[neilep]

The N44 Complex


 A truly giant complex of emission nebulae, N44 is about 1,000 light-years across. It shines in southern skies as a denizen of our neighboring galaxy, the Large Magellanic Cloud, 170,000 light-years away. Winds and intense radiation from hot, young, luminous stars in N44 excite and sculpt filaments and streamers of the glowing nebular gas. But supernovae - the death explosions of the massive short lived stars - have also likely contributed to the region's enormous, blown-out shapes. The cluster of young stars seen near the center lies in a superbubble nearly 250 light-years across. This detailed, false-color view of the intricate structures codes emission from hydrogen, oxygen, and sulfur in shades of blue and green.


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Credit & Copyright: Don Goldman, Macedon Ranges Observatory

[neilep]

Galaxy Wars: M81 versus M82

 On the left, surrounded by blue spiral arms, is spiral galaxy M81. On the right marked by red gas and dust clouds, is irregular galaxy M82. This stunning vista shows these two mammoth galaxies locked in gravitational combat, as they have been for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays. In a few billion years only one galaxy will remain.



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 Credit: Rainer Zmaritsch & Alexander Gross

[neilep]

Embryonic planet imaged around young star
BY EMILY BALDWIN
ASTRONOMY NOW
Posted: April 2, 2008



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This is an image from
 the computer simulation of HL Tau and its
surrounding disc. In the model the dense clump
 (seen here at top right) forms with a mass
of about 8 times that of Jupiter at a distance
 from the star about 75 times that from the
Earth to the Sun. Image: Greaves, Richards,
 Rice & Muxlow 2008).

The youngest planet ever to be seen has been captured in its earliest stage of formation in a disc of gas and rocky debris around a star 520 light years away.

Using the MERLIN and Very Large Array radio observatories in the UK and US respectively, a team of astronomers lead by Dr Jane Greaves of the University of St Andrews studied the disc of gas and rocky particles surrounding the extremely young star HL Tau and identified a 'clump' of material at a distance of about 65 AU from the parent star, twice as far from HL Tau as Neptune is from our Sun.

 
 
"This star is probably less than 100,000 years old," says Greaves, "and we see a distinct ball of gas and dust orbiting around it, which is exactly how a protoplanet should look." The protoplanet is made up of dust grains and fist-sized rocks, and could form a planet about 14 times as massive as Jupiter.

Using computer simulations, team member Dr Ken Rice of the University of Edinburgh showed that a massive protoplanet of around 8 Jupiter masses could condense out of a disc into a self-constrained structure at a distance comparable to that observed by the radio telescopes. "The simulations show that the gravitational instability model really does work," comments Greaves. "This is the first image of a protoplanet that has ever been made and we've also captured the environment in which the planet is forming."

The team hope to use the eMERLIN telescope array to make similar observations of other protoplanetary discs, which may be able to resolve Earth-sized exoplanets.

SOURCE:SPACEFLIGHTNOW.ORG

[neilep]

South of Orion
Credit & Copyright: Johannes Schedler (Panther Observatory)


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BIGGY PICCY

This tantalizing array of nebulae and stars can be found about 2 degrees south of the famous star-forming Orion Nebula. The region abounds with energetic young stars producing jets and outflows that push through the surrounding material at speeds of hundreds of kilometers per second. The interaction creates luminous shock waves known as Herbig-Haro (HH) objects. For example, the graceful, flowing arc just right of center is cataloged as HH 222, also called the Waterfall Nebula. Seen below the Waterfall, HH 401 has a distinctive cone shape. The bright bluish nebula below and left of center is NGC 1999, a dusty cloud reflecting light from an embedded variable star. The entire cosmic vista spans over 30 light-years, near the edge of the Orion molecular cloud complex some 1,500 light-years distant.

[neilep]

'Focused' solar explosions get millions of degrees hotter
NASA-GODDARD NEWS RELEASE


A NASA-funded researcher has discovered that solar flares -- explosions in the atmosphere of the sun -- get much hotter when they stay "focused".

"A flare typically divides its energy between directly heating the solar atmosphere and accelerating particles," said Dr. Ryan Milligan of the Oak Ridge Association of Universities, Tennessee, who is stationed at NASA's Goddard Space Flight Center in Greenbelt, Md. "This flare seemed to focus on one task, devoting all its energy to heating, allowing it to become millions of degrees hotter than its multi-tasking cousins." The result was presented at the Royal Astronomical Society's National Astronomy Meeting 2008 at Queen's University, Belfast, United Kingdom.

