Hunting for the Milky Way's Heaviest Stars

NASA - Chandra X-Ray Observatory logo.

April 14, 2011

Like looking for Easter eggs in a lawn of long grass, the hunt for the Milky Way's most massive stars takes persistence and sharp eyes. In their stellar search through our Galactic backyard, astronomers have used powerful telescopes sensitive to X-ray and infrared radiation to find evidence for a substantial population of X-ray emitting massive stars.

This image shows infrared data from NASA's Spitzer Space Telescope near the plane of the Milky Way galaxy. Both outlined boxes contain an artificially darkened view of the Spitzer data, to highlight a bright X-ray source (blue) detected at the center of each square with NASA's Chandra X-ray Observatory. Each X-ray source coincides with a strong infrared signal.

Analysis of the X-ray and infrared data, as well as optical and radio observations, reveals that these bright sources are, in fact, extremely massive stars. Two other massive stars have also been found near the plane of the Milky Way using similar methods. Deep observations from ESA's XMM-Newton also provided valuable information for these other two objects. All four of these stars are thought to be at least 25 times more massive than the Sun and lie between 7,500 and 18,000 light years from Earth. These stars are expected to last only a few million years and will end their lives with supernova explosions.

Finding these very massive stars is not easy. Dust and gas throughout the Milky Way obscures much of the view from optical telescopes near the plane of the galaxy. Infrared images suffer less obscuration but are extremely crowded with stars. However, these stellar behemoths shine brightly in X-ray light and easily stand out from their neighbors in Chandra images.

Why are these massive stars so bright in X-rays? Some massive stars have winds that blow material away from their surface at over 2 million miles per hour. If this high-speed material collides with the wind from a companion star, it is decelerated so suddenly that acts like it has collided with a Solar System-sized brick wall. The shock waves resulting from this enormous collision generate temperatures up to 100 million degrees, and produce copious amounts of X-rays.

These Chandra observations followed a survey of the plane of our Galaxy by the Advanced Satellite for Cosmology and Astrophysics (ASCA), a previous X-ray mission. This survey detected about 160 X-ray sources, but only a third of them could be definitively identified due to the limited spatial resolution of ASCA. Because Chandra's ability to resolve sources is significantly greater, much more precise positions could be obtained. This has allowed scientists to identify counterparts to the X-ray sources in other wavelengths. There are many other unidentified Galactic X-ray sources with X-ray properties similar to these four sources, so a large population of massive stars may remain to be discovered with future Chandra observations.

These results were published in the February 1st issue of The Astrophysical Journal in a paper led by Gemma Anderson (University of Sydney). Other authors included Bryan Gaensler (University of Sydney), David Kaplan (University of Wisconsin, Milwaukee), Bettina Posselt, Patrick Slane and Stephen Murray (Harvard-Smithsonian Center for Astrophysics, or CfA), Jon Mauerhan (California Institute of Technology), Robert Benjamin (University of Wisconsin, Whitewater), Crystal Brogan (National Radio Astronomy Observatory), Deepto Chakrabarty (Massachusetts Institute of Technology), Jeremy Drake (CfA), Janet Drew (University of Hertfordshire), Jonathan Grindlay and Jaesub Hong (CfA), Joseph Lazio (Naval Research Laboratory), Julia Lee (CfA), Danny Steeghs (University of Warwick), and Marten van Kerkwijk (University of Toronto).

Read more/access larger images: http://chandra.harvard.edu/photo/2011/massive/

Image, Text, Credit: X-ray: NASA / U. of Sydney / G.Anderson et al; IR: NASA / JPL-Caltech.

Greetings, Orbiter.ch

Herschel links star formation to sonic booms

ESA - Herschel Mission patch.

13 April 2011

ESA’s Herschel space observatory has revealed that nearby interstellar clouds contain networks of tangled gaseous filaments. Intriguingly, each filament is approximately the same width, hinting that they may result from interstellar sonic booms throughout our Galaxy.

