samedi 29 septembre 2012

Worldwide LHC Computing Grid tackles 270-year-old maths problem

CERN - European Organization for Nuclear Research logo.

Sept. 29, 2012

In 1742, Prussian mathematician Christian Goldbach wrote down a mathematical conjecture that in its simplest form states: "every even integer greater than 2 can be written as the sum of two primes". Despite the simple formulation, it is notoriously difficult to find a proof for this conjecture; 270 years later, one remains to be found.

Image above: Servers at the CERN Data Centre form Tier-0 of the Worldwide LHC Computing Grid. As well as LHC physics, the Grid is helping to verify the Golbach conjecture for high numbers (Image: CERN).

Now, computer-science technologist Silvio Pardi at the Italian National Institute for Nuclear Physics (INFN) and mathematicians Tomás Oliveira e Silva and Siegfried Herzog are using an algorithm on the Worldwide LHC Computing Grid (WLCG) to verify that the Goldbach conjecture holds for ever larger numbers.


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 20 Member States.

Find out more:
International Science Grid This Week: "Researchers edge closer to solving 270-year-old math problem thanks to grid computing":

National Institute for Nuclear Physics (INFN):

Worldwide LHC Computing Grid (WLCG):

Image, Text, Credit: CERN.


Ariane 5’s fifth launch of 2012

ESA / Arianespace - Flight VA209 poster.

29 September 2012

28 September 2012, an Ariane 5 launcher lifted off from Europe’s Spaceport in French Guiana on its mission to place two telecommunications satellites, Astra-2F and GSAT-10, into their planned geostationary transfer orbits.

Ariane VA209 liftoff

Liftoff of flight VA209, the 65th Ariane 5 mission, came at 21:18 GMT (23:18 CEST; 18:18 French Guiana). The target injection orbit had a perigee altitude of 249.5 km, an apogee altitude of 35 937 km and an inclination of 6° relative to the equator.

Astra 2F  GSAT-10 launch

The satellites were accurately injected into their transfer orbits about 27 minutes and 30 minutes after liftoff, respectively.

From this transfer orbit, the satellites’ own apogee booster motors circularise their orbits to attain geostationary orbit – where they keep pace with Earth’s own rotation, causing them to remain at fixed points in the sky.

Astra-2F will be positioned above the equator at 28.2°E. It will provide new-generation direct-to-home TV broadcast services to Europe, the Middle East and Africa.

Astra-2F satellite

GSAT-10, to be positioned at 83°E, will provide telecommunication, direct-to-home broadcasting and radio-navigation services to India.

GSAT-10 satellite

The payload mass for this launch was 10 211 kg; the satellites totalled 9401 kg, with payload adapters and dispensers making up the additional 810 kg. This was a new record for Ariane 5 ECA performance.

VA209 flight timeline

Ariane 5’s cryogenic, liquid-propellant main engine was ignited first. Seven seconds later, after checking the functioning of the main engine, the solid-propellant boosters also fired, and the vehicle lifted off.

The solid boosters were jettisoned 2 min 21 sec after main engine ignition, and the fairing protecting the payload during the climb through Earth’s atmosphere was discarded at 3 min 17 sec.

The launcher’s main cryogenic engine shut down at 8 min 59 sec and separated from the upper stage and its payload six seconds later.

Four seconds after main stage separation, the engine of the cryogenic upper stage ignited to continue the journey. The engine shut down at 25 min 20 sec into the flight, at which point the vehicle was travelling at 9350 m/s (33 660 km/h) at an altitude of 660.7 km. The conditions for geostationary transfer orbit injection had been achieved.

At 27 min 44 sec after main engine ignition, Astra-2F separated from the upper stage, followed by GSAT-10 at 30 min 45 sec. Ariane 5’s flight operations were completed 46 min 09sec after main engine ignition.

Related links:

Ariane 5:


Images, Video, Text, Credits: ESA / Arianespace / Arianespace TV / ISRO.

Best regards,

vendredi 28 septembre 2012

NASA Rover Finds Old Streambed on Martian Surface

NASA - Mars Science Laboratory (MSL) patch.

