Inexplicable signal from unseen universe provides tantalizing clue about one of astronomy's greatest secrets --- dark matter.

Date:
October 16, 2014
Source:
University of Leicester

The first potential indication of direct detection of dark matter -- something that has been a mystery in physics for over 30 years -- has been attained. Astronomers found what appears to be a signature of 'axions', predicted 'dark matter' particle candidates.

FIGURE: A sketch (not to scale) showing axions (blue) streaming out from the Sun, converting in the Earth's magnetic field (red) into X-rays (orange), which are then detected by the XMM-Newton observatory. (Credit: Coopyright University of Leicester)

Cutting-edge paper by Professor George Fraser -- who tragically died in March this year -- and colleagues at the University of Leicester provides first potential indication of direct detection of Dark Matter -- something that has been a mystery in physics for over 30 years.

Space scientists at the University of Leicester have detected a curious signal in the X-ray sky -- one that provides a tantalising insight into the nature of mysterious Dark Matter.

The Leicester team has found what appears to be a signature of 'axions', predicted 'Dark Matter' particle candidates -- something that has been a puzzle to science for years.

In a study being published on Monday 20 October in the Monthly Notices of the Royal Astronomical Society, the University of Leicester scientists describe their finding of a signal which has no conventional explanation.

As first author Professor George Fraser, who sadly died in March of this year, wrote: "The direct detection of dark matter has preoccupied Physics for over thirty years." Dark Matter, a kind of invisible mass of unknown origin, cannot be seen directly with telescopes, but is instead inferred from its gravitational effects on ordinary matter and on light. Dark Matter is believed to make up 85% of the matter of the Universe.

"The X-ray background -- the sky, after the bright X-ray sources are removed -- appears to be unchanged whenever you look at it," explained Dr. Andy Read, also from the University of Leicester Department of Physics and Astronomy and now leading the paper. "However, we have discovered a seasonal signal in this X-ray background, which has no conventional explanation, but is consistent with the discovery of axions."

This result was found through an extensive study of almost the entire archive of data from the European Space Agency's X-ray observatory, XMM-Newton, which will celebrate its 15th year in orbit this December. Previous searches for axions, notably at CERN, and with other spacecraft in Earth orbit, have so far proved unsuccessful.

As Professor Fraser explains in the paper: "It appears plausible that axions -- Dark Matter particle candidates -- are indeed produced in the core of the Sun and do indeed convert to X-rays in the magnetic field of the Earth." It is predicted that the X-ray signal due to axions will be greatest when looking through the sunward side of the magnetic field because this is where the field is strongest.

Dr. Read concludes: "These exciting discoveries, in George's final paper, could be truly ground-breaking, potentially opening a window to new physics, and could have huge implications, not only for our understanding of the true X-ray sky, but also for identifying the Dark Matter that dominates the mass content of the cosmos."

President of the Royal Astronomical Society Professor Martin Barstow, who is Pro-Vice-Chancellor, Head of the College of Science & Engineering and Professor of Astrophysics & Space Science at the University of Leicester said: "This is an amazing result. If confirmed, it will be first direct detection and identification of the elusive dark matter particles and will have a fundamental impact on our theories of the Universe."

The XMM-Newton observatory, its operations and data archive, constitute a major international collaboration within the European Space Agency (ESA) member states and beyond. The work of a number of authors on the calibration of XMM-Newton was supported by the UK Space Agency (UKSA).

Story Source:
The above story is based on materials provided by University of Leicester. Note: Materials may be edited for content and length.

Journal Reference:
G. W. Fraser, A. M. Read, S. Sembay, J. A. Carter, E. Schyns. Potential solar axion signatures in X-ray observations with the XMM-Newton observatory.Monthly Notices of the Royal Astronomical Society, 20 October, 2014 (in press) [link]

Source

Science Daily

Second experiment hints at seasonal dark matter signal

Things just got a little less lonely for researchers who have been insisting for years not only that their experiment has found dark matter, but also that the dark matter signal varies with the seasons. Now a second experiment, called CoGeNT, is reporting similar findings, though both results are in conflict with two other teams' observations.

No one knows what dark matter is – astronomers merely detect its gravitational pull on normal matter, which it seems to outweigh by a factor of five to one. But many researchers believe it is made of theoretical particles called WIMPs, which interact only weakly with normal matter.

Since 1998, researchers running the DAMA experiment deep inside the Gran Sasso mountain in Italy have claimed to have found evidence of WIMPs.

DAMA uses an array of sodium iodide detectors to spot the rare moments when WIMPs slam into atoms in the detectors, producing flashes of light. The number of flashes ebbs and flows with the seasons, and DAMA team members argue that this is because Earth's velocity relative to the surrounding sea of dark matter changes as the planet orbits the sun. They say their observations could be explained by a WIMP weighing a few gigaelectronvolts.

