Wednesday, September 29, 2010

Newly discovered planet may be first truly habitable exoplanet

Artist illustration of a super Earth around Gliese 581

Discovery suggests our galaxy may be teeming with potentially habitable planets

SANTA CRUZ, CA--A team of planet hunters led by astronomers at the University of California, Santa Cruz, and the Carnegie Institution of Washington has announced the discovery of an Earth-sized planet (three times the mass of Earth) orbiting a nearby star at a distance that places it squarely in the middle of the star's "habitable zone," where liquid water could exist on the planet's surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one.

To astronomers, a "potentially habitable" planet is one that could sustain life, not necessarily one that humans would consider a nice place to live. Habitability depends on many factors, but liquid water and an atmosphere are among the most important.

"Our findings offer a very compelling case for a potentially habitable planet," said Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz. "The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common."

The findings are based on 11 years of observations at the W. M. Keck Observatory in Hawaii. "Advanced techniques combined with old-fashioned ground-based telescopes continue to lead the exoplanet revolution," said Paul Butler of the Carnegie Institution. "Our ability to find potentially habitable worlds is now limited only by our telescope time."

Vogt and Butler lead the Lick-Carnegie Exoplanet Survey. The team's new findings are reported in a paper to be published in the Astrophysical Journal and posted online at arXiv.org. Coauthors include associate research scientist Eugenio Rivera of UC Santa Cruz; associate astronomer Nader Haghighipour of the University of Hawaii-Manoa; and research scientists Gregory Henry and Michael Williamson of Tennessee State University.

The paper reports the discovery of two new planets around the nearby red dwarf star Gliese 581. This brings the total number of known planets around this star to six, the most yet discovered in a planetary system other than our own solar system. Like our solar system, the planets around Gliese 581 have nearly circular orbits.

The most interesting of the two new planets is Gliese 581g, with a mass three to four times that of the Earth and an orbital period of just under 37 days. Its mass indicates that it is probably a rocky planet with a definite surface and that it has enough gravity to hold on to an atmosphere, according to Vogt.

Gliese 581, located 20 light years away from Earth in the constellation Libra, has a somewhat checkered history of habitable-planet claims. Two previously detected planets in the system lie at the edges of the habitable zone, one on the hot side (planet c) and one on the cold side (planet d). While some astronomers still think planet d may be habitable if it has a thick atmosphere with a strong greenhouse effect to warm it up, others are skeptical. The newly discovered planet g, however, lies right in the middle of the habitable zone.

"We had planets on both sides of the habitable zone--one too hot and one too cold--and now we have one in the middle that's just right," Vogt said.

The planet is tidally locked to the star, meaning that one side is always facing the star and basking in perpetual daylight, while the side facing away from the star is in perpetual darkness. One effect of this is to stabilize the planet's surface climates, according to Vogt. The most habitable zone on the planet's surface would be the line between shadow and light (known as the "terminator"), with surface temperatures decreasing toward the dark side and increasing toward the light side.

"Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude," Vogt said.

The researchers estimate that the average surface temperature of the planet is between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius). Actual temperatures would range from blazing hot on the side facing the star to freezing cold on the dark side.

If Gliese 581g has a rocky composition similar to the Earth's, its diameter would be about 1.2 to 1.4 times that of the Earth. The surface gravity would be about the same or slightly higher than Earth's, so that a person could easily walk upright on the planet, Vogt said.

The new findings are based on 11 years of observations of Gliese 581 using the HIRES spectrometer (designed by Vogt) on the Keck I Telescope at the W. M. Keck Observatory in Hawaii. The spectrometer allows precise measurements of a star's radial velocity (its motion along the line of sight from Earth), which can reveal the presence of planets. The gravitational tug of an orbiting planet causes periodic changes in the radial velocity of the host star. Multiple planets induce complex wobbles in the star's motion, and astronomers use sophisticated analyses to detect planets and determine their orbits and masses.

"It's really hard to detect a planet like this," Vogt said. "Every time we measure the radial velocity, that's an evening on the telescope, and it took more than 200 observations with a precision of about 1.6 meters per second to detect this planet."

To get that many radial velocity measurements (238 in total), Vogt's team combined their HIRES observations with published data from another group led by the Geneva Observatory (HARPS, the High Accuracy Radial velocity Planetary Search project).

In addition to the radial velocity observations, coauthors Henry and Williamson made precise night-to-night brightness measurements of the star with one of Tennessee State University's robotic telescopes. "Our brightness measurements verify that the radial velocity variations are caused by the new orbiting planet and not by any process within the star itself," Henry said.

The researchers also explored the implications of this discovery with respect to the number of stars that are likely to have at least one potentially habitable planet. Given the relatively small number of stars that have been carefully monitored by planet hunters, this discovery has come surprisingly soon.

"If these are rare, we shouldn't have found one so quickly and so nearby," Vogt said. "The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that's a large number. There could be tens of billions of these systems in our galaxy."

***

This research was supported by grants from the National Science Foundation and NASA.

Contact:

Tim Stephens
stephens@ucsc.edu
831-459-2495
University of California - Santa Cruz

Milky Way Sidelined in Galactic Tug of War

This plot shows the simulated gas distribution of the Magellanic System resulting from the tidal encounter between the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) as they orbit our home Milky Way Galaxy. The entire sky is plotted in galactocentric coordinates of longitude and latitude. The Magellanic Stream is the pronounced tail of material that stretches 150 degrees across the southern sky. The solid line shows the calculated path of the LMC and the dotted line is the path of the SMC. The color range from dark to light shows the density (lower to higher) of the hydrogen gas making up the Magellanic Stream and the Bridge that connects the two dwarf galaxies. Credit: Plot by G. Besla, Milky Way background image by Axel Mellinger (used with permission). Low Resolution Image (jpg)

Cambridge, MA - The Magellanic Stream is an arc of hydrogen gas spanning more than 100 degrees of the sky as it trails behind the Milky Way's neighbor galaxies, the Large and Small Magellanic Clouds. Our home galaxy, the Milky Way, has long been thought to be the dominant gravitational force in forming the Stream by pulling gas from the Clouds. A new computer simulation by Gurtina Besla (Harvard-Smithsonian Center for Astrophysics) and her colleagues now shows, however, that the Magellanic Stream resulted from a past close encounter between these dwarf galaxies rather than effects of the Milky Way.

"The traditional models required the Magellanic Clouds to complete an orbit about the Milky Way in less than 2 billion years in order for the Stream to form," says Besla. Other work by Besla and her colleagues, and measurements from the Hubble Space Telescope by colleague Nitya Kallivaylil, rule out such an orbit, however, suggesting the Magellanic Clouds are new arrivals and not long-time satellites of the Milky Way.

