DARK MATTER - Cosmologists Produce New Maps of Dark Matter Dynamics

Cosmologists Produce New Maps of Dark Matter Dynamics:

New maps of dark matter dynamics in the Universe have been produced by a team of international cosmologists. Using advanced computer modelling techniques, the research team has translated the distribution of galaxies into detailed maps of matter streams and velocities for the first time. The research was carried out by leading cosmologists from the UK, France and Germany.

Dr Florent Leclercq from the University of Portsmouth’s Institute of Cosmology and Gravitation said: “Dark matter is a substance of yet unknown nature that scientists believe makes up more than 80 per cent of the total mass of the Universe. As it does not emit or react to light, its distribution and evolution are not directly observable and have to be inferred.”

The researchers used legacy survey data obtained during 2000 – 2008 from the Sloan Digital Sky Survey (SDSS), a major three-dimensional survey of the Universe. The survey has deep multi-color images of one fifth of the sky and spectra for more than 900,000 galaxies.

The new dark matter maps cover the Northern Sky up to a distance of 600 megaparsecs, which is the equivalent of looking back about two billion years.

The researchers used a set of phase-space analysis tools and built on research from 2015, which reconstructed the initial conditions of the nearby Universe.

Dr Leclercq said: “Adopting a phase-space approach discloses a wealth of information, which was previously only analysed in simulations and thought to be inaccessible using observations.

“Accessing this information in galaxy surveys opens up new ways of assessing the validity of theoretical models in light of observations.”

The research is published in the Journal of Cosmology and Astroparticle Physics.

Credit: port.ac.uk

GALAXIES - Astronomers Find Young Galaxies that Appeared Soon After the Big Bang

Astronomers Find Young Galaxies that Appeared Soon After the Big Bang:

ASU astronomers Sangeeta Malhotra and James Rhoads, working with international teams in Chile and China, have discovered 23 young galaxies, seen as they were 800 million years after the Big Bang. The results from this sample have been recently published in the Astrophysical Journal.

Long ago, about 300,000 years after the beginning of the universe (the Big Bang), the universe was dark. There were no stars or galaxies, and the universe was filled with neutral hydrogen gas. In the next half-billion years or so, the first galaxies and stars appeared. Their energetic radiation ionized their surroundings, illuminating and transforming the universe.

This dramatic transformation, known as re-ionization, occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang. Astronomers are trying to pinpoint this milestone more precisely, and the galaxies found in this study help in this determination.

“Before re-ionization, these galaxies were very hard to see, because their light is scattered by gas between galaxies, like a car’s headlights in fog,” Malhotra said. “As enough galaxies turn on and ‘burn off the fog’ they become easier to see. By doing so, they help provide a diagnostic to see how much of the ‘fog’ remains at any time in the early universe.”

To detect these galaxies, Malhotra and Rhoads have been using the Dark Energy Camera (DECam), one of the new powerful instruments in the astronomy field. DECam is installed at the National Optical Astronomy Observatory (NOAO)’s 4-meter Blanco Telescope, located at the Cerro Tololo Inter-American Observatory (CTIO), in northern Chile, at an altitude of 7,200 feet.

“Several years ago, we carried out a similar study using a 64-megapixel camera that covers the same amount of sky as the full moon,” Rhoads said. “DECam, by comparison, is a 570-megapixel camera and covers 15 times the area of the full moon in a single image.”

DECam was recently made even more powerful when it was equipped with a special narrowband filter, designed at ASU’s School of Earth and Space Exploration (SESE), primarily by Rhoads and Zhenya Zheng (who was a SESE postdoctoral fellow and is currently at the Shanghai Astronomical Observatory in China), with assistance from Alistair Walker of NOAO.

“We spent several months refining the design of the filter profile, optimizing the design to get maximum sensitivity in our search,” said Zheng, the lead author of this study.

The galaxy search using the ASU-designed filter and DECam is part of the ongoing “Lyman Alpha Galaxies in the Epoch of Reionization” project (LAGER). It is the largest uniformly selected sample that goes far enough back in the history of the universe to reach cosmic dawn.

“The combination of large survey size and sensitivity of this survey enables us to study galaxies that are common but faint, as well as those that are bright but rare, at this early stage in the universe,” said Malhotra.

Junxian Wang, a co-author on this study and the lead of the Chinese LAGER team, adds that “our findings in this survey imply that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

The next steps for the team will be to build on these results. They plan to continue to search for distant star-forming galaxies over a larger volume of the universe and to further investigate the nature of some of the first galaxies in the universe. 

Credit: asu.edu

ASTRONOMY - Large, Distant Comets More Common Than Previously Thought

Large, Distant Comets More Common Than Previously Thought:

Comets that take more than 200 years to make one revolution around the sun are notoriously difficult to study. Because they spend most of their time far from our area of the solar system, many "long-period comets" will never approach the sun in a person's lifetime. In fact, those that travel inward from the Oort Cloud—a group of icy bodies beginning roughly 300 billion kilometers away from the sun—can have periods of thousands or even millions of years.

NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft has delivered new insights about these distant wanderers. A team of astronomers led by James Bauer, a research professor of astronomy at the University of Maryland, found that there are about seven times more long-period comets measuring at least 1 kilometer across than previously predicted.

The researchers also found that long-period comets are, on average, nearly twice as large as "Jupiter family” comets, whose orbits are shaped by Jupiter’s gravity and have periods of less than 20 years. The findings were published July 14, 2017, in The Astronomical Journal.

"The number of comets speaks to the amount of material left over from the solar system's formation," Bauer said. "We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought."

