Half of Everything in the Milky Way—Including Humans—Comes From Far Flung Galaxies

A laser beam pointed at the center of the Milky Way.
A laser beam from the ESO’s Paranal Observatory pointed at the center of the Milky Way. ESO/Y. Beletsky

Up to half of the Milky Way is made up of matter that came from distant galaxies, having been ejected from its home during supernova explosions. This means everything in our home galaxy, including humans, is, in part, of intergalactic origin.

Using supercomputer simulations, scientists were able to track how, over time, matter had been moved around the universe via a process called “intergalactic transfer.” The team, from Northwestern University, say their findings have important implications for galaxy evolution, providing an insight into how matter becomes distributed throughout the cosmos.

In the study, published in the Monthly Notices of the Royal Astronomical Society, researchers developed numerical simulations that produced 3D models of galaxies—showing how they changed from when they formed, just after the Big Bang, to present day.

These supercomputer simulations let the team see how galaxies acquire matter over time, and they found that when stars explode, they eject huge amounts of gas from their host galaxies. This matter can then be sent into other galaxies along powerful galactic winds.

"Given how much of the matter out of which we formed may have come from other galaxies, we could consider ourselves space travelers or extragalactic immigrants,” study leader Daniel Anglés-Alcázar said in a statement. "It is likely that much of the Milky Way's matter was in other galaxies before it was kicked out by a powerful wind, traveled across intergalactic space and eventually found its new home in the Milky Way."

This newly-identified phenomenon of intergalactic transfer, the team say, will be hugely important in understanding galaxy evolution. Their findings showed that up to 50 percent of the matter in larger galaxies, including the Milky Way, is made from matter that has been transferred via galactic winds.

“This study transforms our understanding of how galaxies formed from the Big Bang,” said study co-author Faucher-Giguère. “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,”

Researchers now plan to test their supercomputer predictions by collaborating with observational astronomers using space and ground-based telescopes.