This creates a problem: How can the Stream have formed without a complete orbit about the Milky Way?

To address this, Besla and her team set up a simulation assuming the Clouds were a stable binary system on their first passage about the Milky Way in order to show how the Stream could form without relying on a close encounter with the Milky Way.

The team postulated that the Magellanic Stream and Bridge are similar to bridge and tail structures seen in other interacting galaxies and, importantly, formed before the Clouds were captured by the Milky Way.

"While the Clouds didn't actually collide," says Besla, "they came close enough that the Large Cloud pulled large amounts of hydrogen gas away from the Small Cloud. This tidal interaction gave rise to the Bridge we see between the Clouds, as well as the Stream."

"We believe our model illustrates that dwarf-dwarf galaxy tidal interactions are a powerful mechanism to change the shape of dwarf galaxies without the need for repeated interactions with a massive host galaxy like the Milky Way."

While the Milky Way may not have drawn the Stream material out of the Clouds, the Milky Way's gravity now shapes the orbit of the Clouds and thereby controls the appearance of the tail.

"We can tell this from the line-of-sight velocities and spatial location of the tail observed in the Stream today," says team member Lars Hernquist of the Center.

The paper describing this work has been accepted for publication in the October 1 issue of the Astrophysical Journal Letters and is available online at http://arxiv.org/abs/1008.2210v1.

Besla's co-authors were Nitya Kallivayalil (MIT Kavli Institute for Astrophysics & Space Research), Lars Hernquist, R. P. van der Marel (STScI), T.J. Cox (Carnegie Observatories) and D. Keres (Harvard-Smithsonian Center for Astrophysics). Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463,
cpulliam@cfa.harvard.edu

An Elegant Galaxy in an Unusual Light

PR Image eso1038a
HAWK-I infrared image of the spectacular barred spiral galaxy NGC 1365

Comparison of visible-light and infrared images of the galaxy NGC 1365

PR Image eso1038c
NGC 1365 in the constellation of Fornax

Zooming in on the HAWK-I infrared image of the spectacular barred spiral galaxy NGC 1365

Visible/infrared cross-fade of images of the spectacular barred spiral galaxy NGC 1365

A new image taken with the powerful HAWK-I camera on ESO’s Very Large Telescope at Paranal Observatory in Chile shows the beautiful barred spiral galaxy NGC 1365 in infrared light. NGC 1365 is a member of the Fornax cluster of galaxies, and lies about 60 million light-years from Earth.

NGC 1365 is one of the best known and most studied barred spiral galaxies and is sometimes nicknamed the Great Barred Spiral Galaxy because of its strikingly perfect form, with the straight bar and two very prominent outer spiral arms. Closer to the centre there is also a second spiral structure and the whole galaxy is laced with delicate dust lanes.

This galaxy is an excellent laboratory for astronomers to study how spiral galaxies form and evolve. The new infrared images from HAWK-I are less affected by the dust that obscures parts of the galaxy than images in visible light (potw1037a) and they reveal very clearly the glow from vast numbers of stars in both the bar and the spiral arms. These data were acquired to help astronomers understand the complex flow of material within the galaxy and how it affects the reservoirs of gas from which new stars can form. The huge bar disturbs the shape of the gravitational field of the galaxy and this leads to regions where gas is compressed and star formation is triggered. Many huge young star clusters trace out the main spiral arms and each contains hundreds or thousands of bright young stars that are less than ten million years old. The galaxy is too remote for single stars to be seen in this image and most of the tiny clumps visible in the picture are really star clusters. Over the whole galaxy, stars are forming at a rate of about three times the mass of our Sun per year.

While the bar of the galaxy consists mainly of older stars long past their prime, many new stars are born in stellar nurseries of gas and dust in the inner spiral close to the nucleus. The bar also funnels gas and dust gravitationally into the very centre of the galaxy, where astronomers have found evidence for the presence of a super-massive black hole, well hidden among myriads of intensely bright new stars.

NGC 1365, including its two huge outer spiral arms, spreads over around 200 000 light-years. Different parts of the galaxy take different times to make a full rotation around the core of the galaxy, with the outer parts of the bar completing one circuit in about 350 million years. NGC 1365 and other galaxies of its type have come to more prominence in recent years with new observations indicating that the Milky Way could also be a barred spiral galaxy. Such galaxies are quite common — two thirds of spiral galaxies are barred according to recent estimates, and studying others can help astronomers understand our own galactic home.

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 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 and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

NGC 1365 in visible light

Contacts

Richard Hook
ESO Paranal/La SiIlla and E-ELT Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

Monday, September 27, 2010

Pan-STARRS Discovers Its First Potentially Hazardous Asteroid

Two images of 2010 ST3 (circled in green) taken by PS1 about 15 minutes apart on the night of September 16 show the asteroid moving against the background field of stars and galaxies. Each image is about 100 arc seconds across. Credit: PS1SC. High Resolution Image - Low Resolution Image (jpg)

Cambridge, MA - The Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) PS1 telescope has discovered an asteroid that will come within 4 million miles of Earth in mid-October. The object is about 150 feet in diameter and was discovered in images acquired on September 16, when it was about 20 million miles away.

It is the first "potentially hazardous object" (PHO) to be discovered by the Pan-STARRS survey and has been given the designation "2010 ST3."

"Although this particular object won't hit Earth in the immediate future, its discovery shows that Pan-STARRS is now the most sensitive system dedicated to discovering potentially dangerous asteroids," said Robert Jedicke, a University of Hawaii member of the PS1 Scientific Consortium, who is working on the asteroid data from the telescope. "This object was discovered when it was too far away to be detected by other asteroid surveys," Jedicke noted.

The Harvard-Smithsonian Center for Astrophysics is a major partner in the Consortium.

Most of the largest PHOs have already been catalogued, but scientists suspect that there are many more under a mile across that have not yet been discovered. These could cause devastation on a regional scale if they ever hit our planet. Such impacts are estimated to occur once every few thousand years.

Timothy Spahr, director of the Minor Planet Center (MPC), said, "I congratulate the Pan-STARRS project on this discovery. It is proof that the PS1 telescope, with its Gigapixel Camera and its sophisticated computerized system for detecting moving objects, is capable of finding potentially dangerous objects that no one else has found." The MPC, located in Cambridge, Mass., was established by the International Astronomical Union in 1947 to collect and disseminate positional measurements for asteroids and comets, to confirm their discoveries, and to give them preliminary designations.

Pan-STARRS expects to discover tens of thousands of new asteroids every year with sufficient precision to accurately calculate their orbits around the sun. Any sizable object that looks like it may come close to Earth within the next 50 years or so will be labeled "potentially hazardous" and carefully monitored. NASA experts believe that, given several years warning, it should be possible to organize a space mission to deflect any asteroid that is discovered to be on a collision course with Earth.

