vendredi 13 janvier 2012

Cassini Testing Part of Its Radio System












NASA / ESA - Cassini Mission to Saturn logo.

Jan. 14, 2012

Cassini Mission Status Report

Engineers with NASA's Cassini mission are conducting diagnostic testing on a part of the spacecraft's radio system after its signal was not detected on Earth during a tracking pass in late December. The spacecraft has been communicating with Earth using a backup part.

The issue occurred with the ultra-stable oscillator, which is used for one type of radio science experiment and also as a means of sending data back to Earth. The spacecraft is currently using an auxiliary oscillator, whose frequency stability is adequate for transmitting data from the spacecraft to Earth. Tests later this month will help mission managers decide whether it will be possible to bring the ultra-stable oscillator back into service.

Artist concept of Cassini at Saturn

Some of the data collected for the radio science experiment using the auxiliary oscillator will be of lesser quality than that from the ultra-stable oscillator. Signals used for occultation experiments – where scientists analyze how radio signals are affected as they travel through Saturn's rings or the atmospheres of Saturn and its moons back to Earth – will be of lesser quality. A second kind of radio science investigation using gravity measurements to probe the internal structure of Saturn or its moons will not be affected. Cassini carries 12 science experiments.

The cause is still under investigation, but age may be a factor. The spacecraft launched in 1997 and has orbited Saturn since 2004. Cassini completed its prime mission in 2008 and has had two additional mission extensions. This is the first time its ultra-stable oscillator has had an issue.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory in Pasadena manages the mission for the agency's Science Mission Directorate in Washington.

Welcome Disruption

The line of Saturn's rings disrupts the Cassini spacecraft's view of the moons Tethys and Titan

Larger Titan (3,200 miles, or 5,150 kilometers across) is on the left. Tethys (660 miles, or 1,062 kilometers across) is near the center of the image. This view looks toward the Saturn-facing sides of Tethys and Titan. The angle also shows the northern, sunlit side of the rings from less than one degree above the ring plane. The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on Dec. 7, 2011. The view was acquired at a distance of approximately 1.4 million miles (2.2 million kilometers) from Tethys and 1.9 million miles (3.1 million kilometers) from Titan. Image scale is 8 miles (13 kilometers) per pixel on Tethys and 12 miles (19 kilometers) on Titan.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two on-board cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov

Images, Text, Credit: NASA / JPL-Caltech / Space Science Institute.

Best regards, Orbiter.ch

jeudi 12 janvier 2012

Spacecraft Completes Biggest Maneuver










NASA - Mars Science Laboratory (MSL) patch.

Jan. 12, 2012

Mission Status Report

NASA's Mars Science Laboratory spacecraft successfully refined its flight path Wednesday with the biggest maneuver planned for the mission's journey between Earth and Mars.

"We've completed a big step toward our encounter with Mars," said Brian Portock of NASA's Jet Propulsion Laboratory, Pasadena, Calif., deputy mission manager for the cruise phase of the mission. "The telemetry from the spacecraft and the Doppler data show that the maneuver was completed as planned."

The Mars Science Laboratory mission will use its car-size rover, Curiosity, to investigate whether the selected region on Mars inside Gale Crater has offered environmental conditions favorable for supporting microbial life and favorable for preserving clues about whether life existed.

Engineers had planned today's three-hour series of thruster-engine firings to accomplish two aims: to put the spacecraft's trajectory about 25,000 miles (about 40,000 kilometers) closer to encountering Mars and to advance the time of the encounter by about 14 hours, compared with the trajectory following the mission's Nov. 26, 2011, launch.


Artist's concept illustrations show (left) the Mars Science Laboratory spacecraft during its voyage from Earth to Mars and (right) the mission's rover, Curiosity, working on Mars after landing. Image credit: NASA / JPL-Caltech.

"The timing of the encounter is important for arriving at Mars just when the planet's rotation puts Gale Crater in the right place," said JPL's Tomas Martin-Mur, chief navigator for the mission.

The mission's second trajectory correction maneuver, expected to be about one-sixth the magnitude of this first one, is scheduled for March 26. Up to four additional opportunities for fine-tuning, as needed, are scheduled before the arrival at Mars on Aug. 5, 2012, PDT (Aug. 6, EDT and Universal Time).

The spacecraft's initial trajectory resulting from the launch included an intentional offset to prevent the upper stage of the launch vehicle from hitting Mars. That upper stage was not cleaned the way the spacecraft itself was to protect Mars from Earth's microbes.

The Mars Science Laboratory spacecraft rotates in flight at about two revolutions per minute. Today's maneuver included two different components: one that changed velocity in the direction of the axis of the spacecraft's rotation, and one that changed velocity in a direction perpendicular to that.

The maneuver used the eight thruster engines on the cruise stage of the spacecraft, grouped into two sets of four. It began with a thrust lasting about 19 minutes, using just one thruster in each set and affecting velocity along the direction of the axis of rotation. Then, to affect velocity perpendicular to that line, each set of thrusters was fired for 5 seconds when the rotation put that set facing the proper direction. These 5-second bursts were repeated more than 200 times during a period of about two hours for a total of about 40 minutes.

Mars Science Laboratory Curiosity Rover Animation

The maneuver was calculated to produce a net change in velocity of about 12.3 miles per hour (5.5 meters per second), combining a slight increase in speed with a small change in direction of travel.

As of 9 a.m. PST (noon EST) on Thursday, Jan. 12, the spacecraft will have traveled 81.2 million miles (130.6 million kilometers) of its 352-million-mile (567-million-kilometer) flight to Mars. It will be moving at about 10,300 mph (16,600 kilometers per hour) relative to Earth, and at about 68,700 mph (110,500 kilometers per hour) relative to the sun.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Science Laboratory mission for the NASA Science Mission Directorate, Washington.

More information about Curiosity is online at: http://www.nasa.gov/msl and at http://mars.jpl.nasa.gov/msl

You can follow the mission on Twitter at http://www.twitter.com/marscuriosity and on Facebook at: http://www.facebook.com/marscuriosity

Images (mentioned), Video, Text, Credit: NASA / JPL / Guy Webster.

Greetings, Orbiter.ch

ESA coordinates international satellite reentry campaign







ESA / ESOC logo.

12 January 2012

An international campaign to assess the imminent atmospheric reentry of Russia's Phobos–Grunt Mars craft is being coordinated by experts in ESA's Space Debris Office. Participants include NASA and Roscosmos as part of the 12-member Inter-Agency Space Debris Coordination Committee.

ESA experts are working with international partners in a coordinated prediction campaign focused on Phobos–Grunt, a Russian Mars mission that is expected to largely burn up in Earth's atmosphere in the next few days.

Phobos-Grunt orbiter and lander

Phobos–Grunt was launched on 8 November 2011 into an initial Earth orbit of 206 x 341 km. The injection into an Earth-escape trajectory to Mars failed, and the spacecraft was declared lost by the Russian space agency, Roscosmos, on 13 December.

