Shedding light on darkness: A NASA image taken with the Hubble Space Telescope, shows what is inferred to be a massive ring of dark matter exerting a gravitational effect on light from the galactic cluster CL0024+17.
Credit: NASA
SYDNEY: European astrophysicists have reported on possible evidence of the elusive particles behind dark matter, controversially using data leaked from an international conference.
Dark matter is an invisible form of matter that pervades the universe. It has never been directly detected, but physicists have inferred its presence due to the gravitational pull it exerts on light.
The new research, led by astrophysicists Marco Cirelli, from the Institute of Theoretical Physics of the French Atomic Commission, in Saclay, France, and Alessandro Strumia, from the National Institute of Nuclear Physics, in Italy, has been published on the Arxiv physics website.
Sneak peak
The study has stoked controversy by citing unpublished data from the Russian-Italian PAMELA space mission, which uses a satellite observatory to study charged particles in cosmic radiation, and search for evidence of the elusive particles that are dark matter.
Cirelli and Strumia took the data via a photograph of a PowerPoint slide presented at the Identification of Dark Matter Conference held in Stockholm, Sweden, in late August, but not yet been released by the PAMELA team themselves.
The preliminary results from the image reveal an excess of unusual high-energy positrons, the antimatter counterpart to the electron (see New twist to matter-antimatter mystery, Cosmos Online).
Low-energy positrons are created naturally when ordinary matter interacts. But there is no physical environment involving ordinary matter that can explain the creation of very high-energy positrons. Since normal matter isn't the culprit, dark matter must be involved, the authors believe.
Though the results don't reveal what the dark matter particles are, they do give clues as to what kind of particles must be involved to produce the high-energy positron excess.
Cirelli and Strumia argue that the results from PAMELA fit their adjusted version of the Standard Model, a physics theory which describes the interaction of the known forces acting on all matter in the universe. The Standard Model on its own doesn't explain the existence of dark matter, and various theories have been propounded to adjust the model.
Their new 'Minimal Dark Matter' model adds the minimal amount of ingredients, without ruining the good features of the Standard Model, they said.
Cheeky science
The photograph "doesn't seem to us such a big deal,"
Cirelli told Cosmos Online. "We live in the 21st century, we had our camera in the backpack because we had foreseen some sightseeing of Stockholm after the conference, and we suspected that the PAMELA speaker would have shown these eagerly expected data without releasing the actual image."
"Taking the picture is just a little 'technological step' above keeping a mental record of the results shown and using them in further work," he said. "This is what people have always done and this is what conferences are for: communicating your results and taking the results of others in. With a camera or with your eyes."
Cirelli added that the PAMELA scientists also agreed that they could use the data in their study. The researchers involved with PAMELA have yet to officially comment, or release any of their own findings based on the data.
Australian astrophysicist Geraint Lewis, from the Institute of Astronomy at the University of Sydney, said while taking the photo was "very cheeky", it was not the first instance he'd seen. "People have done this sort of thing for years to try and get ahead in the game".
"It will be interesting to see what happens in the coming days and weeks, especially when the PAMELA results are released. I don't know if there will be a political comeback on these guys for publishing," he said. "[But] I don't think they'll be going for drinks with the PAMELA guys."
Narrowing the search
Commenting on the science itself, Lewis said that the researchers' model, which predicts high-energy positrons at a similar, but lower, level than those found by PAMELA, was a "reasonably good match".
Lewis doesn't believe the research is the "smoking gun" to reveal the particle behind dark matter particle, though: "There's enough freedom in the parameters of [the adjusted standard models] which means they may fit many data sets," he said. "We'll see other people's models appear in the next few days that say the same thing."
Cirelli argued that a crucial test of their own and other physicist's models of dark matter will come from the data at higher energies to be released by the PAMELA (which stands for Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics) team in the future.
If their own model is confirmed, the experiment represented the first time that such clear evidence of dark matter had been seen, said Cirelli. It would mean that scientists could narrow down the search for that dark matter to a particle with specific properties of mass, which interacted weakly with normal matter and yielded high-energy positrons as a consequence of those interactions.