Pan-STARRS has broader goals as well. PS1 and its bigger brother, PS4, which will be operational later in this decade, are expected to discover a million or more asteroids in total, as well as more distant targets such as variable stars, supernovas, and mysterious bursts from galaxies across more than half the universe. PS1 became fully operational in June 2010.

This release is being issued jointly with the University of Hawaii Institute for Astronomy.

The PS1 surveys have been made possible through contributions of the PS1 Science Consortium: the University of Hawaii Institute for Astronomy; the Pan-STARRS Project Office; the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching; the Johns Hopkins University; Durham University; the University of Edinburgh; the Queen's University Belfast; the Harvard-Smithsonian Center for Astrophysics; the Las Cumbres Observatory Global Telescope Network, Inc.; and the National Central University of Taiwan. Construction funding for Pan-STARRS (short for Panoramic Survey Telescope & Rapid Response System) has been provided by the U.S. Air Force Research Laboratory.Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Sunday, September 26, 2010

The Coolest Brown Dwarf: A Neighbor in Space

Figure 1: Original near-infrared (J band) image of UGPS J0722-05 from the UKIRT Infrared Deep Sky Survey.

Figure 2: Gemini North NIRI spectra of UGPS J0722-05. Broad dips in the signal are caused by water and methane absorption at 1.1, 1.4, 1.8, and 2.2 microns.

A team of astronomers, led by Phil Lucas of Hertfordshire University in the UK, have discovered what is currently the coldest star-like object. The object, called UGPS J0722-05, is also of particular interest because it is one of our closest neighbors.

The result is published in The Monthly Notices of the Royal Astronomical Society and can be accessed here.

UGPS J0722-05 is a cold brown dwarf; these small Jupiter-sized objects are hard to find as they are very faint, and they become fainter, and so even harder to find, with decreasing temperature. UGPS J0722-05 was identified as the only possible brown dwarf in a search of over 600 million sources detected in the plane of our Galaxy by the UK Infrared Telescope (UKIRT) as part of the UKIRT Infrared Deep Sky Survey (UKIDSS). Figure 1 shows the UKIDSS discovery image.

Using the Near-Infrared Imager and Spectrometer (NIRI) on Gemini North a spectrum of UGPS J0722-05 was obtained in early February of 2010. This spectrum is shown in Figure 2 and it clearly shows the extremely strong absorption bands of water and methane, confirming that it is indeed a brown dwarf, and specifically a cool, so-called, T-class brown dwarf. The coolest known dwarfs, the latest-type T dwarfs, are difficult to distinguish from each other in the near-infrared because these bands are so very strong - there is no more water or methane to be absorbed to increase the depth of the spectral features. However, the width of the bands is slightly stronger in UGPS J0722-05 than in any other known brown dwarf, suggesting a lower temperature.

At very low temperatures, more significant changes occur at mid-infrared wavelengths, where 60-80% of the total energy emerges. The investigators obtained longer wavelength imaging data using the IRAC camera on the Spitzer Space Telescope and the Thermal-Region Camera and Spectrograph (T-ReCS) on Gemini South. Theoretical modeling fills in the gaps between the observational data, allowing a determination of the total energy radiated.

With additional near-infrared images, the movement of UGPS J0722-05 with respect to background stars allowed its distance to be determined as well. At only four parsecs (about 13 light years) away, this dwarf is one of the closest objects to the Sun outside the Solar System. Combining this distance with the measured energy shows that the luminosity of UGPS J0722-05 is less than one-millionth of that of the Sun.

Brown dwarfs cool over time as their cores are not hot enough to ignite hydrogen fusion. This cooling is well understood, and allows an estimate of the temperature and mass of a brown dwarf based on its luminosity. The luminosity indicates that the surface temperature of UGPS J0722-05 is only 500K (250ºC or 480ºF) and its mass only 5 to 15 times greater that of Jupiter. Another way of looking at UGPS J0722-05 is that it is an isolated object very much like a free-floating planet very close to the Sun.

Thursday, September 23, 2010

New astronomical phenomenon: Coreshine provides insight into stellar births

Science is literally in the dark when it comes to the birth of stars, which occurs deep inside clouds of gas and dust: These clouds are completely opaque to ordinary light. Now, a group of astronomers has discovered a new astronomical phenomenon that appears to be common in such clouds, and promises a new window onto the earliest phases of star formation. The phenomenon – light that is scattered by unexpectedly large grains of dust, which the discoverers have termed “coreshine” – probes the dense cores where stars are born. The results are being published in the September 24, 2010 edition of the journal Science.

Figure 1: The molecular cloud CB 244 in the constellation Cepheus, 650 light-years from Earth. In such clouds, the Milky Way's light is scattered in different ways: Visible light is predominantly scattered by small grains of dust in the cloud's outer regions (“cloudshine”). The false-color image shows mid-infrared light scattered by larger grains of dust in the interior of the cloud, the newly discovered “coreshine”. Image: MPIA [Larger version for download]

Figure 2: Image: MPIA, J. Steinacker et al.
[
Larger version for download]

Figure 3: This image shows the molecular cloud L 183 as observed by two telescopes: the SPITZER Space Telescope in the mid-infrared (wavelength: 3.6 micrometers) and the Canada France Hawaii Telescope in near-infrared light (wavelength: 0.9 micrometers). In near-infrared light (shown in blue, false-color), there is “cloudshine”: the scattering of light by smaller dust grains in the cloud's outer regions. The mid-infrared image (yellow, false-color) shows the newly discovered “coreshine”: light scattered by larger grains of dust in the cloud's denser core regions.
Image: MPIA, J. Steinacker et al. [Larger version for download]

Stars are formed as the dense core regions of cosmic clouds of gas and dust (“molecular clouds”) collapse under their own gravity. As a result, matter in these regions becomes ever denser and hotter until, finally, nuclear fusion is ignited: a star is born. This is how our own star, the Sun, came into being; the fusion processes are responsible for the Sun’s light, on which life on Earth depends. The dust grains contained in the collapsing clouds are the raw material out of which an interesting by-product of star formation is made: solar systems and Earth-like planets.

What happens during the earliest phases of this collapse is largely unknown. Enter an international team of astronomers led by Laurent Pagani (LERMA, Observatoire de Paris) and Jürgen Steinacker (Max Planck Institute for Astronomy, Heidelberg, Germany), who have discovered a new phenomenon which promises information about the crucial earliest phase of the formation of stars and planets: “coreshine”, the scattering of mid-infrared light (which is ubiquitous in our galaxy) by dust grains inside such dense clouds. The scattered light carries information about the size and density of the dust particles, about the age of the core region, the spatial distribution of the gas, the prehistory of the material that will end up in planets, and about chemical processes in the interior of the cloud.

