If darkish matter particles decay, then scientists might hunt for indicators of this course of, together with X-ray or gamma-ray radiation and even emitted “ghost particle” neutrinos, in huge clusters of galaxies.
Not solely might this lastly reveal what particles comprise mysterious darkish matter, nevertheless it might additionally assist astronomers perceive the universe’s construction like by no means earlier than. And new analysis means that NASA’s X-ray Imaging and Spectroscopy Mission (XRISM) might play an vital function on this hunt.
Darkish matter poses a major problem for scientists as a result of, regardless of comprising round 85% of the matter within the cosmos, it stays successfully invisible. It is because it does not work together with electromagnetic radiation, or mild — or, if it does, the interplay is simply too weak to be detected. This has led scientists to counsel an entire host of hypothetical particles to account for dark matter, which go beyond the standard model of particle physics and the electrons, protons and neutrons that make up the atoms that compose all everyday matter, like stars, planets, moons and our bodies.
One particular dark matter model suggests that whatever particles make up this mysterious stuff, they undergo a process called decay. This involves large particles breaking down over vast timescales to lighter particles, releasing energy in the form of photons, the particles of light. One possible signature of this process that astronomers could hunt for are X-ray photons released when decay occurs. In fact, scientists may have already spotted this cosmic fingerprint in the form of an unidentified X-ray emission in the light spectra from galaxy clusters.
“Eighty-five percent of mass in galaxy clusters comes from dark matter, and we can model the dark matter radial distribution well,” study team member Ming Sun, of the University of Alabama in Huntsville (UAH), said in a statement. “Thus, galaxy clusters are nice targets for such a search as they’re darkish matter-rich and we all know the darkish matter mass in clusters effectively.”
Previously, researchers have relied on light-sensitive semiconductor chips known as Cost-Coupled Gadgets (CCDs) to trace the paths of doable decay particles to raised perceive what’s inflicting this X-ray emission. Nevertheless, Solar and colleagues took a distinct strategy, as an alternative turning to knowledge from XRISM.
“Almost all of the previous research used the CCD knowledge, which lack the required power decision to resolve the unidentified line,” Solar mentioned. “Now XRISM supplies high-energy-resolution spectra that may resolve the road. As the road alerts are very weak, we mixed almost three months of the XRISM knowledge for such a search. There are numerous X-ray strains detected. They originate from recognized atoms, comparable to iron, silicon, sulfur, and nickel. X-ray emission strains that seem that aren’t on the recognized place of atomic strains are then the candidates for darkish matter decay strains, which is the main target of this work.”
The workforce theorizes that the main suspects for this unknown emission are “sterile neutrinos.” Neutrinos are virtually massless particles that stream through the cosmos at nearly the speed of light. The second-most abundant particle in the universe after photons, neutrinos are so “ghost-like” that 100 trillion pass through your body every single second, and you never notice a thing. Sterile neutrinos are one of the hypothetical particles that have been proposed to account for dark matter.
“A sterile neutrino is a hypothetical type of neutrino that only interacts with other particles via gravity, unlike the three known ‘active’ neutrinos that also interact via the weak force,” Sun said. “The existence of the sterile neutrino is well-motivated theoretically and can explain the very small but non-zero mass of regular neutrinos. Sterile neutrinos can decay into two photons with the same energy. Models can predict the decay rate of sterile neutrinos, which is then constrained from the data.”
Sterile neutrinos have a long way to go before they replace Weakly Interacting Massive Particles (WIMPs) as the leading suspects for dark matter, but Sun and colleagues are committed to exploring other possible candidates, including sterile neutrinos, even if that process includes ruling them out.
“WIMPs are still the leading candidate for dark matter, but billions of dollars of experiments have been done, only getting stronger and stronger upper limits, so alternative scenarios have to be considered. This study provides the strongest limits from high-energy-resolution data on the sterile neutrino at the 5 to 30 kiloelectronvolts (keV) band, subsequently limiting the models for dark matter,” the UAH researcher concluded. “With more XRISM data in the next five to 10 years or so, we will be able to either detect the line or improve the limit substantially.”
The team’s research was published in November in The Astrophysical Journal Letters.
