понедельник, 13 мая 2019 г.

Gravitational waves leave a detectable mark, physicists say

Gravitational waves, first detected in 2016, offer a new window on the universe, with the potential to tell us about everything from the time following the Big Bang to more recent events in galaxy centers.











Gravitational waves leave a detectable mark, physicists say
A visualization of a supercomputer simulation of merging black holes sending out gravitational waves
[Credit: NASA/C. Henze]

And while the billion-dollar Laser Interferometer Gravitational-Wave Observatory (LIGO) detector watches 24/7 for gravitational waves to pass through the Earth, new research shows those waves leave behind plenty of «memories» that could help detect them even after they’ve passed.


«That gravitational waves can leave permanent changes to a detector after the gravitational waves have passed is one of the rather unusual predictions of general relativity,» said doctoral candidate Alexander Grant, lead author of «Persistent Gravitational Wave Observables: General Framework,» published in Physical Review D.


Physicists have long known that gravitational waves leave a memory on the particles along their path, and have identified five such memories. Researchers have now found three more aftereffects of the passing of a gravitational wave, «persistent gravitational wave observables» that could someday help identify waves passing through the universe.


Each new observable, Grant said, provides different ways of confirming the theory of general relativity and offers insight into the intrinsic properties of gravitational waves.


Those properties, the researchers said, could help extract information from the Cosmic Microwave Background — the radiation left over from the Big Bang.


«We didn’t anticipate the richness and diversity of what could be observed,» said Éanna Flanagan, the Edward L. Nichols Professor and chair of physics and professor of astronomy.


This computer simulation shows the collision of two black holes, a tremendously powerful event detected for the first time 


ever by the Laser Interferometer Gravitational-Wave Observatory, which detected gravitational waves 


as the black holes spiralled toward each other, collided and merged [Credit: Cornell University]


«What was surprising for me about this research is how different ideas were sometimes unexpectedly related,» said Grant. «We considered a large variety of different observables, and found that often to know about one, you needed to have an understanding of the other.»


The researchers identified three observables that show the effects of gravitational waves in a flat region in spacetime that experiences a burst of gravitational waves, after which it returns again to being a flat region. The first observable, «curve deviation,» is how much two accelerating observers separate from one another, compared to how observers with the same accelerations would separate from one another in a flat space undisturbed by a gravitational wave.


The second observable, «holonomy,» is obtained by transporting information about the linear and angular momentum of a particle along two different curves through the gravitational waves, and comparing the two different results.


The third looks at how gravitational waves affect the relative displacement of two particles when one of the particles has an intrinsic spin.


Each of these observables is defined by the researchers in a way that could be measured by a detector. The detection procedures for curve deviation and the spinning particles are «relatively straightforward to perform,» wrote the researchers, requiring only «a means of measuring separation and for the observers to keep track of their respective accelerations.»


Detecting the holonomy observable would be more difficult, they wrote, «requiring two observers to measure the local curvature of spacetime (potentially by carrying around small gravitational wave detectors themselves).» Given the size needed for LIGO to detect even one gravitational wave, the ability to detect holonomy observables is beyond the reach of current science, researchers say.


«But we’ve seen a lot of exciting things already with gravitational waves, and we will see a lot more. There are even plans to put a gravitational wave detector in space that would be sensitive to different sources than LIGO,» Flanagan said.


Author: Linda B. Glaser | Source: Cornell University [May 09, 2019]



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Gravitational forces in protoplanetary disks may push super-Earths close to their stars

The galaxy is littered with planetary systems vastly different from ours. In the solar system, the planet closest to the Sun — Mercury, with an orbit of 88 days — is also the smallest. But NASA’s Kepler spacecraft has discovered thousands of systems full of very large planets — called super-Earths — in very small orbits that zip around their host star several times every 10 days. Now, researchers may have a better understanding how such planets formed.











