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Offline neilep

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Hubble finds extrasolar planets far across galaxy
NASA NEWS RELEASE

NASA's Hubble Space Telescope has discovered 16 extrasolar planet candidates orbiting a variety of distant stars in the central region of our Milky Way galaxy.

The planet bonanza was uncovered during a Hubble survey called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Hubble looked farther than has ever successfully been searched before for extrasolar planets. Hubble peered at 180,000 stars in the crowded central bulge of our galaxy 26,000 light-years away. That is one-quarter the diameter of the Milky Way's spiral disk. The results will appear in the Oct. 5 issue of the journal Nature.


This illustration presents a purely speculative view of what such a
"hot Jupiter" might look like. Credit: NASA, ESA, and A. Schaller (for STScI)



This tally is consistent with the number of planets expected to be uncovered from such a distant survey, based on previous exoplanet detections made in our local solar neighborhood. Hubble's narrow view covered a swath of sky no bigger in angular size than two percent the area of the full moon. When extrapolated to the entire galaxy, Hubble's data provides strong evidence for the existence of approximately six billion Jupiter-sized planets in the Milky Way.

Five of the newly discovered planets represent a new extreme type of planet not found in any nearby searches. Dubbed Ultra-Short-Period Planets (USPPs), these worlds whirl around their stars in less than one Earth day.

"Discovering the very short-period planets was a big surprise," said team leader Kailash Sahu of the Space Telescope Science Institute, Baltimore. "Our discovery also gives very strong evidence that planets are as abundant in other parts of the galaxy as they are in our solar neighborhood."

Hubble could not directly view the 16 newly found planet candidates. Astronomers used Hubble's Advanced Camera for Surveys to search for planets by measuring the slight dimming of a star due to the passage of a planet in front of it, an event called a transit. The planet would have to be about the size of Jupiter to block enough starlight, about one to 10 percent, to be measurable by Hubble.

The planets are called candidates, because astronomers could only obtain follow-up mass measurements for two of them due to the distance and faintness of these systems. Following an exhaustive analysis, the team ruled out alternative explanations such as a grazing transit by a stellar companion that could mimic the predicted signature of a true planet. The finding could more than double the number of planets spied with the transit technique to date.

There is a tendency for the planet candidates to revolve around stars more abundant in elements heavier than hydrogen and helium, such as carbon. This supports theories that stars rich in heavy elements have the necessary ingredients to form planets.

The planet candidate with the shortest orbital period, named SWEEPS-10, swings around its star in 10 hours. Located only 740,000 miles from its star, the planet is among the hottest ever detected. It has an estimated temperature of approximately 3,000 degrees Fahrenheit.

"This star-hugging planet must be at least 1.6 times the mass of Jupiter, otherwise the star's gravitational muscle would pull it apart," said SWEEPS team member Mario Livio. "The star's low temperature allows the planet to survive so near to the star."

"Ultra-Short-Period Planets seem to occur preferentially around normal red dwarf stars that are smaller and cooler than our sun," Sahu explained. "The apparent absence of USPPs around sun-like stars in our local neighborhood indicates that they might have evaporated away when they migrated too close to a hotter star."


This is an image of one-half of the Hubble Space Telescope field of view in
 the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). The green
circles identify 9 stars that are orbited by planets with periods of a few days.
 The bottom frame identifies one of two stars in the field where astronomers
were able to spectroscopically measure the star's back-and-forth wobble due to
the pull of the planet. Credit: NASA, ESA, K. Sahu (STScI) and the SWEEPS Science Team


There is an alternative reason why Jupiter-like planets around cooler stars may migrate in closer to the star than such planets around hotter stars. The circumstellar disk of gas and dust out of which they formed extends in closer to a cooler star. Since the discovery of the first "hot Jupiter" around another star in 1995, astronomers have realized this unusual type of massive planet must have spiraled in close to its parent star from a more distant location where it must have formed. The inner edge of a circumstellar disk halts the migration.

Planetary transits occur only when the planet's orbit is viewed nearly edge-on. However, only about 10 percent of hot Jupiters have edge-on orbits that allow the planet to be observed transiting a star. To be successful, transit surveys must view a large number of stars at once. The SWEEPS transit survey covered a rich field of stars in the Sagittarius Window.

The term "window" implies a clear view into the galactic center, but much of the galactic plane is obscured by dust. Hubble monitored 180,000 stars for periodic, brief dimming in a star's brightness. The star field was observed over a continuous seven-day period Feb. 23-29, 2004.

To ensure the dimming was caused by an object orbiting a star, the team used Hubble to detect from two to 15 consecutive transits for each of the16 planet candidates. Two stars in the field are bright enough that the SWEEPS team could make an independent confirmation of a planet's presence by spectroscopically measuring a slight wobble in the star's motion due to the gravitational pull of an unseen companion. They used the European Southern Observatory's Very Large Telescope, located on Mount Paranal in Chile, to measure a slight wobble in the star.

One of the planetary candidates has a mass below the detection limit of 3.8 Jupiter masses. The other candidate is 9.7 Jupiter masses, which is below the minimum mass of 13 Jupiter masses for a brown dwarf. A brown dwarf is an object that forms like a star but does not have enough mass to shine by nuclear fusion.

Since the stars are so faint and the field of view is so densely packed with stars, measuring the slight wobble in the star's motion using spectroscopy to confirm most of the planet candidates is not feasible. Future telescopes such as NASA's James Webb Space Telescope will provide the needed sensitivity to confirm most of the planet candidates.

The Hubble SWEEPS program is an important proof-of-concept for NASA's future Kepler Mission, scheduled for launch in 2008. The Kepler observatory will continuously monitor a region of the Milky Way galaxy to detect transiting planets around mostly distant stars. Kepler will be sensitive enough to detect possibly hundreds of Earth-size planet candidates in or near the habitable zone, the distance from a star where liquid water could feasibly exist on a planet's surface.

SOURCE: SPACEFLIGHTNOW.COM




 

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Spitzer peels back layers of star's explosion
NASA/JPL NEWS RELEASE
Posted: October 26, 2006

Astronomers using NASA's infrared Spitzer Space Telescope have discovered that an exploded star, named Cassiopeia A, blew up in a somewhat orderly fashion, retaining much of its original onion-like layering.



This image from Spitzer shows the scattered remains of
 an exploded star named Cassiopeia A. In this false-color
 image, the faint, blue glow surrounding the dead star is
material that was energized by a shock wave, called the
 forward shock, which was created when the star blew up.
 The forward shock is now located at the outer edge of
the blue glow. Stars are also seen in blue. Green, yellow
and red primarily represent material that was ejected in
the explosion and heated by a slower shock wave, called the
 reverse shock wave. Credit: NASA/JPL-Caltech
Download larger image version http://photojournal.jpl.nasa.gov/jpeg/PIA01903.jpg

 
 
"Spitzer has essentially found key missing pieces of the Cassiopeia A puzzle," said Jessica Ennis of the University of Minnesota, Minneapolis, lead author of a paper to appear in the Nov. 20 issue of the Astrophysical Journal.

"We've found new bits of the 'onion' layers that had not been seen before," said Dr. Lawrence Rudnick, also of the University of Minnesota, and principal investigator of the research. "This tells us that the star's explosion was not chaotic enough to stir its remains into one big pile of mush."