Sept. 28, 2012

Image above: NASA's Curiosity rover found evidence for an ancient, flowing stream on Mars at a few sites, including the rock outcrop pictured here, which the science team has named "Hottah" after Hottah Lake in Canada’s Northwest Territories. Image credit: NASA/JPL-Caltech/MSSS.

NASA's Curiosity rover mission has found evidence a stream once ran vigorously across the area on Mars where the rover is driving. There is earlier evidence for the presence of water on Mars, but this evidence -- images of rocks containing ancient streambed gravels -- is the first of its kind.

Scientists are studying the images of stones cemented into a layer of conglomerate rock. The sizes and shapes of stones offer clues to the speed and distance of a long-ago stream's flow.

In this image from NASA's Curiosity rover, a rock outcrop called Link pops out from a Martian surface that is elsewhere blanketed by reddish-brown dust. Image credit: NASA/JPL-Caltech/MSSS.

"From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep," said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. "Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it."

The finding site lies between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater. Earlier imaging of the region from Mars orbit allows for additional interpretation of the gravel-bearing conglomerate. The imagery shows an alluvial fan of material washed down from the rim, streaked by many apparent channels, sitting uphill of the new finds.

This image shows the topography, with shading added, around the area where NASA's Curiosity rover landed on Aug. 5 PDT (Aug. 6 EDT). Image credit: NASA/JPL-Caltech/UofA.

The rounded shape of some stones in the conglomerate indicates long-distance transport from above the rim, where a channel named Peace Vallis feeds into the alluvial fan. The abundance of channels in the fan between the rim and conglomerate suggests flows continued or repeated over a long time, not just once or for a few years.

The discovery comes from examining two outcrops, called "Hottah" and "Link," with the telephoto capability of Curiosity's mast camera during the first 40 days after landing. Those observations followed up on earlier hints from another outcrop, which was exposed by thruster exhaust as Curiosity, the Mars Science Laboratory Project's rover, touched down.

This map shows the path on Mars of NASA's Curiosity rover toward Glenelg, an area where three terrains of scientific interest converge. Image credit: NASA/JPL-Caltech/Univ. of Arizona.

"Hottah looks like someone jack-hammered up a slab of city sidewalk, but it's really a tilted block of an ancient streambed," said Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena.

The gravels in conglomerates at both outcrops range in size from a grain of sand to a golf ball. Some are angular, but many are rounded.

"The shapes tell you they were transported and the sizes tell you they couldn't be transported by wind. They were transported by water flow," said Curiosity science co-investigator Rebecca Williams of the Planetary Science Institute in Tucson, Ariz.

This set of images compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right). Image credit: NASA/JPL-Caltech/MSSS and PSI.

The science team may use Curiosity to learn the elemental composition of the material, which holds the conglomerate together, revealing more characteristics of the wet environment that formed these deposits. The stones in the conglomerate provide a sampling from above the crater rim, so the team may also examine several of them to learn about broader regional geology.

The slope of Mount Sharp in Gale Crater remains the rover's main destination. Clay and sulfate minerals detected there from orbit can be good preservers of carbon-based organic chemicals that are potential ingredients for life.

River Fans on Earth and Mars

Video above: Curiosity science team member William Dietrich explores the relationship between river fans found in California’s Death Valley on Earth and similar fans in Gale Crater on Mars. Credit: NASA/JPL-Caltech.

"A long-flowing stream can be a habitable environment," said Grotzinger. "It is not our top choice as an environment for preservation of organics, though. We're still going to Mount Sharp, but this is insurance that we have already found our first potentially habitable environment."

During the two-year prime mission of the Mars Science Laboratory, researchers will use Curiosity's 10 instruments to investigate whether areas in Gale Crater have ever offered environmental conditions favorable for microbial life.

NASA's Jet Propulsion Laboratory, a division of Caltech, built Curiosity and manages the Mars Science Laboratory Project for NASA's Science Mission Directorate, Washington.

For more about Curiosity, visit: and .

You can follow the mission on Facebook and Twitter at: and .

Images (mentioned), Video (mentioned), Text, Credits: NASA / Dwayne Brown / JPL / Guy Webster / D.C. Agle.


Mars, where is Deimos?

ESA - Mars Express Mission patch.

