What is dark matter? Despite making up 80 percent of all matter in the galaxy, we can’t see it, only measure the effects it has on stars and galaxies. Could the d-star hexaquark explain one of the great mysteries of the Cosmos?
By James Maynard
Dark matter was first detected between galaxies by astronomer Fritz Zwicky in the early 1930’s, and within galaxies by Vera Rubin four decades later. Today, we know that this mysterious -something- contains four times as much mass as all the stars, galaxies, planets, and everything else we see in the Cosmos combined. However, despite decades of research, we still don’t understand the nature of dark matter.
Now, researchers at the University of York believe they have a candidate that could explain the underlying nature of this strange substance, a subatomic particle called the d-star hexaquark.
“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 condensates of d-stars are a feasible new candidate for dark matter. This new result is particularly exciting since it doesn’t require any concepts that are new to physics,” said Daniel Watts of the University of York.
The Deep Mystery of Dark Matter
Dark matter gets its name from the fact that, whatever it is, it does not reflect, absorb, or emit light. However, this -something- does have significant gravitational effects, holding galaxies together as they spin, and keeping clusters of galaxies huddled together despite the significant velocities at which members of these galactic groups travel.
Numerous theories have been put forth concerning how dark matter can have gravitational effects without affecting electromagnetic radiation. One school of thought suggested it may be composed of massive compact halo objects (MACHO’s) — objects composed of “normal” matter like planets, gas, and dust, wandering alone through space.
Another idea holds that dark matter is composed of weakly interacting massive particles (WIMPs), subatomic particles that rarely interact with other particles, apart from their gravitational effects.
However, no evidence has yet been found that there are enough loose pieces of matter in the Universe to support the MACHO theory, and no particle has yet been found that would explain dark matter in terms of WIMP’s.
The idea that tiny black holes produced in the earliest ages of the Universe also comes up short, as astronomers cannot find enough primordial black holes to account for the amount of gravitation produced by dark matter.
Up and Atom
Atoms are composed of positively-charged protons and uncharged neutrons in their dense nucleus, surrounded by clouds of negatively-charged electrons. Protons and neutrons are each composed of three quarks (even more elementary particles).
If they exist, d-star hexaquarks would each be composed of six quarks. This would mean that these particles would be bosons, a class of particles that includes photons of light. Groups of these particles are able join together in ways that are impossible for protons and neutrons, and these groups may, theoretically, be able to explain the underlying nature of dark matter.
“[W]e show stable… Bose–Einstein condensates could form in the primordial early universe, with a production rate sufficiently large that they are a plausible new candidate for [dark matter],” researchers wrote in an article describing their findings, published in the Journal of Physics G: Nuclear and Particle Physics.
Bose–Einstein condensates, often called the fifth state of matter, are composed of groups of atoms cooled to temperatures barely above absolute zero. When this takes place, atoms clump together, merging into a form that resembles a single atom. When this occurs, BEC’s act (in many ways) like a large, single atom where the strange rules of quantum mechanics hold sway.
This fifth state of matter was first proposed by Indian physicist Satyendra Nath Bose (1894–1974), the same person who first described bosons. Bose was working on statistical problems in quantum mechanics, when he sent his ideas to Albert Einstein. The world’s most famous physicist ensured the ideas of Bose were published and further developed. The pair soon found the ideas, first developed to explain the behavior of light, would also apply to super-cooled atoms.
To create Bose-Einstein condensates in the laboratory, researchers begin with a cloud of cool gas (usually rubidium), utilizing lasers to take away energy (heat) from the atoms. This thin gas is then subjected to evaporative cooling, confining groups of atoms to smaller and smaller spaces, cooling the sample by driving off atoms with the greatest amount of energy. This process cools atoms into a BEC without forming a lattice-like solid.
Atoms in this state are identical to each other, similar to the way photons of light cannot be distinguished from one another. Materials in this bizarre state obey rules of sub-atomic physics called Bose-Einstein statistics.
In 1991, the Nobel Prize in physics was awarded to the team that first created this bizarre state of matter under laboratory conditions.
“The state was achieved in alkali atom gases, in which the phenomenon can be studied in a very pure manner. Nowhere else in the universe can one find the extreme conditions which BEC in dilute gases represents,” the Nobel Prize committee explained.
Searching for Clues
“In terms of the most astonishing fact about which we know nothing, there is dark matter and dark energy. We don’t know what either of them is. Everything we know and love about the universe and all the laws of physics as they apply, apply to four percent of the universe. That’s stunning.” — Neil deGrasse Tyson
As the Universe cooled following the Big Bang, an energetic “soup” of quarks and gluons (which holds quarks together in our current age) coalesced into the protons and neutrons which makes up most of the “normal” matter we see around us today. This study speculates that during this period, vast quantities of Bose-Einstein condensates were also produced, leading to the dark matter “seen” in our modern Universe as dark matter.
“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 leading new measurements to create d-stars inside an atomic nucleus and see if their properties are different to when they are in free space,” Mikhail Bashkanov of the University of York stated.
Although it may be nearly impossible to see dark matter, astronomers can search for the by-products of BEC. When energetic cosmic rays (high-energy subatomic particles which permeate space) strike these condensates, they decay into products which can be detected by researchers. Evidence for interactions in the early Universe may even be found in the atmosphere of modern-day Earth.
“The existence of [d-star hexaquark]-BEC decays in the Earth’s atmosphere or close to its surface would produce energies comparable with cosmic-ray events, but without directionality. As cosmic-rays should not be able to pass through the Earth based on our current understanding of standard model physics, then upward going ‘cosmic-ray’ events may provide a potential signal,” researchers explain in their journal article.
These d-star hexaquarks may provide some answers as we work to understand the mysterious nature of dark matter. Whether or not this bizarre state of matter could solve this central puzzle of the Universe could depend on the exact (and so-far-unknown) properties of d-star hexaquark condensates.
By searching for signs of d-star hexaquarks, researchers could answer one of the greatest questions in the Universe.
James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.
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