Is The Milky Way Doomed By Galactic Bombardment?

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As scientists attempt to learn more about how galaxies evolve, an open question has been whether collisions with our dwarf galactic neighbors will one day tear apart the disk of the Milky Way.

That grisly fate is unlikely, a new study now suggests.

While astronomers know that such collisions have probably occurred in the past, the new computer simulations show that instead of destroying a galaxy, these collisions “puff up” a galactic disk, particularly around the edges, and produce structures called stellar rings.

The finding solves two mysteries: the likely fate of the Milky Way at the hands of its satellite galaxies — the most massive of which are the Large and Small Magellanic Clouds — and the origin of its puffy edges, which astronomers have seen elsewhere in the universe and dubbed “flares.”

The mysterious dark matter that makes up most of the universe plays a role, the study found.

Astronomers believe that all galaxies are embedded within massive and extended halos of dark matter, and that most large galaxies lie at the intersections of filaments of dark matter, which form a kind of gigantic web in our universe. Smaller satellite galaxies flow along strands of the web, and get pulled into orbit around large galaxies such as our Milky Way.

Ohio State University astronomer Stelios Kazantzidis and his colleagues performed detailed computer simulations of galaxy formation to determine what would happen if a satellite galaxy — such as the Large Magellanic Cloud and its associated dark matter — collided with a spiral galaxy such as our own.

The researchers considered the impacts of many different smaller galaxies onto a larger, primary disk galaxy. They calculated the likely number of satellites and the orbital paths of those satellites, and then simulated what would happen during collision, including when the dark matter interacted gravitationally with the disk of the spiral galaxy.

The conclusion?  None of the disk galaxies were torn apart.  To the contrary, the primary galaxies gradually disintegrated the in-falling satellites, whose material ultimately became part of the larger galaxy.  The satellites passed through the galactic disk over and over, and on each pass, they would lose some of their mass, a process that would eventually destroy them completely.

Though the primary galaxy survived, it did form flared edges which closely resembled our galaxy’s flared appearance today.

Does that settle the question of the fate of the Milky Way?

Kazantzidis couldn’t offer a 100-percent guarantee.

“We can’t know for sure what’s going to happen to the Milky Way, but we can say that our findings apply to a broad class of galaxies similar to our own,” Kazantzidis said. “Our simulations showed that the satellite galaxy impacts don’t destroy spiral galaxies — they actually drive their evolution, by producing this flared shape and creating stellar rings — spectacular rings of stars that we’ve seen in many spiral galaxies in the universe.”

Source: Ohio State University