European scientists have detected a mysterious photon emission in X-ray spectra of the Andromeda galaxy, the Draco dwarf galaxy and some other galaxies and galactic clusters that could be the first evidence of the long-sought dark matter particles.
This Hubble composite image shows a ring of dark matter in the galaxy cluster ZwCl0024+1652; the ring-like structure is evident in the blue map of the cluster’s dark matter distribution; the map is superimposed on a Hubble image of the cluster. Image credit: NASA / ESA / M.J. Jee and H. Ford, Johns Hopkins University.
First proposed by the Swiss astronomer Fritz Zwicky in the 1930s, dark matter is a mysterious substance that cannot be seen, but shows itself by its gravitational attraction for the material around it.
This extra ingredient in the cosmos was originally suggested to explain why the outer parts of galaxies, including our own Milky Way, rotated so quickly, but dark matter now also forms an essential component of theories of how galaxies formed and evolved.
Today it is widely accepted that this dark component constitutes about the 80 percent of the mass in the Universe, despite the fact that it has resisted all attempts to clarify its nature, which remains obscure. All attempts so far to detect dark matter in labs on Earth have failed.
Two teams of scientists have recently announced the detection of a strange signal in X-ray spectra of nearby galaxies.
One of the teams, led by Dr Alexey Boyarsky of Leiden University in the Netherlands, found this signal by analyzing X-rays emitted by the Draco dwarf galaxy, the Perseus galaxy cluster and the Andromeda galaxy (M31).
“After having collected thousands of signals from the ESA’s XMM-Newton telescope and eliminated all those coming from known particles and atoms, we detected an anomaly that caught our attention,”
The signal appears in the X-ray spectrum as an atypical photon emission that could not be attributed to any known form of matter.
“Above all, the signal’s distribution 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,” said team member Dr Oleg Ruchayskiy from the Ecole Polytechnique Federale de Lausanne in Switzerland.
“With the goal of verifying our findings, we then looked at data from our own galaxy, the Milky Way, and made the same observations,” Dr Boyarsky added.
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.’
Sterile neutrinos are a highly attractive candidate for the dark matter particle, because they only call for a minor extension of the already known standard model of elementary particles.
“If the discovery is confirmed, it will open up new avenues of research in particle physics. Apart from that, it could usher in a new era in astronomy,” Dr Ruchayskiy said.
“Confirmation of this discovery may lead to construction of new telescopes specially designed for studying the signals from dark matter particles. 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,” Dr Boyarsky said.
A new, separate paper on the subject will be published next week in the journal Physical Review Letters.
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Alexey Boyarsky et al. 2014. An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster. arXiv: 1402.4119
Mark R. Lovell et al. 2014. Decaying dark matter: the case for a deep X-ray observation of Draco. MNRAS, to be submitted; arXiv: 1411.0311
Alexey Boyarsky et al. 2014. Checking the dark matter origin of 3.53~keV line with the Milky Way center. arXiv: 1408.2503
