Astronomy Cmarchesin

Releases from NASA, NASA Galex, NASA's Goddard Space Flight Center, Hubble, Hinode, Spitzer, Cassini, ESO, ESA, Chandra, HiRISE, Royal Astronomical Society, NRAO, Astronomy Picture of the Day, Harvard-Smithsonian Center For Astrophysics, etc.

Saturday, July 31, 2010

Into the Wild: Spitzer Space Telescope Surveys the Milky Way's Outback

IRAS 21078+5211
Credit:NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin)

A new survey by NASA's Spitzer Space Telescope has turned up treasures aplenty in the outer regions of the Milky Way, where amidst fogs of interstellar chemicals some rare, young and enormous stars are blasting gas out into space.

These very first images from the ongoing GLIMPSE360 survey are but a taste of what will be revealed during Spitzer's scan of the far-flung reaches of our galaxy.

"GLIMPSE360 will see to the edge of the Milky Way galaxy better than any telescope has before," says Barbara Whitney, principal investigator for the survey, Senior Scientist at the University of Wisconsin and a Senior Research Scientist at the Space Science Institute in Boulder, Colorado.

The new survey is an extension of the recent GLIMPSE survey that looked into the Milky Way's bustling center full of stars and dust, and home to a monstrous black hole. From our solar system, which is about two-thirds of the way out from this galactic "downtown," Spitzer's view now shifts to mostly remote areas. In this way, GLIMPSE360 is picking up where the original GLIMPSE left off and will survey the remaining half of the Milky Way's disk out to its very edge.

"It's like looking into the wilderness of our galaxy," says Whitney. "While mapping the stars and dust out there, we hope to answer some major questions about an environment that is very different from the inner Milky Way."

Astronomers want to know how stars arise in this vast expanse that has less star-forming material and a lower concentration of heavy elements, or "metallicity," than found toward the galactic core. Other goals of GLIMPSE360 are detailing the structure of the outer galaxy that is swept by two massive spiral arms and where the Milky Way's star-spangled disk thickens. While trailblazing our galaxy's outback, Spitzer will also come across many fascinating cosmic objects for researchers to further investigate.

Rather like the early westward explorers of North America, GLIMPSE 360 will forge all the way ahead to where our galaxy's shores meet the relative void of intergalactic space. Scientists do not yet know where the Milky Way galaxy "ends," and if recent discoveries in other galaxies are any indication, the outer rim may host unexpected and unknown pockets of star formation.

"We look forward to what GLIMPSE360 will show us," Whitney says. "The adventure is just getting started."

GLIMPSE360, which stands for Galactic Legacy Infrared Mid-Plane Survey Extraordinaire, began last September and will run through early 2011. A full processing of its reams of data will then take another year or so, but chunks of this valuable astronomical information will be released along the way. When combined with the original GLIMPSE and GLIMPSE3D data, the finished survey will offer future researchers a complete field of view of our disk-like, circular galactic abode - hence "360" in the name - ranging in height from 2.7 degrees to 8.4 degrees at the Milky Way's center, or a band five to almost 17 full moons high.

GLIMPSE360 is part of Spitzer's "warm" mission that started in May 2009 when the satellite depleted its liquid coolant and now surveys the cosmos in infrared wavelengths of light 3.6 and 4.5 microns across, or millionths of a meter.

By Adam Hadhazy

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Thursday, July 29, 2010

Blowing in the Wind: Cassini Helps with Dune Whodunit

Cassini radar sees sand dunes on Saturn's giant moon Titan (upper photo) that are sculpted like Namibian sand dunes on Earth (lower photo). The bright features in the upper radar photo are not clouds but topographic features among the dunes. Image credit: NASA/JPL (upper photo); NASA/JSC (lower photo). Larger image

Scientists have used data from the Cassini radar mapper to map the global wind pattern on Saturn's moon Titan using data collected over a four-year period, as depicted in this image. Image credit: NASA/JPL/Space Science Institute. Full image and caption - enlarge image

The answer to the mystery of dune patterns on Saturn's moon Titan did turn out to be blowing in the wind. It just wasn't from the direction many scientists expected.

Basic principles describing the rotation of planetary atmospheres and data from the European Space Agency's Huygens probe led to circulation models that showed surface winds streaming generally east-to-west around Titan's equatorial belt. But when NASA's Cassini spacecraft obtained the first images of dunes on Titan in 2005, the dunes' orientation suggested the sands – and therefore the winds – were moving from the opposite direction, or west to east.

A new paper by Tetsuya Tokano in press with the journal Aeolian Research seeks to explain the paradox. It explains that seasonal changes appear to reverse wind patterns on Titan for a short period. These gusts, which occur intermittently for perhaps two years, sweep west to east and are so strong they do a better job of transporting sand than the usual east-to-west surface winds. Those east-to-west winds do not appear to gather enough strength to move significant amounts of sand.

A related perspective article about Tokano's work by Cassini radar scientist Ralph Lorenz, the lead author on a 2009 paper mapping the dunes, appears in this week's issue of the journal Science.

"It was hard to believe that there would be permanent west-to-east winds, as suggested by the dune appearance," said Tokano, of the University of Cologne, Germany. "The dramatic, monsoon-type wind reversal around equinox turns out to be the key."

The dunes track across the vast sand seas of Titan only in latitudes within 30 degrees of the equator. They are about a kilometer (half a mile) wide and tens to hundreds of kilometers (miles) long. They can rise more than 100 meters (300 feet) high. The sands that make up the dunes appear to be made of organic, hydrocarbon particles. The dunes' ridges generally run west-to-east, as wind here generally sheds sand along lines parallel to the equator.

Scientists predicted winds in the low latitudes around Titan's equator would blow east-to-west because at higher latitudes the average wind blows west-to-east. The wind forces should balance out, based on basic principles of rotating atmospheres.

