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A black hole on a chip made of a metal that behaves like water

In a new paper published in Science, researchers at the Harvard and Raytheon BBN Technology have observed, for the first time, electrons in a metal behaving like a fluid (credit: Peter Allen/Harvard SEAS)

A radical discovery by researchers at Harvard and Raytheon BBN Technology about graphene’s hidden properties could lead to a model system to explore exotic phenomena like black holes and high-energy plasmas, as well as novel thermoelectric devices.

In a paper published Feb. 11 in Science, the researchers document their discovery of electrons in graphene behaving like a fluid. To make this observation, the team improved methods to create ultra-clean graphene* and developed a new way to measure its thermal conductivity.

A black hole on a chip

In ordinary 3D metals, electrons hardly interact with each other. But graphene’s two-dimensional, honeycomb structure acts like an electron superhighway in which all the particles have to travel in the same lane. The electrons in this ultra-clean graphene act like massless relativistic objects, some with positive charge and some with negative charge.

They move at incredible speed — 1/300 of the speed of light — and have been predicted to collide with each other ten trillion times a second at room temperature.  These intense interactions between charge particles have never been observed in an ordinary metal before.

Most of our world is described by classical physics. But very small things, like electrons, are described by quantum mechanics while very large and very fast things, like galaxies, are described by relativistic physics, pioneered by Albert Einstein.

Combining these different sets of laws of physics is notoriously difficult, but there are extreme examples where they overlap. High-energy systems like supernovas and black holes can be described by linking classical theories of hydrodynamics with Einstein’s theories of relativity.

A quantum ‘Dirac’ fluid metal

But since we can’t run an experiment on a black hole (yet), enter graphene.

When the strongly interacting particles in graphene were driven by an electric field, they behaved not like individual particles but like a fluid that could be described by hydrodynamics.

“Physics we discovered by studying black holes and string theory, we’re seeing in graphene,” said Andrew Lucas, co-author and graduate student with Subir Sachdev, the Herchel Smith Professor of Physics at Harvard. “This is the first model system of relativistic hydrodynamics in a metal.”

Industrial implications

A small chip of graphene could also be used to model the fluid-like behavior of other high-energy systems.

To observe the hydrodynamic system, the team turned to noise. At finite temperature, the electrons move about randomly:  the higher the temperature, the noisier the electrons. By measuring the temperature of the electrons to three decimal points, the team was able to precisely measure the thermal conductivity of the electrons.

“This work provides a new way to control the rate of heat transduction in graphene’s electron system, and as such will be key for energy and sensing-related applications,” said Leonid Levitov, professor of physics at MIT.

“Converting thermal energy into electric currents and vice versa is notoriously hard with ordinary materials,” said Lucas. “But in principle, with a clean sample of graphene there may be no limit to how good a device you could make.”

The research was led by Philip Kim, professor of physics and applied physics at The Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).

* The team created an ultra-clean sample by sandwiching the one-atom thick graphene sheet between tens of layers of an electrically insulating perfect transparent crystal with a similar atomic structure of graphene.

“If you have a material that’s one atom thick, it’s going to be really affected by its environment,” said Jesse Crossno, a graduate student in the Kim Lab and first author of the paper. “If the graphene is on top of something that’s rough and disordered, it’s going to interfere with how the electrons move. It’s really important to create graphene with no interference from its environment.”

Next, the team set up a kind of thermal soup of positively charged and negatively charged particles on the surface of the graphene, and observed how those particles flowed as thermal and electric currents.


Harvard John A. Paulson School of Engineering and Applied Sciences | How to Make Graphene

Abstract of Observation of the Dirac fluid and the breakdown of the Wiedemann-Franz law in graphene

Interactions between particles in quantum many-body systems can lead to collective behavior described by hydrodynamics. One such system is the electron-hole plasma in graphene near the charge neutrality point, which can form a strongly coupled Dirac fluid. This charge neutral plasma of quasi-relativistic fermions is expected to exhibit a substantial enhancement of the thermal conductivity, thanks to decoupling of charge and heat currents within hydrodynamics. Employing high sensitivity Johnson noise thermometry, we report an order of magnitude increase in the thermal conductivity and the breakdown of the Wiedemann-Franz law in the thermally populated charge neutral plasma in graphene. This result is a signature of the Dirac fluid, and constitutes direct evidence of collective motion in a quantum electronic fluid.