Cassiopeia A, or Cas A for short, is what is known as a supernova remnant. The original star, about 15 to 20 times more massive than our sun, died in a cataclysmic "supernova" explosion relatively recently in our own Milky Way galaxy. Like all mature massive stars, the Cas A star was once neat and tidy, consisting of concentric shells made up of various elements. The star's outer skin consisted of lighter elements, such as hydrogen; its middle layers were lined with heavier elements like neon; and its core was stacked with the heaviest elements, such as iron.

Until now, scientists were not exactly sure what happened to the Cas A star when it ripped apart. One possibility is that the star exploded in a more or less uniform fashion, flinging its layers out in successive order. If this were the case, then those layers should be preserved in the expanding debris. Previous observations revealed portions of some of these layers, but there were mysterious gaps.

Spitzer was able to solve the riddle. It turns out that parts of the Cas A star had not been shot out as fast as others when the star exploded. Imagine an onion blasting apart with some layered chunks cracking off and zooming away, and other chunks from a different part of the onion shooting off at slightly slower speeds.

"Now we can better reconstruct how the star exploded," said Dr. William Reach of NASA's Spitzer Science Center, Pasadena, Calif. "It seems that most of the star's original layers flew outward in successive order, but at different average speeds depending on where they started."

How did Spitzer find the missing puzzle pieces? As the star's layers whiz outward, they are ramming, one by one, into a shock wave from the explosion and heating up. Material that hit the shock wave sooner has had more time to heat up to temperatures that radiate X-ray and visible light. Material that is just now hitting the shock wave is cooler and glowing with infrared light. Consequently, previous X-ray and visible-light observations identified hot, deep-layer material that had been flung out quickly, but not the cooler missing chunks that lagged behind. Spitzer's infrared detectors were able to find the missing chunks ­ gas and dust consisting of the middle-layer elements neon, oxygen and aluminum.

Cassiopeia A is the ideal target for studying the anatomy of a supernova explosion. Because it is young and relatively close to our solar system, it is undergoing its final death throes right in front of the watchful eyes of various telescopes. In a few hundred years or so, Cas A's scattered remains will have completely mixed together, forever erasing important clues about how the star lived and died.


SOURCE: SPACEFLIGHTNOW.COM


« Last Edit: 27/10/2006 23:00:38 by neilep »
 

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On the cutting edge: Carbon nanotube cutlery
Scanning electron micrograph of a prototype 'nanoknife' shows a single carbon nanotube stretched between two tungsten needles. Triangular probe is the tip of an atomic force cantilever used to determine...
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Researchers at the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder (CU) have designed a carbon nanotube knife that, in theory, would work like a tight-wire cheese slicer. In a paper presented this month at the 2006 International Mechanical Engineering Congress and Exposition*, the research team announced a prototype nanoknife that could, in the future, become a tabletop tool of biology, allowing scientists to cut and study cells more precisely than they can today.

For years, biologists have wrestled with conventional diamond or glass knives, which cut frozen cell samples at a large angle, forcing the samples to bend and sometimes later crack. Because carbon nanotubes are extremely strong and slender in diameter, they make ideal materials for thinly cutting precise slivers of cells. In particular, scientists might use the nanoknife to make 3D images of cells and tissues for electron tomography, which requires samples less than 300 nanometers thick.

By manipulating carbon nanotubes inside scanning electron microscopes, 21st-century nanosmiths have begun crafting a suite of research tools, including nanotweezers, nanobearings and nano-oscillators. To design the nanoknife, the NIST and CU scientists welded a carbon nanotube between two electrochemically sharpened tungsten needles. In the resulting prototype, the nanotube stretches between two ends of a tungsten wire loop. The knife resembles a steel wire that cuts a block of cheese.

To begin demonstrating the feasibility of their knife design, the researchers assessed its mechanical strength in force tests, applying increasing pressure to the device. The team found that the welds were the weakest point of the nanoknife, and they are now experimenting with alternative welding techniques. The researchers plan to test the nanoknife on a block of wax later this year (cells typically are immobilized in wax for dissection and microscopy.)


Caption: Scanning electron micrograph of a prototype
"nanoknife" shows a single carbon nanotube stretched between two tungsten
needles. Triangular probe is the tip of an atomic force cantilever used to
 determine the breaking point of the knife. (Color added for clarity.)

Credit: NIST/CU


SOURCE: EUREKA ALERT
« Last Edit: 23/11/2006 21:46:04 by neilep »
 

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Hubble Finds Evidence for Dark Energy in the Young Universe

Scientists using NASA's Hubble Space Telescope have discovered that dark energy is not a new constituent of space, but rather has been present for most of the universe's history. Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing rate. Investigators used Hubble to find that dark energy was already boosting the expansion rate of the universe as long as nine billion years ago. This picture of dark energy is consistent with Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from empty space. Data from Hubble provides supporting evidence to help astrophysicists to understand the nature of dark energy. This will allow them to begin ruling out some competing explanations that predict that the strength of dark energy changes over time.

Researchers also have found that the class of ancient exploding stars, or supernovae, used to measure the expansion of space today look remarkably similar to those that exploded nine billion years ago and are just now being seen by Hubble. This important finding gives additional credibility to the use of these supernovae for tracking the cosmic expansion over most of the universe's lifetime. Supernovae provide reliable measurements because their intrinsic brightness is well understood. They are therefore reliable distance markers, allowing astronomers to determine how far away they are from Earth. These snapshots, taken by Hubble reveal five supernovae and their host galaxies. The arrows in the top row of images point to the supernovae. The bottom row shows the host galaxies before or after the stars exploded. The supernovae exploded between 3.5 and 10 billion years ago.





SOURCE: HUBBLESITE.ORG



 

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World's oldest ritual discovered
Worshipped the python 70,000 years ago



A startling archaeological discovery this summer changes our understanding of human history. While, up until now, scholars have largely held that man’s first rituals were carried out over 40, 000 years ago in Europe, it now appears that they were wrong about both the time and place.

Associate Professor Sheila Coulson, from the University of Oslo, can now show that modern humans, Homo sapiens, have performed advanced rituals in Africa for 70,000 years. She has, in other words, discovered mankind’s oldest known ritual.

The archaeologist made the surprising discovery while she was studying the origin of the Sanpeople. A group of the San live in the sparsely inhabited area of north-western Botswana known as Ngamiland.



In the excavation they found more than 13,000 artifacts.



Coulson made the discovery while searching for artifacts from the Middle Stone Age in the only hills present for hundreds of kilometers in any direction. This group of small peaks within the Kalahari Desert is known as the Tsodilo Hills and is famous for having the largest concentration of rock paintings in the world.

The Tsodilo Hills are still a sacred place for the San, who call them the “Mountains of the Gods” and the “Rock that Whispers”.

The python is one of the San’s most important animals. According to their creation myth, mankind descended from the python and the ancient, arid streambeds around the hills are said to have been created by the python as it circled the hills in its ceaseless search for water.

Sheila Coulson’s find shows that people from the area had a specific ritual location associated with the python. The ritual was held in a little cave on the northern side of the Tsodilo Hills. The cave itself is so secluded and access to it is so difficult that it was not even discovered by archaeologists until the 1990s.

