Climate Change Threatens Boreal Coniferous Forests

Earth

Impending change for the dark taiga: Global warming is causing an increase in the frequency of forest fires in boreal coniferous forests. This means that deciduous trees, which generally only appear as pioneer plants, could potentially dominate the landscape in the long run. Credit: MPI of Biochemistry, S. Tautenhahn

New research from the Max Planck Institute of Biochemistry reveals that Boreal coniferous forests could see increased occurrences of fire as a result of global warming, with deciduous trees becoming more dominant in the future.

Climate change is transforming the Earth, particularly in high-latitude regions. The boreal coniferous forests of the northern hemisphere will witness an increased abundance of deciduous trees. This is according to discoveries made by an international team of researchers headed by Susanne Tautenhahn, formerly a scientist at the Max Planck Institute of Biochemistry and now working at Friedrich Schiller University Jena. These changes will, in turn, have an impact on the climate – whether global warming will be intensified or decelerated as a result, however, is something that remains to be seen.

The effects of climate change in recent decades have been tangible. And these could potentially become even more serious by the end of the century, even if we do somehow manage to limit global warming to 2 degrees, the latest de facto target for global climate policy. “Even the latest rise in temperature is leading to an increased frequency of extreme weather events,” says Susanne Tautenhahn. She predicts that storms, intense rainfall and thunderstorms will all become more commonplace. The appearance of the Earth is also being transformed as a result of climate change, and this is something that is already being observed, particularly in the cold temperate zones.

Here – from Canada and the US, to Scandinavia and through to Russia and Japan – boreal coniferous forests are still growing. These forests were the subject of a study carried out by Susanne Tautenhahn at the Max Planck Institute of Biochemistry in Jena. Tautenhahn, now a scientist at Friedrich Schiller University Jena, and her colleagues from Jena, Freiberg, Leipzig, Krasnoyarsk (Russia) and Gainesville (US) are using a combination of field studies and statistical modelling approaches to show, for the first time, the radical impact climate change is set to have on these forests. Today, the forest dynamics of the Siberian dark taiga show the prevailing growth of spruce trees, firs and pine trees. Deciduous trees here only appear shortly after disruptions such as fire, i.e. in an early stage of succession, in which various plant species recolonize disturbed habitats one after the other. According to the findings of the researchers, however, global warming will set in motion a chain of events here that will pave the way for the long-term domination of deciduous hardwoods. “Boreal forests are one of the largest stores of carbon on Earth, and two-thirds of these forests are located in Siberia,” says Tautenhahn. Thus, the expectation is that any changes in these forests will have repercussions on global climate.

Forest fires in the taiga to increase as a result of climate change

Forest fires are the reason for this emerging change in the taiga. “Fire acts as an important regulator in the natural development cycle of forests,” says Tautenhahn. Only through the destruction of old tree stock can new plants populate large surface areas. “However, climate change is intensifying the frequency and strength of fires, for instance due to lightning strikes, and the natural regeneration processes are being thrown out of balance,” explains the scientist.

In multiple expeditions lasting several months, Tautenhahn and her colleagues surveyed previously burned areas along the Yenisei River in Siberia. They counted the number of seedlings that have become established since the fire as well as the number of old trees that survived the fire – as the seeds of these trees could ensure new growth. On the basis of this data and with the aid of satellite images of the region, information on the severity of the fires and on the time periods that have elapsed since the fires, the researchers were able to develop a model that can, for the first time, track in detail the regeneration of the forest.

Cooling as a result of higher albedo and increased evaporation

Here, it became clear that the re-colonization of conifers is limited because their ability to disperse their relatively large seeds is limited. Conifer seeds are usually transported by the wind and can only travel relatively short distances. This makes it difficult for the trees to extensively re-colonize burnt areas, especially after severe fires with large burn zones. The seeds of deciduous trees, on the other hand, are very small and capable of covering long distances with the wind. This means that they can take over treeless surfaces a lot quicker and dominate these areas for the long term, even up until the late stage of succession. This advantage can be exploited to its full potential when fires are more intense and have larger burn zones.

