We live in a mysterious Universe–most of which we are unable to see. What is it made of, and has its composition changed over time? The starlit galaxies, galaxy clusters and superclusters are all embedded within invisible halos composed of transparent material that scientists refer to as the “dark matter.” This mysterious substance creates an enormous, invisible structure throughout Space and Time–a fabulous, fantastic tapestry woven of heavy filaments composed of this “dark” stuff, that is thought to be formed from unidentified and exotic non-atomic particles. In March 2020, a team of scientists announced that they have identified a sub-atomic particle that could have formed the dark matter in the Universe during its Big Bang birth.
Scientists think that up to 80% of the Universe could be dark matter, but despite years of investigation, its origin has remained a puzzle. Even though it cannot be observed directly, most astronomers think that this ghostly form of matter is really there because it does dance gravitationally with forms of matter that can be observed–such as stars and planets. This invisible material is made up of exotic particles that do not emit, absorb, or reflect light.
A team of nuclear physicists at the University of York (U.K.) are now proposing a new particle candidate for this ghostly material–a particle that they recently detected called the d-star hexaquark.
The d-star hexaquark is made up of six quarks–the fundamental particles that normally combine in trios to form the protons and neutrons of the atomic nucleus.
Raise A Quark for Muster Mark
The Irish novelist James Joyce (1882-1941) had a drunken character in Finnegan’s Wake raise a quart of dark beer to toast a man named Finnegan who had just died. He mistakenly said “raise a quark for muster Mark”. The American physicist, Nobel laureate Murray Gell-Mann (1929-2019), who was one of the scientists who proposed the existence of the quark in 1964, thought it was so funny that he named this sub-particle after the drunken host. The Russian-American physicist, George Zweig, also independently proposed the existence of the quark that same year.
A quark is a type of elementary particle that is a fundamental constituent of matter. Quarks combine to create composite particles called hadrons. Hadrons are subatomic particles of a type that includes protons and neutrons, which can take part in the strong interaction that holds atomic nuclei together. Indeed, the most stable hadrons are protons and neutrons–the components that form the nuclei of atoms. Because of a phenomenon termed color confinement, quarks have not been directly observed or found in isolation. For this reason, they have been found only within hadrons. Because of this, a great deal of what scientists have learned about quarks has been derived from studying hadrons.
Quarks also show certain intrinsic properties, including mass, color, electric charge, and spin. They are the only known elementary particle in the Standard Model of Particle Physics to display all four fundamental interactions–also termed fundamental forces–the strong interaction, the weak interaction, gravitation, and electromagnetism. Quarks are also the only known elementary particles whose electric charges are not integer multiples of the elementary charge.
The types of quarks are referred to as flavors: up, down, strange, charm, bottom, and top. The heavier quarks quickly experience a metamorphosis into up and down quarks as the result of a process called particle decay. Particle decay refers to the transformation from a higher mass state to lower mass states. For this reason, up and down quarks are stable, as well as the most abundant in the Universe. In contrast, strange, charm, bottom, and top quarks can only be churned out in high energy collisions–such as those involving cosmic rays or particle accelerators. For every quark flavor there is a corresponding antiquark. The antiquark antiparticle differs from the quark only in certain properties, such as electric charge. The antiquark antiparticles have equal magnitude but an opposite sign.
There was little evidence for the physical existence of quarks until deep inelastic scattering experiments were conducted at the Stanford Linear Accelerator Center in 1968. Accelerator experiments have provided evidence for the existence of all six flavors. The top quark, first observed at Fermilab in 1995, was the last to be discovered.
The Universe’s Shadowland
It is often said that most of our Universe is “missing”, primarily composed as it is of an unidentified substance that is referred to as dark energy. The mysterious dark energy is causing the Universe to accelerate in its expansion, and it is thought to be a property of Space itself.
The most recent measurements indicate that the Universe is composed of approximately 70% dark energy and 25% dark matter. Currently, both the origin and nature of the mysterious dark matter and dark energy are unknown. A considerably smaller fraction of our Universe is composed of so-called “ordinary” atomic matter. “Ordinary” atomic matter–which is really extraordinary–is comparatively scarce. Nevertheless, it is the material that accounts for all of the elements listed in the familiar Periodic Table. Despite being the tiny “runt” of the cosmic litter of three, “ordinary” atomic matter is what makes up stars, planets, moons, and people–everything that human beings on Earth are most familiar with. It is also the precious form of matter that caused life to form and evolve in the Universe.
On the largest scales, the Universe looks the same wherever it is observed. It displays a bubbly, foamy appearance, with extremely massive and enormous filaments composed of dark matter intertwining around one another, creating a web-like structure that is referred to as the Cosmic Web. The ghostly, transparent filaments of the great Cosmic Web are traced out by myriad galaxies blazing with the fires of brilliant starlight, thus outlining the immense, intertwining braids of dark matter that contain the galaxies of the visible Universe. Enormous, cavernous, dark, and almost empty Voids interrupt this web-like pattern. The Voids host few galaxies, and this is the reason why they appear to be entirely empty. In dramatic contrast, the massive starlit filaments of the Cosmic Web weave themselves around these almost-empty Voids, creating a fabulous, complicated, braided knot.
Some cosmologists have proposed that the entire large scale structure of the Universe is really composed of only one filament and a single Void twisted together in an intricate and complex tangle.
Enter The d-Star Hexaquark
The d-star hexaquark is made up of six quarks. These fundamental particles normally combine in trios to form the protons and neutrons of the atomic nucleus. Most importantly, the six quarks in a d-star hexaquark create a boson particle. This indicates that when a large number of d-star hexaquarks are present that can dance together and combine in very different ways to the protons and neutrons. A boson is a particle that carries energy. For example, photons are bosons.
The team of scientists at the University of York propose that in the conditions that existed shortly after the Big Bang, a multitude of d-star hexaquarks could have met up and then combined as the Universe cooled down from its original extremely hot state and then expanded to give rise to a fifth state of matter–what is termed a Bose-Einstein Condensate.
A Bose-Einstein Condensate is a state of matter in which separate atoms or subatomic particles, cooled to near absolute zero, coalesce into a single quantum entity–that is, one that can be described by a wave function–on a near-macroscopic scale.
Dr. Mikhail Bashkanov and Dr. Daniel Watts from the Department of Physics at the University of York published the first assessment of the viability of this new dark matter candidate.
Dr. Watts noted in a March 3, 2020 University of York Press Release that “The origin of dark matter in the Universe is one of the biggest questions in science and one that, until now, has drawn a blank.”
“Our first calculations indicate that condensation of d-stars are a feasible new candidate for dark matter and this new possibility seems worthy of further, more detailed investigation,” he added.
“The result is particularly exciting since it doesn’t require any concepts that are new to physics,” Dr. Watts continued to comment.
Co-author, Dr. Bashkanov, explained in the same University of York Press Release that “The next step to establish this new dark matter candidate will be to obtain a better understanding of how the d-stars interact–when do they attract and when do they repel each other. We are teaching new measurements to create d-stars inside an atomic nucleus and see if their properties are different to when they are in free spae.”
The scientists are planning now to collaborate with researchers in Germany and the United States to test their new theory of.dark matter and hunt for d-star hexaquarks in the Universe.