04 March 2009 by Anil Ananthaswamy
IT IS 3.30am on 26 December 2007 in McMurdo, Antarctica. The crew at the long-duration balloon facility have stayed up all night in sub-zero temperatures, waiting for the winds to subside. Finally, the gigantic balloon lifts off. Filled with about a million cubic metres of helium, it soars high into the stratosphere carrying an experiment called ATIC.
For 19 days, ATIC circled the South Pole, studying cosmic rays coming from space. Then, nearly a year later, the ATIC team made a stunning announcement: they found that more high-energy electrons had left their mark on the experiment than expected. That might not sound like much, but the result is remarkable because it might be a telltale sign of dark matter, the invisible stuff thought to make up about 85 per cent of matter in the universe.
And it's not the only one. Just months before, an Italian-led collaboration reported that their satellite-based experiment, called PAMELA, had seen a similar excess of electrons, along with an excess of positrons. Add to this earlier results from gamma-ray satellites and experiments searching for dark matter here on Earth, and suddenly we have an abundance of new clues about dark matter. "It is a very exciting time to be doing dark-matter physics," says Dan Hooper, a physicist at the Fermi National Laboratory in Batavia, Illinois.
The bonanza of evidence suggests that dark matter might be far more complicated than we had ever imagined. For starters, the theoretician's favourite dark-matter candidate is falling out of favour, with the latest experiments making the case for new, exotic varieties of dark matter. If they are right, we could be living next to a "hidden sector", an unseen aspect of the cosmos that exists all around us and includes a new force of nature.
more:
http://www.newscientist.com/article/mg20126981.600-a-bizarre-universe-may-be-lurking-in-the-shadows.html