On 2 January, a comprehensive reentry prediction campaign for Phobos–Grunt was begun by the Inter-Agency Space Debris Coordination Committee (IADC), a technical forum for the worldwide coordination of activities related to human-made and natural debris in space. 

ESOC in Darmstadt hosts reentry database

ESA's Space Debris Office, located at ESOC, the European Space Operations Centre, Darmstadt, Germany, hosts the IADC reentry event database that is used to exchange orbit data and reentry predictions among IADC members.

ESA / ESOC - Main Control Room

Orbit data for Phobos–Grunt are provided mainly by the US Space Surveillance Network and the Russian Space Surveillance System. Based on this, ESA is issuing reentry prediction bulletins to its Members States.

According to its Russian owners, Phobos–Grunt has a mass of 13.5 tonnes, including about 11 tonnes of propellant, and a body size of 3.76 x 3.76 x 6.38 m, with solar wings spanning 7.97 m.

Large number of uncertainties affect reentry

"Right now, due to the large number of uncertainties in the orbit and space environment affecting the satellite, the indications are that Phobos-Grunt could reenter between 13 and 17 January, between 51.4°N and 51.4°S," says Prof. Heiner Klinkrad, Head of ESA's Space Debris Office.

He adds that this window will shorten as we approach reentry.

"Analyses by Roscosmos and NASA indicate that the fuel tanks, filled with unsymmetrical dimethylhydrazine – referred to as UDMH – will burst above 100 km altitude, release the propellant and largely demise thereafter."

H. Klinkrad

"This, combined with a relatively low dry mass of just 2.5 tonnes, means that Phobos–Grunt is not considered to be a high-risk reentry object."

"Roscosmos expects that at most, some 20 to 30 fragments may reach Earth's surface, with a total mass of less than 200 kg."

Since the beginning of the space age, there has been no confirmed report of an injury resulting from reentering space objects.

IADC assesses potentially hazardous reentries

In recent years, IADC members have developed a data exchange network specifically supporting the assessment of potentially hazardous reentries, which allows members to enter and extract orbit data in order to refine reentry predictions.

IADC member agencies include ESA, NASA, European national agencies and the Russian, Chinese, Canadian, Japanese, Ukrainian and Indian space agencies.

Results from the Phobos–Grunt reentry campaign will be used by IADC members to improve reentry models and make future predictions more accurate.

Enhancing Europe's observation capacity

In 2009, ESA launched the Space Situational Awareness Preparatory Programme, which, in part, aims to design a network of surveillance and tracking systems and novel data processing technologies that will enable Europe to build up a complete catalogue of orbiting objects.

This system will provide highly accurate data to reduce the threat from on-orbit collisions and improve predictions of where and when uncontrolled satellite re-entries could occur.

More information:

Phobos-Soil mission: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=122

Inter-Agency Space Debris Coordination Committee (IADC): http://www.iadc-online.org/

Roscosmos: http://www.roscosmos.ru/main.php?lang=en

NPO Lavochkin: http://www.laspace.ru/rus/index.php

Space Debris: http://www.esa.int/SPECIALS/Space_Debris/index.html

Space Situational Awareness: http://www.esa.int/SPECIALS/SSA/index.html

Images, Text, Credits: ESA / P. Shlyaev / J. Mai / Lavochkin Association.

Greetings, Orbiter.ch

mercredi 11 janvier 2012

Rare Ultra-blue Stars Found in Neighboring Galaxy's Hub












ESA - Hubble Space Telescope logo.

Jan. 11, 2012

Peering deep inside the hub of the neighboring Andromeda galaxy, NASA's Hubble Space Telescope has uncovered a large, rare population of hot, bright stars.


The image at left shows the nearby, majestic Andromeda galaxy. The rectangular box marks the region probed by NASA’s Hubble Space Telescope (a blend of visible and ultraviolet light). The photo (top right) is 7,900 light-years across and reveals the galaxy's crowded central region. The bright area near the center of the image is a grouping of stars nestled around the galaxy's black hole. The blue dots sprinkled throughout the image are ultra-blue stars whose population increases around the crowded hub. The square box shows a close-up view of an area around the core. The detailed image, shown at bottom right, reveals a richer population of blue stars huddled around the core. Dark dust clouds also are visible. The right-hand images, taken with Hubble, are part of a census of stars in M31 called the Panchromatic Hubble Andromeda Treasury survey. (Credit: NASA; ESA; B. Williams and J. Dalcanton, University of Washington, Seattle).

Blue is typically an indicator of hot, young stars. In this case, however, the stellar oddities are aging, sun-like stars that have prematurely cast off their outer layers of material, exposing their extremely blue-hot cores.

Astronomers were surprised when they spotted these stars because physical models show that only an unusual type of old star can be as hot and as bright in ultraviolet light.

While Hubble has spied these ultra-blue stars before in Andromeda, the new observation covers a much broader area, revealing that these stellar misfits are scattered throughout the galaxy's bustling center. Astronomers used Hubble's Wide Field Camera 3 to find roughly 8,000 of the ultra-blue stars in a stellar census made in ultraviolet light, which traces the glow of the hottest stars. The study is part of the multi-year Panchromatic Hubble Andromeda Treasury survey to map stellar populations across the galaxy.

"We were not looking for these stars. They stood out because they were bright in ultraviolet light and very different from the stars we expected to see," said Julianne Dalcanton of the University of Washington in Seattle, leader of the Hubble survey.

The team's results are being presented today at the American Astronomical Society meeting in Austin, Texas. A paper describing the finding will be published in The Astrophysical Journal.

The telescope spied the stars within 2,600 light-years of the core. After analyzing the stars for nearly a year, Dalcanton's team determined that they were well past their prime. "The stars are dimmer and have a range of surface temperatures different from the extremely bright stars we see in the star-forming regions of Andromeda," said Phil Rosenfield of the University of Washington, the paper's lead author.

As these stars evolved, puffing up to become red giants, they ejected most of their outer layers to expose their blue-hot cores. When normal sun-like stars swell up to become red giants, they lose much less material and therefore never look as bright in the ultraviolet.

"We caught these stars when they're the brightest, just before they become white dwarfs," said team member Leo Girardi of the National Institute for Astrophysics's Astronomical Observatory of Padua. "It is likely that there are many other similarly hot stars in this central part of Andromeda at earlier stages of their lives. But such stars are too dim for Hubble to see because they're mixed in with a crowd of normal stars."

The astronomers have proposed two possible scenarios to explain why these blue stars evolve differently. According to Rosenfield, the most likely scenario is that the stars are rich in chemical elements other than hydrogen and helium. Observations with ground-based telescopes have shown the stars in the galaxy's hub have an abundant supply of "heavy elements," which makes it easier for stars to eject lots of material into space late in life.

video
Andromeda Galaxy's Double Nucleus

This zoom (video) dives deep into the nucleus of the neighboring spiral galaxy M31, also known as the Andromeda galaxy.