What this change means in concrete terms for the global climate is currently the subject of intense discussions by researchers: they predict that the increased abundance of deciduous trees in the boreal forests of North America will slow down global warming in the medium term and reduce the occurrences of fire; in the long run, they expect the cooling effect to weaken the fire regime in North America, thus enabling a re-colonization of conifers. In contrast, however, Susanne Tautenhahn and her colleagues predict another effect for the Siberian forests in the long term. “As in North America, the Siberian dark taiga will also see a cooling period thanks to a higher albedo and higher evaporative cooling in the medium term. This cooling will be felt around the world,” says the Jena-based botanist. At the same time, however, the reduction of the typical Siberian conifers, which store high levels of moisture at ground level, will increase the likelihood of forest fires even further. “This can become a self-reinforcing process that could effectively change the eco-system and pave the way for the dominance of deciduous trees on a long-term basis in Siberia. “We do not know whether the taiga will store more or less carbon with a changed stock of trees.” This means that the researchers are still unable to accurately predict the impact of the change on the climate. However, the feedback is most likely negative since albedo and evaporative cooling increase.

Magnetic Field Interacting with Gravity and Spin Shape Black Hole’s Environmen

Space

Version 1: A spinning black hole (at center) produces a powerful jet (white-blue) along its spin axis. While near the hole, the disk rotational axis and jet direction are aligned with the black hole spin axis. Farther away the jet deviates and eventually points along the outer disk’s rotational axis. (Credit: Jonathan McKinney, University of Maryland, and Ralf Kaehler, SLAC National Accelerator Laboratory)

A newly published study describes how astrophysicists used simulations, which follow both the rules of general relativity and the laws of magnetism, to demonstrate that gravity isn’t the sole arbiter of a spinning black hole’s behavior.

Black holes are the ultimate Bogeyman. With a well-deserved reputation as monstrous destructive machines, black holes owe their power to huge quantities of mass that warp space and time until the gravitational force they command sucks in everything – even light. No surprise that astrophysicists have long considered gravity the dominant player in shaping the accretion disks of dust and gas surrounding black holes.

But that may not be true, at least for spinning black holes. In a paper published today in Science Express, three astrophysicists focus on a different fundamental force: magnetism. In state-of-the-art simulations that follow both the rules of general relativity and the laws of magnetism, they demonstrate that gravity isn’t the sole arbiter of a spinning black hole’s behavior.

Magneto-spin alignment effect movie by Ralf Kaehler (for Science paper by McKinney, Tchekhovskoy, and Blandford 2012): The black hole spin axis, disk rotational axis, and emergent jet axis are all initially aligned. We instantly tilt the black hole spin by 90 degrees in the middle of the simulation, after which the spinning black hole (at center) reforms the powerful jet (white-blue) along the tilted black hole spin axis. The jet rams into the surrounding accretion disk (infalling hot plasma as white-red near the hole) and causes the disk to align with the black hole spin axis near the black hole. At larger distances from the black hole, the disk finally pushes back on the jet causing the jet to re-align with the outer disk rotational axis.

Version 2: Spinning black hole (at center) produces a powerful jet (white-blue) along its spin axis. The jet affects the orientation of the surrounding accretion disk (infalling hot plasma as white-red near the hole) causing the disk to align with the spin axis near the hole, but at larger distances the disk dominates the jet and the jet re-aligns with the outer disk. (Credit: Jonathan McKinney, University of Maryland, and Ralf Kaehler, SLAC National Accelerator Laboratory)

“We found that the black hole’s magnetic field interacting with its gravity and spin has an even bigger effect” than gravity alone, said first author Jonathan McKinney, who, before he became an assistant professor of physics at the University of Maryland, was a postdoctoral researcher at Stanford University and SLAC National Accelerator Laboratory, where he did much of the work for the paper.

The result, especially in the case of a black hole with a thick accretion disk, is a complex maelstrom of interacting forces: Near the black hole, spiraling magnetic fields cause the material in the accretion disk to orbit about the black hole in the same direction as the black hole’s spin. Twisting lines of magnetic force launch two jets of particles in opposite directions at close to the speed of light. These jets, called relativistic jets, initially speed away parallel to the black hole’s axis of rotation – its north and south poles. But as gravity’s grip weakens, the charged gas in the outermost regions of the accretion disk pulls at the jets, pulling them away from the black hole’s rotational axis even as the jets collide with that gas and knock it away from the black hole.

