Chapter 1: The Enigmatic Nature of Dark Matter

As spring unfolds, many of us remain sheltered indoors, often overlooking the abundance of daylight surrounding us. In such times, it feels appropriate to delve into the topic of dark matter.

The Bullet Cluster is a composite image combining data from the Hubble Space Telescope, the Magellan telescopes, and the Chandra X-ray Observatory. This visualization shows dark matter (in purple) as inferred from gravitational distortions. Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

When we observe the movement of massive celestial bodies, we witness behaviors that can only be rationalized if there exists more mass in the universe than what is visible through our telescopes. This concept was first brought to light by Vera Rubin and Fritz Zwicky while studying galaxies and clusters of galaxies. Today, we understand that approximately 25% of the universe's mass-energy is concealed within this enigmatic substance. Initially, scientists believed that by examining the universe through different wavelengths, we might discover this hidden material in the forms of gas, dust, black holes, and rogue planets. During my graduate studies, Professor Don Winget emphasized the vast emptiness of our universe, suggesting that we could account for all dark matter by placing a single brick in each solar system-sized region of space. This illustrates just how sparse our universe truly is.

In the 1990s and early 2000s, research teams sought to locate black holes and other dark entities that might be obscured in plain sight. They focused their attention on our galactic core and the Magellanic Clouds, searching for the gravitational effects of nearby objects that could lens distant stars, rendering them temporarily brighter. Although these investigations did uncover some gravitationally lensed objects—one of which was even a planet—they ultimately failed to locate enough to explain the observed dark matter effects. Concurrently, astronomers began hypothesizing about how clouds of dark matter particles could gravitationally alter the images of distant galaxies, leading to the discovery of dark matter as a distribution of particles. The Bullet Cluster remains one of the most well-known examples of how dark matter can be mapped by observing its influence on the light from objects behind it.

However, these particles don't seem to interact via electromagnetic forces in the usual manner—they neither emit nor absorb light, only exerting gravitational effects on photons. They also appear to have no interaction with magnetic fields, rendering most traditional observational techniques ineffective in studying dark matter.

The elusive nature of dark matter fuels our desire to uncover it, and researchers worldwide are experimenting with innovative methods for detecting its particles. A recent study published in Science by a team from the University of Michigan, Lawrence Berkeley Labs, and UC Berkeley investigated whether mysterious flickers of light from nearby galaxies might be linked to dark matter. These flickers are believed to originate from a theorized particle known as a sterile neutrino, appearing as x-ray emissions in massive galaxies. It was proposed that these flickers resulted from the decay of sterile neutrinos.

What Exactly is a Sterile Neutrino?

Currently, we lack experimental proof for the existence of sterile neutrinos, but all observed particles in the standard model possess different varieties that exhibit complementary spin. To date, all known neutrinos have left-handed spin, while sterile neutrinos are theorized to have right-handed spin, resembling the elusive nature of dark matter in that they too exhibit minimal interaction. Scientists hoped the existence of sterile neutrinos might provide a partial solution to the dark matter puzzle.

XMM-Newton has detected light flickers in large galaxies, which were thought to be associated with sterile neutrino decay. An abundance of flickers would suggest a significant decay rate, correlating to the dark matter present. However, observations reveal no such flickers in our Milky Way, suggesting that whatever causes these flickers is specific to larger galaxies. Since dark matter is not confined to specific locations, the connection between flickers and dark matter remains ambiguous.

While sterile neutrinos could still play a role in dark matter's mystery, the observed flickers do not seem to result from their decay.

The Quest for New Particles

The challenge of identifying new particles is central to dark matter research. The theoretical aspect of proposing new particles is straightforward—mathematics allows us to envision a variety of possibilities. The real difficulty lies in detecting these particles.

Everything in the universe comprises particles and energy. Ordinary matter consists of fundamental particles like electrons and composite particles such as protons, formed from three quarks. As we understand it, all stable composite particles—leptons—are made up of precisely three quarks. However, quarks can combine in different groupings, and our knowledge of all existing particles is still incomplete.

By utilizing powerful particle colliders, we have been able to collide regular matter at immense energies, resulting in the formation of unstable particles comprised of four or five quarks. It is now theorized that stable particles formed from six quarks, known as hexaquarks, may exist. Researcher Glennys Farrar from NYU speculates that these particles could be trapped within various elements in the Earth's crust, such as oxygen-18. Scientists are actively weighing different oxygen-18 atoms to detect any excess weight that hexaquarks may introduce. Additionally, analyses of past particle collisions at various global accelerators have hinted at a large particle in data from Germany’s WASA experiment at the COSY accelerator, which appears to align with the characteristics of a six-quark particle. While this remains inconclusive, it represents a promising lead in our understanding.

Other researchers are investigating flickers in neutrino detectors that might not be caused by neutrinos but could indicate the presence of dark matter, while some are brainstorming entirely new theories.

Ultimately, no one can definitively state what dark matter is. Based on current observations, we can only conclude that dark matter is a type of particle that proves exceedingly difficult to locate.

And that sums up our findings—dark matter seems to prefer remaining hidden, even in these trying times.

Chapter 2: Insights from Experts

In a compelling conversation, Joe Rogan and David Goggins discuss overcoming dark times and the importance of "decluttering the mind" as a strategy for resilience.

This video explores the distinctions between dark matter and dark energy, providing valuable insights into their unique roles in the universe.