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‘We have detected gravitational waves’ — LIGO scientists

Numerical simulations of the gravitational waves emitted by the inspiral and merger of two black holes. The colored contours around each black hole represent the amplitude of the gravitational radiation; the blue lines represent the orbits of the black holes and the green arrows represent their spins. (credit: C. Henze/NASA Ames Research Center)

On Sept. 14, 2015 at 5:51 a.m. EDT (09:51 UTC) for the first time, scientists observed ripples in the fabric of spacetime called gravitational waves, arriving at Earth from a cataclysmic event in the distant universe, the National Science Foundation and scientists at the LIGO Scientific Collaboration announced today. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window to the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot be obtained from elsewhere. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

The gravitational-wave event on Sept. 14, 2015 at 09:50:45 UTC was observed by the two LIGO detectors in Livingston, Loiusiana (blue) and Hanford, Washington (orange). The matching waveforms represent gravitational-wave strain inferred to be generated by the merger of two inspiraling black holes. (credit: B. P. Abbott et al./PhysRevLett)

The gravitational waves were detected  by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington. The LIGO observatories are funded by the National Science Foundation (NSF), and were conceived, built and are operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT). The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10−21.

Illustration of the collision of two black holes — an event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO — is seen in this still from a computer simulation. LIGO detected gravitational waves, or ripples in space and time, generated as the black holes merged. (credit: SXS)

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the Sun, and the event took place 1.3 billion years ago. About three times the mass of the Sun was converted into gravitational waves in a fraction of a second — with a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signals — the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford — scientists can say that the source was located in the Southern Hemisphere.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide at nearly half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc2. This energy is emitted as a final strong burst of gravitational waves. These are the gravitational waves that LIGO observed.

How our sun and Earth warp spacetime is represented here with a green grid. As Albert Einstein demonstrated in his theory of general relativity, the gravity of massive bodies warps the fabric of space and time — and those bodies move along paths determined by this geometry. His theory also predicted the existence of gravitational waves, which are ripples in space and time. These waves, which move at the speed of light, are created when massive bodies accelerate through space and time. (credit: T. Pyle/LIGO)

The existence of gravitational waves was first demonstrated in the 1970s and 1980s by Joseph Taylor, Jr., and colleagues. In 1974, Taylor and Russell Hulse discovered a binary system composed of a pulsar in orbit around a neutron star. Taylor and Joel M. Weisberg in 1982 found that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves. For discovering the pulsar and showing that it would make possible this particular gravitational wave measurement, Hulse and Taylor were awarded the 1993 Nobel Prize in Physics.

The new LIGO discovery is the first observation of gravitational waves themselves, made by measuring the tiny disturbances the waves make to space and time as they pass through the earth.

“Our observation of gravitational waves accomplishes an ambitious goal set out over five decades ago to directly detect this elusive phenomenon and better understand the universe, and, fittingly, fulfills Einstein’s legacy on the 100th anniversary of his general theory of relativity,” says Caltech’s David H. Reitze, executive director of the LIGO Laboratory.

An aerial view of the Laser Interferometer Gravitational-wave Observatory (LIGO) detector in Livingston, Louisiana. LIGO has two detectors: one in Livingston and the other in Hanford, Washington. (credit: LIGO Laboratory)

LIGO research

The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed — and the discovery of gravitational waves during its first observation run. NSF is the lead financial supporter of Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project.

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1,000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom and the University of the Balearic Islands in Spain.

“This detection is the beginning of a new era: The field of gravitational wave astronomy is now a reality,” says Gabriela González, LSC spokesperson and professor of physics and astronomy at Louisiana State University.

LIGO was originally proposed as a means of detecting gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

“The description of this observation is beautifully described in the Einstein theory of general relativity formulated 100 years ago and comprises the first test of the theory in strong gravitation. It would have been wonderful to watch Einstein’s face had we been able to tell him,” says Weiss.

“With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe — objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples,” says Thorne.

Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.

At each observatory, the 2 1/2-mile (4-km) long, L-shaped LIGO interferometer uses laser light split into two beams that travel back and forth down the arms (four-foot diameter tubes kept under a near-perfect vacuum). The beams are used to monitor the distance between mirrors precisely positioned at the ends of the arms. According to Einstein’s theory, the distance between the mirrors will change by an infinitesimal amount when a gravitational wave passes by the detector. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10-19 meter) can be detected.

Independent and widely separated observatories are necessary to determine the direction of the event causing the gravitational waves, and also to verify that the signals come from space and are not from some other local phenomenon.

Toward this end, the LIGO Laboratory is working closely with scientists in India at the Inter-University Centre for Astronomy and Astrophysics, the Raja Ramanna Centre for Advanced Technology, and the Institute for Plasma to establish a third Advanced LIGO detector on the Indian subcontinent. Awaiting approval by the government of India, it could be operational early in the next decade. The additional detector will greatly improve the ability of the global detector network to localize gravitational-wave sources.

“Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location in the era of multi-messenger astronomy,” says David McClelland, professor of physics and director of the Centre for Gravitational Physics at the Australian National University.

