mercredi 16 août 2017

Supermassive Black Holes Feed on Cosmic Jellyfish

ESO - European Southern Observatory logo.

16 August 2017

ESO’s MUSE instrument on the VLT discovers new way to fuel black holes

Example of a jellyfish galaxy

Observations of “Jellyfish galaxies” with ESO’s Very Large Telescope have revealed a previously unknown way to fuel supermassive black holes. It seems the mechanism that produces the tentacles of gas and newborn stars that give these galaxies their nickname also makes it possible for the gas to reach the central regions of the galaxies, feeding the black hole that lurks in each of them and causing it to shine brilliantly. The results appeared today in the journal Nature.

Example of a jellyfish galaxy

An Italian-led team of astronomers used the MUSE (Multi-Unit Spectroscopic Explorer) instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile to study how gas can be stripped from galaxies. They focused on extreme examples of jellyfish galaxies in nearby galaxy clusters, named after the remarkable long “tentacles” of material that extend for tens of thousands of light-years beyond their galactic discs [1][2].

Visualisation of MUSE view of Jellyfish Galaxy

The tentacles of jellyfish galaxies are produced in galaxy clusters by a process called ram pressure stripping. Their mutual gravitational attraction causes galaxies to fall at high speed into galaxy clusters, where they encounter a hot, dense gas which acts like a powerful wind, forcing tails of gas out of the galaxy’s disc and triggering starbursts within it.

Example of a jellyfish galaxy

Six out of the seven jellyfish galaxies in the study were found to host a supermassive black hole at the centre, feeding on the surrounding gas [3]. This fraction is unexpectedly high — among galaxies in general the fraction is less than one in ten.

Visualisation of galaxy undergoing ram pressure stripping

“This strong link between ram pressure stripping and active black holes was not predicted and has never been reported before,” said team leader Bianca Poggianti from the INAF-Astronomical Observatory of Padova in Italy. “It seems that the central black hole is being fed because some of the gas, rather than being removed, reaches the galaxy centre.” [4]

Artist's impression of ram pressure stripping

A long-standing question is why only a small fraction of supermassive black holes at the centres of galaxies are active. Supermassive black holes are present in almost all galaxies, so why are only a few accreting matter and shining brightly? These results reveal a previously unknown mechanism by which the black holes can be fed.

Yara Jaffé, an ESO fellow who contributed to the paper explains the significance: “These MUSE observations suggest a novel mechanism for gas to be funnelled towards the black hole’s neighbourhood. This result is important because it provides a new piece in the puzzle of the poorly understood connections between supermassive black holes and their host galaxies.”

Visualisation of a galaxy undergoing ram pressure stripping

The current observations are part of a much more extensive study of many more jellyfish galaxies that is currently in progress.

“This survey, when completed, will reveal how many, and which, gas-rich galaxies entering clusters go through a period of increased activity at their cores,” concludes Poggianti. “A long-standing puzzle in astronomy has been to understand how galaxies form and change in our expanding and evolving Universe. Jellyfish galaxies are a key to understanding galaxy evolution as they are galaxies caught in the middle of a dramatic transformation.”


[1] To date, just over 400 candidate jellyfish galaxies have been found.

[2] The results were produced as part of the observational programme known as GASP (GAs Stripping Phenomena in galaxies with MUSE), which is an ESO Large Programme aimed at studying where, how and why gas can be removed from galaxies. GASP is obtaining deep, detailed MUSE data for 114 galaxies in various environments, specifically targeting jellyfish galaxies. Observations are currently in progress.

[3] It is well established that almost every, if not every, galaxy hosts a supermassive black hole at its centre, between a few million and a few billion times as massive as our Sun. When a black hole pulls in matter from its surroundings, it emits electromagnetic energy, giving rise to some of the most energetic of astrophysical phenomena: active galactic nuclei (AGN).