When Coulson entered the cave this summer with her three master’s students, it struck them that the mysterious rock resembled the head of a huge python. On the six meter long by two meter tall rock, they found three-to-four hundred indentations that could only have been man-made.



PYTHON STONE


"You could see the mouth and eyes of the snake. It looked like a real python. The play of sunlight over the indentations gave them the appearance of snake skin. At night, the firelight gave one the feeling that the snake was actually moving".

They found no evidence that work had recently been done on the rock. In fact, much of the rock’s surface was extensively eroded.

When they saw the many indentations in the rock, the archaeologists wondered about more than when the work had been done. They also began thinking about what the cave had been used for and how long people had been going there. With these questions in mind, they decided to dig a test pit directly in front of the python stone.

At the bottom of the pit, they found many stones that had been used to make the indentations. Together with these tools, some of which were more than 70,000 years old, they found a piece of the wall that had fallen off during the work.

In the course of their excavation, they found more than 13,000 artifacts. All of the objects were spearheads and articles that could be connected with ritual use, as well as tools used in carving the stone. They found nothing else.

As if that were not enough, the stones that the spearheads were made from are not from the Tsodilo region but must have been brought from hundreds of kilometers away.

The spearheads are better crafted and more colourful than other spearheads from the same time and area. Surprisingly enough, it was only the red spearheads that had been burned.

"Stone age people took these colourful spearheads, brought them to the cave, and finished carving them there. Only the red spearheads were burned. It was a ritual destruction of artifacts. There was no sign of normal habitation. No ordinary tools were found at the site. Our find means that humans were more organised and had the capacity for abstract thinking at a much earlier point in history than we have previously assumed. All of the indications suggest that Tsodilo has been known to mankind for almost 100,000 years as a very special place in the pre-historic landscape.” says Sheila Coulson.


The spearheads were particularly beautiful and were brought from hundreds of kilometers away.


Sheila Coulson also noticed a secret chamber behind the python stone. Some areas of the entrance to this small chamber were worn smooth, indicating that many people had passed through it over the years.

"The shaman, who is still a very important person in San culture, could have kept himself hidden in that secret chamber. He would have had a good view of the inside of the cave while remaining hidden himself. When he spoke from his hiding place, it could have seemed as if the voice came from the snake itself. The shaman would have been able to control everything. It was perfect.” The shaman could also have “disappeared” from the chamber by crawling out onto the hillside through a small shaft.

While large cave and wall paintings are numerous throughout the Tsodilo Hills, there are only two small paintings in this cave: an elephant and a giraffe. These images were rendered, surprisingly, exactly where water runs down the wall.

Sheila Coulson thinks that an explanation for this might come from San mythology.

In one San story, the python falls into a body of water and cannot get out by itself. The python is pulled from the water by a giraffe. The elephant, with its long trunk, is often used as a metaphor for the python.

"In the cave, we find only the San people’s three most important animals: the python, the elephant, and the giraffe. That is unusual. This would appear to be a very special place. They did not burn the spearheads by chance. They brought them from hundreds of kilometers away and intentionally burned them. So many pieces of the puzzle fit together here. It has to represent a ritual." concludes Sheila Coulson.



It was a major archaeological find five years ago that made it possible for Sheila Coulson to date the finds in this little cave in Botswana. Up until the turn of the century, archaeologists believed that human civilisation developed in Europe after our ancestors migrated from Africa. This theory was crushed by Archaeologist Christopher Henshilwood when he published his find of traces from a Middle Stone Age dwelling in the Blombos Cave in Southern Cape, South Africa.


SOURCE: EURELAALERT.ORG
 

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 Portrait of a Dramatic Stellar Crib


A new, stunning image of the cosmic spider, the Tarantula Nebula and its surroundings, finally pays tribute to this amazing, vast and intricately sculpted web of stars and gas. The newly released image, made with ESO's Wide Field Imager on the 2.2-m ESO/MPG Telescope at La Silla, covers 1 square degree on the sky and could therefore contain four times the full Moon.


ESO PR Photo 50a/06
The Tarantula Nebula
(WFI/2.2m)


Known as the Tarantula Nebula for its spidery appearance, the 30 Doradus complex is a monstrous stellar factory. It is the largest emission nebula in the sky, and can be seen far down in the southern sky at a distance of about 170,000 light-years, in the southern constellation Dorado (The Swordfish or the Goldfish). It is part of one of the Milky Way's neighbouring galaxies, the Large Magellanic Cloud.

The Tarantula Nebula is thought to contain more than half a million times the mass of the Sun in gas and this vast, blazing labyrinth hosts some of the most massive stars known. The nebula owes its name to the arrangement of its brightest patches of nebulosity, that somewhat resemble the legs of a spider. They extend from a central 'body' where a cluster of hot stars (designated 'R136') illuminates and shapes the nebula. This name, of the biggest spiders on the Earth, is also very fitting in view of the gigantic proportions of the celestial nebula - it measures nearly 1,000 light-years across and extends over more than one third of a degree: almost, but not quite, the size of the full Moon. If it were in our own Galaxy, at the distance of another stellar nursery, the Orion Nebula (1,500 light-years away), it would cover one quarter of the sky and even be visible in daylight.

Because astronomers believe that most of the stars in the Universe were formed in large and hectic nurseries such as the 30 Doradus region, its study is fundamental. Early this year, astronomers took a new, wide look at the spider and its web of filaments, using the Wide Field Imager on the 2.2-m MPG/ESO telescope located at La Silla, Chile, while studying the dark clouds in the region. Dark clouds are enormous clouds of gas and dust, with a mass surpassing a million times that of the Sun. They are very cold, with temperatures about -260 degrees Celsius, and are difficult to study because of the heavy walls of dust behind which they hide. Their study is however essential, as it is in their freezing wombs that stars are born.




ESO PR Photo 50b/06
SN 1987A and the Honeycomb Nebula (WFI/2.2m)


Observing in four different bands, the astronomers made a mosaic of the half-degree field of view of the instrument to obtain an image covering one square degree. With each individual image containing 64 million pixels, the resultant mosaic thus contained 4 times as many, or 256 million pixels! The observations were made in very good image quality, the 'seeing' being typically below 1 arcsecond.

The image is based on data collected through four filters, including two narrow-band filters that trace hydrogen (red) and oxygen (green). The predominance of green in the Tarantula is a result of the younger, hotter stars in this region of the complex.

It would be easy to get lost in the meanderings of the filamentary structures or get stuck in the web of the giant arachnid, as is easily experienced with the zoom-in feature provided on the associated photo page, and it is therefore difficult to mention all the unique objects to be discovered. Deserving closer attention perhaps is the area at the right-hand border of the Tarantula. It contains the remains of a star that exploded and was seen with the unaided eye in February 1987, i.e. almost 20 years ago. Supernova SN 1987A, as it is known, is the brightest supernova since the one observed by the German astronomer Kepler in 1604. The supernova is known to be surrounded by a ring, which can be distinguished in the image.

A little to the left of SN 1987A, another distinctive feature is apparent: the Honeycomb Nebula. This characteristic bubble-like structure results apparently from the interaction of a supernova explosion with an existing giant shell, which was itself generated by the combined action of strong winds from young, massive stars and supernova explosions.