28 Sep 2012

 Pioneering images of both Martian moons

Video above: In a first, ESA's Mars Express orbiter imaged the Martian moons Phobos and Deimos together on 5 November 2009. Credits: ESA/DLR/FU Berlin (G. Neukum).

Despite more than a century of observations, the orbit of the Martian moon Deimos is still not known to a high degree of accuracy, but a new study using images taken by ESA's Mars Express orbiter has provided the best orbital model to date.

Mars Express image of the moons Phobos (foreground) and Deimos (background). Credit: ESA/DLR/FU Berlin (G. Neukum).

 135 years have passed since Asaph Hall discovered Phobos and Deimos, two small companions of the planet Mars. Since that time, the satellites have been imaged innumerable times from the Earth and from spacecraft, including recent measurements by the panoramic cameras on the Mars Exploration Rovers and instruments on the Mars Reconnaissance Orbiter.

Although the orbit of the inner moon, Phobos, has been calculated to an accuracy of less than 1 km, the path of more remote Deimos is less well known. In order to improve the orbital models for Deimos, researchers from Germany and Russia have developed a new technique which compares images taken by Mars Express.

Deimos follows an almost circular, near-equatorial orbit at a mean distance of 23 458 km from the centre of Mars. Unlike other Mars orbiters, Mars Express follows an elliptical, near-polar orbit which occasionally enables it to obtain excellent views of Deimos.


Video above: Orbits of Mars Express and the Martian moons. This simulation depicts the relative orbits of Phobos, Deimos and Mars Express around the time of the flyby of Phobos on 7 March 2010. Credit: ESA/DLR/FU Berlin (G. Neukum) and S. Walter/Celestia/NAIF/SPICE.

 Between July 2005 and July 2011, the spacecraft made 50 approaches to Deimos, passing within 14 000 km of the satellite. The closest approach was in March 2011, when the orbiter closed to a range of about 9600 km. However, since the moon is tidally locked to the planet, the spacecraft largely observes the same Mars-facing areas on its surface.

136 images were acquired at different places along Deimos' orbit by the Super Resolution Channel (SRC) of the High Resolution Stereo Camera (HRSC). The SRC is a 1K × 1K CCD-framing camera which is designed to focus on features of interest within the HRSC image strips, when imaging Mars. In comparison with the HRSC, it magnifies features in the image by a factor of about four. In the case of Deimos, the framing images are ideal for astrometric (positional) measurements of the small Martian satellite.

Any astrometric measurement requires good knowledge of the observer's location and viewing direction. In the case of the observations from Mars Express, the position of the spacecraft and the direction in which the camera was pointing were derived from navigational data provided by the European Space Operations Centre (ESOC) in Darmstadt, Germany.

The attitude of the spacecraft (and the pointing of the body-mounted camera) is measured by using two star trackers and three laser gyroscopes. The SRC pointing was verified and corrected for by measuring differences between the observed and predicted positions of background stars in the images. Owing to the SRC's narrow field of view, usually one or two faint stars per image could be observed. The precise positions of these stars are known from catalogues based on data returned by ESA's Hipparcos satellite.

In a paper accepted for publication in Astronomy & Astrophysics, the researchers describe how they used a new astrometric technique, in which the centre-of-figure of non-spherical Deimos was determined by fitting the predicted limb (visible edge) of the satellite to the observed limb.

Over a period of 1.5 to 3.5 minutes, a sequence of seven or eight images was acquired as Deimos moved across the field of view. In all cases, the first and the last image were taken with long time exposures (about 500 ms) to capture faint background stars (magnitudes ranging from 3.4 to 8.8). From the five or six short-time exposures, two to four images usually included Deimos.

"From 50 sets of observations, we fortuitously had nine in which stars were sufficiently bright to be seen in all images," said Andreas Pasewaldt, a PhD student at the Institute of Planetary Research in Berlin, lead author of the paper. "We obtained a set of spacecraft-centred Deimos coordinates with accuracies between 0.6 and 3.6 km.

SRC images of Deimos obtained from different orbits. Credit: ESA/ DLR/FU Berlin (G. Neukum)

"Using a shape model, together with nominal data on Deimos' position and rotational state, we predicted the limb that would be observed from the spacecraft. This limb was projected onto the SRC image, and then fitted to the observed limb during a series of manual and automated steps. This eventually gave us the precise position of the centre of figure for Deimos.