[4] The team also investigated the alternative explanation that the central AGN activity contributes to stripping gas from the galaxies, but considered it less likely. Inside the galaxy cluster, the jellyfish galaxies are located in a zone where the hot, dense gas of the intergalactic medium is particularly likely to create the galaxy’s long tentacles, reducing the possibility that they are created by AGN activity. There is therefore stronger evidence that ram pressure triggers the AGN and not vice versa.

More information:

This research was presented in a paper entitled “Ram Pressure Feeding Supermassive Black Holes” by B. Poggianti et al., to appear in the journal Nature on 17 August 2017.

The team is composed of B. Poggianti (INAF-Astronomical Observatory of Padova, Italy), Y. Jaffé (ESO, Chile), A. Moretti (INAF-Astronomical Observatory of Padova, Italy), M. Gullieuszik (INAF-Astronomical Observatory of Padova, Italy), M. Radovich (INAF-Astronomical Observatory of Padova, Italy), S. Tonnesen (Carnegie Observatory, USA), J. Fritz (Instituto de Radioastronomía y Astrofísica, Mexico), D. Bettoni (INAF-Astronomical Observatory of Padova, Italy), B. Vulcani (University of Melbourne, Australia; INAF-Astronomical Observatory of Padova, Italy), G. Fasano (INAF-Astronomical Observatory of Padova, Italy), C. Bellhouse (University of Birmingham, UK; ESO, Chile), G. Hau (ESO, Chile) and A. Omizzolo (Vatican Observatory, Vatican City State).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.


Research paper in Nature:

Photos of the VLT:

Photos of MUSE:

Further details about the GASP (GAs Stripping Phenomena in galaxies with MUSE) programme:

Jellyfish galaxies 3D models: JW100, JO175, and JO194:

ESOcast 122 Light: Supermassive Black Holes Feed on Cosmic Jellyfish (4K UHD):

Very Large Telescope (VLT):

ESO’s Paranal Observatory:

Images, Videos, Text, Credits: ESO/Richard Hook/INAF-Astronomical Observatory of Padova/Bianca Poggianti/GASP collaboration/Callum Bellhouse/NASA, ESA, and M. Kornmesser/Acknowledgements: Ming Sun (UAH) and Serge Meunier.

Best regards,

Robotic Arm Reaches Out and Grapples Dragon & dock at Station

SpaceX - CRS-12 Dragon Mission patch.

August 16, 2017

Image above: The SpaceX Dragon cargo craft is pictured approaching the International Space Station on Wednesday morning. Image Credit: NASA TV.

While the International Space Station was traveling over the Pacific Ocean north of New Zealand, NASA astronaut Jack Fischer and ESA (European Space Agency) astronaut Paolo Nespoli captured the Dragon spacecraft at 6:52 a.m. EDT using the station’s robotic arm. It then will be installed on the station’s Harmony module.

Dragon Installed to Station for Month of Cargo Swaps

Image above: Flying over South Australian coasts, SpaceX Dragon docked at Space Station, altitude: 415,70 Km / speed: 27'582 Km/h. Image captured (by Roland Berga from Aerospace) with EarthCam from ISS - International Space Station (via ISS HD Live application) on August 16, 2017 at 16:00 UTC. Image Credits: Mentioned.

The SpaceX Dragon cargo spacecraft was berthed to the Harmony module of the International Space Station at 9:07 a.m. EDT. The hatch between the newly arrived spacecraft and the Harmony module of the space station is scheduled to be opened as soon as later today.

CRS-12 is scheduled to deliver more than 6,400 pounds of supplies and payloads to the station, including a sweet treat for the astronauts: ice cream. The small cups of chocolate, vanilla and birthday cake-flavored ice cream are arriving in freezers that will be reloaded with research samples for return to Earth when the Dragon spacecraft departs the station mid-September.

Image above: Four spaceships are parked at the space station including the SpaceX Dragon cargo craft, the Progress 67 resupply ship and two Soyuz crew ships. Image Credit: NASA.

For more information about the SpaceX CRS-12 mission, visit Join the conversation on Twitter by following @Space_Station.