In this scenario radiation from the star is more efficient at pushing on gas laced with heavy elements, which drives away the material, like wind moving a thick sail. Although all the stars in the core are enriched in heavy elements, the bright blue stars may contain especially high amounts, which help trigger the mass loss.

The study also shows that the number of blue stars decreases with distance from the core, tracing the drop in the amount of heavy elements.

Another possible explanation is that the blue stars are in close binary systems and have lost mass to their partners. This mass loss would expose the stars' hot cores. The astronomers were surprised to find that the ultra-blue stars are distributed in the galaxy in the same way as a population of binary stars with similar masses that were found in X-ray observations by NASA's Chandra X-ray Observatory.

The astronomers' next step is to create simulations of these stars to try to determine which scenario is the one that leads them on a different evolutionary path.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For images and more information about this study, visit: http://hubblesite.org/news/2012/03

NASA Hubble website: http://hubblesite.org/

ESA Hubble website: http://www.spacetelescope.org/

Image (mentioned), Video, Text, Credits: NASA / ESA.

Cheers, Orbiter.ch

Herschel and Spitzer See Nearby Galaxies' Stardust














ESA - HERSCHEL Mission logo / NASA - Spitzer Space Telescope patch.

Jan. 11, 2012


This new image shows the Large Magellanic Cloud galaxy in infrared light as seen by the Herschel Space Observatory, a European Space Agency-led mission with important NASA contributions, and NASA's Spitzer Space Telescope. Image credit: ESA / NASA / JPL-Caltech / STScI.

The cold dust that builds blazing stars is revealed in new images that combine observations from the Herschel Space Observatory, a European Space Agency-led mission with important NASA contributions; and NASA's Spitzer Space Telescope. The new images map the dust in the galaxies known as the Large and Small Magellanic Clouds, two of the closest neighbors to our own Milky Way galaxy.

The new images are available at the following links:
http://www.nasa.gov/mission_pages/herschel/multimedia/pia15254.html
http://www.nasa.gov/mission_pages/herschel/multimedia/pia15255.html

The Large Magellanic Cloud looks like a fiery, circular explosion in the combined Herschel-Spitzer infrared data. Ribbons of dust ripple through the galaxy, with significant fields of star formation noticeable in the center, center-left and top right (the brightest center-left region is called 30 Doradus, or the Tarantula Nebula, for its appearance in visible light). The Small Magellanic Cloud has a much more irregular shape. A stream of dust extends to the left in this image, known as the galaxy's "wing," and a bar of star formation appears on the right.

The colors in these images indicate temperatures in the dust that permeate the Magellanic Clouds. Colder regions show where star formation is at its earliest stages or is shut off, while warm expanses point to new stars heating dust surrounding them. The coolest areas and objects appear in red, corresponding to infrared light taken up by Herschel's Spectral and Photometric Imaging Receiver at 250 microns, or millionths of a meter. Herschel's Photodetector Array Camera and Spectrometer fills out the mid-temperature bands, shown in green, at 100 and 160 microns. The warmest spots appear in blue, courtesy of 24- and 70-micron data from Spitzer.

"Studying these galaxies offers us the best opportunity to study star formation outside of the Milky Way," said Margaret Meixner, an astronomer at the Space Telescope Science Institute, Baltimore, Md., and principal investigator for the mapping project. "Star formation affects the evolution of galaxies, so we hope understanding the story of these stars will answer questions about galactic life cycles."


This new image shows the Small Magellanic Cloud galaxy in infrared light from the Herschel Space Observatory a European Space Agency-led mission with important NASA contributions, and NASA's Spitzer Space Telescope. Image credit: ESA / NASA / JPL-Caltech / STScI.

The Large and Small Magellanic Clouds are the two biggest satellite galaxies of our home galaxy, the Milky Way, though they are still considered dwarf galaxies compared to the big spiral of the Milky Way. Dwarf galaxies also contain fewer metals, or elements heavier than hydrogen and helium. Such an environment is thought to slow the growth of stars. Star formation in the universe peaked around 10 billion years ago, even though galaxies contained lesser abundances of metallic dust. Previously, astronomers only had a general sense of the rate of star formation in the Magellanic Clouds, but the new images enable them to study the process in more detail.

The results were presented today at the 219th meeting of the American Astronomical Society in Austin, Texas.

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States' astronomical community.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA.

For more information about Herschel, visit http://www.herschel.caltech.edu, http://www.esa.int/SPECIALS/Herschel/index.html

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

Images (mentioned), Text, Credit: NASA / Trent Perrotto / ESA / JPL / Whitney Clavin.

Best regards, Orbiter.ch

Stars Pop Onto the Scene in New WISE Image







NASA - WISE logo.

Jan. 11, 2012

 (Click on the image for enlarge)

This enormous section of the Milky Way galaxy is a mosaic of images from NASA's Wide-field Infrared Survey Explorer, or WISE. Image credit: NASA / JPL-Caltech / UCLA.

A new, large mosaic from NASA's Wide-Field Infrared Survey Explorer (WISE) showcases a vast stretch of cosmic clouds bubbling with new star birth. The region -- a 1,000-square-degree chunk of our Milky Way galaxy -- is home to numerous star-forming clouds, where massive stars have blown out bubbles in the gas and dust.

"Massive stars sweep up and destroy their natal clouds, but they continuously spark new stars to form along the way," said WISE Mission Scientist Dave Leisawitz of NASA Goddard Space Flight Center, Greenbelt, Md. Leisawitz is co-author of a new paper reporting the results in the Astrophysical Journal. "Occasionally a new, massive star forms, perpetuating the sequence of events and giving rise to the dazzling fireworks display seen in this WISE mosaic."

The new image is online at: http://www.nasa.gov/mission_pages/WISE/multimedia/pia15256.html .

The WISE space telescope mapped the entire sky two times in infrared light, completing its survey in February of 2011. Astronomers studying how stars form took advantage of WISE's all-encompassing view by studying several star-forming clouds, or nebulae, including 10 pictured in this new view.

The observations provide new evidence for a process called triggered star formation, in which the winds and sizzling radiation from massive stars compress gas and dust, inducing a second generation of stars. The same winds and radiation carve out the cavities, or bubbles, seen throughout the image.

Finding evidence for triggered star formation has proved more difficult than some might think. Astronomers are not able to watch the stars grow and evolve like biologists watching zebras in the wild. Instead, they piece together a history of star formation by looking at distinct stages in the process. It's the equivalent of observing only baby, middle-aged and elderly zebras with crude indicators of their ages. WISE is helping to fill in these gaps by providing more and more "specimens" for study.

