The Speaker Editors

Arguably the biggest science story of the week was the discovery of material evidence of dark matter. In this two-part article, two lead researchers on the report explain their findings and the significance of the work. Their accounts are full of–besides beautiful explanations of cutting-edge physics research in layman’s terms–potent philosophy and enthralling sentiment about what these scientists are doing and what will come.

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Never-before detected elements have been found by a group of European physicists looking for anomalies in signals emanating from several galaxies. The findings–pieces of “missing Lego” in the words of researcher Dr. Oleksii Boiarskyi–will validate some of the approaches currently being undertaken to understand the universe while invalidating others, and will bring us one step closer to the complete picture of physics.

“If this signal is confirmed, we will have a completely new tool to study the structure of our Universe, it’s ‘dark side’ and also its history, how did it form,” Dr. Oleksii Boiarskyi of the Instituut-Lorentz for Theoretical Physics and and Leiden University told The Speaker.

“On the particle physics level, we will know more about the missing Lego elements that where used to build this Universe–and that we did not detect so far. This will support some approaches extending our knowledge and will disfavour the others.

“We would make one more step towards the complete picture of physics.”

Read more: Dark matter signals, part one: Ruchayskiy explains

The team detected anomalies in signals–photon emissions in X-ray spectra–using the European Space Agency’s (ESA) XMM-Newton telescope (feature image). The anomalies were something the the team had been seeking–they were acting on a hypothesis that dark matter occasionally decayed, and that they could pick up signals that represented that decaying dark matter. They found just that.

The findings, if confirmed, would be the first ever evidence of the heretofore undetectable material that accounts for an estimated 80 percent of our universe.

Boiarskyi explained to us what the signal was that they had detected, and what it was like reading the data.

“We study the spectra of galaxies and clusters of galaxies,” said Boiarskyi. “This is a function, a number of photons detected for each energy.

“It has a smooth–continuous–part and narrow lines. The lines come from various atomic transitions and continuum from just emission of accelerated charged particles.

“We can find a model that describes all these emissions and find a good fit for the data. If a statistically significant residual to this model exists, this means that there is another line, that is coming from some additional quantum transition.

“In our case the position and normalisation of this lines are not like you expect from atomic transition. Moreover, it changes over the sky as DM density–projected along the line of sight.

“That is why there is a conjecture that this could come from decay of DM particles. You can check this conjecture by comparing signals from various DM dominating objects. So far it is consistent.”

It is not certain whether the type of dark matter found by the team accounts for the full 80 percent of currently unknown matter expected to exist, or whether there were a variety of dark matters.

“Nobody knows,” said Boiarskyi, “both are possible. But of course one first tries a minimal model with one sort of DM.”

Confirmation could be a year away, Boiarskyi told us.

“[W]e still need to wait about a year, once new data are available, to check if this hypothesis is correct or not. If DM will be discovered once, most likely it will be a story similar to the one we are having now…”

The report, “An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster,” was completed by A. Boyarsky, O. Ruchayskiy, D. Iakubovskyi, and J. Franse, and was published on the Cornell University website.

Read the thoughts of another physicist on this study, Dr. Dr. Oleg Ruchayskiy: Dark matter signals, part one: Ruchayskiy explains

Arguably the biggest science story of the week was the discovery of material evidence of dark matter. In this two-part article, two lead researchers on the report explain their findings and significance of the work. Their accounts are full of–besides beautiful explanations of cutting-edge physics research in layman’s terms–potent philosophy and enthralling sentiment about what these scientists are doing and what will come.

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Setting out with the hypothesis that dark matter occasionally though rarely decays, European physicists pointed the European Space Agency’s XMM-Newton telescope at faraway galaxies to seek evidence of the common, though never seen, material that makes up an estimated 80 percent of our universe–in  signal anomalies. In his explanation of the recent work, researcher Dr Oleg Ruchayskiy pointed to the era we are now entering, in which our vision and understanding will reach what we have not before known–both in terms of nature and of time.

“Dark structures that surround us will become ‘visible,'” Dr. Oleg Ruchayskiy, physicist at the École Polytechnique Fédérale de Lausanne (EPFL) and one of the authors of the study, told The Speaker. “Dark matter distribution is not expected to be perfectly smooth and its clumps and streams–they carry important information about the past of the Milky way or the Local Group. We will be able to visualize and maybe even tell the story of ‘our Galactic past.’

