Posted on by Fraser Cain

Venus Express Tests its Engine

Venus Express main engine firing in space. Image credit: ESA Click to enlarge
One hundred days after beginning its cruise to Venus, ESA’s Venus Express spacecraft successfully tested its main engine for the first time in space.

The main engine test is a critical step in the mission. In fact, it is due to its powerful thrust that Venus Express will be able to ‘brake’ on arrival at Venus. The spacecraft must slow down in order to be captured in orbit around the planet.

The engine was fired during the night of 16/17 February, starting at 01:27 CET (00:27 UT) and the ‘burn’ lasted for about three seconds. Thanks to this engine burn, the spacecraft changed its velocity by almost three metres per second.

About one hour later, the data received from the spacecraft by the Venus Express ground control team (via ESA’s New Norcia antenna in Australia) revealed that the test was successful.

The engine performed as expected. The spacecraft reacted correctly to the push and was able to recover the control of its attitude and to correctly point its high-gain antenna back to Earth to communicate with ground control.

All data recorded during the burn will now be carefully analysed by Astrium (who built the spacecraft) and ESA’s engineers to study the performance of the engine in detail.

The next big milestone is the Venus Orbit Insertion manoeuvre on 11 April 2006, which will require the main engine firing sequence to operate for about 51 minutes in the opposite direction to the spacecraft motion. This braking will allow the spacecraft to counteract the pull of the Sun and Venus, and to start orbiting the planet.

Venus Express is currently at a distance of about 47 million kilometres from Earth.

Original Source: ESA Portal

Posted on by Fraser Cain

Greenland Ice Loss Doubled in the Past Decade

Helheim Glacier, located in southeast Greenland. Image credit: NASA/JPL Click to enlarge
The loss of ice from Greenland doubled between 1996 and 2005, as its glaciers flowed faster into the ocean in response to a generally warmer climate, according to a NASA/University of Kansas study.

The study will be published tomorrow in the journal Science. It concludes the changes to Greenland’s glaciers in the past decade are widespread, large and sustained over time. They are progressively affecting the entire ice sheet and increasing its contribution to global sea level rise.

Researchers Eric Rignot of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and Pannir Kanagaratnam of the University of Kansas Center for Remote Sensing of Ice Sheets, Lawrence, used data from Canadian and European satellites. They conducted a nearly comprehensive survey of Greenland glacial ice discharge rates at different times during the past 10 years.

“The Greenland ice sheet’s contribution to sea level is an issue of considerable societal and scientific importance,” Rignot said. “These findings call into question predictions of the future of Greenland in a warmer climate from computer models that do not include variations in glacier flow as a component of change. Actual changes will likely be much larger than predicted by these models.”

The evolution of Greenland’s ice sheet is being driven by several factors. These include accumulation of snow in its interior, which adds mass and lowers sea level; melting of ice along its edges, which decreases mass and raises sea level; and the flow of ice into the sea from outlet glaciers along its edges, which also decreases mass and raises sea level. This study focuses on the least well known component of change, which is glacial ice flow. Its results are combined with estimates of changes in snow accumulation and ice melt from an independent study to determine the total change in mass of the Greenland ice sheet.

Rignot said this study offers a comprehensive assessment of the role of enhanced glacier flow, whereas prior studies of this nature had significant coverage gaps. Estimates of mass loss from areas without coverage relied upon models that assumed no change in ice flow rates over time. The researchers theorized if glacier acceleration is an important factor in the evolution of the Greenland ice sheet, its contribution to sea level rise was being underestimated.

To test this theory, the scientists measured ice velocity with interferometric synthetic-aperture radar data collected by the European Space Agency’s Earth Remote Sensing Satellites 1 and 2 in 1996; the Canadian Space Agency’s Radarsat-1 in 2000 and 2005; and the European Space Agency’s Envisat Advanced Synthetic Aperture Radar in 2005. They combined the ice velocity data with ice sheet thickness data from airborne measurements made between 1997 and 2005, covering almost Greenland’s entire coast, to calculate the volumes of ice transported to the ocean by glaciers and how these volumes changed over time. The glaciers surveyed by those satellite and airborne instrument data drain a sector encompassing nearly 1.2 million square kilometers (463,000 square miles), or 75 percent of the Greenland ice sheet total area.

