Thursday, October 30, 2008

Hubble Scores a Perfect Ten

Credit: NASA, ESA, and M. Livio (STScI)

NASA's Hubble Space Telescope is back in business.

Just a couple of days after the orbiting observatory was brought back online, Hubble aimed its prime working camera, the Wide Field Planetary Camera 2 (WFPC2), at a particularly intriguing target, a pair of gravitationally interacting galaxies called Arp 147.

The image demonstrated that the camera is working exactly as it was before going offline, thereby scoring a "perfect 10" both for performance and beauty.

The two galaxies happen to be oriented so that they appear to mark the number 10. The left-most galaxy, or the "one" in this image, is relatively undisturbed apart from a smooth ring of starlight. It appears nearly on edge to our line of sight. The right-most galaxy, resembling a zero, exhibits a clumpy, blue ring of intense star formation.

The blue ring was most probably formed after the galaxy on the left passed through the galaxy on the right. Just as a pebble thrown into a pond creates an outwardly moving circular wave, a propagating density wave was generated at the point of impact and spread outward. As this density wave collided with material in the target galaxy that was moving inward due to the gravitational pull of the two galaxies, shocks and dense gas were produced, stimulating star formation.

The dusty reddish knot at the lower left of the blue ring probably marks the location of the original nucleus of the galaxy that was hit.

Arp 147 appears in the Arp Atlas of Peculiar Galaxies, compiled by Halton Arp in the 1960s and published in 1966. This picture was assembled from WFPC2 images taken with three separate filters. The blue, visible-light, and infrared filters are represented by the colors blue, green, and red, respectively.

The galaxy pair was photographed on October 27-28, 2008. Arp 147 lies in the constellation Cetus, and it is more than 400 million light-years away from Earth.

For additional information, contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Md.

Mario Livio
Space Telescope Science Institute, Baltimore, Md.

Monday, October 27, 2008

Closest Planetary System Hosts Two Asteroid Belts

Credit: NASA/JPL-Caltech
This artist's conception shows the closest known planetary system to our own, called Epsilon Eridani. Observations from NASA's Spitzer Space Telescope show that the system hosts two asteroid belts, in addition to previously identified candidate planets and an outer comet ring.

Credit: NASA/JPL-Caltech
This artist's diagram compares the Epsilon Eridani system to our own solar system. The two systems are structured similarly, and both host asteroids (brown), comets (blue) and planets (white dots).

New observations from NASA's Spitzer Space Telescope indicate that the nearest planetary system to our own has two asteroid belts. Our own solar system has just one.

The star at the center of the nearby system, called Epsilon Eridani, is a younger, slightly cooler and fainter version of the sun. Previously, astronomers had uncovered evidence for two possible planets in the system, and for a broad, outer ring of icy comets similar to our own Kuiper Belt.

Now, Spitzer has discovered that the system also has dual asteroid belts. One sits at approximately the same position as the one in our solar system. The second, denser belt, most likely also populated by asteroids, lies between the first belt and the comet ring. The presence of the asteroid belts implies additional planets in the Epsilon Eridani system.

"This system probably looks a lot like ours did when life first took root on Earth," said Dana Backman, an astronomer at the SETI Institute, in Mountain View, Calif., and outreach director for NASA's Sofia mission. "The main difference we know of so far is that it has an additional ring of leftover planet construction material." Backman is lead author of a paper about the findings to appear Jan. 10 in the Astrophysical Journal.

Asteroid belts are rocky and metallic debris left over from the early stages of planet formation. Their presence around other stars signals that rocky planets like Earth could be orbiting in the system's inner regions, with massive gas planets circling near the belts' rims. In our own solar system, for example, there is evidence that Jupiter, which lies just beyond our asteroid belt, caused the asteroid belt to form long ago by stirring up material that would have otherwise coalesced into a planet. Nowadays, Jupiter helps keep our asteroid belt confined to a ring.

Astronomers have detected stars with signs of multiple belts of material before, but Epsilon Eridani is closer to Earth and more like our sun overall. It is 10 light-years away, slightly less massive than the sun, and roughly 800 million years old, or one-fifth the age of the sun.

Because the star is so close and similar to the sun, it is a popular locale in science fiction. The television series Star Trek and Babylon 5 referenced Epsilon Eridani, and it has been featured in novels by Issac Asimov and Frank Herbert, among others.

