vendredi 2 septembre 2011

Rare martian lake delta spotted by Mars Express












ESA - Mars Express Mission patch.

2 September 2011

ESA’s Mars Express has spotted a rare case of a crater once filled by a lake, revealed by the presence of a delta. The delta is an ancient fan-shaped deposit of dark sediments, laid down in water. It is a reminder of Mars’ past, wetter climate.

Holden and Eberswalde craters

The delta is in the Eberswalde crater, in the southern highlands of Mars. The 65 km-diameter crater is visible as a semi-circle on the right of the image and was formed more than 3.7 billion years ago when an asteroid hit the planet.

The rim of the crater is intact only on its right-hand side. The rest appears only faintly or is not visible at all. A later impact created the 140 km diameter Holden crater that dominates the centre and left side of the image. The expulsion of large amounts of material from that impact buried parts of Eberswalde.

Eberswalde crater in context

However, within the visible part of Eberswalde, the delta and its feeder channels are well preserved , as seen near the top right of the crater. The delta covers an area of 115 square kilometres. Small, meandering feeder channels are visible towards the top of the crater, which would have filled it to form a lake.

After the deposition of the delta sediments in the crater’s ancient lake, fresher sediments accumulated to cover up a major part of both the channels and the delta. These secondary sediments, presumably deposited by the wind, were later eroded in the delta area, exposing an inverted relief of the delta structure.

Delta in Eberswalde crater

This delta structure, first identified with NASA’s Mars Global Surveyor spacecraft, is characteristic of the presence of a lake in the crater at that time. Such features provide a clear indication that liquid water flowed across the surface of Mars in the planet’s early history.

Both Eberswalde crater and Holden crater were on the shortlist of four possible destinations for the next NASA Mars rover, to be launched late this year. The main objective of the Mars Science Laboratory mission is the search for present or previously habitable environments on Mars. ESA’s Mars Express mission has been helping in the search for the best landing site.

Features in Eberswalde crater

Eberswalde was proposed because its delta indicates the long-lasting presence of liquid water in the past and Holden Crater was a candidate because of its mineral diversity and many structures that again suggest past liquid water. Another candidate, Mawrth Vallis, exposes some of the oldest clay-rich layers on Mars. However, in July, Gale crater, the final entry on the shortlist, was selected as the mission’s landing site, given its high mineral and structural diversity related to water.

Eberswalde crater in perspective

Eberswalde, Holden and Mawrth Vallis will get to hold on to their secrets for a while longer.

Holden crater in perspective

 Eberswalde crater in perspective

 Holden and Eberswalde in high resolution

 Holden and Eberswalde crater in 3D

Related links:

High Resolution Stereo Camera: http://berlinadmin.dlr.de/Missions/express/indexeng.shtml

Behind the lens:http://www.esa.int/SPECIALS/Mars_Express/SEMSXE1PGQD_0.html

Frequently asked questions: http://www.esa.int/SPECIALS/Mars_Express/SEM76D9OY2F_0.html

For specialists:

ESA Planetary Science archive (PSA): http://www.rssd.esa.int/PSA

NASA Planetary Data: http://pds-geosciences.wustl.edu/missions/mars_express/hrsc.htm

SystemHRSC data viewer: http://hrscview.fu-berlin.de/

Images, Text, Credits: ESA / DLR / FU Berlin (G. Neukum) / NASA / MGS / MOLA Science Team.

Greetings, Orbiter.ch

jeudi 1 septembre 2011

NASA's Mars Rover Opportunity Begins Study of Martian Crater











NASA - Mars Exploration Rover "Opportunity" (MER-B) patch.

Sept. 1, 2011

The initial work of NASA's Mars rover Opportunity at its new location on Mars shows surface compositional differences from anything the robot has studied in its first 7.5 years of exploration.

Opportunity arrived three weeks ago at the rim of a 14-mile-wide (22-kilometer-wide) crater named Endeavour. The first rock it examined is flat-topped and about the size of a footstool. It was apparently excavated by an impact that dug a crater the size of a tennis court into the crater's rim. The rock was informally named "Tisdale 2."


