A new twist in the dark matter tale

A new twist in the dark matter tale
Credit: X-ray: NASA/CXO/Oxford University/J. Conlon et al. Radio: NRAO/AUI/NSF/Univ. of Montreal/Gendron-Marsolais et al. Optical: NASA/ESA/IoA/A. Fabian et al.; DSS

An innovative interpretation of X-ray data from a cluster of galaxies could help scientists fulfill a quest they have been on for decades: determining the nature of dark matter.

The finding involves a new explanation for a set of results made with NASA's Chandra X-ray Observatory, ESA's XMM-Newton and Hitomi, a Japanese-led X-ray telescope. If confirmed with future observations, this may represent a major step forward in understanding the nature of the mysterious, invisible substance that makes up about 85% of matter in the universe.

"We expect that this result will either be hugely important or a total dud," said Joseph Conlon of Oxford University who led the new study. "I don't think there is a halfway point when you are looking for answers to one of the biggest questions in science."

The story of this work started in 2014 when a team of astronomers led by Esra Bulbul (Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.) found a spike of intensity at a very specific in Chandra and XMM-Newton observations of the hot gas in the Perseus galaxy .

This spike, or line, is at an energy of 3.5 kiloelectron volts (keV). The intensity of the 3.5 keV emission line is very difficult if not impossible to explain in terms of previously observed or predicted features from astronomical objects, and therefore a origin was suggested. Bulbul and colleagues also reported the existence of the 3.5 keV line in a study of 73 other galaxy clusters using XMM-Newton.

The plot of this dark matter tale thickened when only a week after Bulbul's team submitted their paper a different group, led by Alexey Boyarsky of Leiden University in the Netherlands, reported evidence for an emission line at 3.5 keV in XMM-Newton observations of the galaxy M31 and the outskirts of the Perseus cluster, confirming the Bulbul et al. result.

However, these two results were controversial, with other astronomers later detecting the 3.5 keV line when observing other objects, and some failing to detect it.

The debate seemed to be resolved in 2016 when Hitomi especially designed to observe detailed features such as line emission in the X-ray spectra of cosmic sources, failed to detect the 3.5 keV line in the Perseus cluster.

"One might think that when Hitomi didn't see the 3.5 keV line that we would have just thrown in the towel for this line of investigation," said co-author Francesca Day, also from Oxford. "On the contrary, this is where, like in any good story, an interesting plot twist occurred."

Conlon and colleagues noted that the Hitomi telescope had much fuzzier images than Chandra, so its data on the Perseus cluster are actually comprised of a mixture of the X-ray signals from two sources: a diffuse component of hot gas enveloping the large galaxy in the center of the cluster and X-ray emission from near the supermassive black hole in this galaxy. The sharper vision of Chandra can separate the contribution from the two regions. Capitalizing on this, Bulbul et al. isolated the X-ray signal from the hot gas by removing point sources from their analysis, including X-rays from material near the .

In order to test whether this difference mattered, the Oxford team re-analyzed Chandra data from close to the black hole at the center of the Perseus cluster taken in 2009. They found something surprising: evidence for a deficit rather than a surplus of X-rays at 3.5 keV. This suggests that something in Perseus is absorbing X-rays at this exact energy. When the researchers simulated the Hitomi spectrum by adding this absorption line to the hot gas' emission line seen with Chandra and XMM-Newton, they found no evidence in the summed spectrum for either absorption or emission of X-rays at 3.5 keV, consistent with the Hitomi observations.

The challenge is to explain this behavior: detecting absorption of X-ray light when observing the black hole and emission of X-ray light at the same energy when looking at the hot gas at larger angles away from the black hole.

