среда, 19 июня 2019 г.

ESA’s new mission to intercept a comet

ESA — Comet Interceptor Mission logo.

19 June 2019

‘Comet Interceptor’ has been selected as ESA’s new fast-class mission in its Cosmic Vision Programme. Comprising three spacecraft, it will be the first to visit a truly pristine comet or other interstellar object that is only just starting its journey into the inner Solar System.

Comet Interceptor concept

The mission will travel to an as-yet undiscovered comet, making a flyby of the chosen target when it is on the approach to Earth’s orbit. Its three spacecraft will perform simultaneous observations from multiple points around the comet, creating a 3D profile of a ‘dynamically new’ object that contains unprocessed material surviving from the dawn of the Solar System.

“Pristine or dynamically new comets are entirely uncharted and make compelling targets for close-range spacecraft exploration to better understand the diversity and evolution of comets,” says Günther Hasinger, ESA’s Director of Science.

“The huge scientific achievements of Giotto and Rosetta – our legacy missions to comets – are unrivalled, but now it is time to build upon their successes and visit a pristine comet, or be ready for the next ‘Oumuamua-like interstellar object.”

What is a Fast mission?

Comet Interceptor is a ‘fast’, or F-class mission. The ‘fast’ refers to the implementation time, with a total development duration from selection to launch readiness of about eight years. F-class missions, which have a launch mass of less than 1000 kg, will share the ride into space with a medium-class mission, taking advantage of additional space in the launcher and the boost to the Sun-Earth Lagrange point L2, which is 1.5 million kilometres ‘behind’ Earth as viewed from the Sun.

Comet Interceptor is foreseen for launch as co-passenger with ESA’s exoplanet-studying Ariel spacecraft in 2028. Both missions will be delivered to L2 and from there Comet Interceptor will journey onwards to the chosen target using its own propulsion system.


The selection process has also been fast. Following a call for missions in July 2018, 23 pitches were submitted by the space science community, with six teams subsequently invited to provide more detailed proposals. Among them, Comet Interceptor was chosen at today’s Science Programme Committee to move into a more detailed definition phase.

«We thank the space science community for their excellent proposals, which covered a broad range of novel topics that could be explored within the constraints of the F-class guidelines,» says Director Hasinger.

 «This type of innovative mission will play an important role in supplementing ESA’s Science Programme as we plan for the next decades of scientific exploration of our Universe.

«We are also happy to maintain the ‘fast’ mission philosophy by selecting Comet Interceptor within a year since the original call for proposals was made.»

What new about Comet Interceptor?

Comet Interceptor comprises three spacecraft. The composite spacecraft will wait at L2 for a suitable target, then travel together before the three modules separate a few weeks prior to intercepting the comet. Each module will be equipped with a complementary science payload, providing different perspectives of the comet’s nucleus and its gas, dust, and plasma environment. Such ‘multi-point’ measurements will greatly improve the 3D information needed to understand the dynamic nature of a pristine comet while it is interacting with the constantly changing solar wind environment.

The mission’s instrument suite will draw on heritage from other missions, including a camera based on the one currently flying on the ExoMars Trace Gas Orbiter, along with dust, fields and plasma instruments, as well as a mass spectrometer, like those that flew on ESA’s Rosetta.

Previous comet missions, including ESA’s pioneering spacecraft Giotto and Rosetta, encountered short-period comets. These are comets with orbital periods of less than 200 years that have approached the Sun many times along their orbits in relatively recent times and as a consequence have undergone significant changes: Rosetta’s comet, 67P/Churyumov-Gerasimenko orbits the Sun once every 6.5 years while Comet 1P/Halley, visited by Giotto and other spacecraft in 1986, returns to our skies every 76 years.

Kuiper Belt and Oort Cloud in context

Comet Interceptor is different because it will target a comet visiting the inner Solar System for the first time – perhaps from the vast Oort cloud that is thought to surround the outer reaches of the Sun’s realm. As such, the comet will contain material that has not undergone much processing since the dawn of the Sun and planets. The mission will therefore offer a new insight into the evolution of comets as they migrate inwards from the periphery of the Solar System.

Although much rarer, another example of a potential target is an interstellar interloper from another star system, like the famed ‘Oumuamua that flew past our Sun on a highly inclined orbit in 2017. Studying an interstellar object would offer the chance to explore how comet-like bodies form and evolve in other star systems.

In the past, ‘new’ comets have only been discovered a few months to years before they pass through their closest approach to the Sun, which is too short notice to plan, build and launch a space mission, and for it to travel  to the specific object before it moves away from the Sun again.

Artist impression of ‘Oumuamua

Recent advances in ground-based surveys mean that the sky can be scanned more deeply and longer notice can be provided. Pan-STARRS is currently the most proliferous comet discovery machine, with more than half of all new comets per year uncovered by the survey. The Large Synoptic Survey Telescope, currently under construction in Chile, will also greatly increase the catalogue of new comets.

In any case, the destination for Comet Interceptor does not need to be known while the mission is being prepared; the spacecraft can be ready and waiting in space for a suitable comet encounter, and is expected to complete its mission within five years of launch.

Notes for editors:

The Comet Interceptor proposal team comprises an international group of experts led by Geraint Jones (UCL Mullard Space Science Laboratory, UK) and Colin Snodgrass (University of Edinburgh, UK). Find out more on the proposing team’s website: http://www.cometinterceptor.space

Related links:

Cosmic Vision Programme: http://sci.esa.int/cosmic-vision/

Giotto: http://www.esa.int/Our_Activities/Space_Science/Giotto_overview

Rosetta: http://www.esa.int/Our_Activities/Space_Science/Rosetta

Ariel: http://sci.esa.int/ariel/

ExoMars: http://www.esa.int/Our_Activities/Human_and_Robotic_Exploration/Exploration/ExoMars

Pan-STARRS: https://www.ifa.hawaii.edu/research/Pan-STARRS.shtml

Large Synoptic Survey Telescope: https://www.lsst.org/

What are Lagrange points?: http://www.esa.int/Our_Activities/Operations/What_are_Lagrange_points

Images, Text, Credits: ESA/Hubble, NASA, ESO, M. Kornmesser.

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China reveals scientific experiments for its next space station

CNSA — China National Space Administration logo.

19 June 2019

Projects will probe topics including DNA mutation, fire behaviour and the birth of stars.

Image above: Chinese astronauts are scheduled to have their own major space station from 2022.Image Credits: Chen Bin/Xinhua/Zuma.

China has selected nine scientific experiments — including a project that will probe how DNA mutates in space — to fly on its first major space station, scheduled to be completed in 2022.