"Each region we looked at gave us a single snapshot of star formation in progress," said Xavier Koenig, lead author of the new study at Goddard, who presented the results today in Austin, Texas, at the 219th meeting of the American Astronomical Society. "But when we look at a whole collection of regions, we can piece together the chain of events."

After looking at several of the star-forming nebulae, Koenig and his colleagues noticed a pattern in the spatial arrangement of newborn stars. Some were found lining the blown-out cavities, a phenomenon that had been seen before, but other new stars were seen sprinkled throughout the cavity interiors. The results suggest that stars are born in a successive fashion, one after the other, starting from a core cluster of massive stars and moving steadily outward. This lends support to the triggered star formation theory, and offers new clues about the physics of the process.

The astronomers also found evidence that the bubbles seen in the star-forming clouds can spawn new bubbles. In this scenario, a massive star blasts away surrounding material, eventually triggering the birth of another star massive enough to carve out its own bubble. A few examples of what may be first- and second-generation bubbles can be seen in the new WISE image.

"I can almost hear the stars pop and crackle," said Leisawitz.

The complete WISE catalogue will be released to the public astronomy community in the spring of 2012.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages, and operated WISE for NASA's Science Mission Directorate. The spacecraft was put into hibernation mode after it scanned the entire sky twice, completing its main objectives. Edward Wright is the principal investigator and is at UCLA. The mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information is online at http://www.nasa.gov/wise, http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise

Image (mentioned), Text, Credit: NASA / Trent J. Perrotto / JPL / Whitney Clavin.

Greetings, Orbiter.ch

Hubble Breaks New Ground with Discovery of Distant Exploding Star












NASA - Hubble Space Telescope patch.

Jan. 11, 2012

NASA's Hubble Space Telescope has looked deep into the distant universe and detected the feeble glow of a star that exploded more than 9 billion years ago. The sighting is the first finding of an ambitious survey that will help astronomers place better constraints on the nature of dark energy, the mysterious repulsive force that is causing the universe to fly apart ever faster.


These three images taken by NASA's Hubble Space Telescope reveal the emergence of an exploding star, called a supernova. Nicknamed SN Primo, the exploding star belongs to a special class called Type Ia supernovae, which are distance markers used for studying dark energy and the expansion rate of the universe. The top image shows part of the Hubble Ultra Deep Field, the region where astronomers were looking for a supernova blast. The white box shows where the supernova is later seen. The bottom left image is a close-up of the field without the supernova. A new bright object, identified as the supernova, appears in the image at bottom right. Credit: NASA, ESA, A. Riess (Space Telescope Science Institute and The Johns Hopkins University), and S. Rodney (The Johns Hopkins University).

"For decades, astronomers have harnessed the power of Hubble to unravel the mysteries of the universe," said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. "This new observation builds upon the revolutionary research using Hubble that won astronomers the 2011 Nobel Prize in Physics, while bringing us a step closer to understanding the nature of dark energy which drives the cosmic acceleration." As an astronaut, Grunsfeld visited Hubble three times, performing a total of eight spacewalks to service and upgrade the observatory.

The stellar explosion, nicknamed SN Primo, belongs to a special class called Type Ia supernovae, which are bright beacons used as distance markers for studying the expansion rate of the universe. Type Ia supernovae likely arise when white dwarf stars, the burned-out cores of normal stars, siphon too much material from their companion stars and explode.

SN Primo is the farthest Type Ia supernova with its distance confirmed through spectroscopic observations. In these types of observations, a spectrum splits the light from a supernova into its constituent colors. By analyzing those colors, astronomers can confirm its distance by measuring how much the supernova's light has been stretched, or red-shifted, into near-infrared wavelengths because of the expansion of the universe.

The supernova was discovered as part of a three-year Hubble program to survey faraway Type Ia supernovae, opening a new distance realm for searching for this special class of stellar explosion. The remote supernovae will help astronomers determine whether the exploding stars remain dependable cosmic yardsticks across vast distances of space in an epoch when the cosmos was only one-third its current age of 13.7 billion years.

Called the CANDELS+CLASH Supernova Project, the census uses the sharpness and versatility of Hubble's Wide Field Camera 3 (WFC3) to assist astronomers in the search for supernovae in near-infrared light and verify their distance with spectroscopy. CANDELS is the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and CLASH is the Cluster Lensing and Supernova Survey.

"In our search for supernovae, we had gone as far as we could go in optical light," said Adam Riess, the project's lead investigator, at the Space Telescope Science Institute and The Johns Hopkins University in Baltimore, Md. "But it's only the beginning of what we can do in infrared light. This discovery demonstrates that we can use the Wide Field Camera 3 to search for supernovae in the distant universe."

The new results were presented on Jan. 11 at the American Astronomical Society meeting in Austin, Texas.

The supernova team's search technique involved taking multiple near-infrared images over several months, looking for a supernova's faint glow. After the team spotted the stellar blast in October 2010, they used WFC3's spectrometer to verify SN Primo's distance and to decode its light, finding the unique signature of a Type Ia supernova. The team then re-imaged SN Primo periodically for eight months, measuring the slow dimming of its light.

By taking the census, the astronomers hope to determine the frequency of Type Ia supernovae during the early universe and glean insights into the mechanisms that detonated them.

"If we look into the early universe and measure a drop in the number of supernovae, then it could be that it takes a long time to make a Type Ia supernova," said team member Steve Rodney of The Johns Hopkins University. "Like corn kernels in a pan waiting for the oil to heat up, the stars haven't had enough time at that epoch to evolve to the point of explosion. However, if supernovae form very quickly, like microwave popcorn, then they will be immediately visible, and we'll find many of them, even when the universe was very young. Each supernova is unique, so it's possible that there are multiple ways to make a supernova."

If astronomers discover that Type Ia supernovae begin to depart from how they expect them to look, they might be able to gauge those changes and make the measurements of dark energy more precise. Riess and two other astronomers shared the 2011 Nobel Prize in Physics for discovering dark energy 13 years ago, using Type Ia supernova to plot the universe's expansion rate.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For images and more information about Hubble, visit: http://www.nasa.gov/hubble"

NASA Hubble website: http://hubblesite.org/

ESA Hubble website: http://www.spacetelescope.org/

Images (mentioned), Text, Credit: NASA / Space Telescope Science Institute / Donna Weaver / Ray Villard.

Greetings, Orbiter.ch

Planet Population is Plentiful












ESO - European Southern Observatory logo.

11 January 2012

Planets around stars are the rule rather than the exception

Planets everywhere

An international team, including three astronomers from the European Southern Observatory (ESO), has used the technique of gravitational microlensing to measure how common planets are in the Milky Way. After a six-year search that surveyed millions of stars, the team concludes that planets around stars are the rule rather than the exception. The results will appear in the journal Nature on 12 January 2012.

Over the past 16 years, astronomers have detected more than 700 confirmed exoplanets [1] and have started to probe the spectra (eso1002) and atmospheres (eso1047) of these worlds. While studying the properties of individual exoplanets is undeniably valuable, a much more basic question remains: how commonplace are planets in the Milky Way?