 [ Invalid Attachment ]
An image of the solar flare taken using the X-Ray
 Telescope onboard Hinode on June 7, 2007. This
shows the flare loops in the solar atmopshere
at temperatures exceeding 10 million degree Celsius. Credit: JAXA
 
 
Solar flares are caused by the sudden release of magnetic energy. The largest can release as much energy as a billion one-megaton nuclear bombs. However, the flare observed in this study was a less powerful "micro" flare. NASA researchers want to understand flares because they generate radiation that can be hazardous to unprotected astronauts, like those walking on the surface of the moon.

Flares normally occur above loops of electrically conducting gas, called plasma, in the sun's atmosphere. When a typical flare goes off, it heats the plasma and sends beams of electrons racing down the sides of the loops. The electron beams evaporate more plasma from the sun's visible surface, which expands back up the loops.

"This evaporated plasma has traditionally been believed to be the source of the hottest temperatures seen in solar flares," said Milligan. "However, the flare in this new observation reached a temperature of almost 27 million degrees Fahrenheit -- some nine million degrees hotter than expected for a flare of this size -- without any evidence for beams of accelerated electrons."

Milligan used the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Hinode spacecraft to make his observation of the microflare on June 7, 2007. RHESSI revealed that the flare had a peak temperature of 27 million degrees, and also that the flare showed no evidence for high-energy electrons. Hinode was able to show the effects of the energy released at various layers in the solar atmosphere. In particular, the Extreme-ultraviolet Imaging Spectrometer instrument was used to detect signatures of plasma evaporation from the sun's surface through Doppler shifts of emission lines. The low-velocities observed confirmed the RHESSI observation that high-energy electrons were not present.

"If our assumption is correct, then this result tells us that the energy released during a solar flare is more efficient at achieving a higher temperature if the energy is used to directly heat the plasma in the sun's atmosphere, instead of being divided between heating and particle acceleration. This very effect has recently been shown in computer simulations of energy release during microflares," said Milligan.

The research was funded by the NASA Postdoctoral Program administered by the Oak Ridge Association of Universities, Tennessee.

Hinode is a Japanese mission, collaborating with NASA and the Science and Technology Facilities Council, United Kingdom, as international partners. The RHESSI project is a NASA Small Explorer mission managed by the Space Sciences Laboratory of the University of California, Berkeley. The Explorers Program Office at Goddard provides management and technical oversight under the direction of the Heliophysics Division of the Science Mission Directorate at NASA Headquarters in Washington, D.C

SOURCE: SPACEFLIGHTNEWS.COM

[neilep]

Black hole found in center of enigmatic Omega Centauri
HUBBLE EUROPEAN SPACE AGENCY INFORMATION CENTRE RELEASE

Omega Centauri has been known as an unusual globular cluster for a long time. A new result obtained by the NASA/ESA Hubble Space Telescope and the Gemini Observatory reveals that the explanation behind Omega Centauri's peculiarities may be a black hole hidden in its center. One implication of the discovery is that it is very likely that Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars, as some scientists have suspected for a few years.

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Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
 
 
A new discovery has resolved some of the mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. Images obtained with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope and data obtained by the GMOS spectrograph on the Gemini South telescope in Chile show that Omega Centauri appears to harbour an elusive intermediate-mass black hole in its center.

"This result shows that there is a continuous range of masses for black holes, from supermassive, to intermediate-mass, to small stellar mass types," explained astronomer Eva Noyola of the Max-Planck Institute for Extraterrestrial Physics in Garching, Germany, and leader of the team that made the discovery.

Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers from the southern hemisphere. Although the cluster is 17 000 light-years away, located just above the plane of the Milky Way, it appears almost as large as the full Moon when the cluster is seen from a dark rural area. Exactly how Omega Centauri should be classified has always been a contentious topic.

It was first listed in Ptolemy's catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster. Now, more than a century later, this new result suggests Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars.

Globular clusters consist of up to one million old stars tightly bound by gravity and are found in the outskirts of many galaxies including our own. Omega Centauri has several characteristics that distinguish it from other globular clusters: it rotates faster than a run-of-the-mill globular cluster, its shape is highly flattened and it consists of several generations of stars - more typical globulars usually consist of just one generation of old stars.

Moreover, Omega Centauri is about 10 times as massive as other big globular clusters, almost as massive as a small galaxy. These peculiarities have led astronomers to suggest that Omega Centauri may not be a globular cluster at all, but a dwarf galaxy stripped of its outer stars by an earlier encounter with the Milky Way.

"Finding a black hole at the heart of Omega Centauri could have profound implications for our understanding of its past interaction with the Milky Way," said Noyola.

