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Researchers Detect Possible Signal From Dark Matter

FLI Dark Matter

A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope. To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. The gravity of the cluster’s trillion stars — plus dark matter — acts as a 2-million-light-year-wide lens in space. This gravitational lens bends and magnifies the light of the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6). Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter. Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA.

Could there finally be tangible evidence for the existence of dark matter in the Universe? After sifting through reams of X-ray data, scientists in EPFL’s Laboratory of Particle Physics and Cosmology (LPPC) and Leiden University believe they could have identified the signal of a particle of dark matter. This substance, which up to now has been purely hypothetical, is run by none of the standard models of physics other than through the gravitational force.

Their research will be published next week in Physical Review Letters.

When physicists study the dynamics of galaxies and the movement of stars, they are confronted with a mystery. If they only take into account, their equations simply don’t add up: the elements that can be observed are not sufficient to explain the rotation of objects and the existing . There is something missing. From this they deduced that there must be an invisible kind of matter that does not interact with light, but does, as a whole, interact by means of the gravitational force. Called “dark matter”, this substance appears to make up at least 80% of the Universe.

Andromeda and Perseus revisited

Two groups have recently announced that they have detected the much sought after signal. One of them, led by EPFL scientists Oleg Ruchayskiy and Alexey Boyarsky, also a professor at Leiden University in the Netherlands, found it by analyzing X-rays emitted by two celestial objects – the Perseus galaxy cluster and the Andromeda galaxy. After having collected thousands of signals from the ESA’s XMM-Newton telescope and eliminated all those coming from known particles and atoms, they detected an anomaly that, even considering the possibility of instrument or measurement error, caught their attention.

The signal appears in the X-ray spectrum as a weak, atypical photon emission that could not be attributed to any known form of matter. Above all, “the signal’s distribution within the galaxy corresponds exactly to what we were expecting with dark matter, that is, concentrated and intense in the center of objects and weaker and diffuse on the edges,” explains Ruchayskiy. “With the goal of verifying our findings, we then looked at data from our own galaxy, the Milky Way, and made the same observations,” says Boyarsky.

FLI Oleg Ruchayskiy

Co-author Oleg Ruchayskiy, of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland.

A new era

The signal comes from a very rare event in the Universe: a photon emitted due to the destruction of a hypothetical particle, possibly a “sterile neutrino”. If the discovery is confirmed, it will open up new avenues of research in . Apart from that, “It could usher in a new era in astronomy,” says Ruchayskiy. “Confirmation of this discovery may lead to construction of new telescopes specially designed for studying the signals from particles”, adds Boyarsky. “We will know where to look in order to trace dark structures in space and will be able to reconstruct how the Universe has formed.”

Glimmer of light in the search for dark matter

In February 2014 Leiden University announced the following:
The Leiden astrophysicist Alexey Boyarsky and his fellow researchers may have identified a trace of dark matter that could signify a new particle: the sterile neutrino. A research group in Harvard reported a very similar signal just a few days earlier.

FLI Alexey Boyarsky

Boyarsky is assistant professor at the Leiden Institute for Research in Physics (LION) where he conducts research on dark matter and the early Universe. The discovery of the incidence of the sterile neutrino was made by Boyarsky’s research group together with Oleg Ruchayskiy, a researcher at the Ecole Polytechnique Fédérale de Lausanne in Switzerland.

Sterile neutrino has mass

The two groups this week reported that they have found an indirect signal from dark matter in the spectra of galaxies and clusters of galaxies. They made this discovery independent of one another, but came to the same conclusion: a tiny spike is hidden in the xX-ray spectra of the Perseus galaxy cluster, at a frequency that cannot be explained by any known atomic transition. The Harvard group see the same spike in many other galaxy clusters, while Boyarsky also finds it in the nearby Andromeda galaxy. The researchers put it down to the decay of a new kind of neutrino, called ‘sterile’ because it has no interaction with other known neutrinos. A sterile neutrino does have mass, and so could be responsible for the missing dark matter.

Minor expansion of the standard model for elementary particles

The first indications for the existence of dark matter in space were found more than eighty years ago, but there are still many questions surrounding this invisible matter. Sterile neutrinos are a highly attractive candidate for the dark matter particle, because they only call for a minor extension of the already known and extensively tested standard model for elementary particles. Boyarsky and his colleagues have already had this extension of the standard model ready for some time, but were waiting for the first observation of the mysterious particle. Measurements at higher resolution will shed light on the matter, and there is reason to hope that the spectral line just discovered will finally eliminate the problem of the missing mass.


Sources: / ScienceWise / Leiden University News

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