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.

Experiments Cast Doubt on How the Earth Was Formed

Experiments Cast Doubt on How the Earth Was Formed:

New geochemical research indicates that existing theories of the formation of the Earth may be mistaken. The results of experiments to show how zinc (Zn) relates to sulphur (S) under the conditions present at the time of the formation of the Earth more than 4 billion years ago, indicate that there is a substantial quantity of Zn in the Earth's core, whereas previously there had been thought to be none. This implies that the building blocks of the Earth must be different to what has been supposed. The work is presented at the Goldschmidt geochemistry conference in Paris.

The researchers, from the Institut de Physique du Globe de Paris (IPGP) melted mixtures of iron-rich metal and silicate compounds, containing Zn and S, at high temperatures and pressures up to 80 GPa and 4100 K to experimentally simulate core-mantle differentiation at the time of the Earth's formation. They then measured how these elements were distributed (partitioned) between the core and mantle of their experiments. When they fed their results into computer models of the Earth's formation, they found that none of the canonical models can sufficiently reproduce the S/Zn ratio of the present-day mantle. This means that the current estimates of the Earth's composition, including its core, need to be modified, and therefore the way the core and mantle - i.e. the Earth - formed may also need to be revised.

"Most theories are based on the Earth being formed from only two types of stony meteorite, the CI chondrites or enstatite chondrites. However, this new work indicates that the Earth needs to have formed from a more S-poor source; in terms of the geochemistry, the best candidate for this material is the metal rich CH chondrites", said Brandon Mahan (Institut de Physique du Globe de Paris).

"CH chondrites were first classified in 1985, and only a few dozen examples have been identified. They are rich in metallic iron and poor in easily vaporized elements, which indicates formation at very high temperatures, but they also contain a few percent of water-bearing minerals, which paradoxically indicates low temperatures.

This means that the CH chondrites -- much like the Earth -- have a very complex formation history which has given them features from both extremes of hot and cold. If our results are valid, this indicates that the building blocks of the Earth may be a bit more exotic than we thought" Existing theories of the Earth's formation are largely based on geochemistry. One of the major geochemical clues to the Earth's formation lies in the way elements such as Zn and S in meteorites are associated in a relatively well-known ratio, meaning that if you know the amount of Zn in a meteorite, you can estimate the amount of S. "We decided to test if that ratio was the same for the growing Earth as it is today using various possible source materials.", said Brandon Mahan.

"We found that under conditions similar to those estimated when the Earth formed, Zn has a tendency to be distributed between the core and mantle differently than we had thought, i.e. there will be a significant amount of it bound up in the Earth's core. Based on previous models, if we can place more Zn in the core, then by association you place more S in the core as well, much more in fact than most current observations suggest.

Most leading estimates cap the amount of sulphur in the Earth's core at around 2%. If this is true, then using most known meteorites as a source material for Earth puts the S/Zn ratio of the mantle way above current accepted values, because too much S ends up in the mantle, indicating that perhaps the Earth cannot be made from any of the solar system materials that have previously been proposed as its source material.

But if the building blocks of the Earth were something like the CH Chondrites, this could give us an Earth pretty similar to the one we see today."

Credit: eurekalert.org

New 3-D Simulations Show How Galactic Centers Cool Their Jets

New 3-D Simulations Show How Galactic Centers Cool Their Jets:

Some of the most extreme outbursts observed in the universe are the mysterious jets of energy and matter beaming from the center of galaxies at nearly the speed of light. These narrow jets, which typically form in opposing pairs are believed to be associated with supermassive black holes and other exotic objects, though the mechanisms that drive and dissipate them are not well understood. Now, a small team of researchers has developed theories supported by 3-D simulations to explain what’s at work.

“These jets are notoriously hard to explain,” said Alexander “Sasha” Tchekhovskoy, a former NASA Einstein fellow who co-led the new study as a member of the Nuclear Science Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), and the Astronomy and Physics departments and Theoretical Astrophysics Center at UC Berkeley. “Why are they so stable in some galaxies and in others they just fall apart?”

As much as half of the jets’ energy can escape in the form of X-rays and stronger forms of radiation. The researchers showed how two different mechanisms – both related to the jets’ interaction with surrounding matter, known as the “ambient medium” – serve to reduce about half of the energy of these powerful jets.

“The exciting part of this research is that we are now coming to understand the full range of dissipation mechanisms that are working in the jet,” no matter the size or type of jet, he said.

The study that Tchekhovskoy co-led with Purdue University scientists Rodolfo Barniol Duran and Dimitrios Giannios is published in the Aug. 21 edition of Monthly Notices of the Royal Astronomical Society. The study concludes that the ambient medium itself has a lot to do with how the jets release energy.

“We were finally able to simulate jets that start from the black hole and propagate to very large distances – where they bump into the ambient medium,” said Duran, formerly a postdoctoral research associate at Purdue University who is now a faculty member at California State University, Sacramento.

