The Sun's Core Makes a Complete Rotation in One Week

The Sun's Core Makes a Complete Rotation in One Week:

The rotation rate of the Sun's core has been accurately measured for the first time. The Sun, which has been remarkably stable for the past 4.6 billion years, is held together by the almost perfect equilibrium between the force of gravity, which tends to cause it to collapse, and the pressure of the thermonuclear reactions in its core. Now, researchers working together with a team at the Laboratoire Lagrange (CNRS/Observatoire de la Côte d'Azur/Université Nice Sophia Antipolis) have determined that the Sun's core makes a complete rotation once per week.

Using the GOLF instrument, orbiting around the Sun on board the SOHO space observatory, to measure solar oscillations, they developed a novel approach that enabled them to unambiguously detect gravity oscillation modes within our star. This work, which will certainly stimulate a new era of research into the physics of the solar core, is published in the journal Astronomy & Astrophysics.

The Sun, which has been remarkably stable for the past 4.6 billion years, is held together by the almost perfect equilibrium between the force of gravity, which tends to cause it to collapse, and the pressure of the thermonuclear reactions in its core. The GOLF instrument, orbiting around the Sun on board the SOHO space observatory, measures solar oscillations, which carry information about the physical properties of its different layers. Every ten seconds, GOLF, which has been orbiting our star for over twenty years, records an integrated signal of oscillations of the solar surface. Various teams analyze this flow of data with the aim of identifying the many oscillation modes exhibited by the Sun.

Now, researchers from the Laboratoire Lagrange (CNRS/Observatoire de la Côte d'Azur/Université Nice Sophia Antipolis), the Institut d'Astrophysique Spatiale (CNRS/Université Paris-Sud), the Laboratoire Astrophysique, Interprétation, Modélisation (CNRS/Université Paris Diderot/CEA), the Laboratoire d'Astrophysique de Bordeaux (CNRS/Université de Bordeaux), the Instituto de Astrofísica de Canarias, and UCLA (University of California, Los Angeles) have successfully detected the Sun's gravity modes. 

These are similar to waves in which gravity is the restoring force, such as waves on the surface of the sea, although in the Sun they can only exist in its very deepest layers. Since these oscillations are particularly difficult to observe, the researchers used the GOLF data in a novel way, by making use of a differential parameter of the acoustic oscillation modes, which are observable at the surface. This parameter measures the round trip time of acoustic waves traveling through the center of the Sun. The researchers detected the impact of gravity modes on them, thus demonstrating their existence.

The first result of this detection is that the researchers were able to accurately measure the mean rotation rate of the Sun's thermonuclear core, about which little was previously known. The core makes a complete rotation in one week, which is 3.8 times faster than the outer and intermediate layers. This work should stimulate much research in solar physics, making it possible to further refine models of the Sun's birth, evolution, structure and chemical composition. In particular, the gravity modes indicate that there is a region at the boundary of the thermonuclear core where the speed varies enormously, which is not predicted by the standard model of the Sun. It will also stimulate discussion about the nature of a possible magnetic field in the Sun's center.

Credit: eurekalert.org

Scientists Probe the Conditions of Stellar Interiors to Measure Nuclear Reactions

Scientists Probe the Conditions of Stellar Interiors to Measure Nuclear Reactions:

Most of the nuclear reactions that drive the nucleosynthesis of the elements in our universe occur in very extreme stellar plasma conditions. This intense environment found in the deep interiors of stars has made it nearly impossible for scientists to perform nuclear measurements in these conditions -- until now.

In a unique cross-disciplinary collaboration between the fields of plasma physics, nuclear astrophysics and laser fusion, a team of researchers, including scientists from Lawrence Livermore National Laboratory (LLNL), Ohio University, the Massachusetts Institute of Technology (MIT) and Los Alamos National Laboratory (LANL), describe experiments performed in conditions like those of stellar interiors. The team's findings were published today by Nature Physics.

The experiments are the first thermonuclear measurements of nuclear reaction cross-sections -- a quantity that describes the probability that reactants will undergo a fusion reaction -- in high-energy-density plasma conditions that are equivalent to the burning cores of giant stars, i.e., 10-40 times more massive than the sun. These extreme plasma conditions boast hydrogen-isotope densities compressed by a factor of a thousand to near that of solid lead and temperatures heated to approximately 50 million Kelvin. These are the conditions in stars that lead to supernovae, the most massive explosions in the universe.

"Ordinarily, these kinds of nuclear astrophysics experiments are performed on accelerator experiments in the laboratory, which become particularly challenging at the low energies often relevant for nucleosynthesis," said LLNL physicist Dan Casey, the lead author on the paper. "As the reaction cross-sections fall rapidly with decreasing reactant energy, bound electron screening corrections become significant, and terrestrial and cosmic background sources become a major experimental challenge."

The work was conducted at LLNL's National Ignition Facility (NIF), the only experimental tool in the world capable of creating temperatures and pressures like those found in the cores of stars and giant planets. Using the indirect drive approach, NIF was used to drive a gas-filled capsule implosion, heating capsules to extraordinary temperatures and compressing them to high densities where fusion reactions can occur.

"One of the most important findings is that we reproduced prior measurements made on accelerators in radically different conditions," Casey said. "This really establishes a new tool in the nuclear astrophysics field for studying various processes and reactions that may be difficult to access any other way."