Space Station Research and Technology:

International Space Station (ISS):

Images (mentioned), Text, Credits: NASA/Mark Garcia/ Aerospace/Roland Berga.

Best regards,

Sneak peek in colour

ESA - Gaia Mission patch.

16 August 2017

While surveying the positions of over a billion stars, ESA's Gaia mission is also measuring their colour, a key diagnostic to study the physical properties of stars. A new image provides a preview of Gaia's first full-colour all-sky map, which will be unleashed in its highest resolution with the next data release in 2018.

Image above: Preliminary map of Gaia's sky in colour. Image Credits: ESA/Gaia/DPAC/CU5/CU8/DPCI/F. De Angeli, D.W. Evans, M. Riello, M. Fouesneau, R. Andrae, C.A.L. Bailer-Jones.

Stars come in a variety of colours that depend on their surface temperature, which is, in turn, determined by their mass and evolutionary stage.

Massive stars are hotter and therefore shine most brightly in blue or white light, unless they are approaching the end of their life and have puffed up into a red supergiant. Lower-mass stars, instead, are cooler and tend to appear red.

Measuring stellar colours is important to solve a variety of questions, ranging from the internal structure and chemical composition of stars to their evolution.

Gaia, ESA's astrometry mission to compile the largest and most precise catalogue of stellar positions and motions to date, has also been recording the colour of the stars it observes. The satellite was launched in December 2013 and has been collecting scientific data since July 2014.

A special effort in the Gaia Data Processing and Analysis Consortium (DPAC) is dedicated to the challenging endeavour of extracting stellar colours from the satellite data. While these measurements will be published with Gaia's second data release in April 2018, a preview of the Gaia sky map in colour demonstrates that the ongoing work is progressing well.

The new map, based on preliminary data from 18.6 million bright stars taken between July 2014 and May 2016 [1], shows the middle value (median) of the colours of all stars that are observed in each pixel. It is helpful to look at it next to its companion map, showing the density of stars in each pixel, which is higher along the Galactic Plane – the roughly horizontal structure that extends across the image, corresponding to the most densely populated region of our Milky Way galaxy – and lower towards the poles.

Image above: Star density map. Image Credits: ESA/Gaia/DPAC/CU5/CU8/DPCI/F. De Angeli, D.W. Evans, M. Riello, M. Fouesneau, R. Andrae, C.A.L. Bailer-Jones.

Even though this map is only meant as an appetizer to the full treat of next year's release, which will include roughly a hundred times more stars, it is already possible to spot some interesting features.

The reddest regions in the map, mainly found near the Galactic Centre, correspond to dark areas in the density map: these are clouds of dust that obscure part of the starlight, especially at blue wavelengths, making it appear redder – a phenomenon known as reddening.

It is also possible to see the two Magellanic Clouds – small satellite galaxies of our Milky Way – in the lower part of the map.

The task of measuring colours is performed by the photometric instrument on Gaia. This instrument contains two prisms that split the starlight into its constituent wavelengths, providing two low-resolution spectra for each star: one for the short, or blue, wavelengths (330-680 nm) and the other for the long, or red, ones (640-1050 nm). Scientists then compare the total amount of light in the blue and red spectra to estimate stellar colours.

To precisely calibrate these spectra, however, it is necessary to know the position of each source on Gaia's focal plane to very high accuracy – in fact, to an accuracy that only Gaia itself can provide.

As part of the effort to extract physical parameters from the data sent back by the satellite, scientists feed them to an iterative algorithm that compares the recorded images of stars to models of how such images should look: as a result, the algorithm provides a first estimate of the star's parameters, such as its position, brightness, or colour. By collecting more data and feeding them to the algorithm, the models are constantly improved and so are the estimated parameters for each star.

Image above: Artist's impression of Gaia. Credits: ESA/ATG medialab; background image: ESO/S. Brunier.