Tchekhovskoy, who has studied these jets for over a decade, said that an effect known as magnetic kink stability, which causes a sudden bend in the direction of some jets, and another effect that triggers a series of shocks within other jets, appear to be the primary mechanisms for energy release. The density of the ambient medium that the jets encounter serves as the key trigger for each type of release mechanism.

“For a long time, we have speculated that shocks and instabilities trigger the spectacular light displays from jets. Now these ideas and models can be cast on a much firmer theoretical ground,” said Giannios, assistant professor of physics and astronomy at Purdue.

The length and intensity of the jets can illuminate the properties of their associated black holes, such as their age and size and whether they are actively “feeding” on surrounding matter. The longest jets extend for millions of light years into surrounding space.

“When we look at black holes, the first things we notice are the central streaks of these jets. You can make images of these streaks and measure their lengths, widths, and speeds to get information from the very center of the black hole,” Tchekhovskoy noted. “Black holes tend to eat in binges of tens and hundreds of millions of years. These jets are like the ‘burps’ of black holes – they are determined by the black holes’ diet and frequency of feeding.”

While nothing – not even light – can escape a black hole’s interior, the jets somehow manage to draw their energy from the black hole. The jets are driven by a sort of accounting trick, he explained, like writing a check for a negative amount and having money appear in your account. In the black hole’s case, it’s the laws of physics rather than a banking loophole that allow black holes to spew energy and matter even as they suck in surrounding matter.

The incredible friction and heating of gases spiraling in toward the black hole cause extreme temperatures and compression in magnetic fields, resulting in an energetic backlash and an outflow of radiation that escapes the black hole’s strong pull.

Earlier studies had shown how magnetic instabilities (kinks) in the jets can occur when jets run into the ambient medium. This instability is like a magnetic spring. If you squish the spring from both ends between your fingers, the spring will fly sideways out of your hand. Likewise, a jet experiencing this instability can change direction when it rams into matter outside of the black hole’s reach.

The same type of instability frustrated scientists working on early machines that attempted to create and harness a superhot, charged state of matter known as a plasma in efforts to develop fusion energy, which powers the sun. The space jets, also known as active galactic nuclei (AGN) jets, also are a form of plasma.

The latest study found that in cases where an earlier jet had “pre-drilled” a hole in the ambient medium surrounding a black hole and the matter impacted by the newly formed jet was less dense, a different process is at work in the form of “recollimation” shocks.

These shocks form as matter and energy in the jet bounce off the sides of the hole. The jet, while losing energy from every shock, immediately reforms a narrow column until its energy eventually dissipates to the point that the beam loses its tight focus and spills out into a broad area.

“With these shocks, the jet is like a phoenix. It comes out of the shock every time,” though with gradually lessening energy, Tchekhovskoy said. “This train of shocks cumulatively can dissipate quite a substantial amount of the total energy.”

The researchers designed the models to smash against different densities of matter in the ambient medium to create instabilities in the jets that mimic astrophysical observations.

New, higher-resolution images of regions in space where supermassive black holes are believed to exist – from the Event Horizon Telescope (EHT), for example – should help to inform and improve models and theories explaining jet behavior, Tchekhovskoy said, and future studies could also include more complexity in the jet models, such as a longer sequence of shocks.

“It would be really interesting to include gravity into these models,” he said, “and to see the dynamics of buoyant cavities that the jet fills up with hot magnetized plasma as it drills a hole” in the ambient medium.

He added, “Seeing deeper into where the jets come from – we think the jets start at the black hole’s event horizon (a point of no return for matter entering the black hole) – would be really helpful to see in nature these ‘bounces’ in repeating shocks, for example. The EHT could resolve this structure and provide a nice test of our work.”

Credit: lbl.gov

Supernova Hunters: 'Get Them While They're Young'

Supernova Hunters: 'Get Them While They're Young':

Not many people can say they have watched a star explode before their eyes, but David Sand can. On the evening of March 10, the astronomer happened to be on duty to monitor results coming in from an automated survey scanning faraway galaxies for evidence of such events. Sand was about to go to bed, when the software algorithm alerted him to a point of light where none had been just a few hours earlier, in a galaxy called NGC 5643, located in the constellation Lupus, 55 million light-years from Earth.

"As I was looking at this image, it was clear to me a supernova had just gone off," said Sand, who joined the University of Arizona's Steward Observatory just this month as a new assistant professor. "I took another image right away to get a confirmation."

Because some blips of light that show up unexpectedly in the observations turn out to be asteroids passing in front of the star-studded background and not stellar cataclysms, Sand sent a remote command to the telescope, located at the Cerro Tololo Observatory in Chile, to snap another image. The blip was still there. 

Within minutes of discovery, Sand activated observations with the global network of 18 robotic telescopes of the Las Cumbres Observatory. They are spaced around the globe so that there is always one on the night side of the Earth, ready to conduct astronomical observations. This allowed the team to take immediate and near-continuous observations. 

"In a galaxy like our Milky Way, a supernova goes off, on average, about once per century," Sand said. "We were fortunate to see this phenomenon that never had been observed before." 

