Posted on by Fraser Cain

Galaxy Stripped Clear of Star Forming Material

Image credit: NOAO
New observations from the WIYN 3.5-meter telescope on Kitt Peak show striking visual evidence for a galaxy being stripped bare of its star-forming material by its violent ongoing encounter with the hot gas in the center of a galaxy cluster.

This extremely disruptive process is believed to be a major influence on the evolution of galaxies and their star-forming ability over time, but direct observational evidence has been more circumstantial than incontrovertible.

A new three-color composite image of spiral galaxy NGC 4402, taken as the galaxy falls into the Virgo galaxy cluster, shows several key lines of evidence of an ongoing interaction, according to a presentation today in Denver at the 204th meeting of the American Astronomical Society.

NGC 4402 is located more than 50 million light years from Earth, in the midst of the relatively nearby Virgo cluster. As the galaxy moves toward the center of the cluster (located out of the image toward the bottom left), it experiences a ?wind? from the hot cluster gas, which can reach temperatures of millions of degrees.

?This hot wind strips out the much cooler gas and dust in the galaxy. This is important because the gas is raw material for new stars, and once this gas is stripped, the galaxy can no longer form new stars and becomes ?dead? in a sense,? says Hugh Crowl of Yale University, New Haven, CT, lead author of the paper. ?We see at least four distinct lines of evidence for declaring that this ram-pressure stripping process is cleaning out this infalling spiral galaxy.?

* First, the dust disk appears to be truncated, meaning that the light from stars extends out well beyond where gas and dust is observed. ?Since we believe that stars are born in clouds of gas and dust, this suggests that some of the material must have been stripped from the galaxy after the stars were born,? Crowl explains.
* Second, the dusty disk appears to be ?bowed? upward; that is, it has been bent by the wind blowing from the southeast (from the lower left of the image).
* Third, it appears that the light emitted by the north side of the stellar disk has been reddened and dimmed by dust that has been pushed up in front of it by the pressure of the cluster gas. Simultaneously, the dust to the south of the disk has been removed, revealing young blue stars glowing behind it.
* Finally, some of the most unusual features of NGC 4402 are the linear filaments of dust to the south of its main disk. ?These remarkable filaments originate in clumps that appear to be the densest remnants of the now displaced disk of the galaxy,? Crowl says.

The filaments are being ?ablated,? or stripped away, in an outside-in fashion, similar to the process observed in much smaller filamentary features in hot star-forming nebula such as the Eagle Nebula and Pelican Nebula. The hot galaxy cluster wind strips away the outer layers of the cloud, and the dust from these layers is then pushed away. In one case (the eastern or leftmost filament), ?we can see that the wind has either triggered star formation toward the tip of one of these dense clumps or exposed an already-existing star forming region,? Crowl adds.

The bright blue clusters of young stars in the bottom left region of the galaxy?s disk is further evidence of recently triggered star formation.

?This image clearly shows galactic disruption on a grand scale,? Crowl adds. ?It gives us much more confidence that this widely postulated process truly plays a significant role in shaping the evolution of galaxies in clusters.?

This imaging data was obtained with the help of the WIYN Tip-Tilt module, an adaptive optics device that uses a movable mirror to provide first-order compensation for the jittery motion of the incoming image caused by variable atmospheric conditions and telescope vibrations.

This result will be presented in poster 80.12 at the AAS meeting, located in the Ballroom poster session from 9:20 a.m. to 4:00 p.m. Co-authors of the paper are Jeff Kenney (Yale), J.H. van Gorkom (Columbia University), and B. Vollmer (CDS, Strasbourg).

The Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5-meter telescope is located at Kitt Peak National Observatory, 55 miles southwest of Tucson, AZ. Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF).

Original Source: NOAO News Release

Posted on by Fraser Cain

Cassini Ready to Begin Its Saturn Tour

Image credit: NASA/JPL
The international Cassini-Huygens mission is poised to begin an extensive tour of Saturn, its majestic rings and 31 known moons. After a nearly seven-year journey, Cassini is scheduled to enter orbit around Saturn at 7:30 p.m. PDT (10:30 p.m. EDT) June 30, 2004.

“The Saturn system represents an unsurpassed laboratory, where we can look for answers to many fundamental questions about the physics, chemistry and evolution of the planets and the conditions that give rise to life,” said Dr. Ed Weiler, associate administrator for space science at NASA Headquarters, Washington, D.C.