The China Manned Space Agency selected the projects, which involve scientists from 17 nations, from 42 hopefuls, in a process organized with the United Nations Office for Outer Space Affairs (UNOOSA).

China’s existing space laboratory, Tiangong-2, which launched in 2016, also hosts experiments, but the new space station will be bigger and is intended to last longer. Known as the China Space Station, the outpost will be less than one-quarter of the mass of the International Space Station (ISS).

The science projects cover similar topics to experiments that have flown on the ISS since its launch in 1998, including fluid and fire behaviour, biology and astronomy.

Scientists working on the projects hail from spacefaring nations such as Russia, Japan and India, as well as low- and middle-income countries including Kenya, Mexico and Peru — the result of a special effort to encourage participation from such nations. “The cooperation takes into account the special needs of developing countries, which were encouraged to submit joint project applications with developed countries,” said Wang Qun, China’s ambassador to the United Nations in Vienna, in a statement.

Tiangong-1 and Shenzou-9 docking. Image Credit: China News

The experiments include an Indian–Russian observatory called Spectroscopic Investigations of Nebular Gas, which will map dust clouds and star-forming regions of space using ultraviolet light. A group of European institutions, meanwhile, will study how microgravity and radiation in space affect the mutation of DNA in human ‘organoids’ — 3D biological structures that mimic organs. And a Saudi Arabian team will test how solar cells perform on the outside of the space station.

Other winners include a detector called POLAR-2, a more powerful follow-up to a sensor launched on Tiangong-2 to study the polarization of energetic γ-ray bursts from distant cosmic phenomena. POLAR-2, which will be built by an international collaboration, could even allow astronomers to observe the weak radiation associated with sources of gravitational waves.

But none of the experiments come from the United States, which since 2011 has forbidden NASA researchers from collaborating with China without congressional approval. A spokesperson for UNOOSA told Nature that US scientists were eligible to take part and were involved in several applications, but those projects weren’t ultimately selected.

The United States is planning to cut its funding for the ISS from 2024, as it concentrates its space efforts on building an outpost in the Moon’s orbit from 2022. This could mean that the Chinese space station becomes scientists’ only laboratory in low Earth orbit from 2024.

Related links:

CASC: http://english.spacechina.com/n16421/index.html

CNSA: http://www.cnsa.gov.cn/

Images (mentioned), Text, Credits: Nature/Elizabeth Gibney.

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Self-healing Nerves Your brain and spinal cord are connected…

Self-healing Nerves

Your brain and spinal cord are connected to the rest of your body through a delicate network of nerves. Injury to these nerves causing loss of communication with the brain can result in severe and life-long disabilities. Scientists are keen to learn more about how some species, like the tiny roundworm C. elegans, spontaneously repair damaged nerve fibres through a process called axonal fusion. Now researchers have identified a specific protein, called GTPase RAB-5, which prevents nerve fibre fragments from fusing back together. When this protein was blocked, the fusion process was restored. This image shows one such repaired roundworm neuron (repeated) with different proteins fluorescently coloured. In future, this new knowledge could be applied to encourage nerve fibres to heal and even bring about long-term recovery for patients with peripheral and central nerve injuries.

Written by Gaëlle Coullon

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Jupiter-like exoplanets found in sweet spot in most planetary systems

As planets form in the swirling gas and dust around young stars, there seems to be a sweet spot where most of the large, Jupiter-like gas giants congregate, centered around the orbit where Jupiter sits today in our own solar system.

Jupiter-like exoplanets found in sweet spot in most planetary systems
Results of the survey of 531 stars and their exoplanets in the southern sky are plotted to indicate their distance from 
Earth. Gray dots are stars without exoplanets or a dust disk; red are stars with a dust disk but no planets; blue 
stars have planets. Dots with rings indicated stars imaged multiple times [Credit: Paul Kalas, UC Berkeley; 
Dmitry Savransky, Cornell; Robert De Rosa, Stanford]

The location of this sweet spot is between 3 and 10 times the distance Earth sits from our sun (3-10 astronomical units, or AU). Jupiter is 5.2 AU from our sun.

That’s just one of the conclusions of an unprecedented analysis of 300 stars captured by the Gemini Planet Imager, or GPI, a sensitive infrared detector mounted on the 8-meter Gemini South telescope in Chile.

The GPI Exoplanet Survey, or GPIES, is one of two large projects that search for exoplanets directly, by blocking stars’ light and photographing the planets themselves, instead of looking for telltale wobbles in the star — the radial velocity method — or for planets crossing in front of the star — the transit technique. The GPI camera is sensitive to the heat given off by recently-formed planets and brown dwarfs, which are more massive than gas giant planets, but still too small to ignite fusion and become stars.

The analysis of the first 300 of more than 500 stars surveyed by GPIES, published in the The Astronomical Journal, «is a milestone,» said Eugene Chiang, a UC Berkeley professor of astronomy and member of the collaboration’s theory group. «We now have excellent statistics for how frequently planets occur, their mass distribution and how far they are from their stars. It is the most comprehensive analysis I have seen in this field.»

The study complements earlier exoplanet surveys by counting planets between 10 and 100 AU, a range in which the Kepler Space Telescope transit survey and radial velocity observations are unlikely to detect planets. It was led by Eric Nielsen, a research scientist at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University, and involved more than 100 researchers at 40 institutions worldwide, including the University of California, Berkeley.

One new planet, one new brown dwarf

Since the GPIES survey began five years ago, the team has imaged six planets and three brown dwarfs orbiting these 300 stars. The team estimates that about 9 percent of massive stars have gas giants between 5 and 13 Jupiter masses beyond a distance of 10 AU, and fewer than 1 percent have brown dwarfs between 10 and 100 AU.

Jupiter-like exoplanets found in sweet spot in most planetary systems
GPI captured a planet around the star 51 Eridanus. 51 Eri b is the only previously unknown planet discovered among 
the more than 500 stars surveyed by GPIES. Only 300 of the 531 stars were analyzed in this new study 
[Credit: Jason Wang, Caltech; Robert De Rosa, Stanford]

The new data set provides important insight into how and where massive objects form within planetary systems.

«As you go out from the central star, giant planets become more frequent. Around 3 to 10 AU, the occurrence rate peaks,» Chiang said. «We know it peaks because the Kepler and radial velocity surveys find a rise in the rate, going from hot Jupiters very near the star to Jupiters at a few AU from the star. GPI has filled in the other end, going from 10 to 100 AU, and finding that the occurrence rate drops; the giant planets are more frequently found at 10 than 100. If you combine everything, there is a sweet spot for giant planet occurrence around 3 to 10 AU.»

