A new technique using near-infrared images, obtained with ESO’s 3.58-metre New Technology Telescope (NTT), allows astronomers to see through the opaque dust lanes of the giant cannibal galaxy Centaurus A, unveiling its “last meal” in unprecedented detail — a smaller spiral galaxy, currently twisted and warped. This amazing image also shows thousands of star clusters, strewn like glittering gems, churning inside Centaurus A.

Comparison between a visible-light image (left) of Centaurus A, as seen with the Wide-Field Imager on the MPG/ESO 2.2-metre telescope, and a near-infared view (right) obtained with the SOFI instrument on ESO’s New Technology Telescope, also at La Silla. (ESO)

Centaurus A (NGC 5128) is the nearest giant, elliptical galaxy, at a distance of about 11 million light-years. One of the most studied objects in the southern sky, by 1847 the unique appearance of this galaxy had already caught the attention of the famous British astronomer John Herschel, who catalogued the southern skies and made a comprehensive list of nebulae.

Herschel could not know, however, that this beautiful and spectacular appearance is due to an opaque dust lane that covers the central part of the galaxy. This dust is thought to be the remains of a cosmic merger between a giant elliptical galaxy and a smaller spiral galaxy full of dust.

Between 200 and 700 million years ago, this galaxy is indeed believed to have consumed a smaller spiral, gas-rich galaxy — the contents of which appear to be churning inside Centaurus A’s core, likely triggering new generations of stars.

First glimpses of the “leftovers” of this meal were obtained thanks to observations with the ESA Infrared Space Observatory , which revealed a 16 500 light-year-wide structure, very similar to that of a small barred galaxy. More recently, NASA’s Spitzer Space Telescope resolved this structure into a parallelogram, which can be explained as the remnant of a gas-rich spiral galaxy falling into an elliptical galaxy and becoming twisted and warped in the process. Galaxy merging is the most common mechanism to explain the formation of such giant elliptical galaxies.

The new SOFI images, obtained with the 3.58-metre New Technology Telescope at ESO’s La Silla Observatory, allow astronomers to get an even sharper view of the structure of this galaxy, completely free of obscuring dust. The original images, obtained by observing in the near-infrared through three different filters (J, H, K) were combined using a new technique that removes the dark, screening effect of the dust, providing a clear view of the centre of this galaxy.

What the astronomers found was surprising: “There is a clear ring of stars and clusters hidden behind the dust lanes, and our images provide an unprecedentedly detailed view toward it,” says Jouni Kainulainen, lead author of the paper reporting these results. “Further analysis of this structure will provide important clues on how the merging process occurred and what has been the role of star formation during it.”

The research team is excited about the possibilities this new technique opens: “These are the first steps in the development of a new technique that has the potential to trace giant clouds of gas in other galaxies at high resolution and in a cost-effective way,” explains co-author João Alves. “Knowing how these giant clouds form and evolve is to understand how stars form in galaxies.”

This image of the central parts of Centaurus A reveals the parallelogram-shaped remains of a smaller galaxy that was gulped down about 200 to 700 million years ago. The image is based on data collected with the SOFI instrument on ESO’s New Technology Telescope at La Silla.(ESO)

Looking forward to the new, planned telescopes, both on the ground and in space, “this technique is very complementary to the radio data ALMA will collect on nearby galaxies, and at the same time it poses interesting avenues of research for extragalactic stellar populations with the future European Extremely Large Telescope and the James Webb Space Telescope, as dust is omnipresent in galaxies,” says co-author Yuri Beletsky.

Previous observations done with ISAAC on the VLT (ESO 04/01) have revealed that a supermassive black hole lurks inside Centaurus A. Its mass is about 200 million times the mass of our Sun, or 50 times more massive than the one that lies at the centre of our Milky Way. In contrast to our own galaxy, the supermassive black hole in Centaurus A is continuously fed by material falling onto into it, making the giant galaxy a very active one. Centaurus A is in fact one of the brightest radio sources in the sky (hence the “A” in its name). Jets of high energy particles from the centre are also observed in radio and X-ray images.

The new image of Centaurus A is a wonderful example of how frontier science can be combined with aesthetic aspects. Fine images of Centaurus A have been obtained in the past with ESO’s Very Large Telescope (ESO PR Photo 05b/00) and with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla.

This research was presented in a paper in Astronomy and Astrophysics (vol. 502): “Uncovering the kiloparsec-scale stellar ring of NGC5128”, by J.T. Kainulainen et al.

The team is composed of J. T. Kainulainen (University of Helsinki, Finland, and MPIA, Germany), J. F. Alves (Calar Alto Observatory, Spain and University of Vienna, Austria), Y. Beletsky (ESO), J. Ascenso (Harvard-Smithsonian Center for Astrophysics, USA), J. M. Kainulainen (TKK/Department of Radio Science and Engineering, Finland), A. Amorim, J. Lima, F. D. Santos, and A. Moitinho (SIM-IDL, University of Lisbon, Portugal), R. Marques and J. Pinhão (University of Coimbra, Portugal), and J. Rebordão (INETI, Amadora, Portugal).

SOFI (Son of ISAAC) is an infrared spectro-imager attached to ESO’s 3.58-metre New Technology Telescope (NTT) and a simplified version of the Short Wavelength arm of ISAAC on the Very Large Telescope.