Image above: NASA's Mars Exploration Rover Opportunity used its front hazard-avoidance camera to take this picture showing the rover's arm extended toward a light-toned rock, "Tisdale 2," during the 2,695th Martian day, or sol, of the rover's work on Mars (Aug. 23, 2011). Image credit: NASA / JPL-Caltech.

"This is different from any rock ever seen on Mars," said Steve Squyres, principal investigator for Opportunity at Cornell University in Ithaca, N.Y. "It has a composition similar to some volcanic rocks, but there's much more zinc and bromine than we've typically seen. We are getting confirmation that reaching Endeavour really has given us the equivalent of a second landing site for Opportunity."

The diversity of fragments in Tisdale 2 could be a prelude to other minerals Opportunity might find at Endeavour. In the past two weeks, researchers have used an instrument on the rover's robotic arm to identify elements at several spots on Tisdale 2. Scientists have also examined the rock using the rover's microscopic imager and multiple filters of its panoramic camera.

Observations by Mars orbiters suggest that rock exposures on Endeavour's rim date from early in Martian history and include clay minerals that form in less-acidic wet conditions, possibly more favorable for life. Discontinuous ridges are all that remains of the ancient crater's rim. The ridge at the section of the rim where Opportunity arrived is named "Cape York." A gap between Cape York and the next rim fragment to the south is called "Botany Bay."

"On the final traverses to Cape York, we saw ragged outcrops at Botany Bay unlike anything Opportunity has seen so far, and a bench around the edge of Cape York looks like sedimentary rock that's been cut and filled with veins of material possibly delivered by water," said Ray Arvidson, the rover's deputy principal investigator at Washington University in St. Louis. "We made an explicit decision to examine ancient rocks of Cape York first."

The science team selected Endeavour as Opportunity's long-term destination after the rover climbed out of Victoria crater three years ago this week. The mission spent two years studying Victoria, which is about one twenty-fifth as wide as Endeavour. Layers of bedrock exposed at Victoria and other locations Opportunity has visited share a sulfate-rich composition linked to an ancient era when acidic water was present. Opportunity drove about 13 miles (21 kilometers) from Victoria to reach Endeavour. It has driven 20.8 miles (33.5 kilometers) since landing on Mars.

"We have a very senior rover in good health for having already worked 30 times longer than planned," said John Callas, project manager for Opportunity at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "However, at any time, we could lose a critical component on an essential rover system, and the mission would be over. Or, we might still be using this rover's capabilities beneficially for years. There are miles of exciting geology to explore at Endeavour crater."


Image above: NASA's Mars Exploration Rover Opportunity used its navigation camera to take this picture showing a light-toned rock, "Tisdale 2," during the 2,690th Martian day, or sol, of the rover's work on Mars (Aug. 18, 2011). Image credit: NASA / JPL-Caltech.

Opportunity and its rover twin, Spirit, completed three-month prime missions in April 2004 and continued working for years of extended missions. Both have made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life. Spirit ended communications in March 2010.

video
 Mars rover explores ancient crater Endeavour

"This is like having a brand new landing site for our veteran rover," said Dave Lavery, program executive for NASA's Mars Exploration Rovers at NASA Headquarters in Washington. "It is a remarkable bonus that comes from being able to rove on Mars with well-built hardware that lasts."

NASA will launch its next-generation Mars rover, Curiosity, between Nov. 25 and Dec. 18, 2011. It will land on Mars in August 2012. JPL manages the Mars Exploration Rover Project for NASA's Science Mission Directorate in Washington.

For more about Opportunity, visit: http://www.nasa.gov/rovers

Images (mentioned), Video, text, Credit: NASA / JPL-Caltech / Guy Webster / Dwayne Brown / BBC.

Greetings, Orbiter.ch

Mars500: two months away from ‘arrival at Earth’









ESA - Mars500 Mission patch.

1 September 2011

The ‘mission’ to Mars is now generating unique data – nobody has been isolated as long as these six marsonauts. Soon, the communications delay will end and the crew will feel that much closer to opening the hatch on 4 November.

