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Author Topic: Science Photo of the Week  (Read 469062 times)

Offline neilep

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Galaxy Zoo’s special exhibition of merging galaxies
BY DR EMILY BALDWIN
ASTRONOMY NOW
Posted: May 19, 2008


Since Galaxy Zoo opened its gates almost a year ago, over 125,000 armchair astronomers have visited the online menagerie and made around 40,000,000 individual classifications of elliptical, spiral and merging galaxies. Now the team are appealing to the public to review their set of possible merging galaxies in order to answer some long standing questions about the weird and wonderful world of interacting galaxies.

As with any zoo the oddest creations provide the greatest thrill, and Galaxy Zoo is no exception. From the original classifications, the results of which were recently submitted to peer reviewed journals, a fantastic set of merging galaxies have been identified. The Galaxy Zoo team are now relying on the public to review the set of possible merging galaxies, in order to make sure the team have as many true merger candidates as possible, therefore maximising the pool of scientific data to work with. The results will help to answer some of the long standing questions surrounding the importance and frequency of merging galaxies.

In theoretical simulations, astronomers have found that the merger of spiral galaxies can create an elliptical galaxy, and that an elliptical can become a spiral by accretion of further stars and gas during its lifetime. Since Edwin Hubble first devised the galaxy classification system, which divided galaxies into two main categories – rugby ball shaped ‘elliptical’ galaxies and whirlpool like ‘spiral’ galaxies – there has been controversy among scientists about how these two principal types are even connected in the global understanding of galaxy formation and evolution. By classifying some of these images visitors are helping astronomers to understand the structure of the Universe and how galaxies form and evolve.






The work of the Galaxy Zoo team, and of the interested public, is far from done: Galaxy Zoo 2’s development is well under way, which will see a much more detailed classification system of the brightest galaxies in the Sloan Digital Sky Survey, an ambitious astronomical survey which is systematically mapping a quarter of the entire sky. Even further down the line we will see Galaxy Zoo 3 with brand new data. The ultimate goal of Galaxy Zoo is to perform a census of the one million galaxies captured by the Sloan Digital Sky Survey.

To find instructions on how to contribute to the Galaxy Zoo survey, including an interactive tutorial to teach you how to classify the galaxies, visit www.galaxyzoo.org, but be warned, it’s highly addictive!

 



 

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New red spot appears on Jupiter
BY DR EMILY BALDWIN
ASTRONOMY NOW
Posted: May 23, 2008


In what is beginning to look like a case of planetary measles, a third red spot has appeared alongside the Great Red Spot and Red Spot Junior in the turbulent Jovian atmosphere.

Jupiter has spawned a third, smaller, red oval in the same band of clouds as its big brother, the Great Red Spot (GRS). The new addition to the family was previously a white shaped oval storm; the change to a red colour indicates its swirling storm clouds are rising to heights like the clouds of its siblings, according to detailed analysis of the visible-light images taken by Hubble's Wide Field Planetary Camera 2 on May 9 and 10, and near-infrared adaptive optics images taken by the W.M. Keck telescope on May 11.






The new observations support the idea that Jupiter is in the midst of global climate change, as first proposed by Professor Phil Marcus at the University of California in 2004, causing temperatures to change by about 10 degrees Celsius, getting warmer near the equator and cooler near the south pole. Marcus predicted that large changes would start in the southern hemisphere around 2006, causing the jet streams to become unstable and spawn new vortices, just as has been observed.


"The appearance of the planet's cloud system from just north of the equator down to 34 degrees south latitude keeps surprising us with changes and, in particular, with new cloud features that haven't been previously observed," says Marcus. "Whether or not Jupiter's climate has changed due to a predicted warming, the cloud activity over the last two and a half years shows dramatically that something unusual has happened."

The original two red spots are squeezed between bands called shear flows, where the flow above each storm is moving westward and the flow below is moving eastward. Since the shear flow in each band is slightly different, and the storms are different sizes, the GRS drifts in a westward direction while the Little Red Spot drifts eastward. The result is that the storms pass each other roughly every two years, with the next close encounter in June. But, because the new red spot is located in the same band of clouds as the GRS, if the two storms continue on their present courses they will collide in August, and the small oval will either be be consumed or repelled by Jupiter's persistent GRS.