Tokano re-analyzed a computer-based global circulation model for Titan he put together in 2008. That model, like others for Titan, was adapted from ones developed for Earth and Mars. Tokano added in new data on Titan topography and shape based on Cassini radar and gravity data. In his new analysis, Tokano also looked more closely at variations in the wind at different points in time rather than the averages. Equinox periods jumped out.

Equinoxes occur twice a Titan year, which is about 29 Earth years. During equinox, the sun shines directly over the equator, and heat from the sun creates upwelling in the atmosphere. The turbulent mixing causes the winds to reverse and accelerate. On Earth, this rare kind of wind reversal happens over the Indian Ocean in transitional seasons between monsoons.

The episodic reverse winds on Titan appear to blow around 1 to 1.8 meters per second (2 to 4 mph). The threshold for sand movement appears to be about 1 meter per second (2 mph), a speed that the typical east-to-west winds never appear to surpass. Dune patterns sculpted by strong, short episodes of wind can be found on Earth in the northern Namib sand seas in Namibia, Africa.

"This is a subtle discovery -- only by delving into the statistics of the winds in the model could this rather distressing paradox be resolved," said Ralph Lorenz, a Cassini radar scientist based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "This work is also reassuring for preparations for proposed future missions to Titan, in that we can become more confident in predicting the winds which can affect the delivery accuracy of landers, or the drift of balloons."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the Cassini-Huygens mission for NASA's Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries. JPL is a division of the California Institute of Technology in Pasadena.

More Cassini information is available, at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Contact:

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.

jia-rui.c.cook@jpl.nasa.gov

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Wednesday, July 28, 2010

Brilliant Star in a Colourful Neighbourhood

PR Image eso1031a
The Carina Nebula around the Wolf–Rayet star WR 22

PR Image eso1031b
Panoramic view of the WR 22 and Eta Carinae regions of the Carina Nebula

PR Image eso1031c
The Carina Nebula in the constellation of Carina

PR Video eso1031a
Zooming in on the Carina Nebula around the Wolf–Rayet star WR 22

Panning across the Carina Nebula around the Wolf–Rayet star WR 22

A spectacular new image from ESO’s Wide Field Imager at the La Silla Observatory in Chile shows the brilliant and unusual star WR 22 and its colourful surroundings. WR 22 is a very hot and bright star that is shedding its atmosphere into space at a rate many millions of times faster than the Sun. It lies in the outer part of the dramatic Carina Nebula from which it formed.

Very massive stars live fast and die young. Some of these stellar beacons have such intense radiation passing through their thick atmospheres late in their lives that they shed material into space many millions of times more quickly than relatively sedate stars such as the Sun. These rare, very hot and massive objects are known as Wolf–Rayet stars [1], after the two French astronomers who first identified them in the mid-nineteenth century, and one of the most massive ones yet measured is known as WR 22. It appears at the centre of this picture, which was created from images taken through red, green and blue filters with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. WR 22 is a member of a double star system and has been measured to have a mass at least 70 times that of the Sun.

WR 22 lies in the southern constellation of Carina, the keel of Jason’s ship Argo in Greek mythology. Although the star lies over 5000 light-years from the Earth it is so bright that it can just be faintly seen with the unaided eye under good conditions. WR 22 is one of many exceptionally brilliant stars associated with the beautiful Carina Nebula (also known as NGC 3372) and the outer part of this huge region of star formation in the southern Milky Way forms the colourful backdrop to this image.

The subtle colours of the rich background tapestry are a result of the interactions between the intense ultraviolet radiation coming from hot massive stars, including WR 22, and the vast gas clouds, mostly hydrogen, from which they formed. The central part of this enormous complex of gas and dust lies off the left side of this picture as can be seen in image eso1031b. This area includes the remarkable star Eta Carinae and was featured in an earlier press release (eso0905).

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, 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 VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links
A Wide Field Imager view of the central part of the Carina Nebula

Contacts

Douglas Pierce-Price
ESO
Garching, Germany
Tel: +49 89 3200 6759
Email: dpiercep@eso.org

Richard Hook
ESO, Survey Telescopes PIO
Garching Tel: +49 89 3200 6655
Email: rhook@eso.org

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Subaru Telescope Detects Clues for Understanding the Origin of Mysterious Dark Gamma-Ray Bursts

Figure 1: Afterglow of the dark GRB and its host galaxy taken with the Subaru Telescope's Multi-Object Infrared Camera and Spectrograph (MOIRCS). Image (a) was taken 9 hours after the burst. Image (b) was taken 34 hours after the burst. The afterglow seen at the upper edge of the host galaxy in (a) faded out in (b). Image (c) shows the afterglow after image (b) is subtracted from image (a). A green circle in (a) shows the uncertainty of the position of the X-ray afterglow. (larger image)

Figure 2:Metallicity of GRB host galaxies compared to the stellar masses of their hosts. The black dots refer to the host galaxies from which metallicities were previously derived. GRBs are thought to occur in the environment slightly below the critical metallicity shown with the horizontal solid line. The red cross shows the expected metallicity of the host for this GRB, demonstrating a high-metallicity environment.

A research team led by astronomers from Kyoto University, Tokyo Institute of Technology, and the National Astronomical Observatory of Japan used the Subaru Telescope to observe a dark gamma-ray burst (GRB) that provides clues for understanding the origin of dark gamma-ray bursts. Their research is a very rare case of the detection of a dark GRB's host galaxy and afterglow in the near-infrared wavelength (Fig.1). They not only found that the host galaxy of this GRB is one of the most massive GRB host galaxies but also that a local dusty environment around the GRB significantly suppresses its afterglow. The observational results suggest a high metallicity environment (one that is enriched by elements heavier than helium) around the GRB, a finding that is inconsistent with previous interpretations of GRBs, which associate their origin with a supernova explosion of a low-metallicity massive star (one that contains few elements heavier than helium) at the end of its life. This research suggests the possibility that GRBs classified as "dark" may originate from another mechanism such as the merger of binary stars.