“This will be the epoch of ‘astronomical archaeology–looking at the events that happened a billion years ago.”

“The fact that this can be possible–to explore by the power of our minds the regions of space and periods of time, incomparable with the lifespan of humans–isn’t it beautiful?”

Read more: Dark matter signals, part two: Boiarskyi explains

Ruchayskiy commented on the kinds of improvements that were in store for humanity as our ability to see our universe was expanded to the perception of dark matter.

“Another thing about our research: if this signal is real dark matter decay–we will soon be able to build ‘dark matter telescopes.’ We will be able to do 3D tomography of our own galaxy and of nearby Universe. We will even be able to look into the past of our Universe.

Ruchayskiy explained the teams recent work.

“We were testing the hypothesis that this particle is _the same_ in different galaxies and in the galaxy clusters. Otherwise it would be very difficult to cross-check this signal.”

The physicist provided details about what the signal was that they found–how it was characterized and where it was located–and about the course of the study, which happily coincided with similar results from a completely separate team of physicists.

“Just to give you some background info. We were looking at X-ray spectra of galaxies and galaxy clusters. X-rays do not pass through the atmosphere, therefore all X-ray satellites are in space. So, the data is just files. In essence, the file is very simple: it tells you how many X-ray photons of a given energy had arrive from a given direction.

“It is more or less known how the X-ray signal from a galaxy should look. That is, ‘given X photons of energy 1 keV, we expect Y photons of energy 2 keV,’ etc. This is called ‘an X-ray spectrum of a galaxy’–or any other object.

“So, we were analyzing the spectrum of the Andromeda galaxy we found that there are ‘extra photons’ at energy around 3.5 keV. Several hundreds of them.

“This was not an “accident”–we were looking for these photons. We had a hypothesis, that dark matter particles are not stable, but occasionally decay. This happens very rarely. Any given particle has a probability of something like 1/billion to decay. But in a galaxy like our there are 10^70 such particles, so the resulting signal may be sizable. We searched for such signal for many years–and so did other groups–so we knew that it should be small…

“We found such a signal in Andromeda.

“A signal in one particular object could be anything: fluctuation, emission of ions, instrumental error. So, we looked at the data from a different object–the Perseus galaxy cluster. The galaxies and galaxy clusters have very different X-ray emissions. But masses of both types of objects are ‘dark matter dominated.’ So, seeing a line there was necessary. And we did find the signal. Moreover, we saw that the signal is redshifted–as Perseus is farther away from us–which excluded the instrumental origin of the signal. We saw that the signal’s intensity scales correctly (because the dark matter mass in Perseus cluster is different from that of Andromeda galaxy). We saw that signal becomes weaker as one goes to the outskirts of the cluster because dark matter is more concentrated towards the center — all this was consistent with the decaying dark matter hypothesis.

“Later we did another work where we have found a similar line from the center of our own Galaxy, the Milky Way. And again, its intensity fell into the predicted range.

“Independently from us and at the same time–even couple of days earlier–another group from Harvard CfA/NASA–you probably had seen the press releases of their result–had found a signal at the same energy in various galaxy clusters–both nearby and distant. Their work is completely independent, uses different observations. This is of course extremely important, that this are the independent results of two groups. And that these groups confirm each other–we haven’t seen each other’s works prior to publication on arXiv.”

Next the team will probe space for signals that would corroborate their hypothesis.

“Our strategy now is: find this signal from many dark matter dominated objects, show that its intensity is proportional to the total amount of dark matter in each object.”

Ruchayskiy elaborated on the breadth of work that remained to fill in the full picture of dark matter–namely the possibility of various types of dark matter, which we asked him about.

“Testing a hypothesis that this is only one component of dark matter and there are other types of particles would be harder, because than we need to know whether a portion of decaying particles changes from object from object and this depends on the model of dark matter.

“[W]e were specifically looking for these particles and for this type of signal. We did not know the energy, so we were scanning the energies.

“So, this road, from an idea that dark matter particle could be unstable to seeing an actual signal–it is breathtaking. The fact that people can grasp with their minds something about the whole Universe–it is very fascinating for me. And any ‘predictions’ that becomes a ‘confirmed signal’–this is very impressive. It’s a feeling that is hard to express. Of course, our signal is not unique in this aspect. Every scientific discovery is like that. Which makes it even more fascinating.”