«With future observatories, particularly the Thirty-Meter Telescope and ambitious space-based missions, we will start imaging the planets residing in the sweet spot for sun-like stars,» said team member Paul Kalas, a UC Berkeley adjunct professor of astronomy.

The exoplanet survey discovered only one previously unknown planet — 51 Eridani b, nearly three times the mass of Jupiter — and one previously unknown brown dwarf — HR 2562 B, weighing in at about 26 Jupiter masses. None of the giant planets imaged were around sun-like stars. Instead, giant gas planets were discovered only around more massive stars, at least 50 percent larger than our sun, or 1.5 solar masses.

«Given what we and other surveys have seen so far, our solar system doesn’t look like other solar systems,» said Bruce Macintosh, the principal investigator for GPI and a professor of physics at Stanford. «We don’t have as many planets packed in as close to the sun as they do to their stars and we now have tentative evidence that another way in which we might be rare is having these kind of Jupiter-and-up planets.»

«The fact that giant planets are more common around stars more massive than sun-like stars is an interesting puzzle,» Chiang said.

Because many stars visible in the night sky are massive young stars called A stars, this means that «the stars you can see in the night sky with your eye are more likely to have Jupiter-mass planets around them than the fainter stars that you need a telescope to see,» Kalas said. «That is kinda cool.»

A team of astronomers spent five years on the Gemini South telescope photographing 531 young stars in search of Jupiter-like

 planets. An advanced camera, the Gemini Planet Imager, blocks light from each star in order to image the much fainter 

infrared glow from a planet. Every circle is an observation of a star in the southern sky: blue circles are stars with 

an observed exoplanet; red circles indicate stars with dusty comet belts; gray circles are stars with no detected 

planets. Multiple circles indicate stars, like 51 Eri, that were observed multiple times to track the orbital motion 

of the planet over time. [Credit: GPIES team, with animation by Paul Kalas, UC Berkeley]

The analysis also shows that gas giant planets and brown dwarfs, while seemingly on a continuum of increasing mass, may be two distinct populations that formed in different ways. The gas giants, up to about 13 times the mass of Jupiter, appear to have formed by accretion of gas and dust onto smaller objects — from the bottom up. Brown dwarfs, between 13 and 80 Jupiter masses, formed like stars, by gravitational collapse — from the top down — within the same cloud of gas and dust that gave rise to the stars.

«I think this is the clearest evidence we have that these two groups of objects, planets and brown dwarfs, form differently,» Chiang said. «They really are apples and oranges.»

Direct imaging is the future

The Gemini Planet Imager can sharply image planets around distant stars, thanks to extreme adaptive optics, which rapidly detects turbulence in the atmosphere and reduces blurring by adjusting the shape of a flexible mirror. The instrument detects the heat of bodies still glowing from their own internal energy, such as exoplanets that are large, between 2 and 13 times the mass of Jupiter, and young, less than 100 million years old, compared to our sun’s age of 4.6 billion years. Even though it blocks most of the light from the central star, the glare still limits GPI to seeing only planets and brown dwarfs far from the stars they orbit, between about 10 and 100 AU.

The team plans to analyze data on the remaining stars in the survey, hoping for greater insight into the most common types and sizes of planets and brown dwarfs.

Chiang noted that the success of GPIES shows that direct imaging will become increasingly important in the study of exoplanets, especially for understanding their formation.

«Direct imaging is the best way at getting at young planets,» he said. «When young planets are forming, their young stars are too active, too jittery, for radial velocity or transit methods to work easily. But with direct imaging, seeing is believing.»

Author: Robert Sanders | Source: University of California — Berkeley [June 12, 2019]



Earth’s heavy metals result of supernova explosion

In a finding that may overthrow our understanding of where Earth’s heavy elements such as gold and platinum come from, new research by a University of Guelph physicist suggests that most of them were spewed from a largely overlooked kind of star explosion far away in space and time from our planet.

Earth's heavy metals result of supernova explosion
Artist’s impression of a collapsar [Credit: NASA Goddard Space Flight Centre]

Some 80 per cent of the heavy elements in the universe likely formed in collapsars, a rare but heavy element-rich form of supernova explosion from the gravitational collapse of old, massive stars typically 30 times as weighty as our sun, said physics professor Daniel Siegel.

That finding overturns the widely held belief that these elements mostly come from collisions between neutron stars or between a neutron star and a black hole, said Siegel.

His paper co-authored with Columbia University colleagues appears today in the journal Nature.

Using supercomputers, the trio simulated the dynamics of collapsars, or old stars whose gravity causes them to implode and form black holes.

Under their model, massive, rapidly spinning collapsars eject heavy elements whose amounts and distribution are «astonishingly similar to what we observe in our solar system,» said Siegel. He joined U of G this month and is also appointed to the Perimeter Institute for Theoretical Physics, in Waterloo, Ont.

Most of the elements found in nature were created in nuclear reactions in stars and ultimately expelled in huge stellar explosions.

Heavy elements found on Earth and elsewhere in the universe from long-ago explosions range from gold and platinum, to uranium and plutonium used in nuclear reactors, to more exotic chemical elements such as neodymium found in consumer items such as electronics.

Until now, scientists thought that these elements were cooked up mostly in stellar smashups involving neutron stars or black holes, as in a collision of two neutron stars observed by Earth-bound detectors that made headlines in 2017.

Ironically, said Siegel, his team began working to understand the physics of that merger before their simulations pointed toward collapsars as a heavy element birth chamber. «Our research on neutron star mergers has led us to believe that the birth of black holes in a very different type of stellar explosion might produce even more gold than neutron star mergers.»

What collapsars lack in frequency, they make up for in generation of heavy elements, said Siegel. Collapsars also produce intense flashes of gamma rays.

«Eighty per cent of these heavy elements we see should come from collapsars. Collapsars are fairly rare in occurrences of supernovae, even more rare than neutron star mergers — but the amount of material that they eject into space is much higher than that from neutron star mergers.»

The team now hopes to see its theoretical model validated by observations. Siegel said infrared instruments such as those on the James Webb Space Telescope, set for launch in 2021, should be able to detect telltale radiation pointing to heavy elements from a collapsar in a far-distant galaxy.

«That would be a clear signature,» he said, adding that astronomers might also detect evidence of collapsars by looking at amounts and distribution of heavy element s in other stars across our Milky Way galaxy.

Siegel said this research may yield clues about how our galaxy began.

«Trying to nail down where heavy elements come from may help us understand how the galaxy was chemically assembled and how the galaxy formed. This may actually help solve some big questions in cosmology as heavy elements are a nice tracer.»

