New Study Pinpoints Stress Factor Of Mega-Earthquake Off Japan

Scripps Institution of Oceanography, UC San Diego researchers published new findings on the role geological rock formations offshore of Japan played in producing the massive 2011 Tohoku-oki earthquake, one of only two magnitude 9 mega-earthquakes to occur in the last 50 years.

earthquake

The study, published in the journal Nature, offers new information about the hazard potential of large earthquakes at subduction zones, where tectonic plates converge.

The magnitude 9 quake, which triggered a major tsunami that caused widespread destruction along the coastline of Japan, including the Fukushima nuclear plant disaster, was atypical in that it created an unusually large seismic movement, or slip, of 50 meters (164 feet) within a relatively small rupture area along the earthquake fault.

To better understand what may have caused this large movement, Scripps researchers used gravity and topography data to produce a detailed map of the geological architecture of the seafloor offshore of Japan. The map showed that the median tectonic line, which separates two distinct rock formations, volcanic rocks on one side and metamorphic rocks on the other, extends along the seafloor offshore.

The region over the earthquake-generating portion of the plate boundary off Japan is characterized by variations in water depth and steep topographic gradients of about six kilometers (3.7 miles). These gradients, according to the researchers, can hide smaller variations in the topography and gravity fields that may be associated with geological structure changes of the overriding Japan and subducting Pacific plates.

“The new method we developed has enabled us to consider how changes in the composition of Japan’s seafloor crust along the plate-boundary influences the earthquake cycle,” said Dan Bassett, a postdoctoral researcher at Scripps and lead author of the study.

The researchers suggest that a large amount of stress built up along the north, volcanic rock side of the median tectonic line resulting in the earthquake’s large movement. The plates on the south side of the line do not build up as much stress, and large earthquakes have not occurred there.

“There’s a dramatic change in the geology that parallels the earthquake cycle,” said Scripps geophysicist David Sandwell, a co-author of the study. “By looking at the structures of overriding plates, we can better understand how big the next one will be.”

Mysterious Cosmic Radio Bursts Found To Repeat

Astronomers for the first time have detected repeating short bursts of radio waves from an enigmatic source that is likely located well beyond the edge of our Milky Way galaxy. The findings indicate that these “fast radio bursts” come from an extremely powerful object which occasionally produces multiple bursts in under a minute.

radio burst

Prior to this discovery, reported in Nature, all previously detected fast radio bursts (FRBs) have appeared to be one-off events. Because of that, most theories about the origin of these mysterious pulses have involved cataclysmic incidents that destroy their source — a star exploding in a supernova, for example, or a neutron star collapsing into a black hole. The new finding, however, shows that at least some FRBs have other origins.

FRBs, which last just a few thousandths of a second, have puzzled scientists since they were first reported nearly a decade ago. Despite extensive follow-up efforts, astronomers until now have searched in vain for repeat bursts.

That changed last November 5th, when McGill University PhD student Paul Scholz was sifting through results from observations performed with the Arecibo radio telescope in Puerto Rico — the world’s largest radio telescope. The new data, gathered in May and June and run through a supercomputer at the McGill High Performance Computing Centre, showed several bursts with properties consistent with those of an FRB detected in 2012.

The repeat signals were surprising — and “very exciting,” Scholz says. “I knew immediately that the discovery would be extremely important in the study of FRBs.” As his office mates gathered around his computer screen, Scholz pored over the remaining output from specialized software used to search for pulsars and radio bursts. He found that there were a total of 10 new bursts.

The finding suggests that these bursts must have come from a very exotic object, such as a rotating neutron star having unprecedented power that enables the emission of extremely bright pulses, the researchers say. It is also possible that the finding represents the first discovery of a sub-class of the cosmic fast-radio-burst population.

“Not only did these bursts repeat, but their brightness and spectra also differ from those of other FRBs,” notes Laura Spitler, first author of the new paper and a postdoctoral researcher at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

Scientists believe that these and other radio bursts originate from distant galaxies, based on the measurement of an effect known as plasma dispersion. Pulses that travel through the cosmos are distinguished from human-made interference by the influence of interstellar electrons, which cause radio waves to travel more slowly at lower radio frequencies. The 10 newly discovered bursts, like the one detected in 2012, have three times the maximum dispersion measure that would be expected from a source within the Milky Way.