- ESO, The European Southern Observatory -

Pioneer-Venus visible-light image, and Magellan radar view of Venus. Credit: NASA/JPL/RPIF/DLR.

“Carrying out these observations was a great challenge, as SCIAMACHY was not actually designed for such measurements,” Dr. Manfred Gottwald, responsible for SCIAMACHY at the DLR Remote Sensing Technology Institute (Institut für Methodik der Fernerkundung; IMF), said. “We were surprised how excellently everything worked despite that,” his colleague at the institute, Dr. Sanders Slijkhuis, the specialist responsible for calibrating the instrument, added.

SCIAMACHY on Envisat, Venus Express and COROT complement one another

The Venus observations by SCIAMACHY are useful in two respects. On the one hand, they support the in-situ measurements by the Venus Express space probe of the European Space Agency (ESA), which has been orbiting our neighbouring planet since 2006. Venus Express is studying the dense atmosphere of Venus with great precision using the SPICAV and VIRTIS spectrometers. SCIAMACHY and Venus Express are observing Venus under different viewing geometries and lighting conditions, so that their results complement one another well. In addition, SCIAMACHY’s Venus observations are a further test of the way that an Earth-like planet presents itself spectrally when observed from a great distance.

Since the first extra-solar planets – that is, planets orbiting stars other than our Sun – were discovered in the mid-1990s, the search for Earth-like companions of stars similar to the Sun, in other words a ’second Earth’, has been one of the great challenges in astronomy. Currently, however, most of the so-called exoplanets that have been found are giant gas planets rather like Jupiter. In 2008, researchers succeeded for the first time in discovering a possible Earth-like exoplanet using the CoRoT (Convection, Rotation and Planetary Transits) space telescope, a project in which the DLR is also involved (see article CoRoT discovers extrasolar rocky planets in the right column). But in the near future, small Earth-like planets could also come within reach using improved telescopes. However, they will always appear as small dots due to the enormous distances involved. The spectral analysis of the central star’s light when scattered by the exoplanets and their own thermal radiation emissions could provide information as to whether they might be suitable for harbouring life. Hence, observations of the known planets in our solar system provide an excellent experimental environment for gaining experience with regard to the interpretation of spectral signatures of Earth-like bodies.

Earth observation satellite ENVISAT. Credit: ESA.

DLR planetary researchers pleased about interdisciplinary approach

The observations of Venus, with its hot and hostile environment – surrounded by a dense carbon dioxide atmosphere – can provide outstanding comparative data in our immediate cosmic neighbourhood for the analysis of the atmosphere of exoplanets. “As planetary researchers, we are of course very pleased about these additional measurements from a mission whose aim is actually Earth observation,” Prof. Tilman Spohn, Director of the DLR Institute of Planetary Research (Institut für Planetenforschung) in Berlin-Adlershof, says. He adds: “It is excellent that these data from SCIAMACHY were picked up. They help us to evaluate the data supplied by our experiments on the planetary missions.”

“We are very impressed by the SCIAMACHY observations,” Prof. Heike Rauer, also from the DLR Institute of Planetary Research and the leader of the project through which DLR is involved in the search for exoplanets with CoRoT, said happily. “The new results illustrate excellently what atmospheric signatures would be expected if a Venus-like exoplanet were discovered.” Future satellites could then search for signs of a biosphere, the zone where organisms can live, on such planets. Scientists from the DLR Remote Sensing Technology Institute in Oberpfaffenhofen have been working with the researchers from the DLR Institute of Planetary Research in Berlin-Adlershof for some time in the search for what are known as ‘biomarkers’ – components in the atmosphere or on the surface of planets that have been created through the metabolic activity of life forms.

The intention is to make further use of the SCIAMACHY measurements in the ‘Planetary Evolution and Life’ Helmholtz Alliance. This international research network is investigating the question, among other things, as to what conditions must prevail on a planet in order for life to develop. Here, the data offer a realistic background for modelling the radiation transport in the atmospheres of Earth-like planets.

Additional measurements of spectra in various phases of Venus are planned with SCIAMACHY. In addition, studies are underway as to how the other bright planets of our solar system, Mars, Jupiter and Saturn, can also be used as extraterrestrial objects of investigation.

Venus – bright, small and “difficult to measure”

Relative positions of Earth and Venus, March and June 2009. Credit: DLR/NASA-JPL Solar System Simulator.

Venus, with its 12 100-kilometre diameter, is almost as large as our home planet.  Seen from Earth, it appears as the brightest celestial body after the Sun and Moon – but with a subtended angle of less than one minute of arc (one sixtieth of a degree) it looks relatively small. As a consequence, in order to keep this small ‘Venusian disc’ in SCIAMACHY’s field of view long enough to perform the observations, the instrument configuration had to be changed substantially. Due to the arrangement of SCIAMACHY’s observation windows, Venus only appears above Earth’s horizon briefly after rising – a process which is repeated 14 to 15 times per day as a result of Envisat’s orbit of the Earth. Precise planning as well as chronologically exact measurements finally enabled the derivation of Venus spectra on the basis of the solar radiation reflected and scattered by the planet’s atmosphere. Both in March and in June 2009 SCIAMACHY recorded Venus spectra during several orbits of Earth (see PDF download ‘SCIAMACHY spectra of Venus’ in the right column).