Tense situation

However two other experiments have found no sign of dark matter with their detectors. One, called XENON100, uses 100 kilograms of liquid xenon deep below Gran Sasso mountain, and the other, called CDMS II, uses ultra-pure crystals of germanium and silicon housed in a deep mine in Soudan, Minnesota.

Both experiments are so sensitive that they should have seen dark matter if the DAMA result is due to WIMPs. "The situation has created tension," says Dan Hooper, a theorist at the University of Chicago in Illinois.

Now another dark matter experiment called CoGeNT has found a seasonal variation in its results, reports team leader Juan Collar, who presented an analysis of 442 days of observations at the American Physical Society meeting in Anaheim, California, on Monday.

Germanium crystal

"We tried like everyone else to shut down DAMA, but what happened was slightly different," Collar said during his presentation.

"The annual modulation is the closest thing to a smoking gun [for dark matter]," says theorist Jonathan Feng at the University of California, Irvine, who is not part of the CoGeNT team. "This is the first evidence we've seen it somewhere other than DAMA."

The CoGeNT detector is tiny compared with many other dark matter experiments. It comprises a 440-gram crystal of germanium. Still, dark matter is so abundant that 100 million particles of it are expected to pass through the CoGeNT detector every second.

About once a day, one of these will wallop a germanium nucleus, sending the nucleus careering through the crystal, where it rips electrons from neighbouring atoms. An electric field sweeps these electrons towards an electrode to produce a tiny electrical signal.

Background noise?

Previously, the CoGeNT team reported an excess of events when it ran its experiment in the Soudan mine for 56 days (Physical Review Letters, DOI: 10.1103/PhysRevLett.106.131301). Team members said the excess could be due to some kind of background noise that physicists don't understand, or potentially to WIMPs weighing 7 GeV.

The experiment kept running continuously until a fire in the Soudan mine on 17 March halted observations. This motivated Collar and his colleagues to look for a seasonal variation in the 442 days of observations they had already collected. "I hope this isn't the final data we have taken," says Collar, who has not yet been allowed to return to the Soudan mine to check for damage.

The CoGeNT team finds that their signal changes with the seasons in exactly the same way as the DAMA result does. And it is consistent with a low-mass dark matter particle, like that reported by DAMA.

Weird WIMP

Laura Baudis at the University of Zurich in Switzerland, who reported at the meeting on Monday that XENON100 still had seen no signs of dark matter, is not sure what to make of the results: "I need time to think about them."

Feng suggests that the discrepancy among all the experimental results may simply be due to the assumption that WIMPs interact the same way with protons and neutrons. If this is not the case, that could explain differences in the signals from xenon and germanium detectors, which each have a different ratio of protons to neutrons (arxiv.org/abs/1102.4331). "These experiments may look inconsistent, but a small theoretical tweak can bring everything in to line," he told New Scientist.

Both the CoGeNT and XENON100 teams are planning to enlarge their experiments. Approval has just been given to build the XENON1T experiment in the Gran Sasso mine, which will use 1 tonne of liquid xenon. And the CoGeNT team is planning to replace its single germanium crystal with four separate crystals, each weighing 1 kilogram, starting later this year.

Source New Scientist

Cosmic-ray Detector on Space Shuttle Set to Scan Cosmos for Dark Matter

A fancy cosmic-ray detector, the Alpha Magnetic Spectrometer, is about to scan the cosmos for dark matter, antimatter and more

By George Musser 

The world’s most advanced cosmic-ray detector took 16 years and $2 billion to build, and not long ago it looked as though it would wind up mothballed in some warehouse. NASA, directed to finish building the space station and retire the space shuttle by the end of 2010, said it simply did not have room in its schedule to launch the instrument anymore. Saving it took a lobbying campaign by physicists and intervention by Congress to extend the shuttle program. And so the shuttle ­Endeavour is scheduled to take off on April 19 for the express purpose of delivering the Alpha Magnetic Spectrometer (AMS) to the International Space Station.

 Image: Illustration by Don Foley; Source for ISS model: NASA

Cosmic rays are subatomic particles and atomic nuclei that zip and zap through space, coming from ordinary stars, supernovae explosions, neutron stars, black holes and who knows what—the last category naturally being of greatest interest and the main impetus for a brand-new instrument. Dark matter is one of those possible mystery sources. Clumps of the stuff out in space might occasionally release blazes of particles that would set the detectors alight. Some physicists also speculate that our planet might be peppered with the odd antiatom coming from distant galaxies made not of matter but of its evil antitwin.

Courtesy of Scientific American