Sand's discovery, designated SN 2017cbv, likely marks the first detailed observation of a cosmic event that astronomers only had glimpses of before: a supernova and its explosive ejecta slamming into a nearby companion star. The discovery was made possible by a specialized survey taking advantage of recent advances in linking telescopes across the globe into a robotic network. 

At 55 million light-years, SN 2017cbv was one of the closest supernovae discovered in recent years. It was found by the DLT40 survey, which stands for "Distance Less Than 40 Megaparsecs" or 120 million light-years. The survey uses the PROMPT telescope in Chile, which monitors roughly 500 galaxies nightly. 

"This was one of the earliest catches ever — within a day, perhaps even hours, of its explosion," said Sand, who created the DLT40 survey together with Stefano Valenti, an assistant professor at the University of California, Davis. Both were previously postdoctoral researchers at Las Cumbres Observatory, or LCO. 

SN 2017cbv is a thermonuclear (Type Ia) supernova, the type astronomers use to measure the acceleration of the expansion of the universe. Type Ia supernovae are known to be the explosions of white dwarfs, the dead cores of what used to be normal stars. 

Across the cosmic abyss, a supernova tells of its existence by appearing like a star that wasn't there before. Its brightness peaks within a matter of days to weeks and then slowly fades over weeks or months.

"To turn into a Type Ia supernova, a white dwarf can't be by itself," explained Sand, who serves as the principal investigator of the DLT40 survey. "It has to have some kind of companion, and we are trying to figure out what that companion is."

The identity of this companion has been hotly debated for more than 50 years. 

The prevailing theory over the last few years is that the supernovae happen when two white dwarfs spiral in toward each other and merge in a cataclysmic explosion. The other scenario involves a normal star that is not a white dwarf.

Key to the observations reported in this study is a small bump in the light curve emitted by SN 2017cbv within the first three to four days, a feature that would have been missed were it not for the almost instantaneous reaction times that are the hallmark of the DLT40 survey: a fleeting blue glow from the interaction at an unprecedented level of detail, revealing the surprising identity of the mysterious companion star. 

"We think what happened here was likely scenario number two," Sand said. "The bump in the light curve could be caused by material from the exploding white dwarf as it slams into the companion star." 

This study infers that the white dwarf was stealing matter from a much larger companion star, approximately 20 times the radius of the sun. This caused the white dwarf to explode, and the collision of the supernova with the companion star shocked the supernova material, heating it to a blue glow that was heavy in ultraviolet light. Such a shock could not have been produced if the companion were another white dwarf star, the study's authors say. 

"We've been looking for this effect — a supernova crashing into its companion star — since it was predicted in 2010," said Griffin Hosseinzadeh, a doctoral student at the University of California, Santa Barbara, who led the study, which is soon to be published in the Astrophysical Journal Letters. "Hints have been seen before, but this time the evidence is overwhelming. The data are beautiful! 

"With Las Cumbres Observatory's ability to monitor the supernova every few hours, we were able to see the full extent of the rise and fall of the blue glow for the first time," he added. "Conventional telescopes would have had only a data point or two and missed it."

Eighteen telescopes, spread over eight sites around the world, form the heart of the Las Cumbres Observatory. At any given moment, it is nighttime somewhere in the network, which ensures that a supernova can be observed without interruption. 

Because of their uniform brightness, Type Ia supernovae are akin to a "standard 60-watt lightbulb for cosmology," and scientists use them as yardsticks to measure distances across the universe. 

Because of their rare and fleeting appearance, a targeted observational campaign such as the DLT40 survey and an automated network of observatories such as the LCO are critical to the discovery and study of Type Ia supernovae. Funded by the National Science Foundation, the DLT40 survey started in October 2016 and is scheduled to continue over the next three years.

"The secret sauce to this are the connected telescopes of the Las Cumbres Observatory," Sand said, adding that the survey is not about quantity. "We'd rather focus on a precious few than hundreds of them."

It is likely that Type Ia supernovae come from both types of progenitor systems — two white dwarfs or one white dwarf and a "normal" interacting star — and the goal of these studies is to figure out which of the two processes is more common, Sand explained. 

"Observing supernovae such as SN 2017cbv is an important step in this direction," he said. "If we get them really young, we can get a better idea of these processes, which hold implications for our understanding of the cosmos, including dark energy." 

Credit: arizona.edu

Asteroid 2017 PK25 Flew Past Earth Today

Asteroid 2017 PK25 Flew Past Earth Today:

An asteroid discovered just two days ago safely flew past Earth today at 2:08 UTC at a distance of 2.2 lunar distances (LD), or 845,000 kilometers. The object, known as 2017 PK25, missed our planet with a relative velocity of approximately 16 km/s.

2017 PK25 was first observed by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) at the Mauna Loa Observatory (MLO), Hawaii. It is an astronomical survey system for detection of dangerous asteroids a few weeks to days before their close approaches to Earth.

According to astronomers, 2017 PK25 has an estimated diameter between 23 and 52 meters, and an absolute magnitude of 25.3. The asteroid has a semimajor axis of 0.81 and it takes it about 266 days to fully circle the sun.