The discovery is based on observations with NASA’s SPITZER Space Telescope. As published this February, Steinacker, Pagani and colleagues from Grenoble and Pasadena detected unexpected mid-infrared radiation from the molecular cloud L 183 in the constellation Serpens Cauda (“Head of the snake”), at a distance of 360 light-years. The radiation appeared to originate in the cloud’s dense core. Comparing their measurements with detailed simulations, the astronomers were able to show that they were dealing with light scattered by dust particles with diameters of around 1 micrometer (one millionth of a meter). The follow-up research that is now being published in Science clinched the case: The researchers examined 110 molecular clouds at distances between 300 and 1300 light-years, which had been observed with Spitzer in the course of several survey programs. The analysis showed that the L 183 radiation was more than a fluke. Instead, it revealed that coreshine is a widespread astronomical phenomenon: Roughly half of the cloud cores exhibited coreshine, mid-infrared radiation associated with scattering from dust grains in their densest regions.

The discovery of coreshine suggests a host of follow-on projects – for the SPITZER Space Telescope as well as for the James Webb Space Telescope, which is due to be launched in 2014. The first coreshine observations have yielded promising results: The unexpected presence of larger grains of dust (diameters of around a millionth of a meter) shows that these grains begin their growth even before cloud collapse commences. An observation of particular interest concerns clouds in the Southern constellation Vela, in which no coreshine is present. It is known that this region was disturbed by several stellar (supernova) explosions. Steinacker and his colleagues hypothesize that these explosions have destroyed whatever larger dust grains had been present in this region.

Contact information

Dr. habil. Jürgen Steinacker (Lead author)
Max Planck Institute for Astronomy
Phone: (+33) 476 43 02 32
E-mail: stein@mpia.de

Prof. Dr. Thomas Henning (Co-author)
Max Planck Institute for Astronomy
Phone: (+49|0) 6221 – 528 200
E-mail: henning@mpia.de

Dr. Markus Pössel (Public relations)
Max Planck Institute for Astronomy
Phone: (+49|0) 6221 – 528 261
E-mail: poessel@mpia.de

Dust Models Paint Alien's View of Solar System

These images, produced by computer models that track the movement of icy grains, represent infrared snapshots of Kuiper Belt dust as seen by a distant observer. For the first time, the models include the effects of collisions among grains. By ramping up the collision rate, the simulations show how the distant view of the solar system might have changed over its history. Credit: NASA/Goddard/Marc Kuchner and Christopher Stark. View larger - View unlabeled version

Simulated images of the ancient Kuiper Belt bear a striking resemblance to this Hubble Space Telescope view of the dusty ring around Fomalhaut, a young star located 25 light-years away in the constellation Piscis Austrinus. In 2008, Hubble spotted a planet orbiting inside the ring. The bright central star is masked out so that the faint ring can be seen. Credit: NASA/ESA/P. Kalas (Univ. of California, Berkeley) et al. View larger

New simulations of icy grains moving through the solar system reveal how the ancient Kuiper Belt once appeared strikingly similar to the dusty rings found around some stars today. Credit: NASA's Goddard Space Flight Center. Video formats

New supercomputer simulations tracking the interactions of thousands of dust grains show what the solar system might look like to alien astronomers searching for planets. The models also provide a glimpse of how this view might have changed as our planetary system matured.

"The planets may be too dim to detect directly, but aliens studying the solar system could easily determine the presence of Neptune -- its gravity carves a little gap in the dust," said Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. who led the study. "We're hoping our models will help us spot Neptune-sized worlds around other stars."

fragile grains. A paper on the new models, which are the first to include collisions among grains, appeared in the Sept. 7 edition of The Astronomical Journal.

"People felt that the collision calculation couldn't be done because there are just too many of these tiny grains too keep track of," Kuchner said. "We found a way to do it, and that has opened up a whole new landscape."

With the help of NASA's Discover supercomputer, the researchers kept tabs on 75,000 dust particles as they interacted with the outer planets, sunlight, the solar wind -- and each other.

The size of the model dust ranged from about the width of a needle's eye (0.05 inch or 1.2 millimeters) to more than a thousand times smaller, similar in size to the particles in smoke. During the simulation, the grains were placed into one of three types of orbits found in today's Kuiper Belt at a rate based on current ideas of how quickly dust is produced.

From the resulting data, the researchers created synthetic images representing infrared views of the solar system seen from afar.

Through gravitational effects called resonances, Neptune wrangles nearby particles into preferred orbits. This is what creates the clear zone near the planet as well as dust enhancements that precede and follow it around the sun.

"One thing we've learned is that, even in the present-day solar system, collisions play an important role in the Kuiper Belt's structure," Stark explained. That's because collisions tend to destroy large particles before they can drift too far from where they're made. This results in a relatively dense dust ring that straddles Neptune's orbit.

To get a sense of what younger, heftier versions of the Kuiper Belt might have looked like, the team sped up the dust production rate. In the past, the Kuiper Belt contained many more objects that crashed together more frequently, generating dust at a faster pace. With more dust particles came more frequent grain collisions.

Using separate models that employed progressively higher collision rates, the team produced images roughly corresponding to dust generation that was 10, 100 and 1,000 times more intense than in the original model. The scientists estimate the increased dust reflects conditions when the Kuiper Belt was, respectively, 700 million, 100 million and 15 million years old.

"We were just astounded by what we saw," Kuchner said.

As collisions become increasingly important, the likelihood that large dust grains will survive to drift out of the Kuiper Belt drops sharply. Stepping back through time, today's broad dusty disk collapses into a dense, bright ring that bears more than a passing resemblance to rings seen around other stars, especially Fomalhaut.

"The amazing thing is that we've already seen these narrow rings around other stars," Stark said. "One of our next steps will be to simulate the debris disks around Fomalhaut and other stars to see what the dust distribution tells us about the presence of planets."

The researchers also plan to develop a more complete picture of the solar system's dusty disk by modeling additional sources closer to the sun, including the main asteroid belt and the thousands of so-called Trojan asteroids corralled by Jupiter's gravity.