Version 3: Spinning black hole (at center) produces a powerful jet (white smoke) along its spin axis. The jet affects the orientation of the surrounding accretion disk (infalling hot plasma as purple far from the hole and yellow near the hole) causing the disk to align with the spin axis near the hole, but at larger distances the disk dominates the jet and the jet re-aligns with the outer disk. (Credit: Jonathan McKinney, University of Maryland, and Ralf Kaehler, SLAC National Accelerator Laboratory)

McKinney says the results of the simulations have direct consequences for studies of the delicate balance between how much gas a black hole can pull in from its accretion disk and how much gas it blows away with its jets. The greedier the black hole, the more gas it pulls in and the more energy is funneled to the jets, until they become so powerful they can blast the surrounding area clear – shutting down star formation in the vicinity – and, says McKinney, “The black hole stops its own growth.”

According to their simulations, the boost in energy provided by all the forces interacting around a black hole, including the magnetic force, makes a black hole even better at blasting its surroundings clear than currently thought. “Based on our study we’re saying there are some aspects of the feedback mechanism that we don’t understand,” McKinney said, and this remains a major unsolved problem in astrophysics.

Soon, though, the work of McKinney and his colleagues, Alexander Tchekhovskoy of Princeton and Roger Blandford, director of the Kavli Institute for Particle Astrophysics and Cosmology at SLAC and Stanford, may be confirmed by actual observation. A globe-spanning array of telescopes all acting as one called the Event Horizon Telescope has been making its first close-up observations of black holes – with some help, said McKinney, from their simulations. “Any interpretations are still very preliminary,” he added, but the possibility that their ideas soon might face a direct test is exciting.

Three Closely Orbiting Supermassive Black Holes Could Help in the Search for Gravitational Waves

June 26, 2014

Space

An international team of astronomers discovered three closely orbiting supermassive black holes that could help in the search for gravitational waves.

An international team, including Oxford University scientists, led by Dr Roger Deane from the University of Cape Town, examined six systems thought to contain two supermassive black holes. The team found that one of these contained three supermassive black holes – the tightest trio of black holes detected at such a large distance – with two of them orbiting each other rather like binary stars. The finding suggests that these closely-packed supermassive black holes are far more common than previously thought.

A report of the research is published in this week’s Nature.

Dr Roger Deane from the University of Cape Town said: ‘What remains extraordinary to me is that these black holes, which are at the very extreme of Einstein’s Theory of General Relativity, are orbiting one another at 300 times the speed of sound on Earth. Not only that, but using the combined signals from radio telescopes on four continents we are able to observe this exotic system one third of the way across the Universe. It gives me great excitement as this is just scratching the surface of a long list of discoveries that will be made possible with the Square Kilometer Array (SKA).’

Professor Matt Jarvis of Oxford University’s Department of Physics, an author of the paper, said: ‘General Relativity predicts that merging black holes are sources of gravitational waves and in this work we have managed to spot three black holes packed about as tightly together as they could be before spiraling into each other and merging. The idea that we might be able to find more of these potential sources of gravitational waves is very encouraging as knowing where such signals should originate will help us try to detect these ‘ripples’ in spacetime as they warp the Universe.’

Helical jets from one supermassive black hole caused by a very closely orbiting companion (see blue dots). The third black hole is part of the system, but farther away and therefore emits relatively straight jets.

The team used a technique called Very Long Baseline Interferometry (VLBI) to discover the inner two black holes of the triple system. This technique combines the signals from large radio antennas separated by up to 10,000 kilometers to see detail 50 times finer than that possible with the Hubble Space Telescope. The discovery was made with the European VLBI Network, an array of European, Chinese, Russian and South African antennas, as well as the 305 meter Arecibo Observatory in Puerto Rico. Future radio telescopes such as the SKA will be able to measure the gravitational waves from such black hole systems as their orbits decrease.

At this point, very little is actually known about black hole systems that are so close to one another that they emit detectable gravitational waves. Professor Jarvis said: ‘This discovery not only suggests that close-pair black hole systems emitting at radio wavelengths are much more common than previously expected, but also predicts that radio telescopes such as MeerKAT and the African VLBI Network (AVN, a network of antennas across the continent) will directly assist in the detection and understanding of the gravitational wave signal. Further in the future the SKA will allow us to find and study these systems in exquisite detail, and really allow us gain a much better understanding of how black holes shape galaxies over the history of the Universe.’

