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Half of Our Atoms May Come From Other Galaxies

According to computer simulations, large galaxies may grow by sucking in matter smaller star clusters expel

The Small Magellanic Cloud, where some of your atoms likely originate (NASA)
smithsonian.com

In the early 1980s, astronomer Carl Sagan famously said during his television show Cosmos: “We are all made of star stuff.”

That’s not just some highfalutin metaphor. In fact, everything in our galaxy is foraged from this stellar material. But a new simulation suggests that it may be coming from much farther than previously thought, reports Aylin Woodward for New ScientistAround half of the matter in the Milky Way could come from other galaxies up to one million light years away, swept along by intergalactic winds.

In the beginning, the universe was full of elements, such as hydrogen and helium. Heavier organic elements like carbon, nitrogen and oxygen were created by fusion of those lighter elements inside the cores of stars some 4.5 billion years ago. When those stars eventually died and exploded as supernovae, their elements were blasted out into space. Now, this latest research, published in the journal Monthly Notices of the Royal Astronomical Societysuggests that this star stuff can travel much farther than expected.

When the star explodes, it charges up streams of charged particles, known as galactic winds, writes Woodward. But it has long been believed that these winds were relatively weak and so material only made an intergalactic hop when particularly large systems go supernova or another galaxy is nearby. Galaxies grew, astronomers believed, by encountering and absorbing clumps of material scattered across the universe by the Big Bang.

“We assumed that the winds were confined to the galaxies they came from—that they could recycle by falling back onto the galaxy that ejected them, but not transfer much mass from one galaxy to another,” study leader Claude-André Faucher-Giguère, researcher at Northwestern University, tells Woodward.

But when Faucher-Giguère and his team ran sophisticated supercomputer simulations of galaxy evolution, Ian Sample reports for The Guardian, they found that the power of exploding supernovae was strong enough to fling matter out of small galaxies. That matter is later attracted by the strong gravity of larger galaxies, like our own Milky Way, which draw in the clouds of space dust.

As Woodward reports, it can take between a few hundred million years and 2 billion years for the debris to make the jump from one galaxy to another. Despite the slow speed, a lot of material makes the trip: Over the life of a large galaxy with 100 billion stars or more, 50 percent of the matter likely comes from these intergalactic sources. According to the simulation, the Milky Way hoovers up about one sun’s worth of intergalactic material each year.

According to Faucher-Giguère, it’s likely the Milky Way is drawing its extra matter from the Large and Small Magellanic Clouds, which are two dwarf galaxies roughly 200,000 light years away that act as satellites of our own galaxy.

The research has the potential to change the way astrophysicists understand the way matter moves through the universe—how it was created and transformed. “It’s one of the holy grails of extra galactic cosmology,” Jessica Werk, an astronomer at the University of Washington, tells Woodward. “Now, we’ve found that half these atoms come from outside our galaxy.”

According to a press release, the researchers hope to next use the Hubble Telescope to see if there is real-world evidence to support the model predicted by their simulations.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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