How a Dwarf Galaxy Shook the Milky Way ⚡ экспресс
Before its fall, the Sagittarius dwarf galaxy (Sgr) had a mass of ~10^11 M⊙ and over the last 5–6 billion years, repeatedly crossing the Milky Way’s disk, it lost a great deal of matter. The observed disk disturbances—spiral arms, corrugations, phase spiral, and the Lz–V_R wave—had been linked individually to these encounters. The new study performs a holistic analysis: can a single impulse from a crossing explain all of them at once? Modeling the encounter with a perturbing body like Sgr showed that one passage satisfactorily reproduces the local corrugations and arm segments (Outer, Local, Carina-Sagittarius); thus, the last significant impulse occurred 700–1200 million years ago. The Lz–V_R wave and phase spiral also emerge during this period and broadly match observations, but not in detail. Therefore, the last crossing of Sagittarius about a billion years ago may be the main cause of large-scale disk distortions, yet additional factors such as the Galactic bar or interactions with other satellites are needed to explain the Lz–V_R wave.
The Sagittarius galaxy plunged into the disk of the Milky Way and passed through again and again, like a stone thrown into a still pond. Each strike left ripples: waves and warps in the star field. Once, Sagittarius brimmed with invisible mass (dark matter), but the collisions stripped away its gas and stars, turning it into a faint trail.
Astronomers simulated the last major impact about a billion years ago to see if it could spawn spiral arms, a warped disk, and subtle oscillations in star velocities. Motion measurements via spectroscopy confirmed: the impact explains the arms and warp, but more complex wave patterns aren’t fully reproduced. So our Galaxy remembers other shoves — from the dense central bar or other dwarf companions.
The most surprising part: Sagittarius itself has nearly vanished, but its dark matter likely still permeates the Milky Way, invisibly swaying stellar orbits. Like cosmic detectives, scientists piece together the Galaxy’s violent past.
🎯 The Sagittarius dwarf galaxy is still visible in the sky as a faint ribbon of stars, stretched thin by the Milky Way's gravity.