The first full simulation of a mission to Mars and back is proceeding smoothly in the special facility at the Institute of Biomedical Problems in Moscow.

Mars500 crew seen on video in August 2011

In mid-August the experiment passed the milestone of 438 days that was previously the longest time ever spent apart from the natural world, by cosmonaut Valeri Polyakov aboard Russia’s Mir space station in 1994–95.

Logistics, psychology, health, experiments – now everything is in uncharted territory and providing valuable information for that moment when humans eventually venture out to the planets.

Long two months

 Diego and Romain with red goggles

At the moment the crew is faced with the most demanding and difficult period of the mission, with strong elements of monotony, sensory deprivation and general weakness.

Apart from being pale, the six men are coping with the situation remarkably well. They are always looking for new ways of staying motivated and relaxed.

They are occupied not only with a multitude of scientific experiments and maintaining their ‘spacecraft’, but also keep busy with creative activities.

European participants Diego Urbina and Romain Charles are writing diaries, taking photos and making videos, although less often than at the beginning of their mission.

ESA Director General talking with Mars500

Diego’s deep involvement with Twitter (@diegou) is giving the general public an insider’s view of daily life in the Mars500 modules.

The first real step towards ‘arrival back at Earth’ will take place on 15 September, when direct communication with the crew will be re-established.

A varying artificial delay was introduced during the mission into communications with ground control, as would occur naturally on a real Mars mission because of the great distances involved.

As he was seen on Mars500

The delay has been reducing by about 30 seconds a week during the journey back, dropping to a minute by the end of August. The first planned realtime communication with the crew is a medical check-up.

The screen capture showing where the 'spacecraft' is now

The realtime link will surely be used for cheering the crew up with visitors at mission control – especially visitors speaking their own language. Video messages have already provided brighter moments in the daily routine.

The end of the mission on 4 November is only two months away. The marsonauts are looking forward to that precious moment when the hatch is opened and they can step out, meet their families and friends, and breathe crisp fresh air.

Online video:

ESA TV: One year inside: http://multimedia.esa.int/Videos/2011/05/Mars-500-one-year-inside

Related links:

http://www.esa.int/export/SPECIALS/Mars500/SEMU3SUTTRG_0.html

http://twitter.com/diegou

Images, Text, Credit: ESA.

Best regards, Orbiter.ch

Completed flight spacecraft "Progress M-11M"












ROSCOSMOS logo.

01.09.2011

September 1 flight ended automatic cargo spacecraft "Progress M-11M."

In accordance with a program rooted in its onboard computer, the commands from the Mission Control Center, 13 hours 34 minutes 31 seconds Moscow time (09:34:31 GMT) was included in the ship's boosters inhibition. After working for 180 seconds, he said the truck braking impulse magnitude 91.8 meters per second, followed by "Progress M-11M" descended from orbit and ceased to exist over a given water area of ​​the South Pacific.

Coordinates of the center falls unburned structural elements - 40 ° 8 'south latitude and 135 ° 2' west longitude. The fall at this point - 14 hours 21 minutes 41 seconds (10:21:41 GMT).

Progress M spacecraft

The ship "Progress M-11M" was launched on June 21, 2011, and after two days docked to the assembly compartment service module "Zvezda" of the International Space Station. Truck delivered to the ISS more than 2.6 tons of cargo needed to sustain the crew on board. 23 August "Progress M-11M" undocked from the ISS.

During autonomous flight of the experiment "Radar-Progress" by ground-based observations of the study of reflection characteristics of plasma irregularities in the ionosphere generated by the work of the ship's liquid rocket engines.

Image, Text, Credits Roscosmos / Press Service of the MCC / Translation: Orbiter.ch

Original text in Russian: http://www.federalspace.ru/main.php?id=2&nid=17804

Best regards, Orbiter.ch

mercredi 31 août 2011

Hubble Movies Provide Unprecedented View of Supersonic Jets from Young Stars












ESA - Hubble Space Telescope logo.

31 August 2011

 Stellar jets HH 47, HH 34 and HH 2

Astronomers have combined two decades of Hubble observations to make unprecedented movies revealing never-before-seen details of the birth pangs of new stars. This sheds new light on how stars like the Sun form.