"Perhaps most importantly, this work lays groundwork for potential experimental tests of phenomena that can only be found in the extreme plasma conditions of stellar interiors. One example is of plasma electron screening, a process that is important in nucleosynthesis but has not been observed experimentally," Casey added.

Now that the team has established a technique to perform these measurements, related teams like that led by Maria Gatu Johnson at MIT are looking to explore other nuclear reactions and ways to attempt to measure the impact of plasma electrons on the nuclear reactions.

Casey was joined by co-authors Daniel Sayre, Vladimir Smalyuk, Robert Tipton, Jesse Pino, Gary Grim, Bruce Remington, Dave Dearborn, Laura (Robin) Benedetti, Robert Hatarik, Nobuhiko Izumi, James McNaney, Tammy Ma, Steve MacLaren, Jay Salmonson, Shahab Khan, Arthur Pak, Laura Berzak Hopkins, Sebastien LePape, Brian Spears, Nathan Meezan, Laurent Divol, Charles Yeamans, Joseph Caggiano, Dennis McNabb, Dean Holunga, Marina Chiarappa-Zucca, Tom Kohut and Thomas Parham from LLNL, Carl Brune from Ohio University, Johan Frenje and Maria Gatu Johnson from MIT and George Kyrala from LANL.

Credit: llnl.gov

Partial Lunar Eclipse Seen Across Europe, Asia, Africa and Australia

Partial Lunar Eclipse Seen Across Europe, Asia, Africa and Australia:

A partial lunar eclipse took place on August 7/8, 2017, the second of two lunar eclipses in 2017. The moon was only slightly covered by the Earth's umbral shadow at maximum eclipse. The partial eclipse lasted for one hour and 55 minutes.

Most of Asia, Africa, Europe and Australia was treated to a spectacular partial lunar eclipse. The phenomenon occurs when the moon moves through the outer part of the Earth's shadow, blocking part of the sunlight from reaching the moon and causing it to appear larger than normal.

"The interesting thing about lunar eclipse timings is that anywhere on Earth from where the moon is visible during eclipse, the time will be the same. This is in contrast to a solar eclipse in which the timings of the contacts change as the location changes on Earth," said N Rathnashree, director of the Nehru Planetarium in Delhi, India.

The moon inside the umbral shadow was a subtle red, but hard to see in contrast to the much brighter moon in the outer penumbral shadow.

The solar eclipse of August 21, 2017 occurs fourteen days later, in the same eclipse season. It will be the first total solar eclipse visible in the contiguous United States since the solar eclipse of February 26, 1979.

New Theory on the Origin of Dark Matter

New Theory on the Origin of Dark Matter:

Only a small part of the universe consists of visible matter. By far the largest part is invisible and consists of dark matter and dark energy. Very little is known about dark energy, but there are many theories and experiments on the existence of dark matter designed to find these as yet unknown particles. Scientists at Johannes Gutenberg University Mainz (JGU) have now come up with a new theory on how dark matter may have been formed shortly after the origin of the universe. This new model proposes an alternative to the WIMP paradigm that is the subject of various experiments in current research.

Dark matter is present throughout the universe, forming galaxies and the largest known structures in the cosmos. It makes up around 23 percent of our universe, whereas the particles visible to us that make up the stars, planets, and even life on Earth represent only about four percent of it. The current assumption is that dark matter is a cosmological relic that has essentially remained stable since its creation. "We have called this assumption into question, showing that at the beginning of the universe dark matter may have been unstable," explained Dr. Michael Baker from the Theoretical High Energy Physics (THEP) group at the JGU Institute of Physics. This instability also indicates the existence of a new mechanism that explains the observed quantity of dark matter in the cosmos.

The stability of dark matter is usually explained by a symmetry principle. However, in their paper, Dr. Michael Baker and Professor Joachim Kopp demonstrate that the universe may have gone through a phase during which this symmetry was broken. This would mean that it is possible for the hypothetical dark matter particle to decay. During the electroweak phase transition, the symmetry that stabilizes dark matter would have been reestablished, enabling it to continue to exist in the universe to the present day.

With their new theory, Baker and Kopp have introduced a new principle into the debate about the nature of dark matter that offers an alternative to the widely accepted WIMP theory. Up to now, WIMPs, or weakly interacting massive particles, have been regarded as the most likely components of dark matter, and experiments involving heavily shielded underground detectors have been carried out to look for them. "The absence of any convincing signals caused us to start looking for alternatives to the WIMP paradigm," said Kopp.

The two physicists claim that the new mechanism they propose may be connected with the apparent imbalance between matter and antimatter in the cosmos and could leave an imprint which would be detected in future experiments on gravitational waves. In their paper published in the scientific journal Physical Review Letters, Baker and Kopp also indicate the prospects of finding proof of their new principle at CERN's LHC particle accelerator and other experimental facilities.

Credit: uni-mainz.de

Hint of Relativity Effects in Stars Orbiting Supermassive Black Hole at Center of Galaxy

Hint of Relativity Effects in Stars Orbiting Supermassive Black Hole at Center of Galaxy:

A new analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of stars around the supermassive black hole at the center of the Milky Way may show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of the star S2 is deviating slightly from the path calculated using classical physics. This tantalizing result is a prelude to much more precise measurements and tests of relativity that will be made using the GRAVITY instrument as star S2 passes very close to the black hole in 2018.