Gravitational forces in protoplanetary disks may push super-Earths close to their stars
An artist’s concept of super-Earth planet 55 Cancri e, which races around its host star once every 18 hours.
New research led by Penn State astronomers improves our understanding of how large super-Earth
planets with small, quick orbits form [Credit: NASA/JPL-Caltech]

A team of Penn State-led astronomers found that as planets form out of the chaotic churn of gravitational, hydrodynamic — or, drag — and magnetic forces and collisions within the dusty, gaseous protoplanetary disk that surrounds a star as a planetary system starts to form, the orbits of these planets eventually get in synch, causing them to slide — follow the leader-style — toward the star. The team’s computer simulations result in planetary systems with properties that match up with those of actual planetary systems observed by the Kepler space telescope of solar systems. Both simulations and observations show large, rocky super-Earths orbiting very close to their host stars, according to Daniel Carrera, assistant research professor of astronomy at Penn State’s Eberly College of Science.


He said the simulation is a step toward understanding why super-Earths gather so close to their host stars. The simulations may also shed light on why super-Earths are often located so close to their host star where there doesn’t seem to be enough solid material in the protoplanetary disk to form a planet, let alone a big planet, according to the researchers, who report their findings in the Monthly Notices of the Royal Astronomical Society.


«When stars are very young, they are surrounded by a disc that is mostly gas with some dust — and that dust grows into the planets, like the Earth and these super-Earths,» said Carrera. «But the particular puzzle for us is that this disc doesn’t go the all way to the star — there’s a cavity there. And yet we see these planets closer to the star than the edge of that disc.»


The astronomers’ computer simulation shows that, over time, the planets’ and disk’s gravitational forces lock the planets into synchronized orbits — resonance — with each other. The planets then begin to migrate in unison, with some moving closer to the edge of the disk. The combination of the gas disk affecting the outer planets and the gravitational interactions among the outer and inner planets can continue to push the inner planets very closer to the star, even interior to the edge of the disk.



«With the first discoveries of Jupiter-size exoplanets orbiting close to their host star, astronomers were inspired to develop multiple models for how such planets could form, including chaotic interactions in multiple planet systems, tidal effects and migration through the gas disk,» said Eric Ford, professor of astronomy and astrophysics, director of Penn State’s Center for Exoplanets and Habitable Worlds and Institute for CyberScience (ICS) faculty co-hire. «However, these models did not predict the more recent discoveries of super-Earth-size planets orbiting so close to their host star. Some astronomers had suggested that such planets must have formed very near their current locations. Our work is important because it demonstrates how short-period super-Earth-size planets could have formed and migrated to their current locations thanks to the complex interactions of multiple planet systems.»


Carrera said more work remains to confirm that the theory is correct.


«We’ve shown that it’s possible for planets to get that close to a star in this simulation, but it doesn’t mean that it’s the only way that the universe chose to make them,» said Carrera. «Someone might come up with a different idea of a way to get the planets that close to a star. And, so, the next step is to test the idea, revise it, make predictions that you can test against observations.»


Future research may also explore why our super-Earthless solar system is different from most other solar systems, Carrera added.


«Super-Earths in very close orbits are by far the most common type of exoplanet that we observe, and yet they don’t exist in our own solar system and that makes us wonder why,» said Carrera.


According to the researchers, the best published estimates suggest that about 30 percent of solar-like stars have some planets close to the host star than the Earth is to the Sun. However, they note that additional planets are could go undetected, especially small planets far from their star.


Author: Matt Swayne | Source: Pennsylvania State University [May 09, 2019]




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Climate change is giving old trees a growth spurt

Larch trees in the permafrost forests of northeastern China — the northernmost tree species on Earth — are growing faster as a result of climate change, according to new research.











Climate change is giving old trees a growth spurt
Tree rings collected from old-growth Dahurian larch trees. Trees grow one ring per year
[Credit: Xianliang Zhang]

A new study of growth rings from Dahurian larch in China’s northern forests finds the hardy trees grew more from 2005 to 2014 than in the preceding 40 years. The findings also show the oldest trees have had the biggest growth spurts: Trees older than 400 years grew more rapidly in those 10 years than in the past 300 years, according to the new study.


The study’s authors suspect warmer soil temperatures are fueling the growth spurts by lowering the depth of the permafrost layer, allowing the trees’ roots to expand and suck up more nutrients.