Dr Keith Grainge of the University of Manchester, an author of the paper, said: ‘This exciting discovery perfectly illustrates the power of the VLBI technique, whose exquisite sharpness of view allows us to see deep into the hearts of distant galaxies. The next generation radio observatory, the SKA, is being designed with VLBI capabilities very much in mind.’

While the VLBI technique was essential to discover the inner two black, the team has also shown that the binary black hole presence can be revealed by much larger scale features. The orbital motion of the black hole is imprinted onto its large jets, twisting them into a helical or corkscrew-like shape. So even though black holes may be so close together that our telescopes can’t tell them apart, their twisted jets may provide easy-to-find pointers to them, much like using a flare to mark your location at sea. This may provide sensitive future telescopes like MeerKAT and the SKA a way to find binary black holes with much greater efficiency.

The UK team included researchers from Oxford University, the University of Manchester, and the University of Cambridge. A report of the research, entitled ‘A close-pair binary in a distant triple supermassive black-hole system’, is published in this week’s Nature.

Gravitational Waves Could Soon be Detectable by Existing Radio Telescopes

February 25, 2016

Space

Gravitational waves are ripples in space-time, represented by the green grid, produced by accelerating bodies such as interacting supermassive black holes. These waves affect the time it takes for radio signals from pulsars to arrive at Earth. Credits: David Champion

A newly published study from the North American Nanohertz Observatory for Gravitational Waves reveals that low-frequency gravitational waves could soon be detectable by existing radio telescopes.

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.

“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.”

Astronomers Identify the Precise Location of a Fast Radio Burst in a Distant Galaxy

February 25, 2016

Space

The infrared image on the left shows the field of view of the Parkes radio telescope with the area where the signal came from marked in cyan. On the right are successive zoom-ins on that area. At the bottom right is the Subaru optical image of the FRB galaxy, with the superimposed elliptical regions showing the location of the fading 6-day afterglow seen with ATCA.

An international team of astronomers 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. 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.

This image shows the increased delay in the arrival time of the Fast Radio Burst as a function of the frequency. The delay in the signal is caused by the material it goes through between its point of origin in a distance of 6 billion light years and Earth.

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.

New IBEX Observations Determine the Strength of the Magnetic Field Outside the Heliosphere

February 26, 2016

Space

(Artist concept) Far beyond the orbit of Neptune, the solar wind and the interstellar medium interact to create a region known as the inner heliosheath, bounded on the inside by the termination shock, and on the outside by the heliopause.

A newly published study uses IBEX data and simulations of the interstellar boundary to better describe space in our galactic neighborhood.

Immediately after its 2008 launch, NASA’s Interstellar Boundary Explorer, or IBEX, spotted a curiosity in a thin slice of space: More particles streamed in through a long, skinny swath in the sky than anywhere else. The origin of the so-called IBEX ribbon was unknown – but its very existence opened doors to observing what lies outside our solar system, the way drops of rain on a window tell you more about the weather outside.

A new paper, published in The Astrophysical Journal Letters, precisely determines the strength and direction of the magnetic field outside the heliosphere. Such information gives us a peek into the magnetic forces that dominate the galaxy beyond, teaching us more about our home in space.

This simulation shows the origin of ribbon particles of different energies or speeds outside the heliopause (labeled HP). The IBEX ribbon particles interact with the interstellar magnetic field (labeled ISMF) and travel inwards toward Earth, collectively giving the impression of a ribbon spanning across the sky.

The new paper is based on one particular theory of the origin of the IBEX ribbon, in which the particles streaming in from the ribbon are actually solar material reflected back at us after a long journey to the edges of the sun’s magnetic boundaries. A giant bubble, known as the heliosphere, exists around the sun and is filled with what’s called solar wind, the sun’s constant outflow of ionized gas, known as plasma. When these particles reach the edges of the heliosphere, their motion becomes more complicated.

“The theory says that some solar wind protons are sent flying back towards the sun as neutral atoms after a complex series of charge exchanges, creating the IBEX ribbon,” said Eric Zirnstein, a space scientist at the Southwest Research Institute in San Antonio, Texas, and lead author on the study. “Simulations and IBEX observations pinpoint this process – which takes anywhere from three to six years on average – as the most likely origin of the IBEX ribbon.”

