Mysterious X-ray signal intrigues astronomers

Mysterious X-ray signal intrigues astronomers
Credit: X-ray: NASA/CXC/SAO/E.Bulbul, et al.
(Phys.org) —A mysterious X-ray signal has been found in a detailed study of galaxy clusters using NASA's Chandra X-ray Observatory and ESA's XMM-Newton. One intriguing possibility is that the X-rays are produced by the decay of sterile neutrinos, a type of particle that has been proposed as a candidate for dark matter.

While holding exciting potential, these results must be confirmed with additional data to rule out other explanations and determine whether it is plausible that dark matter has been observed.

Astronomers think dark matter constitutes 85% of the matter in the Universe, but does not emit or absorb light like "normal" matter such as protons, neutrons and electrons that make up the familiar elements observed in planets, stars, and galaxies. Because of this, scientists must use indirect methods to search for clues about dark matter.

The latest results from Chandra and XMM-Newton consist of an unidentified X-ray , that is, a spike of intensity at a very specific wavelength of X-ray light. Astronomers detected this emission line in the Perseus galaxy cluster using both Chandra and XMM-Newton. They also found the line in a combined study of 73 other galaxy clusters with XMM-Newton.

"We know that the dark matter explanation is a long shot, but the pay-off would be huge if we're right," said Esra Bulbul of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. who led the study. "So we're going to keep testing this interpretation and see where it takes us."

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.

"We have a lot of work to do before we can claim, with any confidence, that we've found sterile neutrinos," said Maxim Markevitch, a co-author from NASA's Goddard Space Flight Center in Greenbelt, Maryland. "But just the possibility of finding them has us very excited."

One source of uncertainty is that the detection of this emission line is pushing the capabilities of the two observatories in terms of sensitivity. Also, there may be explanations other than if this X-ray emission line is deemed to be real. There are ways that normal matter in the cluster could have produced the line, although the team's analysis suggested that all of these would involve unlikely changes to our understanding of physical conditions in the galaxy cluster or the details of the atomic physics of extremely hot gases.

The authors note that even if the sterile neutrino interpretation is correct, their detection does not necessarily imply that all of dark matter is composed of these particles.

"Our next step is to combine data from Chandra and JAXA's Suzaku mission for a large number of to see if we find the same X-ray signal," said co-author Adam Foster, also of CfA. "There are lots of ideas out there about what these data could represent. We may not know for certain until Astro-H launches, with a new type of X-ray detector that will be able to measure the line with more precision than currently possible."

Because of the tantalizing potential of these results, after submitting to The Astrophysical Journal the authors posted a copy of the paper to a publicly accessible database, arXiv. This forum allows scientists to examine a paper prior to its acceptance into a peer-reviewed journal. The paper ignited a flurry of activity, with 55 new papers having already cited this work, mostly involving theories discussing the emission line as possible evidence for dark matter. Some of the papers explore the sterile neutrino interpretation, but others suggest different types of candidate particles, such as the axion, may have been detected.

Only a week after Bulbul et al. placed their paper on the arXiv, a different group, led by Alexey Boyarsky of Leiden University in the Netherlands, placed a paper on the arXiv reporting evidence for an emission line at the same energy in XMM-Newton observations of the galaxy M31 and the outskirts of the Perseus cluster. This strengthens the evidence that the emission line is real and not an instrumental artifact.

The paper describing the new Chandra and XMM-Newton observations appears in the June 20, 2014 issue of The Astrophysical Journal. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Mass., controls Chandra's science and flight operations.


Explore further

Glimmer of light in the search for dark matter

More information: The paper describing the new Chandra and XMM-Newton observations appears in the June 20, 2014, issue of The Astrophysical Journal: dx.doi.org/10.1088/0004-637X/789/1/13
Journal information: Astrophysical Journal

Citation: Mysterious X-ray signal intrigues astronomers (2014, June 24) retrieved 19 June 2019 from https://phys.org/news/2014-06-mysterious-x-ray-intrigues-astronomers.html
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Jun 24, 2014
Extremely hot gas and sterile neutrinos? ROFLMAO!
The future of understanding how the universe works will never be solved with that mindset!
Yawning....

Jun 24, 2014
Another fairy tale acrobatic mathematical entity...e la nave va...

Jun 24, 2014
Extremely hot gas and sterile neutrinos? ROFLMAO!
The future of understanding how the universe works will never be solved with that mindset!
Yawning....

Sadly, that is exactly the mindset of those studying in the cul-de-sac of astrophysics.

Jun 25, 2014
As noble as it's supporters on this forum like to claim it is, that the scientific method is adhered to stringentlty, this demonstrates otherwise.


That's complete nonsense. An observation is made, the relevant theorists pitch their hypothesise and the observers try to rule them out. There is absolutely nothing unscientific about this.

Jun 25, 2014
You sound like someone who has no idea of what they're talking about. So now it's not flying in the face of the scientific method, you've rowed back to "best practice", whatever that's means.

Let's stick to the point. Should these papers have been published now? OF COURSE. Prediction from the hypotheses comes before detailed observations, not after, you cannot rule out what you do not know about. What would be the point in waiting for the observations to come in and then claiming your model can fit that? None.

You claim these papers are against the scientific method but you clearly don't understand it. Hypothesis comes before evidence if you want to build theory, that is the scientific method. This is exactly the time for predictions as it sets them up to be knocked down by the observers.

In calling them hacks we expose the real problem which is not their practices but your biases. That's unscientific.

Jun 25, 2014
This comment has been removed by a moderator.

Jun 25, 2014
The similar X-ray signal in Milky Way has been attributed to binary stars


No, that's the 511 keV line, which everyone knew from day one came from positions. The source of positions was what was not known. This feature was never hypothesised to be decaying dark matter. And it's not simple binaries it's compact binaries.

And no, majorana neutrinos are not the same thing as sterile neutrinos. That experiment you posted for looked for evidence of majorana neutrinos in radioactive decay but if they were actually sterile neutrinos they wouldn't be involved in that interaction at all, they don't interact weakly. That experiment is not a test for sterile neutrinos.

Jun 25, 2014
This comment has been removed by a moderator.

Jun 26, 2014
Of course it indeed was - multiple times


No, that is dark matter generating positrons not dark matter creating the feature. As I said.

all sterile neutrinos must be a Majorana neutrinos at the same moment.


As far as I'm aware you can have sterile neutrinos without them being majorana fermions.

Jun 26, 2014
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Jun 26, 2014
What's funny is you talk both about predictions and extrapolations and neglect that they are the same.

X-ray signal is an emission from HYPOTHETICAL particle of which there is no proof of existence. Scientific practice at this point, develope and test means in which to confirm or disprove hypothesis.


That's not the hypothesis, that's the model. An observer on his own cannot test these models, no amount of data will change that. In order to test a model you need to know what it predicts, the hypothesis. Yes that takes extrapolation, but otherwise there is no way to test it, extrapolation is not at conflict with the scientific method. The observers then take these predictions and attempt to rule them out. The point of these papers is to enable that test, as I said. Without these papers the observer has nothing to test.

You talk about predictions, but you seem confused as to where they come from. This is how.

Jun 27, 2014
You guys are idiots.

Jun 29, 2014
You cannot learn the truth about anything if you are choosing a perspective to view information from.

Personally, I have to say the view I get clamoring atop the shoulders of giants is much greater, farther and deeper than the view I get standing on the shoulders of midgets.

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