Big Mystery in the Perseus Cluster

A mysterious X-ray signal from the Perseus cluster of galaxies, which researchers say cannot be explained by known physics, could be a key clue to the nature of Dark Matter.

Detection of An Unidentified Emission Line in the Stacked X-ray spectrum of Galaxy Clusters
Esra Bulbul, Maxim Markevitch, Adam Foster, Randall K. Smith, Michael Loewenstein, Scott W. Randall

We detect a weak unidentified emission line at E=(3.55-3.57)+/-0.03 keV in a stacked XMM spectrum of 73 galaxy clusters spanning a redshift range 0.01-0.35. MOS and PN observations independently show the presence of the line at consistent energies.
When the full sample is divided into three subsamples (Perseus, Centaurus+Ophiuchus+Coma, and all others), the line is significantly detected in all three independent MOS spectra and the PN “all others” spectrum. It is also detected in the Chandra spectra of Perseus with the flux consistent with XMM (though it is not seen in Virgo).
However, it is very weak and located within 50-110eV of several known faint lines, and so is subject to significant modeling uncertainties. On the origin of this line, we argue that there should be no atomic transitions in thermal plasma at this energy.
An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate.
Assuming that all dark matter is in sterile neutrinos with m_s=2E=7.1 keV, our detection in the full sample corresponds to a neutrino decay mixing angle sin^2(2theta)=7e-11, below the previous upper limits.
However, based on the cluster masses and distances, the line in Perseus is much brighter than expected in this model. This appears to be because of an anomalously bright line at E=3.62 keV in Perseus, possibly an Ar XVII dielectronic recombination line, although its flux would be 30 times the expected value and physically difficult to understand.
In principle, such an anomaly might explain our line detection in other subsamples as well, though it would stretch the line energy uncertainties.
Another alternative is the above anomaly in the Ar line combined with the nearby 3.51 keV K line also exceeding expectation by factor 10-20. Confirmation with Chandra and Suzaku, and eventually Astro-H, are required to determine the nature of this new line.(ABRIDGED)


Fermi Catches a ‘Transformer’ Pulsar

Zoom into an artist’s concept of AY Sextantis, a binary star system whose pulsar switched from radio emissions to high-energy gamma rays in 2013. This transition likely means the pulsar’s spin-up process is nearing its end.

In late June 2013, an exceptional binary containing a rapidly spinning neutron star underwent a dramatic change in behavior never before observed. The pulsar’s radio beacon vanished, while at the same time the system brightened fivefold in gamma rays, the most powerful form of light, according to measurements by NASA’s Fermi Gamma-ray Space Telescope.

It’s almost as if someone flipped a switch, morphing the system from a lower-energy state to a higher-energy one,” said Benjamin Stappers, an astrophysicist at the University of Manchester, England, who led an international effort to understand this striking transformation. “The change appears to reflect an erratic interaction between the pulsar and its companion, one that allows us an opportunity to explore a rare transitional phase in the life of this binary.” Continue reading Fermi Catches a ‘Transformer’ Pulsar

Is the universe a bubble? Let’s chek

Never mind the big bang; in the beginning was the vacuum. The vacuum simmered with energy (variously called dark energy, vacuum energy, the inflation field, or the Higgs field). Like water in a pot, this high energy began to evaporate – bubbles formed.

Each bubble contained another vacuum, whose energy was lower, but still not nothing. This energy drove the bubbles to expand. Inevitably, some bubbles bumped into each other. It’s possible some produced secondary bubbles. Maybe the bubbles were rare and far apart; maybe they were packed close as foam.

But here’s the thing: each of these bubbles was a universe. In this picture, our universe is one bubble in a frothy sea of bubble universes.

That’s the multiverse hypothesis in a bubbly nutshell.

It’s not a bad story. It is, as scientists say, physically motivated – not just made up, but rather arising from what we think we know about cosmic inflation.

Cosmic inflation isn’t universally accepted – most cyclical models of the universe reject the idea. Nevertheless, inflation is a leading theory of the universe’s very early development, and there is some observational evidence to support it.

Inflation holds that in the instant after the big bang, the universe expanded rapidly – so rapidly that an area of space once a nanometer square ended up more than a quarter-billion light years across in just a trillionth of a trillionth of a trillionth of a second. It’s an amazing idea, but it would explain some otherwise puzzling astrophysical observations.

Inflation is thought to have been driven by an inflation field – which is vacuum energy by another name. Once you postulate that the inflation field exists, it’s hard to avoid an “in the beginning was the vacuum” kind of story. This is where the theory of inflation becomes controversial – when it starts to postulate multiple universes.

Proponents of the multiverse theory argue that it’s the next logical step in the inflation story. Detractors argue that it is not physics, but metaphysics – that it is not science because it cannot be tested. After all, physics lives or dies by data that can be gathered and predictions that can be checked.

That’s where Perimeter Associate Faculty member Matthew Johnson (cross-appointed at York University) comes in. Working with a small team that also includes Perimeter Faculty member Luis Lehner, Johnson is working to bring the multiverse hypothesis firmly into the realm of testable science.

“That’s what this research program is all about,” he says. “We’re trying to find out what the testable predictions of this picture would be, and then going out and looking for them.”

Specifically, Johnson has been considering the rare cases in which our bubble universe might collide with another bubble universe. He lays out the steps: “We simulate the whole universe. We start with a multiverse that has two bubbles in it, we collide the bubbles on a computer to figure out what happens, and then we stick a virtual observer in various places and ask what that observer would see from there.”