The finding is described in an open-access paper in Physical Review Letters today (Feb. 11).


National Science Foundation | LIGO detects gravitational waves **Begin viewing at 27:14**

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Scientists discover how the human brain folds

This 3D gel model of a smooth fetal brain is coated with a thin layer of elastomer gel and immersed in solvent. The gel absorbs the solvent, causing it to swell relative to the deeper regions. Within minutes, the resulting compression leads to the formation of folds similar in size and shape to real brains. (credit: Mahadevan Lab/Harvard SEAS)

Folded brains likely evolved to fit a large cortex into a small volume, with the added benefit of reducing neuronal wiring length and improving cognitive function. But how does the brain fold?

A simple mechanical instability associated with buckling, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences, collaborating with scientists in Finland and France, have discovered in research published in Nature Physics.

Expanded gray matter

“We found that we could mimic cortical folding using a very simple physical principle and get results qualitatively similar to what we see in real fetal brains,” said L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, Organismic and Evolutionary Biology, and Physics.

The number, size, shape, and position of neuronal cells present during brain growth all lead to the expansion of the gray matter (cortex) relative to the underlying white matter. This puts the cortex under compression, leading in turn to a mechanical instability that causes it to crease locally.

“This simple evolutionary innovation, with iterations and variations, allows for a large cortex to be packed into a small volume, and is likely the dominant cause behind brain folding, known as gyrification,” said Mahadevan, who is also a core faculty member of the Wyss Institute for Biologically Inspired Engineering and a member of the Kavli Institute for Bionano Science and Technology, both at Harvard University.

Mahadevan’s previous research found that the growth differential between the brain’s outer cortex and the soft tissue underneath explains the variations in the folding patterns across organisms in terms of just two parameters: the relative size of the brain and the relative expansion of the cortex.

Testing a 3D gel model

Left: All notable gyri as identified on a real fetal brain. Right: Analogous regions shown in a simulated brain driven by relative constrained growth. In both cases, the coloring is based on visual identification of the major gyri. (credit: adapted from P. D. Griffiths et al./Atlas of fetal and neonatal brain MR imaging, with permission from Elsevier; and Tuomas Tallinen et al./Nature Physics)

Building on this, the team collaborated with neuroanatomists and radiologists in France and directly tested this theory using data from human fetuses. The team made a 3D gel model of a smooth fetal brain based on MRI images. The model’s surface was coated with a thin layer of elastomer gel, as an analog of the cortex. To mimic cortical expansion, the gel brain was immersed in a solvent that is absorbed by the outer layer, causing it to swell relative to the deeper regions. Within minutes of being immersed in liquid solvent, the resulting compression led to the formation of folds similar in size and shape to real brains.

The extent of the similarities surprised even the researchers. “When I put the model into the solvent, I knew there should be folding but I never expected that kind of close pattern compared to human brain,” said Jun Young Chung, a postdoctoral fellow and co-first author of the paper. “It looks like a real brain.”

The key to those similarities lies in the unique shape of the human brain. “The geometry of the brain is really important because it serves to orient the folds in certain directions,” said Chung. “Our model, which has the same large-scale geometry and curvature as a human brain, leads to the formation of folds that matches those seen in real fetal brains quite well.

“Brains are not exactly the same from one human to another, but we should all have the same major folds in order to be healthy,” said Chung. “Our research shows that if a part of the brain does not grow properly, or if the global geometry is disrupted, we may not have the major folds in the right place, which may cause dysfunction in the brain.”

The distinctive folds of the human brain are not present in most animals — only in a handful of species, including some primates, dolphins, elephants, and pigs. In humans, folding begins in fetal brains around the 20th week of gestation and is completed only when the child is about 18 months old.

Scientists at Jyvaskyla University in Finland, the Institut Mines-Télécom in France, and the University of Aix-Marseille, France were also involved in the research, which was supported by the Academy of Finland, the Wyss Institute for Biologically Inspired Engineering, and fellowships from the MacArthur Foundation and the Radcliffe Institute.

Abstract of On the growth and form of cortical convolutions

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Planet Nine from outer space

This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. (credit: Caltech/R. Hurt (IPAC))

Caltech researchers have found evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system that the researchers have nicknamed Planet Nine.

It has a mass about ten times that of Earth and orbits about 20 times farther from the sun on average than does Neptune (which orbits the sun at an average distance of 2.8 billion miles). In fact, it would take this new planet between 10,000 and 20,000 years to make just one full orbit around the sun.

The researchers, Konstantin Batygin and Mike Brown (best known for the significant role he played in the demotion of Pluto from a planet to a dwarf planet), discovered the planet’s existence through mathematical modeling and computer simulations but have not yet observed the object directly.