Stars aren’t shy about sending out birth announcements. They fire off energetic jets of glowing gas travelling at supersonic speeds in opposite directions through space.

Close-up views of stellar jet HH 34

Although astronomers have looked at still pictures of stellar jets for decades, now they can watch movies, thanks to the NASA/ESA Hubble Space Telescope.

An international team of scientists led by astronomer Patrick Hartigan of Rice University in Houston, USA, has collected enough high-resolution Hubble images over a 14-year period to stitch together time-lapse movies of young jets ejected from three stars.

The moving pictures offer a unique view of stellar phenomena that move and change over just a few years. Most astronomical processes change over timescales that are much longer than a human lifetime.

Herbig-Haro objects in the Orion Complex (ground-based image)

The movies reveal the motion of the speedy outflows as they tear through the interstellar environments. Never-before-seen details in the jets’ structure include knots of gas brightening and dimming and collisions between fast-moving and slow-moving material, creating glowing arrowhead features. These phenomena are providing clues about the final stages of a star’s birth, offering a peek at how the Sun behaved 4.5 billion years ago.

“For the first time we can actually observe how these jets interact with their surroundings by watching these time-lapse movies,” said Hartigan. “Those interactions tell us how young stars influence the environments out of which they form. With movies like these, we can now compare observations of jets with those produced by computer simulations and laboratory experiments to see which aspects of the interactions we understand and which we don’t understand.”

video
Stellar jet HH 47

Hartigan’s team’s results appear in the 20 July 2011 issue of the Astrophysical Journal.

Jets are an active, short-lived phase of star formation, lasting only about 100 000 years. They are called Herbig-Haro (HH) objects, named after George Herbig and Guillermo Haro, who studied the outflows in the 1950s. Astronomers still don’t know what role jets play in the star formation process or exactly how the star unleashes them.

video
Bow shock in stellar jet HH 47

A star forms from a collapsing cloud of cold hydrogen gas. As the star grows, it gravitationally attracts more matter, creating a large spinning disc of gas and dust around it. Eventually, planets may arise within the disc as dust clumps together.

video
Stellar jet HH 34

The disc material gradually spirals onto the star and escapes as high velocity jets along the star’s axis of spin. The speedy jets may initially be confined to narrow beams by the star’s powerful magnetic field. The jet phase stops when the disc runs out of material, usually a few million years after the star’s birth.

video
Bow shock in stellar jet HH 34

Hartigan and his colleagues used Hubble’s Wide Field Planetary Camera 2 to study jets HH 1, HH 2, HH 34, HH 46, and HH 47. HH 1-HH 2 and HH 46-HH 47 are pairs of jets emanating in opposite directions from single stars. Hubble followed the jets over three epochs: HH 1 and HH 2 in 1994, 1997, and 2007; HH 34 in 1994, 1998, and 2007; and HH 46 and HH 47 in 1994, 1999, and 2008. The jets are roughly ten times the width of the Solar System and zip along at more than 700 000 kilometres per hour.

video
Stellar jet HH 2

All of the outflows are roughly 1350 light-years from Earth. HH 34, HH 1, and HH 2 reside near the Orion Nebula, in the northern sky. HH 46 and HH 47 are in the southern constellation of Vela (The Sails).

Computer software has woven together these observations, taken over many years, and generated movies that show continuous motion. The movies support previous observations which revealed that the twin jets are not ejected in a steady stream, like water flowing from a garden hose. Instead, they are launched sporadically in clumps. The beaded-jet structure might be like a “ticker tape”, recording episodes when material fell onto the star.

video
Artist’s impression of a Herbig-Haro object

The movies show that the clumpy gas in the jets is moving at different speeds like traffic on a motorway. When fast-moving blobs collide with gas in the slow lane, bow shocks arise as the material heats up. Bow shocks are glowing waves of material similar to waves produced by the bow of a ship ploughing through water. In HH 2, for example, several bow shocks can be seen where several fast-moving clumps have bunched up like cars in a traffic jam. In another jet, HH 34, a grouping of merged bow shocks reveals regions that brighten and fade over time as the heated material cools where the shocks intersect.