Related Links:

Geeked on Goddard: Bodies in motion
NASA Supercomputer Shows How Dust Rings Point to Exo-Earths
Twin Keck Telescopes Probe Dual Dust Disks
Warped Debris Disks around Stars are Blowin’ in the Wind

Goddard Release No. 10-085

Francis Reddy
NASA's Goddard Space Flight Center
301-286-4453
francis.j.reddy@nasa.gov

Shining Starlight on the Dark Cocoons of Star Birth

This series of images from NASA's Spitzer Space Telescope shows a dark mass of gas and dust, called a core, where new stars and planets will likely spring up. Image credit: NASA/JPL-Caltech/Observatoire de Paris/CNRS. Full image and caption

Astronomers have discovered a new, cosmic phenomenon, termed "coreshine," which is revealing new information about how stars and planets come to be.

The scientists used data from NASA's Spitzer Space Telescope to measure infrared light deflecting off cores -- cold, dark cocoons where young stars and planetary systems are blossoming. This coreshine effect, which occurs when starlight from nearby stars bounces off the cores, reveals information about their age and consistency. In a new paper, to be published Friday, Sept. 24, in the journal Science, the team reports finding coreshine across dozens of dark cores.

"Dark clouds in our Milky Way galaxy, far from Earth, are huge places where new stars are born. But they are shy and hide themselves in a shroud of dust so that we cannot see what happens inside," said Laurent Pagani of the Observatoire de Paris and the Centre National de la Recherche Scientifique, both in France. "We have found a new way to peer into them. They are like ghosts because we see them but we also see through them."

Pagani and his team first observed one case of the coreshine phenomenon in 2009. They were surprised to see that starlight was scattering off a dark core in the form of infrared light that Spitzer could see. They had thought the grains of dust making up the core were too small to deflect the starlight; instead, they expected the sunlight would travel straight through. Their finding told them that the dust grains were bigger than previously thought -- about 1 micron instead of 0.1 micron (a typical human hair is about 100 microns).

That might not sound like a big difference, but it can significantly change astronomers' models of star and planet formation. For one thing, the larger grain size means that planets -- which form as dust circling young stars sticks together -- might take shape more quickly. In other words, the tiny seeds for planet formation may be forming very early on, when a star is still in its pre-embryonic phase.

But this particular object observed in 2009 could have been a fluke. The researchers did not know if what they found was true of other dark clouds -- until now. In the new study, they examine 110 dark cores, and find that about half of them exhibit coreshine.

The finding amounts to a new tool for not only studying the dust making up the dark cores, but also for assessing their age. The more developed star-forming cores will have larger dust grains, so, using this tool, astronomers can better map their ages across our Milky Way galaxy. Coreshine can also help in constructing three-dimensional models of the cores -- the deflected starlight is scattered in a way that is dependent on the cloud structures.

Said Pagani, "We're opening a new window on the realm of dark, star-forming cores."

Other authors are Aurore Bacmann of the Astrophysics Laboratory of Grenoble, France, and Jürgen Steinacker, Amelia Stutz and Thomas Henning of the Max-Planck Institute for Astronomy, Germany. Steinacker is also with the Observatoire de Paris, and Stutz is also with the University of Arizona, Tucson.

The Spitzer measurements are based on data from the mission's public archive, taken before the telescope ran out of its liquid coolant in May 2009 and began its current warm mission.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer .
Whitney Clavin/Guy Webster 818-354-4673/6278 Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Wednesday, September 22, 2010

PR Image heic1015a
Image credit: NASA, ESA

PR Video heic1015a
Zooming in on the Lagoon Nebula

PR Video heic1015b
Panning across the Lagoon Nebula

A spectacular new NASA/ESA Hubble Space Telescope image reveals the heart of the Lagoon Nebula. Seen as a massive cloud of glowing dust and gas, bombarded by the energetic radiation of new stars, this placid name hides a dramatic reality.

The Advanced Camera for Surveys (ACS) on the NASA/ESA Hubble Space Telescope has captured a dramatic view of gas and dust sculpted by intense radiation from hot young stars deep in the heart of the Lagoon Nebula (Messier 8). This spectacular object is named after the wide, lagoon-shaped dust lane that crosses the glowing gas of the nebula.

This structure is prominent in wide-field images, but cannot be seen in this close-up. However the strange billowing shapes and sandy texture visible in this image make the Lagoon Nebula’s watery name eerily appropriate from this viewpoint too.

Located four to five thousand light-years away, in the constellation of Sagittarius (the Archer), Messier 8 is a huge region of star birth that stretches across one hundred light-years. Clouds of hydrogen gas are slowly collapsing to form new stars, whose bright ultraviolet rays then light up the surrounding gas in a distinctive shade of red.

The wispy tendrils and beach-like features of the nebula are not caused by the ebb and flow of tides, but rather by ultraviolet radiation’s ability to erode and disperse the gas and dust into the distinctive shapes that we see.

In recent years astronomers probing the secrets of the Lagoon Nebula have found the first unambiguous proof that star formation by accretion of matter from the gas cloud is ongoing in this region.

Young stars that are still surrounded by an accretion disc occasionally shoot out long tendrils of matter from their poles. Several examples of these jets, known as Herbig-Haro objects, have been found in this nebula in the last five years, providing strong support for astronomers’ theories about star formation in such hydrogen-rich regions.

The Lagoon Nebula is faintly visible to the naked eye on dark nights as a small patch of grey in the heart of the Milky Way. Without a telescope, the nebula looks underwhelming because human eyes are unable to distinguish clearly between colours at low light levels.

Charles Messier, the 18th century French astronomer, observed the nebula and included it in his famous astronomical catalogue, from which the nebula’s alternative name comes. But his relatively small refracting telescope would only have hinted at the dramatic structures and colours now visible thanks to Hubble.

Notes

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

Contacts

Oli Usher
Junior ESA/Hubble Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: ousher@eso.org

Spring on Titan brings sunshine and patchy clouds

False-color image of cloud cover dissolving over Titan's north pole and clouds appearing in the southern mid latitudes. Full image and caption

Graphic of cloud coverage over Cassini's six years of observations
Full image and caption - Enlarge image

The northern hemisphere of Saturn's moon Titan is set for mainly fine spring weather, with polar skies clearing since the equinox in August last year. The visual and infrared mapping spectrometer (VIMS) aboard NASA's Cassini spacecraft has been monitoring clouds on Titan regularly since the spacecraft entered orbit around Saturn in 2004. Now, a group led by Sébastien Rodriguez, a Cassini VIMS team collaborator based at Université Paris Diderot, France, has analyzed more than 2,000 VIMS images to create the first long-term study of Titan's weather using observational data that also includes the equinox. Equinox, when the sun shone directly over the equator, occurred in August 2009.

Rodriguez is presenting the results and new images at the European Planetary Science Congress in Rome on Sept. 22.

Though Titan's surface is far colder and lacks liquid water, this moon is a kind of "sister world" to Earth because it has a surface covered with organic material and an atmosphere whose chemical composition harkens back to an early Earth. Titan has a hydrological cycle similar to Earth's, though Titan's cycle depends on methane and ethane rather than water.

