Here's the Surprising Way the Milky Way Galaxy Got So Massive
New research suggests that more than half of all the matter in our home galaxy — and in our bodies — may have come from distant galaxies.
This image shows a pair of galaxies where "intergalactic transfer" may be occurring. Gas ejected by supernova explosions in M82 (upper left) can travel through space and eventually add to the growth of M81 (bottom right).Fred Herrmann/Northwestern University
Just where did all this matter come from? Surprising new research suggests that half of it originated in distant galaxies— a finding that challenges prevailing theories about how galaxies form and that has scientists rethinking the origins of the atoms in our own bodies.
The finding stems from a series of supercomputer simulations showing that exploding stars known as supernovas spew out vast amounts of gas and that the resulting “galactic winds” blast atoms across intergalactic space from one galaxy to another. The winds speed along at hundreds of kilometers per second — but galaxies are so far apart that even at such stupendous velocities it would have taken billions of years for extragalactic matter to make its way to our galaxy.
Previous research suggested that about 10 percent of the mass in galaxies like the Milky Way came about when one galaxy merged with another, Anglés-Alcázar told NBC News MACH in an email. Finding that the amount of matter contributed by intergalactic winds was so much greater, he added, was “very surprising.”
Dr. Frank van den Bosch, a Yale University astronomer with expertise in galaxy evolution who was not involved in the new research, agreed that the magnitude of the contribution of matter from intergalactic winds was greater than previously thought.
“That is quite extreme,” he said of the finding in an email to MACH. It suggests that galaxies like the Milky Way are closely tied to their “large-scale environment” and thus should not be seen as “island universes,” he added.
Which galaxies in particular sent all this mass our way? Anglés-Alcázar said that while there was no way to know for sure, it was probably a couple of dwarf galaxies known as the Large Magellanic Cloud and the Small Magellanic Cloud. The former is located about 163,000 light-years from our galaxy, the latter about 200,000 light-years away.