Humans made of matter from distant galaxies: study

Humans may be made of particles that travelled from distant galaxies, say scientists who found that more than half of the matter in the Milky Way was transported through intergalactic winds.
Researchers from Northwestern University in the US, using supercomputer simulations, found a major and unexpected new mode for how galaxies, including our own Milky Way, acquired their matter: intergalactic transfer.
The simulations show that supernova explosions eject copious amounts of gas from galaxies, which causes atoms to be transported from one galaxy to another via powerful galactic winds, researchers said.
Intergalactic transfer is a newly identified phenomenon, which simulations indicate will be critical for understanding how galaxies evolve.

"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 Angles-Alcazar, a postdoctoral fellow at Northwestern University.
"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," Angles-Alcazar said.

Galaxies are far apart from each other, so even though galactic winds propagate at several hundred kilometres per second, this process occurred over several billion years.

Researchers developed sophisticated numerical simulations that produced realistic 3D models of galaxies, following a galaxy's formation from just after the Big Bang to the present day.
They then developed state-of-the-art algorithms to mine this wealth of data and quantify how galaxies acquire matter from the universe.
"This study transforms our understanding of how galaxies formed from the Big Bang," said Claude-Andre Faucher-Giguere, professor at Northwestern University.
"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," he said.

By tracking in detail the complex flows of matter in the simulations, the team found that gas flows from smaller galaxies to larger galaxies, such as the Milky Way, where the gas forms stars.
This transfer of mass through galactic winds can account for up to 50 per cent of matter in the larger galaxies.
"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," said Angles-Alcazar.
"Our origins are much less local than we previously thought. This study gives us a sense of how things around us are connected to distant objects in the sky," Giguere said.

The study was published in the journal Monthly Notices of the Royal Astronomical Society.