Sat, Jan 05, 2019 - Page 7 News List

Milky Way headed to galactic collision, astronomers find

The Guardian

Astronomers have said that a nearby galaxy will slam into the Milky Way and could knock our solar system far into the cosmic void.

The discovery was made after scientists ran computer simulations on the movement of the Large Magellanic Cloud (LMC), one of the many satellite galaxies that orbits the Milky Way. Rather than circling at a safe distance, or breaking free of the Milky Way’s gravitational pull, the researchers found the LMC is destined to clatter into the galaxy we call home.

At the moment, the LMC is estimated to be about 163,000 light years from the Milky Way and speeding away at more than 400 kilometers per second.

However, simulations by astrophysicists at Durham University show that the LMC would eventually slow down and turn back toward us, ultimately smashing into the Milky Way in about 2.5 billion years’ time.

While individual stars and planets are unlikely to collide, the arrival of a galaxy weighing as much as 250 billion suns would still wreak havoc.

“The whole of the Milky Way will be shaken and the entire solar system could be ejected into outer space,” said Carlos Frenk, director of the Institute for Computational Cosmology at Durham. “If that happens, I don’t see how our descendants, if we have any, will be able to withstand it.”

It is not all doom and gloom though. The odds of the collision casting the solar system into a more rarefied region of space are slim, the researchers wrote in a report in the Monthly Notices of the Royal Astronomical Society.

Marius Cautun, the first author on the paper, said the chances of cosmic exile were about 1 percent to 3 percent.

In one sense, the collision with the LMC is long overdue. The Milky Way is an oddball among spiral galaxies. The halo of stars that surrounds its galactic disc contains far fewer stars than comparable galaxies, while The supermassive black hole at the Milky Way’s center is one-tenth as massive as those found at the hearts of similar galaxies.

A galactic merger would change this.

“Once the LMC gets gobbled up by the Milky Way, our galaxy will become a beautiful, normal spiral,” Frenk said. “Most of the halo will become stars from the LMC and the black hole will gorge on this sudden unexpected abundance of fuel and it will go berserk.”

The LMC holds vast amounts of gas that will be devoured by the supermassive black hole until it reaches up to 10 times its present mass. As it feeds, the black hole will become “active” and send out powerful jets of high-energy radiation. While intense beams of gamma radiation could spark mass extinctions, the radiation driven by the black hole is unlikely to pose a threat to any life that might exist on Earth, the authors wrote.

In the past, astronomers who concerned themselves with the demise of the Milky Way focused their attention on the upcoming collision with the Andromeda galaxy. At five times the mass of the LMC, Andromeda could completely destroy the Milky Way if the two were to collide.

That cosmic catastrophe is expected in about 4 billion years’ time.

However, the merger with the LMC could postpone the cataclysm, Frenk said.

“One of the by-products of the collision with the LMC is it will delay armageddon,” he said. “It will move the Milky Way a bit and that may buy us a couple of billion years.”

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