Gamma-ray bursts (GRBs, [1]) are one of the most profound mysteries in current astronomy. Among the most energetic explosions in the universe, these bursts are bright flashes of enormous gamma rays that appear suddenly in the sky and usually last only several to a few tens of seconds. GRBs originate in distant galaxies far beyond the Milky Way. Their brief appearance and a quickly fading afterglow make them a challenge to research. The afterglow of a GRB can be observed in the X-ray, optical, and near-infrared wavelengths for several hours to several days. Since a gamma-ray detector cannot determine the position of the gamma-ray's source accurately, the discovery and/or identification of a galaxy by optical observations of its afterglow is necessary to examine where the GRB occurred and the nature of the environment around it. Adding to the complexity of understanding GRBs are "dark GRBs", which have extremely faint afterglows and/or cannot be detected in the optical band, are particularly elusive and have rarely been investigated, even though they may make up close to half of all GRBs.

The opportunity to know more about dark GRBs came on March 25, 2008 when a dark GRB without its optical afterglow appeared in the constellation Lyra. Only 9 hours after the burst, a research team of astronomers, primarily from Kyoto University, the Tokyo Institute of Technology, and the National Astronomical Observatory of Japan, used the Subaru Telescope, mounted with its Multi-Object Infrared Camera and Spectrograph (MOIRCS), to obtain near-infrared images of the field around the GRB and unveil its mysterious nature, the only detection of a GRB host galaxy and its afterglow in the near-infrared. The rapid observational system of the Subaru Telescope, its strong light-gathering power, and near-infrared observations with its wide-field instrument facilitated this successful discovery. Theoretical models predict much brighter GRB afterglows than the relatively faint afterglow that the team's images detected in the near-infrared wavelength. The researchers propose that their findings demonstrate that a large amount of dust around the GRB strongly suppressed the brightness of the afterglow in the optical and near-infrared wavelengths. A high-metallicity environment typically produces a very dusty environment like this. Did it do so in this case?

To explore this question, the research team followed-up their research about a year after their initial observation. They used the Subaru Prime Focus Camera (Suprime-Cam) to obtain optical images of the GRB's field that could be used to investigate the properties of the host galaxy. They successfully detected the host galaxy, this time in the optical band. This allowed them to examine various properties of the host galaxy by comparing the observed brightness of the GRB host in various wavelengths with model spectra of the galaxy. The team found that this host galaxy has a so-called "stellar mass" (the total mass of stars in the host galaxy) comparable to that of the Milky Way and is one of the most massive GRB host galaxies. More massive galaxies generally tend to show higher metallicity. The researchers calculated the expected metallicity of the host galaxy by relating its stellar mass to metallicity and found that its expected metallicity is by far the highest among metallicities previously confirmed for GRB host galaxies ([2]; Fig. 2).

How, then, could they explain their findings? A low-metallicity single-star explosion scenario is a generally accepted way of explaining the origin of GRBs. Recent studies indicate that relativistic jets (a narrow stream of superhot gas moving at an extremely high speed) associated with supernovae are observed as GRBs when we see them along our line of sight. Current numerical calculations show that a low-metallicity environment is required to produce a relativistic jet when a massive star explodes as a supernova [3]. Previous observations have shown that GRB galaxies are "light." Since lighter galaxies have lower metallicity, astronomers have inferred that a low-metallicity environment produces GRBs. Direct measurements of metallicity at the location where GRBs occurred have confirmed low metallicity. This evidence has contributed to widespread confidence in the low metallicity single-star explosion theory of GRBs' origin.

However, the low-metallicity single-star explosion scenario does not align with the current team's findings that the host galaxy of this dark GRB has high metallicity. Their findings open the possibility that dark GRBs may originate from a type of explosion process other than that of the more well-investigated GRBs. A binary-star (two stars circling each other in a systematic way) merger scenario [4] has been proposed in the past as another possible explanation for the origin of GRBs. Since this scenario can account for the occurrence of GRBs in high-metallicity environment, the researchers point out the possibility that this dark GRB originated in a binary-star system. The team’s results demonstrate that research on dark GRBs is an important key to revealing the origin of the whole population of GRBs. They may even throw light on the hypothesis that a GRB within the Milky Way may be responsible for the mass extinction that occurred on Earth about 435 million years ago during the Ordovician Period. Until now, this explanation was deemed unlikely because of the high-metallicity environment of the Milky Way.

The details of this research will be published in The Astrophysical Journal, in its August 2010 issue, Volume 719.

Research team:

T. Hashimoto, K. Ohta (Kyoto Univ.), K. Aoki, I. Tanaka (NAOJ), K. Yabe (Kyoto Univ.), N. Kawai (Tokyo Tech), W. Aoki, H. Furusawa, T. Hattori, M. Iye (NAOJ), K. S. Kawabata (Hiroshima Univ.), N. Kobayashi (Tokyo Univ.), Y. Komiyama, G. Kosugi, Y. Minowa, Y. Mizumoto (NAOJ), Y. Niino (Kyoto Univ.), K. Nomoto (Tokyo Univ.), J. Noumaru, R. Ogasawara, Tae-Soo Pyo (NAOJ), T. Sakamoto (NASA), K. Sekiguchi, Y. Shirasaki (NAOJ), M. Suzuki (JAXA), A. Tajitsu, T. Takata (NAOJ), T. Tamagawa (RIKEN), H. Terada (NAOJ), T. Totani (Kyoto Univ.), J. Watanabe (NAOJ), T. Yamada (Tohoku Univ.), and A. Yoshida (Aoyama Gakuin Univ.)

Notes:

[1]: It is well-known that GRBs consist of two populations: 1) long GRBs that have bursts of long duration and 2) short GRBs that have bursts of short duration. Since the properties of these two populations of bursts are clearly different, their origins are probably different. The research team followed a GRB classified as a long GRB, and GRB mentioned here refers to long GRB. The origin of short GRBs also remains a mystery.


