Historically, the warp in our galaxy's disk was attributed to ancient galactic collisions.
Unraveling the mysteries of our home galaxy has long intrigued astronomers. Even with the most advanced telescopes and spacecraft, there are facets of the Milky Way that remain puzzling. Among these enigmas is the discovery of our galaxy’s warped nature. While previous theories pointed to ancient collisions, fresh research offers a new perspective: a slanted dark matter halo.
The Milky Way, once believed to be a simple flat disk, is anything but. Revelations from the Gaia Spacecraft have charted over a billion stars, providing a clearer picture of our galaxy’s intricate outer structure. Contrary to prior beliefs, it not only extends farther than previously thought but also boasts a rippled edge with a distinct warp.
Collisions or Dark Matter: The Prevailing Theories
Historically, the warp in our galaxy’s disk was attributed to ancient galactic collisions. A prominent example is the encounter with the Sagittarius dwarf galaxy approximately 6 billion years ago. However, the latest study proposes a different origin: the influence of a misaligned halo of dark matter.
Enveloping most galaxies, including ours, is a colossal dark matter halo. This unseen halo holds the majority of a galaxy’s mass. Its gravitational force is so immense that over time, it can modify a galaxy’s structure. If a halo leans compared to a galaxy’s plane, this can result in a skewed galactic disk.
Delving Deeper with Simulations
To validate this theory, researchers turned to the TNG50 iteration of the IllustrisTNG simulations, powerful computer-generated models of galactic evolution. These simulations factor in not just dark matter but also intricate interactions like magnetohydrodynamics. The findings indicated that a galaxy’s dark matter halo can notably tilt relative to its plane. Such tilting can arise from both direct collisions and close brushes between galaxies. With these tilted halos able to remain in such a state for billions of years, they could very well induce a galaxy’s warp.
To further cement their hypothesis, the team studied a model galaxy from TNG50 similar in size and age to our Milky Way, complete with a tilted dark matter halo. After simulating 6 billion years of evolution, the outcomes bore striking resemblances between our observed galaxy and its virtual counterpart.
Our galaxy isn’t unique in its warped appearance. Observations reveal that potentially up to half of the spiral galaxies in the cosmos exhibit some degree of warp. This prevalence hints at the regular gravitational interplay between galaxies and their twisted halos. While this study sheds light on a possible explanation, the intricate dance of galaxies continues to necessitate further exploration.
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