From 1996 to 2000, widespread glacial acceleration was found at latitudes below 66 degrees north. This acceleration extended to 70 degrees north by 2005. The researchers estimated the ice mass loss resulting from enhanced glacier flow increased from 63 cubic kilometers in 1996 to 162 cubic kilometers in 2005. Combined with the increase in ice melt and in snow accumulation over that same time period, they determined the total ice loss from the ice sheet increased from 96 cubic kilometers in 1996 to 220 cubic kilometers in 2005. To put this into perspective, a cubic kilometer is one trillion liters (approximately 264 billion gallons of water), about a quarter more than Los Angeles uses in one year.

Glacier acceleration has been the dominant mode of mass loss of the ice sheet in the last decade. From 1996 to 2000, the largest acceleration and mass loss came from southeast Greenland. From 2000 to 2005, the trend extended to include central east and west Greenland.

“In the future, as warming around Greenland progresses further north, we expect additional losses from northwest Greenland glaciers, which will then increase Greenland’s contribution to sea level rise,” Rignot said.

For information about NASA and agency programs on the Web, visit:
http://www.nasa.gov/home.

For University of Kansas Center for Remote Sensing of Ice Sheets information, visit:
http://www.cresis.ku.edu/flashindex.htm.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

Original Source: NASA News Release

Posted on by Fraser Cain

Three Moons in a Row

Dione, Prometheus and Epimetheus all aligned in a row. Click to enlarge
This fortunate view sights along Saturn’s ringplane to capture three moons aligned in a row: Dione (1,126 kilometers, or 700 miles across) at left, Prometheus (102 kilometers, or 63 miles across) at center and Epimetheus (116 kilometers, or 72 miles across) at right.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 2, 2006, at a distance of approximately 2.8 million kilometers (1.7 million miles) from Saturn. The image scale is 19 kilometers (12 miles) per pixel on Dione, and about 17 kilometers (11 miles) per pixel on Prometheus and Epimetheus.

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.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Japan’s New Satellite Sends Back its First Image

An image of Mt. Fuji, the first image acquired by ALOS. Image credit: JAXA Click to enlarge
This image of Mt. Fuji is the first data to be acquired by Japan’s recently launched Advanced Land Observing Satellite (ALOS) on 24 January 2006. ESA is supporting ALOS as a ‘Third Party Mission’, which means the Agency will utilise its multi-mission ground systems of existing national and industrial facilities and expertise to acquire, process and distribute data from the satellite to users.

Mt. Fuji ? Japan?s highest mountain (3 776 metres) ? is a volcano that has been dormant since its last eruption in 1707. It is located near the Pacific coast and straddles the prefectures of Yamanashi and Shizuoka about 100 kilometres west of Tokyo.

Detailed streets and rivers in the Kofu Basin are visible in the front of the image, and Motosu Lake, one of five lakes making up the Fuji Five Lake region, is in the centre right. The Fuji-Subaru road, which leads to the top of the mountain from Motosu Lake, can also be seen.

Motosu Lake, featured on the 5000 Yen note, is the westernmost of the five lakes, all of which were formed by lava flows, and has a circumference of 13 kilometres. The other four lakes are: Kawaguchi Lake, Yamanaka Lake , Sai Lake and Shoji Lake.

Thousands of people ascend Mt. Fuji every year, usually during July and August (the official climbing season) when there is no snow. The mountain hike is divided into ten stations, with paved roads going to the fifth station (around 1400 to 2400 metres above sea level).

The image data was acquired as part of the initial functional verification test since the satellite’s launch. One of ALOS’ three onboard instruments, the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM), observed the mountain at 02:00 CET (10:30 Japan time) on 14 February 2006.

The PRISM is an optical sensor which has three independent optical systems for acquiring terrain and altitude data simultaneously, allowing for three-dimensional images with a high accuracy and frequency.

The other two instruments onboard ALOS are the Phased Array type L-band Synthetic Aperture Radar (PALSAR), a microwave radar instrument that can acquire observations through any weather conditions, and the Advanced Visible and Near Infrared Radiometer type-2 (AVNIR-2), designed to chart land cover and vegetation in visible and near-infrared spectral bands.