The increased growth is good for the trees in the short-term but may be disastrous for the forests in the long-term, according to the authors. As the climate continues to warm, the permafrost underneath the trees may eventually degrade and no longer be able to support the slow-growing trees.


No other tree species can survive the permafrost plains this far north, so if the larch forests of northern Asia disappear, the entire ecosystem would change, according to the study’s authors.


«The disappearance of larch would be a disaster to the forest ecosystem in this region,» said Xianliang Zhang, an ecologist at Shenyang Agricultural University in Shenhang, China, and lead author of the new study in AGU’s Journal of Geophysical Research: Biogeosciences.


Earth’s hardiest trees


Dahurian larch is Earth’s northernmost tree species and its most cold-hardy: These larches are the only trees that can tolerate the frigid permafrost plains of Russia, Mongolia and northern China. Chinese locals refer to Dahurian larch as «thin-old-trees,» because they grow slowly in the thin active layer of soil above the permafrost and can live for more than 400 years.


Permafrost regions around the world have been thawing in recent decades due to rising temperatures, sometimes degrading into swamps and wetlands. In the new study, Zhang and his colleagues analyzed growth rings from more than 400 Dahurian larch in old-growth forests of northeastern China, the southernmost portion of the tree’s range, to see how the trees are faring in a warming climate.


Tree rings allow scientists to measure how much trees grow from year to year. Much like people, trees do most of their growing while young. Dahurian larch generally grow rapidly until they become around 150 years old, at which point their growth slows. When the trees hit 300 years old, their growth basically stalls.


The researchers used the width of each tree’s growth rings to calculate how much area each tree gained in cross-section each year over the course of its lifetime.











Climate change is giving old trees a growth spurt
A graph of Dahurian larch tree growth from 1964-2014. BAI stands for basal area increment – the amount of area
the trees gained in cross-section each year, in square millimeters. The lines represent average growth for trees of
different age groups (150 to 200 years old, 200 to 250 years old, 250 to 300 years old, and older than 300 years).
The spike in growth around 2004 is evident [Credit: Xianliang Zhang et al. 2019]

The results show Dahurian larch trees grew more from 2005 to 2014 than from 1964 to 2004. Interestingly, the effect was most pronounced in the oldest trees: Trees older than 300 years grew 80 percent more from 2005 to 2014 than in the preceding 40 years. Trees between 250 and 300 years old grew 35 percent more during that time period, while trees younger than 250 years grew between 11 and 13 percent more.


The old trees’ growth is unusual — it’s akin to a 100-year-old person suddenly getting taller, according to Zhang. The authors suspect older trees are growing more than younger trees because they have more developed root systems that can harvest resources from the soil more efficiently.


The researchers compared the trees’ growth rates to climate factors like soil temperatures and precipitation data over the past 50 years to see what was causing the unusual growth. They found increased soil temperatures, especially in winter, are likely powering the growth spurts. They suspect the warmer temperatures lower the depth of the permafrost layer, providing the trees’ roots more room to expand and access to more nutrients.


While this initial soil warming has benefitted Dahurian larch, further permafrost thaw could likely decrease tree growth and even cause the forest to decay, according to the authors. Dahurian larch can’t survive in wet conditions, so permafrost changing to wetlands or peatlands would be detrimental to the forest as a whole, they said.


«If the larch forest retreat in this region in the future, it is also not a good sign for the whole boreal forest,» Zhang said.


While other research has examined the effects of a warming climate on temperature-sensitive trees in North America, the new study examined temperature-sensitive trees in permafrost areas, which have been less widely studied but are a vast component of the boreal forest, said Erika Wise, an associate professor of geography at the University of North Carolina — Chapel Hill, who was not involved in the new study. Additionally, previous studies on these larch trees have focused on the effects of air temperature and precipitation, but the new study looked at the influence of ground surface temperatures, which has also not been studied widely, she added.


«Their arguments make a lot of logical sense in terms of why the trees might benefit from the increased winter ground surface temperatures, which is that especially things like an earlier spring thaw could really help trees get growing earlier, more ability to have root activity in the cold months, these sort of things would make sense in why trees would benefit from warmer winters in particular,» Wise said.


