WHY THIS MATTERS IN BRIEF
- If it were not for the gravity of dark matter galaxies wouldn’t be able to hold themselves together and planets and stars would fly into oblivion
Understanding what Dark Matter is has proven to be amazingly difficult. Of course, one might expect this from a thing that is, for all intents and purposes, entirely invisible – albeit omnipotent. Scientists originally came to the conclusion that dark matter existed by observing the way gravity behaves and deciding that either our model of gravity is in need of an update, or dark matter exists. The latter is the most likely conclusion.
While there seem to be several phenomena explainable only by the existence of dark matter, there hasn’t been actual proof that it indeed exists. Studies abound, of course, but to date they have been inconclusive.
What we think we know is that dark matter comprises around almost a quarter of the total mass and energy in the observable universe. It can’t be seen, as it doesn’t seem to interact with photons, but it does interact with gravity, and this is what makes it observable.
By extending the Standard Model of particle physics and using the IBM JUQUEEN BlueGene/Q supercomputer at Jülich’s lab, the team led by Zoltán Fodor came up with elaborate calculations to predict just what particles make up dark matter.
Understanding what dark matter is, scientists believe, depends largely upon figuring out what particles make it up and it could be one of two possibilities – either dark matter is composed of a few very heavy particles or several light ones. Fodor’s team looked towards the latter. Of these, axions seem to be the most promising — although even these are still hypothetical and what the researchers needed was evidence that these extremely light subatomic particles exist.
Theoretically, the existence of axions can be explained as an extension to quantum chromodynamics (QCD), which predicts that very weakly interacting particles whose mass depend on quantum topological fluctuations can exist. To demonstrate this, the team used the JUQEEN supercomputer to calculate the conditions under which axions can exist and how they contribute to the matter that makes up the universe.
The results were promising. If dark matter is largely made up of axions, these should posses a mass of 50 to 1,500 micro-electronvolts (standard units of particle physics), which is up to ten billion times lighter than electrons — that’s an average of 10 million axions per cubic centimeter of the universe and that’s at least plausible.
“To find understand what dark matter is made of it’d be extremely helpful to know what kind of mass we are looking for,” said theoretical physicist Ringwald, “otherwise the search could take decades, because we’d have to scan far too large a range. The results we’ve seen are promising and will lead to a race to discover these particles,” says Fodor who predicts that, within a few years, it will be possible to experimentally confirm or rule out the existence of axions.
Thanks to the Jülich supercomputer, we may be a step closer to figuring out dark matter – now that we know what we need to look for.