Outside the heliosphere lies the interstellar medium, with plasma that has different speed, density, and temperature than solar wind plasma, as well as neutral gases. These materials interact at the heliosphere’s edge to create a region known as the inner heliosheath, bounded on the inside by the termination shock – which is more than twice as far from us as the orbit of Pluto – and on the outside by the heliopause, the boundary between the solar wind and the comparatively dense interstellar medium.

Some solar wind protons that flow out from the sun to this boundary region will gain an electron, making them neutral and allowing them to cross the heliopause. Once in the interstellar medium, they can lose that electron again, making them gyrate around the interstellar magnetic field. If those particles pick up another electron at the right place and time, they can be fired back into the heliosphere, travel all the way back toward Earth, and collide with IBEX’s detector. The particles carry information about all that interaction with the interstellar magnetic field, and as they hit the detector they can give us unprecedented insight into the characteristics of that region of space.

The IBEX ribbon is a relatively narrow strip of particles flying in towards the sun from outside the heliosphere. A new study corroborates the idea that particles from outside the heliosphere that form the IBEX ribbon actually originate at the sun – and reveals information about the distant interstellar magnetic field.

“Only Voyager 1 has ever made direct observations of the interstellar magnetic field, and those are close to the heliopause, where it’s distorted,” said Zirnstein. “But this analysis provides a nice determination of its strength and direction farther out.”

The directions of different ribbon particles shooting back toward Earth are determined by the characteristics of the interstellar magnetic field. For instance, simulations show that the most energetic particles come from a different region of space than the least energetic particles, which gives clues as to how the interstellar magnetic field interacts with the heliosphere.

For the recent study, such observations were used to seed simulations of the ribbon’s origin. Not only do these simulations correctly predict the locations of neutral ribbon particles at different energies, but the deduced interstellar magnetic field agrees with Voyager 1 measurements, the deflection of interstellar neutral gases, and observations of distant polarized starlight.

However, some early simulations of the interstellar magnetic field don’t quite line up. Those pre-IBEX estimates were based largely on two data points – the distances at which Voyagers 1 and 2 crossed the termination shock.

“Voyager 1 crossed the termination shock at 94 astronomical units, or AU, from the sun, and Voyager 2 at 84 AU,” said Zirnstein. One AU is equal to about 93 million miles, the average distance between Earth and the sun. “That difference of almost 930 million miles was mostly explained by a strong, very tilted interstellar magnetic field pushing on the heliosphere.”

But that difference may be accounted for by considering a stronger influence from the solar cycle, which can lead to changes in the strength of the solar wind and thus change the distance to the termination shock in the directions of Voyager 1 and 2. The two Voyager spacecraft made their measurements almost three years apart, giving plenty of time for the variable solar wind to change the distance of the termination shock.

“Scientists in the field are developing more sophisticated models of the time-dependent solar wind,” said Zirnstein.

The simulations generally jibe well with the Voyager data.

“The new findings can be used to better understand how our space environment interacts with the interstellar environment beyond the heliopause,” said Eric Christian, IBEX program scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in this study. “In turn, understanding that interaction could help explain the mystery of what causes the IBEX ribbon once and for all.”

The Southwest Research Institute leads IBEX with teams of national and international partners. NASA Goddard manages the Explorers Program for the agency’s Heliophysics Division within the Science Mission Directorate in Washington.

With its new S7 phone, Samsung looks even more like Apple

Apple and Samsung phones, which have been looking more and more alike over the past few years, are much closer to virtual twins with Samsung's latest Galaxy S7.

The convergence began two years ago when iPhones got larger, mimicking Samsung's once-innovative, plus-sized "phablets." Last spring, Samsung started emphasizing higher quality materials and sophisticated design, just as Apple had for years. And last fall, Apple boosted the resolution on the iPhone camera, narrowing one of the major gaps it had with Samsung.

With the S7, Samsung is lowering its camera's resolution—you read that right—to match the iPhone's 12 megapixels.

To be sure, there are key differences. Only the latest iPhones have special features you activate by pressing harder on an icon or link, while Samsung is among the biggest boosters of virtual reality.

It's too early to say which phone is better. Though Samsung announced the S7 on Sunday at a wireless show in Barcelona, Spain, the phone isn't coming out until March 11. My hands-on time has been limited to controlled settings.

And for most users it may end up being a draw—Samsung leads the pack among Android phones, while Apple has its own self-contained ecosystem, iOS. For many, a choice between the two could come down to preference for one system or another—and the apps available for each.

