Astroboffins discover that half of the Milky Way's matter comes from other galaxies

'We could consider ourselves space travelers or extragalactic immigrants'

Up to half the atoms in the stars, planets, moons – and even in us – could come from distant galaxies beyond the Milky Way, according to a new study.

Daniel Anglés-Alcázar, coauthor of a paper to be published in the Monthly Notices of the Royal Astronomical Society and a postdoctoral fellow at Northwestern University in Arizona in the US, said: "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."

By building a computer model of supernovae explosions, the simulations show how troves of material are ejected and swept away to other galaxies by strong winds. The researchers have dubbed the phenomenon "intergalactic transfer."

"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," said Anglés-Alcázar.

Since the distance between galaxies often stretches over many light years, even if the winds whiz by at several hundred kilometers per second, the process of gathering foreign galactic material takes several billion years.

To probe the process of intergalactic transfer, the researchers had to look back in time – to just after the Big Bang. A research team led by Claude-André Faucher-Giguère, co-author of the paper and an astrophysics professor at Northwestern University, developed 3D models of galaxy formation during the early stages of the universe.

They found that gas flows from smaller galaxies to larger galaxies like the Milky Way. The mass transferred from the stream of particles can make up to 50 per cent of matter in the larger galaxies.

"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," Faucher-Giguère said.

The fact that such a significant portion of mass comes from material ejected from other galaxies, which travelled through such vast distances of space to reach the Milky Way, was quite unexpected, Anglés-Alcázar told The Register.

"We plan to explore the implications of our findings for the chemical evolution and structural properties of galaxies, as well as the properties of gas around galaxies. Next steps also include determining observational diagnostics that may help guide future observations with space telescopes such as Hubble, as well as ground-based observatories," Anglés-Alcázar told us.

The study shows that "our origins are much less local than we previously thought," Faucher-Giguère concluded. "This study gives us a sense of how things around us are connected to distant objects in the sky." ®

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