A new theoretical study published in Physical Review Letters on January 24, 2018, finds that the dark matter which we famously can neither see nor touch may be so elusive owing to its slow speed.
For decades astronomers have been faced with the puzzle of why the vast majority of stars in a spiral galaxy move faster than they should. The only explanation that makes sense to us is if in addition to the matter that we can see there is also a significant component of invisible matter.
One good way to try to detect this so-called “dark matter” is by placing a large vat of dense material such as xenon deep below the Earth’s surface, where it is safely out of the way of terrestrial energy sources. Then, we set a “trap” which will send an alert whenever a particle consistent with a dark matter particle collides with the atoms in the vat.
Unfortunately, despite careful efforts to build these experiments, so far we have fallen short of producing a positive result. The question remains of when will we get to hold a dark matter particle in our lab and say, “Look: here it is?!”
A brand new result from recent computer simulations indicate the motions of old stars in our Galaxy trace the motions of the dark matter, similar to how the tip of an iceberg traces the places where there is a lot of unseen mass under the water.
One interesting fact about very old stars is that they move more slowly than other stars. This result has the implication that the dark matter must therefore also progress about the Galaxy at slower speeds.
If this theoretical result holds, then we may now be able to explain the failure to detect dark matter in those underground experiments. It would be because to set off the traps would require only high-speed impacts with the xenon. The sluggish particles would not be detected at all.
Although exciting, we need to keep in mind that this is the result of a simulation. The next step is to make a prediction which will allow experimentalists to go out and conduct a new search.