In other areas of the jets, bow shocks form from encounters with the surrounding dense gas cloud. In HH 1 a bow shock appears at the top of the jet as it grazes the edge of a dense gas cloud. New glowing knots of material also appear. These knots may represent gas from the cloud being swept up by the jet, just as a swift-flowing river pulls along mud from the shoreline.

The movies also provide evidence that the inherent clumpy nature of the jets begins near the newborn stars. In HH 34 Hartigan traced a glowing knot to within about 14 billion kilometres of the star.

“Taken together, our results paint a picture of jets as remarkably diverse objects that undergo highly structured interactions between material within the outflow and between the jet and the surrounding gas,” Hartigan explained. “This contrasts with the bulk of the existing simulations which depict jets as smooth systems.”

The details revealed by Hubble were so complex that Hartigan consulted with experts in fluid dynamics from Los Alamos National Laboratory in New Mexico, the UK Atomic Weapons Establishment, and General Atomics in San Diego, California, as well as computer specialists from the University of Rochester in New York. Motivated by the Hubble results, Hartigan’s team is now conducting laboratory experiments at the Omega Laser facility in New York to understand how supersonic jets interact with their environment.

“Our collaboration has exploited not just large laser facilities such as Omega, but also computer simulations that were developed for research into nuclear fusion,” explains Paula Rosen of the UK Atomic Weapons Establishment, a co-author of the research. “Using these experimental methods has enabled us to identify aspects of the physics that the astronomers overlooked — it is exciting to know that what we do in the laboratory here on Earth can shed light on complex phenomena in stellar jets over a thousand light-years away. In future, even larger lasers, like the National Ignition Facility at the Lawrence Livermore National Laboratory in California, will be able explore the nuclear processes that take place within stars.”

Notes:

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

[1] The international team of astronomers in this study consists of Patrick Hartigan (Rice University, Texas, USA), Adam Frank (University of Rochester, New York, USA); John Foster (Atomic Weapons Establishment, Aldermaston, UK); Paula Rosen (Atomic Weapons Establishment, Aldermaston, UK); Bernie Wilde (Los Alamos National Laboratory, New Mexico, USA); Rob Coker (Los Alamos National Laboratory, New Mexico, USA); Melissa Douglas (Los Alamos National Laboratory, New Mexico, USA); Brent Blue (General Atomics, San Diego, California, USA) and Freddy Hansen (General Atomics, San Diego, California, USA).

Images, Text, Credits: NASA, ESA, and P. Hartigan (Rice University).

Links:

    Science paper: http://www.spacetelescope.org/static/archives/releases/science_papers/heic1113.pdf

    NASA press release: http://hubblesite.org/news/2011/20

    Rice University release link: http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=16091&SnID=2117462734

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

Video:

Hubblecast 49: Supersonic jets from newborn stars: http://www.spacetelescope.org/videos/heic1113a/

Images, Text, Credit: NASA / ESA and P. Hartigan (Rice University) / Z. Levay (STScI), T.A. Rector (University of Alaska Anchorage), and H. Schweiker (NOAO / AURA / NSF) / Videos: NASA, ESA, P. Hartigan (Rice University), G. Bacon (STScI) / NASA, ESA, P. Hartigan (Rice University), G. Bacon (STScI) / ESA / Hubble (M. Kornmesser).

Best regards, Orbiter.ch

Progress 44 accident and its consequences for Space Station











ISS - Russian Vehicules patch.

31 August 2011

The six astronauts on the International Space Station are safe and continuing their normal work after the loss of their space-bound cargo craft on 24 August.

While the cause of the accident is being sought by a Russian commission, the Station partners are preparing for several scenarios to ensure the safety of the crew and the orbital outpost.

An earlier Progress approaches ISS for docking

The Progress 44 freighter, carrying 2670 kg of cargo for the Station, failed to reach proper orbit after the premature shutdown of its third-stage engine 325 seconds after launch from the Baikonur Cosmodrome in Kazakhstan.