 


 

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NGC 7331 and Beyond
Credit & Copyright: Don Goldman, Sierra Remote Observatories



Big, beautiful spiral galaxy NGC 7331 is often touted as an analog to our own Milky Way. About 50 million light-years distant in the northern constellation Pegasus, NGC 7331 was recognized early on as a spiral nebula and is actually one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. Since the galaxy's disk is inclined to our line-of-sight, long telescopic exposures often result in an image that evokes a strong sense of depth. The effect is further enhanced in this well-framed view by the galaxies that lie beyond this gorgeous island universe. The background galaxies are about one tenth the apparent size of NGC 7331 and so lie roughly ten times farther away. Their strikingly close alignment on the sky with NGC 7331 occurs just by chance. The visual grouping of galaxies is also known as the Deer Lick Group.
 

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A Dark Sky Over Death Valley
Credit: Dan Duriscoe, U.S. National Park Service






 This eerie glow over Death Valley is in danger. Scrolling right will show a spectacular view from one of the darkest places left in the continental USA: Death Valley, California. The above 360-degree full-sky panorama is a composite of 30 images taken two years ago in Racetrack Playa. The image has been digitally processed and increasingly stretched at high altitudes to make it rectangular. In the foreground on the image right is an unusually placed rock that was pushed by high winds onto Racetrack Playa after a slick rain. In the background is a majestic night sky, featuring thousands of stars and many constellations. The arch across the middle is the central band of our Milky Way Galaxy. Light pollution is threatening dark skies like this all across the US and the world, and therefore the International Dark-Sky Association and the US National Parks Service are suggesting methods that can protect them.
 

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Gas and Dust of the Lagoon Nebula
Credit & Copyright: Fred Vanderhaven




Nice eh ?...Being delivered next Tuesday !!





This beautiful cosmic cloud is a popular stop on telescopic tours of the constellation Sagittarius. Eighteenth century cosmic tourist Charles Messier cataloged the bright nebula as M8, while modern day astronomers recognize the Lagoon Nebula as an active stellar nursery about 5,000 light-years distant, in the direction of the center of our Milky Way Galaxy. Striking details can be traced through this remarkable picture, processed to remove stars and hence better reveal the Lagoon's range of filaments of glowing hydrogen gas, dark dust clouds, and the bright, turbulent hourglass region near the image center. This color composite view was recorded under dark skies near Sydney, Australia. At the Lagoon's estimated distance, the picture spans about 50 light-years.
 

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Extra Galaxies
Credit & Copyright: Dietmar Hager





A careful look at the full field of view for this sharp image reveals a surprising number of galaxies both near and far toward the constellation Ursa Major. The most striking is clearly NGC 3718, the warped spiral galaxy right of center. NGC 3718's faint spiral arms look twisted and extended, its bright central region crossed by obscuring dust lanes. A mere 150 thousand light-years to the left is another large spiral galaxy, NGC 3729. The two are likely interacting gravitationally, accounting for the peculiar appearance of NGC 3718. While this galaxy pair lies about 52 million light-years away, the remarkable Hickson Group 56 can also be seen clustered just below NGC 3718. Hickson Group 56 consists of five interacting galaxies and lies over 400 million light-years away.
 

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Fossil feathers preserve evidence of color

.......say Yale scientists





New Haven, Conn. — The traces of organic material found in fossil feathers are remnants of pigments that once gave birds their color, according to Yale scientists whose paper in Biology Letters opens up the potential to depict the original coloration of fossilized birds and their ancestors, the dinosaurs.

Closer study of a number of fossilized bird feathers by Yale PhD student Jakob Vinther revealed that organic imprints in the fossils — previously thought to be carbon traces from bacteria — are fossilized melanosomes, the organelles that contain melanin pigment.








"Birds frequently have spectacularly colored plumage which are often used in camouflage and courtship display," said Vinther. "Feather melanin is responsible for rusty-red to jet-black colors and a regular ordering of melanin even produces glossy iridescence. Understanding these organic remains in fossil feathers also demonstrates that melanin can resist decay for millions of years."

Working with Yale paleontologist Derek E. G. Briggs and Yale ornithologist Richard O. Prum, Vinther analyzed a striped feather found in 100 million-year-old rocks from the Lower Cretaceous Period in Brazil. The team used a scanning electron microscope to show that dark bands of the feather preserved the arrangement of the pigment-bearing structures as a carbon residue — organized much as the structures are in a modern feather. The light bands showed only rock surface.