Source: American Geophysical Union [May 09, 2019]



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The bird that came back from the dead

New research has shown that the last surviving flightless species of bird, a type of rail, in the Indian Ocean had previously gone extinct but rose from the dead thanks to a rare process called ‘iterative evolution’.











The bird that came back from the dead
White-throated rail [Credit: Charles J Sharp]

The research, from the University of Portsmouth and Natural History Museum, found that on two occasions, separated by tens of thousands of years, a rail species was able to successfully colonise an isolated atoll called Aldabra and subsequently became flightless on both occasions. The last surviving colony of flightless rails is still found on the island today.


This is the first time that iterative evolution (the repeated evolution of similar or parallel structures from the same ancestor but at different times) has been seen in rails and one of the most significant in bird records.


The white-throated rail is a chicken-sized bird, indigenous to Madagascar in the south-western Indian Ocean. They are persistent colonisers of isolated islands, who would have frequent population explosions and migrate in great numbers from Madagascar. Many of those that went north or south drowned in the expanse of ocean and those that went west landed in Africa, where predators ate them. Of those that went east, some landed on the many ocean islands such as Mauritius, Reunion and Aldabra, the last-named is a ring-shaped coral atoll that formed around 400,000 years ago.


With the absence of predators on the atoll, and just like the Dodo of Mauritius, the rails evolved so that they lost the ability to fly. However, Aldabra disappeared when it was completely covered by the sea during a major inundation event around 136,000 years ago, wiping out all fauna and flora including the flightless rail.











The bird that came back from the dead
Wing bones fossils of flighted (right) and flightless Dryolimnas rails
[Credit: Dr Julian Hume]

The researchers studied fossil evidence from 100,000 years ago when the sea-levels fell during the subsequent ice age and the atoll was recolonised by flightless rails. The researchers compared the bones of a fossilised rail from before the inundation event with bones from a rail after the inundation event. They found that the wing bone showed an advanced state of flightlessness and the ankle bones showed distinct properties that it was evolving toward flightlessness.


This means that one species from Madagascar gave rise to two different species of flightless rail on Aldabra in the space of a few thousand years.


Lead researcher Dr Julian Hume, avian paleontologist and Research Associate at the Natural History Museum, said: «These unique fossils provide irrefutable evidence that a member of the rail family colonised the atoll, most likely from Madagascar, and became flightless independently on each occasion. Fossil evidence presented here is unique for rails, and epitomises the ability of these birds to successfully colonise isolated islands and evolve flightlessness on multiple occasions.»


Co-author Professor David Martill, from the School of Earth and Environmental Sciences at the University of Portsmouth, said: «We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently. Only on Aldabra, which has the oldest palaeontological record of any oceanic island within the Indian Ocean region, is fossil evidence available that demonstrates the effects of changing sea levels on extinction and recolonisation events.


«Conditions were such on Aldabra, the most important being the absence of terrestrial predators and competing mammals, that a rail was able to evolve flightlessness independently on each occasion.»


The study is published in the latest issue of the Zoological Journal of the Linnean Society.


Source: University of Portsmouth [May 09, 2019]



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Research reveals surprisingly powerful bite of tiny early tetrapod

Micro-CT scanning of a tiny snake-like fossil discovered in Scotland has shed new light on the elusive creature, thought to be one of the earliest known tetrapods to develop teeth that allowed it to crush its prey.











Research reveals surprisingly powerful bite of tiny early tetrapod
Reconstructed skull and lower jaw of Acherontiscus caledoniae [Credit: Professor Jennifer Clack,
University Museum of Zoology, Cambridge]

Detailed scans of Acherontiscus caledoniae showed a unique combination of different tooth shapes and sizes as well as a deep lower jaw which scientists believe would have given the creature the ability to pierce, cut and grind the hard-shelled crustaceans that made up its diet.