Eva Noyola and her colleagues measured the motions and brightnesses of the stars at the center of Omega Centauri. The measured velocities of the stars in the center are related to the total mass of the cluster and were far higher than expected from the mass deduced from the number and type of stars seen. So, there had to be something extraordinarily massive (and invisible) at the center of the cluster responsible for the fast-swirling dance of stars ‹ almost certainly a black hole with a mass of 40 000 solar masses.

"Before this observation, we had only one example of an intermediate-mass black hole ‹ in the globular cluster G1, in the nearby Andromeda Galaxy," said astronomer Karl Gebhardt of the University of Texas at Austin, USA, and a member of the team that made the discovery.

Although the presence of an intermediate-mass black hole is the most likely reason for the stellar speedway near the cluster's center, astronomers have analysed a couple of other possible causes: a collection of unseen burnt-out stars such as white dwarfs or neutron stars adding extra mass, or a group of stars with elongated orbits that would make the stars closest to the center appear to speed up.

According to Noyola these alternative scenarios are unlikely: "The normal evolution of a star cluster like Omega Centauri should not end up with stars behaving in those ways. Even if we assume that either scenario did happen somehow, both configurations are expected to be very short-lived. A clump of burnt-out stars, for example, is expected to move farther away from the cluster center quickly. For stars with elongated orbits, these orbits are expected to become circular very quickly."

According to scientists, these intermediate-mass black holes could turn out to be "baby" supermassive black holes. "We may be on the verge of uncovering one possible mechanism for the formation of supermassive black holes. Intermediate-mass black holes like this could be the seeds of full-sized supermassive black holes." Astronomers have debated the existence of intermediate-mass black holes because they have not found strong evidence for them and there is no widely accepted mechanism for how they could form. They have ample evidence that small black holes of a few solar masses are produced when giant stars die. There is similar evidence that supermassive black holes weighing the equivalent of millions to billions of solar masses sit at the heart of many galaxies, including our own Milky Way.

Intermediate-mass black holes may be rare and exist only in former dwarf galaxies that have been stripped of their outer stars, but they could also be more common than expected, existing at the centers of globular clusters as well. A previous Hubble survey of supermassive black holes and their host galaxies showed a correlation between the mass of a black hole and that of its host. Astronomers estimate that the mass of the dwarf galaxy that may have been the precursor of Omega Centauri was roughly 10 million solar masses. If lower mass galaxies obey the same rule as more massive galaxies that host supermassive black holes, then the mass of Omega Centauri does match that of its black hole.

The team will use the European Southern Observatory's Very Large Telescope in Paranal, Chile to conduct follow-up observations of the velocity of the stars near the cluster's center to confirm the discovery.


SOURCE: SPACEFLIGHTNOW.COM

[neilep]

Stellar birth observed in the galactic wilderness
NASA/JPL NEWS RELEASE


A new image from NASA's Galaxy Evolution Explorer shows baby stars sprouting in the backwoods of a galaxy -- a relatively desolate region of space more than 100,000 light-years from the galaxy's bustling center.

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The blue and pink pinwheel in the center is the
 Southern pinwheel galaxy's main stellar disk,
 while the flapping, ribbon-like structures are
its extended arms. Image credit:
 NASA/JPL-Caltech/VLA/MPIA
 
 
The striking image, a composite of ultraviolet data from the Galaxy Evolution Explorer and radio data from the National Science Foundation's Very Large Array in New Mexico, shows the Southern Pinwheel galaxy, also known simply as M83.

In the new view, the main spiral, or stellar, disk of M83 looks like a pink and blue pinwheel, while its outer arms appear to flap away from the galaxy like giant red streamers. It is within these so-called extended galaxy arms that, to the surprise of astronomers, new stars are forming.

"It is absolutely stunning that we find such an enormous number of young stars up to 140,000 light-years away from the center of M83," said Frank Bigiel of the Max Planck Institute for Astronomy in Germany, lead investigator of the new Galaxy Evolution Explorer observations. For comparison, the diameter of M83 is only 40,000 light-years across.

Some of the "outback" stars in M83's extended arms were first spotted by the Galaxy Evolution Explorer in 2005. Remote stars were also discovered around other galaxies by the ultraviolet telescope over subsequent years. This came as a surprise to astronomers because the outlying regions of a galaxy are assumed to be relatively barren and lack high concentrations of the ingredients needed for stars to form.

The newest Galaxy Evolution Explorer observations of M83 (colored blue and green) were taken over a longer period of time and reveal many more young clusters of stars at the farthest reaches of the galaxy. To better understand how stars could form in such unexpected territory, Bigiel and his colleagues turned to radio observations from the Very Large Array (red). Light emitted in the radio portion of the electromagnetic spectrum can be used to locate gaseous hydrogen atoms, or raw ingredients of stars. When the astronomers combined the radio and Galaxy Evolution Explorer data, they were delighted to see they matched up.