In another fossil of a bird from the Eocene Epoch — 55 million years ago — in Denmark there were similar traces in the feathers surrounding the skull. That fossil also preserved an organic imprint of the eye and showed structures similar to the melanosomes found in eyes of modern birds.
Jacob Vinther


"Many other organic remains will presumably prove to be composed of melanin," said Vinther. He expects that fur of ancient mammals and skin from dinosaurs preserved as organic imprints will likely be the remains of the melanin.

"Now that we have demonstrated that melanin can be preserved in fossils, scientists have a way to reliably predict, for example, the original colors of feathered dinosaurs," said Prum, who is the William Robertson Coe Professor of Ornithology and chair of the Department of Ecology and Evolutionary Biology, as well as curator of ornithology at Yale's Peabody Museum of Natural History.
 

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Jupiter over Ephesus
Credit & Copyright: Tunç Tezel (TWAN)




 A brilliant Jupiter shares the sky with the Full Moon tonight. Since Jupiter is near opposition, literally opposite the Sun in planet Earth's sky, Jupiter will rise near sunset just like the Full Moon. Of course, opposition is also the point of closest approach, with Jupiter shining at its brightest and offering the best views for skygazers. Recorded late last month, this moving skyscape features Jupiter above the southeastern horizon and the marbled streets of the ancient port city of Ephesus, located in modern day Turkey. At the left is a temple dedicated to the Roman emperor Hadrian. The beautiful night sky also includes the arc of the northern summer Milky Way. Lights on the horizon are from the nearby town of Selçuk. Clicking on the image will download the scene as a panorama.
 

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M16 and the Eagle Nebula
Credit & Copyright: Johannes Schedler (Panther Observatory)






Young star cluster M16 is surrounded by natal clouds of cosmic dust and glowing gas also known as The Eagle Nebula. This beautifully detailed image of the region includes fantastic shapes made famous in well-known Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or Pillars of Creation, dense, dusty columns rising near the center are light-years in length but are gravitationally contracting to form stars. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the upper left edge of the nebula is another dusty starforming column known as the Fairy of Eagle Nebula. M16 and the Eagle Nebula lie about 7,000 light-years away, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake).
 

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Crescent Rhea Occults Crescent Saturn
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA





Soft hues, partially lit orbs, a thin trace of the ring, and slight shadows highlight this understated view of the majestic surroundings of the giant planet Saturn. Looking nearly back toward the Sun, the robot Cassini spacecraft now orbiting Saturn captured crescent phases of Saturn and its moon Rhea in color a few years ago. As striking as the above image is, it is but a single frame from a recently released 60-frame silent movie where Rhea can be seen gliding in front of its parent world. Since Cassini was nearly in the plane of Saturn's rings, the normally impressive rings are visible here only as a thin line across the image center. Although Cassini has now concluded its primary mission, its past successes and opportunistic location have prompted NASA to start a two-year Equinox Mission, further exploring not only Saturn's enigmatic moons Titan and Enceladus, but Saturn herself as her grand rings tilt right at the Sun in August 2009.
 

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Quote
NASA has released images of the Moon taken from its Deep Impact spacecraft - some 31 million miles from Earth.

A camera on the probe was turned back towards Earth and in a time lapse sequence, captured the moon passing in front on 29 May.

The video shows a graphic, in the corner, highlighting the position of the earth at the time of the image.

http://news.bbc.co.uk/1/hi/sci/tech/7515249.stm
 

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NASA has on the loose descriptions of the Moon in use from its unfathomable collision rocket ship some 32 million miles from gravel. NASA has on the rampage metaphors of the Moon full from its cavernous Impact spaceship some 31 million miles from terrain.
_________________________________
william rozar
Wide Circles
 

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Nothing amazing but i'm pleased with it considering the speed i set up my camera last night but i captured one of last night's storms in action.