The Milky Way over the 1.54-metre Danish Telescope at La Silla

Most currently known exoplanets were found either by detecting the effect of the gravitational pull of the planet on its host star or by catching the planet as it passes in front of its star and slightly dims it. Both of these techniques are much more sensitive to planets that are either massive or close to their stars, or both, and many planets will be missed.

An international team of astronomers has searched for exoplanets using a totally different method — gravitational microlensing — that can detect planets over a wide range of mass and those that lie much further from their stars.

Arnaud Cassan (Institut dʼAstrophysique de Paris), lead author of the Nature paper, explains: "We have searched for evidence for exoplanets in six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our galaxy. We also found that lighter planets, such as super-Earths or cool Neptunes, must be more common than heavier ones."

The astronomers used observations, supplied by the PLANET [2] and OGLE [3] teams, in which exoplanets are detected by the way that the gravitational field of their host stars, combined with that of possible planets, acts like a lens, magnifying the light of a background star. If the star that acts as a lens has a planet in orbit around it, the planet can make a detectable contribution to the brightening effect on the background star.

video
Planets everywhere

Jean-Philippe Beaulieu (Institut d'Astrophysique de Paris), leader of the PLANET collaboration adds: "The PLANET collaboration was established to follow up promising microlensing events with a round-the-world network of telescopes located in the southern hemisphere, from Australia and South Africa to Chile. ESO telescopes contributed greatly to these surveys.”

Microlensing is a very powerful tool, with the potential to detect exoplanets that could never be found any other way. But a very rare chance alignment of a background and lensing star is required for a microlensing event to be seen at all. And, to spot a planet during an event, an additional chance alignment of the planet’s orbit is also needed.

Although for these reasons finding a planet by microlensing is far from an easy task, in the six year's worth of microlensing data used in the analysis, three exoplanets were actually detected in the PLANET and OGLE searches: a super-Earth [4], and planets with masses comparable to Neptune and Jupiter. By microlensing standards, this is an impressive haul. In detecting three planets, either the astronomers were incredibly lucky and had hit the jackpot despite huge odds against them, or planets are so abundant in the Milky Way that it was almost inevitable [5].

The astronomers then combined information about the three positive exoplanet detections with seven additional detections from earlier work, as well as the huge numbers of non-detections in the six year's worth of data — non-detections are just as important for the statistical analysis and are much more numerous. The conclusion was that one in six of the stars studied hosts a planet of similar mass to Jupiter, half have Neptune-mass planets and two thirds have super-Earths. The survey was sensitive to planets between 75 million kilometres and 1.5 billion kilometres from their stars (in the Solar System this range would include all the planets from Venus to Saturn) and with masses ranging from five times the Earth up to ten times Jupiter.

Combining the results suggests strongly that the average number of planets around a star is greater than one. They are the rule rather than the exception.

“We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way,” concludes Daniel Kubas, co-lead author of the paper.

Notes:

[1] The Kepler mission is discovering huge numbers of “candidate exoplanets” that are not included in this number.

[2] Probing Lensing Anomalies NETwork. More than half of the data from the PLANET survey used in this study come from the Danish 1.54-metre telescope at ESO's La Silla Observatory.

[3] Optical Gravitational Lensing Experiment.

[4] A super-Earth has a mass between two and ten times that of the Earth. So far 12 microlensing planets have been published in total, using various observational strategies.

[5] The astronomers surveyed millions of stars looking for microlensing events. Only 3247 such events in 2002-2007 were spotted as the precise alignment needed is very unlikely. Statistical results were inferred from detections and non-detections on a representative subset of 440 light curves.

More information:

This research was presented in a paper, “One or more bound planets per Milky Way star from microlensing observations”, by A. Cassan et al., to appear in the 12 January issue of the journal Nature.

The team is composed of A. Cassan (Institut dʼAstrophysique de Paris, France [IAP]; ESO), D. Kubas (IAP), J.-P. Beaulieu (IAP), M. Dominik (University of St Andrews, United Kingdom), K. Horne (University of St Andrews), J. Greenhill (University of Tasmania, Australia), J. Wambsganss (Heidelberg University, Germany), J. Menzies (South African Astronomical Observatory), A. Williams (Perth Observatory, Australia), U. G. Jørgensen (Niels Bohr Institute, Copenhagen, Denmark), A. Udalski (Warsaw University Observatory, Poland), M. D. Albrow (University of Canterbury, New Zealand), D. P. Bennett (University of Notre Dame, Notre Dame, USA), V. Batista (IAP), S. Brillant (ESO), J. A. R. Caldwell (McDonald Observatory, Fort Davis, USA), A. Cole (University of Tasmania), Ch. Coutures (IAP), K. Cook (Lawrence Livermore National Laboratory, USA), S. Dieters (University of Tasmania), D. Dominis Prester (University of Rijeka, Croatia), J. Donatowicz (Technical University of Vienna, Austria), P. Fouqué (Université de Toulouse, France), K. Hill (University of Tasmania), N. Kains (ESO), S. Kane (NASA Exoplanet Science Institute, Caltech, USA),  J.-B. Marquette (IAP), K. R. Pollard (University of Canterbury, New Zealand), K. C. Sahu (STScI, Baltimore, USA), C. Vinter (Niels Bohr Institute), D. Warren (University of Tasmania), B. Watson (University of Tasmania), M. Zub (Heidelberg University), T. Sumi (Nagoya University, Japan), M. K. Szymański (Warsaw University Observatory), M. Kubiak (Warsaw University Observatory), R. Poleski (Warsaw University Observatory), I. Soszynski (Warsaw University Observatory), K. Ulaczyk (Warsaw University Observatory), G. Pietrzyński (Warsaw University Observatory), Ł. Wyrzykowski (Warsaw University Observatory).

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

    Research paper in Nature: http://www.eso.org/public/archives/releases/sciencepapers/eso1204/eso1204.pdf

ESO: http://www.eso.org/public/

Images, Video, Text, Credit: ESO / M. Kornmesser / Z. Bardon (www.bardon.cz) / ProjectSoft (www.projectsoft.cz).

Best regards, Orbiter.ch

NASA's Kepler Mission Finds Three Smallest Exoplanets












NASA - Kepler Mission patch.

Jan. 11, 2012

Astronomers using data from NASA's Kepler mission have discovered the three smallest planets yet detected orbiting a star beyond our sun. The planets orbit a single star, called KOI-961, and are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars.

All three planets are thought to be rocky like Earth, but orbit close to their star. That makes them too hot to be in the habitable zone, which is the region where liquid water could exist. Of the more than 700 planets confirmed to orbit other stars -- called exoplanets -- only a handful are known to be rocky.


Mini Planetary System: This artist's conception illustrates KOI-961. Image credit: NASA / JPL-Caltech.