The Oort Cloud is too distant to be seen by current telescopes, but is thought to be a spherical distribution of small icy bodies at the outermost edge of the solar system. The density of comets within it is low, so the odds of comets colliding within it are low. Long-period comets that WISE observed probably got kicked out of the Oort Cloud millions of years ago. The observations were carried out in 2010 during the spacecraft's primary mission, before it was renamed NEOWISE and reactivated to target near-Earth objects (NEOs) in 2013.

"Our study is a rare look at objects perturbed out of the Oort Cloud," said Amy Mainzer, a co-author of the study based at NASA's Jet Propulsion Laboratory in Pasadena, California and principal investigator of the NEOWISE mission. "They are the most pristine examples of what the solar system was like when it formed."

Astronomers already had broader estimates of how many long-period and Jupiter family comets are in our solar system, but had no good way of measuring the sizes of long-period comets. This is because the cloud of gas and dust that surrounds each comet—known as a coma—appears hazy in images and obscures the comet’s nucleus.

By using WISE data that shows the infrared glow of the coma, the scientists were able to "subtract" the coma from each comet and estimate the size of the nucleus. The data came from WISE observations of 164 cometary bodies—including 95 Jupiter family comets and 56 long-period comets.

The results reinforce the idea that comets that pass by the sun more frequently tend to be smaller than those spending much more time away from the sun. That is because Jupiter family comets get more heat exposure, which causes volatile substances like water to sublimate and drag away other material from the comet’s surface as well.

"Our results mean there's an evolutionary difference between Jupiter family and long-period comets," Bauer said.

The existence of so many more long-period comets than predicted suggests that more of them have likely impacted planets, delivering icy materials from the outer reaches of the solar system.

Researchers also found clustered orbits among the long-period comets they studied, suggesting there could have been larger bodies that broke apart to form these groups.

The results will be important for assessing the likelihood of comets impacting our solar system's planets, including Earth.

"Comets travel much faster than asteroids, and some of them are very big," Mainzer said. "Studies like this will help us define what kind of hazard long-period comets may pose." 

NASA's Jet Propulsion Laboratory in Pasadena, California, managed and operated WISE for NASA's Science Mission Directorate in Washington, D.C. The NEOWISE project is funded by the Near-Earth Object Observation Program, now part of NASA’s Planetary Defense Coordination Office. The spacecraft was put into hibernation mode in 2011 after twice scanning the entire sky, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects.

Credit: umd.edu

THE UNIVERSE - International Research Team Sheds Light on the Earth’s ‘Twin Planet’

International Research Team Sheds Light on the Earth’s ‘Twin Planet’:

A research paper published by Nature Astronomy sheds light on the so far unexplored nightside circulation at the upper cloud level of Venus. Researchers from the Rhenish Institute for Environmental Research at the University of Cologne are part of an international research project which has now presented its preliminary findings. They discovered unexpected patterns of slow motion and abundant stationary waves in Venus’s nighttime sky.

Venus is often referred to as Earth's twin because both planets share a similar size and surface composition. Also, they both have atmospheres with complex weather systems. But that is about where the similarities end: Venus is one the most hostile places in our solar system. Its atmosphere consists of 96.5 percent carbon dioxide, with surface temperatures of constantly about 500 degrees Celsius. Venus is a slowly rotating planet – it needs about 243 terrestrial days to complete one rotation. We would expect its atmosphere to rotate with the same rhythm, but in fact it takes only four days. This phenomenon is called superrotation, and it causes substantial turbulences in the planet’s atmosphere. The scientists do not yet fully understand its origin and motor, but are working on an answer to this puzzle. The many waves in the planet's atmosphere may play an important role.

The preliminary research results were generated by an international collaboration headed by the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA). Experts in space and astronautical science and astrophysics from universities and institutions in Japan, Spain, Italy, and Germany are cooperating in the project. From Germany, the Rhenish Institute for Environmental Research at the University of Cologne and the Center for Astronomy and Astrophysics at the Technical University of Berlin are involved.

The research team analysed data generated by the spacecraft Venus Express to investigate components of Venus’s complex atmosphere, including thermal measurements with regard to horizontal and vertical wave patterns. The data also included first global measurements from the tracking of individual features in thermal emission images at 3.8 and 5.0 µm (micrometer) during 2006–2008 and 2015.

Vertical information in unison with horizontal data help to understand the nature of the observed wave patterns. The vertical information from the VeRa instrument (an atmosphere experiment in Venus Express emits radio waves which the scientists then interpret) could help to identify the observed waves as buoyancy waves. This, in turn, is crucial for the analysis of atmospheric processes. 

Dr. Silvia Tellmann is Vice-Director of the Department of Planetary Research at the Rhenish Institute for Environmental Research at the University of Cologne. She is an expert on the structure, dynamics, and circulation of planetary atmospheres and a co-author of the study. ‘We were able to relate the stationary gravity waves found at higher altitudes with the surface elevations of Venus’, she says. ‘Hence, the waves can be explained with wind currents caused by topographical obstacles. We assume that these stationary waves are substantial for the continuity of the superrotation in the atmosphere of Venus.’

Credit: uni-koeln.de

Researchers Show How to Make Your Own Supernova

Researchers Show How to Make Your Own Supernova:

One of the most extreme astrophysical events, supernova explosions are the violent deaths of certain stars that scatter elements heavier than hydrogen and helium into surrounding space. Our own solar system is thought to have formed when a nearby supernova exploded distributing these elements into a cloud of hydrogen that then condensed to form our sun and the planets. In fact, the very atoms that make up our bodies were formed in the remnants of such an explosion.