“This would be a real ninth planet,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

Brown notes that the putative ninth planet—at 5,000 times the mass of Pluto—is sufficiently large that there should be no debate about whether it is a true planet. Unlike the class of smaller objects now known as dwarf planets, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region larger than any of the other known planets—a fact that Brown says makes it “the most planet-y of the planets in the whole solar system.”

Batygin and Brown describe their work in an open-access paper in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete,” said Batygin.

Planet Nine’s existence also helps explain the alignment of distant Kuiper Belt objects and the mysterious orbits that two of them trace.

The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the solar system. Batygin and Brown show that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. (credit: Caltech/R. Hurt (IPAC); [Diagram created using WorldWide Telescope.])

So where did Planet Nine come from and how did it end up in the outer solar system? Scientists have long believed that the early solar system began with four planetary cores that went on to grab all of the gas around them, forming the four gas planets — Jupiter, Saturn, Uranus, and Neptune. Over time, collisions and ejections shaped them and moved them out to their present locations.

“But there is no reason that there could not have been five cores, rather than four,” says Brown. Planet Nine could represent that fifth core, and if it got too close to Jupiter or Saturn, it could have been ejected into its distant, eccentric orbit.

A predicted consequence of Planet Nine is that a second set of confined objects should also exist. These objects are forced into positions at right angles to Planet Nine and into orbits that are perpendicular to the plane of the solar system. Five known objects (blue) fit this prediction precisely. (credit: Caltech/R. Hurt (IPAC) [Diagram was created using WorldWide Telescope.])

Replacing Pluto

Only the planet’s rough orbit is known, not the precise location of the planet on that elliptical path. If the planet happens to be close to its perihelion, Brown says, astronomers should be able to spot it in images captured by previous surveys. If it is in the most distant part of its orbit, the world’s largest telescopes — such as the twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru Telescope, all on Mauna Kea in Hawaii — will be needed to see it. If, however, Planet Nine is now located anywhere in between, many telescopes have a shot at finding it.

“One of the most startling discoveries about other planetary systems has been that the most common type of planet out there has a mass between that of Earth and that of Neptune,” says Batygin. “Until now, we’ve thought that the solar system was lacking in this most common type of planet. Maybe we’re more normal after all.”

“All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found,” Brown says. “Now we can go and find this planet and make the solar system have nine planets once again.”


Caltech AMT | Caltech’s Konstantin Batygin, an assistant professor of planetary science, and Mike Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy, discuss new research that provides evidence of a giant planet tracing a bizarre, highly elongated orbit in the outer solar system.

Abstract of Evidence for a Distant Giant Planet in the Solar System

Recent analyses have shown that distant orbits within the scattered disk population of the Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion. While several hypotheses have been put forward to explain this alignment, to date, a theoretical model that can successfully account for the observations remains elusive. In this work we show that the orbits of distant Kuiper Belt objects (KBOs) cluster not only in argument of perihelion, but also in physical space. We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin. We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass gsim10 m⊕ whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180° away from the perihelia of the minor bodies. In addition to accounting for the observed orbital alignment, the existence of such a planet naturally explains the presence of high-perihelion Sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60° and 150° whose origin was previously unclear. Continued analysis of both distant and highly inclined outer solar system objects provides the opportunity for testing our hypothesis as well as further constraining the orbital elements and mass of the distant planet.

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Fermi paradox resolved: near-universal early extinction?

Despite the “Gaian Bottleneck” hypothesis, CSIRO’s Parkes radio telescope will search for alien civilizations as part of the $100 Million Breakthrough Listen project (credit: Wayne England)

The famous Fermi paradox raises the question: why haven’t we detected signs of alien life, despite high estimates of probability, such as observations of planets in the “habitable zone” around a Sun-like star by the Kepler telescope and calculations of hundreds of billions of Earth-like planets in our galaxy that might support life.

Now astrobiologists from Australian National University (ANU) Research School of Earth Sciences say they have the best answer: Because life on other planets would likely be brief and would become extinct very quickly from runaway heating or cooling.

“The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,” said Aditya Chopra, PhD., lead author on a paper published in Astrobiology. In fact, “early life is fragile, so we believe it rarely evolves quickly enough to survive. Most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.”

The Gaian Bottleneck

For example, about four billion years ago Earth, Venus and Mars may have all been habitable. However, a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox, the authors explain. Early microbial life on Venus and Mars, if there was any, failed to stabilize the rapidly changing environment, while life on Earth probably played a leading role in stabilizing the planet’s climate.

The authors name this near-universal early extinction the “Gaian Bottleneck,” which also leads to the prediction that the vast majority of fossils in the universe (found in future meteorites, for example) will be from extinct microbial life, not from multicellular species such as dinosaurs or humanoids that take billions of years to evolve. So far, that’s the case.