"Astronomers are just beginning to confirm thousands of planet candidates uncovered by Kepler so far," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us."

Kepler searches for planets by continuously monitoring more than 150,000 stars, looking for telltale dips in their brightness caused by crossing, or transiting, planets. At least three transits are required to verify a signal as a planet. Follow-up observations from ground-based telescopes also are needed to confirm the discoveries.


Sizing Up Exoplanets: This chart compares artists' concepts of the smallest known exoplanets, or planets orbiting outside the solar system, to our own planets Mars and Earth. Image credit: NASA / JPL-Caltech.

The latest discovery comes from a team led by astronomers at the California Institute of Technology in Pasadena. The team used data publicly released by the Kepler mission, along with follow-up observations from the Palomar Observatory, near San Diego, and the W.M. Keck Observatory atop Mauna Kea in Hawaii. Their measurements dramatically revised the sizes of the planets from what originally was estimated.

The three planets are very close to their star, taking less than two days to orbit around it. The KOI-961 star is a red dwarf with a diameter one-sixth that of our sun, making it just 70 percent bigger than Jupiter.


'Honey I Shrunk the Planetary System': This artist's concept compares the KOI-961 planetary system to Jupiter and the largest four of its many moons. Image credit: NASA / JPL-Caltech.

"This is the tiniest solar system found so far," said John Johnson, the principal investigator of the research from NASA's Exoplanet Science Institute at the California Institute of Technology in Pasadena. "It's actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy."

Red dwarfs are the most common kind of star in our Milky Way galaxy. The discovery of three rocky planets around one red dwarf suggests that the galaxy could be teeming with similar rocky planets.

"These types of systems could be ubiquitous in the universe," said Phil Muirhead, lead author of the new study from Caltech. "This is a really exciting time for planet hunters."

The discovery follows a string of recent milestones for the Kepler mission. In December 2011, scientists announced the mission's first confirmed planet in the habitable zone of a sun-like star: a planet 2.4 times the size of Earth called Kepler-22b. Later in the month, the team announced the discovery of the first Earth-size planets orbiting a sun-like star outside our solar system, called Kepler-20e and Kepler-20f.

For the latest discovery, the team obtained the sizes of the three planets called KOI-961.01, KOI-961.02 and KOI-961.03 with the help of a well-studied twin star to KOI-961, or Barnard's Star. By better understanding the KOI-961 star, they then could determine how big the planets must be to have caused the observed dips in starlight. In addition to the Kepler observations and ground-based telescope measurements, the team used modeling techniques to confirm the planet discoveries.

Prior to these confirmed planets, only six other planets had been confirmed using the Kepler public data.

NASA's Ames Research Center in Moffett Field, Calif., manages Kepler's ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.

For information about the Kepler Mission, visit: http://www.nasa.gov/kepler

Images (mentioned), Text, Credit: NASA Ames Research Center / Michele Johnson.

Greetings, Orbiter.ch

Hubble Solves Mystery on Source of Supernova in Nearby Galaxy











NASA - Hubble Space Telescope patch.

Jan. 11, 2012

Using NASA's Hubble Space Telescope, astronomers have solved a longstanding mystery on the type of star, or so-called progenitor, which caused a supernova seen in a nearby galaxy. The finding yields new observational data for pinpointing one of several scenarios that trigger such outbursts.


This image of Type Ia Supernova Remnant 0509-67.5 was made by combining data from two of NASA’s Great Observatories. The result shows soft green and blue hues of heated material from the X-ray data surrounded by the glowing pink optical shell, which shows the ambient gas being shocked by the expanding blast wave from the supernova. Credit: NASA, ESA, and B. Schaefer and A. Pagnotta (Louisiana State University, Baton Rouge); Image Credit: NASA, ESA, CXC, SAO, the Hubble Heritage Team (STScI/AURA), J. Hughes (Rutgers University).

Based on previous observations from ground-based telescopes, astronomers knew the supernova class, called a Type Ia, created a remnant named SNR 0509-67.5, which lies 170,000 light-years away in the Large Magellanic Cloud galaxy.

Theoretically, this kind of supernova explosion is caused by a star spilling material onto a white dwarf companion, the compact remnant of a normal star, until it sets off one of the most powerful explosions in the universe.

Astronomers failed to find any remnant of the companion star, however, and concluded that the common scenario did not apply in this case, although it is still a viable theory for other Type Ia supernovae.

"We know Hubble has the sensitivity necessary to detect the faintest white dwarf remnants that could have caused such explosions," said lead investigator Bradley Schaefer of Louisiana State University (LSU) in Baton Rouge. "The logic here is the same as the famous quote from Sherlock Holmes: 'when you have eliminated the impossible, whatever remains, however improbable, must be the truth.'"

The cause of SNR 0509-67.5 can be explained best by two tightly orbiting white dwarf stars spiraling closer and closer until they collided and exploded.

For four decades, the search for Type Ia supernovae progenitors has been a key question in astrophysics. The problem has taken on special importance during the last decade with Type Ia supernovae being the premier tools for measuring the accelerating universe.

Type Ia supernovae release tremendous energy, in which the light produced is often brighter than an entire galaxy of stars. The problem has been to identify the type of star system that pushes the white dwarf's mass over the edge and triggers this type of explosion. Many possibilities have been suggested, but most require that a companion star near the exploding white dwarf be left behind after the explosion.

Therefore, a possible way to distinguish between the various progenitor models has been to look deep in the center of an old supernova remnant to search for the ex-companion star.

In 2010, Schaefer and Ashley Pagnotta of LSU were preparing a proposal to look for any faint ex-companion stars in the center of four supernova remnants in the Large Magellanic Cloud when they discovered the Hubble Space Telescope already had taken the desired image of one of their target remnants, SNR 0509-67.5, for the Hubble Heritage program, which collects images of especially photogenic astronomical targets.

In analyzing the central region, they found it to be completely empty of stars down to the limit of the faintest objects Hubble can detect in the photos. Schaefer suggests the best explanation left is the so-called "double degenerate model" in which two white dwarfs collide.

The results are being reported today at the meeting of the American Astronomical Society in Austin, Texas. A paper on the results will be published in the Jan. 12 issue of the journal Nature.

There are no recorded observations of the star exploding. However, researchers at the Space Telescope Science Institute in Baltimore, Md. have identified light from the supernova that was reflected off of interstellar dust, delaying its arrival at Earth by 400 years. This delay, called a light echo of the supernova explosion also allowed the astronomers to measure the spectral signature of the light from the explosion. By virtue of the color signature, astronomers were able to deduce it was a Type Ia supernova.

Because the remnant appears as a nice symmetric shell or bubble, the geometric center can be determined accurately. These properties make SNR 0509-67.5 an ideal target to search for ex-companions. The young age also means that any surviving stars have not moved far from the site of the explosion.