The report, “An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster,” was completed by A. Boyarsky, O. Ruchayskiy, D. Iakubovskyi, and J. Franse, and was published on the Cornell University website.

Read more: Dark matter signals, part two: Boiarskyi explains

A significant amount of the world’s plastic ends up in our oceans, which has caused something of a mystery for ecologists, who until recently had found evidence of only tens of thousands of tons of that garbage rather than the millions they expected would be floating on the surface. Now a joint-team of researchers has found evidence that plastic particles have been accumulating in deep sea sediment for the past century. But some questions remain–namely the how of the problem. Lead researcher Dr Lucy Woodall points to various methods by which the plastic is making its way to the bottom–methods which reflect the specific nature of the waters in which garbage is discarded.

The team–composed of researchers from the Natural History Museum of London, the Scottish Marine Institute, and the universities of Barcelona, Oxford, and Plymouth– looked at samples of from 12 sites over three bodies of water: the Atlantic, the Indian, and Mediterranean. The samples were collected between 2001 and 2012 at depths of 300-3,000 meters, and contained high levels of plastic garbage particles–called “microplastics” for their size of less than 1mm.

While the surface of the ocean is “mysteriously” clean of garbage–only around 35,000 of the millions of tons of plastic garbage currently in our oceans are expected to still be at the surface–the deposits in the ocean’s sediment were mixed with 1,000 times that amount of plastic.

Read more: Ocean Garbage Mystery: Instead of Expected Millions of Tons, Researchers Find Only 7,000 – 35,000 Tons

The finding by the joint team marks an important step in understanding how plastics make their way through ocean ecosystems. The mystery remains, however, as to how the plastics make their way from the surface to the sediment.

Lead researcher on the study, Dr Lucy Woodall of the Department of Life Sciences at the Natural History Museum in London, told The Speaker that the team also has a pretty good idea of the various processes by which the plastic makes its way to the bottom

“We speculate that similar oceanographic mechanisms as act on plastic fibers act on other particles, such as dense shelf cascading, severe coastal storms, offshore convection and saline subduction,” Woodall told us. “We suggest additionally that ‘Colonization by organisms, adherence to phytoplankton and the aggregation with organic debris and small particles in the form of marine snow will eventually enhance settling.’

“Specific topography of the deep sea will also carry with it specific processes, for example submarine canyons are known to act as conduits to deep areas, and taylor columns–specific currents–over seamounts could result in retention of plastics at these sites.”

Although the total garbage accumulated in the earth’s oceans are calculated at hundreds of thousands to millions of tons, this is only a fraction of the total plastic produced and discarded. A recent study found that the amount of garbage in the ocean is only around 0.1 percent of the amount we produce each year.

“Further studies specifically addressing the process of plastics moving to depth are required so that we can begin to understand the impact of these pollutants in the environment,” said Woodall.

The report, “The deep sea is a major sink for microplastic debris,” was completed by Lucy C. Woodall, Anna Sanchez-Vidal, Miquel Canals, Gordon L.J. Paterson, Rachel Coppock, Victoria Sleight, Antonio Calafat, Alex D. Rogers, Bhavani E. Narayanaswamy, and Richard C. Thompson, and was published in the journal Royal Society Open Science this week.

By James Haleavy

Contrary to intuition, adding pockets of water to solids can actually make them stronger. This finding, the result of research by Yale scientists, offers “a new knob to turn” for engineers, the researchers say. Engineers will be able to add exciting new properties to composite materials–such as electromagnetism–by embedding droplets of liquid, and, on a purely scientific level, the research provides valuable insight into the nature of the material properties at small and large scales–how the relative strengths of a material at one size can be opposite to that at another size.

“This is a great example of how different types of physics emerge at different scales,” Dr. Eric Dufresne, associate professor of mechanical engineering and materials science at Yale and principle investigator of the study, told The Speaker. “Shrinking the scale of an object can really change how it behaves.”

Usually, replacing parts of a solid with liquid–generally considered a soft material–makes the material weaker, but this is not always the case. The researchers strengthened solids with liquids by the virtue of the surface tension of liquid droplets.