The remnants of the stage and Progress fell back to Earth from an altitude of about 200 km over the Altai Republic in southern Siberia.

Soyuz-U launch sequence

No remnants have been found so far and it is possible that the Progress and its third stage – both loaded with fuel and oxygen – burned up in the atmosphere.

The search crews are still probing the large areas of difficult terrain in severe weather conditions looking for evidence.

Launches of Soyuz rockets have been suspended until the cause of the engine malfunction is identified.

ESA recognises the vast experience of its Russian partners as well as the excellent safety record of the Soyuz launcher and is confident that the cause of the mishap will be found soon.

Station crew is safe

ISS

The new situation has not put the Station in danger and the safety of the Expedition 28 aboard is not compromised. There are plenty of supplies for the crew and Station to next spring.

The next Progress freighter arrived in Baikonur on Monday and is being prepared for launch, but the date has not been specified because it depends on the commission’s findings.

Russian planners would like to see two successful unmanned launches of the Soyuz-U rocket before the next manned spacecraft, so the dates of the future missions – including the flight of ESA astronaut André Kuipers – are being assessed.

Mike Fossum working in the Destiny laboratory

It has been decided to postpone the landing of Expedition 26 on Soyuz TMA-21 from 8 September to 16 September. The launch of the next Soyuz flight, Soyuz TMA-22, carrying Expedition 29, will be delayed to the end of October or the beginning of November, depending on the results of the commission.

At the same time, the Station partners are preparing for several scenarios of different likelihoods for near-future operations.

This was the first accident for this venerable spacecraft since the first Progress in 1978. So far, the Russian space agency has launched 745 Soyuz-U vehicles, with 724 successes. Progress freighters were carried on 136.

Launch of Progress 44

Soyuz-U is used not only for taking Progress spacecraft into orbit, but also delivering satellites and dispatching planetary probes.

ESA is preparing to launch its next Automated Transfer Vehicle, Edoardo Amaldi, in March 2012. Together with its Station partners, the Agency is following the Progress mishap investigation closely.

Related links:

International Space Station: http://www.esa.int/esaHS/iss.html

NASA TV: Station Manager Updates ISS Status: http://www.youtube.com/watch?v=e4tB3RqveKQ&feature=youtu.be

Images, Text, Credits: ESA / NASA / ROSCOSMOS.

Greetings, Orbiter.ch

The Star That Should Not Exist












ESO - European Southern Observatory logo.

31 August 2011

 A star that should not exist

A team of European astronomers has used ESO’s Very Large Telescope (VLT) to track down a star in the Milky Way that many thought was impossible. They discovered that this star is composed almost entirely of hydrogen and helium, with only remarkably small amounts of other chemical elements in it. This intriguing composition places it in the “forbidden zone” of a widely accepted theory of star formation, meaning that it should never have come into existence in the first place. The results will appear in the 1 September 2011 issue of the journal Nature.

A faint star in the constellation of Leo (The Lion), called SDSS J102915+172927 [1], has been found to have the lowest amount of elements heavier than helium (what astronomers call “metals”) of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.

The composition of a star that should not exist

“A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed,” [2] said Elisabetta Caffau (Zentrum für Astronomie der Universität Heidelberg, Germany and Observatoire de Paris, France), lead author of the paper. “It was surprising to find, for the first time, a star in this ‘forbidden zone’, and it means we may have to revisit some of the star formation models.”

The team analysed the properties of the star using the X-shooter and UVES instruments on the VLT [3]. This allowed them to measure how abundant the various chemical elements were in the star. They found that the proportion of metals in SDSS J102915+172927 is more than 20 000 times smaller than that of the Sun [4][5].

The remarkable star SDSS J102915+172927 in the constellation of Leo (The Lion)

“The star is faint, and so metal-poor that we could only detect the signature of one element heavier than helium — calcium — in our first observations,” said Piercarlo Bonifacio (Observatoire de Paris, France), who supervised the project. “We had to ask for additional telescope time from ESO’s Director General to study the star’s light in even more detail, and with a long exposure time, to try to find other metals.”

