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 visible matter 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 gravitational forces. 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.
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 particle physics. 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 dark matter 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.
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: Physics.org / ScienceWise / Leiden University News