We're all made of stardust... from a galaxy far, far away

The idea of finding extraterrestrial life on another planet, in a distant solar system or in a far away galaxy has long captured the imagination of humans.

But now scientists have discovered that we are all actually partalien.

According to US astrophysicists up to half of all matter in our Milky Way galaxy comes from distant areas in space, driven here on strong interstellar winds, created when stars explode in spectacular supernovae.

When Carl Sagan, the late American astrophysicist, made his well-known comment that 'we are made of star-stuff' he meant that all the elements on Earth were once produced in the heart of stars before being flung out into the universe in giant explosions.

But it was previously thought that those explosions occurred within Milky Way. Now scientists suspect each one of us is made, in part, from matter created when far away suns exploded in distant galaxies.

"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," said Dr Daniel Angl��s-Alc��zar, of Northwestern University's astrophysics center, who led the study.

"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.

In first-of-its-kind analysis, scientists used computer simulations to recreate 3-D models of galaxies, following their formation from just after the Big Bang to the present day. The simulations show that supernovae explosions eject huge amounts of gas from galaxies, which causes atoms to be transported from one galaxy to another via powerful galactic winds.

"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," added Angl��s-Alc��zar, the study's corresponding author.

Although the atoms travel at great speeds, galaxies are so far apart from each other, that the the process still takes several billion years.

But the team found that the transfer of mass through galactic winds can account for up to 50 percent of matter in the larger galaxies.

"This study transforms our understanding of how galaxies formed from the Big Bang," said Assistant Professor Claude-Andr�� Faucher-Gigu��re of the Weinberg College of Arts and Science, in Illinois.

"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.

"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."

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, but the new study shows matter moved between them.

The new research was published in the Monthly Notices of the Royal Astronomical Society.

(China Daily 08/12/2017 page23)