 

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Wow Exodus that is beautiful
 

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The Colliding Spiral Galaxies of Arp 271
Credit & Copyright: Gemini Observatory, GMOS-South, NSF






What will become of these galaxies? Spiral galaxies NGC 5426 and NGC 5427 are passing dangerously close to each other, but each is likely to survive this collision. Most frequently when galaxies collide, a large galaxy eats a much smaller galaxy. In this case, however, the two galaxies are quite similar, each being a sprawling spiral with expansive arms and a compact core. As the galaxies advance over the next tens of millions of years, their component stars are unlikely to collide, although new stars will form in the bunching of gas caused by gravitational tides. Close inspection of the above image taken by the 8-meter Gemini-South Telescope in Chile shows a bridge of material momentarily connecting the two giants. Known collectively as Arp 271, the interacting pair spans about 130,000 light years and lies about 90 million light-years away toward the constellation of Virgo. Quite possibly, our Milky Way Galaxy will undergo a similar collision with the neighboring Andromeda Galaxy in about five billion years.
 

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Central IC 1805 Cosmic clouds
Credit & Copyright: Keith Quattrocchi



 Cosmic clouds seem to form fantastic shapes in the central regions of emission nebula IC 1805. Of course, the clouds are sculpted by stellar winds and radiation from massive hot stars in the nebula's newborn star cluster (aka Melotte 15). About 1.5 million years young, the cluster stars appear on the right in this colorful skyscape, along with dark dust clouds silhouetted against glowing atomic gas. A composite of narrow and broad band telescopic images, the view spans about 15 light-years and includes emission from hydrogen in green, sulfur in red, and oxygen in blue hues. Wider field images reveal that IC 1805's simpler, overall outline suggests its popular name - The Heart Nebula. IC 1805 is located about 7,500 light years away toward the constellation Cassiopeia.
 

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IC 4406: A Seemingly Square Nebula
C. R. O'Dell (Vanderbilt U.) et al., Hubble Heritage Team, NASA




 How can a round star make a square nebula? This conundrum comes to light when studying planetary nebulae like IC 4406. Evidence indicates that IC 4406 is likely a hollow cylinder, with its square appearance the result of our vantage point in viewing the cylinder from the side. Were IC 4406 viewed from the top, it would likely look similar to the Ring Nebula. This representative-color picture is a composite made by combining images taken by the Hubble Space Telescope in 2001 and 2002. Hot gas flows out the ends of the cylinder, while filaments of dark dust and molecular gas lace the bounding walls. The star primarily responsible for this interstellar sculpture can be found in the planetary nebula's center. In a few million years, the only thing left visible in IC 4406 will be a fading white dwarf star.
 

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The Milky Way Over Ontario
Credit & Copyright: Kerry-Ann Lecky Hepburn (Weather and Sky Photography)






 Sometimes, after your eyes adapt to the dark, a spectacular sky appears. Such was the case earlier this month over Ontario, Canada, when part of a spectacular sky also became visible in a reflection off a lake. To start, the brightest objects visible are bright stars and the planet Jupiter, seen as the brightest spot on the upper left. A distant town appears as a diffuse glow over the horizon. More faint still, the disk of the Milky Way Galaxy becomes apparent as a dramatic diffuse band across the sky that seems to crash into the horizon far in the distance. In the foreground, a picturesque landscape includes trees, a lake, and a stone wall. Finally, on this serene night in July when the lake water was unusually calm, reflections appear. Visible in the lake are not only reflections of several bright stars, but part of the Milky Way band itself. Careful inspection of the image will reveal, however, that bright stars leave small trails in the lake reflections that do not appear in the sky above. The reason for this is because the above image is actually a digital composite of time-consecutive exposures from the same camera. In the first set of exposures, sky images were co-added with slight rotations to keep the stars in one place
 

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The International Space Station Transits the Sun
Credit & Copyright: Martin Wagner





 That's no sunspot. It's the International Space Station (ISS) caught by chance passing in front of the Sun. Sunspots, individually, have a dark central umbra, a lighter surrounding penumbra, and no solar panels. By contrast, the ISS is a complex and multi-spired mechanism, one of the largest and most sophisticated machines ever created by humanity. Also, sunspots occur on the Sun, whereas the ISS orbits the Earth. Transiting the Sun is not very unusual for the ISS, which orbits the Earth about every 90 minutes, but getting one's timing and equipment just right for a great image is rare. Strangely, besides that fake spot, the Sun, last week, lacked any real sunspots. Sunspots have been rare on the Sun since the dawn of the current Solar Minimum, a period of low solar activity. Although fewer sunspots have been recorded during this Solar Minimum than for many previous decades, the low solar activity is not, as yet, very unusual.
 

