Wednesday, July 2, 2014

'Sterile neutrinos' re-ignites and excites Dark Matter debate - video

Astro-physicists remain cautiously excited about an unexpected X-ray signal discovered in a survey of galactic clusters.

Having first put their findings in the public sphere in March, the work has now passed peer review to hit the presses in the prestigious Astrophysical Journal, and re-ignite discussion about whether the rays represent at least a chunk of the missing stuff in the cosmos.

It's the frequency of the signal that's excited the astronomers' imaginations, since spectroscopy even at high energies is sufficiently familiar that something new demands attention.

The emission line occurs at an energy of (3.55-3.57)+/-0.03 keV – let's say “between 3.55 and 3.57 kilo-electron-volts.

Perhaps cautious after the recent BICEP-CMB 'Big Bang' controversy, which still hasn't been completely resolved, the news from ESA and NASA has been given a much more muted reception saying that “this will be huge if it's right”.

It will be huge: the missing matter in the universe remains one of astrophysics' biggest puzzles along with the search for dark energy.

The world is host to a number of sophisticated instruments designed to track down dark matter, but without positively identifying the source.

What the analysis of data from NASA's Chandra X-ray observatory and the ESA's XMM-Newton instrument has turned up is an unexpected line in the X-ray spectrum, while looking at the Perseus cluster.

Galactic clusters are among the largest-scale structures in the universe, consisting of galaxies interacting via gravity, along with the hot gas filling the space between them.

They're also one of the reasons we believe in dark matter, since the observable mass of clusters makes up only 20 per cent of the mass needed to provide the necessary gravity. The rest is presumed to be dark matter.

NASA's press release stated: there's a faint X-ray emission line discovered in the analysis of the Perseus cluster, which is matched by the same line in an analysis of another 73 galactic clusters.

ESA's release explains that while a single image of Perseus showed the line, composite images were needed to detect it in the other galactic clusters.

The research has been posted at Arxiv. NASA stated: “The authors suggest this emission line could be a signature from the decay of a 'sterile neutrino.'

Sterile neutrinos are a hypothetical type of neutrino that is predicted to interact with normal matter only via gravity. Some scientists have proposed that sterile neutrinos may at least partially explain dark matter”.

NASA goes on to point out that 55 other papers offering theories about the X-ray line already cite the original work.

Perseus, about 250 million light years away, has sparked a search for an X-ray emission. 

Credit: NASA

Co-author Maxim Markevitch from Goddard Space Flight Center says the mere possibility that a signature of sterile neutrinos is exciting, but cautions: “We have a lot of work to do before we can claim, with any confidence, that we’ve found sterile neutrinos”.

At ESA, lead author Dr Esra Bulbul from the Harvard-Smithsonian Center for Astrophysics in Cambridge explains: “If this strange signal had been caused by a known element present in the gas, it should have left other signals in the X-ray light at other well-known wavelengths, but none of these were recorded.”

Dr Bulbul doesn't say that sterile neutrinos might make up all of the missing matter in the universe, only that they could be part of it.

Check out more information on this story at NASA Chandra site

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