A Samsung Galaxy S7 Edge mobile phone and Gear 360 portable 360 degree camera, featuring two 192-degree lenses, are demonstrated during a preview of Samsung's flagship store, Samsung 837, in New York's Meatpacking District, Monday, Feb 22, …more

For now, here's how Apple and Samsung phones stack up:

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CAMERA

For both, the rear cameras are now at 12 megapixels—up from 8 for iPhones and down from 18 for Samsung. That doesn't mean Samsung photos are getting worse, though.

In making the change, Samsung adopted the iPhone's 4-by-3 dimension, ditching the widescreen format it had long used. Widescreen produces vertical shots that are awkwardly tall, such that I've had to crop them to 4-by-3 anyway. The 6 megapixel reduction is equivalent to chopping off the excess.

The front cameras are both at 5 megapixels, after Apple boosted its resolution in the iPhone last fall. Apple also turned the screen into a flash for selfies. Samsung, ever the fast follower, is now doing the same with the S7.

Samsung is promising improvements in low-light shots, borrowing techniques from full-bodied, SLR cameras, though it'll require extensive tests to see how well the camera performs. Even with last year's models, Samsung cameras tend to produce brighter night shots than the iPhone. But I've also seen more distortion when those shots are blown up. We'll see if that's been fixed with the S7.

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SIZE

Samsung's 5.1-inch Galaxy S7 is slightly larger and heavier than the 4.7-inch iPhone 6s, but not much so. There's a premium version of the S7 called the S7 Edge; both sides curve like a waterfall, such that the screen flows over the side to the back of the phone. The Edge screen is 5.5 inches, but much of that comes from the curvature. The phone itself is taller, but just a tad wider and heavier.

Compared with the 5.5-inch iPhone 6s Plus, though, the S7 Edge is smaller.

A table of Samsung Galaxy S7 and S7 Edge mobile phones and smartwatches line a table in Samsung's flagship store, Samsung 837, in New York's Meatpacking District, Monday, Feb 22, 2016. Samsung is opening what it calls a "technology …more

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EXTRAS

Neither the iPhone nor the S7 phone lets you replace the battery with a spare. But the S7 does let you add storage. And the base model is 32 gigabytes, double what the iPhone offers for starters.

Unlike the iPhone, the S7 is waterproof. There's no need to keep USB and other ports sealed, as past waterproof phones did. The S7 also offers wireless charging; you simply lay the phone flat on a charging base. However, wireless charging is typically slower than plugging in a USB charger.

Apple and Samsung both let you unlock phones with your fingerprint rather than a passcode. And both let you make payments with a tap at some retail stores. The Samsung Pay service works with a greater range of merchants, but with credit cards from fewer banks and in fewer countries for now than Apple Pay.

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SHORTCUTS

The latest iPhones and the S7 Edge have shortcuts to common tasks, such as taking selfies. With the iPhone, you hard press on an app icon. With the Edge, you swipe from the right edge. That swipe also gets you headlines, frequent contacts and favorite apps.

Apple lets third-party app makers create their own shortcuts, while Samsung does not.

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THE SCREEN

One remaining difference is the screen technology. While the iPhone and most other phones use LCD screens, Samsung uses AMOLED, for active-matrix organic light-emitting diodes. Colors are more vivid, though sometimes unnatural. Individual pixels produce their own light, and no energy is needed to light pixels that are black. LCDs require blacklighting, which uses energy regardless.

In practice, Samsung is able to offer an always-on mode in the S7, constantly displaying a clock, notifications and other highlights when the phone is locked. Because most of the screen is dark, the screen sips rather than drains power in this mode—at least in theory.

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VIRTUAL REALITY

Samsung is ahead of Apple, though it faces competition from other Android manufacturers, including LG.

Samsung already has its own VR headset, while LG is coming out with one. They won't work with each other's phones or any other Android phone. Both companies will soon sell 360-degree cameras for taking VR video. Apps on the phone will ease sharing with friends and viewing on the VR devices.

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AVAILABILITY

The iPhone 6S and 6S Plus have been available since September. There has been speculation that Apple is coming out with a smaller model soon, but it's not expected to have all of the advanced features found in the 6S phones.

Advance orders for the S7 phones started this week. March 11 is the release date in the U.S. and several other markets.