Intriguingly, the most likely implication of the new Arecibo finding — that the repeating FRB originates from a very young extragalactic neutron star — is at odds with the results of a study published last week in Nature by another research team. That paper suggested FRBs are related to cataclysmic events, such as short gamma-ray bursts, which can not generate repeat events. “However, the apparent conflict between the studies could be resolved, if it turns out that there are at least two kinds of FRB sources,” notes McGill physics professor Victoria Kaspi, a senior member of the international team that conducted the Arecibo study.

In future research, the team hopes to identify the galaxy where the radio bursts originated. To do so, they will need to detect bursts using radio telescopes with far more resolving power than Arecibo, a National Science Foundation-sponsored facility with a dish that spans 305 metres and covers about 20 acres. Using a technique called interferometry, performed with radio telescope arrays spread over large geographical distances, the astronomers may be able to achieve the needed resolution.

“Once we have precisely localized the repeater’s position on the sky, we will be able to compare observations from optical and X-ray telescopes and see if there is a galaxy there,” says Jason Hessels, associate professor at the University of Amsterdam and the Netherlands Institute for Radio Astronomy as well as corresponding author of the Nature paper. “Finding the host galaxy of this source is critical to understanding its properties,” he adds.

Canada’s CHIME telescope could help unravel the puzzle, adds Kaspi, who is Director of the McGill Space Institute. Thanks to the novel design of the soon-to-be completed apparatus, it is expected to be able to detect dozens of fast radio bursts per day, she says. “CHIME will further our quest to understand the origin of this mysterious phenomenon, which has the potential to provide a valuable new probe of the Universe.”

Why Objects In The Universe Have Such A Range Of Sizes: Celestial Bodies Born Like Cracking Paint

A Duke theorist says there’s a very good reason why objects in the universe come in a wide variety of sizes, from the largest stars to the smallest dust motes — and it has a lot to do with how paint cracks when it dries.

celestial

In a paper published March 1 in the Journal of Applied Physics, Adrian Bejan, the J.A. Jones Professor of Mechanical Engineering at Duke University, explains how the need to release internal tension shaped the universe as we see it.

Though unknowably large and spread out, the very early universe can be thought of as a finite volume of suspended particles. And because every object in the universe exerts a gravitational force on every other object in the universe, this volume was in internal tension.

It was only a matter of time before particles began coming together to form larger objects. But why did they come together to form objects in such a wide variety of sizes, rather than in a uniform manner?

“We know from common experiences that things in volumetric tension crack, and they crack instantly everywhere,” said Bejan. “The easiest example is paint drying on a wall. As it dries, it shrinks, putting the entire system in tension. Then boom, it suddenly cracks overnight, relieving the tension. And the design responsible for that relief is hierarchical, meaning few large and many small.”

According to Bejan, this pattern of relief follows the constructal law, which he penned in 1996. The constructal law states that any flowing system allowed to change freely over time will trend toward an easier flowing architecture. For rivers, roots and vascular systems, this means a few large channels carry massive flows to numerous smaller branches for evacuation. For a young universe with particles pulling every which way, this means its internal tension released in the fastest way possible.

In a series of thought experiments and simple physics equations, Bejan’s paper shows that the fastest way for the tension to be released was through the formation of bodies in a hierarchy. That is, he demonstrates that if all bodies formed were of the same size, the tension would not be released as affectively as when a few large bodies were formed along with many smaller bodies.

Just like the cracks in the paint.

“All volumetric cracking is hierarchical. You never see uniform cracking or shattering,” said Bejan. “In celestial mechanics, there is this very old idea that bodies coalesce and grow due to gravity, which is of course correct. Growth is one thing, but growing hierarchically rather than all in the same size is another, which is called nature.”

Pulsar Web Could Detect Low-Frequency Gravitational Waves

The recent detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) came from two black holes, each about 30 times the mass of our sun, merging into one. Gravitational waves span a wide range of frequencies that require different technologies to detect. A new study from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has shown that low-frequency gravitational waves could soon be detectable by existing radio telescopes.

pulsar

“Detecting this signal is possible if we are able to monitor a sufficiently large number of pulsars spread across the sky,” said Stephen Taylor, lead author of the paper published this week in The Astrophysical Journal Letters. He is a postdoctoral researcher at NASA’s Jet Propulsion Laboratory, Pasadena, California. “The smoking gun will be seeing the same pattern of deviations in all of them.” Taylor and colleagues at JPL and the California Institute of Technology in Pasadena have been studying the best way to use pulsars to detect signals from low-frequency gravitational waves. Pulsars are highly magnetized neutron stars, the rapidly rotating cores of stars left behind when a massive star explodes as a supernova.