The popular star was also one of the first to be searched for signs of advanced alien civilizations using radio telescopes in 1960. At that time, astronomers did not know of the star's young age.

Spitzer observed Epsilon Eridani with both of its infrared cameras and its infrared spectrometer. When asteroid and comets collide or evaporate, they release tiny particles of dust that give off heat, which Spitzer can see. "Because the system is so close to us, Spitzer can really pick out details in the dust, giving us a good look at the system's architecture," said co-author Karl Stapelfeldt of NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The asteroid belts detected by Spitzer orbit at distances of approximately 3 and 20 astronomical units from the star (an astronomical unit is the average distance between Earth and the sun). For reference, our own asteroid belt lies at about 3 astronomical units from the sun, and Uranus is roughly 19 astronomical units away.

One of the two possible planets previously identified around Epsilon Eridani, called Epsilon Eridani b, was discovered in 2000. The planet is thought to orbit at an average distance of 3.4 astronomical units from the star -- just outside the innermost asteroid belt identified by Spitzer. This is the first time that an asteroid belt and a planet beyond our solar system have been found in a similar arrangement as our asteroid belt and Jupiter.

Some researchers had reported that Epsilon Eridani b orbits in an exaggerated ellipse ranging between 1 and 5 astronomical units, but this means the planet would cross, and quickly disrupt, the newfound asteroid belt. Instead, Backman and colleagues argue that this planet must have a more circular orbit that keeps it just outside the belt.

The other candidate planet was first proposed in 1998 to explain lumpiness observed in the star's outer comet ring. It is thought to lie near the inner edge of the ring, which orbits between 35 and 90 astronomical units from Epsilon Eridani.

The intermediate belt detected by Spitzer suggests that a third planet could be responsible for creating and shepherding its material. This planet would orbit at approximately 20 astronomical units and lie between the other two planets. "Detailed studies of the dust belts in other planetary systems are telling us a great deal about their complex structure," said Michael Werner, co-author of the study and project scientist for Spitzer at JPL. "It seems that no two planetary systems are alike."

These results were presented this week at the "New Light on Young Stars: Spitzer's View of Circumstellar Disks" conference in Pasadena, Calif.

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.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory

Wednesday, October 22, 2008

A Claret-coloured Cloud with a Massive Heart

ESO PR Photo 37/08
Stellar Nursery Gum 29

A new image released by ESO shows the amazing intricacies of a vast stellar nursery, which goes by the name of Gum 29. In the centre, a small cluster of stars — called Westerlund 2 — has been found to be the home of one of the most massive double star systems known to astronomers.

Gum 29 is a huge region of hydrogen gas that has been stripped of its electrons (ionised) by the intense radiation of the hot young stars located at its centre. Astronomers call this an HII (pronounced "H-two") region, and this particularly stunning example stretches out across space for over 200 light-years. The name stems from the fact that it is the 29th entry in the catalogue published by Australian astronomer Colin Stanley Gum in 1955.

Embedded deep within the huge, nebulous expanse of Gum 29, the relatively little known cluster of Westerlund 2 is clearly seen in the centre of this image. The latest measurements indicate that it lies at a distance of some 26 000 light-years from Earth, placing it towards the outside edge of the Carina spiral arm of the Milky Way. The cluster's distance has been the subject of intense scrutiny in the past, as it is one of the parameters needed to understand this intriguing object. Westerlund 2 is very young too, with an age of only 1—2 million years.

Previous observations have shown that two stars to the bottom right of the cluster are true leviathans. Together they form what is known as a double system. The two stars have masses of 82 and 83 times that of our Sun and rotate around each other in approximately 3.7 days. They are amongst the most massive stars known to astronomers.

Detailed observations of this intriguing pair have also shown that they are both Wolf-Rayet stars. These are massive stars nearing the end of their lives, expelling vast quantities of material as their final swansong. Observations made in X-rays have subsequently shown that streams of material from each star continually collide, creating a blaze of X-ray radiation.

The image was obtained with the Wide Field Imager (WFI) camera attached to the 2.2-m Max-Planck/ESO telescope at ESO's La Silla observatory site in Chile. Located at an altitude of 2400 metres in the arid Atacama Desert, this observatory sits under some of the clearest and darkest skies on Earth. The WFI excels at studying the farthest depths of the Universe from this unrivalled vantage point.