As an inner planet, Venus moves faster around the Sun than Earth. Therefore, the relative positions of Earth, Venus and Sun changed significantly between March and June 2009 (see image). In March 2009, Venus was close to what is known as its ‘inferior conjunction’, directly between Earth and the Sun. Seen from Earth, it presented mainly its dark side and only a thin crescent of the sunlit planetary disc was visible. At this time, the distance of Venus from Earth was only 43 million kilometres. In June 2009, by contrast, the Sun, Venus and Earth formed an almost right-angled triangle. Although the distance between Venus and Earth had grown to 127 million kilometres, more than 50 percent of Venus’ disc now lay in sunlight when seen from Earth.

SCIAMACHY on Envisat

ESA’s Envisat Earth observation satellite has been orbiting Earth since 2002 and supplies valuable information about the state of Earth. The SCIAMACHY atmospheric instrument on board Envisat, designed under the lead management of  DLR together with Dutch and Belgian partners, measures the solar radiation scattered back from Earth’s surface and atmosphere from the ultraviolet to the near-infrared parts of the spectrum. These measurements can be used to determine the atmospheric concentration of many different trace gases, which are important with regard to air quality, the greenhouse effect and ozone chemistry. SCIAMACHY is the first and currently the only satellite instrument in the world to carry out measurements of such complexity. The project is managed by DLR and the Netherlands Space Office (NSO). The Institute of Remote Sensing and Environmental Physics (IFE/IUP) of the University of Bremen is responsible for the scientific management the project.

German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR)

The CCD220 detector at the core of the OCam camera has 240 x 240 pixels and has a readout noise ten times smaller than detectors in current use, making it ideal for the faint light camera systems to be used on the second generation of Very Large Telescope instruments. It was developed by the British manufacturer e2v technologies. Source: ESO

“The performance of this breakthrough camera is without an equivalent anywhere in the world. The camera will enable great leaps forward in many areas of the study of the Universe,” says Norbert Hubin, head of the Adaptive Optics department at ESO. OCam will be part of the second-generation VLT instrument SPHERE. To be installed in 2011, SPHERE will take images of giant exoplanets orbiting nearby stars.

A fast camera such as this is needed as an essential component for the modern adaptive optics instruments used on the largest ground-based telescopes. Telescopes on the ground suffer from the blurring effect induced by atmospheric turbulence. This turbulence causes the stars to twinkle in a way that delights poets, but frustrates astronomers, since it blurs the finest details of the images.

Adaptive optics techniques overcome this major drawback, so that ground-based telescopes can produce images that are as sharp as if taken from space. Adaptive optics is based on real-time corrections computed from images obtained by a special camera working at very high speeds. Nowadays, this means many hundreds of times each second. The new generation instruments require these corrections to be done at an even higher rate, more than one thousand times a second, and this is where OCam is essential.

“The quality of the adaptive optics correction strongly depends on the speed of the camera and on its sensitivity,” says Philippe Feautrier from the LAOG, France, who coordinated the whole project. “But these are a priori contradictory requirements, as in general the faster a camera is, the less sensitive it is.” This is why cameras normally used for very high frame-rate movies require extremely powerful illumination, which is of course not an option for astronomical cameras.

OCam and its CCD220 detector, developed by the British manufacturer e2v technologies, solve this dilemma, by being not only the fastest available, but also very sensitive, making a significant jump in performance for such cameras. Because of imperfect operation of any physical electronic devices, a CCD camera suffers from so-called readout noise. OCam has a readout noise ten times smaller than the detectors currently used on the VLT, making it much more sensitive and able to take pictures of the faintest of sources.

OCam is the world’s fastest high precision faint light camera. Developed in Europe, the camera is highly sensitive and able to take 1500 images per second. OCam has been specially designed and built by a team of French engineers from LAM, LAOG and the OHP and uses the CCD220 detector developed by e2v technologies. The technology developed with OCam has been transferred to ESO for use with the second generation instruments of ESO’s Very Large Telescope. Source: ESO

“Thanks to this technology, all the new generation instruments of ESO’s Very Large Telescope will be able to produce the best possible images, with an unequalled sharpness,” declares Jean-Luc Gach, from the Laboratoire d’Astrophysique de Marseille, France, who led the team that built the camera.

“Plans are now underway to develop the adaptive optics detectors required for ESO’s planned 42-metre European Extremely Large Telescope, together with our research partners and the industry,” says Hubin.

Using sensitive detectors developed in the UK, with a control system developed in France, with German and Spanish participation, OCam is truly an outcome of a European collaboration that will be widely used and commercially produced.

More information

The three French laboratories involved are the Laboratoire d’Astrophysique de Marseille (LAM/INSU/CNRS, Université de Provence; Observatoire Astronomique de Marseille Provence), the Laboratoire d’Astrophysique de Grenoble (LAOG/INSU/CNRS, Université Joseph Fourier; Observatoire des Sciences de l’Univers de Grenoble), and the Observatoire de Haute Provence (OHP/INSU/CNRS; Observatoire Astronomique de Marseille Provence).

