Have scientists had their first glimpse of dark matter?

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.
University of Leicester

Researchers at the University of Leicester say they may have detected dark matter particles for the first time.

In a study published in the Monthly Notices of the Royal Astronomical Society say they have no conventional explanation for the curious signal in the X-ray background.

The findings require checking, but if confirmed they would represent a major advance in the understanding of the Universe.

The observation came after 15 years of measurements by the European Space Agency’s orbiting XMM-Newton observatory, which showed an increase in intensity of X-rays at the edge of the Earth’s magnetic field that faces towards the sun.

"The X-ray background – the sky, after the bright X-ray sources are removed – appears to be unchanged whenever you look at it," the lead author Dr. Andy Read from the University of Leicester Department of Physics and Astronomy told reporters."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 (the hypothetical elementary particle that are a candidate as dark matter particles)."

The original lead author of the paper, Professor George Fraser, also from Leicester, died in March, but he wrote 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."

Meanwhile, astronomers from the Max Planck Institute for Astronomy have created the first three-dimensional map of the "adolescent" Universe, just 3 billion years after the Big Bang – when it was a quarter of its current age – which might give further insights into dark matter.

The map gives glimpses of large structures in the "cosmic web" – the backbone of which is dark matter. Dark matter emits no light but is suffused with primordial hydrogen gas left over from the Big Bang.

3D map of the cosmic web at a distance of 10.8 billion light years from Earth. The map was generated from imprints of hydrogen gas observed in the spectrum of 24 background galaxies, which are located behind the volume being mapped. This is the first time that large-scale structures in such a distant part of the Universe have been mapped directly. The coloring represents the density of hydrogen gas tracing the cosmic web, with brighter colors representing higher density.
Caset Stark, UC Berkeley and Khee-Gan Lee, MPIA

Galaxies, such as our own Milky Way, are embedded inside this cosmic web, but make up only a tiny fraction of its volume.

The model was built by a team led by Khee-Gan Lee, a post-doctoral researcher at the Max Planck Institute for Astronomy, using data collected from the W. M. Keck Observatory in Hawaii. It represents dimensions of millions of light-years of a section of the Universe 11 billions light years away from Earth.

It uses faint background galaxies as light sources, against which gas could be seen by the characteristic absorption features of hydrogen. The wavelengths of each hydrogen feature showed the presence of gas at a specific distance from us.

The Keck observatory explained the significance of the findings:

Combining all of the measurements across the entire field of view allowed the team a tantalising glimpse of giant filamentary structures ... and paves the way for more extensive studies that will reveal not only the structure of the cosmic web, but also details of its function – the ways that pristine gas is funneled along the web into galaxies, providing the raw material for the formation of galaxies, stars, and planets.

  1. http://www2.le.ac.uk/offices/press/press-releases/2014/october/inexplicable-signal-from-the-unseen-universe-provides-tantalising-clue-about-one-of-astronomys-greatest-secrets-2013-dark-matter
  2. http://arxiv.org/abs/1403.2436
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