The filaments are huge, stretching for tens of light years through space and Herschel has shown that newly-born stars are often found in the densest parts of them. One filament imaged by Herschel in the Aquila region contains a cluster of about 100 infant stars.

Dense filaments of gas in IC5146

Such filaments in interstellar clouds have been glimpsed before by other infrared satellites, but they have never been seen clearly enough to have their widths measured. Now, Herschel has shown that, regardless of the length or density of a filament, the width is always roughly the same.

“This is a very big surprise,” says Doris Arzoumanian, Laboratoire AIM Paris-Saclay, CEA/IRFU, the lead author on the paper describing this work. Together with Philippe André from the same institute and other colleagues, she analysed 90 filaments and found they were all about 0.3 light years across, or about 20 000 times the distance of Earth from the Sun. This consistency of the widths demands an explanation.

Comparing the observations with computer models, the astronomers concluded that filaments are probably formed when slow shockwaves dissipate in the interstellar clouds. These shockwaves are mildly supersonic and are a result of the copious amounts of turbulent energy injected into interstellar space by exploding stars. They travel through the dilute sea of gas found in the Galaxy, compressing and sweeping it up into dense filaments as they go.

The Polaris filament network

Interstellar clouds are usually extremely cold, about 10 degrees Kelvin above absolute zero, and this makes the speed of sound in them relatively slow at just 0.2 km/s, as opposed to 0.34 km/s in Earth’s atmosphere at sea-level.

These slow shockwaves are the interstellar equivalent of sonic booms. The team suggests that as the sonic booms travel through the clouds, they lose energy and, where they finally dissipate, they leave these filaments of compressed material.

Herschel telescope mirror at ESTEC

“This is not direct proof, but it is strong evidence for a connection between interstellar turbulence and filaments. It provides a very strong constraint on theories of star formation,” says Dr André.

The team made the connection by studying three nearby clouds, known as IC5146, Aquila, and Polaris, using Herschel’s SPIRE and PACS instruments.

“The connection between these filaments and star formation used to be unclear, but now thanks to Herschel, we can actually see stars forming like beads on strings in some of these filaments,” says Göran Pilbratt, the ESA Herschel Project Scientist.

Related links:

Observations: Seeing in infrared wavelengths: http://www.esa.int/esaSC/SEMS72T1VED_index_0.html

Why infrared astronomy is a hot topic: http://www.esa.int/esaCP/SEMX9PZO4HD_FeatureWeek_0.html

Herschel first science results in depth: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=46985

Herschel in depth: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16

Herschel Science Centre: http://herschel.esac.esa.int/

In depth:

This story in depth: http://sci.esa.int/jump.cfm?oid=48623

Images, Text, Credits: ESA / Herschel / SPIRE/ Ph. André (CEA Saclay) and D. Arzoumanian (CEA Saclay) for the Gould Belt survey Key Programme Consortium and A. Abergel (IAS Orsay) for the Evolution of Interstellar Dust Key Programme Consortium.

Greetings, Orbiter.ch

Nespoli performs hot-swap of faulty valve on Columbus

ESA / DLR - Columbus Science Laboratory Module on ISS patch.

13 April 2011

A joint effort is combining sophisticated engineering analysis on the ground with old-fashioned hands-on work in space after ESA astronaut Paolo Nespoli undertook the complex installation of a replacement water valve in ESA's Columbus science laboratory.

ESA's Columbus module on the International Space Station carries a number of life-support systems, including the Thermal Control System, which cools all the equipment and scientific payloads in the orbiting research module.

ESA astronaut Paolo Nespoli removes the failed valve

The thermal system has multiple valves that control the cold water flowing through pipes. The water pipes run from Columbus to the Station's Node-2, where heat exchangers cool the water using radiators. The cooled water then flows back into Columbus.