OCam and the CCD220 are the result of five years work, financed by the European commission, ESO and CNRS-INSU, within the OPTICON project of the 6th Research and Development Framework Programme of the European Union. The development of the CCD220, supervised by ESO, was undertaken by the British company e2v technologies, one of the world leaders in the manufacture of scientific detectors. The corresponding OPTICON activity was led by the Laboratoire d’Astrophysique de Grenoble, France. The OCam camera was built by a team of French engineers from the Laboratoire d’Astrophysique de Marseille, the Laboratoire d’Astrophysique de Grenoble and the Observatoire de Haute Provence. In order to secure the continuation of this successful project a new OPTICON project started in June 2009 as part of the 7th Research and Development Framework Programme of the European Union with the same partners, with the aim of developing a detector and camera with even more powerful functionality for use with an artificial laser star. This development is necessary to ensure the image quality of the future 42-metre European Extremely Large Telescope.

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 14 countries: Austria, Belgium, 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. 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”.

ESO European Organisation for Astronomical Research in the Southern Hemisphere

First view of what goes on below the surface of sunspots. Lighter/brighter colors indicate stronger magnetic field strength in this subsurface cross section of two sunspots. For the first time, NCAR scientists and colleagues have modeled this complex structure in a comprehensive 3D computer simulation, giving scientists their first glimpse below the visible surface to understand the underlying physical processes. (©UCAR, image courtesy Matthias Rempel, NCAR.

The high-resolution simulations of sunspot pairs open the way for researchers to learn more about the vast mysterious dark patches on the Sun’s surface. Sunspots are the most striking manifestations of solar magnetism on the solar surface, and they are associated with massive ejections of charged plasma that can cause geomagnetic storms and disrupt communications and navigational systems. They also contribute to variations in overall solar output, which can affect weather on Earth and exert a subtle influence on climate patterns.

The research, by scientists at NCAR and the Max Planck Institute for Solar System Research (MPS) in Germany, is being published this week in Science Express.

“This is the first time we have a model of an entire sunspot,” says lead author Matthias Rempel, a scientist at NCAR’s High Altitude Observatory. “If you want to understand all the drivers of Earth’s atmospheric system, you have to understand how sunspots emerge and evolve. Our simulations will advance research into the inner workings of the Sun as well as connections between solar output and Earth’s atmosphere.”

Ever since outward flows from the center of sunspots were discovered 100 years ago, scientists have worked toward explaining the complex structure of sunspots, whose number peaks and wanes during the 11-year solar cycle. Sunspots encompass intense magnetic activity that is associated with solar flares and massive ejections of plasma that can buffet Earth’s atmosphere. The resulting damage to power grids, satellites, and other sensitive technological systems takes an economic toll on a rising number of industries.

Creating such detailed simulations would not have been possible even as recently as a few years ago, before the latest generation of supercomputers and a growing array of instruments to observe the Sun. Partly because of such new technology, scientists have made advances in solving the equations that describe the physics of solar processes.

The work was supported by the National Science Foundation, NCAR’s sponsor. The research team improved a computer model, developed at MPS, that built upon numerical codes for magnetized fluids that had been created at the University of Chicago.

Computer model provides a unified physical explanation

The new computer models capture pairs of sunspots with opposite polarity. In striking detail, they reveal the dark central region, or umbra, with brighter umbral dots, as well as webs of elongated narrow filaments with flows of mass streaming away from the spots in the outer penumbral regions. They also capture the convective flow and movement of energy that underlie the sunspots, and that are not directly detectable by instruments.

The interface between a sunspot's umbra (dark center) and penumbra (lighter outer region) shows a complex structure with narrow, almost horizontal (lighter to white) filaments embedded in a background having a more vertical (darker to black) magnetic field. Farther out, extended patches of horizontal field dominate. For the first time, NCAR scientists and colleagues have modeled this complex structure in a comprehensive 3D computer simulation, giving scientists their first glimpse below the visible surface to understand the underlying physical processes. (©UCAR, image courtesy Matthias Rempel, NCAR.)

The models suggest that the magnetic fields within sunspots need to be inclined in certain directions in order to create such complex structures. The authors conclude that there is a unified physical explanation for the structure of sunspots in umbra and penumbra that is the consequence of convection in a magnetic field with varying properties.

The simulations can help scientists decipher the mysterious, subsurface forces in the Sun that cause sunspots. Such work may lead to an improved understanding of variations in solar output and their impacts on Earth.

Supercomputing at 76 trillion calculations per second

To create the model, the research team designed a virtual, three-dimensional domain that simulates an area on the Sun measuring about 31,000 miles by 62,000 miles and about 3,700 miles in depth – an expanse as long as eight times Earth’s diameter and as deep as Earth’s radius. The scientists then used a series of equations involving fundamental physical laws of energy transfer, fluid dynamics, magnetic induction and feedback, and other phenomena to simulate sunspot dynamics at 1.8 billion points within the virtual expanse, each spaced about 10 to 20 miles apart. For weeks, they solved the equations on NCAR’s new bluefire supercomputer, an IBM machine that can perform 76 trillion calculations per second.

The work drew on increasingly detailed observations from a network of ground- and space-based instruments to verify that the model captured sunspots realistically.

The new models are far more detailed and realistic than previous simulations that failed to capture the complexities of the outer penumbral region. The researchers noted, however, that even their new model does not accurately capture the lengths of the filaments in parts of the penumbra. They can refine the model by placing the grid points even closer together, but that would require more computing power than is currently available.

“Advances in supercomputing power are enabling us to close in on some of the most fundamental processes of the Sun,” says Michael Knölker, director of NCAR’s High Altitude Observatory and a co-author of the paper. “With this breakthrough simulation, an overall comprehensive physical picture is emerging for everything that observers have associated with the appearance, formation, dynamics, and the decay of sunspots on the Sun’s surface.”