Besides passing today near our planet, the asteroid also missed the moon few hours earlier at nearly identical distance of about 2.1 LD. Next close approach of 2017 PK25 is expected on Aug. 4, 2020 when it will whiz by Earth at a much larger distance of 133 LD.

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 19.5 LD. However, none of the known PHAs is on a collision course with our planet.

Researchers Redefine Cosmic Velocity Web

Researchers Redefine Cosmic Velocity Web:

The cosmic web -- the distribution of matter on the largest scales in the universe -- has usually been defined through the distribution of galaxies. Now, a new study by a team of astronomers from France, Israel and Hawaii demonstrates a novel approach. Instead of using galaxy positions, they mapped the motions of thousands of galaxies. Because galaxies are pulled toward gravitational attractors and move away from empty regions, these motions allowed the team to locate the denser matter in clusters and filaments and the absence of matter in regions called voids.

Matter was distributed almost homogeneously in the very early universe, with only miniscule variations in density. Over the 14-billion-year history of the universe, gravity has been acting to pull matter together in some places and leave other places more and more empty. Today, the matter forms a network of knots and connecting filaments referred to as the cosmic web. Most of this matter is in a mysterious form, the so-called "dark matter." Galaxies have formed at the highest concentrations of matter and act as lighthouses illuminating the underlying cosmic structure.

The newly defined cosmic velocity web defines the structure of the universe from velocity information alone. In those regions with abundant observations, the structure of the velocity web and the web inferred from the locations of the galaxy lighthouses are similar. This agreement provides strong confirmation of the fundamental idea that structure developed from the growth of initially tiny fluctuations through gravitational attraction.

The cosmic velocity web analysis was led by Daniel Pomarede, Atomic Energy Center, France, with the collaboration of Helene Courtois at the University of Lyon, France; Yehuda Hoffman at the Hebrew University, Israel; and Brent Tully at the University of Hawai'i's Institute for Astronomy.

"With the motions of the galaxies, we can infer where all of the mass is located: the galaxies and the 5 times more abundant transparent matter (usually wrongly called dark matter). This total gravitating mass, together with the expansion of the universe, is responsible for the motions that create the architecture of the universe. The gravity from galaxies alone cannot create this network we see," said Dr. Courtois.

Dr. Tully adds, "Moreover, a wide swath of the universe is hidden behind the obscuring disk of our own Milky Way galaxy. Our reconstruction of structure with the velocity web is revealing for the first time filaments of matter that stretch all the way around the sky and are easily followed through these regions of obscuration."

This definition of the cosmic velocity web was made possible by the large and coherent collection of galaxy distances and velocities in the Cosmicflows series. The current analysis is based on a study of 8,000 galaxies in the second release of Cosmicflows. The third release, with over twice as many galaxy distances and velocities is already available, and will reveal the cosmic velocity web in increasingly rich detail.

The key element of the program is the acquisition of good distances to galaxies. Several methods are used, such as exploiting the known luminosities of old stars that are just beginning to burn Helium in their cores, and the relationship between the rotation speed of galaxies and the number of stars they possess. The observations have involved dozens of telescopes around the world and in space and at wavelengths from visible light through the infrared to radio.

"The velocity web method for mapping the cosmos is analogous to using plate tectonics in geology. It helps understand not just the current layout of the universe, but also the movement of the invisible underlying masses responsible for that topology," said Dr. Courtois.

The team has produced an extensive video demonstrating the cosmic velocity web. It first explains the concepts underlying the cosmic velocity web reconstruction, followed by a description of its major elements. The video then shows how cosmic flows are organized within its structure, and how the basin of attraction of the recently mapped Laniakea Supercluster resides within its elements. In the final sequence, the viewer enters an immersive exploration of the filamentary structure of the local universe, navigating inside the filaments and visiting the major nodes such as the Great Attractor. The 11-minute video is linked below and available at https://vimeo.com/pomarede/vweb.

The 3-dimensional map can also be explored in an interactive visualization, using the free online Sketchfab platform. This is a powerful tool to visualize interactively the structure from any viewpoint and compare it with the distribution of galaxies; one can dive inside the filaments and explore them in immersion. With appropriate virtual reality hardware, it can also be used in VR mode. This visualization marks a milestone as the first time such an interactive dataset will be embedded in the online version of the scientific article appearing in the Astrophysical Journal. Everyone is invited to interact with the data below, or at https://skfb.ly/667Jr.

The team of researchers includes Yehuda Hoffman, Hebrew University's Racah Institute of Physics, Daniel Pomarède, Institut de Recherche sur les Lois Fondamentales de l'Univers, CEA, Université Paris-Saclay, Gif-sur-Yvette, France; R. Brent Tully, Institute for Astronomy (IfA), University of Hawaii, USA; and Hélène M. Courtois, University of Lyon 1, France.

The work appears in the August 10, 2017 issue of the Astrophysical Journal and can be found online here.