What went wrong

In 2010, one of the water valves experienced problems and was inspected several times by Station astronauts to assist engineers with troubleshooting.

Finally, in September last year, the suspect No. 8 Water ON-OFF Valve (WOOV) failed to react to ground commands and stopped working completely.

Columbus seen during spacewalk

"WOOV No. 8 can be commanded remotely by the crew or from ground as well as manually operated by the crew," explained Zoltan Szigetvari, Senior System Engineer for Columbus Thermal and Environmental Control Systems at Astrium.

The valve that failed to operate

"No. 8 failed to operate even after crew intervention and it was decided to replace it by a manifold, which will allow continued nominal operation of Columbus, and download the failed valve for investigation," he added.

The crew also reported traces of an unknown substance seeping out of the valve body and the insulation shell.

Replacement required an in-orbit repair job, and it was decided to return the faulty valve to Earth for detailed analysis.

A thorough troubleshooting plan was mapped out, aiming to identify the root cause of the valve jamming and the nature of the contamination.

A team of engineers perform the first inspection in Bremen

"The contamination could not be explained and was declared toxicity level 2, meaning that the astronauts should not come into contact with it," said Eugenio Gargioli, Engineering Support Manager for Columbus at Thales Alenia Space.

"Once we examine it, and collect samples of the unknown substance for detailed chemical analysis, we can establish a strategy for treating potential failures and provide instructions to the crew for handling the deposits that have been detected at this and also on other, similar, Columbus valves."

As a replacement, Thales Alenia Space made a new manifold, which was launched on Shuttle Discovery on the STS-133 mission on 24 February.

Can we fix it? Yes we can

On 27 February, ESA astronaut Paolo Nespoli rolled up his sleeves to work on what was termed 'major in-flight maintenance' – an hours-long repair job requiring tight coordination between the astronaut in space and engineers at ESA's Columbus Control Centre, near Munich, with continuous voice and video contact.

"The main repair included a procedure of some 80 steps," said Cesare Capararo, of Thales Alenia Space, Lead Increment Flight Director for Columbus and responsible for overseeing the repair.

Columbus Control Centre

"Each step had to be carefully checked before, during and after execution by Paolo and the ground team due to the complexity of performing maintenance on a running system."

Detailed engineering analysis

With the job complete, the faulty valve was packed for return to Earth on the same Shuttle. After arrival at NASA's Kennedy Space Center on 9 March, it was shipped to the Astrium facility in Bremen, Germany, where Columbus was built, for analysis by engineers from Thales Alenia Space, Astrium and ESA.

"We will have the results very soon, which will help to determine the cause," said ESA's Roland Luettgens, Mission Director at Columbus Control Centre.

"Columbus must operate several more years and therefore it's important to know the cause and ensure that we can work together with the crews for this type of complex maintenance."

Columbus laboratory: http://www.esa.int/SPECIALS/Columbus/ESAAYI0VMOC_0.html

ISS On-Orbit Status Report 02-27-2011: http://www.nasa.gov/directorates/somd/reports/iss_reports/2011/02272011_prt.htm

Images, Text, Credits: ESA / NASA / JSC / DLR.

Cheers, Orbiter.ch

Celestial Fireworks from Dying Stars

ESO - European Southern Observatory logo.

13 April 2011

Wide Field Imager view of the star formation region NGC 3582

This image of the nebula NGC 3582, which was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile, shows giant loops of gas bearing a striking resemblance to solar prominences. These loops are thought to have been ejected by dying stars, but new stars are also being born within this stellar nursery. These energetic youngsters emit intense ultraviolet radiation that makes the gas in the nebula glow, producing the fiery display shown here.

NGC 3582 in the constellation of Carina

NGC 3582 is part of a large star-forming region in the Milky Way, called RCW 57. It lies close to the central plane of the Milky Way in the southern constellation of Carina (The Keel of Jason’s ship, the Argo). John Herschel first saw this complex region of glowing gas and dark dust clouds in 1834, during his stay in South Africa.