Working in collaboration with Imperial College, London, and AWE Aldermaston the team, led in Oxford by Professor Gianluca Gregori of the Department of Physics, are currently demonstrating their research at the Royal Society Summer Science Exhibition, a week-long showcase of cutting-edge science from across the UK.

Witnessing and getting to grips with these experiments can help people to understand the inner workings of the Universe. Their ‘How to make a supernova’ exhibit will highlight how lasers like Orion can help us understand and appreciate the origins of the universe.

The team were able to mimic some the properties of these supernovae in the laboratory by using the most powerful lasers on earth, such as the ORION laser at AWE. Each output pulse from the laser only lasts for a few billionths of a second, but, in that time, the power it generates is equivalent to the output of the electricity grid of the whole planet. 

The extremes of density and temperature produced by the lasers allow scientists to study how the supernova acts when it expands into space, and can also provide insight into how high energy particles from space are produced, how the magnetic field in the galaxy formed, and what the interior of a giant planet might look like.

Dr Jena Meinecke, Junior Research Fellow at the University Oxford, said: ‘Lasers are so powerful today that we can actually recreate aspects of tiny supernovae that could fit in the palm of your hand! This allows us to answer fundamental questions such as 'What is the origin of magnetic fields in the universe?' Imagine the possibilities.

‘Our research is helping us better understand some of the most powerful natural processes known to humankind, and more importantly, the origins of our universe.’

Professor Justin Wark, Director of the Oxford Centre for High Energy Density Science (OxCHEDS), said: ‘The Royal Society Exhibition provides an excellent platform to tell the public about the exciting research that is going on in the field of laboratory astrophysics - in particular it is a great opportunity to enthuse young people, who will be the next generation of scientists.’

The ‘How to make a supernova’ research is on display at the Royal Society’s free annual Summer Science Exhibition until 9 July.

Surface of Mars Poses Danger to Life, Tests Show

Surface of Mars Poses Danger to Life, Tests Show:

The environment on Mars may be more harmful to Earth-based life forms than previously thought, experiments by Edinburgh scientists have shown. Researchers investigated the behavior of chemical compounds, called perchlorates, which are found on the surface of the red planet.

They found that, when exposed to UV light whilst in environmental conditions mimicking those on Mars, the chemicals can kill bacteria commonly carried by spacecraft.

Their findings could have implications for potential contamination from robotic and human exploration of Mars.

The study also suggested that the effect of perchlorates can be compounded by two other types of chemicals found on Mars’ surface, iron oxides and hydrogen peroxide.

In experiments in which all three were present, the combination led to a more than 10-fold increase in death of bacterial cells compared with perchlorates alone.

Scientists have speculated on the influence that perchlorates may have on the habitability of the planet, since their discovery there several years ago.

Researchers in the UK Centre for Astrobiology and School of Physics and Astronomy investigated the potential reactivity of perchlorates and their effect on Bacillus subtilis, a bacterium found on spacecraft and common in soils and rocks.

Their experiments showed that when magnesium perchlorate was exposed to UV radiation similar to that on Mars, it became capable of killing bacteria much more effectively than UV light alone.

At concentrations of perchlorate similar to those found on the Martian surface, cells of B. subtilis quickly died.

Although the Martian surface has been suspected for some time to have toxic effects, the latest study suggests that it may be highly damaging to living cells.

This is owing to a toxic mix of oxidants, iron oxides, perchlorates, and UV energy.

"Our findings have important implications for the possible contamination of Mars with bacteria and other materials from space missions. This should be taken into account in designing missions to Mars," said Jennifer Wadsworth of the UK Centre for Astrobiology and School of Physics and Astronomy.

Their study, funded by the Science and Technology Facilities Council, was published in Scientific Reports.

Credit: ed.ac.uk

Understanding Electron Transport in Solar Wind

Understanding Electron Transport in Solar Wind:

The sun constantly emits a flux of electrically charged particles into space, mostly protons and electrons, known as solar wind. This plasma affects the entire solar system, including Earth’s magnetic field and is therefore crucial to our understanding of space weather. Now, a University of Alabama in Huntsville (UAH) student is conducting a research into the transport of electrons and electron heat flux in the solar wind, which could provide new insights about this stream of energized particles emitted by the sun.

Bofeng Tang is a Ph.D. candidate in the Department of Space Science at UAH. He holds a master’s degree in physics and works under the supervision of National Academy of Sciences member Dr. Gary Zank, who serves as both chair of the department and director of UAH’s Center for Space Plasma and Aeronomic Research (CSPAR).

“I am hoping that Bofeng's research will clarify some aspects of the collisionless heat flux associated with the various solar wind electron populations, which will guide us then towards a better description of electron transport throughout the solar wind,” Zank told Astrowatch.net.

Tang has recently received a 2017/2018 NASA Earth and Space Science Fellowship (NESSF). The fellowship includes a $30,000 award and can be renewed for a total of three years.

NASA’s Heliophysics Division, which helps further the space agency’s research objective of investigating the sun and its interactions with the solar system, chose Tang’s study as one of only nine NESSF applications. The fellowship secures funding for Tang’s research and lets him concentrate on in-depth study of the transport of electrons in solar wind.

“The NASA NESSF is important to students, both in terms of the prestige that it typically carries (there are few awarded annually so it is a reflection on the student's potential and also the proposed problem), and in terms of guaranteed support for up to three years. This guarantee of support allows a student to attack a good problem in some depth,” Zank noted.

Backed by NESSF, Tang will focus on solving the problem of how solar wind electrons are transported in the solar wind. This question perplexes researchers and it is still far from being solved, in part because the electrons are quite collisional in the solar corona and below but tend to be collisionless further out from the sun, experiencing scattering primarily due to waves and turbulence.