Launched Oct. 15, 1997, on a journey covering 3.5 billion kilometers (2.2 billion miles), Cassini is the most highly instrumented and scientifically capable planetary spacecraft ever flown. It has 12 instruments on the Cassini orbiter and six more on the Huygens probe. The mission represents the best technical efforts of 260 scientists from the United States and 17 European nations. The cost of the Cassini mission is approximately $3 billion.

The Cassini-Huygens mission is a four-year study of Saturn. The 18 highly sophisticated science instruments will study Saturn’s rings, icy satellites, magnetosphere and Titan, the planet’s largest moon.

For the critical Saturn orbit insertion maneuver, the spacecraft will fire its main engine for 96 minutes. The maneuver will reduce Cassini’s speed and allow it to be captured into orbit as a satellite of Saturn. Cassini will pass through a gap between two of Saturn’s rings, called the F and G rings. Cassini will swing close to the planet and begin the first of 76 orbits around the Saturn system. During Cassini’s four-year mission, it will execute 52 close encounters with seven of Saturn’s 31 known moons.

There are risks involved with orbit insertion, but mission planners have prepared for them. There is a backup engine in case the main engine fails. The region of passage through the ring plane was searched for hazards with the best Earth- and space-based telescopes.

Particles too small to be seen from Earth could be fatal to the spacecraft, so Cassini will be turned to use its high-gain antenna as a shield against small objects.

Saturn is the sixth planet from the sun. It is the second largest planet in our solar system, after Jupiter. The planet and its ring system serve as a miniature model for the disc of gas and dust surrounding the early Sun that formed the planets. Detailed knowledge of the dynamics of interactions among Saturn’s elaborate rings and numerous moons will provide valuable data for understanding how each of the solar system’s planets evolved.

The study of Titan, Saturn’s largest moon, is one of the major goals of the mission. Titan may preserve, in deep-freeze, many of the chemical compounds that preceded life on Earth. Cassini will execute 45 flybys of Titan, coming as close as approximately 950 kilometers (590 miles) above the surface. This will permit high-resolution mapping of the moon’s surface with an imaging radar instrument, which can see through the opaque haze of Titan’s upper atmosphere.

“Titan is like a time machine taking us to the past to see what Earth might have been like,” said Dr. Dennis Matson, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “The hazy moon may hold clues to how the primitive Earth evolved into a life-bearing planet.”

On Dec. 25, 2004 (Dec. 24 in U.S. time zones) Cassini will release the wok-shaped Huygens probe on its journey toward Titan. Huygens will be the first probe to descend to the surface of a moon of another planet. It will also make the most distant descent by a robotic probe ever attempted on another object in the solar system. On Jan. 14, 2005, after a 20-day ballistic freefall, Huygens will enter Titan’s atmosphere. It will deploy parachutes and begin 2.5 hours of intensive scientific observations. The Huygens probe will transmit data to the Cassini spacecraft, which will relay the information back to Earth.

JPL designed, developed and assembled the Cassini orbiter. The European Space Agency managed the development of Huygens and is in charge of operations of the probe from its control center in Darmstadt, Germany. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments. JPL manages the overall program for NASA’s Office of Space Science, Washington, D.C.

For information about the Cassini-Huygens mission to Saturn and Titan on the Internet, visit: http://www.nasa.gov/cassini or http://www.esa.int/Cassini-Huygens.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Watch the Venus Transit on the Internet

Image credit: NASA
NASA invites you to safely view a rare celestial event, one not seen before by any person alive. On June 8, Venus will appear to cross in front of the sun as viewed from Earth. The last “Venus transit” occurred in 1882. The next two Venus transits are on June 6, 2012, and Dec. 11, 2117.