"The degree to which the ultraviolet emission and therefore the distribution of young stars follows the distribution of the atomic hydrogen gas out to the largest distances is absolutely remarkable," said Fabian Walter, also of the Max Planck Institute for Astronomy, who led the radio observations of hydrogen in the galaxy.

The astronomers speculate that the young stars seen far out in M83 could have formed under conditions resembling those of the early universe, a time when space was not yet enriched with dust and heavier elements.

"Even with today's most powerful telescopes, it is extremely difficult to study the first generation of star formation. These new observations provide a unique opportunity to study how early generation stars might have formed," said co-investigator Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena.

M83 is located 15 million light-years away in the southern constellation Hydra.


SOURCE: SPACEFLIGHTNEWS.COM

[neilep]

ABOVE THE CLOUDS

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From the windswept peak of Mauna Kea, on the Big Island of Hawaii, your view of the world at night could look like this. At an altitude of about 13,500 feet, the mountain top is silhouetted in the stunning skyscape recorded near dusk in early December of 2005. The volcanic peak rises just above a sea of storm clouds illuminated by a bright Moon. Planet Venus is setting near the Moon as the brilliant evening star. The scene also includes the faint, milky band of our own galaxy's disk of stars and cosmic dust clouds stretching from the horizon into the sky along the right edge of the frame.

SOURCE:http://antwrp.gsfc.nasa.gov

[rosalind dna]

Neil I think that your Hawaiian (sp) picture is fantastic !!!!!!!!!

[Ronny]

Hurricane Florence was photographed by the crew on board the Space Shuttle Atlantis in November 1994. The hurricane is located over the Atlantic Ocean about 600 km from the coast of Bermuda. The image shows the typical pattern of hurricane systems: a large-scale line of clouds spiralling from bottom centre towards the central and thicker part of the storm, with the small clear "eye" at its very centre.
Source:sciencephotogallery.co.uk

[neilep]

Neil I think that your Hawaiian (sp) picture is fantastic !!!!!!!!!

Glad you like it Rosalind !..it is rather spectacular isn't it ?

[neilep]

NASA spacecraft tracks raging Saturn storm
NASA/JPL NEWS RELEASE
Posted: April 29, 2008

PASADENA, Calif. -- As a powerful electrical storm rages on Saturn with lightning bolts 10,000 times more powerful than those found on Earth, the Cassini spacecraft continues its five-month watch over the dramatic events.



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The view at left was created by combining images
taken using red, green and blue spectral filters,
 and shows Saturn in colors that approximate what
 the human eye would see. The storm stands out
with greater clarity in the sharpened, enhanced
color view at right.
 Credit: NASA/JPL/Space Science Institute
 
 See a larger image here


Scientists with NASA's Cassini-Huygens mission have been tracking the visibly bright, lightning-generating storm -- the longest continually observed electrical storm ever monitored by Cassini.

Saturn's electrical storms resemble terrestrial thunderstorms, but on a much larger scale. Storms on Saturn have diameters of several thousand kilometers (thousands of miles), and radio signals produced by their lightning are thousands of times more powerful than those produced by terrestrial thunderstorms.

Lightning flashes within the persistent storm produce radio waves called Saturn electrostatic discharges, which the radio and plasma wave science instrument first detected on Nov. 27, 2007. Cassini's imaging cameras monitored the position and appearance of the storm, first spotting it about a week later, on Dec. 6.

"The electrostatic radio outbursts have waxed and waned in intensity for five months now," said Georg Fischer, an associate with the radio and plasma wave science team at the University of Iowa, Iowa City. "We saw similar storms in 2004 and 2006 that each lasted for nearly a month, but this storm is longer-lived by far. And it appeared after nearly two years during which we did not detect any electrical storm activity from Saturn."

The new storm is located in Saturn's southern hemisphere -- in a region nicknamed "Storm Alley" by mission scientists -- where the previous lightning storms were observed by Cassini.

"In order to see the storm, the imaging cameras have to be looking at the right place at the right time, and whenever our cameras see the storm, the radio outbursts are there," said Ulyana Dyudina, an associate of the Cassini imaging team at the California Institute of Technology in Pasadena, Calif.

Cassini's radio plasma wave instrument detects the storm every time it rotates into view, which happens every 10 hours and 40 minutes, the approximate length of a Saturn day. Every few seconds the storm gives off a radio pulse lasting for about a tenth of a second, which is typical of lightning bolts and other electrical discharges. These radio waves are detected even when the storm is over the horizon as viewed from Cassini, a result of the bending of radio waves by the planet's atmosphere.