“Understanding what waves and turbulence is responsible for the scattering of the various electron components (core, strahl, halo, energetic electrons) is still rather unclear. At this point, we cannot even accurately write down the correct set of equations that adequately describes how electrons are transported from one part of the solar wind to another,” Zank said.

Currently, the scientists do not have a fundamentally sound description of electrons in the solar wind. Tang’s research is expected to establish a better framework for understanding the solar wind dynamics implicitly advancing our understanding of space weather.

According to Zank, Tang’s study could also help improve the reputation of CSPAR when it comes to research in the field of physics.

“My Department of Space Science and the Center for Space Plasma and Aeronomic Research at UAH regard our students research as vitally important to making progress in the physics of the space environment and in space weather. This research helps build our growing reputation and the value and importance of it relates both to the fundamental science we explore and also the increased reputation of our students,” Zank concluded.

Supernova Forges Billowing, Tangled Knots of New Molecules

Supernova Forges Billowing, Tangled Knots of New Molecules:

Supernovas — the violent endings of the brief yet brilliant lives of massive stars — are among the most cataclysmic events in the cosmos. Though supernovas mark the death of stars, they also trigger the birth of new elements and the formation of new molecules. In February of 1987, astronomers witnessed one of these events unfold inside the Large Magellanic Cloud, a tiny dwarf galaxy located approximately 163,000 light-years from Earth.

Over the next 30 years, observations of the remnant of that explosion revealed never-before-seen details about the death of stars and how atoms created in those stars — like carbon, oxygen, and nitrogen — spill out into space and combine to form new molecules and dust. These microscopic particles may eventually find their way into future generations of stars and planets.

Recently, astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to probe the heart of this supernova, named SN 1987A. ALMA’s ability to see remarkably fine details allowed the researchers to produce an intricate 3-D rendering of newly formed molecules inside the supernova remnant. These results are published in the Astrophysical Journal Letters.

The researchers also discovered a variety of previously undetected molecules in the remnant. These results appear in the Monthly Notices of the Royal Astronomical Society.

“When this supernova exploded, now more than 30 years ago, astronomers knew much less about the way these events reshape interstellar space and how the hot, glowing debris from an exploded star eventually cools and produces new molecules,” said Rémy Indebetouw, an astronomer at the University of Virginia and the National Radio Astronomy Observatory (NRAO) in Charlottesville. “Thanks to ALMA we can finally see cold ‘star dust’ as it forms, revealing important insights into the original star itself and the way supernovas create the basic building blocks of planets.”

Prior to ongoing investigations of SN 1987A, there was only so much astronomers could say about the impact of supernovas on their interstellar neighborhoods.

It was well understood that massive stars, those approximately 10 times the mass of our sun or more, ended their lives in spectacular fashion.

When these stars run out of fuel, there is no longer enough heat and energy to fight back against the force of gravity. The outer reaches of the star, once held up by the power of fusion, then come crashing down on the core with tremendous force. The rebound of this collapse triggers a powerful explosion that blasts material into space.

As the endpoint of massive stars, scientists have learned that supernovas have far-reaching effects on their home galaxies. To get a better understanding of these effects, Indebetouw helps break down the impact of these star-shattering events. “The reason some galaxies have the appearance that they do today is in large part because of the supernovas that have occurred in them,” he said. “Though less than ten percent of stars become supernovas, they nonetheless are key to the evolution of galaxies.”

Throughout the observable universe, supernovas are quite common, but since they appear – on average – about once every 50 years in a galaxy the size of the Milky Way, astronomers have precious few opportunities to study one from its first detonation to the point where it cools enough to form new molecules. Though SN 1987A is not in our home galaxy, it is still close enough for ALMA and other telescopes to study in fine detail.

This artist's illustration of Supernova 1987A reveals the cold, inner regions of the exploded star's remnants (red) where tremendous amounts of dust were detected and imaged by ALMA. This inner region is contrasted with the outer shell (blue), where the energy from the supernova is colliding (green) with the envelope of gas ejected from the star prior to its powerful detonation. Credit: A. Angelich; NRAO/AUI/NSF

For decades, radio, optical, and even X-ray observatories have studied SN 1987A, but obscuring dust in the remnant made it difficult to analyze the supernova’s innermost core. ALMA’s ability to observe at millimeter wavelengths – a region of the electromagnetic spectrum between infrared and radio light – make it possible to see through the intervening dust and gas. The researchers were then able to study the abundance and location of newly formed molecules – especially silicon monoxide (SiO) and carbon monoxide (CO), which shine brightly at the short submillimeter wavelengths that ALMA can perceive.

The new ALMA image and animation show vast new stores of SiO and CO in discrete, tangled clumps within the core of SN 1987A. Scientists previously modeled how and where these molecules would appear. With ALMA, the researchers finally were able to capture images with high enough resolution to confirm the structure inside the remnant and test those models.

Aside from obtaining this 3-D image of SN 1987A, the ALMA data also reveal compelling details about how its physical conditions have changed and continue to change over time. These observations also provide insights into the physical instabilities inside a supernova.

Earlier observations with ALMA verified that SN 1987A produced a massive amount of dust. The new observations provide even more details on how the supernova made the dust as well as the type of molecules found in the remnant.

“One of our goals was to observe SN 1987A in a blind search for other molecules,” said Indebetouw. “We expected to find carbon monoxide and silicon monoxide, since we had previously detected these molecules.” The astronomers, however, were excited to find the previously undetected molecules formyl cation (HCO+) and sulfur monoxide (SO).