Simulating the whole universe – or more than one – seems like a tall order, but apparently that’s not so.

“Simulating the universe is easy,” says Johnson. Simulations, he explains, are not accounting for every atom, every star, or every galaxy – in fact, they account for none of them.

“We’re simulating things only on the largest scales,” he says. “All I need is gravity and the stuff that makes these bubbles up. We’re now at the point where if you have a favourite model of the multiverse, I can stick it on a computer and tell you what you should see.”

That’s a small step for a computer simulation program, but a giant leap for the field of multiverse cosmology. By producing testable predictions, the multiverse model has crossed the line between appealing story and real science.

In fact, Johnson says, the program has reached the point where it can rule out certain models of the multiverse: “We’re now able to say that some models predict something that we should be able to see, and since we don’t in fact see it, we can rule those models out.”

For instance, collisions of one bubble universe with another would leave what Johnson calls “a disk on the sky” – a circular bruise in the cosmic microwave background. That the search for such a disk has so far come up empty makes certain collision-filled models less likely.

Meanwhile, the team is at work figuring out what other kinds of evidence a bubble collision might leave behind. It’s the first time, the team writes in their paper, that anyone has produced a direct quantitative set of predictions for the observable signatures of bubble collisions. And though none of those signatures has so far been found, some of them are possible to look for.

The real significance of this work is as a proof of principle: it shows that the multiverse can be testable. In other words, if we are living in a bubble universe, we might actually be able to tell.


A Universal Solution For A Quantum Three-Body Problem

Have physicists conquered the scaling behavior of exotic giant molecules?

When a two-body relation becomes a three-body relation, the behavior of the system changes. The basic physics of two interacting particles is well understood but the mathematical description of a three- or many-body system becomes so difficult that calculating the dynamics can blast the capacities of even modern super computers.

Under certain conditions, the quantum mechanical three-body problem may have a universal scaling solution and physicists from Heidelberg University say they have experimentally confirmed such a model. The scientists under Prof. Dr. Matthias Weidemüller investigated three-particle molecules, known as trimers, under exotic conditions.

The work is based on a theory posed by Russian physicist Vitaly Efimov more than 40 years ago. It focuses on finding physical laws capable of predicting the behaviour and energy states of an arbitrary number of particles. According to Efimov’s prediction, bound states of three atoms can be universally described under certain conditions.

Schematic representation of Efimov trimers formed from two cesium atoms and one lithium atom. While the trimer’s proportions are microscopic in its ground state, in the second excited state it is nearly a micrometer in size. The size of trimers scales based on a universal scaling law. These trimer states were observed in a mixture of cesium and lithium atoms at temperatures approaching absolute zero. Picture credits: Juris Ulmanis

Schematic representation of Efimov trimers formed from two cesium atoms and one lithium atom. While the trimer’s proportions are microscopic in its ground state, in the second excited state it is nearly a micrometer in size. The size of trimers scales based on a universal scaling law. These trimer states were observed in a mixture of cesium and lithium atoms at temperatures approaching absolute zero. Picture credits: Juris Ulmanis

The scientist found that infinitely many quantum mechanical bound states for the “ménage à trois” exist, even if two of the atoms cannot bind together. These so-called Efimov trimers are formed due to the long-range quantum mechanical interaction and they are completely independent of the underlying type of the three interacting particles. Continue reading A Universal Solution For A Quantum Three-Body Problem

Highly-Charged Ions

Multiply-ionized atoms for clocks, qubits, and constants

The best highly charged ions seem to be atoms such as Nd, Pr, and Sm that can be ionized to have the same number of electrons as four successive elements -- Ag, Cd, In, and Sn -- in another part of the periodic table.

The best highly charged ions seem to be atoms such as Nd, Pr, and Sm that can be ionized to have the same number of electrons as four successive elements — Ag, Cd, In, and Sn — in another part of the periodic table.

The world is mostly neutral. That is, most of the atoms in our environment are electrically neutral. The number of electrons in the outer parts of atoms equals the number of protons at the centers of atoms. As one or more electrons are plucked away from the atoms, the remaining electrons feel a much stronger positive pull from the nucleus. This enhanced pull, causing the atoms to shrink in size, ensures that those electrons are less vulnerable to the distractions of their environment, making them potentially valuable for next-generation atomic clocks, for quantum information schemes (where the loss of quantum coherence in qubits is a paramount danger), and for experiments trying to detect slight variations in the fine structure constant, the parameter that sets the overall strength of the electromagnetic force.
Continue reading Highly-Charged Ions

Why an extra helix becomes a third wheel in cell biology

dna3Every high school biology student knows the structure of DNA is a double helix, but after DNA is converted into RNA, parts of RNA also commonly fold into the same spiral staircase shape.

In a literal scientific twist, researchers are finding examples of a third strand that wraps itself around RNA like a snake, a structure rarely found in nature. Researchers recently have discovered evidence of a triple helix forming at the end of MALAT1, a strand of RNA that does not code for proteins. Yale postdoctoral fellow Jessica Brown and her colleagues working in the labs of Joan A. Steitz and Thomas A. Steitz describe the bonds that maintain the structure of a rare triple helix.

This extra strand of RNA, which is seen in the accompanying movie, prevents degradation of MALAT1. The formation of a triple helix explains how MALAT1 accumulates to very high levels in cancer cells, allowing MALAT1 to promote metastasis of lung cancer and likely other cancers.

The work is published in the journal Nature Structural and Molecular Biology.