Galaxy 'mega-merger' 10 billion years ago forged Milky Way

The Milky Way Has a Gigantic Skeleton in Its Closet

The Milky Way Has a Gigantic Skeleton in Its Closet

Comparison of distribution of velocities of the heavenly bodies with the simulation results of the collision of the milky Way with another galaxy shows that, most likely, they are the "aliens".

Helmi: "The youngest stars from Gaia-Enceladus are actually younger than the native Milky Way stars in what is now the thick disk region".

That galaxies collide is hardly surprising.

We often think of space as peaceful and serene. Instead, massive galaxies bulk up by catching and consuming smaller galaxies. That means that while this is hardly the only galactic collision scientists have pinpointed, it's a comparatively huge one, the scientists said.

There's now more work to be done, trying to locate the stars left over from other collisions - and learning more about the Enceladus event. "It wasn't known whether the Milky Way had experienced any mergers", Helmi says. For U.S. readers snacking their way through a Halloween haul, consider the injection of caramel that turns a simple 3 Musketeers bar into the cosmic candy we know and love called Milky Way. Helmi and her team found 13 globular clusters they were able to associate with the dwarf galaxy, based on their orbits and the compositions of their stars.

In other words, the collection is what they expected from stars that were once part of another galaxy and have been consumed by the Milky Way. "It was incredible to look at the new Gaia data and realize that I had seen it before!", says the astronomer.

"Seeing that we are now starting to unravel the formation history of the Milky Way is very exciting", says Anthony Brown, Leiden University, The Netherlands, who is a co-author of the paper and also chair of the Gaia Data Processing and Analysis Consortium Executive.

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If those stars had been born in this galaxy, they would be marching around the core in the same direction as the rest of us.

Then, Helmi and her colleagues noticed something else.

"When we looked at their chemical composition, we saw that the stars defined a separate sequence in "chemical space", Helmi says. "We can now say this is the way the Galaxy formed in those early epochs". Collision with object of this size had to warm up the young galactic disk, forming a thicker modern disk. But proving this is not easy and it is only now possible with Gaia for the Milky Way, or for events that have happened relatively recently.

The experts discovered that some 10 billion years ago, the Milky Way merged with a large galaxy. In Greek mythology, Enceladus was a child of the gods Gaia and Uranus. In about four billion years, the Milky Way and the neighbouring Andromeda Galaxy will have a similar collision. It models the Milky Way's merger with the Small Magellanic Cloud, a dwarf galaxy.

Simulations suggest that in another two billion or so years, the Milky Way will swallow the Large Magellanic Cloud, forever erasing it from the southern sky. Its partner will suffer the same fate. For example, researchers always been a question about how it was formed halos - large-scale structure of stars, dark matter and gas that surrounds the galactic disk.

If that sounds extreme, don't forget that in roughly five billion years, the Milky Way will collide with our nearest neighbour, the giant Andromeda galaxy. Now hurtling toward one another at 402,336 kilometres an hour, these galaxies will merge and change our night sky forever-that is, if there are any sentient beings left clinging to this rock we call home.

The Gaia satellite gathers data on 100,000 stars per minute, taking some 500 million measurements per day. By zooming into the incredible shot, filmmaker Dave Achtemichuk creates an unforgettable interactive experience.

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