“These molecules had never been detected in a young supernova remnant before,” noted Indebetouw. “HCO+ is especially interesting because its formation requires particularly vigorous mixing during the explosion.” Stars forge elements in discrete onion-like layers. As a star goes supernova, these once well-defined bands undergo violent mixing, helping to create the environment necessary for molecule and dust formation.

The astronomers estimate that about 1 in 1000 silicon atoms from the exploded star is now found in free-floating SiO molecules. The overwhelming majority of the silicon has already been incorporated into dust grains. Even the small amount of SiO that is present is 100 times greater than predicted by dust-formation models. These new observations will aid astronomers in refining their models.

These observations also find that ten percent or more of the carbon inside the remnant is currently in CO molecules. Only a few out of every million carbon atoms are in HCO+ molecules.

Even though the new ALMA observations shed important light on SN 1987A, there are still several questions that remain. Exactly how abundant are the molecules of HCO+ and SO? Are there other molecules that have yet to be detected? How will the 3-D structure of SN 1987A continue to change over time?

Future ALMA observations at different wavelengths may also help determine what sort of compact object — a pulsar or neutron star — resides at the center of the remnant. The supernova likely created one of these dense stellar objects, but as yet none has been detected.

Credit: nrao.edu

Astronomers Track the Birth of a 'Super-Earth'

Astronomers Track the Birth of a 'Super-Earth':

A new model giving rise to young planetary systems offers a fresh solution to a puzzle that has vexed astronomers ever since new detection technologies and planet-hunting missions such as NASA's Kepler space telescope have revealed thousands of planets orbiting other stars: While the majority of these exoplanets fall into a category called super-Earths — bodies with a mass somewhere between Earth and Neptune — most of the features observed in nascent planetary systems were thought to require much more massive planets, rivaling or dwarfing Jupiter, the gas giant in our solar system.

In other words, the observed features of many planetary systems in their early stages of formation did not seem to match the type of exoplanets that make up the bulk of the planetary population in our galaxy. 

"We propose a scenario that was previously deemed impossible: how a super-Earth can carve out multiple gaps in disks," says Ruobing Dong, the Bart J. Bok postdoctoral fellow at the University of Arizona's Steward Observatory and lead author on the study, soon to be published in the Astrophysical Journal. "For the first time, we can reconcile the mysterious disk features we observe and the population of planets most commonly found in our galaxy." 

How exactly planets form is still an open question with a number of outstanding problems, according to Dong. 

"Kepler has found thousands of planets, but those are all very old, orbiting around stars a few billion years old, like our sun," he explains. "You could say we are looking at the senior citizens of our galaxy, but we don't know how they were born."

To find answers, astronomers turn to the places where new planets are currently forming: protoplanetary disks — in a sense, baby sisters of our solar system. 

Such disks form when a vast cloud of interstellar gas and dust condenses under the effect of gravity before collapsing into a swirling disk. At the center of the protoplanetary disk shines a young star, only a few million years old. As microscopic dust particles coalesce to sand grains, and sand grains stick together to form pebbles, and pebbles pile up to become asteroids and ultimately planets, a planetary system much like our solar system is born. 

"These disks are very short-lived," Dong explains. "Over time the material dissipates, but we don't know exactly how that happens. What we do know is that we see disks around stars that are 1 million years old, but we don't see them around stars that are 10 million years old."

In the most likely scenario, much of the disk's material gets accreted onto the star, some is blown away by stellar radiation and the rest goes into forming planets. 

Although protoplanetary disks have been observed in relative proximity to the Earth, it is still extremely difficult to make out any planets that may be forming within. Rather, researchers have relied on features such as gaps and rings to infer the presence of planets. 

"Among the explanations for these rings and gaps, those involving planets certainly are the most exciting and drawing the most attention," says co-author Shengtai Li, a research scientist at Los Alamos National Laboratory in Los Alamos, New Mexico. "As the planet orbits around the star, the argument goes, it may clear a path along its orbit, resulting in the gap we see."

Except that reality is a bit more complicated, as evidenced by two of the most prominent observations of protoplanetary disks, which were made with ALMA, the Atacama Large Millimeter/submillimeter Array in Chile. ALMA is an assembly of radio antennas between 7 and 12 meters in diameter and numbering 66 of them once completed. The images of HL Tau and TW Hydra, obtained in 2014 and 2016, respectively, have revealed the finest details so far in any protoplanetary disk, and they show some features that are difficult, if not impossible, to explain with current models of planetary formation, Dong says. 

"Among the gaps in HL Tau and TW Hya revealed by ALMA, two pairs of them are extremely narrow and very close to each other," he explains. "In conventional theory, it is difficult for a planet to open such gaps in a disk. They can never be this narrow and this close to each other for reasons of the physics involved." 

In the case of HL Tau and TW Hya, one would have to invoke two planets whose orbits hug each other very closely — a scenario that would not be stable over time and therefore is unlikely. 

While previous models could explain large, single gaps believed to be indicative of planets clearing debris and dust in their path, they failed to account for the more intricate features revealed by the ALMA observations. 

The model created by Dong and his co-authors results in what the team calls synthetic observations — simulations that look exactly like what ALMA would see on the sky. Dong's team accomplished this by tweaking the parameters going into the simulation of the evolving protoplanetary disk, such as assuming a low viscosity and adding the dust to the mix. Most previous simulations were based on higher disk viscosity and accounted only for the disk's gaseous component. 

"The viscosity in protoplanetary disks may be driven by turbulence and other physical effects," Li says. "It's a somewhat mysterious quantity — we know it's there, but we don't know its origin or how large its value is, so we think our assumptions are reasonable, considering that they result in the pattern that has actually been observed on the sky." 