Original Source: ESA Portal

Posted on by Fraser Cain

Surgery in Space

Surgery in space might be not that far away. Image credit: NASA Click to enlarge
If scientists can put a man on the moon, or send him into space for a few years at time, can they enable astronauts to perform complex surgical procedures there, too?

Professor Adam Dubrowksi of surgery doesn’t see why not, and he’s making space surgery a focus of his research. There’ll be a need for it once astronauts in the International Space Station begin to stay on board for extended periods, says Dubrowski, who is also a kinesiologist in the Surgical Skills Centre at Mount Sinai Hospital. The U.S. National Aeronautics and Space Administration (NASA) and the Canadian Space Agency (CSA) are also looking towards a mission to Mars, a journey that will take three to four years each way.

“The longer you stay, the more potential there is for things to happen,” Dubrowski points out, noting that lacerations and trauma injuries are certainly possible. Currently, astronauts get a few hours of medical training on the ground, which is insufficient for treating more serious injuries, he says. Although typically a medical doctor is on board the space station, “everybody has to know a bit of everything.” On longer missions, he anticipates having a physician and a highly skilled medical assistant who are both trained in surgery, while the rest of the crew will be trained in the basics.

Currently, emergencies are dealt with on board the space station and surgery can be performed using a remote-controlled robot. But as spaceships get further away from Earth, robotic surgery is no longer possible because the signals take longer to reach the mission, Dubrowski explains. And “no one understands what happens when you’re in zero gravity” and need to suture or staple a wounded person.

So Dubrowski, his wife, Waterloo kinesiology professor Heather Carnahan, and Dr. Gary Gray, a Canadian Space Agency consultant from Defence Research and Development Canada, hope to explore these questions with CSA funding. The three have already conducted zero-gravity research into basic motor skills such as touching one’s nose or tying one’s shoes. A weightless environment affects a person’s hand-eye co-ordination, aim and ability to apply a certain amount of force when undertaking tasks, he says. Dubrowski’s interest in space research began after he received his PhD in kinesiology in 2001 from the University of Waterloo. A native of Poland who immigrated to the Toronto area, Dubrowski was influenced by a visit to Dr. Otmar Bock, a leading German researcher in zero-gravity, following completion of his doctoral studies. The two maintained a collaboration, which helped Dubrowski get funding from the European Space Agency and the German Space Agency.

Now, the Canadian Space Agency plans to develop a surgery training protocol for astronauts and Dubrowski, Carnahan and Gray ? with the support of the experts from the Surgical Skills Centre and the Wilson Centre ? plan to bid for the contract. At the same time, they will be applying for smaller funds for parabolic flight research.

Space-surgery training will be three-pronged, Dubrowski explains. The first step is adaptation to zero gravity using an inverted paradigm in which experimental participants are placed upside down on something similar to a bed to “get more of an idea of weightlessness.”

The second step will be simulating zero gravity in a swimming pool; Dubrowski and Surgical Skills Centre manager Lisa Satterthwaite are working on procuring something similar to the huge swimming pool with the replica of the space station used in the NASA centre in Houston. “You can adjust the buoyancy of the person so they’re suspended in water,” Dubrowski says. “That’s another way of simulating zero gravity.”

Third, trainees will take their basic surgery skills on parabolic flights in which an airplane ascends and descends roughly 40 times, creating a transient zero-gravity environment on the descents. Dubrowski uses a variety of simple and complex simulators to allow students at the Surgical Skills Centre to practise skills such as stitching with skin patches.

Surgery in space isn’t that far away, Dubrowksi predicts; there are plans to put a manned lunar base on the moon in the next five to 10 years, which will necessitate better surgical skills for the longer missions. And the sooner the better, he says.

Original Source: U of T News Release

Posted on by Fraser Cain

Ski Jumping on the Moon

“Go big or go home.” That’s what aerialists on the US Olympic ski team say, and when they say “big,” they mean it.

Big means “Big Air,” 20 meters above the ground, as high as a five-story building. Aerial skiers fly into the void as fast as a motorcycle speeds down a city street, flipping head over heels, twisting and flipping again. The sky tumbles, but dizziness is not allowed, because only 3 heart-pumping seconds after launch, it’s time to land.

“And you don’t want to land on your ? well ? you know,” says aerial skier and Olympic gold medalist Eric Bergoust: educational video.