"Comparisons with current orbit models indicate that Deimos is ahead of, or falling behind, its predicted position by as much as +3.4 km or -4.7 km, depending on the chosen model. The data obtained by our 'limb fit method' should considerably improve the models of its orbit."

There is considerable interest in the orbital tracking of the Martian moons. Phobos, moving deep within the gravity field of Mars, is strongly affected by tidal interaction with the planet. This will eventually cause the moon to crash into Mars or break apart, creating a ring of debris. In contrast, Deimos is far enough from Mars to take more than one Martian day to complete each orbit, so it is spiralling slowly outwards.

Improved knowledge of their orbits will also shed new light on the history of the satellite system. Such knowledge is particularly important in the interpretation of gravity field data, acquired during very close flybys. This enables the researchers to model the interiors of the moons and put constraints on their origin.

"It is unclear whether they are asteroids that were captured by Mars or whether they coalesced from a ring of material that formed around the planet after a large object collided with Mars, although the latter scenario seems to be favoured in recent years," said Olivier Witasse, ESA's Mars Express project scientist. "Simultaneous modelling of both orbits may provide strong constraints on the origin and evolution of Phobos and Deimos."

"Better orbital models are also important for future satellite missions, such as automated sample returns currently being studied at ESA, when high navigational accuracy is needed."

For more information about Mars Express Mission, visit:

Images (mentioned), Text, Credits: ESA-ESTEC / Olivier Witasse / German Aerospace Center (DLR) / Andreas Pasewaldt.

Best regards,

mercredi 26 septembre 2012

The Rich Colours of a Cosmic Seagull

ESO - European Southern Observatory logo.

26 September 2012

 Close-up view of the head of the Seagull Nebula

This new image from ESO’s La Silla Observatory shows part of a stellar nursery nicknamed the Seagull Nebula. This cloud of gas, formally called Sharpless 2-292, seems to form the head of the seagull and glows brightly due to the energetic radiation from a very hot young star lurking at its heart. The detailed view was produced by the Wide Field Imager on the MPG/ESO 2.2-metre telescope.

Nebulae are among the most visually impressive objects in the night sky. They are interstellar clouds of dust, molecules, hydrogen, helium and other ionised gases where new stars are being born. Although they come in different shapes and colours many share a common characteristic: when observed for the first time, their odd and evocative shapes trigger astronomers’ imaginations and lead to curious names. This dramatic region of star formation, which has acquired the nickname of the Seagull Nebula, is no exception.

The Seagull Nebula on the borders of the constellations of Monoceros and Canis Major

This new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile shows the head part of the Seagull Nebula [1]. It is just one part of the larger nebula known more formally as IC 2177, which spreads its wings with a span of over 100 light-years and resembles a seagull in flight. This cloud of gas and dust is located about 3700 light-years away from Earth. The entire bird shows up best in wide-field images.

The Seagull Nebula lies just on the border between the constellations of Monoceros (The Unicorn) and Canis Major (The Great Dog) and is close to Sirius, the brightest star in the night sky. The nebula lies more than four hundred times further away than the famous star.

Wide-field view of the entire Seagull Nebula (IC 2177)

The complex of gas and dust that forms the head of the seagull glows brightly in the sky due to the strong ultraviolet radiation coming mostly from one brilliant young star — HD 53367 [2] — that can be spotted in the centre of the image and could be taken to be the seagull’s eye.

The radiation from the young stars causes the surrounding hydrogen gas to glow with a rich red colour and become an HII region [3]. Light from the hot blue-white stars is also scattered off the tiny dust particles in the nebula to create a contrasting blue haze in some parts of the picture.

Zooming in on the Seagull Nebula (IC 2177)

Although a small bright clump in the Seagull Nebula complex was observed for the first time by the German-British astronomer Sir William Herschel back in 1785, the part shown here had to await photographic discovery about a century later.