This year marks the 150th anniversary of Dmitri Mendeleev’s creation of the periodic table of the chemical elements. Since then, scientists have added many more elements to the periodic table, a staple of science textbooks and classrooms worldwide.

Referring to the Russian chemist, Siegel said, «We know many more elements that he didn’t. What’s fascinating and surprising is that, after 150 years of studying the fundamental building blocks of nature, we still don’t quite understand how the universe creates a big fraction of the elements in the periodic table.»

Source: University of Guelph [June 13, 2019]



Fermi mission reveals its highest-energy gamma-ray bursts

For 10 years, NASA’s Fermi Gamma-ray Space Telescope has scanned the sky for gamma-ray bursts (GRBs), the universe’s most luminous explosions. A new catalog of the highest-energy blasts provides scientists with fresh insights into how they work.

Fermi mission reveals its highest-energy gamma-ray bursts
Green dots show the locations of 186 gamma-ray bursts observed by the Large Area Telescope (LAT) on NASA’s Fermi
satellite during its first decade. Some noteworthy bursts are highlighted and labeled. Background: Constructed from
 nine years of LAT data, this map shows how the gamma-ray sky appears at energies above 10 billion electron volts.
The plane of our Milky Way galaxy runs along the middle of the plot. Brighter colors indicate brighter
 gamma-ray sources [Credit: NASA/DOE/Fermi LAT Collaboration]

«Each burst is in some way unique,» said Magnus Axelsson, an astrophysicist at Stockholm University in Sweden. «It’s only when we can study large samples, as in this catalog, that we begin to understand the common features of GRBs. These in turn give us clues to the physical mechanisms at work.»

The catalog was published in The Astrophysical Journal and is now available online. More than 120 authors contributed to the paper, led by Axelsson, Elisabetta Bissaldi at the National Institute of Nuclear Physics and Polytechnic University in Bari, Italy, and Nicola Omodei and Giacomo Vianello at Stanford University in California.

GRBs emit gamma rays, the highest-energy form of light. Most GRBs occurs when some types of massive stars run out of fuel and collapse to create new black holes. Others happen when two neutron stars, superdense remnants of stellar explosions, merge. Both kinds of cataclysmic events create jets of particles that move near the speed of light. The gamma rays are produced in collisions of fast-moving material inside the jets and when the jets interact with the environment around the star.

Astronomers can distinguish the two GRB classes by the duration of their lower-energy gamma rays. Short bursts from neutron star mergers last less than 2 seconds, while long bursts typically continue for a minute or more. The new catalog, which includes 17 short and 169 long bursts, describes 186 events seen by Fermi’s Large Area Telescope (LAT) over the last 10 years.

Fermi observes these powerful bursts using two instruments. The LAT sees about one-fifth of the sky at any time and records gamma rays with energies above 30 million electron volts (MeV)—millions of times the energy of visible light. The Gamma-ray Burst Monitor (GBM) sees the entire sky that isn’t blocked by Earth and detects lower-energy emission. All told, the GBM has detected more than 2,300 GRBs so far.

Below is a sample of five record-setting and intriguing events from the LAT catalog that have helped scientists learn more about GRBs.

1. GRB 081102B

The short burst 081102B, which occurred in the constellation Bootes on Nov. 2, 2008, is the briefest LAT-detected GRB, lasting just one-tenth of a second. Although this burst appeared in Fermi’s first year of observations, it wasn’t included in an earlier version of the collection published in 2013.

This animation shows the most common type of gamma-ray burst, which occurs when the core of a massive star 

collapses, forms a black hole, and blasts particle jets outward at nearly the speed of light. Viewing into 

a jet greatly boosts its apparent brightness. A Fermi image of GRB 130427A ends the sequence 

[Credit: NASA’s Goddard Space Flight Center]

«The first LAT catalog only identified 35 GRBs,» Bissaldi said. «Thanks to improved data analysis techniques, we were able to confirm some of the marginal observations in that sample, as well as identify five times as many bursts for the new catalog.»

2. GRB 160623A

Long-lived burst 160623A, spotted on June 23, 2016, in the constellation Cygnus, kept shining for almost 10 hours at LAT energies—the longest burst in the catalog. But at the lower energies recorded by Fermi’s GBM instrument, it was detected for only 107 seconds.

This stark difference between the instruments confirms a trend hinted at in the first LAT catalog. For both long and short bursts, the high-energy gamma-ray emission lasts longer than the low-energy emission and happens later.

3. GRB 130427A

The highest-energy individual gamma ray detected by Fermi’s LAT reached 94 billion electron volts (GeV) and traveled 3.8 billion light-years from the constellation Leo. It was emitted by 130427A, which also holds the record for the most gamma rays—17—with energies above 10 GeV.

A popular model proposed that charged particles in the jet, moving at nearly the speed of light, encounter a shock wave and suddenly change direction, emitting gamma rays as a result. But this model can’t account for the record-setting light from this burst, forcing scientists to rethink their theories.

The original findings on 130427A show that the LAT instrument tracked its emission for twice as long as indicated in the catalog. Due to the large sample size, the team adopted the same standardized analysis for all GRBs, resulting in slightly different numbers than reported in the earlier study.

4. GRB 080916C

The farthest known GRB occurred 12.2 billion light-years away in the constellation Carina. Called 080916C, researchers calculate the explosion contained the power of 9,000 supernovae.

This movie shows Fermi Large Area Telescope observations of GRB 080916C. About 8 minutes of data are 

compressed into 6 seconds. Colored dots represent gamma rays of different energies. The blue dots 

represent lower-energy gamma rays; green, moderate energies; and red, the highest energies 

[Credit: NASA/DOE/Fermi LAT Collaboration]

Telescopes can observe GRBs out to these great distances because they are so bright, but pinpointing their exact distance is difficult. Distances are only known for 34 of the 186 events in the new catalog.

5. GRB 090510

The known distance to 090510 helped test Einstein’s theory that the fabric of space-time is smooth and continuous. Fermi detected both a high-energy and a low-energy gamma ray at nearly the same instant. Having traveled the same distance in the same amount of time, they showed that all light, no matter its energy, moves at the same speed through the vacuum of space.

«The total gamma-ray emission from 090510 lasted less than 3 minutes, yet it allowed us to probe this very fundamental question about the physics of our cosmos,» Omodei said. «GRBs are really one of the most spectacular astronomical events that we witness.»

What’s missing?