NASA has formed partnerships with observatories, museums, and amateur astronomers to help people safely observe the event. Special precautions are necessary to safely observe the sun. NASA’s Office of Space Science is offering exciting activities and resources for classrooms and museums. Information, resources, opportunities for educational participation, local events and viewing times, are available on the Internet at:
http://sunearthday.nasa.gov

The event may be safely observed over the Internet with images from solar observatories and satellites. For Internet viewing options, including a live webcast from Athens, Greece, made in partnership with the Exploratorium in San Francisco, Calif., visit:
Centennial Challenges Workshops

The Venus transit will be visible from approximately 75 percent of the Earth. For a map of the transit visibility on the Internet, visit:
http://sunearth.gsfc.nasa.gov/eclipse/transit/TV2004/TV2004-Map1b.GIF

Transit times for cities worldwide are available on the Internet at:
http://sunearth.gsfc.nasa.gov/eclipse/transit/TV2004.html

“People using a filter approved for safe solar viewing can expect to see a small black dot, about 1/30 the size of the solar disk, very slowly moving across the sun,” said Fred Espenak, an eclipse expert at NASA’s Goddard Space Flight Center, Greenbelt, Md.

During the 19th century, Venus transits were essential for astronomers to determine the scale of the heavens. Transits were used to calculate a relatively accurate distance from the Earth to the sun. Once that distance was determined, astronomers calculated the size of our solar system. They also calculated distances to nearby stars by measuring how much they appeared to shift against remote background stars, as the Earth progressed in its orbit around the sun.

So critical was this measurement that, beginning in 1761, leading nations sent expeditions to remote corners of the globe to exactly time when Venus appeared to begin its transit of the sun. The precise timing of the transit depended on location, because different places on the Earth observed the event from different angles. The times were compared, and the distance to the sun calculated using the known distances between expedition locations on the Earth and trigonometry.

The transit phenomenon also has relevance for the future of astronomy. Scientists with NASA’s Kepler mission hope to discover Earth-like planets outside our solar system by searching for transits of other stars by planets that might be orbiting them.

NASA’s Kepler mission is scheduled for launch in October 2007. It will allow astronomers to find planets, perhaps the size of Earth, orbiting other stars by looking for tiny dips in the brightness of a star when a planet crosses in front of it. Periodic brightness dips will signal the presence of a planet in orbit around the star, even if the planet is not directly visible. For information about the Kepler mission on the Internet, visit:

NASA Kepler

Posted on by Fraser Cain

Speakers Announced for Centennial Challenges Workshop

NASA’s Centennial Challenges program will feature prominent speakers and panelists during its inaugural workshop, June 15 and 16, at the Hilton Hotel, Washington.

Centennial Challenges is a new NASA prize competition program designed to tap the nation’s ingenuity to make revolutionary advances to support the Vision for Space Exploration and NASA goals. The 2004 Centennial Challenges Workshop is also an opportunity for potential participants to provide input to NASA about future competitions.

Featured speakers:

Senator Sam Brownback, R-Kan., Chairman, Commerce Subcommittee on Science,
Technology, and Space

Dr. John H. Marburger III, Director, White House Office of Science and Technology Policy

Edward C. “Pete” Aldridge, Chairman, President’s Commission on Moon, Mars and
Beyond

Elon Musk, CEO and CTO, Space Exploration Technologies Corporation

Panels include:

Financing Prize Competitors
The panel will provide tutorials on various fundraising sources for potential Centennial Challenge competitors. Panelists: Jay Coleman, Founder and President of Electronic Marketing and Communications International Ltd.; Monty Deel, President of GST Protocol Services; Frank DiBello, President and CEO of Florida’s Space Finance Corporation; and Marco Rubin, Managing Partner of Exoventure Associates, LLC.

Past, Present, and Future Prize Competitions
The panel will provide a broad perspective on prize competitions, including early 20th century aviation prizes, the Defense Advanced Research Projects Agency’s (DARPA) Grand Challenge, and the privately funded Ansari X PRIZE and future X PRIZE Cup. Panelists: Eric Lindbergh, Vice President of the X PRIZE Foundation and grandson of aviation pioneer Charles Lindbergh; Air Force Colonel Jose Negron, Program Manager for the DARPA Grand Challenge; and Peter Diamandis, Chairman of the X PRIZE Foundation.

Launch Vehicles for Spacecraft Prize Competitions
The panel will provide an overview of existing and emergent launch vehicle capabilities for potential competitors in Centennial Challenges spacecraft competitions. Panel presenters: Kistler Aerospace Corporation; Space Exploration Technologies Corporation (Space-X); and XCOR Aerospace.