Credit: hawaii.edu

Cassini Sees Cloudy Waves on Saturn

Cassini Sees Cloudy Waves on Saturn:

Clouds on Saturn take on the appearance of strokes from a cosmic brush thanks to the wavy way that fluids interact in Saturn's atmosphere. Neighboring bands of clouds move at different speeds and directions depending on their latitudes. This generates turbulence where bands meet and leads to the wavy structure along the interfaces. Saturn’s upper atmosphere generates the faint haze seen along the limb of the planet in this image.

This false color view is centered on 46 degrees north latitude on Saturn. The images were taken with the Cassini spacecraft narrow-angle camera on May 18, 2017 using a combination of spectral filters which preferentially admit wavelengths of near-infrared light. The image filter centered at 727 nanometers was used for red in this image; the filter centered at 750 nanometers was used for blue. (The green color channel was simulated using an average of the two filters.)

The view was obtained at a distance of approximately 750,000 miles (1.2 million kilometers) from Saturn. Image scale is about 4 miles (7 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Credit: NASA

Tracking a Solar Eruption Through the Solar System

Tracking a Solar Eruption Through the Solar System:

Ten spacecraft, from ESA’s Venus Express to NASA’s Voyager-2, felt the effect of a solar eruption as it washed through the solar system while three other satellites watched, providing a unique perspective on this space weather event. Scientists working on ESA’s Mars Express were looking forward to investigating the effects of the close encounter of Comet Siding Spring on the Red Planet’s atmosphere on October 19, 2014, but instead they found what turned out to be the imprint of a solar event.

While this made the analysis of any comet-related effects far more complex than anticipated, it triggered one of the largest collaborative efforts to trace the journey of an interplanetary coronal mass ejection – a CME – from the sun to the far reaches of the outer solar system.

Although Earth itself was not in the firing line, a number of sun-watching satellites near Earth – ESA’s Proba-2, the ESA/NASA SOHO and NASA’s Solar Dynamics Observatory – had witnessed a powerful solar eruption a few days earlier, on October 14, 2014.

NASA’s STEREO-A not only captured images of the other side of the sun with respect to Earth, but also collected in situ information as the CME rushed passed.

Thanks to the fortuitous locations of other satellites lying in the direction of the CME’s travel, unambiguous detections were made by three Mars orbiters – ESA’s Mars Express, NASA’s MAVEN and Mars Odyssey – and NASA’s Curiosity Rover operating on the Red Planet’s surface, ESA’s Rosetta at Comet 67P/Churyumov–Gerasimenko, and the international Cassini mission at Saturn.

Hints were even found as far out as NASA’s New Horizons, which was approaching Pluto at the time, and beyond to Voyager-2. However, at these large distances it is possible that evidence of this specific eruption may have merged with the background solar wind.

“CME speeds with distance from the sun is not well understood, in particular in the outer solar system,” said Olivier Witasse, a planetary scientist for the European Space Agency and lead author of the study published in Journal of Geophysical Research: Space Physics, a journal of the American Geophysical Union. “Thanks to the precise timings of numerous in situ measurements, we can better understand the process, and feed our results back into models.”

The measurements give an indication of the speed and direction of travel of the CME, which spread out over an angle of at least 116 degrees to reach Venus Express and STEREO-A on the eastern flank, and the spacecraft at Mars and Comet 67P Churyumov–Gerasimenko on the western flank.

From an initial maximum of about 1000 kilometers per second (621 miles per second) estimated at the sun, a strong drop to 647 kilometers per second (402 miles per second) was measured by Mars Express three days later, falling further to 550 kilometers per second (342 miles per second) at Rosetta after five days. This was followed by a more gradual decrease to 450–500 kilometers per second (280-311 miles per second) at the distance of Saturn a month since the event.

The data also revealed the evolution of the CME’s magnetic structure, with the effects felt by spacecraft for several days, providing useful insights on space weather effects at different planetary bodies. The signatures at the various spacecraft typically included an initial shock, a strengthening of the magnetic field, and increases in the solar wind speed.

In the case of ESA’s Venus Express, its science package was not switched on because Venus was “behind” the sun as seen from Earth, limiting communication capabilities. A faint indication was inferred from its star tracker being overwhelmed with radiation at the expected time of passage.

Furthermore, several craft carrying radiation monitors – Curiosity, Mars Odyssey, Rosetta and Cassini ­­– revealed an interesting and well-known effect: a sudden decrease in galactic cosmic rays. As a CME passes by, it acts like a protective bubble, temporarily sweeping aside the cosmic rays and partially shielding the planet or spacecraft.

A drop of about 20 percent in cosmic rays was observed at Mars – one of the deepest recorded at the Red Planet – and persisted for about 35 hours. At Rosetta, a reduction of 17 percent was seen that lasted for 60 hours, while at Saturn the reduction was slightly lower and lasted for about four days. The increase in the duration of the cosmic ray depression corresponds to a slowing of the CME and the wider region over which it was dispersed at greater distances.

“The comparison of the decrease in galactic cosmic ray influx at three widely separated locations due to the same CME is quite novel,” Witasse said. “While multispacecraft observations of CMEs have been done in the past, it is uncommon for the circumstances to be such to include so many spread across the inner and outer solar system like this.”