The image is based on observations carried out by João Alves (Calar Alto, Spain), Benoit Vandame and Yuri Bialetski (ESO) with the Wide Field Imager (WFI) at the 2.2-m telescope on La Silla. The colour composite was made by Bob Fosbury (ST-EcF).

Super Massive Piccys here http://www.eso.org/outreach/press-rel/pr-2006/phot-50-06.html

Excellent Zoomify here  http://www.eso.org/outreach/press-rel/pr-2006/images/phot-50a-06-w0.html

SOURCE:


>European Organisation for Astronomical Research in the Southern Hemisphere      
ESO
European Organisation
for Astronomical
Research in the
Southern Hemisphere
www.eso.rg
 

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Psychedelic Saturn
CASSINI PHOTO RELEASE





Credit: NASA/JPL/Space Science Institute
Download larger image version here http://photojournal.jpl.nasa.gov/jpeg/PIA08858.jpg


This psychedelic view of Saturn and its rings is a composite made from images taken with the Cassini spacecraft wide-angle camera using spectral filters sensitive to wavelengths of infrared light centered at 728, 752 and 890 nanometers.

Cassini acquired the view in December at a distance of approximately 822,000 kilometers (511,000 miles) from Saturn. Image scale is 46 kilometers (28 miles) per pixel.



SOURCE: SPACEFLIGHTNOW.ORG
« Last Edit: 30/01/2007 17:04:22 by neilep »
 

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Shadows on ice
CASSINI PHOTO RELEASE

Canyons and mountain peaks snake along the terminator on the crater-covered, icy moon Dione. With the Sun at a low angle on their local horizon, the line of mountain ridges above center casts shadows toward the east.

Sunlit terrain seen here is on the anti-Saturn hemisphere of Dione (1,126 kilometers, or 700 miles across) -- the side that always faces away from Saturn. North is up.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera in December at a distance of approximately 299,000 kilometers (186,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 81 degrees. Image scale is 2 kilometers (1 mile) per pixel.








Credit: NASA/JPL/Space Science Institute
Download larger image version here

http://photojournal.jpl.nasa.gov/jpeg/PIA08856.jpg[/color]




SOURCE: SPACEFLIGHTNOW.ORG
 

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Pan's progress
CASSINI PHOTO RELEASE




Credit: NASA/JPL/Space Science Institute
Download larger image version here


http://photojournal.jpl.nasa.gov/jpeg/PIA08857.jpg

Pan is seen in this color view as it sweeps through the Encke Gap with its attendant ringlets. As the lemon-shaped little moon orbits Saturn, it always keeps its long axis pointed along a line toward the planet. From this vantage point, the dark side of the moon is visible.

This view looks toward Pan (26 kilometers, or 16 miles across) within the Encke Gap (325 kilometers, or 200 miles wide), on the unlit side of the rings, and from an inclination of about 33 degrees above the ringplane.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The image was taken with the Cassini spacecraft narrow-angle camera in December at a distance of approximately 779,000 kilometers (484,000 miles) from Pan and at a Sun-Pan-spacecraft, or phase, angle of 83 degrees. Image scale is 5 kilometers (3 miles) per pixel.


SOURCE: SPACEFLIGHTNOW.ORG



 

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On January 24, 2007, a minor cloud system blossomed in the Indian Ocean between Indonesia and northwestern Australia.  The cloud system was driven by powerful thunderstorms that previously raged beneath the now-ragged cirrus clouds at the system’s center. The clouds formed as an afternoon convection system that tends to occur at this time of year near Australia’s tropical northern coast. The cloud system traveled over land in Austalia’s Northern Territory heading roughly westward. Close to the Western Australia border, the system blew over the coastline in one of the most remote and unpopulated parts of Australia, putting it over the Indian Ocean. Over the warm moist air over the ocean, the cloud system grew rapidly with powerful convection drawing warm moist ocean air up into the top of the storm. At the top of this convection system, the air ceased to flow upward and spilled out into an expanding ring.
Source:earthobservatory.nasa.gov
 

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Cassini images mammoth cloud engulfing Titan’s North Pole
 
1 February 2007
A giant cloud half the size of the United States has been imaged on Saturn’s moon Titan by the Cassini spacecraft. The cloud may be responsible for the material that fills the lakes discovered last year by Cassini's radar instrument.
 
Cloaked by winter's shadow, this cloud has now come into view as winter turns to spring. The cloud extends down to 60 degrees north latitude, is roughly 2400 kilometers in diameter and engulfs almost the entire north pole of Titan.

The new image was acquired on 29 December 2006, by Cassini's visual and infrared mapping spectrometer (VIMS). Scientific models predicted this cloud system but it had never been imaged with such details before.

"We knew this cloud had to be there but were amazed at its size and structure," said Dr. Christophe Sotin of the University of Nantes, France, a member of the visual and infrared mapping spectrometer team and distinguished visiting scientist at NASA's Jet Propulsion Laboratory, Pasadena, California. "This cloud system may be a key element in the global formation of organics and their interaction with the surface."

The same cloud system seen on 29 December 2006, was still there two weeks later during the flyby which took place on 13 January 2007, even though observing conditions were slightly less favorable than in December.



Titan's Giant North Pole Cloud

The Cassini radar team reported last year that the lakes at the north pole are partly filled and some appear to have evaporated, likely contributing to this cloud formation, which is made up of ethane, methane and other organics.

These findings reinforce the idea that methane rains down onto the surface to form lakes, and then evaporates to form clouds. Scientists compare this methane cycle to the hydrological cycle on Earth, dubbing it 'methane-ologic cycle'.

Ground-based observations show this Titan cloud system comes and goes with the seasons. A season on Titan lasts approximately seven Earth years. Based on the global circulation models, it seems that such cloud activity can last about 25 Earth years before almost vanishing for four to five years, and then appearing again for 25 years.

Scientists expect this cloud to be around for several years. As the seasons change, scientists expect a shift of these clouds and lakes from the north pole to the south pole. On Titan's south pole, scientists have seen only one kidney-shaped lake with Cassini’s imaging cameras.

"With 16 more flybys to come this year, we should have the opportunity to monitor the evolution of this cloud system over time," said Dr. Stephane Le Mouelic, working with the Cassini visual and infrared mapping spectrometer team, and also at the University of Nantes.
 



Liquid lakes on Titan



SOURCE: EUREKAALERT.ORG & European Space Agency










 

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Photo Release - heic0703: The colourful demise of a Sun-like star



   

13-Feb-2007: A brand new image taken with Hubble’s Wide
 Field Planetary Camera 2 shows the planetary nebula NGC 2440
- the chaotic structure of the demise of a star.


This image, just taken by the NASA/ESA Hubble Space Telescope, shows the colourful “last hurrah” of a star like our Sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star’s remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the centre. Our Sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years.

Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers called them the name because through small telescopes they resembled the disks of the distant planets Uranus and Neptune. The planetary nebula in this image is called NGC 2440. The white dwarf at the centre of NGC 2440 is one of the hottest known, with a surface temperature of more than 200,000 degrees Celsius. The nebula’s chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bowtie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.