Wide-field view of the sky around NGC 3582

Some of the stars forming in regions like NGC 3582 are much heavier than the Sun. These monster stars emit energy at prodigious rates and have very short lives that end in explosions as supernovae. The material ejected from these dramatic events creates bubbles in the surrounding gas and dust. This is the probable cause of the loops visible in this picture.

This image was taken through multiple filters. From the Wide Field Imager, data taken through a red filter are shown in green and red, and data taken through a filter that isolates the red glow characteristic of hydrogen are also shown in red. Additional infrared data from the Digitized Sky Survey are shown in blue.

ESO - Zooming in on the star-forming region NGC 3582

 

The image was processed by ESO using the observational data identified by Joe DePasquale, from the United States [1], who participated in ESO’s Hidden Treasures 2010 astrophotography competition [2]. The competition was organised by ESO in October–November 2010, for everyone who enjoys making beautiful images of the night sky using astronomical data obtained using professional telescopes.

Notes:

[1] Joe searched through ESO’s archive and identified datasets that he used to compose his image of NGC 3582, which was the tenth highest ranked entry in the competition, out of almost 100 entries. His original work can be seen here: http://www.flickr.com/photos/45615208@N02/5201711319/

[2] ESO’s Hidden Treasures 2010 competition gave amateur astronomers the opportunity to search through ESO’s vast archives of astronomical data, hoping to find a well-hidden gem that needed polishing by the entrants. To find out more about Hidden Treasures, visit http://www.eso.org/public/outreach/hiddentreasures/.

More information:

ESO, the European Southern Observatory, 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 VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Link:

    * Photos of the La Silla Observatory: http://www.eso.org/public/images/archive/category/lasilla/

Images, Text, Credits: ESO / Digitized Sky Survey 2 and Joe DePasquale, Acknowledgment: Davide De Martin  / IAU and Sky & Telescope / Video: ESO / A. Fujii / Digitized Sky Survey 2. Music: John Dyson (from the album Moonwind).

Best regards, Orbiter.ch

Air France Airbus A380 impounded after JFK airport shunt

Civil Aviation.

12 April 2011

US investigators have impounded an Air France jet which collided with a smaller plane at New York's John F Kennedy airport.

The Airbus A380 superjumbo, the world's largest jetliner, with a wingspan of almost 80 metres, hit the tail of a Comair regional jet, which span a quarter-turn on the taxiway. The incident was caught on amateur video.

A CNN correspondent on the Air France flight to Paris reported that he felt a "slight rumble akin to hitting a patch of rough pavement" as the superjumbo, with 520 people on board, was moving on the ground at about 8.15pm local time on Tuesday.

The correspondent said about a foot of the superjumbo's left wing appeared to be damaged.

Air France confirmed the incident and said both aircraft had been "immobilised" pending an investigation. A spokeswoman declined to estimate the time and cost of repairs to the wing.

Air France Airbus A380

Air France, which flies five times a day to New York including one flight using the Airbus double-decker, will operate its daily A380 flight on Tuesday as normal, she said.

"This collision caused only material damage. The two aircraft have been immobilised and the passengers were given accommodation or placed on [other] flights," she added.

Bombardier CRJ-700 Comair

Amateur video footage posted on Flightglobal.com showed the 70-seat Bombardier CRJ-700 operated by Comair rocking sharply to one side as the A380 wing flipped it into an almost 90-degree turn to the left.

There were no reports of injuries.

Images, Video, Text, Credits: Reuters / Guardian.co.uk / Wikipedia.

Greetings, Orbiter.ch

Mars500 Crewmembers recall what Yuri Gagarin's historic flight is meaning for them

ESA / ROSCOSMOS - Mars500 Mission patch.