At the center of the Milky Way, 26 000 light-years from Earth, lies the closest supermassive black hole, which has a mass four million times that of the Sun. This monster is surrounded by a small group of stars orbiting at high speed in the black hole’s very strong gravitational field. It is a perfect environment in which to test gravitational physics, and particularly Einstein’s general theory of relativity.

A team of German and Czech astronomers have now applied new analysis techniques to existing observations of the stars orbiting the black hole, accumulated using ESO’s Very Large Telescope (VLT) in Chile and others over the last twenty years. They compare the measured star orbits to predictions made using classical Newtonian gravity as well as predictions from general relativity.

The team found suggestions of a small change in the motion of one of the stars, known as S2, that is consistent with the predictions of general relativity. The change due to relativistic effects amounts to only a few percent in the shape of the orbit, as well as only about one sixth of a degree in the orientation of the orbit. If confirmed, this would be the first time that a measurement of the strength of the general relativistic effects has been achieved for stars orbiting a supermassive black hole.

Marzieh Parsa, PhD student at the University of Cologne, Germany and lead author of the paper, is delighted: "The Galactic Center really is the best laboratory to study the motion of stars in a relativistic environment. I was amazed how well we could apply the methods we developed with simulated stars to the high-precision data for the innermost high-velocity stars close to the supermassive black hole."

The high accuracy of the positional measurements, made possible by the VLT’s near-infrared adaptive optics instruments, was essential for the study. These were vital not only during the star’s close approach to the black hole, but particularly during the time when S2 was further away from the black hole. The latter data allowed an accurate determination of the shape of the orbit.

"During the course of our analysis we realized that to determine relativistic effects for S2 one definitely needs to know the full orbit to very high precision," comments Andreas Eckart, team leader at the University of Cologne.

As well as more precise information about the orbit of the star S2, the new analysis also gives the mass of the black hole and its distance from Earth to a higher degree of accuracy.

Co-author Vladimir Karas from the Academy of Sciences in Prague, the Czech Republic, is excited about the future: "This opens up an avenue for more theory and experiments in this sector of science."

This analysis is a prelude to an exciting period for observations of the Galactic Center by astronomers around the world. During 2018 the star S2 will make a very close approach to the supermassive black hole. This time the GRAVITY instrument, developed by a large international consortium led by the Max-Planck-Institut für extraterrestrische Physik in Garching, Germany, and installed on the VLT Interferometer, will be available to help measure the orbit much more precisely than is currently possible. Not only is GRAVITY, which is already making high-precision measurements of the Galactic Center, expected to reveal the general relativistic effects very clearly, but also it will allow astronomers to look for deviations from general relativity that might reveal new physics.

Credit: ESO

Chaotic Magnetic Field Lines May Answer the Coronal Heating Problem

Chaotic Magnetic Field Lines May Answer the Coronal Heating Problem:

It is known that the sun's corona -- the outermost layer of the sun's atmosphere -- is roughly 100 times hotter than its photosphere -- the sun's visible layer. The reason for this mysterious heating of the solar coronal plasma, however, is not yet entirely understood. A research team in India has developed a set of numerical computations to shed light on this phenomenon, and present this week in Physics of Plasmas, from AIP Publishing, analysis examining the role of chaotic magnetic fields in potential heating mechanisms.

Operating under the idea that chaotically tangled magnetic field lines exist throughout astrophysical plasmas, the team used high-performance computer simulation to gain an understanding of these chaotic field lines. Specifically, they investigated conditions that create ribbons of intense electric current, known as current sheets.

The current sheets, believed to be produced in the coronal plasma, are potential sites for magnetic reconnections, which provide a mechanism for extreme heating of the corona. Moreover, within the current sheets, the electric field peaks up and accelerates charged particles.

"We want to go one step forward to explain the spontaneous generation of these current sheets," said Sanjay Kumar, a member of the research team.

The research method focused on allowing an incompressible, thermally homogeneous magnetofluid with infinite electrical conductivity to relax via viscous dissipation, toward a characterized final state. The computations were made consistent with well-accepted magnetostatic theory and resulted in spontaneous current sheet development, making them relevant for the study of particle acceleration in astrophysical plasmas.

Using Vikram-100, the 100TF High Performance Computing facility at the Physical Research Laboratory, the researchers simulated the viscous relaxation and verified accurate flux-freezing, a conservative behavior a reliable simulation must demonstrate. The team plotted the maximal intensities of volume current densities for specific trends of increasing magnetic field chaos, which provided a measure of the production of current sheets. Additionally, the maximal magnitudes of volume current density were found to scale with the numerical resolution used in the computer simulation, which showed the expected scaling of current sheet development.

The simple fact that the maximum value of volume current density was increased with increasing magnetic field line chaos, called "chaoticity," suggests a direct proportionality between the intensity of the current sheet and chaoticity.

In the three cases studied, the researchers found the formation of two different sets of current sheets. One set was arranged along the y-axis, while the second formed in a different location and at a time later than the first. From their analysis of this occurrence, the team determined that a favorable evolution bring non-parallel magnetic field lines into close proximity and intensify current sheets.

These simulations provide new and novel insight regarding the influence of chaotic magnetic field lines on the spontaneous development of current sheets, and hence potential places of particle acceleration.

"This is the first time we have explained the role of chaotic field line in generating these spontaneous current sheets," Kumar said, referring to the scientific community as a whole.