A season on Titan lasts about seven Earth years. Rodriguez and colleagues observed significant atmospheric changes between July 2004 (early summer in Titan's southern hemisphere) and April 2010 (the very start of northern spring). The images showed that cloud activity has recently decreased near both of Titan's poles. These regions had been heavily overcast during the late southern summer until 2008, a few months before the equinox.

Over the past six years, the scientists found that clouds clustered in three distinct latitude regions of Titan: large clouds at the north pole, patchy clouds at the south pole and a narrow belt around 40 degrees south. "However, we are now seeing evidence of a seasonal circulation turnover on Titan – the clouds at the south pole completely disappeared just before the equinox and the clouds in the north are thinning out," Rodriguez said. "This agrees with predictions from models and we are expecting to see cloud activity reverse from one hemisphere to another in the coming decade as southern winter approaches."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate, Washington, D.C. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson.

For a full version of this release, go to: http://www.europlanet-eu.org/outreach/index.php?option=com_content&task=view&id=288&Itemid=41

For more information about Cassini, go to: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Tuesday, September 21, 2010

A Very Young Circumstellar Disk in Scattered Light

Figure 1: Gemini NIRI image of L1527 taken in L'-band (3.8 microns). The bright yellow areas are the disk surfaces separated by the narrow dark lane of the disk mid-plane. The fainter, diffuse red features are scattered light from the inner outflow cavities of the protostar.

Figure 2: Left is the Gemini NIRI image from Figure 1 and the right is the Spitzer Space Telescope image taken at a similar wavelength 3.6 micron. The dashed boxes mark the region that the Gemini NIRI image covers encompassing the point-like feature in the Spitzer Space telescope image.

Figure 3: Top row: Observations of L1527 from Spitzer and Gemini. Middle row: First model of L1527 that was constructed without the Gemini data. Bottom row: Refined model using new Gemini imaging of the disk.

Recent observations with the Near-Infrared Imager (NIRI) on the Gemini North telescope have revealed the presence of a large circumstellar disk around the young embedded protostar L1527. The discovery team, led by University of Michigan astronomer John Tobin and including Lee Hartmann also of the University of Michigan and Laurent Loinard of the Centro de Radioastronomía y Astrofísica - Universidad Nacional Autonoma de Mexico, detected the disk in scattered mid-infrared light, as shown in Figure 1. The upper layers of the disk appear as two bright bowl-shaped features. The mid-plane of the disk hides the central protostar from direct view, resulting in the dark band between the disk surfaces.

The object, located in a star-forming region in the constellation of Taurus, is at a distance of about 450 light-years (140 parsecs) making it one of the nearest and youngest protostars known. Although L1527 is otherwise a fairly typical protostar and will probably result in a star with a final mass about that of the Sun, L1527 is set apart from other young stars with disks because it is very early in the star formation process, even compared to its contemporaries within its host star-forming region. This stage of evolution is called the Class 0 phase, where the protostar is surrounded by a dense infalling envelope composed of gas and dust. The protostar is emitting ultraviolet and visible light, but at this early stage, radiation at these wavelengths remains directly undetectable, being absorbed by the dense envelope and disk and then re-radiated mainly in the far-infrared.

No optical or near-infrared radiation has ever been detected toward the center of the L1527 protostar, but the Spitzer Space Telescope detected a small, faint point of light coming from the center in the mid-infrared (Figure 2). The light’s source was unknown because the central protostar was expected to be completely obscured. Tobin’s team hypothesized that there must be some structure that obscures the protostar but bright and compact enough to appear unresolved in the Spitzer Space Telescope images. Tobin et al. constructed a model that resembled a large disk and proposed Gemini observations to test the hypothesis. The initial model is shown in Figure 3.

According to Tobin, “We utilized Gemini's unique ability to take images in the mid-infrared from the ground at high resolution. Under natural seeing conditions Gemini was able to give exquisite image quality; the seeing for the observations was 0.3 arcseconds, the equivalent angular size of a penny 8 miles away.”

While Tobin states that the team was “astounded” by how similar their model, based on only the Spitzer images was to the observations, the team refined the model (shown in Figure 3) to better fit the new detailed Gemini images. They found that the disk must be 190 AU in radius or 5 times the size of Pluto's orbit to reproduce the images. This disk size is typical for young stars without envelopes; however, it was expected that L1527 would have a smaller disk because it is at such an early stage of evolution, before the disk has grown. This result implies that disks can grow quite fast, which requires a rapid collapse of the natal cloud. The team also noticed that the disk extends vertically from it equator about twice as far as other disks; this may be due to material from the surrounding envelope falling onto the disk. Finally, the team concludes that these images from Gemini have captured a protoplanetary disk-in-formation around this young star implying that the ingredients for planet formation are already in-place at a very early time in protostellar evolution. The complete work will appear in The Astrophysical Journal Letters and is currently available on astro-ph.

Thursday, September 16, 2010

Cosmic Ice Sculptures: Dust Pillars in the Carina Nebula

Carina Nebula
Credit: NASA, ESA, and the Hubble Heritage Project (STScI/AURA)
Acknowledgment: M. Livio (STScI)
and N. Smith (University of California, Berkeley)

Videos

Enjoying a frozen treat on a hot summer day can leave a sticky mess as it melts in the Sun and deforms. In the cold vacuum of space, there is no edible ice cream, but there is radiation from massive stars that is carving away at cold molecular clouds, creating bizarre, fantasy-like structures. These one-light-year-tall pillars of cold hydrogen and dust, imaged by the Hubble Space Telescope, are located in the Carina Nebula.

This image is a composite of Hubble observations taken of the Carina Nebula region in 2005 in hydrogen light (light emitted by hydrogen atoms) along with observations taken in oxygen light (light emitted by oxygen atoms) in 2010, both times with Hubble's Advanced Camera for Surveys. The immense Carina Nebula is an estimated 7,500 light-years away in the southern constellation Carina.

For additional information, contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Mario Livio
Space Telescope Science Institute, Baltimore, Md.
410-338-4439
mlivio@stsci.edu

Keith Noll
Space Telescope Science Institute, Baltimore, Md.
410-338-1828
noll@stsci.edu

Wednesday, September 15, 2010

Planck's first glimpse at galaxy clusters and a new supercluster

Surveying the microwave sky, Planck has obtained its very first images of galaxy clusters, amongst the largest objects in the Universe, by means of the Sunyaev-Zel'dovich effect, a characteristic signature they imprint on the Cosmic Microwave Background. Joining forces in a fruitful collaboration between ESA missions, XMM-Newton followed up Planck's detections and revealed that one of them is a previously unknown supercluster of galaxies.