NASA invites interested individuals and organizations to attend the 2004 Centennial Challenges Workshop. For agenda and registration information on the Internet, visit:
http://centennialchallenges.nasa.gov/workshop.htm

NASA plans to have annual Centennial Challenges workshops. For information about the program on the Internet, visit:
http://centennialchallenges.nasa.gov

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

Original Source: NASA News Release

Posted on by Fraser Cain

New Details at the Heart of the Trifid Nebula

Image credit: Hubble
Three huge intersecting dark lanes of interstellar dust make the Trifid Nebula one of the most recognizable and striking star birth regions in the night sky. The dust, silhouetted against glowing gas and illuminated by starlight, cradles the bright stars at the heart of the Trifid Nebula. This nebula, also known as Messier 20 and NGC 6514, lies within our own Milky Way Galaxy about 9,000 light-years (2,700 parsecs) from Earth, in the constellation Sagittarius.

This new image from the Hubble Space Telescope offers a close-up view of the center of the Trifid Nebula, near the intersection of the dust bands, where a group of recently formed, massive, bright stars is easily visible. These stars, which astronomers classify as belonging to the hottest and bluest types of stars called type “O,” are releasing a flood of ultraviolet radiation that dramatically influences the structure and evolution of the surrounding nebula. Many astronomers studying nebulae like the Trifid are focusing their research on the ways that waves of star formation move through such regions.

The group of bright O-type stars at the center of the Trifid illuminates a dense pillar of gas and dust, seen to the right of the center of the image, producing a bright rim on the side facing the stars. At the upper left tip of this pillar, there is a complex filamentary structure. This wispy structure has a bluish color because it is made up of glowing oxygen gas that is evaporating into space.

Star formation is no longer occurring in the immediate vicinity of the conspicuous group of bright O-type stars, because their intense radiation has blown away the gas and dust from which stars are made. However, not far away there are signs of interstellar material collapsing under its own gravity, leading to ongoing star formation. One such example is a very young star that is still surrounded by a ring of gas and dust left over from the star’s formation. These circumstellar rings, called protoplanetary disks, or “proplyds” for short, are believed to be the locations where planetary systems are formed. A proplyd in the Trifid Nebula is visible near the lower right of the main Hubble image. An image enlargement of the proplyd is shown in the lower left box, where its elongated shape can be seen.

In the box at upper right, a jet of material is seen being ejected from a very young, low-mass star. The jet, extending to the lower right of the box, protrudes from the head of a dense pillar and extends three-quarters of a light-year out into the surrounding thin gas. The jet’s source is a very young stellar object that lies buried within the pillar. Previous Hubble images of the Trifid Nebula, taken in 1997, show very small, but noticeable changes in the knotty material being ejected from this jet. Accompanying the jet is a nearby stalk that points directly toward the central stars in the Trifid Nebula. This finger-like stalk is similar to the large pillars of gas in the well-known Eagle Nebula, also imaged by Hubble.

The Hubble image of the Trifid Nebula has given astronomers insight into the nature of the interaction of gaseous, dusty and stellar material in an area where dust, gas clouds, and new and old stars coexist. The science team, composed of Farhad Yusef-Zadeh (Northwestern U.), John Biretta (STScI), Bob O’Dell (Vanderbilt U.), and Mark Wardle (Macquarie U.), took exposures in filters that transmit light emitted by oxygen, hydrogen, and sulfur ions. The images were taken with the Wide Field Planetary Camera 2 onboard Hubble in mid-summer 2001 and 2002. This image was produced by the Hubble Heritage Team.

Original Source: Hubble News Release

Posted on by Fraser Cain

Getting Closer to Saturn

Image credit: NASA/JPL/Space Science Institute
As Cassini coasts into the final month of its seven-year trek, the serene majesty of its destination looms ahead. The spacecraft’s cameras are functioning beautifully and continue to return stunning views from Cassini’s position, 1.2 billion kilometers (750 million miles) from Earth and now 15.7 million kilometers (9.8 million miles) from Saturn.

In this narrow angle camera image from May 21, 2004, the ringed planet displays subtle, multi-hued atmospheric bands, colored by yet undetermined compounds. Cassini mission scientists hope to determine the exact composition of this material.

This image also offers a preview of the detailed survey Cassini will conduct on the planet’s dazzling rings. Slight differences in color denote both differences in ring particle composition and light scattering properties.

