result of powerful supernova explosions
The dramatic conclusion emerges from computer simulations that reveal how galaxies grow over aeons by absorbing huge amounts of material that is blasted out of neighbouring galaxies when stars explode at the end of their lives.
Powerful supernova explosions can fling trillions of tonnes of atoms into space with such ferocity that they escape their home galaxy’s gravitational pull and fall towards larger neighbours in enormous clouds that travel at hundreds of kilometres per second.
Astronomers have long known that elements forged in stars can travel from one galaxy to another, but the latest research is the first to reveal that up to half of the material in the Milky Way and similar-sized galaxies can arrive from smaller galactic neighbours.
Much of the hydrogen and helium that falls into galaxies forms new stars, while heavier elements, themselves created in stars and dispersed in the violent detonations, become the raw material for building comets and asteroids, planets and life.
“Science is very useful for finding our place in the universe,” said Daniel Anglés-Alcázar, an astronomer at Northwestern University in Evanston, Illinois. “In some sense we are extragalactic visitors or immigrants in what we think of as our galaxy.”
|Animation of gas flows during Milky Way-like galaxy formation|
“The surprising thing is that galactic winds contribute significantly more material than we thought,” said Anglés-Alcázar. “In terms of research in galaxy evolution, we’re very excited about these results. It’s a new mode of galaxy growth we’ve not considered before.” The simulations showed that elements carried on intergalactic winds could travel a million light years before settling in a new galaxy, according to a report in the Monthly Notices of the Royal Astronomical Society.
Claude-André Faucher-Giguère, another astronomer on the team, said that before their simulations, galaxies were thought to grow primarily by absorbing material left over from the big bang. “What we did not anticipate, and what’s the big surprise, is that about half of the atoms that end up in Milky Way-like galaxies come from other galaxies,” he said. “It gives us a sense of how we can come from very far corners of the universe.”
|This image shows M81 (bottom right) and M82 (upper left), a pair of nearby galaxies where “intergalactic transfer” may be happening. Gas ejected by supernova explosions in M82 can travel through space and eventually contribute to the growth of M81|
The simulations show that more powerful intergalactic winds flow from bigger galaxies, because there are home to more exploding stars, but also because the material has to be moving faster to escape the galaxy’s gravitational pull. Plenty of material does not reach a high enough speed and simply falls back into the galaxy where the supernova occurred.
“Our origins are much less local than we thought,” said Faucher-Giguère. “This study gives us a sense of how things around us are connected to distant objects in the sky.”