“Surface tension is a force that tries to reduce the surface area of a material,” Dufresne told us. “It is familiar in fluids–it’s the force that pulls water into a sponge, makes wet hair clump together and lets insects walk on water. Solids have surface tension too, but usually the ‘elastic force’ of the solid is so strong that surface tension doesn’t have much of an effect. The ‘elastic force’ of a solid is what makes a solid spring back to its originial shape after you stop pushing on it.

Because the tendency of a liquid is to have as small a surface as possible, embedding small drops of liquid–about a micron in diameter–strengthen solids because the surface tension of the water provides stiffness to the composite.

Dufresne commented on what would be, in his words, “a new knob to turn” for engineers, who can achieve greater control over the properties of composite materials by including fluids.

“As the solid gets stiffer, the liquid droplets need to be smaller in order to have this stiffening or cloaking effect. By embedding the solid with droplets of different materials, one can give it new electrical, optical or mechanical properties.

“On the simple scale, they could lower the cost be replacing expensive polymers with simple liquids. More excitingly, embedded droplets could provide an electromagnetic handle to actuate structures.”

In the recent research, the team embedded the small drops of liquid into silicone and then stretched the silicone. Silicone embedded with large drops of water deformed easily–the material was weakened by the liquid. Silicone with small droplets resisted deformation–the material was strengthened.

The team found that a composite up to 30 percent stronger than pure silicone could be created by embedding a large amount of small liquid droplets.

Dufresne explained how the current work came about.

“A few years back, we discovered, on accident, some surprises on how liquid droplets sit on top of solid surfaces,” said Dufresne. “In the course of that work, we realized people needed to pay attention to solid surface tension. Since then, we have been looking for other examples where solid surface tension might be an important and neglected component of the behaviour of materials. These experiments were inspired by ongoing efforts in ‘metamaterials’ where engineers tune the microstructure of a material to give it new properties.”

“It turns out that the importance of surface tension is inversely proportional to the size,” Dufresne said of the study. “So what’s just a negligible force for big things becomes a strong force for very small things–which in turn can strongly affect the material as a whole.”

The report, “Stiffening solids with liquid inclusions,” was completed by Drs. W. Style, Rostislav Boltyanskiy, Benjamin Allen, Katharine E.Jensen, Henry P. Foote, John S. Wettlaufer, and Eric R. Dufresne, and was publishe in December’s Nature Physics.

Photos: all belong to the work of the Yale team

Women feel what is happening to their partners over three times as much as men do. According to new research, the difference between the empathy felt by women and men was the biggest of many factors analyzed.

“In our work, we were trying to measure how partners affect each other’s mental health through life events,” Dr Cindy Mervin, research fellow at Griffith University’s Centre for Applied Health Economics and lead author of the study, told The Speaker. “[O]ur work showed that negative and positive things that happen to individuals not only affect them but also affect their family.”

Mervin explained the research team’s findings about the levels of empathy felt by women and men, most notably, that women’s levels of empathy for their partners–at 24 percent of what they would have felt had an event happened to themselves–are over 300 percent of men’s levels.

“We can interpret the 24 percent by saying that on average women will be affected by the events happening to their partner by about 24 percent of the degree to which they are affected by their own,” Mervin told us. “In other words, women are affected about four times as much by the events happening to them than events happening to their partners.”

The research involved questionnaire data from the Australian study Household, Income and Labour Dynamics in Australia (HILDA) on over 20,000 people across the country. The team looked at partners in both straight and same-sex relationships who did not separate during the observed panel, which amounted to just under 11,000 individuals and over 53,000 person-year observations.

The research led the team to conclude that while women’s empathy toward their partners was the strongest found in their study, men on average were found to not be empathetic in any significant way.

“We estimated this coefficient for different types of respondents–women vs men, parents vs their counterparts, and individual from high-income households vs. those from low-income households,” stated Mervin. “The highest value we found was for women when compared to men. For men, we found a value around seven percent and therefore found that men were not significantly affected by things happening to their partner.”

Mervin clarified that the findings do not mean that men are unemotional or uncaring, but that their care does not extend to their partner the way women’s care does.

“Although the degree measured for women and men is different, it does not mean that men are unemotional as they are quite strongly affected by what happens to themselves,” said Mervin. “They are just not very emotional when it comes to their feelings of their partner.”

The report, “Is shared misery double misery,” was authored by Drs Merehau Cindy Mervin and Paul Frigters of University of Queensland’s School of Economics, and was published in the journal Social Science and Medicine.

By James Haleavy