12 April 2011

Mars500 crewmembers Diego Urbina, Romain Charles and Wang Yue recall what Yuri Gagarin's historic flight is meaning for them:

Web-site of the Russian Federal Space Agency opens a new section to publish materials devoted to Yury Gagarin himself, and anything linked with the birth of the human space exploration era.

The First Rare Photo of Gagarin in the New Section of Roscosmos Web: http://www.federalspace.ru/main.php?id=86

Yuri's Night - International (visit the website for looking where are your party place on your country) celebration April 12: http://yurisnight.net/

Logo, Video, Text, Cedit: ESA / ROSCOSMOS.

Cheers, Orbiter.ch

First galaxies were born much earlier than expected

ESA - Hubble Space Telescope logo.

12 April 2011

Lensing cluster Abell 383

Using the amplifying power of a cosmic gravitational lens, astronomers have discovered a distant galaxy whose stars were born unexpectedly early in cosmic history. This result sheds new light on the formation of the first galaxies, as well as on the early evolution of the Universe.

Johan Richard, the lead author of a new study [1] says: “We have discovered a distant galaxy that began forming stars just 200 million years after the Big Bang. This challenges theories of how soon galaxies formed and evolved in the first years of the Universe. It could even help solve the mystery of how the hydrogen fog that filled the early Universe was cleared.”

Annotated view of Abell 383

Richard’s team spotted the galaxy in recent observations from the NASA/ESA Hubble Space Telescope, verified it with observations from the NASA Spitzer Space Telescope and measured its distance using W. M. Keck Observatory in Hawaii.

The distant galaxy is visible through a cluster of galaxies called Abell 383, whose powerful gravity bends the rays of light almost like a magnifying glass [2]. The chance alignment of the galaxy, the cluster and the Earth amplifies the light reaching us from this distant galaxy, allowing the astronomers to make detailed observations. Without this gravitational lens, the galaxy would have been too faint to be observed even with today’s largest telescopes.

Gravitational lensing in action

After spotting the galaxy in Hubble and Spitzer images, the team carried out spectroscopic observations with the Keck-II telescope in Hawaii. Spectroscopy is the technique of breaking up light into its component colours. By analysing these spectra, the team was able to make detailed measurements of its redshift [3] and infer information about the properties of its component stars.

The galaxy’s redshift is 6.027, which means we see it as it was when the Universe was around 950 million years old [4]. This does not make it the most remote galaxy ever detected — several have been confirmed at redshifts of more than 8, and one has an estimated redshift of around 10 (heic1103), placing it 400 million years earlier. However the newly discovered galaxy has dramatically different features from other distant galaxies that have been observed, which generally shine brightly with only young stars.

Wide field view of Abell 383

“When we looked at the spectra, two things were clear,” explains co-author Eiichi Egami. “The redshift placed it very early in cosmic history, as we expected. But the Spitzer infrared detection also indicated that the galaxy was made up of surprisingly old and relatively faint stars. This told us that the galaxy was made up of stars already nearly 750 million years old — pushing back the epoch of its formation to about 200 million years after the Big Bang, much further than we had expected.”

Co-author Dan Stark continues: “Thanks to the amplification of the galaxy’s light by the gravitational lens, we have some excellent quality data. Our work confirms some earlier observations that had hinted at the presence of old stars in early galaxies. This suggests that the first galaxies have been around for a lot longer than previously thought.”

The NASA-ESA Hubble Space Telescope during Servicing Mission 4

The discovery has implications beyond the question of when galaxies first formed, and may help explain how the Universe became transparent to ultraviolet light in the first billion years after the Big Bang. In the early years of the cosmos, a diffuse fog of neutral hydrogen gas blocked ultraviolet light in the Universe. Some source of radiation must therefore have progressively ionised the diffuse gas, clearing the fog to make it transparent to ultraviolet rays as it is today — a process known as reionisation.

Astronomers believe that the radiation that powered this reionisation must have come from galaxies. But so far, nowhere near enough of them have been found to provide the necessary radiation. This discovery may help solve this enigma.