A new twist in the dark matter tale
The latest work shows that absorption of X-rays at an energy of 3.5 keV is detected when observing the region surrounding the supermassive black hole at the center of Perseus. This suggests that dark matter particles in the cluster are both absorbing and emitting X-rays. If the new model turns out to be correct, it could provide a path for scientists to one day identify the true nature of dark matter. For next steps, astronomers will need further observations of the Perseus cluster and others like it with current X-ray telescopes and those being planned for the next decade and beyond. Credit: NASA/CXC/M. Weiss

In fact, such behavior is well known to astronomers who study stars and clouds of gas with optical telescopes. Light from a star surrounded by a cloud of gas often shows absorption lines produced when starlight of a specific energy is absorbed by atoms in the gas cloud. The absorption kicks the atoms from a low to a high energy state. The atom quickly drops back to the low energy state with the emission of light of a specific energy, but the light is re-emitted in all directions, producing a net loss of light at the specific energy—an absorption line—in the observed spectrum of the star. In contrast, an observation of a cloud in a direction away from the star would detect only the re-emitted, or fluorescent light at a specific energy, which would show up as an emission line.

The Oxford team suggests in their report that dark matter particles may be like atoms in having two energy states separated by 3.5 keV. If so, it could be possible to observe an absorption line at 3.5 keV when observing at angles close to the direction of the black hole, and an when looking at the cluster hot gas at large angles away from the black hole.

"This is not a simple picture to paint, but it's possible that we've found a way to both explain the unusual X-ray signals coming from Perseus and uncover a hint about what dark matter actually is," said co-author Nicholas Jennings, also of Oxford.

To write the next chapter of this story, astronomers will need further observations of the Perseus cluster and others like it. For example, more data is needed to confirm the reality of the dip and to exclude a more mundane possibility, namely that we have a combination of an unexpected instrumental effect and a statistically unlikely dip in X-rays at an energy of 3.5 keV. Chandra, XMM-Newton and future X-ray missions will continue to observe clusters to address the dark matter mystery.

A paper describing these results was published in Physical Review D on December 19, 2017 and a preprint is available online.


Explore further

Mysterious X-ray signal intrigues astronomers

More information: Consistency of Hitomi, XMM-Newton and Chandra 3.5 keV data from Perseus, arXiv:1608.01684 [astro-ph.HE] arxiv.org/abs/1608.01684
Journal information: Physical Review D

Citation: A new twist in the dark matter tale (2017, December 19) retrieved 25 May 2019 from https://phys.org/news/2017-12-dark-tale.html
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Dec 19, 2017
I remember recent articles on 3.5 keV photon being explained as the ionization energy of sulfur with one remaining electron...

A Google search finds: https://arxiv.org...6557.pdf
That says: A bare sulfur nucleus can capture an electron from an neutral hydrogen to become S(15+), emitting a 3.5 kEv photon in the process. The S(15+) then has a 3.5 keV absorption line.

Why postulate a dark-matter atom with a 3.5 keV transition when a real atom is already thought to have such a transition?

Dec 19, 2017
https://www.nextb...ter.html

quite a different detection of dark matter

Dec 20, 2017
First of all you'd have to account for all that sulfur, @RealScience.

Dec 20, 2017
it seems like dark matter is invisible to the higgs particle. The bullet cluster shows colliding normal matter heating up and dm passing through each other without effect. Lisa Randall has suggested a dm disk and a dm sphere halo. One reacts to the higgs and one region of space does not.

Dec 20, 2017
the temperature of dm should be different than visible matter because it had no cooling mechanism like normal matters neutrino cooling before the universe became transparent. The only cooling came from expansion.

Dec 20, 2017
That nonexistent dark matter. Why-o-why it is so hard to find? Or maybe it is a blessing in disguise: dark matter, dark energy, many other dark nonexistent things - a gold mine for pH:d projects and para-scientific articles!