Amateur astronomers have kept track of the storm over its five-month lifetime. "Since Cassini's camera cannot track the storm every day, the amateur data are invaluable," said Fischer. "I am in continuous contact with astronomers from around the world."

The long-lived storm will likely provide information on the processes powering Saturn's intense lightning activity. Cassini scientists will continue to monitor Storm Alley as the seasons change, bringing the onset of autumn to the planet's southern hemisphere.

SOURCE: SPACELIGHTNOW.COM

[neilep]

Compact galaxies in early universe pack a big punch
SPACE TELESCOPE SCIENCE INSTITUTE NEWS RELEASE
Posted: April 29, 2008

Imagine receiving an announcement touting the birth of a baby 20 inches long and weighing 180 pounds. After reading this puzzling message, you would immediately think the baby's weight was a misprint.

Astronomers looking at galaxies in the universe's distant past received a similar perplexing announcement when they found nine young, compact galaxies, each weighing in at 200 billion times the mass of the Sun. The galaxies, each only 5,000 light-years across, are a fraction of the size of today's grownup galaxies but contain approximately the same number of stars. Each galaxy could fit inside the central hub of our Milky Way Galaxy.

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This illustration from a hypothetical planet
in a distant ultradense galaxy reveals a sky
packed with thousands of stars. There are 200
 times more stars in this sky than in our Earth's
 nighttime sky. Credit: NASA, ESA, G. Bacon (STScI),
 and P. van Dokkum (Yale University)
 
 
Astronomers used NASA's Hubble Space Telescope and the W.M. Keck Observatory on Mauna Kea, Hawaii, to study the galaxies as they existed 11 billion years ago, when the universe was less than 3 billion years old.

"Seeing the compact sizes of these galaxies is a puzzle," said Pieter G. van Dokkum of Yale University in New Haven, Conn., who led the study. "No massive galaxy at this distance has ever been observed to be so compact. It is not yet clear how they would build themselves up to become the large galaxies we see today. They would have to change a lot over 11 billion years, growing five times bigger. They could get larger by colliding with other galaxies, but such collisions may not be the complete answer."

To determine the sizes of the galaxies, the team used the Near Infrared Camera and Multi-Object Spectrometer on Hubble. The Keck observations were carried out with assistance of a powerful laser to correct for image blurring caused by the Earth's atmosphere. "Only Hubble and Keck can see the sizes of these galaxies because they are very small and far away," van Dokkum explained.

Van Dokkum and his colleagues studied the galaxies in 2006 with the Gemini South Telescope Near-Infrared Spectrograph, on Cerro Pachon in the Chilean Andes. Those observations provided the galaxies' distances and showed that the stars are a half a billion to a billion years old. The most massive stars had already exploded as supernovae.

"In the Hubble Deep Field, astronomers found that star-forming galaxies are small," said Marijn Franx of Leiden University, The Netherlands. "However, these galaxies were also very low in mass. They weigh much less than our Milky Way. Our study, which surveyed a much larger area than in the Hubble Deep Field, surprisingly shows that galaxies with the same weight as our Milky Way were also very small in the past. All galaxies look really different in early times, even massive ones that formed their stars early."

 [ Invalid Attachment ]
This illustration shows the comparative sizes
 of our Milky Way Galaxy and an ultracompact
galaxy, which existed in the early universe.
 Although the compact galaxy is only a fraction
 of the size of our Milky Way, it contains the
same number of stars. The small, dense galaxy
could fit inside the central hub of our Milky Way.
 Credit: NASA, ESA, A. Feild (STScI), and P.
van Dokkum (Yale University)
 
 
The ultradense galaxies might comprise half of all galaxies of that mass 11 billion years ago, van Dokkum said, forming the building blocks of today's largest galaxies.

How did these small, crowded galaxies form? One way, suggested van Dokkum, involves the interaction of dark matter and hydrogen gas in the nascent universe. Dark matter is an invisible form of matter that accounts for most of the universe's mass. Shortly after the Big Bang, the universe contained an uneven landscape of dark matter. Hydrogen gas became trapped in puddles of the invisible material and began spinning rapidly in dark matter's gravitational whirlpool, forming stars at a furious rate.

Based on the galaxies' masses, which are derived from their color, the astronomers estimated that the stars are spinning around their galactic disks at roughly 890,000 to 1 million miles an hour (400 to 500 kilometers a second). Stars in today's galaxies, by contrast, are traveling at about half that speed because they are larger and rotate more slowly than the compact galaxies.