[2]: Conceptual diagram of GRB and supernova. The rapid rotation of a progenitor of a supernova and the formation of a gas disk near the progenitor's central region are necessary to make a relativistic jet (GRB). However, in this process, the stellar wind, which is material outflow from the surface of the progenitor, carries the rotating momentum (spin angular momentum) of the progenitor away. Thus the rotation velocity becomes slow if the stellar wind outflows a large amount of material before the explosion. How large the amount of material that the stellar wind takes away depends strongly on metallicity. If the metallicity is low, the stellar wind takes the small spin angular momentum of the progenitor away, which results in a star rapidly rotating before its explosion. If metallicity is very high, the stellar wind takes the large spin angular momentum, the progenitor does not rotate rapidly and is not likely to generate a GRB.

[3]: Research teams at the Space Telescope Science Institute (STScI) and the University of Hawaii in the USA have also reported recently that dark GRBs have appeared in high-metallicity environments.
[4]: Conceptual diagram of the binary-star merger scenario. Binary stars are celestial objects consisting of a more massive star (primary) and a less massive star (secondary) that orbit a common center of mass. As the primary star evolves, its atmospheric layer expands and surrounds two stars. In this process, two stars move gradually closer to each other and finally merge. As the stars merge, the angular momentum associated with the orbital motion of the two stars (orbital angular momentum) remains. The merged star rotates rapidly and may become the progenitor of a GRB. Therefore, this scenario suggests that a GRB can occur even in a high-metallicity environment.

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Friday, July 23, 2010

Comet P/2010 A2, an Activated Asteroid from the Main Asteroid Belt

Comet-like object P/2010 A2 was discovered by the LINEAR survey on January 6, 2010. Service observations carried out using ACAM on the William Herschel Telescope on January 21, 2010, show an asteroidal nucleus detached from the dust tail (see Figure 1). Owing to its orbital parameters and its cometary appearance, the object is classified as a main-belt comet, in other words, an activated asteroid from the main asteroid belt. Comet P/2010 A2's orbit is the nearest to the Sun known so far, for this kind of object (semi-major axis of 2.29 AU).
Figure 1. Image of the nucleus of P/2010 A2 (indicated with an arrow) and the dust tail, detached from the asteroid. This image was obtained with ACAM on the WHT on January 21, 2010. The x- and y-axes are labelled in kilometers, and the direction of the Sun is to the right. This object is the first Main-Belt Comet discovered at heliocentric distances as small as 2 AU (figure extracted from F. Moreno et al., 2010, ApJ, 718, L132). [ JPEG | TIFF ]

Modelling of the dust feature indicates that the asteroid became active in late March 2009, reached maximum activity in early June 2009 with a dust loss mass rate of about 5 kg/s, and ceased activity in early December 2009. The size of the particles ejected was between 0.001 and 1 cm, with speeds compatible with water-ice-drive cometary activity at such heliocentric distances.

The diameter of the asteroid is estimated at 220±40 m, and dust in the tail accounts for about 0.3% of the object mass.

While the event may have been triggered by a collision, this cannot be confirmed with the available observations, but in any case the models indicate that sustained activity over a period of some eight months is required to explain the observations.

More information:

F. Moreno, J. Licandro, G.-P. Tozzi, J.L. Ortiz, A. Cabrera-Lavers, T. Augusteijn, T. Liimets, J.E. Lindberg, T. Pursimo, P. Rodríguez-Gil, O. Vaduvescu, 2009, "Water-ice driven activity on Main-Belt Comet P/2010 A2 (LINEAR) ?", ApJ, 718, L132. Astro-ph | ApJ.

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Thursday, July 22, 2010

NASA Telescope Finds Elusive Buckyballs in Space for First Time

NASA's Spitzer Space Telescope has at last found buckyballs in space, as illustrated by this artist's conception. Image credit: NASA/JPL-Caltech.

These data from NASA's Spitzer Space Telescope show the signatures of buckyballs in space. Image credit: NASA/JPL-Caltech/University of Western Ontario

Mini Soccer Balls in Space

Buckyballs Jiggle like Jello

PASADENA, Calif. - Astronomers using NASA's Spitzer Space Telescope have discovered carbon molecules, known as "buckyballs," in space for the first time. Buckyballs are soccer-ball-shaped molecules that were first observed in a laboratory 25 years ago.

They are named for their resemblance to architect Buckminster Fuller's geodesic domes, which have interlocking circles on the surface of a partial sphere. Buckyballs were thought to float around in space, but had escaped detection until now.

"We found what are now the largest molecules known to exist in space," said astronomer Jan Cami of the University of Western Ontario, Canada, and the SETI Institute in Mountain View, Calif. "We are particularly excited because they have unique properties that make them important players for all sorts of physical and chemical processes going on in space." Cami has authored a paper about the discovery that will appear online Thursday in the journal Science.

Buckyballs are made of 60 carbon atoms arranged in three-dimensional, spherical structures. Their alternating patterns of hexagons and pentagons match a typical black-and-white soccer ball. The research team also found the more elongated relative of buckyballs, known as C70, for the first time in space. These molecules consist of 70 carbon atoms and are shaped more like an oval rugby ball. Both types of molecules belong to a class known officially as buckminsterfullerenes, or fullerenes.

The Cami team unexpectedly found the carbon balls in a planetary nebula named Tc 1. Planetary nebulas are the remains of stars, like the sun, that shed their outer layers of gas and dust as they age. A compact, hot star, or white dwarf, at the center of the nebula illuminates and heats these clouds of material that has been shed.

The buckyballs were found in these clouds, perhaps reflecting a short stage in the star's life, when it sloughs off a puff of material rich in carbon. The astronomers used Spitzer's spectroscopy instrument to analyze infrared light from the planetary nebula and see the spectral signatures of the buckyballs. These molecules are approximately room temperature -- the ideal temperature to give off distinct patterns of infrared light that Spitzer can detect. According to Cami, Spitzer looked at the right place at the right time. A century from now, the buckyballs might be too cool to be detected.