See a video animation of this and other sunspot visualizations as well as still “photo” images in the Sunspots Multimedia Gallery.

The University Corporation for Atmospheric Research

This color image is the highest resolution topography map to date of the moon's south pole. Credit: NASA

The map was created by scientists at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., who collected the data using the Deep Space Network’s Goldstone Solar System Radar located in California’s Mojave Desert. The map will help Lunar Crater Observation and Sensing Satellite (LCROSS) mission planners as they target for an encounter with a permanently dark crater near the lunar South Pole.

“Since the beginning of time, these lunar craters have been invisible to humanity,” said Barbara Wilson, a scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and manager of the study. “Now we can see detailed topography inside these craters down to 40 meters [132 feet] per pixel, with height accuracy of better than 5 meters [16 feet].”

The terrain map of the moon’s south pole is online at: http://www.nasa.gov/topics/moonmars/features/moon-20090618.html .

Scientists targeted the moon’s south polar region using Goldstone’s 70-meter (230-foot) radar dish. The antenna, three-quarters the size of a football field, sent a 500-kilowatt-strong, 90-minute-long radar stream 373,046 kilometers (231,800 miles) to the moon. Signals were reflected back from the rough-hewn lunar terrain and detected by two of Goldstone’s 34-meter (112-foot) antennas on Earth. The roundtrip time, from the antenna to the moon and back, was about two-and-a-half seconds.

The scientists compared their data with laser altimeter data recently released by the Japanese Aerospace Exploration Agency’s Kaguya mission to position and orient the radar images and maps. The new map provides contiguous topographic detail over a region approximately 500 kilometers (311 miles) by 400 kilometers (249 miles).

Funding for the program was provided by NASA’s Exploration Systems Mission Directorate. JPL manages the Goldstone Solar System Radar and the Deep Space Network for NASA. JPL is managed for NASA by the California Institute of Technology in Pasadena.

More information about the Goldstone Solar System Radar and Deep Space Network is at http://deepspace.jpl.nasa.gov/dsn . More information about NASA’s exploration program to return humans to the moon is at http://www.nasa.gov/exploration .

NASA Jet Propulsion Laboratory

Reconstructed landscape showing the Shalbatana lake on Mars as it may have looked roughly 3.4 billion years ago. Data used in reconstruction are from NASA and the European Space Agency. Image credit: Gaetano Di Achille/University of Colorado

Estimated to be more than 3 billion years old, the lake appears to have covered as much as 80 square miles and was up to 1,500 feet deep — roughly the equivalent of Lake Champlain bordering the United States and Canada, said CU-Boulder Research Associate Gaetano Di Achille, who led the study. The shoreline evidence, found along a broad delta, included a series of alternating ridges and troughs thought to be surviving remnants of beach deposits.

“This is the first unambiguous evidence of shorelines on the surface of Mars,” said Di Achille. “The identification of the shorelines and accompanying geological evidence allows us to calculate the size and volume of the lake, which appears to have formed about 3.4 billion years ago.”

A paper on the subject by Di Achille, CU-Boulder Assistant Professor Brian Hynek and CU-Boulder Research Associate Mindi Searls, all of the Laboratory for Atmospheric and Space Physics, has been published online in Geophysical Research Letters, a publication of the American Geophysical Union.

Images used for the study were taken by a high-powered camera known as the High Resolution Imaging Science Experiment, or HiRISE. Riding on NASA’s Mars Reconnaissance Orbiter, HiRISE can resolve features on the surface down to one meter in size from its orbit 200 miles above Mars.

An analysis of the HiRISE images indicate that water carved a 30-mile-long canyon that opened up into a valley, depositing sediment that formed a large delta. This delta and others surrounding the basin imply the existence of a large, long-lived lake, said Hynek, also an assistant professor in CU-Boulder’s geological sciences department. The lake bed is located within a much larger valley known as the Shalbatana Vallis.

“Finding shorelines is a Holy Grail of sorts to us,” said Hynek.

In addition, the evidence shows the lake existed during a time when Mars is generally believed to have been cold and dry, which is at odds with current theories proposed by many planetary scientists, he said. “Not only does this research prove there was a long-lived lake system on Mars, but we can see that the lake formed after the warm, wet period is thought to have dissipated.”

Planetary scientists think the oldest surfaces on Mars formed during the wet and warm Noachan epoch from about 4.1 billion to 3.7 billion years ago that featured a bombardment of large meteors and extensive flooding. The newly discovered lake is believed to have formed during the Hesperian epoch and postdates the end of the warm and wet period on Mars by 300 million years, according to the study.

The deltas adjacent to the lake are of high interest to planetary scientists because deltas on Earth rapidly bury organic carbon and other biomarkers of life, according to Hynek. Most astrobiologists believe any present indications of life on Mars will be discovered in the form of subterranean microorganisms.

But in the past, lakes on Mars would have provided cozy surface habitats rich in nutrients for such microbes, Hynek said.

The retreat of the lake apparently was rapid enough to prevent the formation of additional, lower shorelines, said Di Achille. The lake probably either evaporated or froze over with the ice slowly turning to water vapor and disappearing during a period of abrupt climate change, according to the study.

Di Achille said the newly discovered pristine lake bed and delta deposits would be would be a prime target for a future landing mission to Mars in search of evidence of past life.