GRB 170817A marked the first time light and ripples in space-time, called gravitational waves, were detected from the merger of two neutron stars. The event was captured by the Laser Interferometer Gravitational Wave Observatory (LIGO), the Virgo interferometer and Fermi’s GBM instrument, but it wasn’t observed by the LAT because the instrument was switched off as the spacecraft passed through a region of Fermi’s orbit where particle activity is high.

«Now that LIGO and Virgo have begun another observation period, the astrophysics community will be on the lookout for more joint GRB and gravitational wave events» said Judy Racusin, a co-author and Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. «This catalog was a monumental team effort, and the result helps us learn about the population of these events and prepares us for delving into future groundbreaking finds.»

Author: Jeanette Kazmierczak | Source: NASA’s Goddard Space Flight Center [June 13, 2019]



Environmental oxygen triggers loss of webbed digits

Free fingers have many obvious advantages on land, such as in locomotion and grasping, while webbed fingers are typical of aquatic or gliding animals. But both amphibians and amniotes—which include mammals, reptiles, and birds—can have webbed digits. In new research from Japan, scientists show for the first time that during embryo development, some animal species detect the presence of atmospheric oxygen, which triggers removal of interdigital webbing. Their research is published in the journal Developmental Cell.

Environmental oxygen triggers loss of webbed digits
This graphic shows how interdigital cell death and environmental oxygen are correlated
in various tetrapods [Credit: Cordeiro et al. 2019]

Amphibians—animals like frogs, toads, salamanders, and newts—form fingers without webbing by differential growth patterns between the digits and the areas between them, or interdigital regions. By comparison, amniotes rely on interdigital cell death, or death of cells in the webbing between digits, a mechanism that contributes to a greater variation of limb shapes.

«We found that the removal of the interdigital membrane by cell death depends on the production of reactive oxygen species (ROS), which only occurs in embryos exposed to sufficient oxygen levels during development,» said senior author Mikiko Tanaka of the Tokyo Institute of Technology.

Since high oxygen levels can induce cell death in a frog, the researchers believe this mechanism is likely shared by all tetrapods—both amphibians and amniotes. «But amphibians do not employ cell death to shape their interdigital regions; it is the difference in growth rate between the digital and interdigital regions that will determine their final proportions,» she says. «We think that interdigital cell death appeared in amphibians only as a by-product of the high oxygen levels, a first step in this evolutionary process. This new step eventually was integrated to the limb development and became essential to shape the limbs of modern amniotes.»

In their study, Tanaka’s team examined embryos from several species. In chicken embryos, an amniote with interdigital cell death, changing the oxygen levels directly affected the number of dying cells. They also noted that increasing the amount of environmental oxygen induced interdigital cell death in the African clawed frog, an amphibian that typically lacks it. And increasing the density of blood vessels in the limbs of these frogs also induced cell death.

Environmental oxygen triggers loss of webbed digits
The balance between growth of the digits (black arrows) and interdigital regions (red arrows) determine if the hands
and feet form a webbing in amphibians. Amniotes employ another strategy: their interdigital regions are actively
removed by cell death (dark blue). In some species, inhibition of cell death (light blue) was important
 for the evolution of new limb shapes [Credit: Tokyo Tech]

To gain an evolutionary perspective, researchers also studied cell death and ROS in two other amphibian species, the Japanese fire-bellied newt and the coqui frog. Like the African clawed frog, the Japanese fire-bellied newt had no interdigital cell death, but the coqui frogs had dying cells in their interdigital regions. Importantly, unlike the other two amphibians, the coqui frogs grow without a tadpole stage in terrestrial eggs and breathe oxygen from the air. «This way, we show both experimentally and comparatively that interdigital cell death is correlated with life history strategy and oxygen availability in tetrapods (four-legged vertebrates),» says Tanaka.
The researchers explain that the interdigital region is rich in blood vessels, the source of oxygen to the tissues. Part of the oxygen can be converted to ROS. «Paradoxically, ROS are traditionally considered villains such as in aging and infertility,» she says, «but it is becoming clear that there are physiological levels of ROS which vary according to each cell and regulate several signaling pathways during the development and in the adult organism.»

The team believes there are two main factors that made the interdigital region sensitive to this increase in ROS—active Bmp signaling and blood vessel remodeling. For almost 20 years, Bmps have been described as key for the induction of cell death in amniote limbs. «However, this pathway also plays a role in patterning the number of digits and joints, and is active in the interdigital region of amphibians as well,» she says. In the same way, blood vessel remodeling increases the oxygen availability to the limbs and is correlated with interdigital cell death in amniotes but is part of another process: ossification of the fingers.

Environmental oxygen triggers loss of webbed digits
Increased oxygen levels are essential for production of reactive oxygen species (ROS) and cell death in the limbs.
During evolution, this new process — ICD — became essential to shape the limbs of amniotes
[Credit: Tokyo Tech]

«But the interesting point is that, while both amniotes and amphibians can have either free or webbed fingers, they are formed in different ways in these two groups,» says Tanaka. «The new developmental mechanism acquired by amniotes — interdigital cell death -allowed for the evolution of a great variety of limb shapes, such as the lobed fingers of coots, and even removal of some fingers in horses and camels.»

Looking ahead, the team is interested in understanding exactly which pathways are regulated by ROS during development. They hope to uncover how cell death became an integral part of the limb development of amniotes during evolution. And they also hope to gain insight into how drugs that may lead to excessive ROS production, such as ethanol, phenytoin, and thalidomide, may cause developmental defects in humans.

Source: Cell Press [June 13, 2019]



Determining the Earth’s gravity field more accurately than ever before

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using satellite-supported recordings, they document the strong fluctuations and the associated spatial and seasonal distributions of mass on and in the Earth. From this, gravity field models can be calculated by which researchers can track rising sea levels or melting glaciers, investigate regional groundwater reserves more closely or analyze oceanic currents.

Determining the Earth's gravity field more accurately than ever before
The graphic shows the ice-sheet loss in Greenland – based on GOCO06S
[Credit: IFG – TU Graz]

A team at the Institute of Geodesy of TU Graz has published a new combined gravity field model. The model, which is called GOCO06S, represents changes in mass on and under the Earth’s surface at unprecedented accuracy.

Model brings together different measuring processes

The name refers to the initiative itself: Gravity Observation Combination (GOCO), in whose framework the model was developed together with international partners. The consortium combines 1.16 billion measurements recorded by 19 satellites. «Due to the combination of data, the strengths of the individual measurement methods can be taken advantage of to the best of our ability.

This makes it possible for us to detect changes in the gravity field on a scale of one millionth of the mean force of gravity [Note: 9.81m/s2],» explains Torsten Mayer-Gurr, head of the Working Group of Theoretical Geodesy and Satellite Geodesy at TU Graz’s Institute of Geodesy. To achieve consistent global accuracy, it was decided to do without terrestrial data. Compared to the previous model, results have been improved by 25 percent.