The team plans to look at other supernova remnants in the Large Magellenic Cloud to further test their observations.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.


NASA Hubble website: http://hubblesite.org/

ESA Hubble website: http://www.spacetelescope.org/

Image (mentioned), Text, Credit: NASA / Space Telescope Science Institute / Ray Villard / Donna Weaver.

Cheers, Orbiter.ch

mardi 10 janvier 2012

China Launches Ziyuan 3 Geological Mapping Satellite










CNSA - China National Space Administration logo.

Jan. 10, 2012

The Long March 4B launcher lifted off at 0317 GMT Monday (10:17 p.m. EST Sunday) from the Taiyuan space center in Shanxi province, according to the state-run Xinhua news agency. It was 11:17 a.m. Beijing time.

China successfully launched Ziyuan 3, its first high-resolution geological mapping satellite for civil purposes, Jan. 9 from the Taiyuan Satellite Launch Center in northern Shanxi Province, the state-run Xinhua News Agency reported.


Image above: China successfully launched the Ziyuan III satellite Monday from the Taiyuan Satellite Launch Center in northern Shanxi province. (Xinhua Photo).

The satellite was lofted aboard a Long March 4B rocket that also carried a satellite from Luxembourg, Xinhua said. It previously reported that Ziyuan 3 will “conduct surveys on land resources, help with natural disaster-reduction and prevention and lend assistance to farming, water conservation, urban planning and other sectors.”

The satellite, a high-resolution remote-sensing satellite for civilian use, was launched at 11:17 a.m. aboard a Long March 4B rocket, according to a statement from the center.


Image above: On January 9, 2012, China's civil satellite Ziyuan 3 launched from the Taiyuan Satellite Launch Center. Credit: Ministry of National Defense of the People's Republic of China.

The satellite, weighing 2650 kg, entered an orbit of 500 km above the Earth about 12 minutes after it was launched. It has a designed life expectancy of five years.

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Long March 4B rocket carrying Ziyuan 3

According to the center, the satellite is tasked with offering services to aid the country's land-resources surveys, natural-disaster prevention, agriculture development, water-resources management, and urban planning. The rocket also carried a satellite from Luxemburg, according to the launch center.

The orbiter was developed and produced by the China Academy of Space Technology, a subsidiary of China Aerospace Science and Technology Corporation (CASC).

The Long March 4B rocket is developed by Shanghai Academy of Spaceflight Technology, another CASC subsidiary. Monday's mission marked the 156th flight of China's Long March series of carrier rockets.

For more information about CNSA, visit: http://www.cnsa.gov.cn/n615709/cindex.html

Images, Video, Text, Credits: CNSA / CASC / Xinhua / Ministry of National Defense of the People's Republic of China / CNTV / News.cn / Orbiter.ch.

Best regards, Orbiter.ch

NASA's Fermi Space Telescope Explores New Energy Extremes











NASA - Fermi Gamma-ray Space Telescope logo.

Jan. 10, 2012

After more than three years in space, NASA's Fermi Gamma-ray Space Telescope is extending its view of the high-energy sky into a largely unexplored electromagnetic range. Today, the Fermi team announced its first census of energy sources in this new realm.


Images above: New sources emerge and old sources fade as the LAT's view extends into higher energies. Credit: NASA / DOE / Fermi LAT Collaboration and A. Neronov et al.

Fermi's Large Area Telescope (LAT) scans the entire sky every three hours, continually deepening its portrait of the sky in gamma rays, the most energetic form of light. While the energy of visible light falls between about 2 and 3 electron volts, the LAT detects gamma rays with energies ranging from 20 million to more than 300 billion electron volts (GeV).

At higher energies, gamma rays are rare. Above 10 GeV, even Fermi's LAT detects only one gamma ray every four months.

"Before Fermi, we knew of only four discrete sources above 10 GeV, all of them pulsars," said David Thompson, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "With the LAT, we've found hundreds, and we're showing for the first time just how diverse the sky is at these high energies."

Any object producing gamma rays at these energies is undergoing extraordinary astrophysical processes. More than half of the 496 sources in the new census are active galaxies, where matter falling into a supermassive black hole powers jets that spray out particles at nearly the speed of light.


Image above: Fermi's view of the gamma-ray sky continually improves. This image of the entire sky includes three years of observations by Fermi's Large Area Telescope (LAT). It shows how the sky appears at energies greater than 1 billion electron volts (1 GeV). Brighter colors indicate brighter gamma-ray sources. A diffuse glow fills the sky and is brightest along the plane of our galaxy (middle). Discrete gamma-ray sources include pulsars and supernova remnants within our galaxy as well as distant galaxies powered by supermassive black holes. Credit: NASA / DOE / Fermi LAT Collaboration.

Only about 10 percent of the known sources lie within our own galaxy. They include rapidly rotating neutron stars called pulsars, the expanding debris from supernova explosions, and in a few cases, binary systems containing massive stars.

More than a third of the sources are completely unknown, having no identified counterpart detected in other parts of the spectrum. With the new catalog, astronomers will be able to compare the behavior of different sources across a wider span of gamma-ray energies for the first time.

Just as bright infrared sources may fade to invisibility in the ultraviolet, some of the gamma-ray sources above 1 GeV vanish completely when viewed at higher, or "harder," energies.

One example is the well-known radio galaxy NGC 1275, which is a bright, isolated source below 10 GeV. At higher energies it fades appreciably and another nearby source begins to appear. Above 100 GeV, NGC 1275 becomes undetectable by Fermi, while the new source, the radio galaxy IC 310, shines brightly.


This all-sky Fermi view includes only sources with energies greater than 10 GeV. From some of these sources, Fermi's LAT detects only one gamma-ray photon every four months. Brighter colors indicate brighter gamma-ray sources. Credit: NASA / DOE / Fermi LAT Collaboration.

The Fermi hard-source list is the product of an international team led by Pascal Fortin at the Ecole Polytechnique's Laboratoire Leprince-Ringuet in Palaiseau, France, and David Paneque at the Max Planck Institute for Physics in Munich.

The catalog serves as an important roadmap for ground-based facilities called Atmospheric Cherenkov Telescopes, which have amassed about 130 gamma-ray sources with energies above 100 GeV. They include the Major Atmospheric Gamma Imaging Cherenkov telescope (MAGIC) on La Palma in the Canary Islands, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia.

"Our catalog will have a significant impact on ground-based facilities' work by pointing them to the most likely places to find gamma-ray sources emitting above 100 GeV," Paneque said.

Compared to Fermi's LAT, these ground-based observatories have much smaller fields of view. They also make fewer observations because they cannot operate during daytime, bad weather or a full moon.


Graphic above: More than half of the sources above 10 GeV are black-hole-powered active galaxies. More than a third of the sources are completely unknown, having no identified counterpart detected in other parts of the spectrum. Credit: NASA's Goddard Space Flight Center.