He should know. In the sport of aerial skiing, Bergoust has done it all. He was one of the first skiers ever to complete a quad-twist triple flip–four twists and three flips in mid-air. In 1998, hours after a frightening crash in practice, he used the move to win gold at the Nagano Olympic Games. At the time, his score was the highest ever recorded. This year, he’s a top contender again in Torino.

Bergoust has a knack for invention. He has designed new skis to soften the impact of practice landings in swimming pools. He has altered the shape of ski jumps, called “kickers,” to make flights longer-lasting and safer. And his take-off method, raising one arm propeller-style to add twist to his flight, is widely imitated.

His next innovation: “We should jump on the moon! There’s plenty of fresh powder (moondust),” he explains. “And I figure the 1/6 g would give us a lot of hang time.” More hang time means more flips–and more gold.

Consider the following:

On Earth, a typical run begins with Bergoust hurtling down a 23-degree slope. By the time he reaches bottom, 20 meters below the starting gate, he’s traveling almost 70 km/hr?directly into the kicker. From a skier’s point of view, the kicker looks uncomfortably like a wall, but it’s really a ramp guiding the aerialist almost straight up in the air. Bergoust’s favorite kickers are angled at 70 degrees! Up he goes, hanging for nearly 3 seconds before landing in soft snow another 20+ meters beyond the ramp.

see captionNow imagine the same run?same hill, same kicker, same skier?on the moon. Because lunar gravity is less, Bergoust would accelerate downslope at a more gradual pace, reaching bottom with a speed of only 28 km/hr. On Earth, such a slow start would be a disaster. On the moon, it’s perfect. Leaving the kicker at that speed, Bergoust hangs in the “air” for a whopping seven seconds, more than twice his hang-time on Earth: proof.

“I might be able to double my quad-triple,” he says.

Remember, Bergoust won gold in 1998 with a quad-triple. Since then other skiers have added a single twist to his move, turning it into a quint-triple. “Quints” are expected to win the men’s freestyle aerials in Torino. On the moon, Bergoust would have time to add four more twists and three more flips to his routine. “Let’s see?” calculates Bergoust, “that would be an octuple-twist sextuple flip.” Guaranteed gold.

Now for the problems:

skiing on the moonMoondust, although it is powdery, is not as slippery as snow. On the contrary, moondust is very abrasive. It is made of tiny sharp fragments of glass and rock produced by eons of meteoroids pulverizing the moon. Compared to snow, moondust is a “slow surface,” maybe too slow for a good jump.

To combat this, skiers are going to need extra-slick skis coated with Teflon or some other low-friction material. Thin films of diamond might be the answer. Diamond-like carbon films in Earth laboratories rival Teflon in slipperiness, with the advantage of diamond-like hardness to resist the scratching action of sharp-edged dust.

Another problem is the kicker. On Earth, kickers are made of snow. Workers blow snow into large wooden forms laid out at the base of the slope. A spray of water helps the snow stick together and makes the ramp slippery-smooth. Disassemble the forms and?voila!?a kicker.

Imagine the same process on the moon. Workers assemble their form and begin dumping moondust into it. There’s no water hose to squirt the dust to make it stick together. Water exposed to lunar vacuum sublimates (vaporizes) in a flash. So the dust remains dry. Disassemble the forms and?voila!?the kicker slumps into a shapeless pile.

The solution in this case might be a microwave water hose. In labs on Earth, researchers have discovered that grains of moondust cooked in a microwave oven quickly melt and stick together. Spraying moondust with microwaves might allow Olympic workers to mold a good kicker.

And finally?the landing.

On Earth, aerial skiers land on a layer of soft snow, which cushions their impact. On the moon, they’ll land on a layer of soft moondust. Very likely, the dust will spray upwards, coating the skier’s suit.

What’s the problem? Ask any Apollo astronaut. They hated it when moondust got on their spacesuits. Dark dust absorbed sunlight, causing the suit to overheat. Sharp edges of the dust cut into seals, springing leaks. Dust-covered visors were hard to see through. A skier’s suit, thoroughly “dusted,” might be useless after a single run. Another problem to solve….

Bergoust loves solving problems. For years he’s been tinkering with skis, redesigning kickers, inventing new moves, and he’s ready for a new frontier.