Even more important, the synthetic observations emerged from the simulations without the necessity to invoke gas giants the size of Jupiter or larger. 

"One super-Earth turned out to be sufficient to create the multiple rings and multiple, narrow gaps we see in the actual observations," Dong says. 

As future research uncovers more of the inner workings of protoplanetary disks, Dong and his team will refine their simulations with new data. For now, their synthetic observations offer an intriguing scenario that provides a missing link between the features observed in many planetary infants and their grown-up counterparts. 

The study, "Multiple Disk Gaps and Rings Generated by a Single Super-Earth," by Ruobing Dong, Shentai Li, Eugene Chiang and Hui Li, will be published on July 13 in the Astrophysical Journal. 

Credit: arizona.edu

Juno Completes Flyby over Jupiter’s Great Red Spot

Juno Completes Flyby over Jupiter’s Great Red Spot:

NASA's Juno mission completed a close flyby of Jupiter and its Great Red Spot on July 10, during its sixth science orbit. All of Juno's science instruments and the spacecraft's JunoCam were operating during the flyby, collecting data that are now being returned to Earth. Juno's next close flyby of Jupiter will occur on Sept. 1. Raw images from the spacecraft’s latest flyby will be posted in coming days.

"For generations people from all over the world and all walks of life have marveled over the Great Red Spot," said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. "Now we are finally going to see what this storm looks like up close and personal."

The Great Red Spot is a 10,000-mile-wide (16,000-kilometer-wide) storm that has been monitored since 1830 and has possibly existed for more than 350 years. In modern times, the Great Red Spot has appeared to be shrinking. 

Juno reached perijove (the point at which an orbit comes closest to Jupiter's center) on July 10 at 6:55 p.m. PDT (9:55 p.m. EDT). At the time of perijove, Juno was about 2,200 miles (3,500 kilometers) above the planet's cloud tops. Eleven minutes and 33 seconds later, Juno had covered another 24,713 miles (39,771 kilometers), and was passing directly above the coiling crimson cloud tops of the Great Red Spot. The spacecraft passed about 5,600 miles (9,000 kilometers) above the clouds of this iconic feature.

On July 4 at 7:30 p.m. PDT (10:30 p.m. EDT), Juno logged exactly one year in Jupiter orbit, marking 71 million miles (114.5 million kilometers) of travel around the giant planet.

Juno launched on Aug. 5, 2011, from Cape Canaveral, Florida. During its mission of exploration, Juno soars low over the planet's cloud tops -- as close as about 2,100 miles (3,400 kilometers). During these flybys, Juno is probing beneath the obscuring cloud cover of Jupiter and studying its auroras to learn more about the planet's origins, structure, atmosphere and magnetosphere.

Early science results from NASA's Juno mission portray the largest planet in our solar system as a turbulent world, with an intriguingly complex interior structure, energetic polar aurora, and huge polar cyclones.

JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute. The Juno mission is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, for the Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is a division of Caltech in Pasadena.

Credit: missionjuno.swri.edu

Hidden Stars May Make Planets Appear Smaller

Hidden Stars May Make Planets Appear Smaller:

In the search for planets similar to our own, an important point of comparison is the planet's density. A low density tells scientists a planet is more likely to be gaseous like Jupiter, and a high density is associated with rocky planets like Earth. But a new study suggests some are less dense than previously thought because of a second, hidden star in their systems.

As telescopes stare at particular patches of sky, they can't always differentiate between one star and two. A system of two closely orbiting stars may appear in images as a single point of light, even from sophisticated observatories such as NASA's Kepler space telescope. This can have significant consequences for determining the sizes of planets that orbit just one of these stars, says a forthcoming study in the Astronomical Journal by Elise Furlan of Caltech/IPAC-NExScI in Pasadena, California, and Steve Howell at NASA's Ames Research Center in California's Silicon Valley.

"Our understanding of how many planets are small like Earth, and how many are big like Jupiter, may change as we gain more information about the stars they orbit," Furlan said. "You really have to know the star well to get a good handle on the properties of its planets."

Some of the most well-studied planets outside our solar system -- or exoplanets -- are known to orbit lone stars. We know Kepler-186f, an Earth-size planet in the habitable zone of its star, orbits a star that has no companion (the habitable zone is the distance at which a rocky planet could support liquid water on its surface). TRAPPIST-1, the ultra-cool dwarf star that is home to seven Earth-size planets, does not have a companion either. That means there is no second star complicating the estimation of the planets' diameters, and therefore their densities.

But other stars have a nearby companion, high-resolution imaging has recently revealed. David Ciardi, chief scientist at the NASA Exoplanet Science Institute (NExScI) at Caltech, led a large-scale effort to follow up on stars that Kepler had studied using a variety of ground-based telescopes. This, combined with other research, has confirmed that many of the stars where Kepler found planets have binary companions. In some cases, the diameters of the planets orbiting these stars were calculated without taking the companion star into consideration. That means estimates for their sizes should be smaller, and their densities higher, than their true values. 

Previous studies determined that roughly half of all the sun-like stars in our sun's neighborhood have a companion within 10,000 astronomical units (an astronomical unit is equal to the average distance between the sun and Earth, 93 million miles or 150 million kilometers). Based on this, about 15 percent of stars in the Kepler field could have a bright, close companion -- meaning planets around these stars may be less dense than previously thought. 

When a telescope spots a planet crossing in front of its star -- an event called a "transit" -- astronomers measure the resulting apparent decrease in the star's brightness. The amount of light blocked during a transit depends on the size of the planet -- the bigger the planet, the more light it blocks, and the greater the dimming that is observed. Scientists use this information to determine the radius -- half the diameter -- of the planet.