The data from Spitzer were compared with data from laboratory measurements of the same molecules and showed a perfect match.

"We did not plan for this discovery," Cami said. "But when we saw these whopping spectral signatures, we knew immediately that we were looking at one of the most sought-after molecules."

In 1970, Japanese professor Eiji Osawa predicted the existence of buckyballs, but they were not observed until lab experiments in 1985. Researchers simulated conditions in the atmospheres of aging, carbon-rich giant stars, in which chains of carbon had been detected. Surprisingly, these experiments resulted in the formation of large quantities of buckminsterfullerenes. The molecules have since been found on Earth in candle soot, layers of rock and meteorites.

The study of fullerenes and their relatives has grown into a busy field of research because of the molecules' unique strength and exceptional chemical and physical properties. Among the potential applications are armor, drug delivery and superconducting technologies.

Sir Harry Kroto, who shared the 1996 Nobel Prize in chemistry with Bob Curl and Rick Smalley for the discovery of buckyballs, said, "This most exciting breakthrough provides convincing evidence that the buckyball has, as I long suspected, existed since time immemorial in the dark recesses of our galaxy."

Previous searches for buckyballs in space, in particular around carbon-rich stars, proved unsuccessful. A promising case for their presence in the tenuous clouds between the stars was presented 15 years ago, using observations at optical wavelengths. That finding is awaiting confirmation from laboratory data. More recently, another Spitzer team reported evidence for buckyballs in a different type of object, but the spectral signatures they observed were partly contaminated by other chemical substances.

For more information about Spitzer, visit: http://www.nasa.gov/spitzer

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

Contact

Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.Clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
NASA Headquarters, Washington

j.d.harrington@nasa.gov

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Hyperfast Star Was Booted from Milky Way

Going, Going, Gone: Star Leaves the Milky Way
Illustration Credit: NASA, ESA, and G. Bacon (STScI)
Science Credit: NASA, ESA, O. Gnedin (University of Michigan, Ann Arbor),
and W. Brown (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.)

A hundred million years ago, a triple-star system was traveling through the bustling center of our Milky Way galaxy when it made a life-changing misstep. The trio wandered too close to the galaxy's giant black hole, which captured one of the stars and hurled the other two out of the Milky Way. Adding to the stellar game of musical chairs, the two outbound stars merged to form a super-hot, blue star.

This story may seem like science fiction, but astronomers using NASA's Hubble Space Telescope say it is the most likely scenario for a so-called hypervelocity star, known as HE 0437-5439, one of the fastest ever detected. It is blazing across space at a speed of 1.6 million miles (2.5 million kilometers) an hour, three times faster than our Sun's orbital velocity in the Milky Way. Hubble observations confirm that the stellar speedster hails from the Milky Way's core, settling some confusion over where it originally called home.

Most of the roughly 16 known hypervelocity stars, all discovered since 2005, are thought to be exiles from the heart of our galaxy. But this Hubble result is the first direct observation linking a high-flying star to a galactic center origin.

"Using Hubble, we can for the first time trace back to where the star comes from by measuring the star's direction of motion on the sky. Its motion points directly from the Milky Way center," says astronomer Warren Brown of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., a member of the Hubble team that observed the star. "These exiled stars are rare in the Milky Way's population of 100 billion stars. For every 100 million stars in the galaxy lurks one hypervelocity star."

The movements of these unbound stars could reveal the shape of the dark matter distribution surrounding our galaxy. "Studying these stars could provide more clues about the nature of some of the universe's unseen mass, and it could help astronomers better understand how galaxies form," says team leader Oleg Gnedin of the University of Michigan in Ann Arbor. "Dark matter's gravitational pull is measured by the shape of the hyperfast stars' trajectories out of the Milky Way."

The stellar outcast is already cruising in the Milky Way's distant outskirts, high above the galaxy's disk, about 200,000 light-years from the center. By comparison, the diameter of the Milky Way's disk is approximately 100,000 light-years. Using Hubble to measure the runaway star's direction of motion and determine the Milky Way's core as its starting point, Brown and Gnedin's team calculated how fast the star had to have been ejected to reach its current location.

"The star is traveling at an absurd velocity, twice as much as the star needs to escape the galaxy's gravitational field," explains Brown, a hypervelocity star hunter who found the first unbound star in 2005. "There is no star that travels that quickly under normal circumstances — something exotic has to happen."

There's another twist to this story. Based on the speed and position of HE 0437-5439, the star would have to be 100 million years old to have journeyed from the Milky Way's core. Yet its mass — nine times that of our Sun — and blue color mean that it should have burned out after only 20 million years — far shorter than the transit time it took to get to its current location.

The most likely explanation for the star's blue color and extreme speed is that it was part of a triple-star system that was involved in a gravitational billiard-ball game with the galaxy's monster black hole. This concept for imparting an escape velocity on stars was first proposed in 1988. The theory predicted that the Milky Way's black hole should eject a star about once every 100,000 years.

Brown suggests that the triple-star system contained a pair of closely orbiting stars and a third outer member also gravitationally tied to the group. The black hole pulled the outer star away from the tight binary system. The doomed star's momentum was transferred to the stellar twosome, boosting the duo to escape velocity from the galaxy. As the pair rocketed away, they went on with normal stellar evolution. The more massive companion evolved more quickly, puffing up to become a red giant. It enveloped its partner, and the two stars spiraled together, merging into one superstar — a blue straggler.

"While the blue straggler story may seem odd, you do see them in the Milky Way, and most stars are in multiple systems," Brown says.

This vagabond star has puzzled astronomers since its discovery in 2005 by the Hamburg/European Southern Observatory sky survey. Astronomers had proposed two possibilities to solve the age problem. The star either dipped into the Fountain of Youth by becoming a blue straggler, or it was flung out of the Large Magellanic Cloud, a neighboring galaxy.

In 2008 a team of astronomers thought they had solved the mystery. They found a match between the exiled star's chemical makeup and the characteristics of stars in the Large Magellanic Cloud. The rogue star's position also is close to the neighboring galaxy, only 65,000 light-years away. The new Hubble result settles the debate over the star's birthplace.