Scientists led by the University Museum of Zoology in Cambridge alongside the University of Lincoln, the Natural History Museum in London and the University of Southampton, found that the dental pattern of Acherontiscus is at odds with that of several other tetrapods of this period, which tended to have uniform rows of cone-like teeth sometimes curved backwards at the tip. The variation in the shape and size of teeth shown in this fossil displays a level of dental adaptation that is unprecedented in such an early tetrapod.


As co-author Dr Marcello Ruta from the University of Lincoln’s School Of Life Sciences explains: «We found that Acherontiscus preceded the origin of modern tetrapod lineages and joined an array of primitive groups that independently acquired long and often miniaturized bodies, and exhibited either reduced or no limbs.»


The fossil is the only known specimen of this limbless tetrapod, which measured just 6 inches long and existed in swampy marshlands on the outskirts of Edinburgh some 330 million years ago. The delicate nature of the fossil meant that scientists were unable to use mechanical or chemical methods to free its skeleton from the surrounding rock, or study the specimen under a microscope.


Lead author Professor Jennifer Clack from the University Museum of Zoology in Cambridge said: «Using advanced techniques of micro-CT scanning, we were able to make sense of Acherontiscus’ complex skull, revealing minute anatomical details that allowed us to produce a greatly revised and much more complete reconstruction.


«We were particularly surprised to realize the great variety of shapes and sizes of its teeth. Acherontiscus is the earliest known tetrapod showing a crushing dentition, a feature with a rather discontinuous distribution in fossil and modern tetrapods.»


Fragments in the surrounding matrix have also revealed more about Acherontiscus’ habitat which will inform further research into the area as co-author Professor John Marshall from the University of Southampton’s School of Ocean and Earth Science explains: «Our study provided impetus for exploring the ecology and environments of the Scottish wetlands where Acherontiscus lived. Analysis of the content of fossil spores from about 0.2 grams of the matrix surrounding the creature suggests that this animal lived close to or within a still water body surrounded by herbaceous plants related to clubmosses. A more distant forest of larger, tree-like relatives of modern quillworts was also present.»


The paper was published in the Royal Society Open Science journal.


Source: University of Lincoln [May 09, 2019]



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2019 May 13 Rho Ophiuchi Wide Field Image Credit &…


2019 May 13


Rho Ophiuchi Wide Field
Image Credit & Copyright: Mario Cogo (Galax Lux)


Explanation: The colorful clouds surrounding the star system Rho Ophiuchi compose one of the closest star forming regions. Rho Ophiuchi itself is a binary star system visible in the blue reflection nebula just to the left of the image center. The star system, located only 400 light years away, is distinguished by its multi-colored surroundings, which include a red emission nebula and numerous light and dark brown dust lanes. Near the lower left of the Rho Ophiuchi molecular cloud system is the yellow star Antares, while a distant but coincidently-superposed globular cluster of stars, M4, is visible just to the right of Antares. Near the image top lies IC 4592, the Blue Horsehead nebula. The blue glow that surrounds the Blue Horsehead’s eye – and other stars around the image – is a reflection nebula composed of fine dust. On the featured image right is a geometrically angled reflection nebula cataloged as Sharpless 1. Here, the bright star near the dust vortex creates the light of surrounding reflection nebula. Although most of these features are visible through a small telescope pointed toward the constellations of Ophiuchus, Scorpius, and Sagittarius, the only way to see the intricate details of the dust swirls, as featured above, is to use a long exposure camera.


∞ Source: apod.nasa.gov/apod/ap190513.html


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Rhodochrosite with Quartz, Chalcopyrite | #Geology #GeologyPage #Mineral


Location: Sweet Home mine, Alma, Colorado, USA


Size: 9.5 x 8.0 x 4.0 cm (cabinet)


Photo Copyright © Weinrich Minerals


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Fluorite | #Geology #GeologyPage #Mineral


Locality: Davib East Farm, Karibib District, Erongo Region, Namibia


Size: 3.4 × 3.8 × 2.5 cm

Largest Crystal: 2.40cm


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Largest Crystal: 1.10cm


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Prehistoric wrought iron blade and bronze hilt and chape, The British Museum, London,...





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Prehistoric ‘La Tene’ influenced Hand Mirrors, The British Museum, London, 20.4.19.






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