Einstein’s general theory of relativity predicts that gravitational waves — ripples in spacetime — emanate from accelerating massive objects. Nanohertz gravitational waves are emitted from pairs of supermassive black holes orbiting each other, each of which contain millions or a billion times more mass than those detected by LIGO. These black holes each originated at the center of separate galaxies that collided. They are slowly drawing closer together and will eventually merge to create a single super-sized black hole.

As they orbit each other, the black holes pull on the fabric of space and create a faint signal that travels outward in all directions, like a vibration in a spider’s web. When this vibration passes Earth, it jostles our planet slightly, causing it to shift with respect to distant pulsars. Gravitational waves formed by binary supermassive black holes take months or years to pass Earth and require many years of observations to detect.

“Galaxy mergers are common, and we think there are many galaxies harboring binary supermassive black holes that we should be able to detect,” said Joseph Lazio, one of Taylor’s co-authors, also based at JPL. “Pulsars will allow us to see these massive objects as they slowly spiral closer together.”

Once these gigantic black holes get very close to each other, the gravitational waves are too short to detect using pulsars. Space-based laser interferometers like eLISA, a mission being developed by the European Space Agency with NASA participation, would operate in the frequency band that can detect the signature of supermassive black holes merging. The LISA Pathfinder mission, which includes a stabilizing thruster system managed by JPL, is currently testing technologies necessary for the future eLISA mission.

Finding evidence for supermassive black hole binaries has been a challenge for astronomers. The centers of galaxies contain many stars, and even monstrous black holes are quite small — comparable to the size of our solar system. Seeing visible signatures of these binaries amid the glare of the surrounding galaxy has been difficult for astronomers.

Radio astronomers search instead for the gravitational signals from these binaries. In 2007, NANOGrav began observing a set of the fastest-rotating pulsars to try to detect tiny shifts caused by gravitational waves.

Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation. Astronomers detect this as a rapid pulse of radio emission. Most pulsars rotate several times a second. But some, called millisecond pulsars, rotate hundreds of times faster.

“Millisecond pulsars have extremely predictable arrival times, and our instruments are able to measure them to within a ten-millionth of a second,” said Maura McLaughlin, a radio astronomer at West Virginia University in Morgantown and member of the NANOGrav team. “Because of that, we can use them to detect incredibly small shifts in Earth’s position.”

But astrophysicists at JPL and Caltech caution that detecting faint gravitational waves would likely require more than a few pulsars. “We’re like a spider at the center of a web,” said Michele Vallisneri, another member of the JPL/Caltech research group. “The more strands we have in our web of pulsars, the more likely we are to sense when a gravitational wave passes by.”

Vallisneri said accomplishing this feat will require international collaboration. “NANOGrav is currently monitoring 54 pulsars, but we can only see some of the southern hemisphere. We will need to work closely with our colleagues in Europe and Australia in order to get the all-sky coverage this search requires.”

The feasibility of this approach was recently called into question when a group of Australian pulsar researchers reported that they were unable to detect such signals when analyzing a set of pulsars with the most precise timing measurements. After studying this result, the NANOGrav team determined that the reported non-detection was not a surprise, and resulted from the combination of optimistic gravitational wave models and analysis of too few pulsars. Their one-page response was released recently via the arXiv electronic print service.

Despite the technical challenges, Taylor is confident their team is on the right track. “Gravitational waves are washing over Earth all the time,” Taylor said. “Given the number of pulsars being observed by NANOGrav and other international teams, we expect to have clear and convincing evidence of low-frequency gravitational waves within the next decade.”

NANOGrav is a collaboration of over 60 scientists at more than a dozen institutions in the United States and Canada. The group uses radio pulsar timing observations acquired at NRAO’s Green Bank Telescope in West Virginia and at Arecibo Radio Observatory in Puerto Rico to search for ripples in the fabric of spacetime. In 2015, NANOGrav was awarded $14.5 million by the National Science Foundation to create and operate a Physics Frontiers Center.