“On Earth, deltas and lakes are excellent collectors and preservers of signs of past life,” said Di Achille. “If life ever arose on Mars, deltas may be the key to unlocking Mars’ biological past.”

University of Colorado at Boulder

This false-color image of our glowing galactic neighbor, the Andromeda Galaxy, was created by layering 400 individual images captured by the PTF camera in February 2009. In one pointing, the PTF camera has a seven-square-degree field of view, equivalent to approximately 25 full moons. (Palomar Transient Factory/Peter Nugent, Berkeley Lab)

In fact, during the commissioning phase alone, the survey has already uncovered more than 40 supernovae, stellar explosions, and astronomers expect to discover thousands more each year. Such events occur about once a century in our own Milky Way galaxy and are visible for only a few months.

“This survey is a trail blazer in many ways – it is the first project dedicated solely to finding transient events, and as part of this mission we’ve worked with NERSC to develop an automated system that will sift through terabytes of astronomical data every night to find interesting events, and have secured time on some of the world’s most powerful ground-based telescopes to conduct immediate follow up observations as events are identified,” says Shrinivas Kulkarni, a professor of astronomy and planetary science at the California Institute of Technology (Caltech), and Director of Caltech Optical Observatories. He is also principle investigator of the PTF survey.

“This truly novel survey combines the power of a wide-field telescope, a high-resolution camera, and high-performance network and computing, as well as the ability to conduct rapid follow-up observations with telescopes around the globe for the first time,” says Peter Nugent, a computational staff scientist in Berkeley Lab’s Computational Research Division (CRD) and the NERSC Analytics Group. Nugent is also the Real-time Transient Detection Lead for the PTF project.

Every night the PTF camera – a 100-megapixel machine mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in Southern California – will automatically snap pictures of the sky, then send those images to NERSC for archiving via a high-speed network provided by DOE’s Energy Sciences Network (ESnet) and the National Science Foundation’s (NSF’s) High Performance Wireless Research and Education Network (HPWREN).

At NERSC, computers running machine-learning algorithms in the Real-time Transient Detection pipeline scour the PTF observations for “transient” sources, cosmic objects that change in brightness or position, by comparing the new observations with all of the data collected from previous nights. Once an interesting event is discovered, machines at NERSC will immediately, within minutes, send its coordinates to Palomar’s 60-inch telescope and others for follow up observations.

Astronomers using NERSC’s Real-Time Detection pipeline uncovered supernova SN2009av-1a in the act of exploding. At left, the image of a galaxy 800 million light-years away was created by layering observations taken by the Palomar Transient Factory camera from February 23-27. Second from left is the image captured by the PTF camera on February 28. Next, using the NERSC pipeline to digitally subtract the earlier image from the new one, scientists exposed this cosmic transient, a supernova. At right, subtracting the previous images from one taken March 2 showed the source getting brighter. Follow-up observations caught the Type Ia supernova, now called SN2009av, at peak brightness. (Palomar Transient Factory/Dovi Poznanski, Berkeley Lab)

“PTF is an example of the growing need to provide data services for science; it combines automated, real-time analysis with high-end systems and networks in a way that changes the way the scientific community works,” says NERSC Director Kathy Yelick.

“We are currently uncovering one event every 12 minutes. This project will be keeping the astronomical community busy for quite a while,” says Kulkarni.

“These tools are extremely valuable because they not only help us identify supernova, they uncover them while the star is in the act of exploding,” says Robert Quimby of Caltech, who is the software lead for the PTF program. “This gives us valuable information about how cosmic dust is spread across the universe.”

He notes that all chemical elements in the universe besides hydrogen and helium are created inside stars. When massive stars die in fiery supernova explosions, they blast these chemical creations out into space. The cosmic dust will eventually come together to form stars, planets, comets – even humans. Everything around us is made of stardust.

In addition to spreading stardust across the cosmos, some species of supernovae also play a vital role in helping us understand the nature of the universe. For example, because Type Ia supernova are relatively uniform in brightness, they act as cosmic lighthouses, helping astronomers judge distance. Many astronomers participating in the PTF survey are specifically searching for these cosmic creatures.

“It is very exciting to find so many supernovae, so early in the project. It’s like we’ve just turned on the spigot and are now waiting for the fire hose to blast,” says Quimby.

PTF is a collaboration of Berkeley Lab, Caltech, Columbia University, the NSF’s HPWREN, the Infrared Processing and Analysis Center, Las Cumbres Observatory Global Telescope Network, Oxford University, University of California at Berkeley, and the Weizmann Institute of Science, Israel. PTF is partly supported by DOE’s Scientific Discovery through Advanced Computing program; NERSC provided the storage and systems infrastructure. NERSC and ESnet are managed by the Berkeley Lab on behalf of the Office of Advanced Scientific Computing Research within the DOE Office of Science.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at http://www.lbl.gov.

Lawrence Berkeley National Laboratory (Berkeley Lab)

A comparison of all subdwarf Galactic orbits as seen from 150,000 light years above Galactic plane, without globular clusters. Courtesy / Adam Burgasser

Adam Burgasser and John Bochanski of the Massachusetts Institute of Technology presented the findings on Tuesday, June 9, in a press conference at the American Astronomical Society’s semi-annual meeting in Pasadena, Calif. The result clarifies the origins of these peculiar, faint stars, and may provide new details on the types of stars the Milky Way has acquired from other galaxies.

