Milky way to face a one-two punch of galaxy collisions


Picture of a web of blue threads, representing dark matter, and orange galaxies that form along them.
Increase / A simulation of galaxies forming in the early Universe. By chance, some of them experience a story similar to the Milky Way.

If our knowledge of galaxy structures is limited to the Milky Way, we'd get a lot of things wrong. The Milky Way, it turns out, is unusual. It got a smaller central black hole than its other galaxies; Its halo is also smaller and contains less of the highest elements. Luckily, we've seen enough other galaxies knowing that ours is a bit of an oddball. What is less clear is why.

Luckily, a recent study gives a likely answer: compared to most galaxies, the Milky Way has a very quiet 10 billion years or so. But the new study suggests we are coming to an end only a few billion years ago. A collision with a closer cherry galaxy should turn the Milky Way into something more typical-just in time for Andromeda Smack into it.


The researchers behind the new work of the UK's Durham University are not looking to solve the mystery of the Milky Way look so unusual. Instead, they are intrigued by fresh estimates suggesting one of its satellite galaxies might be significantly more massive than thought. A variety of analyzes have suggested that the Large Magellanic Cloud has more dark matter than the number of stars it suggests. (The stellar load is estimated at only five percent of the Milky Way.)

Using several updated values, researchers are simulating the local group of galaxies, including Milky Way, Andromeda, and the Magellanic Cloud. While the large Magellanic Cloud is now moving away from our galaxy, its simulation suggests that it will gradually bring it back to us. And, just under 3 billion years ago, it will end up merging with the Milky Way.

That's about a billion years before the Andromeda Galaxy (which is more like the Milky Way) was set to run in our head-on. But the interactions between the Milky Way and the great Magellanic Cloud will mean that the Milky Way will not be complete where we would be expected at that time. As a result, the Andromeda Milky Way broke a billion years later than expected, and there will be something oblique.


So what is the Milky Way-Large Magellanic Cloud Smash product? Normally, the way to handle that question would be to observe a model of the collision with the actual conditions we observe now. But the researchers are a few different routes, taking advantage of a system that, incidentally, has run a multiple model of similar collisions. The EAGLE project starts out with the conditions for the formation of the Cosmic Microwave background, and it simulates the evolution of the universe over billions of years that follow. EAGLE covers a band that is large enough to fit around 10,000 galaxies, and at least some of them under collisions that look like a single we recognize the Milky Way to experience.

One thing that is similar to EAGLE is that the unusual properties of the Milky Way-small black hole and halo, a metal-low halo-is the product of a relatively collision history. In most, the galaxies may have experienced a couple of collisions with very little dwarf galaxies over the last 10 billion years or so. Conveniently, that's consistent with data from the Gaia mission, as tracks from the Star indicate the Milky Way's last major collision was at least 8 billion years ago.

A collision with the large Magellanic Cloud would, in essence, fix all this. It would make disturbances in the heart of the Milky Way, which would strip some momentum out of the gas, allowing it to fall inward to the center, feeding the black hole there. Most similar collisions in the gum simulation saw central black holes increase by at least 2.5. (Many of them also resulted in a strong bleaching and jet formation in the black hole, creating an active galactic nucleus.)

About 20 percent of the large Magellanic Cloud would end up being ejected into an intergalactic spot, and a few of the milky way parts would be. But many more stars from the center of the Milky Way end up being ejected into the halo. The center of the Milky Way is rich in higher elements, and the process makes the Milky Way look more typical in that regard. The combination of the Galaxy Center and the large Magellanic Cloud stripped stars also increases the visibility of the halo, handling as well.

While none of the starting conditions match those of the Local Group of Galaxies, Eagle Simulation offers a range of possibilities for the future of the Milky Way. As such, we probably still want to build a model that runs ahead of current conditions. Afterwards, all we have to do is wait about three billion years to see how the model is.

Monthly notices from the Royal Astronomical Society, 2019. DOI: 10.1093 / mnras / sty3084 (about dos).

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