“I just need to find a spacesuit!”

Original Source: NASA News Release

Posted on by Fraser Cain

Stormy Saturn

Great oval-shaped storms breaking through Saturn’s cloudy atmosphere. Image credit: NASA/JPL/SSI Click to enlarge
Great, oval-shaped storms churn through Saturn’s clouds in this Cassini spacecraft view of southern latitudes. The thin, linear striations in cloud features extending away from the ovals suggests that there is very little horizontal (as opposed to vertical) mixing at those latitudes. Low contrast in the original image was enhanced to make small-scale details visible.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 2, 2006, at a distance of approximately 2.8 million kilometers (1.7 million miles) from Saturn. The image scale is 16 kilometers (10 miles) 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.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Tiny Crystals in Violent Galaxies

An artist’s illustration showing the greenish tiny crystals sprinkled throughout the core of a pair of colliding galaxies. Image credit: NASA Click to enlarge
NASA’s Spitzer Space Telescope has observed a rare population of colliding galaxies whose entangled hearts are wrapped in tiny crystals resembling crushed glass.

The crystals are essentially sand, or silicate, grains that were formed like glass, probably in the stellar equivalent of furnaces. This is the first time silicate crystals have been detected in a galaxy outside of our own.

“We were surprised to find such delicate, little crystals in the centers of some of the most violent places in the universe,” said Dr. Henrik Spoon of Cornell University, Ithaca, N.Y. He is first author of a paper on the research appearing in the Feb. 20 issue of the Astrophysical Journal. “Crystals like these are easily destroyed, but in this case, they are probably being churned out by massive, dying stars faster than they are disappearing.”

The discovery will ultimately help astronomers better understand the evolution of galaxies, including our Milky Way, which will merge with the nearby Andromeda galaxy billions of years from now.

“It’s as though there’s a huge dust storm taking place at the center of merging galaxies,” said Dr. Lee Armus, a co-author of the paper from NASA’s Spitzer Science Center at the California Institute of Technology in Pasadena. “The silicates get kicked up and wrap the galaxies’ nuclei in giant, dusty glass blankets.”

Silicates, like glass, require heat to transform into crystals. The gem-like particles can be found in the Milky Way in limited quantities around certain types of stars, such as our sun. On Earth, they sparkle in sandy beaches, and at night, they can be seen smashing into our atmosphere with other dust particles as shooting stars. Recently, the crystals were also observed by Spitzer inside comet Tempel 1, which was hit by NASA’s Deep Impact probe (http://www.spitzer.caltech.edu/Media/releases/ssc2005-18/release.shtml).

The crystal-coated galaxies observed by Spitzer are quite different from our Milky Way. These bright and dusty galaxies, called ultraluminous infrared galaxies, or “Ulirgs,” are swimming in silicate crystals. While a small fraction of the Ulirgs cannot be seen clearly enough to characterize, most consist of two spiral-shaped galaxies in the process of merging into one. Their jumbled cores are hectic places, often bursting with massive, newborn stars. Some Ulirgs are dominated by central supermassive black holes.

So, where are all the crystals coming from? Astronomers believe the massive stars at the galaxies’ centers are the main manufacturers. According to Spoon and his team, these stars probably shed the crystals both before and as they blow apart in fiery explosions called supernovae. But the delicate crystals won’t be around for long. The scientists say that particles from supernova blasts will bombard and convert the crystals back to a shapeless form. This whole process is thought to be relatively short-lived.

“Imagine two flour trucks crashing into each other and kicking up a temporary white cloud,” said Spoon. “With Spitzer, we’re seeing a temporary cloud of crystallized silicates created when two galaxies smashed together.”

Spitzer’s infrared spectrograph spotted the silicate crystals in 21 of 77 Ulirgs studied. The 21 galaxies range from 240 million to 5.9 billion light-years away and are scattered across the sky. Spoon said the galaxies were most likely caught at just the right time to see the crystals. The other 56 galaxies might be about to kick up the substance, or the substance could have already settled.

Others authors of this work include Drs. A.G.G.M. Tielens and J. Cami of NASA’s Ames Research Center, Moffett Field, Calif.; Drs. G.C. Sloan and Jim R. Houck of Cornell; B. Sargent of the University of Rochester, N.Y.; Dr. V. Charmandaris of the University of Crete, Greece; and Dr. B.T. Soifer of the Spitzer Science Center.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center. JPL is a division of Caltech. Spitzer’s infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck.