Images taken through blue, green and red filters were combined to create this natural color view. The image scale is 132 kilometers (82 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

Original Source: CICLOPS News Release

Posted on by Fraser Cain

Spirit Sees Layered Rock in Nearby Hills

Image credit: NASA/JPL
More than a month into bonus time after a successful primary mission on Mars, NASA’s Spirit rover has sighted possibly layered rock in hills just ahead, while twin Opportunity has extended its arm to pockmarked stones on a crater rim to gather clues of a watery past.

Both robotic geologists of the Mars Exploration Rover Project remain healthy. Engineers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., quickly restored Spirit from two unexpected computer reboots in May triggered by low- probability software glitches. “We had bad luck to hit two very unlikely scenarios just eight days apart, but in both cases the software team was able to figure out the problem within a day,” said Joe Snyder, a Lockheed Martin software engineer on JPL’s rover team.

Spirit has driven more than 2.9 kilometers (1.8 miles) since arriving at Mars five months ago, more than three-fourths of that since completing its three-month primary mission. It now has only about 400 meters (440 yards) to go — possibly less than a week of driving — before reaching the base of a range of hills informally named “Columbia Hills,” which scientists identified in January as a desirable but potentially unreachable destination for the rover.

“This is the first time we’ve ever had a close look at hills on Mars,” said Dr. James Rice of Arizona State University, Tempe, a member of the rovers’ science team. In 1997, hills called “Twin Peaks” tantalized scientists from only about one kilometer (1,100 yards) away from the Mars Pathfinder landing site. “We could only observe Twin Peaks from a distance and wonder about them, but now with a more capable rover we can get to Columbia Hills,” Rice said. He spoke at a press briefing today at JPL.

Rocks in Columbia Hills may provide insight both into both how hills form on Mars and whether the ancient environment at this part of Mars was wet. Images Spirit has taken as it nears the hills already show boulders and potential rock outcrops. “These rocks are much older than what we’ve been driving across,” Rice said. “We could find a lot of geological history locked in them. They may be some of the oldest material ever seen on Mars.”

On the rim of stadium-sized “Endurance Crater,” halfway around Mars from Spirit, Opportunity has been using its microscopic imager to examine the texture of rocks, adding information about a past lake or sea environment that also left its mark in the smaller crater, “Eagle,” where Opportunity landed.

“We’re looking at rocks that have very interesting surface textures,” said science-team member Dr. Wendy Calvin of the University of Nevada, Reno. “These rocks appear to be from the same geological layer as the outcrop at Eagle Crater, but they have some differences from what we saw there.” One rock called “Pyrrho” on the Endurance rim has a braided ripple pattern. Another, “Diogenes,” compared with rocks seen earlier, has more of the disc-shaped cavities that scientists interpret as sites where crystals formed in the rocks, then disappeared as the chemistry of water in the rocks varied.

From an overlook point on the southeastern edge of Endurance, Opportunity used its panoramic camera and miniature thermal emission spectrometer to study the inside of the crater, supplementing a similar survey made earlier from the western edge. Both instruments can be used to assess mineral composition from a distance. “We see a strong basaltic character in the sand at the bottom and in some of the rocks in the wall of the crater,” Calvin said. That is a contrast to the sulfate-rich composition of the overlying layer, which resembles the Eagle Crater outcrop. “We expect the basaltic material to tell us about environmental conditions from an earlier time,” she said.

Scientists and engineers are evaluating the potential science benefits of sending Opportunity into Endurance Crater and assessing whether the rover would be able to climb back out. A decision about whether to enter the crater will be based on those factors.

Mission controllers have begun frequent use of a “deep sleep” mode for Opportunity, reported JPL’s Matt Wallace, mission manager. It is a more complete overnight shutdown that conserves energy but at a calculated tradeoff of risking damage to the miniature thermal emission spectrometer. The strategy has approximately tripled the amount of time the solar-powered rover can work during the day. So far, the spectrometer has survived, but as the martian winter advances, scientists expect to lose the use of that instrument.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Chandra Finds a Gamma Ray Blast Remnant

Image credit: Chandra
Combined data from NASA’s Chandra X-ray Observatory and infrared observations with the Palomar 200-inch telescope have uncovered evidence that a gamma-ray burst, one of nature’s most catastrophic explosions, occurred in our Galaxy a few thousand years ago. The supernova remnant, W49B, may also be the first remnant of a gamma-ray burst discovered in the Milky Way.