ESO - Gravitational lensing in action

“It seems probable that there are in fact far more galaxies out there in the early Universe than we previously estimated — it’s just that many galaxies are older and fainter, like the one we have just discovered,” says co-author Jean-Paul Kneib. “If this unseen army of faint, elderly galaxies is indeed out there, they could provide the missing radiation that made the Universe transparent to ultraviolet light.”

ESO - Zoom on Abell 383

As of today, we can only discover these galaxies by observing through massive clusters that act as cosmic telescopes. In coming years, the NASA/ESA/CSA James Webb Space Telescope, scheduled for launch later this decade, will specialise in high resolution observations of distant, highly redshifted objects. It will therefore be in an ideal position to solve this mystery once and for all.

ESO - Pan across Abell 383

Notes:

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

[1] The research will appear in a paper entitled “Discovery of a possibly old galaxy at z=6.027, multiply imaged by the massive cluster Abell 383”, to be published in the Monthly Notices of the Royal Astronomical Society. The international team of astronomers in this study consists of Johan Richard (CRAL, Observatoire de Lyon, Université Lyon 1, France and Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark), Jean-Paul Kneib (Laboratoire d’Astrophysique de Marseille, France), Harald Ebeling (University of Hawaii, USA), Daniel P Stark (University of Cambridge, UK), Eiichi Egami (University of Arizona, USA) and Andrew K Fiedler (University of Arizona, USA). Lead author Johan Richard is a former Marie Curie fellow. The European Union's Marie Curie research fund provides grants at post-graduate and post-doctoral level to encourage mobility among Europe's best researchers. The EU will allocate more than €4.5 billion through the scheme in 2007-2013.

[2] Gravity distorts space-time, the fabric of the cosmos. This means that for extremely massive objects with very strong gravitational fields, light is visibly bent as it travels through and around them. Massive galaxy clusters like Abell 383 therefore act like an enormous lens, concentrating the light from distant objects behind them, in a process known as gravitational lensing. While the galaxies seen through gravitational lenses are typically distorted and multiply imaged (this newly discovered galaxy is actually visible twice in the Hubble observations), using these gravitational lenses multiplies a telescope’s power and lets it see galaxies that would otherwise be too faint to be visible. Abell 383, the gravitational lens used in this study, was imaged as part of the CLASH survey (Cluster Lensing And Supernova survey with Hubble), a Multi Cycle Treasury project to observe a sample of 25 galaxy clusters using Hubble (PI: Marc Postman). Abell 383 is also one of the 50 clusters imaged with the Spitzer Warm mission large project led by Eiichi Egami.

[3] Because the Universe is expanding, the light from distant objects is stretched and reddened as it moves towards us, a phenomenon known as redshift. The further an object is away, the more heavily redshifted it is. For very remote objects, redshift can be used to quantify their distance.

[4] Because light travels at a finite speed, the further away an object is, the further back in time we see it. For an object at a redshift of 6, the light has taken around 12.8 billion years to travel to Earth. Since we know that the Universe is about 13.75 billion years old, this means we are seeing the object in the state it was in less than a billion years after the Big Bang. Redshift is therefore a measure of time elapsed since the Big Bang as well as of an object’s distance.

Links:

    * Images of Hubble: http://www.spacetelescope.org/images/archive/category/spacecraft/

    * Research paper link: http://www.spacetelescope.org/static/archives/releases/science_papers/heic1106.pdf

    * NASA Hubble release: http://hubblesite.org/newscenter/archive/releases/2011/12

Images, Text, Credits: ESO / NASA / ESA / J. Richard (CRAL) and J.-P. Kneib (LAM). Acknowledgement: Marc Postman (STScI). Videos: NASA / ESA & L. Calçada / Digitized Sky Survey 2 / J. Richard (CRAL) and J.-P. Kneib (LAM). Acknowledgement: Marc Postman (STScI).

Greetings, Orbiter.ch