Original Source: NASA News Release

Posted on by Fraser Cain

Gamma-ray Afterglow reveals Pre-Historic Particle Accelerator

The gamma-ray image of the galactic centre region taken by H.E.S.S. Click to enlarge
Astrophysicists using the H.E.S.S. gamma-ray telescopes, in Namibia, have announced the detection of very-high-energy gamma rays from huge gas clouds known to pervade the centre of our Galaxy. These gamma rays are expected to result from the even more energetic cosmic-ray particles, which permeate our entire Galaxy, crashing into the clouds. However, thanks to the extreme sensitivity of the H.E.S.S instrument in this energy range, precise measurements of the intensity and energies of these gamma rays further show that in the central region of our Galaxy these cosmic-ray particles are typically more energetic than those measured falling onto the Earth’s atmosphere. Possible reasons why cosmic rays are enhanced and of higher energies at the heart of our Galaxy include the echo of a supernova which exploded some ten thousand years beforehand, or a burst of particle acceleration from the super massive black hole at the very centre of our Galaxy.

Gamma rays resemble normal light or X-rays, but are much more energetic. Visible light has an energy of about one electronvolt (1 eV), in physicist’s terms. X-rays are thousands to millions of eV. H.E.S.S. detects very-high-energy gamma-ray photons with an energy of a million million eVs, or one teraelectronvolt. These high-energy gamma rays are quite rare; even for relatively strong astrophysical sources, only about one gamma ray per month hits a square metre at the top of the Earth’s atmosphere.

High-energy particles from space continuously bombard the Earth’s atmosphere from all directions. Their energies exceed, by far, those that can be reached using man-made particle accelerators. Cosmic rays were discovered in 1912 by Victor Hess, and while they have been extensively studied for almost a century, their origin – often declared as one of the key themes of astrophysics – is still not completely understood. One important early result of the H.E.S.S. experiment was to reveal a supernova explosion shock-wave [1] as a site of intense particle acceleration

In a recent publication in Nature magazine, the international H.E.S.S. collaboration reported the discovery of gamma-ray emission from a complex of gas clouds near the centre of our own Milky Way Galaxy. These giant clouds of hydrogen gas encompass an amount of gas equivalent to 50 million times the mass of the sun. With the highly sensitive H.E.S.S. gamma-ray telescopes, it is possible for the first time to show that these clouds are glowing in very-high-energy gamma rays.

One key issue in our understanding of cosmic rays is their distribution in space. Do they permeate the entire Galaxy uniformly, or do their density and distribution in energy vary depending on one’s location in the Galaxy (for example, due to the proximity of cosmic particle accelerators)? Direct measurements of cosmic rays can only taken within our solar system, located about 25,000 light years from the centre of the Galaxy. However, a subterfuge allows astrophysicists to investigate cosmic rays elsewhere in the Galaxy; when a cosmic-ray particle collides with an interstellar gas particle, gamma rays are produced.

The central part of our Galaxy is a complex astronomical zoo, containing examples of every type of exotic object known to astronomers, such as the remnants of supernova explosions and a super-massive black hole. It also contains huge quantities of interstellar gas, which tends to clump into clouds. If gamma rays are detected from the direction of such a gas cloud, scientists can infer the density of cosmic rays at the location of the cloud. The intensity and distribution in energy of these gamma rays reflects that of the cosmic rays.

At low energies, around 100 million electronvolts (man-made accelerators reach energies up to 1,000,000 million electronvolts), this technique has been used by the EGRET satellite to map cosmic rays in our Galaxy. At really high energies – the true domain of cosmic-ray accelerators – no instrument has been so far sensitive enough to “see” interstellar gas clouds shining in very-high-energy gamma rays. H.E.S.S. has for the first time demonstrated the presence of cosmic rays in this central region of our Galaxy.