The working group is occupied with determining the temporal changes in the Earth’s gravity and the evaluation of gravity measurements. The Graz team processes data from satellite missions and makes available gravity field solutions to the scientific community. «Our models are also used, for instance, in research into flood events,» says Mayer-Gurr, naming one particular field of activity.

Source: Graz University of Technology [June 13, 2019]



Oldest axial fossils discovered for the genus Australopithecus

Scientists have published an article describing the oldest axial fossils yet discovered for the genus Australopithecus. Dated 4.2 million years ago, these and other fossils recovered from the Assa Issie site in the Middle Awash extend the known range of A. anamensis into northeastern Ethiopia. The fossils from the Assa Issie are extremely fragmentary, but each represents an important element previously unknown for the species Australopithecus anamensis.

Oldest axial fossils discovered for the genus Australopithecus
One of the fossils is an axis, or second cervical vertebra (C2) shown here in (a) ventral view, (b) dorsal view, (c) lateral
view, and D) ventral view in articulation with modern H. sapiens atlas (C1). Note the correspondence between
the Assa Issie axis and human atlas [Credit: Meyer & Williams, 2019]

In an upcoming article in the Journal of Human Evolution, paleoanthropologists Dr. Marc Meyer of Chaffey College and Scott Williams of New York University describe tell-tale signs that these early hominins had already evolved a human-like posture of the head and neck. «The bilobated facets of the first cervical vertebra are something we don’t see in the great apes, but in humans is thought to provide a passive locking mechanism that keeps the head stable in erect posture,» explains Meyer.

The scientists also point to the lack the pronounced retroglenoid tubercle of the great apes on two of the atlas (C1) fossils that indicate that like humans, anamensis lacked the atlantoclavicularis muscle, which would have reduced their capacity for climbing relative to the great apes—something scientists did not know until now.

Other features of the non-human ape spine are also absent in the hominin fossils, such as the ponticulus posticus, the bony form of a membrane in apes that protects the vertebral artery from being crushed when the head is cantilevered in front of the spine. The scientists report «lack of this feature in anamensis is consistent with a humanlike posture where the head is more centered above the spine».

The spinal column reveals other surprisingly human characters, such as an enlarged epiphyseal surface area that is a hallmark feature of bipedalism, as it improves the ability to resist the increased load magnitudes of upright posture. «Such a feature would also provide energy return during bipedal locomotion from the intervertebral discs in the form of elastic strain energy with rotary spinal movement» explain the scientists.

Finally, despite their great antiquity, like humans, the A. anamensis fossils from Issie exhibit an enlarged spinal canal compared to the apes. «This would confer an increase in the neurovascular contents of the canal, including the motor pool in the ventral horn of the australopith spinal cord well before the advent of genus Homo», says Meyer.

The enlarged spinal canal provides the earliest evidence for an enlarged spinal cord in the hominin lineage and imparts significant neurological and vascular benefits for bipedal locomotion, and shatters the notion that spinal cord size in early hominins was small and apelike. This was another surprise, say the scientists, and provides evidence that a human-sized spinal cord evolved well before human brain size.

Source: Chaffey College [June 14, 2019]



Spanish hamlet pins hopes of prosperity on its Roman Empire legacy

Once upon a time, there was an immensely rich man. He was so wealthy that he could afford to have wine sent from Syria to his home, nearly 5,000 kilometers away, even though this was back in the fourth century, in Roman Hispania. His estate, known as Villa de Noheda, was a testament to his great power: it covered more than 10 hectares, according to recent geo-radar measurements. Just his dining room (known in Roman as a triclinium) was 291 square meters, and it was decorated with mosaics fit for the palace of an emperor.

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
A section of the triclinium at the Roman villa of Noheda. This scene depicts Dionysus’ retinue, including centaurs,
 musicians, satires and Silenus, represented as an old man riding a donkey [Credit: R.G./El Pais]

“This man really existed,” explains Miguel Ángel Valero, professor of ancient history at the University of Castilla-La Mancha. His name is not yet known “but sooner or later, we’ll find out,” says Valero, who has spent a decade uncovering the dazzling features of the villa, which is located in Villar de Domingo, a hamlet of 218 inhabitants in Cuenca province, in the central region of Castilla-La Mancha.
The regional government is now planning to open the archaeological site to the public. While only 5% of Villa de Noheda has been excavated, researchers have already found the largest collection of marble sculptures in Roman Hispania, featuring more than 500 large fragments, and the largest figurative mosaic in the entire Roman Empire.

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
Miguel Angel Valero sprays deionized water on a scene representing
a pantomime. A pipe organ can be seen to the right
[Credit: R.G./El Pais]

The mayor of Villar de Domingo García, Javier Parrilla, of the Popular Party (PP), wants the opening of the site to coincide with a new campaign of archaeological work scheduled for the summer, which will include the excavation of the villa’s reception hall. This room “is normally bigger than the triclinium,” explains Valero.

Villa de Noheda was discovered more than a decade ago, when a tractor hit a hard spot of land in the village. This area had been nicknamed The Stony Field (El Pedregal) after the numerous stone blocks and metal objects that kept turning up there. When the tractor dug up the ground, it pulled up hundreds of small, brightly colored stone pieces – they were part of the tiles of the mosaic. The discovery prompted archaeologists to begin excavating the site.

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
A scene showing one of the two pantomimes represented in the mosaic. One of the characters is wearing a long,
solid shoe that was used to keep time to the music. This is one of the very few remaining representations
of this item in the world [Credit: R.G./El Pais]

What they found far exceeded all expectations. Noheda is a mammoth residential complex that mixed “business with pleasure” within a large estate (fundus). The fundus – which covered more than 80 square kilometers – was made up of crop fields (ager), pastures for livestock (saltus) and a mountainous area (silva) where wood could be harvested. The villa was located far enough away from the Roman road so as to not be detected by unwanted visitors or attacked by hungry legions.
The decorative paintings, floor mosaics, sculptures and other ornamental elements highlight the great wealth of the owner. Researchers have found more than 30 types of marble brought here from all corners of the known world at that time, and they are still unsure how it was possible for the landowner to acquire such wealth.

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
A section of the mosaic inside the triclinium representing the Judgement of Paris
and the abduction of Helen of Troy [Credit: R.G./El Pais]

“The dominus [Roman landowner] could have been connected to the emperor, who at that moment was Theodosius I, we don’t know yet, but it is clear that he belonged to the high aristocracy,” explains Valero.

