10:00 24 June 2007
NewScientist.com news service

IF THE universe has weird extra-spatial dimensions in parallel to the 3D world we see around us, then billion-dollar particle accelerators may not be the only place to find them.

So say Gergely Gabor Barnaföldi and colleagues at the Research Institute for Particle and Nuclear Physics in Budapest, Hungary, who propose that extra dimensions may show their face in areas of extreme gravity around dense stars. The concept could also solve a 25-year-old puzzle about the origin of mysterious particles emanating from a distant star system.

Some string theories predict that there are many more dimensions than the four we experience: the 3D world plus time. From next year, particle physicists hope to spot these dimensions at the Large Hadron Collider near Geneva, Switzerland.

Instead, Barnaföldi's team looked to outer space for evidence of extra dimensions interacting with matter. They analysed the Cygnus X-3 binary system, in which a normal star orbits a second object, generally thought to be a neutron star.

Objects in Cygnus X-3 are under extreme gravity, which the researchers say would provide the necessary conditions for extra dimensions to affect matter. Moreover, it spews out ultra-high-energy particles as far as Earth, which the team say could have been tweaked by an extra dimension inside the system. Astronomers believe these high-energy particles, dubbed "cygnets", strike our atmosphere and decay into muons. Since 1981, underground detectors on Earth have recorded sporadic showers of muon particles coming from the direction of Cygnus X-3. The cygnets are a puzzle because no known particles could last the 37,000-light-year journey from Cygnus X-3 to Earth without decaying.

Some astrophysicists have speculated that these long-lived cygnets may originate in a quark star - a hypothetical star that may form when neutron stars collapse. If such quark stars contained a large number of "strange" type quarks, they might radiate out long-lived cygnets. The problem is that so many strange quarks in a star would make it collapse into a black hole.

According to Barnaföldi's team, the necessary stability could be provided by a universe-spanning fifth dimension rolled up into tiny "rings". In most places in the universe, this fifth dimension would not affect matter, but under the extreme gravity conditions inside Cygnus X-3 it could cause other types of quark to behave like strange quarks. "If we could watch these quarks, they would seem to travel along our three dimensions more slowly than expected because, at the same time, they have to circle round this invisible curly extra dimension," says team member Peter Levai. "Effectively they behave as strange quarks."

Fridolin Weber, an astrophysicist at San Diego State University, California, likes the proposal. "Cygnus X-3 is perfect for searching for extra dimensions," he says. "It's basically a cosmic particle accelerator." But he adds that more evidence is needed to explain the cygnets' origin. The work will appear in the journal Astronomische Nachrichten.

http://space.newscientist.com/article/dn12120-astronomers-look-to-quark-stars-for-a-fifth-dimension.html