Astronomers used the sharp vision of Hubble's Advanced Camera for Surveys to make two separate observations of the wayward star 3 1/2 years apart. Team member Jay Anderson of the Space Telescope Science Institute in Baltimore, Md., developed a technique to measure the star's position relative to each of 11 distant background galaxies, which form a reference frame.

Anderson then compared the star's position in images taken in 2006 with those taken in 2009 to calculate how far the star moved against the background galaxies. The star appeared to move, but only by 0.04 of a pixel (picture element) against the sky background. "Hubble excels with this type of measurement," Anderson says. "This observation would be challenging to do from the ground."

The team is trying to determine the homes of four other unbound stars, all located on the fringes of the Milky Way.

"We are targeting massive 'B' stars, like HE 0437-5439," says Brown, who has discovered 14 of the 16 known hypervelocity stars. "These stars shouldn't live long enough to reach the distant outskirts of the Milky Way, so we shouldn't expect to find them there. The density of stars in the outer region is much less than in the core, so we have a better chance to find these unusual objects."

The results were published online in The Astrophysical Journal Letters on July 20, 2010. Brown is the paper's lead author.

CONTACT

Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
410-338-4493

dweaver@stsci.edu

Warren Brown
Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.
617-496-7905

wbrown@cfa.harvard.edu

Jay Anderson
Space Telescope Science Institute, Baltimore, Md.
410-338-4982

jayander@stsci.edu

Oleg Gnedin
University of Michigan, Ann Arbor, Mich.
734-647-4272

ognedin@umich.edu

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Wednesday, July 21, 2010

4C+00.58: Black Hole Jerked Around Twice

Credit X-ray (NASA/CXC/UMD/Hodges-Kluck et al);
Radio (NSF/NRAO/VLA/UMD/Hodges-Kluck et al);
Optical (SDSS)


This image shows the effects of a giant black hole that has been flipped around twice, causing its spin axis to point in a different direction from before. The large optical image, from the Sloan Digital Sky Survey, is centered on a radio galaxy named 4C +00.58. The smaller image to the right shows a close-up view of this galaxy in X-rays (in gold) from the Chandra X-ray Observatory, and radio waves (in blue) from the Very Large Array.

At the center of 4C +00.58 is a supermassive black hole that is actively pulling in large quantities of gas. Gas swirling toward the black hole forms a disk around the black hole, generating strong electromagnetic forces that propel some of the gas away from the disk at high speed, producing radio jets. A radio image of this galaxy shows a bright pair of jets pointing from left to right and a fainter, more distant line of radio emission running approximately from the top to the bottom of the image. A labeled image shows these two sets of radio emission. This galaxy belongs to a class of "X-shaped" galaxies because of the outline of the radio emission.


The X-ray image of hot gas in and around 4C +00.58 reveals four different cavities -- regions of lower than average X-ray emission -- around the black hole. These cavities come in pairs: one in the top-right and bottom-left (labeled cavities #1 and #2 respectively), and another in the top-left and bottom-right (labeled cavities #3 and #4 respectively). Special processing was applied to this image to make the cavities more obvious.

According to the scenario presented by a new study, the spin axis of the black hole ran along a diagonal line from top-right to bottom-left. The galaxy then collided with a smaller galaxy. Possible evidence for this collision is seen in the optical image, in the form of a stellar shell. After this collision, a jet powered by the black hole ignited, blowing away gas to form cavities #1 and #2 in the hot gas. Since the gas falling onto the black hole was not aligned with the spin of the black hole, the spin axis of the black hole rapidly changed direction, and the jets then pointed in a roughly top-left to bottom-right direction, creating cavities #3 and #4 and radio emission in this direction.

Then, either a merging of the two central black holes from the colliding galaxies, or more gas falling onto the black hole caused the spin axis to jerk around to its present direction in roughly a left to right direction.

Fast Facts for 4C+00.58:

Credit X-ray (NASA/CXC/UMD/Hodges-Kluck et al): Radio (NSF/NRAO/VLA/UMD/Hodges-Kluck et al); Optical (SDSS)
Scale: Wide field image is 15 arcmin across (3.4 million light years), inset image is 1.6 arcmin across (363,000 light years)
Category:
Cosmology/Deep Fields/X-ray Background, Black Holes, Galaxies
Coordinates (J2000) RA 16h 06m 12.70s | Dec +00° 00' 27.10"
Constellation:
Serpens
Observation Date: Dec 22, 2007 & Apr 29, 2009
Observation Time: 30 hours
Obs. ID: 9274, 10304
Color Code: X-ray (Red-Gold), Radio (Blue)
Instrument:
ACIS
References: E.Hodges-Kluck et al, 2010 ApJL, 717:L37-L41
Distance Estimate: About 780 million light years (z=0.059)

More information, including images and other multimedia, can be found at:
http://chandra.harvard.edu and http://chandra.nasa.gov

Media contacts:

Janet Anderson
NASA Marshall Space Flight Center, Ala.
256-544-6162
janet.l.anderson@nasa.gov

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu

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Stars Just Got Bigger

The young cluster RMC 136a

The sizes of stars (annotated)

The young cluster RMC 136a

Zooming in on the young cluster RMC 136a

Using a combination of instruments on ESO’s Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters — millions of times more luminous than the Sun, losing weight through very powerful winds — may provide an answer to the question “how massive can stars be?”

A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO’s Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula’s extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613).

The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birthweight of as much as 320 times that of the Sun.

In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system [1], as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses.

Very massive stars produce very powerful outflows. “Unlike humans, these stars are born heavy and lose weight as they age,” says Paul Crowther. “Being a little over a million years old, the most extreme star R136a1 is already ‘middle-aged’ and has undergone an intense weight loss programme, shedding a fifth of its initial mass over that time, or more than fifty solar masses.”