The mosaic in the villa’s triclinium is the largest figurative mosaic of the Roman Empire known to date. It is comparable to the famous Villa Romana del Casale in Piazza Armerina in Italy (which is slightly smaller, 270 square meters) and is made up of “innumerable” tiles. In each 25-square-centimeter area, an average of 1,243 tiny tiles were used, some measuring just a few millimeters.

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
The decapitated heads of the suitors of Hippodamia, daughter of King Oenomaus. These men lost chariot races
against the king, who made them pass this test in order to award his daughter’s hand in marriage
[Credit: R.G./El Pais]

Given the scale of the work, archaeologists believe there was not just “one pictor imaginarius [designer],” but several. They also discovered that some areas of the large mosaic were covering a previous one. “It’s as if the owner of the villa didn’t like the first result and ordered to have a different one made on top. Money was not going to be a problem,” jokes Valero.
As well as the mosaic, archaeologists have also excavated “550 large sculpture fragments, made from marble imported from the East and from Carrara [Italy]. It is the largest sculpture set in all of Hispania, and includes the figures of Dionysus, Venus and the Dioscuri,” adds Valero.

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
A scene representing Helen of Troy when she was abducted by Paris,
a move that led to a war [Credit: R.G./El Pais]

So how did the luxury villa come to be forgotten? The fall of the Roman Empire sparked the rapid Christianization of all of Hispania. The pagan sculptures were destroyed and thrown in a dump. Part of them was used to make marble dust, but many survived. Archaeologists are now trying to piece the fragments back together like a jigsaw puzzle. Some have been recovered and are now on display at an exhibition in Cuenca titled Noheda: the image of power.

“Now what’s left is to be able to show the site,” says Parrilla, the mayor of Villar de Domingo García. “Everything is almost ready for its opening, as well as an information center in the village. The idea is for visitors to enjoy this while they watch the archaeologists at work.“

 Spanish hamlet pins hopes of prosperity on its Roman Empire legacy
The southern portion of the mosaic. The center once held a fountain, and the water-supply system
has survived all these centuries [Credit: R.G./El Pais]

The hope is that the site will attract visitors to the hamlet, which often loses tourists to the nearby city of Cuenca. Local authorities and researchers have been giving courses and hosting activities with the locals to get them involved in what could become a big tourist and cultural attraction.

Sources from the regional government confirmed to EL PAÍS that Villa de Noheda will be opened to the public “as soon as possible.” “It’s unique in the world. When I show the photos in international congresses, specialists from other countries are astonished. And the best is yet to come, because we have only excavated a small part,” says Valero with a big smile.

Author Vicente G. Olaya (transl. Melissa Kitson) | Source: El Pais [June 12, 2019]



Scotland’s crannogs date back to 3,700 BC

Archaeologists have made the astounding discovery that some of the Scottish crannogs — artificial islands constructed in lakes and sea inlets — date to the Neolithic period.

Scotland's crannogs date back to 3,700 BC
Neolithic pottery was previously found near crannogs in the Western Isles
[Credit: Chris Murray]

This is far earlier than previously assumed, as the general consensus had been until now that they were built, used, and re-used over a period of 2,500 years from the Iron Age to the postmedieval period. Four crannog sites in the Outer Hebrides have now been conclusively radiocarbon dated to c.3640–3360 BC, shifting the timeline by thousands of years.
In 2012, Chris Murray, a resident of Lewis and former Royal Navy diver, decided to explore the loch bed around one such islet, and in doing so he made a remarkable discovery. Scattered around the islet were a series of extraordinarily well-preserved Early/Middle Neolithic pots lying on the loch bed. Following this discovery, Murray and Mark Elliot, the then-conservation officer at Museum nan Eilean in Stornoway, found similar assemblages at five more crannog sites across Lewis.

Scotland's crannogs date back to 3,700 BC
Four crannogs in the Western Isles were found to date to the Neolithic period
[Credit: Fraser Sturt]

Garrow and Sturt, publishing in Antiquity, present the results of their collaboration with Murray in 2016/17, which aimed to confirm what this pottery suggested — that these crannogs could date to the Neolithic period.
Using a combination of ground and underwater survey, photogrammetry, palaeoenvironmental coring and excavation, the project obtained conclusive evidence of artificial islet construction in the Outer Hebrides during the Neolithic period. These crannogs therefore represent a monumental effort thousands of years ago, through the piling up of boulders on the loch bed, and in the case of Loch Bhorgastail, the building of a stone causeway.

Scotland's crannogs date back to 3,700 BC
One of the crannogs in the Western Isles has a stone causeway
[Credit: Fraser Sturt]

Substantial quantities of Neolithic ceramic vessels were recovered from the lochs, and the large fragmental sizes suggest that at least some, and possibly all, of the vessels were complete when they entered the water. This means there was a systematic and possibly ritualised deposition from the islets. The sites on Lewis were certainly monumental, in terms of the work it took to construct them and their location, with their watery surroundings creating separation from everyday life.
These Neolithic crannogs remind us to ‘question the binary opposition sometimes assumed between Neolithic settlements and monuments (e.g. passage graves), and there may be many more. Although the Outer Hebrides have a significant number of crannogs, they are also common across the rest of Scotland and Ireland.

Only 10% of these have been radiocarbon dated, and only 20% in total have been dated at all. The research team believe it is possible that more Neolithic crannogs exist, but cannot be certain until further investigations are conducted. They represent a new type of site for the British Neolithic, with new deposition practices, and the possibilities for future work.

Source: University of Reading [June 14, 2019]



Evidence of Sangam Age settlement unearthed at Nangur, Tamil Nadu

Evidence indicating the existence of human settlement dating back to the Sangam Age was unearthed at Nangur village in Nagapattinam district during an excavation carried out recently by the Department of Marine History and Marine Archaeology, Tamil University, Thanjavur, with the consent of Archaeological Survey of India.

Evidence of Sangam Age settlement unearthed at Nangur, Tamil Nadu
Excavations at Nangur carried out by the Department of Marine History and Marine Archaeology,
Tamil University, at Nangur village in Nagapattinam district 
[Credit: Times of India]

The excavation, funded by University Grants Commission, was carried out by the students of Tamil University, University of Madras, Lady Doak College, Madurai, and Madras Christian College, Chennai, and faculty of A.V.C.College, Mayiladuthurai.
The team discovered Chola-period roof tiles with folded ends and rounded tips, terracotta figurines, sealings, ear ornaments and dies, glass beads, stone beads and bangle fragments. The terracotta figurines reveal exquisite workmanship, sources said.