These galaxies are ideal targets for the Wide Field Camera 3, which is scheduled to be installed aboard Hubble during Servicing Mission 4 in the fall of 2008. "We hope to use the Wide Field Camera 3 to find thousands of these galaxies. The Hubble images, together with the laser adaptive optics at Keck and similar large telescopes, should lead to a better understanding of the evolution of galaxies early in the life of the universe," said Garth Illingworth of the University of California, Santa Cruz, and Lick Observatory.

The findings appeared in the April 10 issue of The Astrophysical Journal Letters.

[neilep]

Moon Meets Mercury
Credit & Copyright: P-M Hedén (Clear Skies, TWAN)


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 On Tuesday, May 6, while standing on planet Earth and sweeping your binoculars along the western horizon just after sunset, you might have encountered this arresting skyscape. The view features a slender crescent Moon and bright planet Mercury separated on the sky by only about 2 degrees. Cradled in the sunlit lunar crescent, the night side of the Moon is faintly illuminated by earthshine -- sunlight reflected from planet Earth. Of course, the clouds in silhouette and fading twilight colors are common elements in pictures of the sky after sunset, but much less often seen is inner planet Mercury, usually hiding close to the Sun in Earth's sky. Still, the coming week will be a good time to spot Mercury near the western horizon about 30 minutes after sunset. As for the Moon, tonight and tomorrow night the crescent Moon will wander close to Mars in the early evening sky.

[neilep]

The Gegenschein Over Chile
Credit & Copyright: Yuri Beletsky (ESO)


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BIG PICCY HERE



 Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets. Pictured above from last October is one of the most spectacular pictures of the gegenschein yet taken. Here a deep exposure of an extremely dark sky over Paranal Observatory in Chile shows the gegenschein so clearly that even a surrounding glow is visible. In the foreground are several of the European Southern Observatory's Very Large Telescopes, while notable background objects include the Andromeda galaxy toward the lower left and the Pleiades star cluster just above the horizon. The gegenschein is distinguished from zodiacal light near the Sun by the high angle of reflection. During the day, a phenomenon similar to the gegenschein called the glory can be seen in reflecting air or clouds opposite the Sun from an airplane.

[neilep]

Part of missing matter in the universe now discovered
EUROPEAN SPACE AGENCY NEWS RELEASE


ESA's orbiting X-ray observatory XMM-Newton has been used by a team of international astronomers to uncover part of the missing matter in the universe.

Ten years ago, scientists predicted that about half of the 'ordinary' or normal matter made of atoms exists in the form of low-density gas, filling vast spaces between galaxies.
 
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Composite optical and X-ray image of galaxy
clusters Abell 222 and Abell 223. The cluster
 pair is connected by a filament permeated by
 hot X-ray emitting gas. Credits:
 ESA/ XMM-Newton/ EPIC/ ESO (J. Dietrich)/
 SRON (N. Werner)/ MPE (A. Finoguenov)
 
 
All the matter in the universe is distributed in a web-like structure. At dense nodes of the cosmic web are clusters of galaxies, the largest objects in the universe. Astronomers suspected that the low-density gas permeates the filaments of the web.

The low density of the gas hampered many attempts to detect it in the past. With XMM-Newton's high sensitivity, astronomers have discovered its hottest parts. The discovery will help them understand the evolution of the cosmic web.

Only about 5% of our universe is made of normal matter as we know it, consisting of protons and neutrons, or baryons, which along with electrons, form the building blocks of ordinary matter. The rest of our universe is composed of elusive dark matter (23%) and dark energy (72%).   

Small as the percentage might be, half of the ordinary baryonic matter is unaccounted for. All the stars, galaxies and gas observable in the universe account for less than a half of all the baryons that should be around.

Scientists predicted that the gas would have a high temperature and so it would primarily emit low-energy X-rays. But its very low density made observation difficult.

Astronomers using XMM-Newton were observing a pair of galaxy clusters, Abell 222 and Abell 223, situated at a distance of 2300 million light-years from Earth, when the images and spectra of the system revealed a bridge of hot gas connecting the clusters.

"The hot gas that we see in this bridge or filament is probably the hottest and densest part of the diffuse gas in the cosmic web, believed to constitute about half the baryonic matter in the universe," says Norbert Werner from SRON Netherlands Institute for Space Research, leader of the team reporting the discovery.

"The discovery of the warmest of the missing baryons is important. That's because various models exist and they all predict that the missing baryons are some form of warm gas, but the models tend to disagree about the extremes," adds Alexis Finoguenov, a team member.

Even with XMM-Newton's sensitivity, the discovery was only possible because the filament is along the line of sight, concentrating the emission from the entire filament in a small region of the sky. The discovery of this hot gas will help better understand the evolution of the cosmic web.