The first Gaia data release, published in September 2016, was based on less than a quarter of the total amount of data that will be collected by the satellite over its entire five-year mission, which is expected to observe each star an average of 70 times. This first release, listing unprecedentedly accurate positions on the sky for 1.142 billion stars, along with their brightness, contained no information on stellar colours: by then, it had not been possible to run enough iterations of the algorithm to accurately estimate additional parameters.

As the satellite continues to observe more stars, scientists have now had more time to feed data to the iterative algorithm to obtain estimates of stellar colours, like the ones shown in the new map. These estimates will be validated, over the coming months, as part of the overall data processing effort leading to the second Gaia data release.

Since the first data release, scientists across the world have been using Gaia's brightness measurements – which are obtained over the full G-band, from 330 to 1050 nm – along with datasets from other missions to estimate stellar colours. These studies have been applied to a variety of subjects, from variable stars and stellar clusters in our Galaxy to the characterisation of stars in the Magellanic Clouds.

Next year, the second release of Gaia data will include not only the position and G-band brightness, but also the blue and red colour for over a billion stars – in addition to the long-awaited estimates of stellar parallaxes and proper motions based on Gaia measurements for all the observed stars [2]. This extraordinary dataset will allow scientists to delve into the secrets of our Galaxy, investigating its composition, formation and evolution to an unparalleled degree of detail.


[1] The preliminary colour map shows a sample of stars that have been selected randomly from all Gaia stars with G-band magnitudes brighter than 17 and for which both colour measurements (from the blue and the red channels of Gaia's photometric instrument) are available.

[2] Gaia's goal is to measure the parallax (a small, periodic change in the apparent position of a star caused by Earth's yearly revolution around the Sun, which depends on the star's distance from us) and proper motion (the motion of stars across the plane of the sky caused by their physical movement through the Galaxy) for over one billion stars. In the process, Gaia will measure also the brightness and colour of these stars, take spectra for a subset of them, and observe a variety of other celestial objects, from asteroids in our own Solar System to distant galaxies beyond the Milky Way.

Related links:

Data Processing and Analysis Consortium (DPAC):

Photometric instrument:

First Gaia data release:

Preliminary View of the Gaia sky in colour:

ESA Gaia:

Images (mentioned), Text, Credit: European Space Agency (ESA).

Best regards,

mardi 15 août 2017

NASA Studies CubeSat Mission to Solve Venusian Mystery

NASA - Goddard Space Flight Center logo.

Aug. 15, 2017

Venus looks bland and featureless in visible light, but change the filter to ultraviolet, and Earth’s twin suddenly looks like a different planet. Dark and light areas stripe the sphere, indicating that something is absorbing ultraviolet wavelengths in the planet’s cloud tops.

A team of scientists and engineers working at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, has received funding from the agency’s Planetary Science Deep Space SmallSat Studies, or PSDS3, program to advance a CubeSat mission concept revealing the nature of this mysterious absorber situated within the planet’s uppermost cloud layer.

Called the CubeSat UV Experiment, or CUVE, the mission would investigate Venus’ atmosphere using ultraviolet-sensitive instruments and a novel, carbon-nanotube light-gathering mirror.

Similar in structure and size to Earth, Venus spins slowly in the opposite direction of most planets. Its thick atmosphere, consisting mainly of carbon dioxide, with clouds of sulfuric acid droplets, traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system with surface temperatures hot enough to melt lead.

Image above: The cloud-enshrouded Venus appears featureless, as shown in this image taken by NASA’s MESSENGER mission. In ultraviolet, however, the planet takes on a completely different appearance as seen below. Image Credit: NASA.

Although NASA and other international space programs have dispatched multiple missions to Venus, “the exact nature of the cloud top absorber has not been established,” said CUVE Principal Investigator Valeria Cottini, a researcher at the University of Maryland who is leading a team of experts in the composition, chemistry, dynamics, and radiative transfer of the planet’s atmosphere. “This is one of the unanswered questions and it’s an important one,” she added.