“With the recent detection of gravitational waves by LIGO, the outstanding work of the NANOGrav collaboration is particularly relevant and timely,” said Pedro Marronetti, National Science Foundation program director for gravitational wave research. “This NSF-funded Physics Frontier Center is poised to complement LIGO observations, extending the window of gravitational wave detection to very low frequencies.”.”

ATLASGAL Survey Of Milky Way Completed

APEX, the Atacama Pathfinder EXperiment telescope, is located at 5100 metres above sea level on the Chajnantor Plateau in Chile’s Atacama region. The ATLASGAL survey took advantage of the unique characteristics of the telescope to provide a detailed view of the distribution of cold dense gas along the plane of the Milky Way galaxy. The new image includes most of the regions of star formation in the southern Milky Way.

milky way

The new ATLASGAL maps cover an area of sky 140 degrees long and 3 degrees wide, more than four times larger than the first ATLASGAL release [3]. The new maps are also of higher quality, as some areas were re-observed to obtain a more uniform data quality over the whole survey area.

The ATLASGAL survey is the single most successful APEX large programme with nearly 70 associated science papers already published, and its legacy will expand much further with all the reduced data products now available to the full astronomical community .

At the heart of APEX are its sensitive instruments. One of these, LABOCA (the LArge BOlometer Camera) was used for the ATLASGAL survey. LABOCA measures incoming radiation by registering the tiny rise in temperature it causes on its detectors and can detect emission from the cold dark dust bands obscuring the stellar light.

The new release of ATLASGAL complements observations from ESA’s Planck satellite. The combination of the Planck and APEX data allowed astronomers to detect emission spread over a larger area of sky and to estimate from it the fraction of dense gas in the inner Galaxy. The ATLASGAL data were also used to create a complete census of cold and massive clouds where new generations of stars are forming.

“ATLASGAL provides exciting insights into where the next generationof high-mass stars and clusters form. By combining these with observations from Planck, we can now obtain a link to the large-scale structures of giant molecular clouds,” remarks Timea Csengeri from the Max Planck Institute for Radio Astronomy (MPIfR), Bonn, Germany, who led the work of combining the APEX and Planck data.

The APEX telescope recently celebrated ten years of successful research on the cold Universe. It plays an important role not only as pathfinder, but also as a complementary facility to ALMA, the Atacama Large Millimeter/submillimeter Array, which is also located on the Chajnantor Plateau. APEX is based on a prototype antenna constructed for the ALMA project, and it has found many targets that ALMA can study in great detail.

Leonardo Testi from ESO, who is a member of the ATLASGAL team and the European Project Scientist for the ALMA project, concludes: “ATLASGAL has allowed us to have a new and transformational look at the dense interstellar medium of our own galaxy, the Milky Way. The new release of the full survey opens up the possibility to mine this marvellous dataset for new discoveries. Many teams of scientists are already using the ATLASGAL data to plan for detailed ALMA follow-up

Discovery Of A Fast Radio Burst Reveals ‘Missing Matter’ In The Universe

An international research team including scientists from the Max Planck Institute for Radio Astronomy in Bonn, Germany used a combination of radio and optical telescopes to identify the precise location of a fast radio burst (FRB) in a distant galaxy, allowing them to conduct a unique census of the Universe’s matter content.

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Their result, published in today’s edition of Nature, confirms current cosmological models of the distribution of matter in the Universe.

On April 18, 2015, a fast radio burst or FRB was detected by the 64-m Parkes radio telescope of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia within the framework of the SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) project. An international alert was triggered to follow it up with other telescopes and within a few hours, a number of telescopes around the world were looking for the signal, including CSIRO’s Australia Telescope Compact Array (ATCA) and the Effelsberg Radio Telescope in Germany.

FRBs are mysterious bright radio flashes generally lasting only a few milliseconds. Their origin is still unknown, with a long list of potential phenomena associated with them. FRBs are very difficult to detect; before this discovery only 16 had been detected.

“In the past FRBs have been found by sifting through data months or even years later. By that time it is too late to do follow up observations.” says Evan Keane, Project Scientist at the Square Kilometre Array Organisation and the lead scientist behind the study. To remedy this, the team developed their own observing system (SUPERB) to detect FRBs within seconds, and to immediately alert other telescopes, when there is still time to search for more evidence in the aftermath of the initial flash.