“Finally, coming back to our original intended observation of the passage of Comet Siding Spring at Mars, the results show the importance of having a space weather context for understanding how these solar events might influence or even mask the comet’s signature in a planet’s atmosphere,” he said.

Credit: agu.org

Tidally Locked Exoplanets May Be More Common than Previously Thought

Tidally Locked Exoplanets May Be More Common than Previously Thought:

Many exoplanets to be found by coming high-powered telescopes will probably be tidally locked — with one side permanently facing their host star — according to new research by astronomer Rory Barnes of the University of Washington.

Barnes, a UW assistant professor of astronomy and astrobiology, arrived at the finding by questioning the long-held assumption that only those stars that are much smaller and dimmer than the sun could host orbiting planets that were in synchronous orbit, or tidally locked, as the moon is with the Earth. His paper, “Tidal Locking of Habitable Exoplanets,” has been accepted for publication by the journal Celestial Mechanics and Dynamical Astronomy.

Tidal locking results when there is no side-to-side momentum between a body in space and its gravitational partner and they become fixed in their embrace. Tidally locked bodies such as the Earth and moon are in synchronous rotation, meaning that each takes exactly as long to rotate around its own axis as it does to revolve around its host star or gravitational partner. The moon takes 27 days to rotate once on its axis, and 27 days to orbit the Earth once.

The moon is thought to have been created by a Mars-sized celestial body slamming into the young Earth at an angle that set the world spinning initially with approximately 12-hour days.

“The possibility of tidal locking is an old idea, but nobody had ever gone through it systematically,” said Barnes, who is affiliated with the UW-based Virtual Planetary Laboratory.

In the past, he said, researchers tended to use that 12-hour estimation of Earth’s rotation period to model exoplanet behavior, asking, for example, how long an Earthlike exoplanet with a similar orbital spin might take to become tidally locked.

“What I did was say, maybe there are other possibilities — you could have slower or faster initial rotation periods,” Barnes said. “You could have planets larger than Earth, or planets with eccentric orbits — so by exploring that larger parameter space, you find that in fact the old ideas were very limited, there was just one outcome there.”

“Planetary formation models, however, suggest the initial rotation of a planet could be much larger than several hours, perhaps even several weeks,” Barnes said. “And so when you explore that range, what you find is that there’s a possibility for a lot more exoplanets to be tidally locked. For example, if Earth formed with no moon and with an initial ‘day’ that was four days long, one model predicts Earth would be tidally locked to the sun by now.”

Barnes writes: “These results suggest that the process of tidal locking is a major factor in the evolution of most of the potentially habitable exoplanets to be discovered in the near future.”

Being tidally locked was once thought to lead to such extremes of climate as to eliminate any possibility of life, but astronomers have since reasoned that the presence of an atmosphere with winds blowing across a planet’s surface could mitigate these effects and allow for moderate climates and life.

Barnes said he also considered the planets that will likely be discovered by NASA’s next planet-hunting satellite, the Transiting Exoplanet Survey Satellite or TESS, and found that every potentially habitable planet it will detect will likely be tidally locked.

Even if astronomers discover the long-sought Earth “twin” orbiting a virtual twin of the sun, that world may be tidally locked.

“I think the biggest implication going forward,” Barnes said, “is that as we search for life on any exoplanets we need to know if a planet is tidally locked or not.”

The research was funded by a NASA grant through the Virtual Planetary Laboratory.

Credit: washington.edu

Newly Detected House-Sized Asteroid to Pass by Earth on Wednesday

Newly Detected House-Sized Asteroid to Pass by Earth on Wednesday:

A newly discovered house-sized near-Earth object (NEO) is expected to fly by our planet on Wednesday, Aug. 16. The space rock, designated 2017 PD25, will miss the Earth at 3:45 UTC at a safe distance of about 9.6 lunar distances (LD), or 3.7 million kilometers with a relative velocity of 7.87 km/s.

2017 PD25 was discovered Aug. 12 by the Pan-STARRS 1 (PS1) telescope at the summit of Haleakala on the Hawaiian island of Maui. The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is an astronomical survey consisting of astronomical cameras, telescopes and a computing facility, surveying the sky for moving objects on a continual basis.

Astronomers reveal that 2017 PD25 has an absolute magnitude of 25.3 and a diameter between 16 and 52 meters. The asteroid has an orbital period of 3.26 years and a semimajor axis of 2.2 AU.

Besides the close approach on Wednesday, no other fly-bys of this asteroid are known at the moment.

There are 1,803 potentially hazardous asteroids (PHAs) discovered to date. PHAs are space rocks larger than approximately 100 meters that can come closer to Earth than 19.5 LD. However, none of the known PHAs is on a collision course with our planet.