Past observations of Venus show that half of the solar energy is absorbed in the ultraviolet by an upper layer of the sulfuric-acid clouds, giving the planet its striped dark and light features. Other wavelengths are scattered or reflected into space, which explains why the planet looks like a featureless, yellowish-white sphere in the optical — wavelengths visible to the human eye.

Theories abound as to what causes these streaked, contrasting features, Cottini said. One explanation is that convective processes dredge the absorber from deep within Venus’ thick cloud cover, transporting the substance to the cloud tops. Local winds disperse the material in the direction of the wind, creating the long streaks. Scientists theorize the bright areas as observed in the ultraviolet are probably stable against convection and do not contain the absorber, while the dark areas do.

“Since the maximum absorption of solar energy by Venus occurs in the ultraviolet, determining the nature, concentration, and distribution of the unknown absorber is fundamental,” Cottini said. “This is a highly-focused mission — perfect for a CubeSat application.”

Image above: As seen in the ultraviolet, Venus is striped by light and dark areas indicating that an unknown absorber is operating in the planet’s top cloud layer. The image was taken by NASA’s Pioneer-Venus Orbiter in 1979. Image Credit: NASA.

To learn more about the absorber, the CUVE team, which includes Goddard scientists as well researchers affiliated with the University of Maryland and Catholic University, is leveraging investments Goddard has made in miniaturized instruments and other technologies. In addition to flying a miniaturized ultraviolet camera to add contextual information and capture the contrast features, CUVE would carry a Goddard-developed spectrometer to analyze light over a broad spectral band — 190-570 nanometers — covering the ultraviolet and visible. The team also plans to leverage investments in CubeSat navigation, electronics, and flight software.

“A lot of these concepts are driven by important Goddard research-and-development investments,” said Tilak Hewagama, a CUVE team member who has worked with Goddard scientists Shahid Aslam, Nicolas Gorius, and others to demonstrate a CubeSat-compatible spectrometer. “That’s what got us started.”

One of the other novel CUVE adaptations is the potential use of a lightweight telescope equipped with a mirror made of carbon nanotubes in an epoxy resin. To date, no one has been able to make a mirror using this resin.

Such optics offer several advantages. In addition to being lightweight and highly stable, they are relatively easy to reproduce. They do not require polishing — a time-consuming and often-times expensive process that assures a smooth, perfectly shaped surface.

Developed by Goddard contractor Peter Chen, the mirror is made by pouring a mixture of epoxy and carbon nanotubes into a mandrel, or mold, fashioned to meet a specific optical prescription. Technicians then heat the mold to cure and harden the epoxy. Once set, the mirror is coated with a reflective material of aluminum and silicon dioxide.

Study Objectives

The team plans to further enhance the mission’s technologies and evaluate technical requirements to reach a polar orbit around Venus as a secondary payload. The team believes it would take CUVE one-and-a-half years to reach its destination. Once in orbit, the team would gather data for about six months.

“CUVE is a targeted mission, with a dedicated science payload and a compact bus to maximize flight opportunities such as a ride-share with another mission to Venus or to a different target,” Cottini said. “CUVE would complement past, current, and future Venus missions and provide great science return at lower cost.”

Small satellites, including CubeSats, are playing an increasingly larger role in exploration, technology demonstration, scientific research and educational investigations at NASA, including: planetary space exploration; Earth observations; fundamental Earth and space science; and developing precursor science instruments like cutting-edge laser communications, satellite-to-satellite communications and autonomous movement capabilities.

Related links:


Small Satellite Missions:

For more technology news, go to

Images (mentioned), Text, Credits: NASA/Lynn Jenner/Goddard Space Flight Center, by Lori Keesey.


Tracking a solar eruption through the Solar System

ESA- European Space Agency logo / NASA - National Aeronautics and Space Administration logo.

15 August 2017

Ten spacecraft, from ESA’s Venus Express to NASA’s Voyager-2, felt the effect of a solar eruption as it washed through the Solar System while three other satellites watched, providing a unique perspective on this space weather event.