Panning across the head of the Seagull Nebula

By chance this nebula lies close in the sky to the Thor’s Helmet Nebula (NGC 2359), which was the winner of ESO’s recent Choose what the VLT Observes contest (ann12060). This nebula, with its distinctive shape and unusual name, was picked as the first ever object selected by members of the public to be observed by ESO’s Very Large Telescope. These observations are going to be part of the celebrations on the day of ESO’s 50th anniversary, 5 October 2012. The observations will be streamed live from the VLT on Paranal. Stay tuned!


[1] This object has received many other names through the years  — it is known as Sh 2-292, RCW 2 and Gum 1. The name Sh 2-292 means that the object is the #292 in the second Sharpless catalogue of HII regions, published in 1959. The RCW number refers to the catalogue compiled by Rodgers, Campbell and Whiteoak and published in 1960. This object was also the first in an earlier list of southern nebulae compiled by Colin Gum, and published in 1955.

[2] HD 53367 is a young star with twenty times the mass of our Sun. It is classified as a Be star, which are a type of B star with prominent hydrogen emission lines in its spectrum. This star has a five solar mass companion in a highly elliptical orbit.

[3] HII regions are so named as they consist of ionised hydrogen (H) in which the electrons are no longer bound to protons. HI is the term used for un-ionised, or neutral, hydrogen. The red glow from HII regions occurs because the protons and electrons recombine and in the process emit energy at certain well-defined wavelengths or colours. One such prominent transition (called hydrogen alpha, or H-alpha) leads to the strong red colour.

More information:
The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). 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 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. 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, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.


    Photos of the MPG/ESO 2.2-metre telescope:

    Other photos taken with the MPG/ESO 2.2-metre telescope:

    Photos of La Silla:

Images, Text, Credits: ESO / Richard Hook / IAU and Sky & Telescope / Digitized Sky Survey 2. Acknowledgement: Davide De Martin / Videos: ESO/Digitized Sky Survey 2/Nick Risinger ( Music: Disasterpeace.


Hubble goes to the eXtreme to assemble the deepest ever view of the Universe

ESA - Hubble Space Telescope logo.

26 September 2012

 The Hubble eXtreme Deep Field

Like photographers assembling a portfolio of their best shots, astronomers have assembled a new, improved portrait of our deepest-ever view of the Universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by combining ten years of NASA/ESA Hubble Space Telescope observations taken of a patch of sky within the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full Moon.

Location and size of the Hubble eXtreme Deep Field (ground-based image)

The Hubble Ultra Deep Field is an image of a small area of space in the constellation of Fornax (The Furnace), created using Hubble Space Telescope data from 2003 and 2004. By collecting faint light over one million seconds of observation, the resulting image revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the Universe ever taken at that time.

The Hubble eXtreme Deep Field (annotated)

The new full-colour XDF image is even more sensitive than the original Hubble Ultra Deep Field image, thanks to the additional observations, and contains about 5500 galaxies, even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness that the unaided human eye can see [1].

Distances in the Hubble eXtreme Deep Field

Magnificent spiral galaxies similar in shape to the Milky Way and its neighbour the Andromeda galaxy appear in this image, as do large, fuzzy red galaxies in which the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years as the stars within them age.

Peppered across the field are tiny, faint, and yet more distant galaxies that are like the seedlings from which today’s magnificent galaxies grew. The history of galaxies — from soon after the first galaxies were born to the great galaxies of today, like the Milky Way — is laid out in this one remarkable image.
eXtreme Deep Field zoom and flythrough

Hubble pointed at a tiny patch of southern sky in repeat visits made over the past decade with a total exposure time of two million seconds [2]. More than 2000 images of the same field were taken with Hubble’s two primary cameras: the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble’s vision into near-infrared light. These were then combined to form the XDF.

“The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. XDF allows us to explore further back in time than ever before,” said Garth Illingworth of the University of California at Santa Cruz, principal investigator of the Hubble Ultra Deep Field 2009 (HUDF09) programme.

The Universe is 13.7 billion years old, and the XDF reveals galaxies that span back 13.2 billion years in time. Most of the galaxies in the XDF are seen when they were young, small, and growing, often violently as they collided and merged together. The early Universe was a time of dramatic birth for galaxies containing brilliant blue stars far brighter than our Sun. The light from those past events is just arriving at Earth now, and so the XDF is a time tunnel into the distant past when the Universe was just a fraction of its current age. The youngest galaxy found in the XDF existed just 450 million years after the Universe’s birth in the Big Bang.

