Energy Signals From Milky Way’s Core Hint at New Type of Dark Matter – ScienceAlert

Dark matter continues to confound us, so far defying every attempt to decipher it.According to a new study, clues may lurk in the Milky Way’s Central Molecular Zone, a vast region of hydrogen molecules surrounding our galaxy’s center.It constitutes about 85 percent of matter in the Universe, yet dark matter doesn’t interact with light, and seems to interact with ordinary matter only via gravity. We know it’s there because of its gravitational effects, but we know little else.”The data is telling us that dark matter could potentially be a lot lighter than we thought,” says theoretical physicist Shyam Balaji from King’s College London.The Milky Way’s Central Molecular Zone (CMZ), is unlike most of the galaxy. Almost 80 percent of its dense gas is held there, packed into frigid clusters called molecular clouds. Gases churn through at hundreds of kilometers per second.New molecules form in these giant clouds, especially from molecular hydrogen. Some of the clouds are also stellar nurseries, where clumps of gas and dust become stars.The CMZ has many quirks, but the new study focused on one in particular: an oddly positive charge to what is typically a neutral gas, implying something was knocking the electrons from the hydrogen molecules.Beyond trying to explain this, Balaji and his colleagues from Spain and France explored its potential link to the dark sector – a hypothetical array of quantum fields, mostly detached from our visible sector, that could enable dark matter’s existence.In the quest for a dark matter particle, scientific attention has gravitated to a group called ‘weakly interacting massive particles’, or WIMPs.These hypothetical particles interact with ordinary matter only through two of the four fundamental forces: gravity and the weak nuclear force.WIMPs remain unconfirmed despite decades of research targeting them. Many experts now advocate a broader, less WIMP-centric approach to dark matter.That could mean particles with even less connection to our visible sector, for example, or particles less massive than WIMPs.A leaner dark matter particle is not only possible, says Balaji, but might explain the CMZ’s positively charged hydrogen clouds.”At the center of our galaxy sit huge clouds of positively charged hydrogen, a mystery to scientists for decades because normally the gas is neutral. So what is supplying enough energy to knock the negatively charged electrons out of them?” Balaji says.”The energy signatures radiating from this part of our galaxy suggest that there is a constant, roiling source of energy doing just that, and our data says it might come from a much lighter form of dark matter than current models consider.”As lighter dark matter particles crash together, pairs of oppositely charged, non-dark particles emerge in a process known as annihilation, the researchers explain.These charged particles could then ionize hydrogen gas, potentially creating positively charged molecular clouds like those in the CMZ.Previous research has explored cosmic rays as a possible source of ionization, but energy signatures from CMZ observations seem too small to support that scenario.They don’t implicate WIMPs, either. Whatever is ionizing the hydrogen is slower than a cosmic ray and less massive than a WIMP, the researchers conclude.Their study outlines the plausibility of lighter dark matter, and while it makes a compelling case, this is still speculative. More research is needed, both to confirm what’s happening in the CMZ and to unmask dark matter.In the meantime, this demonstrates the value in casting a wider net for dark matter particles, the authors conclude, and in casting it far.”The search for dark matter is one of fundamental science’s most important objectives, but a lot of experiments are based on Earth, waiting with hands outstretched for the dark matter to come to them,” Balaji says.”By peering into the center of our Milky Way, the hydrogen gas in the CMZ is suggesting that we may be closer to identifying evidence on the possible nature of dark matter.”The study was published in Physical Review Letters.

Source: https://www.sciencealert.com/energy-signals-from-milky-ways-core-hint-at-new-type-of-dark-matter