According to a recent study, our galaxy’s familiar flat shape has been dramatically distorted by a massive, imperceptible dark matter mass. Originally, scientists believed the Milky Way to be a flat, disk-shaped structure dominated by two spiral arms, with stars trailing from a central bar. However, measurements taken since the mid-20th century have shown that it has inexplicably warped from this expected form. This warping is most pronounced at the galaxy’s outer boundaries, where some regions curve downward while others arch upward, resulting in a shape reminiscent of a crushed sombrero. Computer simulations now suggest a potential explanation for this phenomenon: an enigmatic event that disrupted the alignment of the invisible dark matter halo surrounding our galaxy. These findings were published on September 14th in the journal Nature Astronomy.
In their study, the scientists stated, “These results, combined with data concerning the stellar halo, offer compelling evidence that our Galaxy is ensconced within a tilted dark matter halo.” Dark matter, a mysterious and somewhat paradoxical form of matter, constitutes 85% of the universe’s matter. However, since it does not interact directly with light, it remains entirely invisible. Nonetheless, scientists can detect its gravitational influence on its surroundings. Dark matter manifests its presence by accelerating stars to speeds that cannot be explained otherwise as they orbit galactic centers, distorting distant starlight, and shaping the Milky Way’s galactic halo.
The galactic halo, an expansive sphere of stars suspended like leaves on the surface of a dark matter pond, resides just beyond the Milky Way’s spiral arms. In a study conducted in 2022, astronomers examined this region using the European Space Agency’s Gaia spacecraft, which charts the positions and movements of approximately 2 billion stars in the Milky Way. Analyzing Gaia’s data, they discovered that the stars within the galactic halo exhibited peculiar deviations from alignment.
To investigate the implications of an unbalanced stellar halo for the dark matter halo it is embedded within, researchers employed computer models to replicate a young galaxy resembling the Milky Way, featuring a dark matter halo tilted at a 25-degree angle relative to its disk. After simulating the galaxy’s evolution over 5 billion years, they found that it closely resembled our own galaxy. The researchers noted, “Here we show that a dark halo tilted in the same direction as the stellar halo can induce a warp and flare in the Galactic disk at the same amplitude and orientation as the data.”
While the cause of the dark matter around our galaxy falling out of alignment remains unclear, the simulations by the researchers suggest it may have resulted from a colossal collision, likely involving another galaxy colliding with our own. This collision could have caused the dark matter halo to tilt by as much as 50 degrees before gradually settling into its current elevation angle of 20 degrees.