Are scientists close to identifying dark matter?
It's one of science's deepest mysteries – but could the quest to identify dark matter, that intangible stuff that makes up a quarter of the known universe, be reaching its conclusion? New research could bring us a step closer to finding the answer.
It was the astronomer Fritz Zwicky, pointing his telescope at the Coma galaxy cluster back in 1933, who first coined the phrase 'dark matter' to describe a theoretical, unidentified substance holding stars and galaxies together. Calculating the gravitational mass of the cluster, he found the value was at least 400 times more than their luminosity would suggest. He also noticed that the Coma galaxies moved much too fast than if they were held together by the gravitational pull of just the visible matter. Some other, extra mass must be holding it together, he reasoned.
Cornell University physicist Vera Rubin added weight to this idea in 1950, noting that bodies at the edge of the universe moved at the same speed as those at the centre, apparently defying Newton's laws. There must be something holding them together, she concluded, and that thing had to be dark matter.
Fast-forward to 1973 and Jeremiah Ostriker and Jim Peebles, physics professors at Princeton University, are drawing up a theoretical model of the universe in a pioneering computer simulation. Something is missing from the picture; there is more mass in the universe than their calculations accounted for. They know that adding considerably more matter to the model will generate the gravity needed to hold their model together. Sitting down at the computer, they work Zwicky's theory of dark matter into the equation, and the experiment proves to be a success.
Dark matter does not absorb or emit light or other electromagnetic waves, so discovering and identifying it has long proven to be a difficult task. Nonetheless, we have been able to measure its gravitational pull on celestial bodies. There is believed to be five times more of it than of regular matter.
The strongest evidence of dark matter to date has been picked up by NASA's Fermi satellite since 2009. This unexplained barrage of gamma rays emanating from the Milky Way has been suspected to hold our strongest chance of discovering the key to the mystery of dark matter. Later discoveries of a similar signal coming from dwarf galaxies added weight to the evidence of this gamma ray.
Now the findings of two independent studies, both at Cornell University, suggest that these signals may be made up of thousands of as-yet-undiscovered pulsars; the rotting, gyrating corpses of dead stars. If these studies are correct, there would appear to be many more pulsars out there in space than we were previously aware of.
Although inconclusive, these studies significantly reduce the plausibility of the theory that these gamma rays hold the true identity of dark matter.
However, a further chapter is about to begin, as new data is expected to be released by the Fermi satellite soon, allowing physicists to refine their research – and so the interstellar detective story continues…