ESO Press Officer: Dr. Henri Boffin - +49 89 3200 6222 -
ESO Press Officer in Chile: Valentina Rodriguez - +56 2 463 3123 -

Monday, October 20, 2008

Massive Young Stars Trigger Stellar Birth


RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars.

This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image.

The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193.

Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas clouds in RCW 108 to be compressed, leading to gravitational collapse and the formation of new stars.

New Pulsar

Credit:NASA/S. Pineault, DRAO

A dying star collapses and a nugget of condensed matter called a neutron star is left behind amidst the debris. Finding this nugget is important since it tells alot about how dying stars die.

Radio observations had revealed an extended nebula called CTA 1 which astronomers recognized as the supernova remnant produced when a dead star exploded. X-ray observations showed a source near the center of the remnant.

This source is bright in X-rays but optically faint, characteristics appropriate for a neutron star. Observations with the Chandra X-ray observatory showed that this source is associated with a small nebula which surrounds it and a tail of X-ray emitting gas extending from its surface.

But pulsations, which can be used to determine the rotation period of the object and to help confirm that it is a neutron star, were never found in radio or X-ray studies.

But new observations with the Fermi Gamma-Ray Space Telescope revealed pulsations in this object's gamma-ray emission - the first time a neutron star pulsar has been seen only in gamma-rays.

The image above shows CTA 1 and the location of the X-ray source; the inset shows an artist rendition of the pulsar, its magnetic field and the gamma-ray beam originating from its magnetic poles. Scientists speculate that the object's radio beams are rather narrow and don't intersect the earth when the pulsar rotates, but that the gamma-ray beam is wider and shines on the earth once each rotation.

How many new pulsars will Fermi find? Time will tell.

The High Energy Astrophysics Science Archive Research Center (HEASARC)

Wednesday, October 15, 2008

Violent flickering in Black Holes

ESO PR Photo 36/08
Star-Forming Region NGC 366
Credit: ESO/L. Calçada

VLT and Rossi XTE satellite probe violently variable black holes

Unique observations of the flickering light from the surroundings of two black holes provide new insights into the colossal energy that flows at their hearts. By mapping out how well the variations in visible light match those in X-rays on very short timescales, astronomers have shown that magnetic fields must play a crucial role in the way black holes swallow matter.

Like the flame from a candle, light coming from the surroundings of a black hole is not constant — it flares, sputters and sparkles. "The rapid flickering of light from a black hole is most commonly observed at X-ray wavelengths," says Poshak Gandhi, who led the international team that reports these results. "This new study is one of only a handful to date that also explore the fast variations in visible light, and, most importantly how these fluctuations relate to those in X-rays."

The observations tracked the shimmering of the black holes simultaneously using two different instruments, one on the ground and one in space. The X-ray data were taken using NASA's Rossi X-ray Timing Explorer satellite. The visible light was collected with the high speed camera ULTRACAM, a visiting instrument at ESO's Very Large Telescope (VLT), recording up to 20 images a second. ULTRACAM was developed by team members Vik Dhillon and Tom Marsh. "These are among the fastest observations of a black hole ever obtained with a large optical telescope," says Dhillon.

To their surprise, astronomers discovered that the brightness fluctuations in the visible light were even more rapid than those seen in X-rays. In addition, the visible-light and X-ray variations were found not to be simultaneous, but to follow a repeated and remarkable pattern: just before an X-ray flare the visible light dims, and then surges to a bright flash for a tiny fraction of a second before rapidly decreasing again.

None of this radiation emerges directly from the black hole, but from the intense energy flows of electrically charged matter in its vicinity. The environment of a black hole is constantly being reshaped by a riotous mêlée of strong and competing forces such as gravity, magnetism and explosive pressure. As a result, light emitted by the hot flows of matter varies in brightness in a muddled and haphazard way. "But the pattern found in this new study possesses a stable structure that stands out amidst an otherwise chaotic variability, and so, it can yield vital clues about the dominant underlying physical processes in action," says team member Andy Fabian.

