The Milky Way our galaxy, is a vast and complex structure, filled with swirling gas, luminous stars, and dark matter. But look closely, and you’ll find that it bears the marks of a violent history. These scars, however, aren’t always easy to detect, often blending in with the galaxy’s natural evolution. Recent research, using data from the Gaia satellite, has uncovered intriguing new details about a potential cosmic clash between the Milky Way and a smaller orbiting galaxy.
Since the 1960s, astronomers have noticed a peculiar S-shaped bend in the Milky Way’s disk, suggesting that our galaxy may have experienced repeated encounters with a smaller neighbor, such as the Sagittarius Dwarf Spheroidal Galaxy. This bend, or “warp,” in the galaxy’s structure has been the subject of much speculation, with scientists debating whether it is the result of a cataclysmic event or simply a natural occurrence.
In a recent study led by astronomer Eloisa Poggio from the Italian National Institute for Astrophysics, an international team of researchers analyzed data on the positions and movements of tens of thousands of stars, particularly focusing on 16,000 young giant stars and about 3,400 Cepheid stars, which are used as “distance markers.” By correlating the stars’ radial (back-and-forth) and vertical (up-and-down) motions, the team discovered a subtle oscillation within the galaxy’s warp a wave that resembles the rolling motion of ocean swells.
This wave, though barely noticeable above the plane of the galaxy, extends across a vast region, stretching over a quarter of the way to the edges of the Milky Way’s disk. The stars involved in this motion are moving outward at speeds of around 10 to 15 kilometers per second (approximately 6 to 9 miles per second), deviating from their expected paths.
The researchers are still debating whether the radial and vertical motions of these stars are connected, and whether the observed wave and the underlying warp share a common origin. Interestingly, it was only after removing the signature of the Milky Way’s bend that the team noticed the remaining variations in star positions, hinting at an abnormality possibly linked to past cosmic encounters.
“The warp and the wave do not necessarily need to be caused by the same event,” Poggio told ScienceAlert. “However, we will try to explore this point in the future using numerical simulations.”
The Milky Way hides its turbulent past well, but by carefully studying stars that are out of place or moving in unusual ways, astronomers are beginning to piece together the galaxy’s hidden history. The researchers conclude that future studies, including the analysis of other datasets and galaxy formation models, will likely reveal more details about the formation and evolution of these features and provide a better understanding of how waves propagate through the Milky Way’s disk.
In essence, our galaxy’s story is far from peaceful, with the echoes of past events still rippling through its structure today.
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