Dec 20, 2017
Again ignorance of the structure of the universe !!
The substance is formed from the substance Aether, which was rejected by science, because this is a big obstacle for inventing the many misconceptions that brought them great wages. The basic and first variant of the matter are electrons and positrons "packed" into the form of gluon, and quarks, from which a quark gluon plasma is formed (MAGNETAR's celestial body).
From this formation, due to the process in the chain of formation of other celestial bodies, there is a superficial expansion of the magnetars, when the Gamma Ray Burst is emitted, which are the quasars, behind them the pulsars (can also be dual stars), only after the formation of neutron stars, and the supernova which, when exploded, follows the chain of the formation of celestial bodies (sun, planets, and the like). What they discovered can be one type of GRB.

Dec 20, 2017
First of all you'd have to account for all that sulfur, @RealScience.

Sulfur is quite abundant in the universe. Google it.

Dec 20, 2017
First of all you'd have to account for all that sulfur, @RealScience.


Yes, the sulfur needs to be accounted for.

Sulfur is produced in stars and is ejected by supernovae. A quick search says it is the 10th most common element in our galaxy, with tens of millions of solar masses of sulfur. The S(16+) ionization energy is high, equivalent to ~4 million Kelvins, but a quick search says that clusters are full of hot gas at millions of Kelvins.

So in a cluster we should expect a significant portion of a common atom to be in the right state to emit (16+ to 15+) or absorb (15+ to 16+) photons at the energy observed.

Sure, it MIGHT be some new form of matter that is dark EXCEPT for photons at 3.5 keV, and that MIGHT be because it forms 'dark atoms' that have a 3.5 keV transition, but I would take a really good look at sulfur before focusing on dark matter as a significant suspect.

Dec 20, 2017
Sulfur is improbable answer, as there would be many other elements which would produce similar spectrum too, i.e. no peaks...


The last electron ionization energy goes with the square of the atomic, so the peaks would not be that close. The nearest common element would be silicon at ~2.66 keV.

Let's see... Huh. Fig. 2D of the article that I linked shows the residual from the Perseus cluster, and it does indeed have a peak near 2.7 keV, and it is even labelled 'Si XIV n=8'. So yes, there is a peak that would fit the analogous silicon (14+) to Silicon (13+) transition.

Dec 21, 2017
@mackita, great statistics
whose "young generation" and the newborn generation.
Is it all "out-of-wedlock", without a known father.

Dec 24, 2017
When science explains phenomena in the universe, then everyone behaves as if they were totally gone astray in an unknown space and time. And that's why they try to find a way out of the blind street in any way. Einstein, with his theories of relativity and fatamorganic curvature of space time, completely drugged most scientists and scientists, so much that there is no method by which those deceived people could sober up and see the real way of knowing the true causes of the phenomenon.
Is there a greater nonsense than "assertion": we do not know, nor can we determine the existence of dark matter, but there is 85% of the universe, we do not know what time and space, but Einstein left us a message that space and time have some "love" "bond, so they embark on a solid" sexual "embrace and it's so fascinating that when the matter encounters that" love "and it loses control of itself, it remains" in the second state, "and

Dec 24, 2017
gravity is born. It's just a matter of science that neither Einstein knows what gravity is and how it arises.
It seems that space and time are "homosexuals" and something was born about which we know almost nothing.
The same, we know what is matter and antimatter, but we can not see why the matter was overcome in the universe, and we did not see this battle. We count that our great-grandfather left us some traces to find out, but he was too "excited" when he came out of nothing, and now most scientists have behaviors, as if they were originated from nothing. So if they believe in it, then there really are nobody and nothing, because they do not know who, how and why they were created, none of them knows who their BB was.
We take our own creation of the PC, make it stronger than BB,

Dec 24, 2017
, have entered into our minds and formed MODELS, and these are our deities we believe in. "Surely" these models will bring us the truth because they are much more perfect than those who made them.
And to look at the terrain where our great-grandfather BB was born, we have taken away some of the elements from nature and built telescopes, which should "love" photons, which must, under the laser and pressure curve, temperature and the like. to reveal to us the secret, what is happening far from us, and we do not know without a witness of associates -telescopes and photons. Continue on, because you better know the ignorance of science, from me !!

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