The visible-light emission from the neighbourhoods of black holes was widely thought to be a secondary effect, with a primary X-ray outburst illuminating the surrounding gas that subsequently shone in the visible range. But if this were so, any visible-light variations would lag behind the X-ray variability, and would be much slower to peak and fade away. "The rapid visible-light flickering now discovered immediately rules out this scenario for both systems studied," asserts Gandhi. "Instead the variations in the X-ray and visible light output must have some common origin, and one very close to the black hole itself."

Strong magnetic fields represent the best candidate for the dominant physical process. Acting as a reservoir, they can soak up the energy released close to the black hole, storing it until it can be discharged either as hot (multi-million degree) X-ray emitting plasma, or as streams of charged particles travelling at close to the speed of light. The division of energy into these two components can result in the characteristic pattern of X-ray and visible-light variability.

More Information

The two black holes studied here, GX 339-4 and SWIFT J1753.5-0127, are the remnants of massive dead stars in the Milky Way. They are embedded in separate "binary" stellar systems, where the black hole is bound to a normal star that is losing matter to its dark companion. Both black holes have masses of around ten times that of our Sun, yet the size of their orbits is only a few million kilometres, much more compact than the orbit of Mercury around our Sun.

Apart from Gandhi, Dhillon, Durant, Fabian, and Marsh, the other members of the team are Kazuo Makishima at the University of Tokyo, Japan, Jon Miller at the University of Michigan, USA, Tariq Shahbaz at the Instituto de Astrofisica de Canarias, Spain, and Henk Spruit of the Max-Planck-Institute for Astrophysics, Germany.

Gandhi, P., Makishima, K., Durant, M., Fabian, A. C., Dhillon, V. S., Marsh, T. R., Miller, J. M., Shahbaz, T. & Spruit, H. C., Rapid optical and X-ray timing observations of GX 339-4: flux correlations at the onset of a low/hard state, Monthly Notices of the Roy. Astron. Soc. Letters, 390, L29 (2008), astro-ph/0807.1529
Durant, M., Gandhi, P., Shahbaz, T., Fabian, A., Miller, J., Dhillon, V. S. & Marsh, T. R,. SWIFT J1753.5-0127: a surprising optical/X-ray cross-correlation function,The Astrophysical Journal, 682, L45 (2008), astro-ph/0806.2530


Poshak Gandhi
RIKEN Cosmic Radiation Lab
Wako, Saitama, Japan
Phone: +81 48 467 9334
E-mail: pg (at)

Martin Durant
Instituto de Astrofísica de Canarias
La Laguna, Tenerife, Spain
Phone: +34 922 605 388
E-mail: durant (at)

Vik Dhillon
University of Sheffield, UK
Phone: +44 114 222 4528
Email: Vik.Dhillon (at)

Tom R. Marsh
University of Warwick, UK
Phone: +44 247 657 4739
Email: t.r.marsh (at)

Andy Fabian
Institute of Astronomy
Cambridge, UK
Phone: +44 1223 337548
Email: acf (at)

ESO Press Officer: Dr. Henri Boffin - +49 89 3200 6222 -
ESO Press Officer in Chile: Valentina Rodriguez - +56 2 463 3123 -

Tuesday, October 14, 2008

Giant Cyclones at Saturn's Poles Create a Swirl of Mystery

Infrared Images of Saturn’s Poles
Credit: NASA/JPL/University of Arizona

New images from NASA’s Cassini spacecraft reveal a giant cyclone at Saturn’s north pole, and show that a similarly monstrous cyclone churning at Saturn’s south pole is powered by Earth-like storm patterns.

The new-found cyclone at Saturn’s north pole is only visible in the near-infrared wavelengths because the north pole is in winter, thus in darkness to visible-light cameras. At these wavelengths, about seven times greater than light seen by the human eye, the clouds deep inside Saturn’s atmosphere are seen in silhouette against the background glow of Saturn’s internal heat.

Saturn's South Polar Region Revealed
Credit: NASA/JPL/University of Arizona

The entire north pole of Saturn is now mapped in detail in infrared, with features as small as 120 kilometers (75 miles) visible in the images. Time-lapse movies of the clouds circling the north pole show the whirlpool-like cyclone there is rotating at 530 kilometers per hour (325 miles per hour), more than twice as fast as the highest winds measured in cyclonic features on Earth. This cyclone is surrounded by an odd, honeycombed-shaped hexagon, which itself does not seem to move while the clouds within it whip around at high speeds, also greater than 500 kilometers per hour (300 miles per hour). Oddly, neither the fast-moving clouds inside the hexagon nor this new cyclone seem to disrupt the six-sided hexagon.