NIBIRU - Melhor Explicação Sobre Nibiru VERSÃO ORIGINAL

O ECLIPSE SOLAR de 21 de Agosto de 2017 | Curiosidades + o Sinal de 23 de Setembro

Gamma-ray Burst Captured in Unprecedented Detail

Gamma-ray Burst Captured in Unprecedented Detail:

Gamma-ray bursts are among the most energetic and explosive events in the universe. They are also short-lived, lasting from a few milliseconds to about a minute. This has made it tough for astronomers to observe a gamma-ray burst in detail. Using a wide array of ground- and space-based telescope observations, an international team led by University of Maryland astronomers constructed one of the most detailed descriptions of a gamma-ray burst to date.

The event, named GRB160625B, revealed key details about the initial “prompt” phase of gamma-ray bursts and the evolution of the large jets of matter and energy that form as a result of the burst. The group’s findings are published in the July 27, 2017 issue of the journal Nature.

“Gamma-ray bursts are catastrophic events, related to the explosion of massive stars 50 times the size of our sun. If you ranked all the explosions in the universe based on their power, gamma-ray bursts would be right behind the Big Bang,” said Eleonora Troja, an assistant research scientist in the UMD Department of Astronomy and lead author of the research paper. “In a matter of seconds, the process can emit as much energy as a star the size of our sun would in its entire lifetime. We are very interested to learn how this is possible.”

The group’s observations provide the first answers to some long-standing questions about how a gamma-ray burst evolves as the dying star collapses to become a black hole. First, the data suggest that the black hole produces a strong magnetic field that initially dominates the energy emission jets. Then, as the magnetic field breaks down, matter takes over and begins to dominate the jets. Most gamma-ray burst researchers thought that the jets were dominated by either matter or the magnetic field, but not both. The current results suggest that both factors play key roles.

“There has been a dichotomy in the community. We find evidence for both models, suggesting that gamma-ray burst jets have a dual, hybrid nature,” said Troja, who is also a visiting research scientist at NASA’s Goddard Space Flight Center. “The jets start off magnetic, but as the jets grow, the magnetic field degrades and loses dominance. Matter takes over and dominates the jets, although sometimes a weaker vestige of the magnetic field might survive.”

The data also suggest that synchrotron radiation—which results when electrons are accelerated in a curved or spiral pathway—powers the initial, extremely bright phase of the burst, known as the “prompt” phase. 

“Synchrotron radiation is the only emission mechanism that can create the same degree of polarization and the same spectrum we observed early in the burst,” Troja said. “Our study provides convincing evidence that the prompt gamma-ray burst emission is driven by synchrotron radiation. This is an important achievement because, despite decades of investigation, the physical mechanism that drives gamma-ray bursts had not yet been unambiguously identified.”

Comprehensive coverage of GRB160625B from a wide variety of telescopes that gathered data in multiple spectra made these conclusions possible, the researchers said.

“Gamma-ray bursts occur at cosmological distances, with some dating back to the birth of the universe,” said Alexander Kutyrev, an associate research scientist in the UMD Department of Astronomy and a co-author of the research paper. “The events are unpredictable and once the burst occurs, it’s gone. We are very fortunate to have observations from a wide variety of sources, especially during the prompt phase, which is very difficult to capture.” 

NASA’s Fermi Gamma-ray Space Telescope first detected the gamma-ray emission from GRB160625B. Soon afterward, the ground-based MASTER-IAC telescope, a part of Russia’s MASTER robotic telescope network located at the Teide Observatory in Spain’s Canary Islands, followed up with optical light observations while the prompt phase was still active. 

MASTER-IAC gathered critical data on the proportion of polarized optical light relative to the total light produced by the prompt phase,, providing the crucial link between synchrotron radiation and the prompt phase of this gamma-ray burst. 

A magnetic field can also influence how much polarized light is emitted as time passes and the burst evolves. Because the researchers were able to analyze polarization data that spanned nearly the entire timeframe of the burst—a rare achievement—they were able to discern the presence of a magnetic field and track how it changed as GRB160625B progressed.

“There is very little data on polarized emission from gamma-ray bursts,” said Kutyrev, who is also an associate scientist at NASA’s Goddard Space Flight Center. “This burst was unique because we caught the polarization state at an early stage. This is hard to do because it requires a very fast reaction time and there are relatively few telescopes with this capability. This paper shows how much can be done, but to get results like this consistently, we will need new rapid-response facilities for observing gamma-ray bursts.”

In addition to the gamma-ray and optical light observations, NASA’s Swift Gamma-ray Burst Mission spacecraft captured X-ray and ultraviolet data. The Reionization and Transient InfraRed/Optical Project camera—a collaboration between NASA, the University of California system and the National Autonomous University of Mexico installed at Mexico’s Observatorio Astrónomico Nacional in Baja California—captured infrared data. 

The group also gathered radio observations from Commonwealth Scientific and Industrial Research Organisation’s Australia Telescope Compact Array, located north of Sydney in rural New South Wales, and the National Radio Astronomy Observatory’s Very Large Array outside of Socorro, New Mexico.

In addition to Troja and Kutyrev, UMD co-authors of this paper include Adjunct Assistant Professor Brad Cenko and Astronomy Graduate Student Vicki Toy.

