Scientists say an ancient galactic collision flipped the entire Milky Way's thick disk

[ECWAlex98]

Astronomers studying the Milky Way's structure have found evidence that its thick disk, the older and slower rotating population of stars, actually underwent a disk flip driven by an ancient merger with another galaxy. The European Space Agency's Gaia mission had already shown that the thick disk rotates more slowly than the thinner disk where most stars including our sun reside, and powerful new simulations now point to a merger as the culprit behind that difference. This reshapes part of the story of how our own galaxy came to look the way it does today

A disk flip of this kind means the orientation of the thick disk's rotation was essentially knocked and reset by the gravitational chaos of an ancient galactic collision, rather than simply forming gradually the way the thin disk did. Reconstructing an event like this from present day stellar motions is an impressive piece of detective work, since the collision itself would have happened billions of years before anyone could have directly observed it

This adds another layer to the increasingly clear picture that the Milky Way's history is full of past mergers and collisions that shaped its current structure, rather than the galaxy simply growing in isolation. Every new Gaia based study seems to peel back another layer of a surprisingly violent and eventful galactic childhood

The Milky Way Flipped its Disk Billions of Years Agowww.universetoday.com

[Weary Renegade]

The Milky Way having a violent early history keeps getting more and more confirmed the more Gaia data comes in

[Tracey49]

Reconstructing a billions of years old collision from present day stellar motion alone is remarkable scientific detective work

[FairDos47]

Curious what galaxy actually collided with us to cause this disk flip and whether we can identify any surviving remnant of it

[Zoe90]

This explains the rotation speed difference between the thick and thin disk in a really satisfying way

[TheRizz96]

Gaia has been one of the most quietly impactful missions in modern astronomy and this is another great example why

[Tundra]

Makes me want a full timeline of every known merger event in the Milky Way's history laid out visually

[Chris_50]

Simulations matching up this well with actual observed stellar kinematics is a nice validation of the underlying models

[Protocol15]

Makes you wonder what other secrets are hiding in stellar motions. Maybe the next big discovery is that the Sun's orbit is slightly off because we got sideswiped by Andromeda's cousin. Or maybe that's just bad parking.

[Beta]

Would love to know roughly how long ago this particular merger and disk flip actually happened

[Luca73]

Flip the entire disk? That's not a collision; that's a cosmic judo move. The Milky Way's thick disk took a hit and responded with 'hold my beer.' Space is dramatic.

[Highland Kev]

The thick disk is older and slower, right? So some ancient merger hit us, and our stars did a collective 'my bad' and flipped. Meanwhile, the thin disk kept spinning like nothing happened. Classic older sibling vs. younger sibling energy.

[Sophie86]

The thick/thin disk distinction is fascinating. Thick disk stars are older, metal-poor, and now apparently traumatized by ancient mergers. Thin disk stars are younger, metal-rich, and probably smug about it. Galactic classism at its finest.

[DrewMcIntyre]

Visual timeline would be epic. Color-code the mergers by size, add arrows showing the flip, maybe a little 'you are here' for the Solar System. Bonus points for sound effects. 'Crash!' 'Flip!' 'Oof!'

[NeuralTrace]

The precision here is insane. We're talking about events billions of years ago, reconstructed from star positions and velocities. It's like forensic astronomy. 'The culprit was a dwarf galaxy, approximately 10 billion years ago, in the galactic halo.'

[AmberCrossing]

Timeline request is solid. Imagine a visual showing every merger-Gaia-Enceladus, the Sausage, whatever else we've swallowed. It'd look like a cosmic Pac-Man game. 'Eat stars, avoid black holes.'