The H.E.S.S. data show that the density of cosmic rays exceeds that in the solar neighbourhood by a significant factor. Interestingly, this difference increases as we go up in energy, which implies that the cosmic rays have been recently accelerated. So, these data hint that the clouds are illuminated by a nearby cosmic-ray accelerator, which was active over the last ten thousand years. Candidates for such accelerators are a gigantic stellar explosion which apparently went off near the heart of our Galaxy in “recent” history; another possible acceleration site is the super-massive black hole at the centre of the Galaxy. Jim Hinton, one of the scientists involved in the discovery, concludes “This is only the first step. We are of course continuing to point our telescopes at the centre of the Galaxy, and will work hard to pinpoint the exact acceleration site – I’m sure that there are further exciting discoveries to come.”

The High Energy Stereoscopic System (H.E.S.S.) team consists of scientists from Germany, France, the UK, the Czech Republic, Ireland, Armenia, South Africa and Namibia.

The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in south-western Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of very-high-energy gamma rays. These are absorbed in the atmosphere, where they give a short-lived shower of particles. The H.E.S.S. telescopes detect the faint, short flashes of bluish light which these particles emit (named Cherenkov light, lasting a few billionths of a second), collecting the light with large mirrors which reflect onto extremely sensitive cameras. Each image gives the position in the sky of a single gamma-ray photon, and the amount of light collected gives the energy of the initial gamma ray. Building up the images photon-by-photon allows H.E.S.S. to create maps of astronomical objects as they appear in gamma rays.

The H.E.S.S. telescope array represents a multi-year construction effort by an international team of more than 100 scientists and engineers. The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.

Original Source: Max Planck Society

Posted on by Fraser Cain

Invisible Metal-Rich Cloud Revealed

Detecting metals in invisible galaxies. Image credit: ESO Click to enlarge
Astronomers, using the unique capabilities offered by the high-resolution spectrograph UVES on ESO’s Very Large Telescope, have found a metal-rich hydrogen cloud in the distant universe. The result may help to solve the missing metal problem and provides insight on how galaxies form.

“Our discovery shows that significant quantities of metals are to be found in very remote galaxies that are too faint to be directly seen”, said C??bf?line P??bf?roux (ESO), lead-author of the paper presenting the results.

The astronomers studied the light emitted by a quasar located 9 billion light-years away that is partially absorbed by an otherwise invisible galaxy sitting 6.3 billion light-years away along the line of sight.

The analysis of the spectrum shows that this galaxy has four times more metals than the Sun. This is the first time one finds such a large amount of ‘metals’ in a very distant object. The observations also indicate that the galaxy must be very dusty.

Almost all of the elements present in the Universe were formed in stars, which themselves are members of galaxies. By estimating how many stars formed over the history of the Universe, it is possible to estimate how much metals should have been produced. This apparently straightforward reasoning has however since several years been confronted with an apparent contradiction: adding up the amount of metals observable today in distant astronomical objects falls short of the predicted value. When the contribution of galaxies now observed at cosmological distances is added to that of the intergalactic medium, the total amounts for no more than a tenth of the metals expected.

Studying distant galaxies is however a difficult task. The further a galaxy, the fainter it is, and the small or intrinsically faint ones won’t be observed. This may introduce severe biases in the observations as only the largest and most active galaxies are picked up.

Astronomers therefore came up with other ways to study distant galaxies: they use quasars, most probably the brightest distant objects known, as beacons in the Universe.

Interstellar clouds of gas in galaxies, located between the quasars and us on the same line of sight, absorb parts of the light emitted by the quasars. The resulting spectrum consequently presents dark ‘valleys’ that can be attributed to well-known elements. Thus, astronomers can measure the amount of metals present in these galaxies – that are in effect invisible – at various epochs.

“This can best be done by high-resolution spectrographs on the largest telescopes, such as the Ultra-violet and Visible Echelle Spectrograph (UVES) on ESO’s Kueyen 8.2-m telescope at the Paranal Observatory,” declared P??bf?roux.

Her team studied in detail the spectrum of the quasar SDSS J1323-0021 that shows clear indications of absorption by a cloud of hydrogen and metals located between the quasar and us. From a careful analysis of the spectrum, the astronomers found this ‘system’ to be four times richer in zinc than the Sun. Other metals such as iron appear to have condensed into dust grains.

“If a large number of such ‘invisible’ galaxies with high metal content were to be discovered, they might well alleviate considerably the missing metals problem”, said Peroux.

Original Source: ESO News Release