Credit: umdrightnow.umd.edu

Galactic David and Goliath

Galactic David and Goliath:

The gravitational dance between two galaxies in our local neighborhood has led to intriguing visual features in both as witnessed in this new NASA/ESA Hubble Space Telescope image. The tiny NGC 1510 and its colossal neighbor NGC 1512 are at the beginning of a lengthy merger, a crucial process in galaxy evolution. Despite its diminutive size, NGC 1510 has had a significant effect on NGC 1512’s structure and amount of star formation.

Galaxies come in a range of shapes and sizes, and astronomers use this fact to classify them based on their appearance. NGC 1512, the large galaxy to the left in this image, is classified as a barred spiral, named after the bar composed of stars, gas and dust slicing through its center. The tiny NGC 1510 to the right, on the other hand, is a dwarf galaxy. Despite their very different sizes, each galaxy affects the other through gravity, causing slow changes in their appearances.

The bar in NGC 1512 acts as a cosmic funnel, channeling the raw materials required for star formation from the outer ring into the heart of the galaxy. This pipeline of gas and dust in NGC 1512 fuels intense star birth in the bright, blue, shimmering inner disc known as a circumnuclear starburst ring, which spans 2400 light-years.

Both the bar and the starburst ring are thought to be at least in part the result of the cosmic scuffle between the two galaxies — a merger that has been going on for 400 million years.

NGC 1512, which has been observed by Hubble in the past, is also home to a second, more serene, star-forming region in its outer ring. This ring is dotted with dozens of HII regions, where large swathes of hydrogen gas are subject to intense radiation from nearby, newly formed stars. This radiation causes the gas to glow and creates the bright knots of light seen throughout the ring.

Remarkably, NGC 1512 extends even further than we can see in this image — beyond the outer ring — displaying malformed, tendril-like spiral arms enveloping NGC 1510. These huge arms are thought to be warped by strong gravitational interactions with NGC 1510 and the accretion of material from it. But these interactions are not just affecting NGC 1512; they have also taken their toll on the smaller of the pair.

The constant tidal tugging from its neighbor has swirled up the gas and dust in NGC 1510 and kick-started star formation that is even more intense than in NGC 1512. This causes the galaxy to glow with the blue hue that is indicative of hot new stars.

NGC 1510 is not the only galaxy to have experienced the massive gravitational tidal forces of NGC 1512. Observations made in 2015 showed that the outer regions of the spiral arms of NGC 1512 were indeed once part of a separate, older galaxy. This galaxy was ripped apart and absorbed by NGC 1512, just as it is doing now to NGC 1510.

Together, the pair demonstrate how interactions between galaxies, even if they are of very different sizes, can have a significant influence on their structures, changing the dynamics of their constituent gas and dust and even triggering starbursts. Such interactions between galaxies, and galaxy mergers in particular, play a key role in galactic evolution.

Credit: spacetelescope.org

A Tale of Three Stellar Cities

A Tale of Three Stellar Cities:

Using new observations from ESO’s VLT Survey Telescope, astronomers have discovered three different populations of young stars within the Orion Nebula Cluster. This unexpected discovery adds very valuable new insights for the understanding of how such clusters form. It suggests that star formation might proceed in bursts, where each burst occurs on a much faster time-scale than previously thought.

OmegaCAM — the wide-field optical camera on ESO’s VLT Survey Telescope (VST) — has captured the spectacular Orion Nebula and its associated cluster of young stars in great detail, producing a beautiful new image. This object is one of the closest stellar nurseries for both low and high-mass stars, at a distance of about 1350 light-years.

But this is more than just a pretty picture. A team led by ESO astronomer Giacomo Beccari has used these data of unparallelled quality to precisely measure the brightness and colors of all the stars in the Orion Nebula Cluster. These measurements allowed the astronomers to determine the mass and ages of the stars. To their surprise, the data revealed three different sequences of potentially different ages.

“Looking at the data for the first time was one of those ‘Wow!’ moments that happen only once or twice in an astronomer's lifetime,” says Beccari, lead ­author of the paper presenting the results. “The incredible quality of the OmegaCAM images revealed without any doubt that we were seeing three distinct populations of stars in the central parts of Orion.”

Monika Petr-Gotzens, co-author and also based at ESO Garching, continues, “This is an important result. What we are witnessing is that the stars of a cluster at the beginning of their lives didn’t form altogether simultaneously. This may mean that our understanding of how stars form in clusters needs to be modified.”

The astronomers looked carefully at the possibility that instead of indicating different ages, the different brightnesses and colors of some of the stars were due to hidden companion stars, which would make the stars appear brighter and redder than they really were. But this idea would imply quite unusual properties of the pairs, which have never before been observed. Other measurements of the stars, such as their rotation speeds and spectra, also indicated that they must have different ages.

“Although we cannot yet formally disprove the possibility that these stars are binaries, it seems much more natural to accept that what we see are three generations of stars that formed in succession, within less than three million years,” concludes Beccari.

The new results strongly suggest that star formation in the Orion Nebula Cluster is proceeding in bursts, and more quickly than had been previously thought.

Credit: ESO