Size of the eXtreme Deep Field

Before Hubble was launched in 1990, astronomers were able to see galaxies up to about seven billion light-years away, half way back to the Big Bang. Observations with telescopes on the ground were not able to establish how galaxies formed and evolved in the early Universe.

Hubble gave astronomers their first view of the actual forms of galaxies when they were young. This provided compelling, direct visual evidence that the Universe is truly changing as it ages. Like watching individual frames of a motion picture, the Hubble deep surveys reveal the emergence of structure in the infant Universe and the subsequent dynamic stages of galaxy evolution.

The NASA/ESA/CSA James Webb Space Telescope (Webb telescope), scheduled for launch in 2018, will be aimed at the XDF, and will study it with its infrared vision. The Webb telescope will find even fainter galaxies that existed when the Universe was just a few hundred million years old. Because of the expansion of the Universe, light from the distant past is stretched into longer, infrared wavelengths. The Webb telescope’s infrared vision is ideally suited to push the XDF even deeper, into a time when the first stars and galaxies formed and filled the early “dark ages” of the Universe with light.


The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The HUDF09 team members are G. Illingworth (University of California, Santa Cruz), R. Bouwens (Leiden University), M. Carollo (Swiss Federal Institute of Technology, Zurich (ETH)), M. Franx (Leiden University), I. Labbe (Leiden University), D. Magee and P. Oesch (University of California, Santa Cruz), M. Stiavelli (Space Telescope Science Institute), M. Trenti (University of Cambridge), P. van Dokkum (Yale University), and V. Gonzalez (University of California Observatories/Lick Observatory).

[1] The faintest objects detected in the XDF are 31st magnitude.

[2] The total exposure time is approximately two million seconds, or 23 days. Because Hubble can only observe for about 45 minutes of every 97-minute orbit, the observations that make up the XDF represent 50 days of telescope time.

Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team.


    Images of Hubble:

    NASA release:

Images, Text, Credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team /  Z. Levay (STScI) /  T. Rector, I. Dell'Antonio/NOAO/AURA/NSF / Videos: NASA, ESA, G. Bacon (STScI) and F. Summers (STScI).

Best regards,

Angling Saturn

NASA / ESA - Cassini "Insider's" logo.

Sept. 26, 2012

The Cassini spacecraft takes an angled view toward Saturn, showing the southern reaches of the planet with the rings on a dramatic diagonal.

North on Saturn is up and rotated 16 degrees to the left. This view looks toward the southern, unilluminated side of the rings from about 14 degrees below the ringplane. The rings cast wide shadows on the planet's southern hemisphere.

The moon Enceladus (313 miles, or 504 kilometers across) appears as a small, bright speck in the lower left of the image.

The image was taken with the Cassini spacecraft wide-angle camera on June 15, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.8 million miles (2.9 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 72 degrees. Image scale is 11 miles (17 kilometers) per pixel.

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

More Cassini information is available at and

ESA website: and

Image, Text, Credit: NASA / ESA / JPL-Caltech / Space Science Institute.


mardi 25 septembre 2012

NASA'S Chandra Shows Milky Way is Surrounded by Halo of Hot Gas

NASA - Chandra X-ray Observatory patch.

Sept. 25, 2012

Astronomers have used NASA's Chandra X-ray Observatory to find evidence our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. The estimated mass of the halo is comparable to the mass of all the stars in the galaxy.

If the size and mass of this gas halo is confirmed, it also could be an explanation for what is known as the "missing baryon" problem for the galaxy.

Baryons are particles, such as protons and neutrons, that make up more than 99.9 percent of the mass of atoms found in the cosmos. Measurements of extremely distant gas halos and galaxies indicate the baryonic matter present when the universe was only a few billion years old represented about one-sixth the mass and density of the existing unobservable, or dark, matter. In the current epoch, about 10 billion years later, a census of the baryons present in stars and gas in our galaxy and nearby galaxies shows at least half the baryons are unaccounted for.