Abstract of The Case for a Gaian Bottleneck: The Biology of Habitability

The prerequisites and ingredients for life seem to be abundantly available in the Universe. However, the Universe does not seem to be teeming with life. The most common explanation for this is a low probability for the emergence of life (an emergence bottleneck), notionally due to the intricacies of the molecular recipe. Here, we present an alternative Gaian bottleneck explanation: If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable. In the Gaian bottleneck model, the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star. Key Words: Life—Habitability—Gaia—Abiogenesis habitable zone (AHZ)—Circumstellar habitable zone (CHZ). Astrobiology 16, 7–22.

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‘Fast radio burst’ signals from space a better test of Einstein’s General Relativity theory

This illustration shows how two photons, one at a high frequency (blue wave) and another at a low frequency (yellow wave), travel in curved space-time from their origin in a distant fast radio burst (FRB) source until reaching the Earth. A lower-limit estimate of the gravitational pull that the photons experience along their way is given by the mass (red) in the center of the Milky Way Galaxy. (credit: Purple Mountain Observatory, Chinese Academy of Sciences)

Physicists have developed a new way to test one of the basic principles underlying Einstein’s theory of General Relativity, which states that the geometry of spacetime is curved by the mass density of individual galaxies, stars, planets, and other objects.

The new method uses brief blasts of rare radio signals from space called fast radio bursts (FRBs) (see “Mysterious cosmic burst of radio waves detected by astronomers” and “Arecibo detects mystery radio burst from beyond our galaxy“). These FRBs have achieved up to 100 times better results than previous testing methods that used gamma-ray bursts, according to a paper published in the journal Physical Review Letters.

A schematic illustration of CSIRO’s Parkes radio telescope receiving a polarized signal from a “fast radio burst” (credit: Swinburne Astronomy Productions)

Fast radio bursts are super-brief blasts of energy lasting just a few milliseconds. Until now, only about a dozen FRBs have been detected on Earth. They appear to be caused by mysterious events beyond our Milky Way Galaxy, and possibly even beyond the Local Group of galaxies that includes the Milky Way.

“If Fast Radio Bursts are proven to originate outside the Milky Way Galaxy, and if their distances can be measured accurately, they will be a new powerful tool for testing Einstein’s Equivalence Principle and for extending the tested energy range down to radio-band frequencies,” said Peter Mészáros, Holder of the Eberly Family Chair in Astronomy and Astrophysics and Professor of Physics at Penn State, the senior author of the research paper.

Testing Einstein’s Equivalence Principle

Einstein’s Equivalence Principle requires that any two photons of different frequencies, emitted at the same time from the same source and traveling through the same gravitational fields, should arrive at Earth at exactly the same time. “If Einstein’s Equivalence Principle is correct, any time delay that might occur between these two photons should not be due to the gravitational fields they experienced during their travels, but should be due only to other physical effects,” Mészáros said. “By measuring how closely in time the two different-frequency photons arrive, we can test how closely they obey Einstein’s Equivalence Principle.”

Specifically, Mészáros said the test that he and his coauthors developed involves an analysis of how much space curvature the photons experienced due to massive objects along or near their path through space.

Mészáros said his research team’s analysis of the less-than-a-dozen recently detected Fast Radio Bursts “supersedes by one to two orders of magnitude the previous best limits on the accuracy of the Einstein Equivalence Principle,” which were based on gamma rays and other energies from a 1987 supernova explosion. “Our analysis using radio frequencies shows that the Einstein Equivalence Principle is obeyed to one part in a hundred million,” Mészáros said.

This research is supported, in part, by the National Basic Research Program of China, NASA, the National Natural Science Foundation of China, and the Chinese Academy of Sciences.

Abstract of Testing Einstein’s Equivalence Principle With Fast Radio Bursts

The accuracy of Einstein’s equivalence principle (EEP) can be tested with the observed time delays between correlated particles or photons that are emitted from astronomical sources. Assuming as a lower limit that the time delays are caused mainly by the gravitational potential of the Milky Way, we prove that fast radio bursts (FRBs) of cosmological origin can be used to constrain the EEP with high accuracy. Taking FRB 110220 and two possible FRB/gamma-ray burst (GRB) association systems (FRB/GRB 101011A and FRB/GRB 100704A) as examples, we obtain a strict upper limit on the differences of the parametrized post-Newtonian parameter γ values as low as [γ(1.23  GHz)−γ(1.45  GHz)]<4.36×10−9. This provides the most stringent limit up to date on the EEP through the relative differential variations of the γparameter at radio energies, improving by 1 to 2 orders of magnitude the previous results at other energies based on supernova 1987A and GRBs.