Cosmologists believe that the lightest chemical elements — hydrogen and helium — were created shortly after the Big Bang, together with some lithium [6], while almost all other elements were formed later in stars. Supernova explosions spread the stellar material into the interstellar medium, making it richer in metals. New stars form from this enriched medium so they have higher amounts of metals in their composition than the older stars. Therefore, the proportion of metals in a star tells us how old it is.

The spectrum of a star that should not exist

“The star we have studied is extremely metal-poor, meaning it is very primitive. It could be one of the oldest stars ever found,” adds Lorenzo Monaco (ESO, Chile), also involved in the study.

Also very surprising was the lack of lithium in SDSS J102915+172927. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But the team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang.

“It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star.” Bonifacio added.

Wide-field view of the sky around the remarkable star SDSS J102915+172927

The researchers also point out that this freakish star is probably not unique. “We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case,” concludes Caffau.

video
Zooming in on the remarkable star SDSS J102915+172927

Notes:

[1] The star is catalogued in the Sloan Digital Sky Survey or SDSS. The numbers refer to the object’s position in the sky.

[2] Widely accepted star formation theories state that stars with a mass as low as SDSS J102915+172927 (about 0.8 solar masses or less) could only have formed after supernova explosions enriched the interstellar medium above a critical value. This is because the heavier elements act as “cooling agents”, helping to radiate away the heat of gas clouds in this medium, which can then collapse to form stars. Without these metals, the pressure due to heating would be too strong, and the gravity of the cloud would be too weak to overcome it and make the cloud collapse. One theory in particular identifies carbon and oxygen as the main cooling agents, and in SDSS J102915+172927 the amount of carbon is lower than the minimum deemed necessary for this cooling to be effective.

[3] X-shooter and UVES are VLT spectrographs — instruments used to separate the light from celestial objects into its component colours and allow detailed analysis of the chemical composition. X-shooter can capture a very wide range of wavelengths in the spectrum of an object in one shot (from the ultraviolet to the near-infrared). UVES is the Ultraviolet and Visual Echelle Spectrograph, a high-resolution optical instrument.

[4] The star HE 1327-2326, discovered in 2005, has the lowest known iron abundance, but it is rich in carbon. The star now analysed has the lowest proportion of metals when all chemical elements heavier than helium are considered.

[5] ESO telescopes have been deeply involved in many of the discoveries of the most metal-poor stars. Some of the earlier results were reported in eso0228 and eso0723 and the new discovery shows that observations with ESO telescopes have let astronomers make a further step closer to finding the first generation of stars.

[6] Primordial nucleosynthesis refers to the production of chemical elements with more than one proton a few moments after the Big Bang. This production happened in a very short time, allowing only hydrogen, helium and lithium to form, but no heavier elements. The Big Bang theory predicts, and observations confirm, that the primordial matter was composed of about 75% (by mass) of hydrogen, 25% of helium, and trace amounts of lithium.

More information:

This research was presented in a paper, “An extremely primitive halo star“, by Caffau et al. to appear in the 1 September 2011 issue of the journal Nature.

The team is composed of Elisabetta Caffau (Zentrum für Astronomie der Universität Heidelberg [ZAH], Germany and GEPI — Observatoire de Paris, Université Paris Diderot, CNRS, France [GEPI]), Piercarlo Bonifacio (GEPI), Patrick François (GEPI and Université de Picardie Jules Verne, Amiens, France), Luca Sbordone (ZAH, Max-Planck Institut für Astrophysik, Garching, Germany, and GEPI), Lorenzo Monaco (ESO, Chile), Monique Spite (GEPI), François Spite (GEPI), Hans-G. Ludwig (ZAH and GEPI), Roger Cayrel (GEPI), Simone Zaggia (INAF, Osservatorio Astronomico di Padova, Italy), François Hammer (GEPI), Sofia Randich (INAF, Osservatorio Astrofisico di Arcetri, Firenze, Italy), Paolo Molaro (INAF, Osservatorio Astronomico di Trieste, Italy), and Vanessa Hill (Université de Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, CNRS, Laboratoire Cassiopée, Nice, France).