W49B is a barrel-shaped nebula located about 35,000 light years from Earth. The new data reveal bright infrared rings, like hoops around a barrel, and intense X-radiation from iron and nickel along the axis of the barrel.

“These results provide intriguing evidence that an extremely massive star exploded in two powerful, oppositely directed jets that were rich in iron,” said Jonathan Keohane of NASA’s Jet Propulsion Laboratory at a press conference at the American Astronomical Society meeting in Denver. “This makes W49B a prime candidate for being the remnant of a gamma ray burst involving a black hole collapsar.”

“The nearest known gamma-ray burst to Earth is several million light years away ? most are billions of light years distant ? so the detection of the remnant of one in our galaxy would be a major breakthrough,” said William Reach, one of Keohane’s collaborators from the California Institute of Technology.

According to the collapsar theory, gamma-ray bursts are produced when a massive star runs out of nuclear fuel and the star’s core collapses to form a black hole surrounded by a disk of extremely hot, rapidly rotating, magnetized gas. Much of this gas is pulled into the black hole, but some is flung away in oppositely directed jets of gas traveling at near the speed of light.

An observer aligned with one these jets would see a gamma-ray burst, a blinding flash in which the concentrated power equals that of ten quadrillion Suns for a minute or so. The view perpendicular to the jets is a less astonishing, although nonetheless spectacular supernova explosion. For W49B, the jet is tilted out of the plane of the sky by about 20 degrees.

Four rings about 25 light years in diameter can be identified in the infrared image. These rings, which are due to warm gas, were presumably flung out by the rapid rotation of the massive star a few hundred thousand years before the star exploded. The rings were pushed outward by a hot wind from the star a few thousand years before it exploded.

Chandra’s image and spectral data show that the jets of multimillion-degree-Celsius gas extending along the axis of the barrel are rich in iron and nickel ions, consistent with their being ejected from the center of the star. This distinguishes the explosion from a conventional type II supernova in which most of the Fe and Ni goes into making the neutron star, and the outer part of the star is what is flung out. In contrast, in the collapsar model of gamma ray bursts iron and nickel from the center is ejected along the jet.

At the ends of the barrel, the X-ray emission flares out to make a hot cap. The X-ray cap is surrounded by a flattened cloud of hydrogen molecules detected in the infrared. These features indicate that the shock wave produced by the explosion has encountered a large, dense cloud of gas and dust.

The scenario that emerges is one in which a massive star formed from a dense cloud of dust, shone brightly for a few million years while spinning off rings of gas and pushing them away, forming a nearly empty cavity around the star. The star then underwent a collapsar-type supernova explosion that resulted in a gamma-ray burst.

The observations of W49B may help to resolve a problem that has bedeviled the collapsar model for gamma-ray bursts. On the one hand, the model is based on the collapse of a massive star, which is normally formed from a dense cloud. On the other hand, observations of the afterglow of many gamma-ray bursts indicate that the explosion occurred in a low-density gas. Based on the W49B data, the resolution proposed by Keohane and colleagues is that the star had carved out an extensive low-density cavity in which the explosion subsequently occurred.

“This star appears to have exploded inside a bubble it had created,” said Keohane. “In a sense, it dug its own grave.”

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release

Posted on by Fraser Cain

Super-Clusters of Galaxies Give Clues to the Big Bang

Image credit: ESO
Clusters of galaxies are very large building blocks of the Universe. These gigantic structures contain hundreds to thousands of galaxies and, less visible but equally interesting, an additional amount of “dark matter” whose origin still defies the astronomers, with a total mass of thousands of millions of millions times the mass of our Sun. The comparatively nearby Coma cluster, for example, contains thousands of galaxies and measures more than 20 million light-years across. Another well-known example is the Virgo cluster at a distance of about 50 million light-years, and still stretching over an angle of more than 10 degrees in the sky!

Clusters of galaxies form in the densest regions of the Universe. As such, they perfectly trace the backbone of the large-scale structures in the Universe, in the same way that lighthouses trace a coastline. Studies of clusters of galaxies therefore tell us about the structure of the enormous space in which we live.