"This is only the beginning. To understand the distribution of the matter within the cosmic web, we have to see more systems like this one. And ultimately launch a dedicated space observatory to observe the cosmic web with a much higher sensitivity than possible with current missions. Our result allows to set up reliable requirements for those new missions." concludes Norbert Werner.

ESA's XMM-Newton Project Scientist, Norbert Schartel, comments on the discovery, "This important breakthrough is great news for the mission. The gas has been detected after hard work and more importantly, we now know where to look for it. I expect many follow-up studies with XMM-Newton in the future targeting such highly promising regions in the sky."

[neilep]

Hubble sees the Antennae Galaxies moving closer
HUBBLE EUROPEAN SPACE AGENCY INFORMATION CENTRE RELEASE

New research on the Antennae Galaxies using the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope shows that this benchmark pair of interacting galaxies is in fact much closer than previously thought - 45 million light-years instead of 65 million light-years.

 [ Invalid Attachment ]
Credit: NASA, ESA & Ivo Saviane (European Southern Observatory)
 See larger image here
 
 
The Antennae Galaxies are among the closest known merging galaxies. The two galaxies, also known as NGC 4038 and NGC 4039, began interacting a few hundred million years ago, creating one of the most impressive sights in the night sky. They are considered by scientists as the archetypal merging galaxy system and are used as a standard against which to validate theories about galaxy evolution.

An international group of scientists led by Ivo Saviane from the European Southern Observatory has used Hubble's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to observe individual stars spawned by the colossal cosmic collision in the Antennae Galaxies. They reached an interesting and surprising conclusion. By measuring the colours and brightnesses of red giant stars in the system, the scientists found that the Antennae Galaxies are much closer than previously thought: 45 million light-years instead of the previous best estimate of 65 million light-years.

The team targeted a region in the relatively quiescent outer regions in the southern tidal tail, away from the active central regions. This tail consists of material thrown from the main galaxies as they collided. The scientists needed to observe regions with older red giant stars to derive an accurate distance. Red giants are known to reach a standard brightness, which can then be used to infer their distance. The method is known as the tip of the red giant branch (TRGB).

The proximity of the Antennae system means it is the best-studied galaxy merger in the sky, with a wealth of observational data to be compared to the predictions of theoretical models. Saviane says: "All aspiring models for galaxy evolution must be able to account for the observed features of the Antennae Galaxies, just as respectable stellar models must be able to match the observed properties of the Sun. Accurate models require the correct merger parameters, and of these, the distance is the most essential".

The previous canonical distance to the Antennae Galaxy was about 65 million light-years although values as high as 100 million light years have been used. Our Sun is only eight light-minutes away from us, so the Antennae Galaxies may seem rather distant, but if we consider that we already know of galaxies that are more than ten billion light-years away, the two Antennae Galaxies are really our neighbours.

The previous larger distance required astronomers to invoke some quite exceptional physical characteristics to account for the spectacular system: very high star-formation rates, supermassive star clusters, ultraluminous X-ray sources etc. The new smaller distance makes the Antennae Galaxies less extreme in terms of the physics needed to explain the observed phenomena. For instance, with the smaller distance its infrared radiation is now that expected of a 'standard' early merging event rather than that of an ultraluminous infrared galaxy. The size of the star clusters formed as a consequence of the Antennae merger now agree with those of clusters created in other mergers instead of being 1.5 times as large.

The Antennae Galaxies are named for the two long tails of stars, gas and dust that resemble the antennae of an insect. These 'antennae' are a physical result of the collision between the two galaxies. Studying their properties gives us a preview of what may happen when our Milky Way galaxy collides with the neighbouring Andromeda galaxy in several billion years. Although galaxy mergers today are not common, it is believed that in the past they were an important channel of galaxy evolution. Therefore understanding the physics of galaxy mergers is a very important task for astrophysicists.

The Antennae are located in the constellation of Corvus, the Crow.

The findings appeared in the May 2008 issue of The Astrophysical Journal.

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ARCHEOLOGY
Oldest bust of Caesar found in France

French archaeologists have found what is thought to be the oldest existing statue of Julius Caesar in southern France. The bust is believed to be the sole portrait made during his life.

A bust of Julius Caesar, believed to be the oldest representation of the Roman emperor yet known, has been found at the bottom of the River Rhone in Arles, a town founded by him in 46 BC, the French culture ministry said Tuesday.
 
The imperial bust, showing a balding and aging man, was found with other artefacts in the bed of the river in the south of France.

 
It is "the oldest representation yet known of Caesar," and "typical of a series of realistic portraits from the period of the (Roman) republic," said a ministry statement.
 