Ultracool subdwarfs were first recognized as a unique class of stars in 2003, and are distinguished by their low temperatures (“ultracool”) and low concentrations of elements other than hydrogen and helium (“subdwarf”). They sit at the bottom end of the size range for stars, and some are so small that they are closer to the planet-like objects called brown dwarfs. Only a few dozen ultracool subdwarfs are known today, as they are both very faint – up to 10,000 times fainter than the Sun – and extremely rare.

Burgasser, associate professor of physics at MIT and lead author of the study, was intrigued by the fast motions of ultracool subdwarfs, which zip past the Sun at astonishing speeds. “Most nearby stars travel more or less in tandem with the Sun tracing circular orbits around the center of the Milky Way once every 250 million years,” he explains. The ultracool subdwarfs, on the other hand, appear to pass us by at very high speeds, up to 500 km/s, or over a million miles per hour.

“If there are interstellar cops out there, these stars would surely lose their driver’s licenses,” says Burgasser.

Burgasser’s team of astronomers assembled measurements of the positions, distances and motions of roughly two dozen of these rare stars. Robyn Sanderson, co-author and MIT graduate student, then used these measurements to calculate the orbits of the subdwarfs using a numerical code developed to study galaxy collisions. Despite doing similar calculations for other types of low-mass stars, “these orbits were like nothing I’d ever seen before,” says Sanderson.

Sanderson’s calculations showed an unexpected diversity in the ultracool subdwarf orbits. Some plunge deep into the center of the Milky Way on eccentric, comet-like tracks; others make slow, swooping loops far beyond the Sun’s orbit. Unlike the majority of nearby stars, most of the ultracool subdwarfs spend a great deal of time thousands of light-years above or below the disk of the Milky Way.

“Someone living on a planet around one of these subdwarfs would have an incredible nighttime view of a beautiful spiral galaxy – our Milky Way – spread across the sky,” Burgasser speculates.

Sanderson’s orbit calculations confirm that all of the ultracool subdwarfs are part of the Milky Way’s halo, a widely dispersed population of stars that likely formed in the Milky Way’s distant past. However, one of the subdwarfs, a star named 2MASS 1227-0447 in the constellation Virgo, has an orbit indicating that it might have a very different lineage, possibly extragalactic.

“Our calculations show that this subdwarf travels up to 200,000 light years away from the center of the Galaxy, almost 10 times farther than the Sun,” says Bochanski, a postdoctoral researcher in Burgasser’s group at MIT. This is farther than many of the Milky Way’s nearest galactic neighbors, suggesting that this particular subdwarf may have originated somewhere else.

“Based on the size of its one billion-year orbit and direction of motion, we speculate that 2MASS 1227-0447 might have come from another, smaller galaxy that at some point got too close to the Milky Way and was ripped apart by gravitational forces,” explains Bochanksi.

Astronomers have previously identified streams of stars in the Milky Way originating from neighboring galaxies, but all have been distant, massive, red giant stars. The ultracool subdwarf identified by Burgasser and his team is the first nearby, low-mass star to be found on such a trajectory. “If we can identify what stream this star is associated with, or which dwarf galaxy it came from, we could learn more about the types of stars that have built up the Milky Way’s halo over the past 10 billion years,” says Burgasser.

The results presented at the meeting are based in part on two studies recently published in the Astrophysical Journal by Burgasser and coauthor Michael Cushing, a postdoctoral researcher at the University of Hawaii’s Institute for Astronomy.

Other authors of this paper are Andrew West of MIT; Dagny Looper of the University of Hawaii, Manoa; and Jacqueline Faherty of the American Museum of Natural History, New York, NY.

Artist's illustration of a gamma-ray burst occurring in a dusty region of intense star formation. If a dust cloud lies between the burst and Earth, the optical light will be almost entirely absorbed, but the gamma-rays and X-rays will easily penetrate the dust. New evidence suggests that most "dark" gamma-ray bursts — those without optical afterglows — form in similar dusty environments. (Aurore Simonnet/Sonoma State University, NASA Education & Public Outreach)

The conclusion comes from a survey of “dark” gamma-ray bursts — bright in gamma- and X-ray emissions, but with little or no visible light — reported today at a meeting of the American Astronomical Society in Pasadena, Calif., by astronomers from the University of California, Berkeley, and institutions around the world.

“Our study provides compelling evidence that a large fraction of star formation in the universe is hidden by dust in galaxies that do not appear otherwise dusty,” said Joshua Bloom, associate professor of astronomy at UC Berkeley and senior author of the study.

Star formation occurs in dense clouds that quickly fill with dust as the most massive stars rapidly age and explode, spewing newly created elements into the interstellar medium to seed new star formation. Hence, astronomers presume that a large amount of star formation is occurring in dust-filled galaxies, although actually measuring how much dust this process has built up in the most distant galaxies has proved extremely challenging.

Long-duration gamma-ray bursts, the most brilliant flashes of light in the universe, are thought to originate from the explosion of massive stars. These events create two pencil-like beams of light, akin to lighthouse beacons, bright enough to be seen from as far away as 13 billion light years, near the limits of the observable universe.

While most gamma-ray bursts continue to shine brightly in optical light for many hours after the gamma-ray emission subsides — a phenomenon known as an ‘afterglow’ — those with little or no detectable afterglow, dubbed “dark GRBs,” have puzzled astronomers. Some have speculated that most were so far away, and thus at such high redshift, that their optical afterglow shifted out of the wavelength region that optical telescopes can detect.