New Cassini imagery of Saturn’s south pole shows complementary aspects of the region through the eyes of two different instruments. Near-infrared images from the visual and infrared mapping spectrometer instrument show the whole region is pockmarked with storms, while the imaging cameras show close-up details.

The new views are available online at: and

Convection in Saturn's Southern Vortex
Credit: NASA/JPL/Space Science Institute

Unlike Earth-bound hurricanes, powered by the ocean’s heat and water, Saturn's cyclones have no body of water at their bases, yet the eye-walls of Saturn’s and Earth’s storms look strikingly similar. Saturn's hurricanes are locked to the planet's poles, whereas terrestrial hurricanes drift across the ocean.

"These are truly massive cyclones, hundreds of times stronger than the most giant hurricanes on Earth," said Kevin Baines, Cassini scientist on the visual and infrared mapping spectrometer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Dozens of puffy, convectively formed cumulus clouds swirl around both poles, betraying the presence of giant thunderstorms lurking beneath. Thunderstorms are the likely engine for these giant weather systems," said Baines.

Just as condensing water in clouds on Earth powers hurricane vortices, the heat released from the condensing water in Saturnian thunderstorms deep down in the atmosphere may be the primary power source energizing the vortex.

The Yet Yawning Gulf
Credit: NASA/JPL/Space Science Institute

In the south, the new infrared images of the pole, under the daylight conditions of southern summer, show the entire region is marked by hundreds of dark cloud spots. The clouds, like those at the north pole, are likely a manifestation of convective, thunderstorm-like processes extending some 100 kilometers (62 miles) below the clouds. They are likely composed of ammonium hydrosulfide with possibly a mixture of materials dredged up from the depths. By contrast, most of the hazes and clouds seen on Saturn are thought to be composed of ammonia, which condenses at high, visible altitudes.

Complementary images of the south pole from Cassini’s imaging cameras, obtained in mid-July, are 10 times more detailed than any seen before. "What looked like puffy clouds in lower resolution images are turning out to be deep convective structures seen through the atmospheric haze," said Cassini imaging team member Tony DelGenio of NASA’s Goddard Institute for Space Studies in New York. "One of them has punched through to a higher altitude and created its own little vortex."

The "eye" of the vortex is surrounded by an outer ring of high clouds. The new images also hint at an inner ring of clouds about half the diameter of the main ring, and so the actual clear "eye" region is smaller than it appears in earlier low-resolution images.

"It’s like seeing into the eye of a hurricane," said Andrew Ingersoll, a member of Cassini's imaging team at the California Institute of Technology, Pasadena. "It’s surprising. Convection is an important part of the planet’s energy budget because the warm upwelling air carries heat from the interior. In a terrestrial hurricane, the convection occurs in the eyewall; the eye is a region of downwelling. Here convection seems to occur in the eye as well."

Further observations are planned to see how the features at both poles evolve as the seasons change from southern summer to fall in August 2009.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The visual and infrared mapping spectrometer team is based at the University of Arizona. The imaging team is based at the Space Science Institute, Boulder, Colo.

Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

NASA's Spitzer Gets Sneak Peak Inside Comet Holmes

Credit:NASA/JPL-Caltech/B. Reach (Spitzer Science Center)

When comet Holmes unexpectedly erupted in 2007, professional and amateur astronomers around the world turned their telescopes toward the spectacular event. Their quest was to find out why the comet had suddenly exploded.

Observations taken of the comet after the explosion by NASA's Spitzer Space Telescope deepen the mystery, showing oddly behaving streamers in the shell of dust surrounding the nucleus of the comet. The data also offer a rare look at the material liberated from within the nucleus, and confirm previous findings from NASA's Stardust and Deep Impact missions.

"The data we got from Spitzer do not look like anything we typically see when looking at comets," said Bill Reach of NASA's Spitzer Science Center at the California Institute of Technology, Pasadena, Calif. Reach is lead investigator of the Spitzer observations. "The comet Holmes explosion gave us a rare glimpse at the inside of a comet nucleus." The findings were presented at the 40th meeting of the Division of Planetary Sciences in Ithaca, N.Y.

Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes exploded as it approached the asteroid belt, and brightened a millionfold overnight.

In an attempt to understand these odd occurrences, astronomers pointed NASA's Spitzer Space Telescope at the comet in November 2007 and March 2008. By using Spitzer's infrared spectrograph instrument, Reach was able to gain valuable insights into the composition of Holmes' solid interior. Like a prism spreading visible-light into a rainbow, the spectrograph breaks up infrared light from the comet into its component parts, revealing the fingerprints of various chemicals.

In November of 2007, Reach noticed a lot of fine silicate dust, or crystallized grains smaller than sand, like crushed gems. He noted that this particular observation revealed materials similar to those seen around other comets where grains have been treated violently, including NASA's Deep Impact mission, which smashed a projectile into comet Tempel 1; NASA's Stardust mission, which swept particles from comet Wild 2 into a collector at 13,000 miles per hour (21,000 kilometers per hour), and the outburst of comet Hale-Bopp in 1995.

"Comet dust is very sensitive, meaning that the grains are very easily destroyed, said Reach. "We think the fine silicates are produced in these violent events by the destruction of larger particles originating inside the comet nucleus."

When Spitzer observed the same portion of the comet again in March 2008, the fine-grained silicate dust was gone and only larger particles were present. "The March observation tells us that there is a very small window for studying composition of comet dust after a violent event like comet Holmes' outburst," said Reach.

Comet Holmes not only has unusual dusty components, it also does not look like a typical comet. According to Jeremie Vaubaillon, a colleague of Reach's at Caltech, pictures snapped from the ground shortly after the outburst revealed streamers in the shell of dust surrounding the comet. Scientists suspect they were produced after the explosion by fragments escaping the comet's nucleus.

In November 2007, the streamers pointed away from the sun, which seemed natural because scientists believed that radiation from the sun was pushing these fragments straight back. However, when Spitzer imaged the same streamers in March 2008, they were surprised to find them still pointing in the same direction as five months before, even though the comet had moved and sunlight was arriving from a different location. "We have never seen anything like this in a comet before. The extended shape still needs to be fully understood," said Vaubaillon.

He notes that the shell surrounding the comet also acts peculiarly. The shape of the shell did not change as expected from November 2007 to March 2008. Vaubaillon said this is because the dust grains seen in March 2008 are relatively large, approximately one millimeter in size, and thus harder to move.

"If the shell was comprised of smaller dust grains, it would have changed as the orientation of the sun changes with time," said Vaubaillon. "This Spitzer image is very unique. No other telescope has seen comet Holmes in this much detail, five months after the explosion."

"Like people, all comets are a little different. We've been studying comets for hundreds of years -- 116 years in the case of comet Holmes -- but still do not really understand them," said Reach. "However, with the Spitzer observations and data from other telescopes, we are getting closer."

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.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory

Friday, October 10, 2008

Astronomers get best view yet of infant stars at feeding time

ESO PR Photo 35/08
Credit: ESO/L. Calçada

Tracing gas emission close to young stellar objects

Astronomers have used ESO's Very Large Telescope Interferometer to conduct the first high resolution survey that combines spectroscopy and interferometry on intermediate-mass infant stars. They obtained a very precise view of the processes acting in the discs that feed stars as they form. These mechanisms include material infalling onto the star as well as gas being ejected, probably as a wind from the disc.

Infant stars form from a disc of gas and dust that surrounds the new star and, later, may also provide the material for a planetary system. Because the closest star-forming regions to us are about 500 light-years away, these discs appear very small on the sky, and their study requires special techniques to be able to probe the finer details.

This is best done with interferometry, a technique that combines the light of two or more telescopes so that the level of detail revealed corresponds to that which would be seen by a telescope with a diameter equal to the separation between the interferometer elements, typically 40 to 200 metres. ESO's Very Large Telescope Interferometer (VLTI) has allowed astronomers to reach a resolution of about a milli-arcsecond, an angle equivalent to the size of the full stop at the end of this sentence seen from a distance of about 50 kilometres.

"So far interferometry has mostly been used to probe the dust that closely surrounds young stars," says Eric Tatulli from Grenoble (France), who co-led this international project. "But dust is only one percent of the total mass of the discs. Their main component is gas, and its distribution may define the final architecture of planetary systems that are still forming."