Credit: eurekalert.org

Why Massive Galaxies Don’t Dance in Crowds

Why Massive Galaxies Don’t Dance in Crowds:

Scientists have discovered why heavyweight galaxies living in a dense crowd of galaxies tend to spin more slowly than their lighter neighbors. “Contrary to earlier thinking, the spin rate of the galaxy is determined by its mass, rather than how crowded its neighborhood is,” says study first author Associate Professor Sarah Brough of UNSW Sydney and the ARC Centre of Excellence for All-sky Astrophysics, CAASTRO.

The finding, based on a detailed study of more than 300 galaxies, is published in The Astrophysical Journal.

To measure how fast their galaxies rotated, the researchers used an instrument called the Sydney-AAO Multi-object Integral field spectrograph (SAMI) on the 4-meter Anglo-Australian Telescope in eastern Australia.

SAMI ‘dissects’ galaxies, obtaining optical spectra from 61 points across the face of each galaxy, 13 galaxies at a time.

“We want to know which factors really drive how galaxies evolve,” says team member Dr Matt Owers of the Australian Astronomical Observatory and Macquarie University. “In this case, we’ve sorted out nature versus nurture.”

The new finding runs counter to previous studies, made with smaller samples of galaxies, which concluded that a galaxy’s spin rate is determined by the other galaxies in its neighborhood.

Associate Professor Brough says this earlier conclusion was spurious. “Once you take into account the strong association with mass, there’s no link between a galaxy’s spin rate and its environment,” she says.

The research team was drawn from the Australian Astronomical Observatory; UNSW Sydney; the universities of Sydney, Melbourne, Queensland and Oxford; The Australian National University, Macquarie University, Swinburne University of Technology; Yonsei University in South Korea and the California Institute of Technology.

The ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) is a collaboration between The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University, the last two participating together as the International Centre for Radio Astronomy Research (ICRAR).

CAASTRO is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government's Science Leveraging Fund.

Credit: unsw.edu.au

IC 10: A Starburst Galaxy with the Prospect of Gravitational Waves

IC 10: A Starburst Galaxy with the Prospect of Gravitational Waves:

In 1887, American astronomer Lewis Swift discovered a glowing cloud, or nebula, that turned out to be a small galaxy about 2.2 billion light years from Earth. Today, it is known as the "starburst" galaxy IC 10, referring to the intense star formation activity occurring there.

More than a hundred years after Swift's discovery, astronomers are studying IC 10 with the most powerful telescopes of the 21st century. New observations with NASA's Chandra X-ray Observatory reveal many pairs of stars that may one day become sources of perhaps the most exciting cosmic phenomenon observed in recent years: gravitational waves.

By analyzing Chandra observations of IC 10 spanning a decade, astronomers found over a dozen black holes and neutron stars feeding off gas from young, massive stellar companions. Such double star systems are known as "X-ray binaries" because they emit large amounts of X-ray light. As a massive star orbits around its compact companion, either a black hole or neutron star, material can be pulled away from the giant star to form a disk of material around the compact object. Frictional forces heat the infalling material to millions of degrees, producing a bright X-ray source.

When the massive companion star runs out of fuel, it will undergo a catastrophic collapse that will produce a supernova explosion, and leave behind a black hole or neutron star. The end result is two compact objects: either a pair of black holes, a pair of neutron stars, or a black hole and neutron star. If the separation between the compact objects becomes small enough as time passes, they will produce gravitational waves. Over time, the size of their orbit will shrink until they merge. LIGO has found three examples of black hole pairs merging in this way in the past two years.

Starburst galaxies like IC 10 are excellent places to search for X-ray binaries because they are churning out stars rapidly. Many of these newly born stars will be pairs of young and massive stars. The most massive of the pair will evolve more quickly and leave behind a black hole or a neutron star partnered with the remaining massive star. If the separation of the stars is small enough, an X-ray binary system will be produced.

This new composite image of IC 10 combines X-ray data from Chandra (blue) with an optical image (red, green, blue) taken by amateur astronomer Bill Snyder from the Heavens Mirror Observatory in Sierra Nevada, California. The X-ray sources detected by Chandra appear as a darker blue than the stars detected in optical light.

The young stars in IC 10 appear to be just the right age to give a maximum amount of interaction between the massive stars and their compact companions, producing the most X-ray sources. If the systems were younger, then the massive stars would not have had time to go supernova and produce a neutron star or black hole, or the orbit of the massive star and the compact object would not have had time to shrink enough for mass transfer to begin. If the star system were much older, then both compact objects would probably have already formed. In this case transfer of matter between the compact objects is unlikely, preventing the formation of an X-ray emitting disk.

Chandra detected 110 X-ray sources in IC 10. Of these, over forty are also seen in optical light and 16 of these contain "blue supergiants", which are the type of young, massive, hot stars described earlier. Most of the other sources are X-ray binaries containing less massive stars. Several of the objects show strong variability in their X-ray output, indicative of violent interactions between the compact stars and their companions.

A pair of papers describing these results were published in the February 10th, 2017 issue of The Astrophysical Journal and is available online here and here. The authors of the study are Silas Laycock from the UMass Lowell's Center for Space Science and Technology (UML); Rigel Capallo, a graduate student at UML; Dimitris Christodoulou from UML; Benjamin Williams from the University of Washington in Seattle; Breanna Binder from the California State Polytechnic University in Pomona; and, Andrea Prestwich from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Credit: chandra.harvard.edu

Galactic Winds Push Researchers to Probe Galaxies at Unprecedented Scale

Galactic Winds Push Researchers to Probe Galaxies at Unprecedented Scale:

When astronomers peer into the universe, what they see often exceeds the limits of human understanding. Such is the case with low-mass galaxies—galaxies a fraction of the size of our own Milky Way. These small, faint systems made up of millions or billions of stars, dust, and gas constitute the most common type of galaxy observed in the universe. But according to astrophysicists’ most advanced models, low-mass galaxies should contain many more stars than they appear to contain.