Evidence of Sangam Age settlement unearthed at Nangur, Tamil Nadu
A terracotta figurine unearthed during an excavation
[Credit: The Hindu]

A structure reflecting a blacksmith’s workshop was also excavated at the settlement found at a depth of three metres. Black and red ware potteries with one of them having a mark of fish were also found at the excavation site. G. Balasubramanian, Vice-Chancellor, Tamil University, and Mark Hauser, Professor, Northwestern University, USA, who was on an exploration of a Danish Settlement at the nearby Tranquebar village in Nagapattinam district, visited the excavation site.
Research suggests that many of the Divyadesams and Devara thalangal bear evidences of human settlement from the iron age, according to V. Selvakumar, Associate Professor, Department of Marine History and Marine Archaeology, Tamil University, who led the excavation. Some of these old settlements (Moothoor) may have been the territorial headquarters called Naadu.

Evidence of Sangam Age settlement unearthed at Nangur, Tamil Nadu
Black and red ware pottery with fish graffitto
[Credit: Deccan Herald]

Further, the current research seeks to find answers to questions relating to the formation of settlements and beginning of agriculture in the lower Cauvery valley. More research and radiocarbon dating are to be undertaken at this site, he added.
“Nangur seems to be an important settlement of the Sangam Age as it was mentioned in the Pattinathupalai and Porunaraatruppadai ’.

Evidence of Sangam Age settlement unearthed at Nangur, Tamil Nadu
Earthenware bowls found at the site [Credit: Deccan Herald]

According to local legends, the Sangam Age king, Karikalan, married the daughter of Nangur Vel, chief of Nangur village.

Another evidence relating to Nangur was found in an inscription at Takua Pa in Thailand where it was mentioned that a person by name Nangurutaiyan dug a tank and placed it in the custody of Manigramattar, Prof. Selvakumar pointed out.

Author: V. Venkatasubramanian | Source: The Hindu [June 17, 2019]



2019 June 19 Our Galaxy’s Magnetic Center Image Credit:…

2019 June 19

Our Galaxy’s Magnetic Center
Image Credit: NASA, SOFIA, Hubble

Explanation: What’s the magnetic field like in the center of our Milky Way Galaxy? To help find out, NASA’s SOFIA – an observatory flying in a modified 747 – imaged the central region with an instrument known as HAWC+. HAWC+ maps magnetism by observing polarized infrared light emitted by elongated dust grains rotating in alignment with the local magnetic field. Now at our Milky Way’s center is a supermassive black hole with a hobby of absorbing gas from stars it has recently destroyed. Our galaxy’s black hole, though, is relatively quiet compared to the absorption rate of the central black holes in active galaxies. The featured image gives a clue as to why – a surrounding magnetic field may either channel gas into the black hole – which lights up its exterior, or forces gas into an accretion-disk holding pattern, causing it to be less active – at least temporarily. Inspection of the featured image – appearing perhaps like a surreal mashup of impasto art and gravitational astrophysics – brings out this telling clue by detailing the magnetic field in and around a dusty ring surrounding Sagittarius A*, the black hole in our Milky Way’s center.

∞ Source: apod.nasa.gov/apod/ap190619.html

Does the Gas in Galaxy Clusters Flow Like Honey?

Coma Cluster

Credit X-ray: NASA/CXC/Univ. of Chicago, I. Zhuravleva et al, 

Optical: SDSS Release Date June 

This image represents a deep dataset of the Coma galaxy cluster obtained by NASA’s Chandra X-ray Observatory. Researchers have used these data to study how the hot gas in the cluster behaves, as reported in our press release. One intriguing and important aspect to study is how much viscosity, or «stickiness,» the hot gas demonstrates in these cosmic giants.

Galaxy clusters are comprised of individual galaxies, hot gas, and dark matter. The hot gas in Coma glows in X-ray light observed by Chandra. Seen as the purple and pink colors in this new composite image, the hot gas contains about six times more mass than all of the combined galaxies in the cluster. The galaxies appear as white in the optical part of the composite image from the Sloan Digital Sky Survey. (The unusual shape of the X-ray emission in the lower right is caused by the edges of the Chandra detectors being visible.)

Despite its abundance, the density of the multimillion-degree gas in Coma, which is permeated by a weak magnetic field, is so low that the particles do not interact with each other very often. Such a low-density, hot gas cannot be studied in a laboratory on Earth, and so scientists must rely on cosmic laboratories such as the one provided by the intergalactic gas in Coma.

The researchers used the Chandra data to probe whether the hot gas was smooth on the smallest scales they could detect. They found that it is not, suggesting that turbulence is present even on these relatively small scales and the viscosity is low.

Why is the viscosity of Coma’s hot gas so low? One explanation is the presence of small-scale irregularities in the cluster’s magnetic field. These irregularities can deflect particles in the hot gas, which is composed of electrically charged particles, mostly electrons, and protons. These deflections reduce the distance a particle can move freely and, by extension, the gas viscosity.

Knowledge of the viscosity of gas in a galaxy cluster and how easily turbulence develops helps scientists understand the effects of important phenomena such as collisions and mergers with other galaxy clusters, and galaxy groups. Turbulence generated by these powerful events can act as a source of heat, preventing the hot gas in clusters from cooling to form billions of new stars.

A paper describing this research appeared in Nature Astronomy on June 17th, 2019 and is available online. The authors of the paper are Irina Zhuravleva (University of Chicago), Eugene Churazov, (Max Planck Institute for Astrophysics in Garching and the Space Research Institute in Moscow), Alexander Schekochihin (University of Oxford), Steven Allen (Stanford University, SLAC), Alexey Vikhlinin (Harvard-Smithsonian Center for Astrophysics), and Norbert Werner (MTA-Eötvös University Lendulet, Masaryk University, Hiroshima University). NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

Fast Facts for Coma Cluster:

Scale: Image is about 25 arcmin (2.2 million light years) across.
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 12h 59m 42s | Dec +27° 56´ 40.9″
Constellation: Coma Berenices
Observation Date: 36 pointings from March 2008 to March 2017
Observation Time: 416 hours 40 minutes (17 days 8 hours 40 minutes)

Obs. ID: 9714, 10672, 13993–13996, 14406, 14410, 14411, 14415, 18271–18276, 18761, 18791–18798, 19998, 20010, 20011, 20027–20031, 20037–20039

Instrument: ACIS
References: Zhuravleva, I. et al, 2019, Nature Astronomy, arXiv:1906.06346
Color Code: X-ray: purple; Optical: white
Distance Estimate: About 320 million light years (z=0.023)

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