The ability of the VLTI and the AMBER instrument to take spectra while probing objects at milli-arcsecond resolution has allowed astronomers to map the gas. Astronomers studied the inner gaseous environments of six young stars belonging to the family of Herbig Ae/Be objects. These objects have masses a few times that of our Sun and are still forming, increasing in mass by swallowing material from the surrounding disc.

The team used these observations to show that gas emission processes can be used to trace the physical processes acting close to the star.

"The origin of gas emissions from these young stars has been under debate until now, because in most earlier investigations of the gas component, the spatial resolution was not high enough to study the distribution of the gas close to the star," says co-leader Stefan Kraus from Bonn in Germany. "Astronomers had very different ideas about the physical processes that have been traced by the gas. By combining spectroscopy and interferometry, the VLTI has given us the opportunity to distinguish between the physical mechanisms responsible for the observed gas emission."

Astronomers have found evidence for matter falling into the star for two cases, and for mass outflow in four other stars, either in an extended stellar wind or in a disc wind.

It also seems that, for one of the stars, dust may be present closer to the star than had been generally expected. The dust is so close that the temperature should be high enough for it to evaporate, but since this is not observed, it must mean that gas shields the dust from the star's light.

These new observations demonstrate that it is now possible to study gas in the discs around young stars. This opens new perspectives for understanding this important phase in the life of a star.

"Future observations using VLTI spectro-interferometry will allow us to determine both the spatial distribution and motion of the gas, and might reveal whether the observed line emission is caused by a jet launched from the disc or by a stellar wind", concludes Stefan Kraus.

More Information

Tatulli E., Malbet F., Menard F., Gil C.,Testi L., Natta A., Kraus S., Stee P., Robbe-Dubois S., Spatially resolving the hot CO around the young Be star 51 Ophiuchi, Astronomy and Astrophysics 489, 1151 (2008).
Kraus S., Hofmann K.-H., Benisty M., Berger J.-P., Chesneau O., Isella A., Malbet F., Meilland A., Nardetto N., Natta A., Preibisch T., Schertl D., Smith M., Stee P., Tatulli E., Testi L., Weigelt G., The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry, Astronomy and Astrophysics 489, 1157 (2008).
The team includes S. Kraus, K.-H. Hofmann, A. Meilland, N. Nardetto, T. Preibisch, D. Schertl, and G. Weigelt (MPI, Bonn, Germany), E. Tatulli (INAF, Italy and Laboratoire d'Astrophysique de Grenoble, France), M. Benisty, J.-P. Berger, F. Malbet, and F. Ménard (Laboratoire d'Astrophysique de Grenoble, France), O. Chesneau and P. Stee, (OCA, France), A. Natta (INAF, Italy), M. Smith (Univ. of Kent, UK), C. Gil and L. Testi (ESO), and S. Robbe-Dubois (Université de Nice, France).


Stefan Kraus
Max-Planck-Institute for Radio Astronomy
Bonn, Germany
E-mail: skraus (at)
Phone: +49 228 52 53 95

Eric Tatulli
Observatoire de Grenoble, France
E-mail: etatulli (at)
Phone: +33 476 63 57 75

ESO Press Officer: Dr. Henri Boffin - +49 89 3200 6222 -
ESO Press Officer in Chile: Valentina Rodriguez - +56 2 463 3123 -

Thursday, October 09, 2008

Born from the Wind - Unique Multi-wavelength Portrait of Star Birth

ESO PR Photo 34/08
Credit: ESO/ESA/JPL-Caltech/NASA/D. Gouliermis (MPIA) et al.

Telescopes on the ground and in space have teamed up to compose a colourful image that offers a fresh look at the history of the star-studded region NGC 346. This new, ethereal portrait, in which different wavelengths of light swirl together like watercolours, reveals new information about how stars form.

The picture combines infrared, visible and X-ray light from NASA's Spitzer Space Telescope, ESO's New Technology Telescope (NTT) and the European Space Agency's XMM-Newton orbiting X-ray telescope, respectively. The NTT visible-light images allowed astronomers to uncover glowing gas in the region and the multi-wavelength image reveals new insights that appear only thanks to this unusual combination of information.