Thanks to the ATCA’s six 22-m dishes and their combined resolution, the team was able to pinpoint the location of the signal with much greater accuracy than has been possible in the past and detected a radio afterglow that lasted for around 6 days before fading away. This afterglow enabled them to pinpoint the location of the FRB about 1000 times more precisely than for previous events.

The puzzle still required another piece to be put in place. The team used the National Astronomical Observatory of Japan (NAOJ)’s 8.2-m Subaru optical telescope in Hawaii to look at where the signal came from, and identified an elliptical galaxy some 6 billion light years away. “It’s the first time we’ve been able to identify the host galaxy of an FRB” adds Evan Keane. The optical observation also gave them the redshift measurement (the speed at which the galaxy is moving away from us due to the accelerated expansion of the Universe), the first time a distance has been determined for an FRB.

For understanding the physics of such events it is important to know basic properties like the exact position, the distance of the source and whether it will be repeated. “Our analysis leads us to conclude that this new radio burst is not a repeater, but resulting from a cataclysmic event in that distant galaxy,” states Michael Kramer from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany who analysed the radio profile’s structure of the event. MPIfR’s Effelsberg Radio Telescope was also used for radio follow up observations after the alert.

FRBs show a frequency-dependent dispersion , a delay in the radio signal caused by how much material it has gone through. “Until now, the dispersion measure is all we had. By also having a distance we can now measure how dense the material is between the point of origin and Earth, and compare that with the current model of the distribution of matter in the Universe” explains Simon Johnston, co-author of the study, from CSIRO’s Astronomy and Space Science division. “Essentially this lets us weigh the Universe, or at least the normal matter it contains.”

In the current model, the Universe is believed to be made of 70% dark energy, 25% dark matter and 5% ‘ordinary’ matter, the matter that makes everything we see. However, through observations of stars, galaxies and hydrogen, astronomers have only been able to account for about half of the ordinary matter, the rest could not be seen directly and so has been referred to as ‘missing’.

“The good news is our observations and the model match, we have found the missing matter” explains Evan Keane. “It’s the first time a fast radio burst has been used to conduct a cosmological measurement.”

“This shows the potential for FRBs as new tools for cosmology,” concludes Michael Kramer who also worked on the calculation to weigh the missing matter. “Just think what we can do when we have discovered hundreds of these.”

Looking forward, the Square Kilometre Array, with its extreme sensitivity, resolution and wide field of view is expected to be able to detect many more FRBs and to pinpoint their host galaxies. A much larger sample will enable precision measurements of cosmological parameters such as the distribution of matter in the Universe, and provide a refined understanding of dark energy.

The SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) is a large-scale astrophysics project using several telescopes, high-speed GPU analysis codes, a large supercomputer and artificial neural networks to identify new astrophysical discoveries. In particular it deals with pulsars, and explosions in space known as Fast Radio Bursts (FRBs).

Bulusan Volcano Spews Ash

Bulusan Volcano spewed a grayish steam and an ash column reaching 500 meters on Monday afternoon, February 22, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said.

bulusan

In the latest bulletin issued by PHIVOLCS at 6:00 pm, Bulusan Volcano’s ash fall occurred at 5:01 pm, which also reflected as an explosion type earthquake that lasted for four minutes and twenty-one seconds.

PHIVOLCS detected a total of 12 volcanic earthquakes prior to the ash fall.

The agency raised Alert Level 1 over Bulusan Volcano and the public is reminded not to go inside the 4-kilometer radius Permanent Danger Zone (PDZ) due to risks of sudden steam and ash explosions.

PHIVOLCS said it is closely monitoring the volcano’s activity and advised residents located in the northwest and southwest sectors of the volcano to take precautions against ash falls.

PHIVOLCS also reminded residents near valleys and river channels to be watchful against lahar.

Bulusan Volcano is the southernmost volcano on Luzon Island. It is located in the province of Sorsogon in the Bicol region, 70 km southeast of Mayon Volcano and approximately 250 km southeast of Manila.

It is considered as the Philippines’ 4th most active volcano after Mayon, Taal, and Kanlaon. Its last eruption was in June 2015.