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 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: http://www.eso.org/public/archives/releases/sciencepapers/eso1132/eso1132.pdf

    Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/

Images, Text, Credit: ESO / Digitized Sky Survey 2 / A. Fujii / E. Caffau / Video: ESO / A. Fujii / Digitized Sky Survey 2 Music: John Dyson (from the album Moonwind).

Best regards, Orbiter.ch

NASA'S Chandra Finds Nearest Pair Of Supermassive Black Holes

NASA - Chandra X-ray Observatory patch.

Aug. 31, 2011

Astronomers using NASA's Chandra X-ray Observatory discovered the first pair of supermassive black holes in a spiral galaxy similar to the Milky Way. Approximately 160 million light years from Earth, the pair is the nearest known such phenomenon.

The black holes are located near the center of the spiral galaxy NGC 3393. Separated by only 490 light years, the black holes are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago.


Composite image of spiral galaxy NGC 3393. (X-ray: NASA /CXC /SAO / G. Fabbiano et al; Optical: NASA / STScI).

"If this galaxy weren't so close, we'd have no chance of separating the two black holes the way we have," said Pepi Fabbiano of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led the study that appears in this week's online issue of the journal Nature. "Since this galaxy was right under our noses by cosmic standards, it makes us wonder how many of these black hole pairs we've been missing."

Previous observations in X-rays and at other wavelengths indicated that a single supermassive black hole existed in the center of NGC 3393. However, a long look by Chandra allowed the researchers to detect and separate the dual black holes. Both black holes are actively growing and emitting X-rays as gas falls towards them and becomes hotter.

When two equal-sized spiral galaxies merge, astronomers think it should result in the formation of a black hole pair and a galaxy with a disrupted appearance and intense star formation. A well-known example is the pair of supermassive black holes in NGC 6240, which is located about 330 million light years from Earth.

However, NGC 3393 is a well-organized spiral galaxy, and its central bulge is dominated by old stars. These are unusual properties for a galaxy containing a pair of black holes. Instead, NGC 3393 may be the first known instance where the merger of a large galaxy and a much smaller one, dubbed a "minor merger" by scientists, has resulted in the formation of a pair of supermassive black holes.

In fact, some theories say that minor mergers should be the most common way for black hole pairs to form, but good candidates have been difficult to find because the merged galaxy is expected to look so typical.

"The two galaxies have merged without a trace of the earlier collision, apart from the two black holes," said co-author Junfeng Wang, also from CfA. "If there were a mismatch in size between the two galaxies it wouldn't be a surprise for the bigger one to survive unscathed."

If this were a minor merger, the black hole in the smaller galaxy should have had a smaller mass than the other black hole before their host galaxies started to collide. Good estimates of the masses of both black holes are not yet available to test this idea, although the observations do show that both black holes are more massive than about a million suns. Assuming a minor merger occurred, the black holes should eventually merge after about a billion years.

Both of the supermassive black holes are heavily obscured by dust and gas, which makes them difficult to observe in optical light. Because X-rays are more energetic, they can penetrate this obscuring material. Chandra's X-ray spectra show clear signatures of a pair of supermassive black holes.

The NGC 3393 discovery has some similarities to a possible pair of supermassive black holes found recently by Julia Comerford of the University of Texas at Austin, also using Chandra data. Two X-ray sources, which may be due to supermassive black holes in a galaxy about two billion light years from Earth, are separated by about 6,500 light years.

As in NGC 3393, the host galaxy shows no signs of disturbance or extreme amounts of star formation. However, no structure of any sort, including spiral features, is seen in the galaxy. Also, one of the sources could be explained by a jet, implying only one supermassive black hole is located in the galaxy.

"Collisions and mergers are one of the most important ways for galaxies and black holes to grow," said co-author Guido Risaliti of CfA and the National Institute for Astrophysics in Florence, Italy. "Finding a black hole pair in a spiral galaxy is an important clue in our quest to learn how this happens."

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

For more information about the Chandra mission and this result, including images and other multimedia, visit: http://www.nasa.gov/chandra and http://chandra.si.edu

Image (mentioned), Text, Credits: NASA / CXC.

Cheers, Orbiter.ch