The material expelled by the star glows with different colours depending on its composition, its density and how close it is to the hot central star. Blue samples helium; blue-green oxygen, and red nitrogen and hydrogen. The image was taken 6 February, 2007 with Hubble’s Wide Field Planetary Camera 2.



Credit: NASA, ESA, and K. Noll (STScI)

Acknowledgment: The Hubble Heritage Team (STScI/AURA)
 

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Hubble Sees 'Comet Galaxy' Being Ripped Apart By Galaxy Cluster



NASA's Hubble Space Telescope, in collaboration with several other ground- and space- based telescopes, has captured a galaxy being ripped apart by a galaxy cluster's gravitational field and harsh environment.

The finding sheds light on the mysterious process by which gas-rich spiral-shaped galaxies might evolve into gas-poor irregular- or elliptical-shaped galaxies over billions of years. The new observations also reveal one mechanism for forming the millions of "homeless" stars seen scattered throughout galaxy clusters.




Hubble Sees 'Comet Galaxy' Being Ripped Apart By Galaxy Cluster




SOURCE: HUBBLESITE
« Last Edit: 05/03/2007 19:41:05 by neilep »
 

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NASA's Hubble Telescope Celebrates SN 1987A's 20th Anniversary


Twenty years ago, astronomers witnessed one of the brightest stellar explosions in more than 400 years. The titanic supernova, called SN 1987A, blazed with the power of 100 million suns for several months following its discovery on Feb. 23, 1987. Observations of SN 1987A, made over the past 20 years by NASA’s Hubble Space Telescope and many other major ground- and space-based telescopes, have significantly changed astronomers' views of how massive stars end their lives. Astronomers credit Hubble's sharp vision with yielding important clues about the massive star's demise.

This Hubble telescope image shows the supernova’s triple-ring system, including the bright spots along the inner ring of gas surrounding the exploded star. A shock wave of material unleashed by the stellar blast is slamming into regions along the inner ring, heating them up, and causing them to glow. The ring, about a light-year across, was probably shed by the star about 20,000 years before it exploded.


A String of 'Cosmic Pearls' Surrounds an Exploding Star




SOURCE: HUBBLESITE

 

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Hubble Illuminates Cluster of Diverse Galaxies

This NASA Hubble Space Telescope image shows the diverse collection of galaxies in a galaxy cluster called Abell S0740, located more than 450 million light-years away in the constellation Centaurus. The giant elliptical galaxy ESO 325-G004 looms large at the cluster's center. This galaxy is as massive as 100 billion suns. Hubble resolves thousands of globular star clusters orbiting ESO 325-G004. Globular clusters are compact groups of hundreds of thousands of stars that are gravitationally bound together. At the galaxy's distance they appear as pinpoints of light contained within the diffuse halo. Other elliptical and spiral galaxies appear in the image. The photo was made from images taken using Hubble's Advanced Camera for Surveys in January 2005 and February 2006.






Source: HUBBLESITE
 

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Artist's rendition released by NASA shows an asteroid belt in orbit around a star






    
 Astronomers have pieced together the remnants of a mighty collision that smashed apart a planet-sized rock in the Kuiper Belt, on the far-flung fringes of the Solar System.

Breitbart.com (source)
   
   
   
 

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European spacecraft tracking turbulence at Venus

EUROPEAN SPACE AGENCY NEWS RELEASE


New images and data from the European Space Agency's mission to Venus provide new insights into the turbulent and noxious atmosphere of Earth's sister planet. What causes violent winds and turbulences? Is the surface topography playing a role in the complex global dynamics of the atmosphere? Venus Express is on the case.


Four different views of the Venusian cloud system are seen here from
 Venus Express. The grey-scale of the images is such that black means
 more transparency, therefore less clouds, while white means more opacity,
 therefore more cloud concentration. Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA

 
 
Venus' atmosphere represents a true puzzle for scientists. Winds are so powerful and fast that they circumnavigate the planet in only four Earth days - the atmospheric 'super-rotation' - while the planet itself is very slow in comparison, taking 243 Earth days to perform one full rotation around its axis.

At the poles things get really complicated with huge double-eyed vortices providing a truly dramatic view. In addition, a layer of dense clouds covers the whole planet as a thick curtain, preventing observers using conventional optical means from seeing what lies beneath.

Venus Express is on the contrary capable of looking through the atmosphere at different depths, by probing it at different infrared wavelengths. The Ultraviolet, Visible and Near-Infrared Mapping Spectrometer (VIRTIS) on board is continuing its systematic investigation of Venus' atmospheric layers to solve the riddle of the causes for such turbulent and stormy atmosphere.

The images presented with this article focus on Venusian atmospheric turbulences and cloud features, whose shape and size vary with planetary latitudes. At the equator, clouds are irregular and assume a peculiar 'bubble'-shape. At mid latitudes they are more regular and streaky, running almost parallel to the direction of the super rotation with speed reaching more than 400 kilometres per hour. Going higher up in latitude, in the polar region, the clouds end up in entering a vortex shape.
 

SOURCE: SPACEFLIGHT.COM
 

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Beauty of barred spiral galaxy shown by Hubble
HUBBLE INFORMATION CENTER NEWS RELEASE


The NASA/ESA Hubble Space Telescope has delivered an unrivalled snapshot of the nearby barred spiral galaxy NGC 1672. This remarkable image provides a high definition view of the galaxy's large bar, its fields of star-forming clouds and dark bands of interstellar dust.


Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration
Download larger image version here http://www.spacetelescope.org/goodies/printlayouts/screen/heic0706.jpg

 
 
NGC 1672, visible from the Southern Hemisphere, is seen almost face on and shows regions of intense star formation. The greatest concentrations of star formation are found in the so-called starburst regions near the ends of the galaxy's strong galactic bar. NGC 1672 is a prototypical barred spiral galaxy and differs from normal spiral galaxies in that the spiral arms do not twist all the way into the centre. Instead, they are attached to the two ends of a straight bar of stars enclosing the nucleus.

Astronomers believe that barred spirals have a unique mechanism that channels gas from the disk inwards towards the nucleus. This allows the bar portion of the galaxy to serve as an area of new star generation. It appears that the bars are short-lived, begging the question: will non-barred galaxies develop a bar in the future, or have they already hosted one that has disappeared?

In the new image from the NASA/ESA Hubble Space Telescope, clusters of hot young blue stars form along the spiral arms, and ionize surrounding clouds of hydrogen gas that glow red. Delicate curtains of dust partially obscure and redden the light of the stars behind them. NGC 1672's symmetric look is emphasised by the four principal arms, edged by eye-catching dust lanes that extend out from the centre.

Galaxies lying behind NGC 1672 give the illusion they are embedded in the foreground galaxy, even though they are really much farther away. They also appear reddened as they shine through NGC 1672's dust. A few bright foreground stars inside our own Milky Way Galaxy appear in the image as bright, diamond-like objects.

NGC 1672 is a member of the family of Seyfert galaxies, named after the astronomer, Carl Keenan Seyfert, who studied a family of galaxies with active nuclei extensively in the 1940s. The energy output of these nuclei can sometimes outshine their host galaxies. The active galaxy family include the exotically named quasars and blazars. Although each type has distinctive characteristics, they are thought to be all driven by the same engine - supermassive black holes - but are viewed from different angles.