If there are two stars in the system, the telescope measures the combined light of both stars. But a planet orbiting one of these stars will cause just one of them to dim. So, if you don't know that there is a second star, you will underestimate the size of the planet.

For example, if a telescope observes that a star dims by 5 percent, scientists would determine the transiting planet's size relative to that one star. But if a second star adds its light, the planet must be larger to cause the same amount of dimming.

If the planet orbits the brighter star in a binary pair, most of the light in the system comes from that star anyway, so the second star won't have a big effect on the planet's calculated size. But if the planet orbits the fainter star, the larger, primary star contributes more light to the system, and the correction to the calculated planet radius can be large -- it could double, triple or increase even more. This will affect how the planet's orbital distance is calculated, which could impact whether the planet is found to be in the habitable zone.

If the stars are roughly equal in brightness, the "new" radius of the planet is about 40 percent larger than if the light were assumed to come from a single star. Because density is calculated using the cube of the radius, this would mean a nearly three-fold decrease in density. The impact of this correction is most significant for smaller planets because it means a planet that had once been considered rocky could, in fact, be gaseous.

In the new study, Furlan and Howell focused on 50 planets in the Kepler observatory's field of view whose masses and radii were previously estimated. These planets all orbit stars that have stellar companions within about 1,700 astronomical units. For 43 of the 50 planets, previous reports of their sizes did not take into account the contribution of light from a second star. That means a revision to their reported sizes is necessary.

In most cases, the change to the planets' reported sizes would be small. Previous research showed that 24 of the 50 planets orbit the bigger, brighter star in a binary pair. Moreover, Furlan and Howell determined that 11 of these planets would be too large to be planets if they orbited the fainter companion star. So, for 35 of the 50 planets, the published sizes will not change substantially.

But for 15 of the planets, they could not determine whether they orbit the fainter or the brighter star in a binary pair. For five of the 15 planets, the stars in question are of roughly equal brightness, so their densities will decrease substantially regardless of which star they orbit.

This effect of companion stars is important for scientists characterizing planets discovered by Kepler, which has found thousands of exoplanets. It will also be significant for NASA's upcoming Transiting Exoplanet Survey Satellite (TESS) mission, which will look for small planets around nearby, bright stars and small, cool stars.

"In further studies, we want to make sure we are observing the type and size of planet we believe we are," Howell said. "Correct planet sizes and densities are critical for future observations of high-value planets by NASA's James Webb Space Telescope. In the big picture, knowing which planets are small and rocky will help us understand how likely we are to find planets the size of our own elsewhere in the galaxy."

Credit: NASA

Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages

Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages:

Astronomers studying the distant Universe have found that small star-forming galaxies were abundant when the Universe was only 800 million years old, a few percent of its present age. The results suggest that the earliest galaxies, which illuminated and ionized the Universe, formed at even earlier times.

Long ago, about 300,000 years after the beginning of the Universe (the Big Bang), the Universe was dark. There were as yet no stars and galaxies, and the Universe was filled with neutral hydrogen gas. At some point the first galaxies appeared, and their energetic radiation ionized their surroundings, the intergalactic gas, illuminating and transforming the Universe.

While this dramatic transformation is known to have occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang, determining when the first galaxies formed is a challenge. The intergalactic gas, which is initially neutral, strongly absorbs and scatters the ultraviolet light emitted by the galaxies, making them difficult to detect.

To home in on when the transformation occurred, astronomers take an indirect approach. Using the demographics of small star-forming galaxies to determine when the intergalactic gas became ionized, they can infer when the ionizing sources, the first galaxies, formed. If star forming galaxies, which glow in the light of the hydrogen Lyman alpha line, are surrounded by neutral hydrogen gas, the Lyman alpha photons are readily scattered, much like headlights in fog, obscuring the galaxies. When the gas is ionized, the fog lifts, and the galaxies are easier to detect.

A new study taking this approach has discovered 23 candidate Lyman alpha emitting galaxies (LAEs) that were present 800 million years after the Big Bang (at a redshift of z~7), the largest sample detected to date at that epoch. The study, “Lyman-Alpha Galaxies in the Epoch of Reionization” (LAGER), was carried out by an international team of astronomers from China, the US, and Chile using the Dark Energy Camera (DECam) on the CTIO 4-m Blanco telescope.

While the study detected many LAEs, it also found that LAEs were 4 times less common at 800 million years than they were a short time later, at 1 billion years (at a redshift of z~5.7). The results imply that the process of ionizing the Universe began early and was still incomplete at 800 million years, with the intergalactic gas about half neutral and half ionized at that epoch. The low incidence rate of LAEs at 800 million years results from the suppression of their Lyman alpha emission by neutral intergalactic gas.

The study shows that “the fog was already lifting when the universe was 5% of its current age”, explained Sangeeta Malhotra (Goddard Space Flight Center and Arizona State University), one of the co-leads of the survey.

Junxian Wang (USTC), the organizer of the study, further explained, “Our finding that the intergalactic gas is 50% ionized at z ~ 7 implies that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

For Zhenya Zheng (Shanghai Astronomical Observatory, CAS), the lead author of the paper describing these results, “800 million years is the current frontier in reionization studies.” While hundreds of LAEs have been found at later epochs, only about two dozen candidate LAEs were known at 800 million years prior to the current study. The new results dramatically increase the number of LAEs known at this epoch.

“None of this science would have been possible without the widefield capabilities of DECam and its community pipeline for data reduction,” remarked coauthor James Rhoads. “These capabilities enable efficient surveys and thereby the discovery of faint galaxies as well as rare, bright ones.”