A leading theory for this discrepancy hinges on the fountain-like outflows of gas observed exiting some galaxies. These outflows are driven by the life and death of stars, specifically stellar winds and supernova explosions, which collectively give rise to a phenomenon known as “galactic wind.” As star activity expels gas into intergalactic space, galaxies lose precious raw material to make new stars. The physics and forces at play during this process, however, remain something of a mystery.

To better understand how galactic wind affects star formation in galaxies, a two-person team led by the University of California, Santa Cruz, turned to high-performance computing at the Oak Ridge Leadership Computing Facility (OLCF), a US Department of Energy (DOE) Office of Science User Facility located at DOE’s Oak Ridge National Laboratory (ORNL). Specifically, UC Santa Cruz astrophysicist Brant Robertson and University of Arizona graduate student Evan Schneider (now a Hubble Fellow at Princeton University), scaled up their Cholla hydrodynamics code on the OLCF’s Cray XK7 Titan supercomputer to create highly detailed simulations of galactic wind.

“The process of generating galactic winds is something that requires exquisite resolution over a large volume to understand—much better resolution than other cosmological simulations that model populations of galaxies,” Robertson said. “This is something you really need a machine like Titan to do.”

After earning an allocation on Titan through DOE’s INCITE program, Robertson and Schneider started small, simulating a hot, supernova-driven wind colliding with a cool cloud of gas across 300 light years of space. (A light year equals the distance light travels in 1 year.) The results allowed the team to rule out a potential mechanism for galactic wind.

Now the team is setting its sights higher, aiming to generate nearly a trillion-cell simulation of an entire galaxy, which would be the largest simulation of a galaxy ever. Beyond breaking records, Robertson and Schneider are striving to uncover new details about galactic wind and the forces that regulate galaxies, insights that could improve our understanding of low-mass galaxies, dark matter, and the evolution of the universe.

About 12 million light years from Earth resides one of the Milky Way’s closest neighbors, a disk galaxy called Messier 82 (M82). Smaller than the Milky Way, M82’s cigar shape underscores a volatile personality. The galaxy produces new stars about five times faster than our own galaxy’s rate of star production. This star-making frenzy gives rise to galactic wind that pushes out more gas than the system keeps in, leading astronomers to estimate that M82 will run out of fuel in just 8 million years.

Analyzing images from NASA’s Hubble Space Telescope, scientists can observe this slow-developing exodus of gas and dust. Data gathered from such observations can help Robertson and Schneider gauge if they are on the right track when simulating galactic wind.

“With galaxies like M82, you see a lot of cold material at large radius that’s flowing out very fast. We wanted to see, if you took a realistic cloud of cold gas and hit it with a hot, fast-flowing, supernova-driven outflow, if you could accelerate that cold material to velocities like what are observed,” Robertson said.

Answering this question in high resolution required an efficient code that could solve the problem based on well-known physics, such as the motion of liquids. Robertson and Schneider developed Cholla to carry out hydrodynamics calculations entirely on GPUs, highly parallelized accelerators that excel at simple number crunching, thus achieving high-resolution results.

In Titan, a 27-petaflop system containing more than 18,000 GPUs, Cholla found its match. After testing the code on a GPU cluster at the University of Arizona, Robertson and Schneider benchmarked Cholla under two small OLCF Director’s Discretionary awards before letting the code loose under INCITE. In test runs, the code has maintained scaling across more than 16,000 GPUs.

“We can use all of Titan,” Robertson said, “which is kind of amazing because the vast majority of the power of that system is in GPUs.”

The pairing of code and computer gave Robertson and Schneider the tools needed to produce high-fidelity simulations of gas clouds measuring more than 15 light years in diameter. Furthermore, the team can zoom in on parts of the simulation to study phases and properties of galactic wind in isolation. This capability helped the team to rule out a theory that posited cold clouds close to the galaxy’s center could be pushed out by fast-moving, hot wind from supernovas.

“The answer is it isn’t possible,” Robertson said. “The hot wind actually shreds the clouds and the clouds become sheared and very narrow. They’re like little ribbons that are very difficult to push on.”

Having proven Cholla’s computing chops, Robertson and Schneider are now planning a full-galaxy simulation about 10 to 20 times larger than their previous effort. Expanding the size of the simulation will allow the team to test an alternate theory for the emergence of galactic wind in disk galaxies like M82. The theory suggests that clouds of cold gas condense out of the hot outflow as they expand and cool.

“That’s something that’s been posited in analytical models but not tested in simulation,” Robertson said. “You have to model the whole galaxy to capture this process because the dynamics of the outflows are such that you need a global simulation of the disk.”

The full-galaxy simulation will likely be composed of hundreds of billions of cells representing more than 30,000 light years of space. To cover this expanse, the team must sacrifice resolution. It can rely on its detailed gas cloud simulations, however, to bridge scales and inform unresolved physics within the larger simulation.

“That’s what’s interesting about doing these simulations at widely different scales,” Robertson said. “We can calibrate after the fact to inform ourselves in how we might be getting the story wrong with the coarser, larger simulation.”

