As soon as once more, a seek for indicators of dark matter outdoors its gravitational impact has turned up zilch – however this time it is somewhat extra controversial. Astronomers peering into empty house haven’t discovered an X-ray glow hypothesised to be the product of 1 explicit darkish matter candidate: the sterile neutrino.
It’s, the researchers say, a end result that throws a little bit of a dampener on this candidate as a number one contender for darkish matter – however does not extinguish it fully.
Darkish matter is a large outdated query mark. Though we will not detect it instantly, we all know it is on the market as a result of it is having a very large gravitational impact on the stuff we are able to detect, often known as regular matter.
As an illustration, stuff on the outer edges of galaxies strikes sooner than it ought to if it have been below the gravitational affect of regular matter alone. And gravitational lensing – the way in which gravity bends the trail of sunshine – is stronger than we’d count on, too. From these results, astronomers have calculated that as a lot as 85 p.c of the matter within the Universe is darkish matter.
As a result of we will not detect it, although, we do not know what it’s. And there are a variety of hypothetical candidates, with astronomers attempting to provide you with methods to detect these.
The sterile neutrino is a hypothetical particle. Regular neutrinos, probably the most plentiful particles within the Universe, are very laborious to detect at the most effective of instances – they’re much like electrons, however with no cost and little or no mass, in order that they barely work together with regular matter. A sterile neutrino, physicists have hypothesised, would not work together with regular matter in any respect, besides perhaps gravitationally.
However these hypothetical neutrinos are unstable, too. They need to decay into regular neutrinos and electromagnetic radiation. And, if they’re so decaying, then that radiation ought to be detectable. Very faint, however detectable.
That is what a 2014 study claimed to have completed – detected the faint X-rays from sterile neutrino decay from distant galaxies, an emission known as the three.5 KeV line. However then follow-up research – one in 2016 on a dwarf galaxy 260,000 light-years away, and another in 2017 on a galaxy cluster 240 million light-years away – discovered no such factor.
So, a staff of researchers determined to look a bit nearer to residence. We all know the Milky Method has a substantial dark matter halo, so if sterile neutrinos are decaying in it, they need to be detectable across the galaxy.
The staff performed a meta-analysis of 20 years of uncooked archival X-ray information of empty house across the Milky Method, the place different glowing objects would not create interference, taken by the XMM-Newton house telescope, in search of indicators of that 3.5 KeV emission. They did not discover any.
“This 2014 paper and follow-up works confirmed the sign generated a big quantity of curiosity within the astrophysics and particle physics communities due to the potential for understanding, for the primary time, exactly what darkish matter is at a microscopic stage,” said physicist Ben Safdi of the College of Michigan.
“Our discovering doesn’t imply that the darkish matter just isn’t a sterile neutrino, but it surely implies that – opposite to what was claimed in 2014 – there isn’t a experimental proof to-date that factors in direction of its existence.”
The end result means that one thing else was inflicting the three.5 KeV glow seen in that 2014 research, the researchers mentioned. However not everyone seems to be satisfied. Physicist Alexey Boyarsky of Leiden College within the Netherlands posted a similar survey to preprint server arXiv, trying on the clean sky of the Milky Method. His staff believes they did discover the three.5 KeV line.
“I feel this paper is fallacious,” he said of the new research to Science Magazine. The totally different outcomes might be the product of the 2 totally different evaluation strategies; each groups consider their methodology is superior, though Boyarsky’s paper is but to be peer-reviewed.
So it appears the query should still be considerably open, and solely extra analysis might help to resolve it.
In the meantime, there’s one other route that may be taken, too. Safdi says that his staff’s conclusions open up a brand new avenue for additional search on the matter.
“Whereas this work does, sadly, throw chilly water on what seemed like what might need been the primary proof for the microscopic nature of darkish matter, it does open up a complete new method to in search of darkish matter which might result in a discovery within the close to future,” he said.
The analysis has been revealed in Science.