To build on these results, the team is “continuing the search for distant star forming galaxies over a larger volume of the Universe”, said Leopoldo Infante (Pontificia Catolica University of Chile and the Carnegie Institution for Science), “to study the clustering of LAEs.” Clustering provides unique insights into how the fog lifts. The team is also investigating the nature of these distant galaxies.

Credit: noao.edu

New Evidence in Support of the Planet Nine Hypothesis

New Evidence in Support of the Planet Nine Hypothesis:

Last year, the existence of an unknown planet in our solar system was announced. However, this hypothesis was subsequently called into question as biases in the observational data were detected. Now Spanish astronomers have used a novel technique to analyse the orbits of the so-called extreme trans-Neptunian objects and, once again, they point out that there is something perturbing them: a planet located at a distance between 300 to 400 times the Earth-Sun separation.

Scientists continue to argue about the existence of a ninth planet within our solar system. At the beginning of 2016, researchers from the California Institute of Technology (Caltech, USA) announced that they had evidence of the existence of this object, located at an average distance of 700 AU or astronomical units (700 times the Earth-Sun separation) and with a mass ten times that of the Earth. Their calculations were motivated by the peculiar distribution of the orbits found for the trans-Neptunian objects (TNO) of the Kuiper belt, which apparently revealed the presence of a Planet Nine or X in the confines of the solar system.

However, scientists from the Canadian-French-Hawaiian project OSSOS detected biases in their own observations of the orbits of the TNOs, which had been systematically directed towards the same regions of the sky, and considered that other groups, including the Caltech group, may be experiencing the same issues. According to these scientists, it is not necessary to propose the existence of a massive perturber (a Planet Nine) to explain these observations, as these are compatible with a random distribution of orbits.

Now, however, two astronomers from the Complutense University of Madrid have applied a new technique, less exposed to observational bias, to study a special type of trans-Neptunian objects: the extreme ones (ETNOs, located at average distances greater than 150 AU and that never cross Neptune's orbit). For the first time, the distances from their nodes to the Sun have been analysed, and the results, published in the journal ‘MNRAS: Letters’, once again indicate that there is a planet beyond Pluto.

The nodes are the two points at which the orbit of an ETNO, or any other celestial body, crosses the plane of the solar system. These are the precise points where the probability of interacting with other objects is the largest, and therefore, at these points, the ETNOs may experience a drastic change in their orbits or even a collision.

“If there is nothing to perturb them, the nodes of these extreme trans-Neptunian objects should be uniformly distributed, as there is nothing for them to avoid, but if there are one or more perturbers, two situations may arise,” explains Carlos de la Fuente Marcos, one of the authors, to SINC. “One possibility is that the ETNOs are stable, and in this case they would tend to have their nodes away from the path of possible perturbers, he adds, but if they are unstable they would behave as the comets that interact with Jupiter do, that is tending to have one of the nodes close to the orbit of the hypothetical perturber”.

Using calculations and data mining, the Spanish astronomers have found that the nodes of the 28 ETNOs analysed (and the 24 extreme Centaurs with average distances from the Sun of more than 150 AU) are clustered in certain ranges of distances from the Sun; furthermore, they have found a correlation, where none should exist, between the positions of the nodes and the inclination, one of the parameters which defines the orientation of the orbits of these icy objects in space.

“Assuming that the ETNOs are dynamically similar to the comets that interact with Jupiter, we interpret these results as signs of the presence of a planet that is actively interacting with them in a range of distances from 300 to 400 AU,” says De la Fuente Marcos, who emphasizes: “We believe that what we are seeing here cannot be attributed to the presence of observational bias”.

Until now, studies that challenged the existence of Planet Nine using the data available for these trans-Neptunian objects argued that there had been systematic errors linked to the orientations of the orbits (defined by three angles), due to the way in which the observations had been made. Nevertheless, the nodal distances mainly depend on the size and shape of the orbit, parameters which are relatively free of observational bias.

“It is the first time that the nodes have been used to try to understand the dynamics of the ETNOs”, the co-author points out, as he admits that discovering more ETNOs (at the moment, only 28 are known) would permit the proposed scenario to be confirmed and subsequently constrain the orbit of the unknown planet via the analysis of the distribution of the nodes.

The authors note that their study supports the existence of a planetary object within the range of parameters considered both in the Planet Nine hypothesis of Mike Brown and Konstantin Batygin from Caltech, and in the original one proposed in 2014 by Scott Sheppard from the Carnegie Institute and Chadwick Trujillo from the University of North Arizona; in addition to following the lines of their own earlier studies (the latest led by the Instituto de Astrofísica de Canarias), which suggested that there is more than one unknown planet in our solar system.

De la Fuente Marcos explains that the hypothetical Planet Nine suggested in this study has nothing to do with another possible planet or planetoid situated much closer to us, and hinted at by other recent findings. Also applying data mining to the orbits of the TNOs of the Kuiper Belt, astronomers Kathryn Volk and Renu Malhotra from the University of Arizona (USA) have found that the plane on which these objects orbit the Sun is slightly warped, a fact that could be explained if there is a perturber of the size of Mars at 60 AU from the Sun.

“Given the current definition of planet, this other mysterious object may not be a true planet, even if it has a size similar to that of the Earth, as it could be surrounded by huge asteroids or dwarf planets,” explains the Spanish astronomer, who goes on to say: “In any case, we are convinced that Volk and Malhotra's work has found solid evidence of the presence of a massive body beyond the so-called Kuiper Cliff, the furthest point of the trans-Neptunian belt, at some 50 AU from the Sun, and we hope to be able to present soon a new work which also supports its existence”.

Credit: agenciasinc.es