Matter in the Universe is distributed in a highly clustered fashion; stars congregate in galaxies and galaxies clump together, forming enormous clusters surrounded by vast, empty spaces. Galaxy clusters can host up to a thousand galaxies and they are permeated by hot gas that shines brightly in X-rays; furthermore, most of their mass consists of dark matter. On an even grander scale are the superclusters, large assemblies of galaxy groups and clusters, located at the intersections of sheets and filaments in the wispy cosmic web. As clusters and superclusters trace the distribution of both luminous and dark matter throughout the Universe, their observation is crucial to probe how cosmic structures formed and evolved.

Large-scale structure in the Universe.
Credit: Sloan Digital Sky Survey Team, NASA, NSF, DOE

Planck's primary goal is to capture the most ancient light of the cosmos, the Cosmic Microwave Background (CMB), and for this purpose it boasts a superb set of nine frequency channels, spanning the spectral range from 30 to 857 GHz. Such a broad spectral coverage is not only instrumental in removing all sources of contamination from the CMB, in order to deliver what will be the sharpest image of the early Universe ever achieved - it also makes Planck an excellent hunter of galaxy clusters.

In fact, the nine frequency channels were carefully chosen by the Planck team with a particular phenomenon, known as the Sunyaev-Zel'dovich Effect (SZE), very much in mind. This effect describes the change of energy experienced by CMB photons when they encounter a galaxy cluster as they travel towards us, in the process imprinting a distinctive signature on the CMB itself. Hence, the SZE represents a unique tool to detect galaxy clusters, even at high redshift.

"As the fossil photons from the Big Bang cross the Universe, they interact with the matter that they encounter: when travelling through a galaxy cluster, for example, the CMB photons scatter off free electrons present in the hot gas that fills the cluster," explains Nabila Aghanim of the Institut d'Astrophysique Spatiale in Orsay, France, a leading member of the group of Planck scientists investigating SZE clusters and secondary anisotropies. "These collisions redistribute the frequencies of photons in a particular way that enables us to isolate the intervening cluster from the CMB signal."

Since the hot electrons in the cluster are much more energetic than the CMB photons, interactions between the two species typically result in the photons being scattered to higher energies. This means that, when looking at the CMB in the direction of a galaxy cluster, one observes a deficit, with respect to the average CMB signal, of low-energy photons and a surplus of more energetic ones. The threshold frequency, separating deficit and surplus, corresponds to 217 GHz. Planck's channels probe the spectrum both below and above this threshold, with one of them centred exactly on 217 GHz.

Multi-band observations of the galaxy cluster Abell 2319
Credit: ESA/ LFI & HFI Consortia. Hi-Res [jpg] 1,389.07 kb

"With its unprecedented spectral coverage, Planck can detect both the positive and the negative signal of galaxy clusters, and is thus an exceptional tool to identify the locations of these enormous structures over the entire sky, and to measure their physical characteristics," says Jan Tauber, Planck Project Scientist, commenting on the first observations of the SZE in the Planck frequency bands. These first images include some clusters that are well known to astronomers, such as Coma, a very hot and nearby cluster extending over more than two degrees in the sky, and Abell 2319, another nearby cluster.

The Coma cluster as it appears through the Sunyaev-Zel'dovich Effect (top left) and X-ray emission (top right). The images are superimposed on a wide-field view of the region from the Digitised Sky Survey (lower two panels). Hi-Res [jpg] 695.29 kb

Planck's design, optimised for detecting the SZE signal from clusters scattered throughout the sky, is however not suited for in-depth investigations— its resolution is simply not sufficient to discern much detail for most of them, especially any newly discovered, high-redshift ones. Observations at other wavelengths are necessary to pin down the details of these massive structures. Since the hot gas in galaxy clusters emits copious amounts of X-rays, observations in this spectral band prove particularly useful as they probe the very same component responsible for producing the SZE.

In order to confirm their identity, Planck's cluster candidates are compared with existing catalogues of clusters, like the ROSAT all-sky X-ray catalogue of clusters. When the Planck candidates do not correspond to any known structure, and after careful quality checks of the SZ signal, they may become the target of brand new, follow-up observations with ESA's X-ray observatory, XMM-Newton.

"With its exceptional sensitivity, XMM-Newton is the ideal partner to follow-up the sources detected by Planck via the SZE," says Monique Arnaud, from the Service d'Astrophysique, Commissariat à l'Energie Atomique, France, who leads the Planck group following up sources with XMM-Newton. It is the special synergy between these two ESA missions that has allowed astronomers to use snapshot XMM-Newton observations to confirm that Planck's first detections are indeed clusters, and has revealed an even larger structure: a supercluster of galaxies.

A new supercluster, seen by Planck and XMM-Newton
Credit: Planck image: ESA/LFI & HFI Consortia;
XMM-Newton image: ESA

"The XMM-Newton observations have shown that one of the candidate clusters is in fact a supercluster composed of at least three individual, massive clusters of galaxies, which Planck alone could not have resolved," explains Arnaud.

"The synergy between the two missions has proved extremely successful, and XMM-Newton will continue following up Planck detections in order to confirm the nature of the cluster candidates," says Norbert Schartel, XMM-Newton Project Scientist. In the future, XMM-Newton may conduct further, deeper observations of some of these clusters in order to measure their properties in greater detail.

"This is the first time that a supercluster has been discovered via the SZE," adds Aghanim. "This important discovery opens a brand new window on superclusters, one which complements the observations of the individual galaxies therein."

The SZ signal from the newly discovered supercluster arises from the sum of the signal from the three individual clusters, with a possible additional contribution from an inter-cluster filamentary structure. This provides important clues about the distribution of gas on very large scales which is, in turn, crucial also for tracing the underlying distribution of dark matter.

"These first detections, revealing both previously known clusters and brand new ones, show that Planck is working extremely well," comments Tauber. "Of course, this is only a preview of the numerous discoveries that will surely come along during the lifetime of the mission."

Notes for editors

ESA’s Planck mission maps the sky in nine frequencies using two state-of-the-art instruments, designed to produce high-sensitivity, multi-frequency measurements of the diffuse sky radiation: the High Frequency Instrument (HFI) includes the frequency bands 100 - 857 GHz, and the Low Frequency Instrument (LFI) includes the frequency bands 30 - 70 GHz.

The first Planck all-sky survey began in mid-August 2009 and was completed in June 2010. Planck will continue to gather data until the end of 2011, during which time it will complete over four all-sky scans.