Credit: olcf.ornl.gov

Sun Shreds Its Own Eruption

Sun Shreds Its Own Eruption:

On Sept. 30, 2014, multiple NASA observatories watched what appeared to be the beginnings of a solar eruption. A filament — a serpentine structure consisting of dense solar material and often associated with solar eruptions — rose from the surface, gaining energy and speed as it soared. But instead of erupting from the Sun, the filament collapsed, shredded to pieces by invisible magnetic forces.

Because scientists had so many instruments observing the event, they were able to track the entire event from beginning to end, and explain for the first time how the Sun’s magnetic landscape terminated a solar eruption. Their results are summarized in a paper published in The Astrophysical Journal on July 10, 2017.

“Each component of our observations was very important,” said Georgios Chintzoglou, lead author of the paper and a solar physicist at Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, California, and the University Corporation for Atmospheric Research in Boulder, Colorado. “Remove one instrument, and you’re basically blind. In solar physics, you need to have good coverage observing multiple temperatures — if you have them all, you can tell a nice story.”

The study makes use of a wealth of data captured by NASA’s Solar Dynamics Observatory, NASA’s Interface Region Imaging Spectrograph, JAXA/NASA’s Hinode, and several ground-based telescopes in support of the launch of the NASA-funded VAULT2.0 sounding rocket. Together, these observatories watch the Sun in dozens of different wavelengths of light that reveal the Sun’s surface and lower atmosphere, allowing scientists to track the eruption from its onset up through the solar atmosphere — and ultimately understand why it faded away.

The day of the failed eruption, scientists pointed the VAULT2.0 sounding rocket — a sub-orbital rocket that flies for some 20 minutes, collecting data from above Earth’s atmosphere for about five of those minutes — at an area of intense, complex magnetic activity on the Sun, called an active region. The team also collaborated with IRIS to focus its observations on the same region.

“We were expecting an eruption; this was the most active region on the Sun that day,” said Angelos Vourlidas, an astrophysicist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, principal investigator of the VAULT2.0 project and co-author of the paper. “We saw the filament lifting with IRIS, but we didn’t see it erupt in SDO or in the coronagraphs. That’s how we knew it failed.” 

The Sun’s landscape is controlled by magnetic forces, and the scientists deduced the filament must have met some magnetic boundary that prevented the unstable structure from erupting. They used these observations as input for a model of the Sun’s magnetic environment. Much like scientists who use topographical data to study Earth, solar physicists map out the Sun’s magnetic features, or topology, to understand how these forces guide solar activity.

Chintzoglou and his colleagues developed a model that identified locations on the Sun where the magnetic field was especially compressed, since rapid releases of energy — such as those they observed when the filament collapsed — are more likely to occur where magnetic field lines are strongly distorted.

“We computed the Sun’s magnetic environment by tracing millions of magnetic field lines and looking at how neighboring field lines connect and diverge,” said Antonia Savcheva, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and co-author of the paper. “The amount of divergence gives us a measure of the topology.”

Their model shows this topology shapes how solar structures evolve on the Sun’s surface. Typically, when solar structures with opposite magnetic orientations collide, they explosively release magnetic energy, heating the atmosphere with a flare and erupting into space as a coronal mass ejection — a massive cloud of solar material and magnetic fields.

But on the day of the Sept. 2014 near-eruption, the model indicated the filament instead pushed up against a complex magnetic structure, shaped like two igloos smashed against each other. This invisible boundary, called a hyperbolic flux tube, was the result of a collision of two bipolar regions on the sun’s surface — a nexus of four alternating and opposing magnetic fields ripe for magnetic reconnection, a dynamic process that can explosively release great amounts of stored energy.

“The hyperbolic flux tube breaks the filament’s magnetic field lines and reconnects them with those of the ambient Sun, so that the filament’s magnetic energy is stripped away,” Chintzoglou said.

This structure eats away at the filament like a log grinder, spraying chips of solar material and preventing eruption. As the filament waned, the model demonstrates heat and energy were released into the solar atmosphere, matching the initial observations. The simulated reconnection also supports the observations of bright flaring loops where the hyperbolic flux tube and filament met — evidence for magnetic reconnection.

While scientists have speculated such a process exists, it wasn’t until they serendipitously had multiple observations of such an event that they were able to explain how a magnetic boundary on the Sun is capable of halting an eruption, stripping a filament of energy until it’s too weak to erupt.

“This result would have been impossible without the coordination of NASA’s solar fleet in support of our rocket launch,” Vourlidas said.

This study indicates the Sun’s magnetic topology plays an important role in whether or not an eruption can burst from the Sun. These eruptions can create space weather effects around Earth. 

“Most research has gone into how topology helps eruptions escape,” Chintzoglou said. “But this tells us that apart from the eruption mechanism, we also need to consider what the nascent structure encounters in the beginning, and how it might be stopped.”

Credit: NASA

TRAPPIST-1 is Older Than Our Solar System

TRAPPIST-1 is Older Than Our Solar System:

If we want to know more about whether life could survive on a planet outside our solar system, it’s important to know the age of its star. Young stars have frequent releases of high-energy radiation called flares that can zap their planets' surfaces. If the planets are newly formed, their orbits may also be unstable. On the other hand, planets orbiting older stars have survived the spate of youthful flares, but have also been exposed to the ravages of stellar radiation for a longer period of time.