Three other statues, including one of the god Neptune dating from the beginning of the third century AD, were found at the same site.
 
"I suspect the bust was thrown in the river after he was assassinated  because it would not have been good at that time to be considered a follower of his," said French archaeologist Luc Long, who directed excavations at the underwater site.
 
"In Rome you don't find any statues of Caesar dating from the time he lived, they were all posthumous," he added.


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Discovery of most recent supernova in our galaxy
NASA NEWS RELEASE


WASHINGTON -- The most recent supernova in our galaxy has been discovered by tracking the rapid expansion of its remains. This result, using NASA's Chandra X-ray Observatory and the National Radio Astronomy Observatory's Very Large Array, will help improve our understanding of how often supernovae explode in the Milky Way galaxy.



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Credit: X-ray (NASA/CXC/NCSU/S.Reynolds et al.
); Radio (NSF/NRAO/VLA/Cambridge/D.Green et al.)
 
 
The supernova explosion occurred about 140 years ago, making it the most recent in the Milky Way. Previously, the last known supernova in our galaxy occurred around 1680, an estimate based on the expansion of its remnant, Cassiopeia A.

Finding such a recent, obscured supernova is a first step in making a better estimate of how often the stellar explosions occur. This is important because supernovae heat and redistribute large amounts of gas, and pump heavy elements out into their surroundings. They can trigger the formation of new stars as part of a cycle of stellar death and rebirth. The explosion also can leave behind, in addition to the expanding remnant, a central neutron star or black hole.

The recent supernova explosion was not seen with optical telescopes because it occurred close to the center of the galaxy and is embedded in a dense field of gas and dust. This made the object about a trillion times fainter, in optical light, than an unobscured supernova. However, the remnant it caused can be seen by X-ray and radio telescopes.

"We can see some supernova explosions with optical telescopes across half of the universe, but when they're in this murk we can miss them in our own cosmic backyard," said Stephen Reynolds of North Carolina State University in Raleigh, who led the Chandra study. "Fortunately, the expanding gas cloud from the explosion shines brightly in radio waves and X-rays for thousands of years. X-ray and radio telescopes can see through all that obscuration and show us what we've been missing."

Astronomers regularly observe supernovae in other galaxies like ours. Based on those observations, researchers estimate about three explode every century in the Milky Way.

"If the supernova rate estimates are correct, there should be the remnants of about 10 supernova explosions that are younger than Cassiopeia A," said David Green of the University of Cambridge in the United Kingdom, who led the Very Large Array study. "It's great to finally track one of them down."

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Clear expansion is seen between these Very
Large Array images obtained in 1985 and 2008.
 Credit: NSF/NRAO/VLA/Cambridge/D.Green et al.
 
 
The tracking of this object began in 1985, when astronomers, led by Green, used the Very Large Array to identify the remnant of a supernova explosion near the center of our galaxy. Based on its small size, it was thought to have resulted from a supernova that exploded about 400 to 1000 years ago.

Twenty-two years later, Chandra observations revealed the remnant had expanded by a surprisingly large amount, about 16 percent, since 1985. This indicates the supernova remnant is much younger than previously thought.

That young age was confirmed in recent weeks when the Very Large Array made new radio observations. This comparison of data pinpoints the age of the remnant at 140 years - possibly less if it has been slowing down - making it the youngest on record in the Milky Way.

Besides being the record holder for youngest supernova, the object is of considerable interest for other reasons. The high expansion velocities and extreme particle energies that have been generated are unprecedented and should stimulate deeper studies of the object with Chandra and the Very Large Array.

"No other object in the galaxy has properties like this," Reynolds said. "This find is extremely important for learning more about how some stars explode and what happens in the aftermath."

SOURCE: SPACEFLIGHNOW.COM

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The Perseus Cluster of Galaxies
Credit & Copyright:
 Jean-Charles Cuillandre (CFHT) & Giovanni
Anselmi (Coelum Astronomia), Hawaiian Starlight


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BIGGER PICCY HERE


 Here is one of the largest objects that anyone will ever see on the sky. Each of these fuzzy blobs is a galaxy, together making up the Perseus Cluster, one of the closest clusters of galaxies. The cluster is seen through a foreground of faint stars in our own Milky Way Galaxy. Near the cluster center, roughly 250 million light-years away, is the cluster's dominant galaxy NGC 1275, seen above as the large galaxy on the image left. A prodigious source of x-rays and radio emission, NGC 1275 accretes matter as gas and galaxies fall into it. The Perseus Cluster of Galaxies is part of the Pisces-Perseus supercluster spanning over 15 degrees and containing over 1,000 galaxies. At the distance of NGC 1275, this view covers about 1.5 million light-years.