Redshift refers to the Doppler-shifted reddening of light from distant stars because they are speeding away from us, a consequence of the expansion of the universe after the Big Bang.

“Whatever the cause, it was like hearing the foghorn without seeing the lighthouse,” explained Bloom. “Something interesting was happening towards those shores.”

The new study, which focused on 14 bursts whose optical light was either much fainter than expected or completely absent, shows that almost every “dark” gamma-ray burst has a host galaxy detectable with Earth’s largest optical telescopes – in this case, the Keck 10-meter telescopes in Hawaii. Because these galaxies would not be detectable if they were at high redshifts, this indicates that most “dark” bursts are similar to normal bursts with an afterglow, except that nearly all of the visible light is obscured by patchy dust within these host galaxies.

The findings suggest that gamma-ray bursts may be able to help track the rate at which stars form and die in distant galaxies, and confirm previous estimates that “25 percent of the time, when massive stars form, they form in a dusty place,” said UC Berkeley graduate student Daniel Perley and lead author of the study.

“However, based on our survey of these dark gamma-ray bursts, the galaxies look normal and not dust filled,” he said. “The dust is probably in clouds and knots around the forming stars.”

Mosaic of 11 "dark" gamma-ray burst host galaxies imaged at the W. M. Keck Observatory in Hawaii. The circles indicate the position of the burst determined by NASA's Swift satellite or from ground-based optical or infrared imaging and, in all of the cases shown, contain a faint host galaxy. At distances of billions of light years from Earth, these galaxies appear only as faint smudges to ground-based telescopes. (Daniel Perley, Joshua Bloom/UC Berkeley)

Perley, Bloom, UC Berkeley post-doctoral fellow S. Bradley Cenko and their colleagues report the results at a 9 a.m. PDT press conference today, and have submitted a paper about the study to The Astronomical Journal.

Bloom and Perley were using some of the world’s largest telescopes, the twin 10-meter telescopes of the W. M. Keck Observatory, to look for the host galaxies of “dark” gamma-ray bursts when Cenko, recently arrived from Palomar Observatory, suggested focusing on a specific sample of bursts observed by Palomar’s 60-inch telescope. Through March 2008, Palomar conducted follow-up observations of 29 bursts discovered by NASA’s Swift gamma-ray satellite, 14 of which were classified as dark. The Swift mission, equipped with a gamma-ray detector and X-ray, ultraviolet and optical telescopes, is operated by NASA’s Goddard Spaceflight Center.

For 11 of these 14 dark bursts, the team successfully detected a distant galaxy hosting the explosion, while the remaining three bursts without detectable hosts had faint optical counterparts. This indicates that none of these bursts had come from the most distant regions of the universe, since at distances greater than about 12.9 billion light years all the detectable light from both the afterglow and the host galaxy would be shifted into the infrared due to the expansion of the universe.

“And while 12.9 billion light years is a large distance even by most astronomers’ standards, gamma-ray bursts are so powerful that if these were frequent occurrences 13 billion years ago, we ought to be detecting large numbers of those same explosions today as high redshift events,” Cenko said. “We don’t, which indicates that the first stars formed at a less frenzied pace than some models suggested.”

The lack of any very high redshift events in the sample indicates that these distant explosions cannot comprise more than a few percent of all gamma-ray bursts, Cenko said. However, such distant bursts are known to exist. Just two months ago, a gamma-ray burst at a distance of 13.1 billion years was discovered.

“Putting this recent event together with the others in our study, for the first time we can provide both an upper and lower limit to the fraction of gamma-ray bursts at very high redshift,” Perley said. Specifically, the authors conclude that the high redshift fraction is between 0.2 and 7 percent.

Because none of the 14 bursts studied in the survey is at this distance, by far the most likely cause of the bursts’ optical dimness is dust inside the host galaxy absorbing light from the afterglow before it escapes, the team concluded. However, the starlight shows no obvious signatures of dust, indicating that the dust may be hiding in patches or clouds where it is difficult to detect.

Consequently, there could be much more dust than has been suspected as the result of measurements using other techniques, and “dark gamma-ray bursts could provide a complementary way of answering the question of how much star formation was going on inside galaxies in the early universe,” Perley said.

The authors of the report propose more radio and sub-millimeter observations of the host galaxies of dark gamma-ray bursts to better understand the reasons behind the obscured optical emissions from GRBs.

Coauthors of the paper were Hsiao-Wen Chen of the University of Chicago; Nathaniel R. Butler and D. Starr of UC Berkeley; D. Kocevski of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University; J. X. Prochaska of the University of California’s Lick Observatory; M. Brodwin and A. M. Soderberg of the Harvard-Smithsonian Center for Astrophysics; K. Glazebrook of the Swinburne University of Technology in Australia; M. M. Kasliwal, S. R. Kulkarni and E. O. Ofek of the California Institute of Technology; S. Lopez of the University of Chile in Santiago; and M. Pettini of the Institute of Astronomy in Cambridge, U.K.

The work was funded in part by the Las Cumbres Observatory Global Telescope Network, the NASA/Swift guest observer program, Gary and Cynthia Bengier and the Richard & Rhoda Goldman Fund.

By Robert Sanders – University of California, Berkeley