Scientists now have a good estimate for the age of one of the most intriguing planetary systems discovered to date -- TRAPPIST-1, a system of seven Earth-size worlds orbiting an ultra-cool dwarf star about 40 light-years away. Researchers say in a new study that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago.

The seven wonders of TRAPPIST-1 were revealed earlier this year in a NASA news conference, using a combination of results from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, NASA's Spitzer Space Telescope, and other ground-based telescopes. Three of the TRAPPIST-1 planets reside in the star’s "habitable zone," the orbital distance where a rocky planet with an atmosphere could have liquid water on its surface. All seven planets are likely tidally locked to their star, each with a perpetual dayside and nightside.

At the time of its discovery, scientists believed the TRAPPIST-1 system had to be at least 500 million years old, since it takes stars of TRAPPIST-1’s low mass (roughly 8 percent that of the Sun) roughly that long to contract to its minimum size, just a bit larger than the planet Jupiter. However, even this lower age limit was uncertain; in theory, the star could be almost as old as the universe itself. Are the orbits of this compact system of planets stable? Might life have enough time to evolve on any of these worlds?

"Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago," said Adam Burgasser, an astronomer at the University of California, San Diego, and the paper's first author. Burgasser teamed up with Eric Mamajek, deputy program scientist for NASA's Exoplanet Exploration Program based at NASA's Jet Propulsion Laboratory, Pasadena, California, to calculate TRAPPIST-1's age. Their results will be published in The Astrophysical Journal.

It is unclear what this older age means for the planets' habitability. On the one hand, older stars flare less than younger stars, and Burgasser and Mamajek confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. On the other hand, since the planets are so close to the star, they have soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water. In fact, the equivalent of an Earth ocean may have evaporated from each TRAPPIST-1 planet except for the two most distant from the host star: planets g and h. In our own solar system, Mars is an example of a planet that likely had liquid water on its surface in the past, but lost most of its water and atmosphere to the Sun’s high-energy radiation over billions of years.

However, old age does not necessarily mean that a planet's atmosphere has been eroded. Given that the TRAPPIST-1 planets have lower densities than Earth, it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation. A thick atmosphere could also help redistribute heat to the dark sides of these tidally locked planets, increasing habitable real estate. But this could also backfire in a "runaway greenhouse" process, in which the atmosphere becomes so thick the planet surface overheats – as on Venus.

"If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years," Burgasser said.

Fortunately, low-mass stars like TRAPPIST-1 have temperatures and brightnesses that remain relatively constant over trillions of years, punctuated by occasional magnetic flaring events. The lifetimes of tiny stars like TRAPPIST-1 are predicted to be much, much longer than the 13.7 billion-year age of the universe (the Sun, by comparison, has an expected lifetime of about 10 billion years).

"Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae," Mamajek said. "But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe."

Some of the clues Burgasser and Mamajek used to measure the age of TRAPPIST-1 included how fast the star is moving in its orbit around the Milky Way (speedier stars tend to be older), its atmosphere’s chemical composition, and how many flares TRAPPIST-1 had during observational periods. These variables all pointed to a star that is substantially older than our Sun.

Future observations with NASA's Hubble Space Telescope and upcoming James Webb Space Telescope may reveal whether these planets have atmospheres, and whether such atmospheres are like Earth's.

"These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not," said Tiffany Kataria, exoplanet scientist at JPL, who was not involved in the study.

Future observations with Spitzer could help scientists sharpen their estimates of the TRAPPIST-1 planets’ densities, which would inform their understanding of their compositions.

Credit: spitzer.caltech.edu

Scientists Help Predict Neptune’s Chemical Make-Up

Scientists Help Predict Neptune’s Chemical Make-Up:

Scientists have helped solve the mystery of what lies beneath the surface of Neptune - the most distant planet in our solar system. A new study sheds light on the chemical make-up of the planet, which lies around 4.5 billion kilometers from the sun.

Extremely low temperatures on planets like Neptune - called ice giants - mean that chemicals on these distant worlds exist in a frozen state, researchers say.

Frozen mixtures of water, ammonia and methane make up a thick layer between the planets' atmosphere and core - known as the mantle. However, the form in which these chemicals are stored is poorly understood.

Using laboratory experiments to study these conditions is difficult, as it is very hard to recreate the extreme pressures and temperatures found on ice giants, researchers say.

Instead, scientists at the University of Edinburgh ran large-scale computer simulations of conditions in the mantle. By looking at how the chemicals there react with each other at very high pressures and low temperatures, they were able to predict which compounds are formed in the mantle.

The team found that frozen mixtures of water and ammonia inside Neptune - and other ice giants, including Uranus - are likely to form a little-studied compound called ammonia hemihydrate.

The findings will influence how ice giants are studied in future and could help astronomers classify newly discovered planets as they look deeper into space.

The study, published in the journal Proceedings of the National Academy of Sciences, was supported by Engineering and Physical Sciences Research Council. The work was carried out in collaboration with scientists at Jilin University, China.

Dr Andreas Hermann, of the University of Edinburgh's Centre for Science at Extreme Conditions, said: "This study helps us better predict what is inside icy planets like Neptune. Our findings suggest that ammonia hemihydrate could be an important component of the mantle in ice giants, and will help improve our understanding of these frozen worlds. Computer models are a great tool to study these extreme places, and we are now building on this study to get an even more complete picture of what goes on there."

