Mysterious phenomenon at center of galaxy could reveal new kind of dark matter

A mysterious phenomenon at the center of our galaxy could be the result of a different type of dark matter.

Dark matter, the mysterious form of unobserved matter which could make up 85% of the mass of the known universe, is one of science’s biggest manhunts.

In this first of its kind study, scientists have taken a step closer to understanding the elusive mystery matter. They believe a reimagined candidate for dark matter could be behind unexplained chemical reactions taking place in the Milky Way.

Dr. Shyam Balaji, Postdoctoral Research Fellow at King’s College London and one of the lead authors of the study explains, “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?

“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.”

The most established theory for dark matter is that it is likely a group of particles known as Weakly Interacting Massive Particles (WIMPs), which pass through regular matter without much interaction—making them extremely hard to detect.

However, this study, published today in Physical Review Letters, has potentially revived another type of dark matter with much lower mass than a WIMP.

The researchers think that these tiny dark matter particles are crashing into each other and producing new charged particles in a process called “annihilation.” These newly produced charged particles can subsequently ionize the hydrogen gas.

Previous attempts to explain this ionization process had relied on cosmic rays, fast and energetic particles that travel throughout the universe. However, this explanation has faced some difficulties, as energy signatures recorded from observations of the Central Molecular Zone (CMZ) where this is happening, don’t seem to be large enough to be attributed to cosmic rays. Such a process doesn’t seem to be possible with WIMPs either.

The research team were left with the explanation that the energy source causing the annihilation is slower than a cosmic ray and less massive than a WIMP.

Dr. Balaji said. “The search for dark matter is science’s biggest manhunt, but a lot of experiments are based on Earth. By using gas at the CMZ for a different kind of observation, we can get straight to the source. The data is telling us that dark matter could potentially be a lot lighter than we thought.”

“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. 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 of the possible nature of dark matter.”

This finding may simultaneously explain wider mysteries of our galaxy, such as a specific type of X-ray observation found at the center of the Milky Way—known as the “511-keV emission line.” This specific energy signature could also be due to the same low-mass dark matter colliding and producing charged particles.