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Moon Games
Credit & Copyright: Laurent Laveder (PixHeaven.net / TWAN)





The Moon's measured diameter is around 3,476 kilometers (2,160 miles). But apparent angular size, or the angle covered by an object, can also be important to Moon enthusiasts. Angular size depends on distance, the farther away an object is, the smaller an angle it covers. Since the Moon is 400,000 kilometers away, its angular size is only about 1/2 degree, a span easily covered by the tip of your finger held at arms length, or a measuring tape held in the distance by a friend. Of course the Sun is much larger than the Moon, 400 times larger in fact, but today the New Moon will just cover the Sun. The total solar eclipse can be seen along a track across northern Canada, the Arctic, Siberia, and northern China. (A partial eclipse is visible from a broader region). Solar eclipses illustrate the happy coincidence that while the Sun is 400 times the diameter of the Moon, it is also 400 times farther away giving the Sun and Moon exactly the same angular size.
 

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X-Rays from the Cat's Eye Nebula
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI






 Haunting patterns within planetary nebula NGC 6543 readily suggest its popular moniker -- the Cat's Eye nebula. Starting in 1995, stunning false-color optical images from the Hubble Space Telescope detailed the swirls of this glowing nebula, known to be the gaseous shroud expelled from a dying sun-like star about 3,000 light-years from Earth. This composite picture combines the latest Hubble optical image of the Cat's Eye with new x-ray data from the orbiting Chandra Observatory and reveals surprisingly intense x-ray emission indicating the presence of extremely hot gas. X-ray emission is shown as blue-purple hues superimposed on the nebula's center. The nebula's central star itself is clearly immersed in the multimillion degree, x-ray emitting gas. Other pockets of x-ray hot gas seem to be bordered by cooler gas emitting strongly at optical wavelengths, a clear indication that expanding hot gas is sculpting the visible Cat's Eye filaments and structures. Gazing into the Cat's Eye, astronomers see the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.
 

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Perseid over Vancouver
Credit & Copyright: Yuichi Takasaka (www.blue-moon.ca / TWAN)






Colorful and bright, the city lights of Vancouver, Canada are reflected in the water in this portrait of the world at night. Recorded on August 12 during the Perseid Meteor Shower, the wide-angle view takes in a large swath along the photographer's eastern horizon. The picture is a composite of many consecutive 2 second exposures that, when added together, cover a total time of an hour and 33 minutes. During that time, stars trailed through the night sky above Vancouver, their steady motion along concentric arcs a reflection of planet Earth's rotation. The dotted trails of aircraft also cut across the scene. Of course, two of the frames captured the brief, brilliant flash of a Perseid fireball as it tracked across the top of the field of view. The large gap in the single meteor trail corresponds to the time gap between the consecutive frames.
 

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Brightest star in the galaxy has new competition
NASA/JPL NEWS RELEASE
Posted: July 20, 2008

A contender for the title of brightest star in our Milky Way galaxy has been unearthed in the dusty metropolis of the galaxy's center.




The 'Peony nebula' star, circled,
 is now the second-brightest star
in our galaxy.
Credit: NASA/JPL-Caltech/Potsdam Un
iv.
 
 
Nicknamed the "Peony nebula star," the bright stellar bulb was revealed by NASA's Spitzer Space Telescope and other ground-based telescopes. It blazes with the light of an estimated 3.2 million suns.

The reigning "brightest star" champion is Eta Carina, with a whopping solar wattage of 4.7 million suns. But according to astronomers, it's hard to pin down an exact brightness, or luminosity, for these scorching stars, so they could potentially shine with a similar amount of light.

"The Peony nebula star is a fascinating creature. It appears to be the second-brightest star that we now know of in the galaxy, and it's located deep into the galaxy's center," said Lidia Oskinova of Potsdam University in Germany. "There are probably other stars just as bright if not brighter in our galaxy that remain hidden from view." Oskinova is principal investigator for the research and second author of a paper appearing in a future issue of the journal Astronomy and Astrophysics.

Scientists already knew about the Peony nebula star, but because of its sheltered location in the dusty central hub of our galaxy, its extreme luminosity was not revealed until now. Spitzer's dust-piercing infrared eyes can see straight into the heart of our galaxy, into regions impenetrable by visible light. Likewise, infrared data from the European Southern Observatory's New Technology Telescope in Chile were integral in calculating the Peony nebula star's luminosity.