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Nearby star hosts closest alien planet in the ‘habitable zone’

 

A simulation of the orbital configuration of the Wolf 1061 system. Wolf 1061 is an inactive red dwarf star, smaller and cooler than our sun, 14 light years away. The planetary habitable zone around the star is marked in green — the colors grade from red (where a planet would be too hot), through green (where the surface of a planet could sustain liquid water), through to blue (where a planet would be too cold). (credit: Made using Universe Sandbox 2 software)

UNSW Australia astronomers have discovered the closest potentially habitable planet found outside our solar system so far, orbiting a star just 14 light years away.

The planet, more than four times the mass of the Earth, is one of three that the team detected around a red dwarf star called Wolf 1061.

“It is a particularly exciting find because all three planets are of low enough mass to be potentially rocky and have a solid surface, and the middle planet, Wolf 1061c, sits within the ‘Goldilocks’ zone where it might be possible for liquid water — and maybe even life — to exist,” says lead study author UNSW’s Duncan Wright.

“While a few other planets have been found that orbit stars closer to us than Wolf 1061, those planets are not considered to be remotely habitable,” Dr Wright says.

The three newly detected planets orbit the small, relatively cool and stable star about every 5, 18 and 67 days.  Their masses are at least 1.4, 4.3 and 5.2 times that of Earth, respectively. The larger outer planet falls just outside the outer boundary of the habitable zone and is also likely to be rocky, while the smaller inner planet is too close to the star to be habitable.

The discovery will be published in The Astrophysical Journal Letters (an open access article).

Small rocky planets like our own are now known to be abundant in our galaxy, and multi-planet systems also appear to be common. However most of the rocky exoplanets discovered so far are hundreds or thousands of light years away.

An exception is Gliese 667Cc which lies 22 light years from Earth. It orbits a red dwarf star every 28 days and is at least 4.5 times as massive as Earth.

“The close proximity of the planets around Wolf 1061 means there is a good chance these planets may pass across the face of the star. If they do, then it may be possible to study the atmospheres of these planets in future to see whether they would be conducive to life,” says team member UNSW’s  Dr Rob Wittenmyer.


UNSW Science | A simulation of the orbital configuration of the Wolf 1061 system. Wolf 1061 is an inactive red dwarf star, smaller and cooler than our sun, 14 light years away.

The orbits for the planets b, c and d (ordered from the inner planet to the outer) have periods of 4.9 days, 17.9 days and 67.2 days. In the simulation we show the planet orbits as all lying in a single plane.

The planetary habitable zone around the star is marked in green – the colours grade from red (where a planet would be too hot), through green (where the surface of a planet could sustain liquid water), through to blue (where a planet would be too cold).

Credit: This simulation was made using the Universe Sandbox 2 software from universesandbox.com

Abstract of  Three planets orbiting Wolf 1061

We use archival HARPS spectra to detect three planets orbiting the M3 dwarf Wolf 1061 (GJ 628). We detect a 1.36 M⊕ minimum-mass planet with an orbital period P = 4.888 d (Wolf 1061b), a 4.25 M⊕ minimum-mass planet with orbital period P = 17.867 d (Wolf 1061c), and a likely 5.21 M⊕ minimum-mass planet with orbital period P = 67.274 d (Wolf 1061d). All of the planets are of suffi- ciently low mass that they may be rocky in nature. The 17.867 d planet falls within the habitable zone for Wolf 1061 and the 67.274 d planet falls just outside the outer boundary of the habitable zone. There are no signs of activity observed in the bisector spans, cross-correlation full-width-half-maxima, Calcium H & K indices, NaD indices, or Hα indices near the planetary periods. We use custom methods to generate a cross-correlation template tailored to the star. The resulting velocities do not suffer the strong annual variation observed in the HARPS DRS velocities. This differential technique should deliver better exploitation of the archival HARPS data for the detection of planets at extremely low amplitudes.

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New mass spectral imaging instrument maps cells’ composition in 3-D at more than 100 times higher resolution

A mass spectral imaging instrument instrument developed at Colorado State University (credit: William Cotton/Colorado State University)

A one-of-a-kind mass spectral imaging instrument built at Colorado State University (CSU) lets scientists map cellular composition in three dimensions at a nanoscale image resolution of 75 nanometers wide and 20 nanometers deep — more than 100 times higher resolution than was earlier possible, according to the scientists.

The instrument may be able to observe how well experimental drugs penetrate and are processed by cells as new medications are developed to combat disease, customize treatments for specific cell types in specific conditions, identify the sources of pathogens propagated for bioterrorism, or investigate new ways to overcome antibiotic resistance among patients with surgical implants, according to professor Dean Crick of the CSU Mycobacteria Research Laboratories.