If R136a1 replaced the Sun in our Solar System, it would outshine the Sun by as much as the Sun currently outshines the full Moon. “Its high mass would reduce the length of the Earth's year to three weeks, and it would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible,” says Raphael Hirschi from Keele University, who belongs to the team.

These super heavyweight stars are extremely rare, forming solely within the densest star clusters. Distinguishing the individual stars — which has now been achieved for the first time — requires the exquisite resolving power of the VLT’s infrared instruments [2].

The team also estimated the maximum possible mass for the stars within these clusters and the relative number of the most massive ones. “The smallest stars are limited to more than about eighty times more than Jupiter, below which they are ‘failed stars’ or brown dwarfs,” says team member Olivier Schnurr from the Astrophysikalisches Institut Potsdam. “Our new finding supports the previous view that there is also an upper limit to how big stars can get, although it raises the limit by a factor of two, to about 300 solar masses.”

Within R136, only four stars weighed more than 150 solar masses at birth, yet they account for nearly half of the wind and radiation power of the entire cluster, comprising approximately 100 000 stars in total. R136a1 alone energises its surroundings by more than a factor of fifty compared to the Orion Nebula cluster, the closest region of massive star formation to Earth.

Understanding how high mass stars form is puzzling enough, due to their very short lives and powerful winds, so that the identification of such extreme cases as R136a1 raises the challenge to theorists still further. “Either they were born so big or smaller stars merged together to produce them,” explains Crowther.

Stars between about 8 and 150 solar masses explode at the end of their short lives as supernovae, leaving behind exotic remnants, either neutron stars or black holes. Having now established the existence of stars weighing between 150 and 300 solar masses, the astronomers’ findings raise the prospect of the existence of exceptionally bright, “pair instability supernovae” that completely blow themselves apart, failing to leave behind any remnant and dispersing up to ten solar masses of iron into their surroundings. A few candidates for such explosions have already been proposed in recent years.

Not only is R136a1 the most massive star ever found, but it also has the highest luminosity too, close to 10 million times greater than the Sun. “Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon,” concludes Crowther.

Notes

[1] The star A1 in NGC 3603 is a double star, with an orbital period of 3.77 days. The two stars in the system have, respectively, 120 and 92 times the mass of the Sun, which means that they have formed as stars weighing, respectively, 148 and 106 solar masses.

[2] The team used the SINFONI, ISAAC and MAD instruments, all attached to ESO’s Very Large Telescope at Paranal, Chile.

More information
This work is presented in an article published in the Monthly Notices of the Royal Astronomical Society (“The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit”, by P. Crowther et al.).

The team is composed of Paul A. Crowther, Richard J. Parker, and Simon P. Goodwin (University of Sheffield, UK), Olivier Schnurr (University of Sheffield and Astrophysikalisches Institut Potsdam, Germany), Raphael Hirschi (Keele University, UK), and Norhasliza Yusof and Hasan Abu Kassim (University of Malaya, Malaysia).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, 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 VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links
Research paper

Contacts

Paul Crowther
University of Sheffield
UK
Tel: +44 114 222 4291
Cell: +44 7946 638 474
Email:
Paul.Crowther@sheffield.ac.uk

Olivier Schnurr
Astrophysikalisches Institut Potsdam
Potsdam, Germany
Tel: +49 331 7499 353
Email:
oschnurr@aip.de

Henri Boffin
ESO, La Silla, Paranal and E-ELT Press Officer
Garching, Germany
Tel: +49 89 3200 6222
Cell: +49 174 515 43 24
Email
: hboffin@eso.org


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Friday, July 16, 2010

NASA's WISE Mission to Complete Extensive Sky Survey

This image shows the famous Pleiades cluster of stars as seen through the eyes of WISE, or NASA's Wide-field Infrared Survey Explorer. The mosaic contains a few hundred image frames -- just a fraction of the more than one million WISE has captured so far as it completes its first survey of the entire sky in infrared light. Image credit: NASA/JPL-Caltech/UCLA

This animation shows the progress of the WISE all-sky survey over time. WISE, or NASA's Wide-field Infrared Survey Explorer, is perched up in the sky like a wise, old owl, scanning the whole sky one-and-a-half times in infrared light. Image credit: NASA/JPL-Caltech/UCLA

PASADENA, Calif. -- NASA's Wide-field Infrared Survey Explorer, or WISE, will complete its first survey of the entire sky on July 17, 2010. The mission has generated more than one million images so far, of everything from asteroids to distant galaxies.

"Like a globe-trotting shutterbug, WISE has completed a world tour with 1.3 million slides covering the whole sky," said Edward Wright, the principal investigator of the mission at the University of California, Los Angeles.

Some of these images have been processed and stitched together into a new picture being released today. It shows the Pleiades cluster of stars, also known as the Seven Sisters, resting in a tangled bed of wispy dust. The pictured region covers seven square degrees, or an area equivalent to 35 full moons, highlighting the telescope's ability to take wide shots of vast regions of space.

The new picture was taken in February. It shows infrared light from WISE's four detectors in a range of wavelengths. This infrared view highlights the region's expansive dust cloud, through which the Seven Sisters and other stars in the cluster are passing. Infrared light also reveals the smaller and cooler stars of the family.

To view the new image, as well as previously released WISE images, visit http://www.nasa.gov/wise and http://wise.astro.ucla.edu .

"The WISE all-sky survey is helping us sift through the immense and diverse population of celestial objects," said Hashima Hasan, WISE Program scientist at NASA Headquarters in Washington. "It's a great example of the high impact science that's possible from NASA's Explorer Program."

The first release of WISE data, covering about 80 percent of the sky, will be delivered to the astronomical community in May of next year. The mission scanned strips of the sky as it orbited around the Earth's poles since its launch last December. WISE always stays over the Earth's day-night line. As the Earth moves around the sun, new slices of sky come into the telescope's field of view. It has taken six months, or the amount of time for Earth to travel halfway around the sun, for the mission to complete one full scan of the entire sky.