"Infrared astronomy opens extraordinary views into the environment of the central region of our galaxy," said Oskinova.

The brightest stars in the universe are also the biggest. Astronomers estimate the Peony nebula star kicked off its life with a hefty mass of roughly 150 to 200 times that of our sun. Stars this massive are rare and puzzle astronomers because they push the limits required for stars to form. Theory predicts that if a star starts out too massive, it can't hold itself together and must break into a double or multiple stars instead.

Not only is the Peony nebula star hefty, it also has a wide girth. It is a type of giant blue star called a Wolf-Rayet star, with a diameter roughly 100 times that of our sun. That means this star, if placed where our sun is, would extend out to about the orbit of Mercury.

With so much mass, the star barely keeps itself together. It sheds an enormous amount of stellar matter in the form of strong winds over its relatively short lifetime of a few million years. This matter is pushed so hard by strong radiation from the star that the winds speed up to about 1.6 million kilometers per hour (one million miles per hour) in only a few hours.

Ultimately, the Peony nebula star will blow up in a fantastic explosion of cosmic proportions called a supernova. In fact, Oskinova and her colleagues say that the star is ripe for exploding soon, which in astronomical terms mean anytime from now to millions of years from now.

"When this star blows up, it will evaporate any planets orbiting stars in the vicinity," said Oskinova. "Farther out from the star, the explosion could actually trigger the birth of new stars."

In addition to the star itself, the astronomers noted a cloud of dust and gas, called a nebula, surrounding the star. The team nicknamed this cloud the Peony nebula because it resembles the ornate flower.

"The nebula was probably created from the spray of dust leaking off the massive Peony nebula star," said Andreas Barniske of Potsdam University, lead author of the study.

Wolf-Rainer Hamann, also of Potsdam University, is another co-author of the paper and the principal investigator of a Spitzer program enabling this research.

 

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A new way developed to weigh giant black holes
CHANDRA X-RAY CENTER NEWS RELEASE
Posted: July 19, 2008

How do you weigh the biggest black holes in the universe? One answer now comes from a completely new and independent technique that astronomers have developed using data from NASA's Chandra X-ray Observatory.


Credit: X-ray (NASA/CXC/Univ. of
California Irvine/P.Humphrey et al.); Optical (NASA/STScI)

 
 
By measuring a peak in the temperature of hot gas in the center of the giant elliptical galaxy NGC 4649, scientists have determined the mass of the galaxy's supermassive black hole. The method, applied for the first time, gives results that are consistent with a traditional technique.

Astronomers have been seeking out different, independent ways of precisely weighing the largest supermassive black holes, that is, those that are billions of times more massive than the Sun. Until now, methods based on observations of the motions of stars or of gas in a disk near such large black holes had been used.

"This is tremendously important work since black holes can be elusive, and there are only a couple of ways to weigh them accurately," said Philip Humphrey of the University of California at Irvine, who led the study. "It's reassuring that two very different ways to measure the mass of a big black hole give such similar answers."

NGC 4649 is now one of only a handful of galaxies for which the mass of a supermassive black hole has been measured with two different methods. In addition, this new X-ray technique confirms that the supermassive black hole in NGC 4649 is one of the largest in the local universe with a mass about 3.4 billion times that of the Sun, about a thousand times bigger than the black hole at the center of our galaxy.

The new technique takes advantage of the gravitational influence the black hole has on the hot gas near the center of the galaxy. As gas slowly settles towards the black hole, it gets compressed and heated. This causes a peak in the temperature of the gas right near the center of the galaxy. The more massive the black hole, the bigger the temperature peak detected by Chandra.

This effect was predicted by two of the co-authors -- Fabrizio Brighenti from the University of Bologna, Italy, and William Mathews from the University of California at Santa Cruz -- almost 10 years ago, but this is the first time it has been seen and used.

"It was wonderful to finally see convincing evidence of the effects of the huge black hole that we expected," said Brighenti. "We were thrilled that our new technique worked just as well as the more traditional approach for weighing the black hole."

The black hole in NGC 4649 is in a state where it does not appear to be rapidly pulling in material towards its event horizon, nor generating copious amounts of light as it grows. So, the presence and mass of the central black hole has to be studied more indirectly by tracking its effects on stars and gas surrounding it. This technique is well suited to black holes in this condition.