Crick’s primary research interest is tuberculosis, an infectious respiratory disease that contributes to an estimated 1.5 million deaths around the world each year. “We’ve developed a much more refined instrument,” Crick said. “It’s like going from using a dull knife to using a scalpel. You could soak a cell in a new drug and see how it’s absorbed, how quickly, and how it affects the cell’s chemistry.”

Schematics showing the focused extreme ultraviolet laser beam ablating (removal of material from the surface) a sample to produce an ion stream that is analyzed by a mass spectrometer. (b) Atomic force microscope (AFM) images of craters ablated in polymethyl methacrylate (PMMA) by a single EUV laser shot at different irradiation particle rated. The craters show smooth profiles with no signs of thermal damage. (c) Schematic of the instrument setup including the collimating extreme ultraviolet laser optics, focusing zone plate and spectrometer. (credit: Ilya Kuznetsov et al./Nature Communications)

The earlier generation of laser-based mass-spectral imaging could identify the chemical composition of a cell and could map its surface in two dimensions at microscale (about one micrometer), but could not chart cellular anatomy at more-detailed nanoscale dimensions and in 3-D, Crick said.

The research is described in an open-access paper in Nature Communications and was funded by a $1 million grant from the National Institutes of Health as part of an award to the Rocky Mountain Regional Center of Excellence for Biodefense and Emerging Infectious Disease Research. The optical equipment that focuses the laser beam was created by the Center for X-Ray Optics at the Lawrence Berkeley National Laboratory in Berkeley, Calif.

A special issue of Optics and Photonics News this month highlights the CSU research as among “the most exciting peer-reviewed optics research to have emerged over the past 12 months.”


CSU College of Veterinary Medicine and Biomedical Sciences | Nanoscale Mass-Spectral Imaging in 3-D at Colorado State University

Abstract of Three-dimensional nanoscale molecular imaging by extreme ultraviolet laser ablation mass spectrometry

Analytical probes capable of mapping molecular composition at the nanoscale are of critical importance to materials research, biology and medicine. Mass spectral imaging makes it possible to visualize the spatial organization of multiple molecular components at a sample’s surface. However, it is challenging for mass spectral imaging to map molecular composition in three dimensions (3D) with submicron resolution. Here we describe a mass spectral imaging method that exploits the high 3D localization of absorbed extreme ultraviolet laser light and its fundamentally distinct interaction with matter to determine molecular composition from a volume as small as 50 zl in a single laser shot. Molecular imaging with a lateral resolution of 75 nm and a depth resolution of 20 nm is demonstrated. These results open opportunities to visualize chemical composition and chemical changes in 3D at the nanoscale.

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Evidence that our Sun could release ‘superflares’ 1000x greater than previously recorded

What the Sun might look like if it were to produce a superflare. A large flaring coronal loop structure is shown towering over a solar active region. (credit: University of Warwick/Ronald Warmington)

Astrophysicists have discovered a stellar “superflare” on a star observed by NASA’s Kepler space telescope with wave patterns similar to those that have been observed in the Sun’s solar flares. (Superflares are flares that are thousands of times more powerful than those ever recorded on the Sun, and are frequently observed on some stars.)

The scientists found the evidence in the star KIC9655129 in the Milky Way. They suggest there are similarities between the superflare on KIC9655129 and the Sun’s solar flares, so the underlying physics of the flares might be the same.

Disastrous for life on Earth

Typical solar flares can have energies equivalent to a 100 million megaton bombs, but a superflare on our Sun could release energy equivalent to 100 billion megaton bombs, the scientists say.

The effects on the power grid in the U.S. would be similar to those resulting from a major cyberattack on America’s power grid, as described in the just-published book, Lights Out: A Cyberattack, A Nation Unprepared, Surviving the Aftermath.

The Earth’s communications and energy systems could be at serious risk of failing, the scientists note, and disastrous for life on Earth. Our GPS and radio communication systems could be severely disrupted and there could be large-scale power blackouts as a result of strong electrical currents being induced in power grids.

The evidence

Research co-author Anne-Marie Broomhall, PhD, from the University of Warwick explains: “When a flare occurs, we typically see a rapid increase in intensity followed by a gradual decline. Usually the decline phase is relatively smooth but occasionally there are noticeable bumps, which are termed ‘quasi-periodic pulsations’ or QPPs.”

The scientists used techniques called wavelet analysis and Monte Carlo modeling to assess the periodicity and statistical significance of these QPPs. The analysis revealed two significant periodicities, with less than a 1% probability that these pulsations would be observed by chance. The most plausible explanation for the presence of two independent periodicities: the QPPs were caused by magnetohydrodynamic (MHD) oscillations, which are also frequently observed in solar flares, the scientists say.