The REFLEX survey
Following this idea, a European team of astronomers, under the leadership of Hans B?hringer (MPE, Garching, Germany), Luigi Guzzo (INAF, Milano, Italy), Chris A. Collins (JMU, Liverpool), and Peter Schuecker (MPE, Garching) has embarked on a decade-long study of these gargantuan structures, trying to locate the most massive of clusters of galaxies.

Since about one-fifth of the optically invisible mass of a cluster is in the form of a diffuse very hot gas with a temperature of the order of several tens of millions of degrees, clusters of galaxies produce powerful X-ray emission. They are therefore best discovered by means of X-ray satellites.

For this fundamental study, the astronomers thus started by selecting candidate objects using data from the X-ray Sky Atlas compiled by the German ROSAT satellite survey mission. This was the beginning only – then followed a lot of tedious work: making the final identification of these objects in visible light and measuring the distance (i.e., redshift) of the cluster candidates.

The determination of the redshift was done by means of observations with several telescopes at the ESO La Silla Observatory in Chile, from 1992 to 1999. The brighter objects were observed with the ESO 1.5-m and the ESO/MPG 2.2-m telescopes, while for the more distant and fainter objects, the ESO 3.6-m telescope was used.

Carried out at these telescopes, the 12 year-long programme is known to astronomers as the REFLEX (ROSAT-ESO Flux Limited X-ray) Cluster Survey. It has now been concluded with the publication of a unique catalogue with the characteristics of the 447 brightest X-ray clusters of galaxies in the southern sky. Among these, more than half the clusters were discovered during this survey.

Constraining the dark matter content
Galaxy clusters are far from being evenly distributed in the Universe. Instead, they tend to conglomerate into even larger structures, “super-clusters”. Thus, from stars which gather in galaxies, galaxies which congregate in clusters and clusters tying together in super-clusters, the Universe shows structuring on all scales, from the smallest to the largest ones. This is a relict of the very early (formation) epoch of the Universe, the so-called “inflationary” period. At that time, only a minuscule fraction of one second after the Big Bang, the tiny density fluctuations were amplified and over the eons, they gave birth to the much larger structures.

Because of the link between the first fluctuations and the giant structures now observed, the unique REFLEX catalogue – the largest of its kind – allows astronomers to put considerable constraints on the content of the Universe, and in particular on the amount of dark matter that is believed to pervade it. Rather interestingly, these constraints are totally independent from all other methods so far used to assert the existence of dark matter, such as the study of very distant supernovae (see e.g. ESO PR 21/98) or the analysis of the Cosmic Microwave background (e.g. the WMAP satellite). In fact, the new REFLEX study is very complementary to the above-mentioned methods.

The REFLEX team concludes that the mean density of the Universe is in the range 0.27 to 0.43 times the “critical density”, providing the strongest constraint on this value up to now. When combined with the latest supernovae study, the REFLEX result implies that, whatever the nature of the dark energy is, it closely mimics a Universe with Einstein’s cosmological constant.

A giant puzzle
The REFLEX catalogue will also serve many other useful purposes. With it, astronomers will be able to better understand the detailed processes that contribute to the heating of the gas in these clusters. It will also be possible to study the effect of the environment of the cluster on each individual galaxy. Moreover, the catalogue is a good starting point to look for giant gravitational lenses, in which a cluster acts as a giant magnifying lens, effectively allowing observations of the faintest and remotest objects that would otherwise escape detection with present-day telescopes.

But, as Hans B?hringer says: “Perhaps the most important advantage of this catalogue is that the properties of each single cluster can be compared to the entire sample. This is the main goal of surveys: assembling the pieces of a gigantic puzzle to build the grander view, where every single piece then gains a new, more comprehensive meaning.”

Original Source: ESO News Release

Posted on by Fraser Cain

SpaceShipOne’s Launch Date Set

Image credit: Scaled
A privately-developed rocket plane will launch into history on June 21 on a mission to become the world?s first commercial manned space vehicle. Investor and philanthropist Paul G. Allen and aviation legend Burt Rutan have teamed to create the program, which will attempt the first non-governmental flight to leave the earth?s atmosphere.

SpaceShipOne will rocket to 100 kilometers (62 miles) into sub-orbital space above the Mojave Civilian Aerospace Test Center, a commercial airport in the California desert. If successful, it will demonstrate that the space frontier is finally open to private enterprise. This event could be the breakthrough that will enable space access for future generations.