Tracking a solar eruption through the Solar System

Scientists working on ESA’s Mars Express were looking forward to investigating the effects of the close encounter of Comet Siding Spring on the Red Planet’s atmosphere on 19 October 2014, but instead they found what turned out to be the imprint of a solar event.

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

SOHO’s view

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

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

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

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

“CME speeds with distance from the Sun is not well understood, in particular in the outer Solar System,” says ESA’s Olivier Witasse, who led the study.

In the firing line

“Thanks to the precise timings of numerous in situ measurements, we can better understand the process, and feed our results back into models.”

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

From an initial maximum of about 1000 km/s estimated at the Sun, a strong drop to 647 km/s was measured by Mars Express three days later, falling further to 550 km/s at Rosetta after five days. This was followed by a more gradual decrease to 450–500 km/s at the distance of Saturn a month since the event.

Multispacecraft view

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

In the case of ESA’s Venus Express, its science package was not switched on because Venus was ‘behind’ the Sun as seen from Earth, limiting communication capabilities.

A faint indication was inferred from its star tracker being overwhelmed with radiation at the expected time of passage.

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

Cosmic ray drop

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

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

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

Notes for Editors:

“Interplanetary coronal mass ejection observed at Stereo-A, Mars, comet 67P/Churyumov–Gerasimenko, Saturn and New Horizons en route to Pluto. Comparison of its Forbush decreases at 1.4, 3.1 and 9.9 AU,” by O. Witasse et al. is published in Journal of Geophysical Research: Space Physics, a journal of the American Geophysical Union.

Journal of Geophysical Research: Space Physics:

Related links:

ESA's SOHO home page:

Mars Express:



Venus Express:

Curiosity Rover (MSL):

Mars Odyssey:


New Horizons:

Solar Dynamics Observatory:



Images, Videos, Text, Credits: ESA/Markus Bauer/Olivier Witasse/SDO/NASA; SOHO (ESA & NASA); NASA/Stereo; ESA/Royal Observatory of Belgium.

Best regards,

lundi 14 août 2017

Study Finds Drought Recoveries Taking Longer

JPL - Jet Propulsion Laboratory logo.

Aug. 14, 2017

As global temperatures continue to rise, droughts are expected to become more frequent and severe in many regions during this century. A new study with NASA participation finds that land ecosystems took progressively longer to recover from droughts in the 20th century, and incomplete drought recovery may become the new normal in some areas, possibly leading to tree death and increased emissions of greenhouse gases.

In results published Aug. 10 in the journal Nature, a research team led by Christopher Schwalm of Woods Hole Research Center, Falmouth, Massachusetts, and including a scientist from NASA’s Jet Propulsion Laboratory, Pasadena, California, measured recovery time following droughts in various regions of the world. They used projections from climate models verified by observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Terra satellite and ground measurements. The researchers found that drought recovery was taking longer in all land areas. In two particularly vulnerable regions -- the tropics and northern high latitudes -- recovery took ever longer than in other regions.

Image above: Global patterns of drought recovery time, in months. The longest recovery times are depicted in shades of blue and pink, with the shortest recovery times in yellow. White areas indicate water, barren lands, or regions that did not experience a drought during the study period. Image Credits: Woods Hole Research Center.

Schwalm noted that in model projections that assumed no new restrictions on greenhouse gas emissions (the so-called business-as-usual scenario), "Time between drought events will likely become shorter than the time needed for land ecosystems to recover from them.”

”Using the vantage point of space, we can see all of Earth’s forests and other ecosystems getting hit repeatedly and increasingly by droughts,“ said study co-author Josh Fisher of JPL. “Some of these ecosystems recover, but, with increasing frequency, others do not. Data from our ‘eyes’ in space allow us to verify our simulations of past and current climate, which, in turn, helps us reduce uncertainties in projections of future climate.”