"Monster black holes like this one power spectacular light shows in the distant, early universe, but not in the local universe," said Humphrey. "So, we can't wait to apply our new method to other nearby galaxies harboring such inconspicuous black holes."

source:spaceflightnow.org
 

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Using gravitational lensing to weigh 70 galaxies
UNIVERSITY OF HAWAII NEWS RELEASE
Posted: July 22, 2008

An international team of astronomers, including Dr. Adam S. Bolton of the University of Hawaii's Institute for Astronomy, has recently announced a finding that helps to settle a long-standing debate over the relationship between mass (the amount of matter) and luminosity (brightness) in galaxies.


The larger panel shows the Hubble Space Telescope
 image of one of the SLACS gravitational lenses,
 with the lensed background galaxy enhanced in blue.
 The smaller right-hand panels show the components
of a model of this image: top, a model for how the
more distant background galaxy would appear in the
absence of the lensing effect; center, a smooth model
 for the brightness of the more nearby massive galaxy;
bottom, the appearance of the background galaxy when
its image is distorted by the gravity of the nearer
galaxy. Credit: A. Bolton (UH/IfA) for SLACS and NASA/ESA

 
 
The team achieved this result by compiling the largest-ever single collection of "gravitational lens" galaxies-70 in all. A gravitational lens is a phenomenon similar to a terrestrial mirage, but it occurs on a scale of many thousands of light-years. When two galaxies happen to be precisely aligned with one another in the sky, the gravitational field of the nearer galaxy distorts the image of the more distant galaxy into multiple arc-shaped images or even into a complete ring, known as an "Einstein ring." These Einstein ring images can be up to 30 times brighter than the image of the distant galaxy would be in the absence of the lensing effect.

The discovery represents the culmination of the Sloan Lens ACS (or SLACS) Survey. The gravitational lenses were originally identified using data from the Sloan Digital Sky Survey, a major project that has used a dedicated 2.5-meter telescope in New Mexico to measure precise distances to nearly one million distant galaxies and quasars throughout one quarter of the sky. To observe and measure the details of the Einstein ring images, the SLACS astronomers then took advantage of the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope, which delivers pictures of unparalleled sharpness.

"The SLACS collection of lenses is especially powerful for science," said Bolton, lead author of two papers describing these latest results, which will be published in the Astrophysical Journal in August and September. "For each lens, we measured the apparent sizes of the Einstein rings on the sky using the Hubble images, and we measured the distances to the two galaxies of the aligned pair using Sloan data. By combining these measurements, we were able to deduce the mass of the nearer galaxy."

In other lens surveys of this scale, distances to the lens and background galaxies-and hence the lens galaxy masses-have not been measured precisely.

By considering these galaxy masses along with measurements of their sizes, brightnesses, and stellar velocities, the SLACS astronomers were able to infer the presence of "dark matter" in addition to the visible stars within the galaxies. Dark matter is the mysterious, unseeable material that is the majority of matter in the universe. And with such a large number of lens galaxies across a range of masses, they found that the fraction of dark matter relative to stars increases systematically when going from galaxies of average mass to galaxies of high mass.

The existence of gravitational lenses was first predicted by Albert Einstein in the 1930s, but the first example was not discovered until the late 1970s. In the 30 years since then, many more lenses have been discovered, but their scientific potential has been limited by the disparate assortment of known examples. The SLACS Survey has significantly changed this situation by discovering a single large and uniformly selected sample of strong lens galaxies. The SLACS collection promises to form the basis of many further scientific studies.

Other members of the SLACS collaboration are Dr. L.V.E. Koopmans (Kapteyn Instituut, Groningen, The Netherlands), Prof. Tommaso Treu (University of California, Santa Barbara), Dr. Raphael Gavazzi (Institut d'astrophysique de Paris), Dr. Leonidas A. Moustakas (JPL/Caltech), and Dr. Scott Burles (MIT).

Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea.

Established in 1907 and fully accredited by the Western Association of Schools and Colleges, the University of Hawaii is the state's sole public system of higher education. The UH System provides an array of undergraduate, graduate, and professional degrees and community programs on 10 campuses and through educational, training, and research centers across the state. UH enrolls more than 50,000 students from Hawaii, the U.S. mainland, and around the world.

Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England.

This work was based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. Support was provided by NASA through grants from STScI.


SOURCE:SPACEFLIGHTNOW.ORG
 

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