Revealing Hidden Dark Matter Clues with Asymmetric Galaxies

Scientists determine the velocity of dark matter by examining galaxies that are irregular in shape due to dynamical friction provoked by the presence of dark matter. Identifying the interactions between dark matter and galaxies facilitates advancements in theoretical physics and cosmology. Credit: SciTechDaily.com

Instrumental in revealing the enigmas of dark matter, the examination of irregularly shaped galaxies uncovers how gravitational forces and dynamical friction contribute to our understanding of the cosmos.

So, how does one go about measuring dark matter's speed? The first step involves identifying a galaxy that is moving relative to dark matter within the universe, which isn't typically an arduous task given the motion inherent in the universe and the significant abundance of dark matter.

Large celestial bodies, such as galaxies, exhibit a gravitational pull that impacts all matter, seen or unseen. When dark matter passes by a galaxy, it is drawn toward it, a process that requires time to affect the speed and direction of the particles. Notably, prior to the adjustment of their flight path toward the galaxy, these particles already bypass the galaxy.

As a result, dark matter particles do not integrate into the galaxy but rather pursue a route behind it. Consequently, the density of the matter increases behind the galaxy, contributing to a slowdown referred to as dynamical friction. The level of dynamical friction is contingent upon the speed at which the dark matter particles traverse past the galaxy, indicating how much time is needed for the galaxy to influence the trajectory of the dark matter particles. If the particles move slowly, a high-density matter builds closer to the galaxy, inducing further slowing.

Imagine a galaxy represented by a green dot, depicted in the upper panels, which demonstrates the movement of dark matter particles in relation to the galaxy. The lower panels expose the various trajectories influenced by the galaxy's gravity field, leading to an overdensity of matter behind the galaxy. This overdensity compels the galaxy to decrease its speed and alter its shape. Credit: Rain Kipper

Let's suppose the galaxy executing dynamical friction is considerable in size. In this scenario, variances in the intensity of friction exist throughout the galaxy due to the elevated density behind it, and these disparities contribute to the unusual shape of the galaxy. On Earth, we encounter a parallel transformation in shape caused by the moon's gravity, resulting in fluctuating tide levels.

The size of the dark matter particles matters little; they will consistently curve behind a galaxy. However, if particles are roughly equivalent in size to galaxies, the accuracy of results may be compromised. Yet, such models of dark matter have been largely ruled out.

Discovering galaxies that are irregular in shape isn't generally difficult as they constitute approximately 30 percent of all galaxy formations. Naturally, the parameters differ depending on how far we can observe the outer portions of a galaxy and what degree of irregularity categorizes a galaxy as lopsided.

Dynamical friction isn't the sole cause of irregularly shaped galaxies. Other factors, such as the merging of multiple galaxies, can also induce asymmetry. In such instances, it's possible to identify within the newly formed galaxy the core of another galaxy or an enlarged stellar halo. Additionally, consistent gas inflow can mediate the shape of a galaxy, although restoration back to its original shape requires billions of years.

Hence, to ascertain precise measurements of the speed of dark matter, a lopsided, relatively isolated galaxy is necessary. With minimal interactions with other galaxies, there's more assurance that the lopsided form resulted solely from the passage of dark matter.

We have recently discerned how to accurately compute the forces at work during the tidal cycles on galaxies. The subsequent challenge involves locating galaxies that are sufficiently lopsided to facilitate the investigation of the speed of dark matter in relation to the galaxies.+

Cosmology is an important test polygon of theoretical physics. Calculating the speed of dark matter can be important for testing new dark matter models and lifting the veil of secrecy over the nature of dark matter.