For the next three months, the mission will map half of the sky again. This will enhance the telescope's data, revealing more hidden asteroids, stars and galaxies. The mapping will give astronomers a look at what's changed in the sky. The mission will end when the instrument's block of solid hydrogen coolant, needed to chill its infrared detectors, runs out.

"The eyes of WISE have not blinked since launch," said William Irace, the mission's project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Both our telescope and spacecraft have performed flawlessly and have imaged every corner of our universe, just as we planned."

So far, WISE has observed more than 100,000 asteroids, both known and previously unseen. Most of these space rocks are in the main belt between Mars and Jupiter. However, some are near-Earth objects, asteroids and comets with orbits that pass relatively close to Earth. WISE has discovered more than 90 of these new near-Earth objects. The infrared telescope is also good at spotting comets that orbit far from Earth and has discovered more than a dozen of these so far.

WISE's infrared vision also gives it a unique ability to pick up the glow of cool stars, called brown dwarfs, in addition to distant galaxies bursting with light and energy. These galaxies are called ultra-luminous infrared galaxies. WISE can see the brightest of them.

"WISE is filling in the blanks on the infrared properties of everything in the universe from nearby asteroids to distant quasars," said Peter Eisenhardt of JPL, project scientist for WISE. "But the most exciting discoveries may well be objects we haven't yet imagined exist."

JPL manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate in Washington. The mission was selected under NASA's Explorers Program managed by the Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington

j.d.harrington@nasa.gov

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Cluster's decade of discovery

Artist's impression of the four Cluster spacecraft flying in formation. Credits: ESA

ESA’s pioneering Cluster mission is celebrating its 10th anniversary. During the past decade, Cluster’s four satellites have provided extraordinary insights into the largely invisible interaction between the Sun and Earth.

Cluster’s four satellites, Rumba, Samba, Salsa, and Tango, fly in formation around Earth to provide a 3D picture of how the continuous ‘solar wind’ of charged particles or plasma from the Sun affects our near-Earth space environment and its protective ‘magnetic bubble, known as the magnetosphere.
Occasionally, the solar wind becomes turbulent and gusty, buffeting Earth’s magnetic field and producing high-energy particles. These storms in the magnetosphere can hamper electrical systems aboard satellites and on the ground. In the worst cases, they can destroy vital electronic components, rendering satellites and other electrical technology dead.

Scientists have found that extreme solar activity drastically compresses the magnetosphere and modifies the composition of ions in the near-Earth environment. They are now challenged to model how these changes affect orbiting satellites, including the GPS system.

Under normal solar conditions, satellites orbit within the magnetosphere — the protective magnetic bubble carved out by Earth’s magnetic field. But when solar activity increases, the picture changes significantly: the magnetosphere gets compressed and particles get energized, exposing satellites to higher doses of radiation that can perturb signal reception. This is why monitoring and forecasting its impact on near-Earth space is becoming increasingly critical to safeguard daily life on Earth. One way to do this is by studying the physics of near-Earth space and observing the impact of such activity in time. Credits: NASA/ ESA

“Cluster has provided us with a wealth of data to understand the physical processes behind space weather better,” says Philippe Escoubet, ESA Cluster Mission Manager.

The observations have revealed a dramatic realm of invisible violence. Cluster has investigated how the solar wind penetrates near-Earth space and discovered that, under certain circumstances, magnetic whirlpools larger than the entire Earth bore into our magnetosphere, injecting their venomous particles.

When these solar wind particles reach Earth’s atmosphere, they trigger the sublime glow of the northern and southern auroras. Here too, Cluster has been a revelation.

Cluster has confirmed that black auroras, strange electrical phenomenon that generate dark, empty regions within the Northern and Southern Lights, are a kind of 'anti-aurora', sucking electrons from the ionosphere.

This artist's impression shows the four Cluster spacecraft encompassing a 'magnetic null' region. A magnetic null region is a three dimensional zone where the magnetic fields break and reconnect. Before ESA's Cluster started exploring the Earth's magnetosphere it was not possible to identify any of such regions, as the detection required at least four simultaneous points of measurements.
Cluster measurements made on 15 September 2001 showed that the null point exists in an unexpected vortex structure about 500 kilometres across, a characteristic size never been reported before in observations, theory or simulations. Credits: Dr. Xiao/Chinese Academy of Sciences (Beijing). HI-RES JPEG (Size: 1886 kb)

Undoubtedly one of the major highlights of the mission has been the first 3D map of the heart of a ubiquitous magnetic process called reconnection.

This takes place when magnetic fields collide, releasing energy and allowing previously separated plasmas of electrified gas to mix. At the very centre of the event is something called a null point.

Cluster has provided scientists with the first 3D picture of a null point, delivering vital new information. At the time of the reconnection event, the magnetic field was found to be twisted into a 500 km-wide tube in this region.

Understanding magnetic reconnection is a major quest in physics. It is responsible for solar flares, tremendous solar explosions that can be a billion times more powerful than an atomic bomb. In Earth’s laboratories, unwanted reconnection frustrates efforts to produce electricity in fusion reactors.

Such success came eventually after a dramatic beginning when, on 4 June 1996, the first Cluster quartet was destroyed in a catastrophic failure of the Ariane 501 shortly after launch.

But the Cluster team turned this disaster into a resounding success. The satellites were rebuilt and launched just four years later. “It was a tremendous achievement by the whole team to rebuild, test, and relaunch this mission in such a short time,” says John Ellwood, at that time ESA Cluster Project Manager.

The second time, Cluster was sent into orbit two at a time using Russian Soyuz launchers. The first pair lifted off from the Baikonur Cosmodrome in Kazakhstan on 16 July 2000, and the second pair a month later. All four have been circling Earth in formation ever since, conducting their own style of complex orbital dance.

And so began a decade of extraordinary science. Cluster is helping scientists to understand how plasma behaves in all environments. With the four satellites still in excellent condition, the mission has now been extended to 2012.

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