The new Hubble observations, performed with the Advanced Camera for Surveys aboard the observatory, have shed light on the process of starburst activity and on why some galaxies are ablaze with extremely active star formation.

NGC 1672 is more than 60 million light-years away in the direction of the Southern constellation of Dorado. These observations of NGC 1672 were taken with Hubble's Advanced Camera for Surveys in August of 2005. This composite image contains filters that isolate light from the blue, green, and infrared portions of the spectrum, as well as emission from ionized hydrogen.

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


Source: spaceflightnow.com
 

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Future space telescopes could detect Earth twin
NASA/JPL NEWS RELEASE
Posted: April 11, 2007

For the first time ever, NASA researchers have successfully demonstrated in the laboratory that a space telescope rigged with special masks and mirrors could snap a photo of an Earth-like planet orbiting a nearby star. This accomplishment marks a dramatic step forward for missions like the proposed Terrestrial Planet Finder, designed to hunt for an Earth twin that might harbor life.


Three simulated planets -- one as bright as Jupiter, one half as bright as
Jupiter and one as faint as Earth -- stand out plainly in this image created
 from a sequence of 480 images captured by the High Contrast Imaging Testbed
at JPL. The asterisk marks the location of the system's simulated star.
 Credit: NASA/JPL-Caltech
 

 
Trying to image an exoplanet - a planet orbiting a star other than the sun - is a daunting task, because its relatively dim glow is easily overpowered by the intense glare of its much bigger, brighter parent star. The challenge has been compared to looking for a firefly next to a searchlight.

Now, two researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., have shown that a fairly simple coronagraph - an instrument used to "mask" a star's glare - paired with an adjustable mirror, could enable a space telescope to image a distant planet 10 billion times fainter than its central star.

"Our experiment demonstrates the suppression of glare extremely close to a star, clearing a field dark enough to allow us to see an Earth twin. This is at least a thousand times better than anything demonstrated previously," said John Trauger, lead author of a paper appearing in the April 12 issue of Nature. This paper describes the system, called the High Contrast Imaging Testbed, and how the technique could be used with a telescope in space to see exoplanets. The lab experiment used a laser as a simulated star, with fainter copies of the star serving as "planets."

To date, scientists have used various techniques to detect more than 200 exoplanets. Most of these exoplanets are from five to 4,000 times more massive than Earth, and are either too hot, too cold or too much of a giant gas ball to be considered likely habitats for life. So far, no one has managed to capture an image of an exoplanetary system that resembles our own solar system. Scientists are eager to take a closer look at nearby systems, to hunt for and then characterize any Earth-like planets - those with the right size, orbit and other traits considered friendly for life.

In the lab demonstration, the High Contrast and Imaging Testbed overcame two significant hurdles that all telescopes face when trying to image exoplanets - diffracted and scattered light.

When starlight hits the edge of a telescope's primary mirror, it becomes slightly disturbed, producing a pattern of rings or spikes surrounding the major source of light in the focused image. This diffracted light can completely obscure any planets in the field of view.

To address this problem, Trauger and his colleagues at JPL fashioned a pair of masks for their system. The first, which resembles a blurry barcode, directly blocks most of the starlight, while the second clears away the diffracted rings and spikes. The combination creates enough darkness to allow the light of any planets to shine through.

"Mathematically, and sort of magically, this coronagraph blocks both the central star and its rings," said Wesley Traub of JPL, co-author of the new paper and Terrestrial Planet Finder project scientist.

Scattered light presents the additional hurdle. Minor ripples on a telescope's mirror produce "speckles" - faint copies of a star, shifted to the side, which can also hide planets. In the High Contrast Imaging Testbed, a deformable mirror the size of a large coin limits scattered light. With a surface that can be altered ever so slightly by computer-controlled actuators, this mirror compensates for the effects of minor imperfections in the telescope and instrument.

"This result is important because it points the way to building a space telescope with the ability to detect and characterize Earth-like planets around nearby stars," Traub said.

For their next steps, Trauger and Traub plan to improve the suppression of speckles by a factor of 10, and extend the method to accommodate many wavelengths of light simultaneously.

JPL manages the Terrestrial Planet Finder mission for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology in Pasadena.



SOURCE: SPACEFLIGHTNOW.COM

 

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Mystery of galaxy's spiral arms possibly explained
NASA-GSFC NEWS RELEASE
Posted: April 12, 2007

Using a quartet of space observatories, University of Maryland astronomers may have cracked a 45-year mystery surrounding two ghostly spiral arms in the galaxy M106.

The Maryland team, led by Yuxuan Yang, took advantage of the unique capabilities of NASA's Chandra X-ray Observatory, NASA's Spitzer Space Telescope, the European Space Agency's XMM-Newton X-ray observatory, and data obtained almost a decade ago with NASA's Hubble Space Telescope.


In this composite image of spiral galaxy M106 (NGC 4258), radio data from
the Very Large Array appears as blue, X-ray data from Chandra is coded red,
 and infrared data from the Spitzer Space Telescope appears green. The
anomalous arms appear as purple and blue emission.
 Credit: X-ray: NASA/CXC/Univ. of Maryland/A.S. Wilson et al. IR: NASA/JPL-Caltech; VLA & NRAO/AUI/NSF

 
 
M106 (also known as NGC 4258) is a stately spiral galaxy 23.5 million light-years away in the constellation Canes Venatici. In visible-light images, two prominent arms emanate from the bright nucleus and spiral outward. These arms are dominated by young, bright stars, which light up the gas within the arms. "But in radio and X-ray images, two additional spiral arms dominate the picture, appearing as ghostly apparitions between the main arms," says team member Andrew Wilson of the University of Maryland. These so-called "anomalous arms" consist mostly of gas.

"The nature of these anomalous arms is a long-standing puzzle in astronomy," says Yang. "They have been a mystery since they were first discovered in the early 1960s."

By analyzing data from XMM-Newton, Spitzer, and Chandra, Yang, Bo Li, Wilson, and Christopher Reynolds, all at the University of Maryland at College Park, have confirmed earlier suspicions that the ghostly arms represent regions of gas that are being violently heated by shock waves.

Previously, some astronomers had suggested that the anomalous arms are jets of particles being ejected by a supermassive black hole in M106's nucleus. But radio observations by the National Radio Astronomy Observatory's Very Long Baseline Array, and the Very Large Array in New Mexico, later identified another pair of jets originating in the core. "It is highly unlikely that an active galactic nucleus could have more than one pair of jets," says Yang.

In 2001, Wilson, Yang, and Gerald Cecil, of the University of North Carolina, Chapel Hill, noted that the two jets are tipped 30 degrees with respect to the galaxy disk. But if one could vertically project the jets onto the disk, they would line up almost perfectly with the anomalous arms. Figuring that this alignment was not strictly a matter of chance, Wilson, Yang, and Cecil proposed that the jets heat the gas in their line of travel, forming an expanding cocoon. Because the jets lie close to M106's disk, the cocoon heats gas in the disk and generates shock waves, heating the gas to millions of degrees and causing it to radiate brightly in X-rays and other wavelengths.

To test this idea, Yang and his colleagues looked at archival spectral observations from XMM-Newton. With XMM-Newton's superb sensitivity, the team could measure the gas temperature in the anomalous arms and also see how strongly X-rays from the gas are absorbed en route by intervening material.