The scientists argue that recovery time is a crucial metric for assessing the resilience of ecosystems, shaping the odds of crossing a tipping point after which trees begin to die. Shorter times between droughts, combined with longer drought recovery times, may lead to widespread tree death, decreasing the ability of land areas to absorb atmospheric carbon.

The research is funded by the National Science Foundation and NASA. Other participating institutions include Northern Arizona University, Flagstaff; the University of Utah, Salt Lake City; Carnegie Institution for Science, Stanford, California; the University of New Mexico, Albuquerque; the U.S. Forest Service, Ogden, Utah; Arable Labs Inc., Princeton, New Jersey; the National Snow and Ice Data Center, Boulder, Colorado; Oak Ridge National Laboratory, Oak Ridge, Tennessee; the University of Maine, Orono; Pacific Northwest National Laboratory, Richland, Washington; the University of Illinois, Urbana; the University of Nevada, Reno; and Auburn University, Auburn, Alabama.

Related links:


Jet Propulsion Laboratory (JPL):

Image (mentioned), Text, Credits: NASA/Tony Greicius/JPL/Andrew Good/Woods Hole Research Center/Dave McGlinchey.


ATLAS observes direct evidence of light-by-light scattering

CERN - European Organization for Nuclear Research logo.

14 Aug 2017

Physicists from the ATLAS experiment at CERN have found the first direct evidence ofhigh energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published today in Nature Physics, confirms one of the oldest predictions of quantum electrodynamics (QED).

"This is a milestone result: the first direct evidence of light interacting with itself at high energy,” says Dan Tovey(University of Sheffield), ATLAS Physics Coordinator. “This phenomenon is impossible in classical theories of electromagnetism; hence this result provides a sensitive test of our understanding of QED, the quantum theory of electromagnetism."

Image above: A light-by-light scattering event measured in the ATLAS detector (Image: ATLAS/CERN).

Direct evidence for light-by-light scattering at high energy had proven elusive for decades – until the Large Hadron Collider’s second run began in 2015. As the accelerator collided lead ions at unprecedented collision rates, obtaining evidence for light-by-light scattering became a real possibility. “This measurement has been of great interest to the heavy-ion and high-energy physics communities for several years, as calculations from several groups showed that we might achieve a significant signal by studying lead-ion collisions in Run 2,” says Peter Steinberg (Brookhaven National Laboratory), ATLAS Heavy Ion Physics Group Convener.

Heavy-ion collisions provide a uniquely clean environment tostudy light-by-light scattering. As bunches of lead ions are accelerated, an enormous flux of surrounding photons is generated. When ions meet at the centre of the ATLAS detector, very few collide, yet their surrounding photons can interact and scatter off one another. These interactions are known as ‘ultra-peripheral collisions’.

Studying more than 4 billion events taken in 2015, the ATLAS collaboration found 13 candidates for light-by-light scattering. This result has a significance of 4.4 standard deviations, allowing the ATLAS collaboration to report the first direct evidence of this phenomenon at high energy.

“Finding evidence of this rare signature required the development of a sensitive new ‘trigger’ for the ATLAS detector,” says Steinberg. “The resulting signature — two photons in an otherwise empty detector — is almost the diametric opposite of the tremendously complicated eventstypically expected from lead nuclei collisions. The new trigger’s success in selecting these events demonstrates the power and flexibility of the system, as well as the skill and expertise of the analysis and trigger groups who designed and developed it.”

 Large Hadron Collider (LHC). Animation Credit: CERN

ATLAS physicists will continue to study light-by-light scattering during the upcoming LHC heavy-ion run, scheduled for 2018. More data will further improve the precision of theresult and may open a new window to studies of new physics. In addition, the study of ultra-peripheral collisions should play a greater role in the LHC heavy-ion programme, as collision rates further increase in Run 3 and beyond.​


CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

Related links:

ATLAS experiment:

Large Hadron Collider (LHC):

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Image (mentioned), Animation (mentioned), Text, Credits: CERN/Katarina Anthony.

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