The Planck team is currently analysing the data from the first all-sky survey to identify both known and new galaxy clusters for the early Sunyaev-Zel'dovich catalogue, which will be released in January of 2011 as part of the Early Release Compact Source Catalogue. Companion scientific papers will accompany the catalogue.

The initial programme of follow-up observations using XMM-Newton, undertaken in Director's Discretionary Time, has the main goal of confirming the nature of a selected set of cluster candidates detected by Planck via the SZE.

Contacts

Nabila Aghanim
Institut d'Astrophysique Spatiale
CNRS-Université Paris Sud
Orsay, France
Email:
nabila.aghanim@ias.u-psud.fr
Phone: +33 1 69 85 86 46

Monique Arnaud
CEA Saclay
Service d'Astrophysique
France
Email:
Monique.Arnaud@cea.fr
Phone: +33 1 69 08 20 41

Jan Tauber
ESA Planck Project Scientist
Directorate of Science & Robotic Exploration
ESA, The Netherlands
Email:
jtauberrssd@esa.int
Phone: +31 71 5655342

Norbert Schartel
ESA XMM-Newton Project Scientist
Directorate of Science and Robotic Exploration
ESA, The Netherlands
Email:
Norbert.Schartel@esa.int
Phone: +34 91 8131 184

Tuesday, September 14, 2010

BP Psc: Chandra Finds Evidence for Stellar Cannibalism

Credit X-ray (NASA/CXC/RIT/J.Kastner et al),
Optical (UCO/Lick/STScI/M.Perrin et al);
Illustration: NASA/CXC/M.Weiss

The composite image on the left shows X-ray and optical data for BP Piscium (BP Psc), a more evolved version of our Sun about 1,000 light years from Earth. Chandra X-ray Observatory data are colored in purple, and optical data from the 3-meter Shane telescope at Lick Observatory are shown in orange, green and blue. BP Psc is surrounded by a dusty and gaseous disk and has a pair of jets several light years long blasting out of the system. A close-up view is shown by the artist's impression on the right. For clarity a narrow jet is shown, but the actual jet is probably much wider, extending across the inner regions of the disk. Because of the dusty disk, the star's surface is obscured in optical and near-infrared light. Therefore, the Chandra observation is the first detection of this star in any wavelength.

The disk and the jets, seen distinctly in the optical data, provide evidence for a recent and catastrophic interaction in which BP Psc consumed a nearby star or giant planet. This happened when BP Psc ran out of nuclear fuel and expanded into its "red giant" phase.

Jets and a disk are often characteristics of very young stars, so astronomers thought BP Psc might be one as well. However, the new Chandra results argue against this interpretation, because the X-ray source is fainter than expected for a young star. Another argument previously used against the possible youth of BP Psc was that it is not located near any star-forming cloud and there are no other known young stars in its immediate vicinity. The Chandra image supports this absence of a cluster of young stars, since multiwavelength studies show that most of the X-ray sources in the composite image are likely to be rapidly growing supermassive black holes in the centers of distant galaxies.

Fast Facts for BP Psc:

Scale: Left panel is 7 arcmin across (2 light years)
Category:
Normal Stars & Star Clusters
Coordinates: (J2000) RA 22h 22m 24.70s | Dec -02° 13' 41.40"
Constellation: Pisces
Observation Date: 12 & 13 Jan 2009
Observation Time: 21 hours
Obs. ID: 8900, 10856
Color Code: X-ray (Purple); Optical (Orange, Green, Blue)
Instrument:
ACIS
References: Kastner, J et al, 2010, ApJL, 719:L65-L68
Distance Estimate: About 1000 light years

Monday, September 13, 2010

NASA's Hubble Harvests Distant Solar System Objects

This is an artist's concept of a craggy piece of Solar System debris that belongs to a class of bodies called trans-Neptunian objects (TNOs). Astronomers culling the data archives of NASA's Hubble Space Telescope have added 14 new TNOs to the catalog. The newfound TNOs range from 25 to 60 miles (40-100 km) across. Their method promises to turn up hundreds more. In this illustration, the distant Sun is reduced to a bright star at a distance of over 3 billion miles. Credit: NASA, ESA, and G. Bacon (STScI)

Cambridge, MA - Beyond the orbit of Neptune reside countless icy rocks known as trans-Neptunian objects (TNOs). One of the biggest, Pluto, is classified as a dwarf planet. The region also supplies us with comets such as famous Comet Halley. Most TNOs are small and receive little sunlight, making them faint and difficult to spot.

Now, astronomers using clever techniques to cull the data archives of NASA's Hubble Space Telescope have added 14 new TNOs to the catalog. Their method promises to turn up hundreds more.

"Trans-Neptunian objects interest us because they are building blocks left over from the formation of the solar system," explained lead author Cesar Fuentes, formerly with the Harvard-Smithsonian Center for Astrophysics and now at Northern Arizona University.

As TNOs slowly orbit the sun, they move against the starry background, appearing as streaks of light in time exposure photographs. The team developed software to analyze hundreds of Hubble images hunting for such streaks. After promising candidates were flagged, the images were visually examined to confirm or refute each discovery.

Most TNOs are located near the ecliptic -- a line in the sky marking the plane of the solar system (since the solar system formed from a disk of material). Therefore, the team searched within 5 degrees of the ecliptic to increase their chance of success.

They found 14 objects, including one binary (two TNOs orbiting each other like a miniature Pluto-Charon system). All were very faint, with most measuring magnitude 25-27 (more than 100 million times fainter than objects visible to the unaided eye).

By measuring their motion across the sky, astronomers calculated an orbit and distance for each object. Combining the distance and brightness (plus an assumed albedo or reflectivity), they then estimated the size. The newfound TNOs range from 25 to 60 miles (40-100 km) across.

Unlike planets, which tend to have very flat orbits (known as low inclination), some TNOs have orbits significantly tilted from the ecliptic (high inclination). The team examined the size distribution of TNOs with low- versus high-inclination orbits to gain clues about how the population has evolved over the past 4.5 billion years.

Generally, smaller trans-Neptunian objects are the shattered remains of bigger TNOs. Over billions of years, these objects smack together, grinding each other down. The team found that the size distribution of TNOs with low- versus high-inclination orbits is about the same as objects get fainter and smaller. Therefore, both populations (low and high inclination) have similar collisional histories.

This initial study examined only one-third of a square degree of the sky, meaning that there is much more area to survey. Hundreds of additional TNOs may lurk in the Hubble archives at higher ecliptic latitudes. Fuentes and his colleagues intend to continue their search.

"We have proven our ability to detect and characterize TNOs even with data intended for completely different purposes," Fuentes said.

This research has been accepted for publication in The Astrophysical Journal and is available online.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462

daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463

cpulliam@cfa.harvard.edu