Allen, founder and chairman of Vulcan Inc, is financing the project. Along with Allen, Vulcan?s technology research and development team — which takes the lead in developing high impact science and technology projects for Allen — has been active in the project?s development and management.

“This flight is one of the most exciting and challenging activities taking place in the fields of aviation and aerospace today,” said Paul G. Allen, sole sponsor in the SpaceShipOne program. “Every time SpaceShipOne flies we demonstrate that relatively modest amounts of private funding can significantly increase the boundaries of commercial space technology. Burt Rutan and his team at Scaled Composites have accomplished amazing things by conducting the first mission of this kind without any government backing.”

Today?s announcement came after SpaceShipOne completed a May 13th, 2004 test flight in which pilot Mike Melvill reached a height of 211,400 feet (approximately 40 miles), the highest altitude ever reached by a non-government aerospace program.

Sub-orbital space flight refers to a mission that flies out of the atmosphere but does not reach the speeds needed to sustain continuous orbiting of the earth. The view from a sub-orbital flight is similar to being in orbit, but the cost and risks are far less.

The pilot (to be announced at a later date) of the up-coming June sub-orbital space flight will become the first person to earn astronaut wings in a non-government sponsored vehicle, and the first private civilian to fly a spaceship out of the atmosphere.

?Since Yuri Gagarin and Al Shepard?s epic flights in 1961, all space missions have been flown only under large, expensive Government efforts. By contrast, our program involves a few, dedicated individuals who are focused entirely on making spaceflight affordable,? said Burt Rutan. ?Without the entrepreneur approach, space access would continue to be out of reach for ordinary citizens. The SpaceShipOne flights will change all that and encourage others to usher in a new, low-cost era in space travel.?

SpaceShipOne was designed by Rutan and his research team at the California-based aerospace company, Scaled Composites. Rutan made aviation news in 1986 by developing the Voyager, the only aircraft to fly non-stop around the world without refueling.

?To succeed takes more than the work of designers and builders?, Rutan said, ?The vision, the will, the commitment and the courage to direct the program is the most difficult hurdle. We are very fortunate to have the financial support and the confidence of a visionary like Paul Allen to make this effort possible.?

To reach space, a carrier aircraft, the White Knight, lifts SpaceShipOne from the runway. An hour later, after climbing to approximately 50,000 feet altitude just east of Mojave, the White Knight releases the spaceship into a glide. The spaceship pilot then fires his rocket motor for about 80 seconds, reaching Mach 3 in a vertical climb. During the pull-up and climb, the pilot encounters G-forces three to four times the gravity of the earth.

SpaceShipOne then coasts up to its goal height of 100 km (62 miles) before falling back to earth. The pilot experiences a weightless environment for more than three minutes and, like orbital space travelers, sees the black sky and the thin blue atmospheric line on the horizon. The pilot (actually a new astronaut!) then configures the craft?s wing and tail into a high-drag configuration. This provides a ?care-free? atmospheric entry by slowing the spaceship in the upper atmosphere and automatically aligning it along the flight path. Upon re-entry, the pilot reconfigures the ship back to a normal glider, and then spends 15 to 20 minutes gliding back to earth, touching down like an airplane on the same runway from which he took off. The June flight will be flown solo, but SpaceShipOne is equipped with three seats and is designed for missions that include pilot and two passengers.

Unlike any previous manned space mission, the June flight will allow the public to view, up close, the takeoff and landing as well as the overhead rocket boost to space. This will be an historic and unique spectator opportunity. Information for the general public on attending the event is available at www.scaled.com.

Based on the success of the June space flight attempt, SpaceShipOne will later compete for the Ansari X Prize, an international competition to create a reusable aircraft that can launch three passengers into sub-orbital space, return them safely home, then repeat the launch within two weeks with the same vehicle.

The Discovery Channel and Vulcan Productions are producing RUTAN?S RACE FOR SPACE (wt), a world premiere television special that documents the entire process of the historic effort to create the first privately-funded spacecraft. From design to flight testing to the moments of the actual launch and return, the special takes viewers behind-the-scenes for the complete, inside story of this historic aerospace milestone. RUTAN?S RACE FOR SPACE will be broadcast later this year.

Original Source: Scaled News Release