A candidate particle for dark matter has been discovered by scientists, with researchers suggesting a d-star heaxaquark is another target in the bid to solve one of the universe's biggest mysteries.
Dark matter makes up about a quarter of the universe. Dark energy, which is thought to be the force driving the expansion of the universe, makes up about 68 percent. The rest, about five percent, makes up the visible universe—including all the stars, planets and galaxies. Scientists know dark matter exists because of the gravitational force it appears to exert on the visible universe. It is thought that without dark matter, galaxies would be torn apart.
But because dark matter neither absorbs or emits light, it cannot be seen. This means scientists do not know what it is. Several particles have been put forward as dark matter candidates, and researchers are currently conducting experiments using particle colliders to try to narrow it down.
In a study published in the Journal of Physics G: Nuclear and Particle Physics, MIkhail Bashkanov Daniel Watts, from the U.K.'s University of York have put forward a new candidate.
As Bashkanov explained to Newsweek in an email, "Matter around us is made of molecules, molecules are made of atoms, atoms are made of atomic nuclei with electrons orbiting around them. Atomic nuclei are made of protons and neutrons. Protons and neutrons are made of quarks. In this sense quarks are the building blocks of matter."
Traditionally, protons and neutrons are made of three quarks each. Over recent years, scientists have found exotic particles that are made of four or five quarks, known as tetraquarks and pentaquarks.
The hexaquark, which is six quarks, was also recently discovered. It contains only light quarks, Bashkanov said. "As a matter of fact one can form d* by smashing protons and neutrons together," he explained. "We believe that this particle is very compact, despite the fact that it has six quarks in it, it [is] expected to have a size of the proton, which has three quarks only."
They discovered the particle during experiments at the Juelich accelerator in Germany, in which they were smashing proton beams on neutrons. At some energy, they found a new particle was produced. They are currently carrying out more experiments in an attempt to study the internal structure of the d-star hexaquark.
As a dark matter candidate, Bashkanov said the d-star has a number of advantages. Firstly, they know it exists. Second, in the early universe, there were lots of quarks at high densities, which is similar to their laboratory experiments. Finally, they know particles with bosons can form Bose-Einstein condensates—which are believed to be dark matter candidates.
"So we have motive (hexaquarks are bosons) and opportunity (high density at early universe)," Bashkanov said. "What we do not yet know is capability: we do not know yet if the interaction between hexaquarks permit them to form condensate of desired properties. We are currently working on this question."
He said there is more work to be done and that there are many unanswered questions—but their proposal is testable. "The hypothesis might easily be wrong. It is science. We know plenty of nice looking hypotheses [that] were proved to be wrong. But with the help of [the] scientific community we hope to clarify this question pretty fast. That is the power of science."
Justin Read, Head of Physics at the University of Surrey, U.K., who was not involved in the study, said the findings present "an interesting new idea." He told Newsweek, "There's lots of work to be done to really show that it can work in detail, but given that we have not yet found a dark matter particle candidate, we should leave no stone unturned.
"These are encouraging first steps, but plenty of questions remain. Such hexaquarks will interact with photons which could violate current observational constraints. Detailed calculations may also uncover challenges in producing them in sufficient numbers in the early Universe, or in maintaining stability. It will be interesting to see how this unfolds in future work."
Uncommon Knowledge
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.
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Hannah Osborne is Nesweek's Science Editor, based in London, UK. Hannah joined Newsweek in 2017 from IBTimes UK. She is ... Read more
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