This artist's illustration shows an enormous halo of hot gas (in blue) around the Milky Way galaxy. Also shown, to the lower left of the Milky Way, are the Small and Large Magellanic Clouds, two small neighboring galaxies. The halo of gas is shown with a radius of about 300,000 light years, although it may extend significantly further.

In a recent study, a team of five astronomers used data from Chandra, the European Space Agency's XMM-Newton space observatory and Japan's Suzaku satellite to set limits on the temperature, extent and mass of the hot gas halo. Chandra observed eight bright X-ray sources located far beyond the galaxy at distances of hundreds of millions of light-years. The data revealed X-rays from these distant sources are absorbed selectively by oxygen ions in the vicinity of the galaxy. The scientists determined the temperature of the absorbing halo is between 1 million and 2.5 million kelvins, or a few hundred times hotter than the surface of the sun.

Other studies have shown that the Milky Way and other galaxies are embedded in warm gas with temperatures between 100,000 and 1 million kelvins. Studies have indicated the presence of a hotter gas with a temperature greater than 1 million kelvins. This new research provides evidence the hot gas halo enveloping the Milky Way is much more massive than the warm gas halo.

"We know the gas is around the galaxy, and we know how hot it is," said Anjali Gupta, lead author of The Astrophysical Journal paper describing the research. "The big question is, how large is the halo, and how massive is it?"

To begin to answer this question, the authors supplemented Chandra data on the amount of absorption produced by the oxygen ions with XMM-Newton and Suzaku data on the X-rays emitted by the gas halo. They concluded that the mass of the gas is equivalent to the mass in more than 10 billion suns, perhaps as large as 60 billion suns.

"Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way," said co-author Smita Mathur of Ohio State University in Columbus. "It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large."

The estimated mass depends on factors such as the amount of oxygen relative to hydrogen, which is the dominant element in the gas. Nevertheless, the estimation represents an important step in solving the case of the missing baryons, a mystery that has puzzled astronomers for more than a decade.

Although there are uncertainties, the work by Gupta and colleagues provides the best evidence yet that the galaxy's missing baryons have been hiding in a halo of million-kelvin gas that envelopes the galaxy. The estimated density of this halo is so low that similar halos around other galaxies would have escaped detection.

Chandra X-ray Observatory

The paper describing these results was published in the Sept. 1 issue of The Astrophysical Journal. Other co-authors were Yair Krongold of Universidad Nacional Autonoma de Mexico in Mexico City; Fabrizio Nicastro of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; and Massimiliano Galeazzi of University of Miami in Coral Gables, Fla.

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

For Chandra images, multimedia and related materials, visit:

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Images, Text, Credits: NASA / CXC / M.Weiss; NASA / CXC / Ohio State / A.Gupta et al.


Hubble portrays a dusty spiral galaxy

ESA - Hubble Space Telescope logo.

25 September 2012

The NASA/ESA Hubble Space Telescope has provided us with another outstanding image of a nearby galaxy. This week, we highlight the galaxy NGC 4183, seen here with a beautiful backdrop of distant galaxies and nearby stars.

Hubble portrays a dusty spiral galaxy

Located about 55 million light-years from the Sun and spanning about 80 000 light-years, NGC 4183 is a little smaller than the Milky Way. This galaxy, which belongs to the Ursa Major Group, lies in the northern constellation of Canes Venatici (The Hunting Dogs).

NGC 4183 is a spiral galaxy with a faint core and an open spiral structure. Unfortunately, this galaxy is viewed edge-on from Earth, and we cannot fully appreciate its spiral arms. But we can admire its galactic disc.

The discs of galaxies are mainly composed of gas, dust and stars. There is evidence of dust over the galactic plane, visible as dark intricate filaments that block the visible light from the core of the galaxy.

In addition, recent studies suggest that this galaxy may have a bar structure. Galactic bars are thought to channel gas from the spiral arms to the centre, increasing star formation, which is typically more pronounced in the spiral arms than in the bulge of the galaxy.

British astronomer William Herschel first observed NGC 4183 on 14 January 1778.

Hubble Space Telescope

This picture was created from visible and infrared images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. The field of view is about 3.4 arcminutes wide.

This image is co-released with the Hubble Space Telescope Picture of the Week:

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Hubble's Universe:

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Images, Text, Credits: ESA / Hubble & NASA.

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