Credit: ed.ac.uk

Gravitational Waves as Astronomical Tools: LIGO Team Members Awarded 2018 Berkeley Prize

Gravitational Waves as Astronomical Tools: LIGO Team Members Awarded 2018 Berkeley Prize:

The importance of the discovery of gravitational waves is being more widely recognized by the scientific community. Recently, the American Astronomical Society (AAS) has awarded the 2018 Berkeley Prize to three researchers for their leadership roles in the development of the Advanced LIGO detectors, which have opened a new window on the universe. This decision marks the significance of gravitational waves for future research in the field of astronomy.

AAS announced in late July that Dennis C. Coyne (Caltech), Peter K. Fritschel (MIT), and David H. Shoemaker (MIT) will share the 2018 Lancelot M. Berkeley - New York Community Trust Prize for Meritorious Work in Astronomy. This trio of researchers represents the team that developed the second-generation detectors for the Laser Interferometer Gravitational-Wave Observatory (LIGO) and used them to detect oscillations in the fabric of space-time.

“It is of course a personal pleasure, and I am very happy they chose the three persons they did — we worked very closely and in a complementary fashion to guide the project to a successful conclusion,” Shoemaker told Astrowatch.net.

Shoemaker is the title Senior Research Scientist at MIT’s Kavli Institute for Astrophysics and Space Research. Moreover, he led the Advanced LIGO team and serves as Spokesperson for the LIGO Scientific Collaboration (LSC), which includes nearly 1,200 scientists from more than 100 institutions and 18 countries worldwide.

“The LSC is charged to ‘do the science’ — instrument science as well as astrophysics — and the LIGO Lab (part of the LSC) has the ‘niche’ responsibility to make projects happen, maintain the observatories, and generally manage the machinery that makes us an observatory. That is a great complement to the approximately 100 other groups in the LSC who work to solve problems on many scales to get the science done,” Shoemaker said.

Shoemaker underlined how challenging was the development of the new LIGO detectors. It required a lot of work from the team and it cost them a lot of stress few times when things did not go as planned. He noted that people participating in the project were fantastic and the dedication of everyone involved, including technicians, junior engineers, administrative staff, and others, was phenomenal.

Left to right: Dennis Coyne, Peter Fritschel, and David Shoemaker

“I would like also to mention Carol Wilkinson, who served as Project Manager for much of the project. It is not easy to spend more than 200 million dollars legally, efficiently, and to communicate that to the funding agencies in review panels. Carol did all that and more,” Shoemaker said.

He pointed out that the award shows the work done by the LIGO team was acknowledged by astronomical community as the Berkeley Prize is given by a society of professional astronomers.

“Most important for me though is the source of the prize: the American Astronomical Society. I could not be happier that the organization sponsoring the prize is one led by and serving the astronomy community — it shows that the gravitational-wave field is starting to be considered an astronomical tool and not just a demonstration of general relativity,” Shoemaker said.

Gravitational waves are 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the universe. So far, the LIGO team has announced three confirmed detections of cosmic gravitational waves, all from merging pairs of massive black holes.

“Einstein’s General Theory of Gravitation makes predictions that are, as far as we can tell, exactly right, even in the case of pure warped space-time. That is astonishing. Add to that the fact that there are bigger stellar-mass black holes than most anyone predicted, and you have a new field,” Shoemaker concluded.

Asteroid Apophis Has One in 100,000 Chance of Hitting Earth, Expert Estimates

Asteroid Apophis Has One in 100,000 Chance of Hitting Earth, Expert Estimates:

The huge nearly 400-meter wide asteroid Apophis is still on a list of hazardous near-Earth objects (NEOs), regarded as a potential threat to our planet. However, new calculations made by NASA’s Jet Propulsion Laboratory (JPL) scientist, show that Apophis’ odds of Earth impact are lower than previously estimated.

“We cannot yet exclude the possibility that it could impact our planet, but we can calculate that the chance of Earth impact is only a 1-in-100-thousand over the next century, which of course is extremely small,” Paul Chodas, Manager of JPL’s Center for Near Earth Object Studies told Astrowatch.net.

Discovered in 2004, asteroid Apophis is slated to fly by our planet on April 13, 2029. Initial observations of this space rock indicated that it has one in 36 chance of hitting the Earth on that day, but additional monitoring of Apophis completely ruled out this possibility.

However, Alberto Cellino of the Observatory of Turin in Italy told Astrowatch.net in June, that although the potential impact in 2029 was excluded, we cannot rule out such event in more distant future. Given the fact that NEO orbits are chaotic, what is not dangerous today can become a candidate impactor in the future.

That is why astronomers, including Chodas, underline the importance of detailed observations of Apophis and its constant monitoring, which could confirm that this asteroid poses no danger to us.

“Apophis is certainly a hazardous asteroid, and for that reason it has been tracked extensively, and so we know its orbit very accurately. In all likelihood further tracking measurements will eliminate even that possibility (one in 100,000), Chodas noted.

Astronomers estimate that on April 13, 2029, Apophis will pass by the Earth at a distance of no closer than 18,300 miles (29,470 kilometers). Next close approach of this asteroid is expected to take place in April 2036 when it will miss our planet at a much larger distance of approximately 30.5 million miles (49 million kilometers).

Currently, there are 1,803 potentially hazardous asteroids (PHAs) detected to date. PHAs are space rocks larger than approximately 100 meters that can come closer to Earth than 4.65 million miles (7.5 million kilometers). However, none of the known PHAs is on a collision course with our planet.