New research suggests that up to half of the matter in the Milky Way may come from galaxies far, far away. Scientists say this could mean that each of us is made, in part, from extragalactic matter.
Using supercomputer simulations, researchers found a major and unexpected new mode for how galaxies, including our own Milky Way, acquired their matter: intergalactic transfer.
“This study transforms our understanding of how galaxies formed from the Big Bang…”
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. 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 travelers or extragalactic immigrants,” says Daniel Anglés-Alcázar, a postdoctoral fellow at the CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics) 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, traveled across intergalactic space and eventually found its new home in the Milky Way,” he says.
Galaxies are far apart from each other, so even though galactic winds propagate at several hundred kilometers per second, the process occurred over several billion years.
“This study transforms our understanding of how galaxies formed from the Big Bang,” says Claude-André Faucher-Giguère, an assistant professor of physics and astronomy and coauthor of the study that appears in the Monthly Notices of the Royal Astronomical Society.
“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 and colleagues developed numerical simulations that produced realistic 3D models of galaxies, following formation from just after the Big Bang to the present day. Anglés-Alcázar then developed algorithms to mine the data and quantify how galaxies acquire matter from the universe.
By tracking in detail the complex flows of matter in the simulations, researchers 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 percent 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,” says Anglés-Alcázar, the study’s corresponding author.
“Our origins are much less local than we previously thought.”
In a galaxy, stars are bound together: a large collection of stars orbiting a common center of mass. After the Big Bang 14 billion years ago, the universe was filled with a uniform gas—no stars, no galaxies. But there were tiny perturbations in the gas, and these started to grow by force of gravity, eventually forming stars and galaxies. After galaxies formed, each had its own identity.
“Our origins are much less local than we previously thought,” Faucher-Giguère says. “This study gives us a sense of how things around us are connected to distant objects in the sky.”
The findings open a new line of research in understanding galaxy formation and opens the door to test the prediction of intergalactic transfer. The team plans to collaborate with observational astronomers who are working with the Hubble Space Telescope and ground-based observatories to test the simulation predictions.