“This result is, therefore, an indication that the same physical processes are involved in both solar flares and stellar superflares. The latter finding supports the hypothesis that the Sun is able to produce a potentially devastating superflare.”

(Also see previous KurzweilAI coverage of this subject.)

The research is published by The Astrophysical Journal Letters and was funded by the European Research Council.

Abstract for A Multi-Period Oscillation In A Stellar Superflare

Flares that are orders of magnitude larger than the most energetic solar flares are routinely observed on Sun-like stars, raising the question of whether the same physical processes are responsible for both solar and stellar flares. In this Letter, we present a white-light stellar superflare on the star KIC 9655129, observed by NASA’s Kepler mission, with a rare multi-period quasi-periodic pulsation (QPP) pattern. Two significant periodic processes were detected using the wavelet and autocorrelation techniques, with periods of 78 ± 12 minutes and 32 ± 2 minutes. By comparing the phases and decay times of the two periodicities, the QPP signal was found to most likely be linear, suggesting that the two periodicities are independent, possibly corresponding either to different magnetohydrodynamic (MHD) modes of the flaring region or different spatial harmonics of the same mode. The presence of multiple periodicities is a good indication that the QPPs were caused by MHD oscillations and suggests that the physical processes in operation during stellar flares could be the same as those in solar flares.

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Supermassive black-hole-eating star ejects high-speed flare

Artist’s conception of a star being drawn toward a black hole and destroyed (left), and the black hole later emitting a “jet” of plasma composed of the debris left from the star’s destruction (credit: modified from an original image by Amadeo Bachar)

An international team of astrophysicists has for the first time witnessed a black hole swallowing a star and ejecting a flare of matter moving at nearly the speed of light.

The finding, reported in the journal Science, tracks the star — about the size of our sun — as it shifts from its customary path, slips into the gravitational pull of a supermassive black hole and is sucked in, said Sjoert van Velzen, a Hubble fellow at Johns Hopkins University.

Jet escapes from near the event horizon

“These events are extremely rare,” van Velzen said. “It’s the first time we see everything from the stellar destruction followed by the launch of a conical outflow, also called a jet, and we watched it unfold over several months.”

The astrophysicists had predicted that when a black hole is force-fed a large amount of gas, in this case a whole star, a fast-moving jet of plasma — elementary particles in a magnetic field — can escape from near the black hole rim, or “event horizon.” This study suggests this prediction was correct, the scientists said.

“Previous efforts to find evidence for these jets, including my own, were late to the game,” said van Velzen, who led the analysis and coordinated the efforts of 13 other scientists in the United States, the Netherlands, Great Britain and Australia.

Supermassive black holes, the largest of black holes, are believed to exist at the center of most massive galaxies. This particular one lies at the lighter end of the supermassive black hole spectrum, at only about a million times the mass of our sun, but still packing the force to gobble a star.

Witnessing a star destruction

The first observation of the star being destroyed was made by a team at The Ohio State University, using an optical telescope in Hawaii. That team announced its discovery on Twitter in early December 2014.

After reading about the event, van Velzen contacted an astrophysics team led by Rob Fender at the University of Oxford in Great Britain. That group used radio telescopes to follow up as fast as possible. They were just in time to catch the action.

By the time it was done, the international team had data from satellites and ground-based telescopes that gathered X-ray, radio and optical signals, providing a stunning “multi-wavelength” portrait of this event.

It helped that the galaxy in question is closer to Earth than those studied previously in hopes of tracking a jet emerging after the destruction of a star. This galaxy is about 300 million light years away, while the others were at least three times farther away. One light year is 5.88 trillion miles.

The first step for the international team was to rule out the possibility that the light was from a pre-existing expansive swirling mass called an “accretion disk” that forms when a black hole is sucking in matter from space. That helped to confirm that the sudden increase of light from the galaxy was due to a newly trapped star.

“The destruction of a star by a black hole is beautifully complicated, and far from understood,” van Velzen said. “From our observations, we learn the streams of stellar debris can organize and make a jet rather quickly, which is valuable input for constructing a complete theory of these events.”

Abstract of A radio jet from the optical and X-ray bright stellar tidal disruption flare ASASSN-14li

The tidal disruption of a star by a supermassive black hole leads to a short-lived thermal flare. Despite extensive searches, radio follow-up observations of known thermal stellar tidal disruption flares (TDFs) have not yet produced a conclusive detection. We present a detection of variable radio emission from a thermal TDF, which we interpret as originating from a newly-launched jet. The multi-wavelength properties of the source present a natural analogy with accretion state changes of stellar mass black holes, suggesting all TDFs could be accompanied by a jet. In the rest frame of the TDF, our radio observations are an order of magnitude more sensitive than nearly all previous upper limits, explaining how these jets, if common, could thus far have escaped detection.