"As Fermi's exposure constantly improves our view of hard sources, ground-based telescopes are becoming more sensitive to lower-energy gamma rays, allowing us to bridge these two energy regimes," Fortin added.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. Fermi is managed by Goddard. It was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Related Links:

    › For images related to this story: http://www.nasa.gov/fermi

    › Major Atmospheric Gamma Imaging Cherenkov telescope (MAGIC) on La Palma in the Canary Islands: http://magic.mppmu.mpg.de/

    › Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona: http://veritas.sao.arizona.edu/

    › High Energy Stereoscopic System (H.E.S.S.) in Namibia: http://www.mpi-hd.mpg.de/hfm/HESS/

Images (mentioned), Text, Credit: NASA / Trent J. Perrotto.

Greetings, Orbiter.ch

El Gordo — A “Fat” Distant Galaxy Cluster












ESO - European Southern Observatory logo.

10 January 2012


 El Gordo: a massive distant merging galaxy cluster

An extremely hot, massive young galaxy cluster — the largest ever seen in the distant Universe — has been studied by an international team using ESO’s Very Large Telescope (VLT) in the Atacama Desert in Chile along with NASA's Chandra X-ray Observatory and the Atacama Cosmology Telescope. The new results are being announced on 10 January 2012 at the 219th meeting of the American Astronomical Society in Austin, Texas.

The newly discovered galaxy cluster [1] has been nicknamed El Gordo — the "big" or "fat one" in Spanish. It consists of two separate galaxy subclusters colliding at several million kilometres per hour, and is so far away that its light has travelled for seven billion years to reach the Earth.

El Gordo: a massive distant merging galaxy cluster

"This cluster is the most massive, the hottest, and gives off the most X-rays of any cluster found so far at this distance or beyond," said Felipe Menanteau of Rutgers University, who led the study. "We devoted a lot of our observing time to El Gordo, and I'm glad our bet paid off and we found an amazing cluster collision."

Clusters of galaxies are the largest objects in the Universe held together by gravity. The process of their formation, when smaller groups of galaxies merge together, very much depends on the amount of dark matter and dark energy in the Universe at that time — so studying clusters can shed some light on these mysterious components of the cosmos.

video
El Gordo: a massive distant merging galaxy cluster

"Gigantic galaxy clusters like this one are just what we were aiming to find," said team member Jack Hughes, also of Rutgers. "We want to see if we understand how these extreme objects form, using the best models of cosmology that are currently available."

The team, led by Chilean and Rutgers astronomers, found El Gordo by detecting a distortion of the cosmic microwave background radiation. This faint glow is the remnant of the first light from the Big Bang, the extremely hot and dense origin of the Universe about 13.7 billion years ago. This radiation left over from the Big Bang interacts with electrons in the hot gas in galaxy clusters, distorting the appearance of the background glow seen from Earth [2]. The denser and bigger the cluster, the bigger this effect. El Gordo was picked up in a survey of the microwave background with the Atacama Cosmology Telescope [3].

video
El Gordo: a massive distant merging galaxy cluster

ESO’s Very Large Telescope was used by the team to measure the velocities of the galaxies in this huge cluster collision and also to measure its distance from Earth. In addition NASA's Chandra X-ray Observatory was used to study the hot gas in the cluster.

Although a cluster of El Gordo's size and distance is very rare, the authors say that the new results are still consistent with astronomers’ current understanding of a Universe that started with a Big Bang and is mostly made of dark matter and dark energy.

El Gordo most probably formed just like the Bullet Cluster (visit: http://chandra.harvard.edu/photo/2006/1e0657/), a spectacular interacting cluster of galaxies that is almost four billion light-years closer to Earth. In both clusters there is evidence that normal matter, mainly composed of hot, X-ray-bright gas, has been wrenched apart from the dark matter. The hot gas was slowed down by the collision, but the dark matter was not.

"This is the first time we've found a system like the Bullet Cluster at such a large distance," said Cristóbal Sifón, student at the Pontificia Universidad Católica de Chile (PUC) in Santiago. "It's like the old saying: If you want to understand where you're going, you have to know where you've been."

Notes:

[1] The formal name of the cluster is ACT-CL J0102-4915, the first part of the name shows that it is a galaxy cluster found using data from the Atacama Cosmology Telescope and the second part indicates the location of the object on the sky, in the southern constellation of Phoenix.

[2] The effect is called the Sunyaev–Zel'dovich (SZ) effect after the Russian astronomers, Rashid Sunyaev and Yakov Zel'dovich who predicted it in the late 1960s.

[3] The Atacama Cosmology Telescope (ACT) is a six-metre telescope on Cerro Toco in the Atacama Desert in the north of Chile and close to the site of ALMA. It is designed to make high-resolution surveys of the microwave sky to study the cosmic microwave background radiation.

More information:

These results on El Gordo are being announced on 10 January 2012 at the 219th meeting of the American Astronomical Society in Austin, Texas. A paper, “The Atacama Cosmology Telescope: ACT-CL J0102−4915 ‘El Gordo’, A Massive Merging Cluster at Redshift 0.87” by Felipe Menanteau et al, describing these results has been accepted for publication in The Astrophysical Journal.

The team consists of: Felipe Menanteau (Rutgers University, USA), John P. Hughes (Rutgers), Crisóbal Sifón (Pontificia Universidad Católica de Chile [PUC]), Matt Hilton (University of Nottingham, UK), Jorge González (PUC), Leopoldo Infante (PUC), L. Felipe Barrientos (PUC) , Andrew J. Baker (Rutgers) , Sudeep Das (University of California, Berkeley, USA; Princeton University, USA), Mark J. Devlin (University of Pennsylvania, USA), Joanna Dunkley (Oxford University, UK) , Adam D. Hincks (Princeton University), Arthur Kosowsky (University of Pittsburgh, USA) , Danica Mardsen (University of Pennsylvania), Tobias A. Marriage (The Johns Hopkins University, Baltimore, USA) , Kavilan Moodley (University of KwaZulu-Natal, Durban, South Africa), Michael D. Niemack (NIST, Boulder, USA) , Lyman A. Page (Princeton University) , Erik D. Reese (University of Pennsylvania) , Neelima Sehgal (Stanford University, USA), Jon Sievers (University of Toronto, Canada) , David N. Spergel (Princeton University), Suzanne T. Staggs (Princeton University) and Edward Wollack (Goddard Space Flight Center, USA).

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

    Link to preprint of the science paper: http://arxiv.org/abs/1109.0953

    Images of VLT at the Paranal Observatory: http://www.eso.org/public/images/archive/category/paranal/

    Information about NASA’s Chandra observatory: http://www.nasa.gov/chandra

    Further information about the Atacama Cosmology Telescope: http://physics.princeton.edu/act/about.html

Images, Text, Credit: ESO / SOAR / NASA / Videos: Credit: ESO / SOAR / NASA.

Greetings, orbiter.ch