"One of the predictions of this scenario is that the anomalous arms will gradually be pushed out of the galactic disk plane by jet-heated gas," says Yang. The XMM-Newton spectra show that X-rays are more strongly absorbed in the direction of the northwest arm than in the southeast arm. The results strongly suggest that the southeast arm is partly on the near side of M106's disk, and the northwest arm is partly on the far side.

The scientists noted that these observations show clear consistency with their scenario. Confirmation of this interpretation has recently come from archival observations from NASA's Spitzer Space Telescope, whose infrared view shows clear signs that X-ray emission from the northwest arm is being absorbed by warm gas and dust in the galaxy's disk. Moreover, Chandra's superior imaging resolution gives clear indications of gas shocked by interactions with the two jets.

Besides addressing the mystery of the anomalous arms, these observations allowed the team to estimate the energy in the jets and gauge their relationship to M106's central black hole. The team's paper will appear in the May 10 issue of the Astrophysical Journal.


SOURCE: SPACEFLIGHTNOW,COM
 

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The Red Square Nebula



MWC 922: The Red Square Nebula
Explanation: What could cause a nebula to appear square? No one is quite sure. The hot star system known as MWC 922, however, appears to be imbedded in a nebula with just such a shape. The above image combines infrared exposures from the Hale Telescope on Mt. Palomar in California, and the Keck-2 Telescope on Mauna Kea in Hawaii. A leading progenitor hypothesis for the square nebula is that the central star or stars somehow expelled cones of gas during a late developmental stage. For MWC 922, these cones happen to incorporate nearly right angles and be visible from the sides. Supporting evidence for the cone hypothesis includes radial spokes in the image that might run along the cone walls. Researchers speculate that the cones viewed from another angle would appear similar to the gigantic rings of supernova 1987A, possibly indicating that a star in MWC 922 might one day itself explode in a similar supernova
 

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Astronomers map out planetary danger zone
NASA/JPL NEWS RELEASE


PASADENA, Calif. - Astronomers have laid down the cosmic equivalent of yellow "caution" tape around super hot stars, marking the zones where cooler stars are in danger of having their developing planets blasted away.


This infrared image from Spitzer shows the Rosette nebula,
 a pretty star-forming region more than 5,000 light-years away in the constellation
 Monoceros. In optical light, the nebula looks like a rosebud, or the "rosette"
adornments that date back to antiquity. Credit: NASA/JPL-Caltech/Z. Balog
(Univ. of Ariz./Univ. of Szeged)

 
 
In a new study from NASA's Spitzer Space Telescope, scientists report the first maps of so-called planetary "danger zones." These are areas where winds and radiation from super hot stars can strip other young, cooler stars like our sun of their planet-forming materials. The results show that cooler stars are safe as long as they lie beyond about 1.6 light-years, or nearly 10 trillion miles, of any hot stars. But cooler stars inside the zone are likely to see their potential planets boiled off into space.

"Stars move around all the time, so if one wanders into the danger zone and stays for too long, it will probably never be able to form planets," said Zoltan Balog of the University of Arizona, Tucson, lead author of the new report, appearing May 20 in the Astrophysical Journal.

The findings are helping astronomers pinpoint the types of environments where planets beyond our solar system, including some that might be hospitable to life, are most likely to form.

Planets are born out of a flat disk of gas and dust, called a protoplanetary disk, that swirls around a young star. They are believed to clump together out of the disk over millions of years, growing in size like dust bunnies as they sweep through the dust.

Previous studies revealed that these protoplanetary disks can be destroyed by the most massive, hottest type of star in the universe, called an O-star, over a period of about a million years. Ultraviolet radiation from an O-star heats and evaporates the dust and gas in the disk, then winds from the star blow the material away. Last year, Balog and his team used Spitzer to capture a stunning picture of this "photoevaporation" process at work.

The team's new study is the first systematic survey for disks in and around the danger zone, or "blast radius" of an O-star. They used Spitzer's heat-seeking infrared eyes to look for disks around 1,000 stars in the Rosette Nebula, a turbulent star-forming region 5,200 light-years away in the constellation Monoceros. The stars range between one-tenth and five times the mass of the sun and are between 2 and 3 million years old. They are all near at least one of the region's massive O-stars.




This artist's concept illustrates an O-star near the top right,
 just behind a young, cooler star and its swirling disk of planet-forming
 material. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

 
 
The observations revealed that, beyond 10 trillion miles of an O-star, about 45 percent of the stars had disks - about the same amount as there were in safer neighborhoods free of O-stars. Within this distance, only 27 percent of the stars had disks, with fewer and fewer disks spotted around stars closest to the O-star. In other words, an O-star's danger zone is a sphere whose damaging effects are worst at the core. For reference, our sun's closest star, a small star called Proxima Centauri, is nearly 30 trillion miles away.

In addition, the new study indicates that a protoplanetary disk will boil off faster in the zone's perilous core. For example, a disk two times closer to an O-star than another disk will evaporate twice as fast. "The edges of the danger zone are sharply defined," said Balog. "It is relatively safe for protoplanetary disks outside it, whereas a disk that gets dragged along by its star to be really close to an O-star could disappear in as fast as a hundred thousand years."

Despite this doomsday scenario, there is a chance some planets could survive a close encounter with an O-star. According to one alternative theory of planet formation, some gas giants like Jupiter might form in less than one million years. If such a planet already existed around a young star whose disk is blown away, the gas giant would stay put while any burgeoning rocky planets like Earth would be forever swept away.

Some astronomers think our sun was born in a similarly violent neighborhood studded with O-stars before migrating to its present, more spacious home. If so, it was lucky enough to escape a harrowing ride into any danger zones, or our planets, and life as we know it, wouldn't be here today.


SOURCE: SPACEFLIGHTNOW.COM

 
 

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Casting a shadow
CASSINI PHOTO RELEASE



Credit: NASA/JPL/University of Arizona
Download larger image version here http://photojournal.jpl.nasa.gov/jpeg/PIA08921.jpg
 
 
Blazing like an icy torch, the plume of Enceladus shines in scattered sunlight as the moon casts a shadow onto Saturn's E ring. Some of the tiny ice particles erupted from the moon's south polar region go into Saturn orbit, forming the doughnut-shaped ring, onto which the moon's shadow is cast in this view.

The shadow of Enceladus (505 kilometers, or 314 miles across) stretches away to the upper left at around the 10 o'clock position. The Sun-Enceladus-spacecraft, or phase, angle is 164 degrees here, with the Sun being located toward the lower right. This means that Enceladus' shadow extends toward the Cassini spacecraft -- through part of the E ring.

Some of the bright dots in this heavily processed view are background stars. Others are due to cosmic ray hits on the camera detector.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 11, 2006 at a distance of approximately 2.2 million kilometers (1.3 million miles) from Enceladus. Image scale is 13 kilometers (8 miles) per pixel.

SOURCE: SPACEFLIGHTNOW.COM

 

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Cosmic weight loss: The lowest mass white dwarf
HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS NEWS RELEASE


Astronomers have found the lowest mass white dwarf known in our galaxy: a Saturn-sized ball of helium containing only about one-fifth the mass of the Sun. In addition, they have spotted the source of the white dwarf's radical weight-loss plan. An unseen companion, likely another white dwarf, has sucked away much of the tiny white dwarf's material, leaving it a shadow of its former self.


