"We are all made of stars" used to sing Moby in 2002 and though science has known it for a while, a new study went as far as to claim half of the atoms making up everything around us, and in us, may have formed beyond the Milky Way.

Using computer simulations, the research team at Northwestern University revealed how galaxies, including our own Milky Way, grow their matter through 'intergalactic transfer', that is by acquiring huge amounts of material that is ejected after supernova explosions from neighbouring galaxies.

"Given how much of the matter out of which we formed may have come from other galaxies, we could consider ourselves space travellers or extragalactic immigrants," said Daniel Anglés-Alcázar, a postdoctoral fellow in Northwestern's astrophysics center, CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics), who led the study.

"It is likely that much of the Milky Way's matter was in other galaxies before it was kicked out by a powerful wind, travelled across intergalactic space and eventually found its new home in the Milky Way."

Galactic winds

Powerful galactic winds cause gas blasted out from dying, exploding stars in smaller galaxies to be transported to the Milky Way and similar-sized galaxies. The whole transfer of mass would have taken place over several billion years, according to the study, which was published in the Monthly Notices of the Royal Astronomical Society.

"In our simulations, we were able to trace the origins of stars in Milky Way-like galaxies and determine if the star formed from matter endemic to the galaxy itself or if it formed instead from gas previously contained in another galaxy," Anglés-Alcázar said.

While astronomers knew that elements ejected by supernovae could ferry from one galaxy to another, it was previously thought the galactic winds couldn't be powerful enough to cross such vast distances.

The galactic core of our Milky Way galaxy and the International Space Station, taken on the south Pembrokeshire coastline in Wales. Image: Drew Buckley/REX/Shutterstock

Instead, 3D models of galaxy evolutions showed galactic winds were moving matter faster than previously thought and could transfer about 50% of the matter.

"What this new mode implies is that up to one-half of the atoms around us—including in the solar system, on Earth and in each one of us—comes not from our own galaxy but from other galaxies, up to one million light years away," said Faucher-Giguère, a co-author of the study and assistant professor of physics and astronomy in the Weinberg College of Arts and Sciences.

In a galaxy, stars are bound together, orbiting around a common centre of mass. Following the Big Ben, 14 billion years ago, the universe was filled with a uniform gas. Tiny perturbations in the gas then started to grow by force of gravity, eventually forming stars and galaxies.

"Our origins are much less local than we previously thought," said Faucher-Giguère, a CIERA member. "This study gives us a sense of how things around us are connected to distant objects in the sky."