Simulations reveal that up to half the material in our galaxy arrived from smaller galactic neighbours, as a result of powerful supernova explosions

Nearly half of the atoms that make up our bodies may have formed beyond the Milky Way and travelled to the solar system on intergalactic winds driven by giant exploding stars, astronomers claim.

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.

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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.

Play Video 1:10 Animation of gas flows during Milky Way-like galaxy formation – video

“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.”

The researchers ran supercomputer simulations to watch what happened as galaxies evolved over billions of years. They noticed that as stars exploded in smaller galaxies, the blasts ejected clouds of elements that fell into neighbouring, larger galaxies. The Milky Way absorbs about one sun’s-worth of extragalactic material every year.

“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.

Facebook Twitter Pinterest 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. Photograph: Fred Herrmann, 2014

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.”



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The scientists used computer models that created detailed 3D models of galaxies that they could watch evolve in a dramatically speeded-up form from the moment they were born to the present day. The animations can show whether stars in a galaxy formed from material already in the galaxy, or from huge clouds of gas that fell in from neighbouring galaxies.

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.”