This artist's conception shows the lowest-mass white dwarf known in our galaxy
 and its companion star, which likely is another white dwarf. The foreground white
 dwarf underwent a radical weight-loss plan about 500 million years ago, losing
 mass to its companion. The low-mass white dwarf now weighs only about 17 percent
 as much as the Sun. Credit: David A. Aguilar (CfA)

 
 
"This star is bizarre," said Warren Brown of the Harvard-Smithsonian Center for Astrophysics. "It takes extraordinary circumstances to make such a low mass white dwarf."

When a Sun-like star ages and dies, it becomes a white dwarf. The newfound white dwarf, with the unwieldy designation of SDSS J091709.55+463821.8 (hereafter J0917+46) lies about 7,400 light-years from Earth near the border of the constellations Lynx and Ursa Major. Where a typical white dwarf holds about half a Sun's worth of material, the newfound white dwarf contains only a fraction of that mass.

"Our white dwarf is skinny in terms of mass, yet it looks fat in terms of its physical size," stated first author Mukremin Kilic of Ohio State University. "It's about nine times bigger than a typical white dwarf in diameter."

When the astronomers first found J0917+46, they predicted that it must have an unseen companion that had aided its weight loss. A subsequent radial velocity search, which looked for signs that the white dwarf wobbled when tugged by a companion's gravity, confirmed the prediction. The astronomers ruled out the possibility that the companion is either a low-mass main sequence star or a black hole. It must be either another white dwarf or a neutron star, with a white dwarf being the more likely candidate.

"No star is old enough to produce such an extremely low-mass white dwarf by itself," explained Brown. "Therefore, we knew that mass must have been stripped from the white dwarf by a companion."

"Finding the companion means that stellar evolution theories have passed a major test," added co-author Scott Kenyon of the Smithsonian Astrophysical Observatory. "The fact that the companion is a more massive white dwarf or neutron star is also consistent with theory."

The team also described the oddball pair's history. This binary system began with one star about twice the mass of the Sun and a second star slightly less massive than the Sun. The more massive star was the first to evolve, becoming a white dwarf weighing perhaps one-third as much as the Sun. Ten billion years later, its companion became another white dwarf. In each step, the puffed-up outer layers of the evolving star enveloped the companion, causing friction that moved the two stars closer together. They now orbit each other every 7.6 hours at a distance of about 650,000 miles and a stunning speed of 335,000 miles per hour.

"The relation between our white dwarf and its companion is like a cosmic marriage in which both people have to give a lot," said Kilic. "Two stars start out close to each other. One of them engulfs the other (like a hug) and gives continuously (losing mass), and they get closer. Then the other star evolves and becomes a giant and engulfs the first star (hugging back) and now it has to give a lot, or lose a lot of mass. They get closer and closer and end up dancing continuously."

The astronomers predict that the two white dwarfs eventually will merge. However, that merger will not take place for 10 billion years or more.

Key observations were made with the MMT Observatory in Arizona, which is operated jointly by the Smithsonian Astrophysical Observatory and the University of Arizona

SOURCE: SPACEFLIGHTNOW.COM
 

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Hubble sees extreme star birth in the Carina Nebula
HUBBLE NEWS RELEASE



Credit: NASA, ESA, N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA)

Bigger piccy here

 
 
One of the largest panoramic images ever taken with Hubble's cameras has been released to celebrate the 17th anniversary of the launch and deployment of the NASA/ESA Hubble Space Telescope. The image shows a 50 light-year-wide view of the tumultuous central region of the Carina Nebula where a maelstrom of star birth - and death - is taking place.

Hubble's new view of the Carina Nebula shows the process of star birth at a new level of detail. The bizarre landscape of the nebula is sculpted by the action of outflowing winds and scorching ultraviolet radiation from the monster stars that inhabit this inferno. These stars are shredding the surrounding material that is the last vestige of the giant cloud from which the stars were born.

This immense nebula contains a dozen or more brilliant stars that are estimated to be at least 50 to 100 times the mass of our Sun. The most opulent is the star eta Carinae, seen at far left. Eta Carinae is in the final stages of its brief eruptive lifespan, as shown by two billowing lobes of gas and dust that presage its upcoming explosion as a titanic supernova.


A series of so-called Bok globules from a mosaic of the Carina Nebula assembled
 from 48 frames taken with Hubble's Advanced Camera for Surveys. The island-like
 clumps of dark clouds scattered across the nebula are nodules of dust and gas
that have so far resisted being eaten away by photoionisation. Credit: NASA, ESA,
 N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA)
 
 

 
The fireworks in the Carina region started three million years ago when the nebula's first generation of newborn stars condensed and ignited in the middle of a huge cloud of cold molecular hydrogen. Radiation from these stars carved out an expanding bubble of hot gas. The island-like clumps of dark clouds scattered across the nebula are nodules of dust and gas that have so far resisted being eaten away by photoionisation.

The hurricane-strength blast of stellar winds and blistering ultraviolet radiation within the cavity is now compressing the surrounding walls of cold hydrogen. This is triggering a second stage of new star formation.

Our Sun and Solar System may have been born inside such a cosmic crucible 4.6 billion years ago. In looking at the Carina Nebula we are seeing star formation as it commonly occurs along the dense spiral arms of a galaxy.

This immense nebula is an estimated 7,500 light-years away in the southern constellation Carina, the Keel of the old southern constellation Argo Navis, the ship of Jason and the Argonauts from Greek mythology.

This image is an immense (29,566 x 14,321 pixels) mosaic of the Carina Nebula assembled from 48 frames taken with Hubble's Advanced Camera for Surveys. The Hubble images were taken in the light of ionized hydrogen. Colour information was added with data taken at the Cerro Tololo Inter- American Observatory in Chile. Red corresponds to sulphur, green to hydrogen, and blue to oxygen emission.


These three snapshots reveal nuggets of cold molecular hydrogen in the Carina Nebula. Credit: NASA, ESA, N. Smith (University of California, Berkeley), and The Hubble Heritage Team (STScI/AURA)

 
 
In its 17 years of exploring the heavens, NASA's Hubble Space Telescope has made nearly 800,000 observations and snapped nearly 500,000 images of more than 25,000 celestial objects. Hubble does not travel to stars, planets and galaxies. It takes pictures of them as it whirls around Earth at 17,500 miles an hour. In its 17-year lifetime, the telescope has made nearly 100,000 trips around our planet. Those trips have racked up plenty of frequent-flier-miles, about 2.4 billion, which is the equivalent of a round trip to Saturn.

The 17 years' worth of observations has produced more than 30 terabytes of data, equal to about 25 percent of the information stored in the Library of Congress.

Each day the orbiting observatory generates about 10 gigabytes of data, enough information to fill the hard drive of a typical home computer in two weeks.

The Hubble archive sends about 66 gigabytes of data each day to astronomers throughout the world.

Astronomers using Hubble data have published nearly 7,000 scientific papers, making it one of the most productive scientific instruments ever built.

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



SOURCE: SPACEFLIGHTNOW.COM
« Last Edit: 24/04/2007 21:47:21 by neilep »
 

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