NGC 346 is the brightest star-forming region in the Small Magellanic Cloud, an irregular dwarf galaxy that orbits the Milky Way at a distance of 210 000 light-years.

"NGC 346 is a real astronomical zoo," says Dimitrios Gouliermis of the Max Planck Institute for Astronomy in Heidelberg, Germany, and lead author of the paper describing the observations. "When we combined data at various wavelengths, we were able to tease apart what's going on in different parts of this intriguing region."

Small stars are scattered throughout the NGC 346 region, while massive stars populate its centre. These massive stars and most of the small ones formed at the same time out of one dense cloud, while other less massive stars were created later through a process called "triggered star formation". Intense radiation from the massive stars ate away at the surrounding dusty cloud, triggering gas to expand and create shock waves that compressed nearby cold dust and gas into new stars. The red-orange filaments surrounding the centre of the image show where this process has occurred.

But another set of younger low-mass stars in the region, seen as a pinkish blob at the top of the image, couldn't be explained by this mechanism. "We were particularly interested to know what caused this seemingly isolated group of stars to form," says Gouliermis.

By combining multi-wavelength data of NGC 346, Gouliermis and his team were able to pinpoint the trigger as a very massive star that blasted apart in a supernova explosion about 50 000 years ago. Fierce winds from the massive dying star, and not radiation, pushed gas and dust together, compressing it into new stars, bringing the isolated young stars into existence. While the remains of this massive star cannot be seen in the image, a bubble created when it exploded can be seen near the large, white spot with a blue halo at the upper left (this white spot is actually a collection of three stars).

The finding demonstrates that both wind- and radiation-induced triggered star formation are at play in the same cloud. According to Gouliermis, "the result shows us that star formation is a far more complicated process than we used to think, comprising different competitive or collaborative mechanisms."

The analysis was only possible thanks to the combination of information obtained through very different techniques and equipments. It reveals the power of such collaborations and the synergy between ground- and space-based observatories.

More Information

D. Gouliermis et al., NGC 346 in the Small Magellanic Cloud. IV. Triggered Star Formation in the H II Region N 66, to appear in the Astrophysical Journal.
Other authors of this paper include Thomas Henning, Wolfgang Brandner, Eva Hennekemper, and Felix Hormuth of the Max Planck Institute for Astronomy, and You-Hua Chu and Robert Gruendl of the University of Illinois at Urbana-Champaign, USA.
The ESO 3.5-m New Technology Telescope (NTT), located at La Silla in Chile, was the first in the world to have a computer-controlled deformable main mirror (active optics), a technology developed at ESO and now applied to most of the world's current large telescopes.


Dimitrios Gouliermis
Max Planck Institute for Astronomy, Heidelberg, Germany
Phone: +49 6221 528 401
E-mail: dgoulier (at)

ESO Press Officer: Dr. Henri Boffin - +49 89 3200 6222 -
ESO Press Officer in Chile: Valentina Rodriguez - +56 2 463 3123 -

Wednesday, October 08, 2008

Big Galaxy Collisions Can Stunt Star Formation

Credit: Tomer Tal and Jeffrey Kenney/
Yale University and NOAO/AURA/NSF

A deep new image of the Virgo cluster has revealed monumental tendrils of ionized hydrogen gas 400,000 light-years long connecting the elliptical galaxy M86 and the disturbed spiral galaxy NGC 4438.

Taken with the wide-field Mosaic imager on the National Science Foundation’s Mayall 4-meter telescope at Kitt Peak National Observatory, this Hydrogen-alpha image and related spectroscopic measurements of the filament provide striking evidence of a previously unsuspected high-speed collision between the two galaxies.

“Our data show that this system represents the nearest recent collision between a large elliptical galaxy and a large spiral,” said Jeffrey Kenney of Yale University, lead author of a paper to be published in a November 2008 issue of Astrophysical Journal Letters. “This discovery provides some of the clearest evidence yet for high-speed collisions between large galaxies, and it suggests that the consequences of such collisions are a plausible alternative to black holes in trying to explain the mystery of what process turns off star formation in the biggest galaxies.”

The Virgo cluster is located approximately 50 million light-years from Earth. Previous studies had noticed disturbed H-alpha gas around each of the two galaxies, but no connection from the two had been inferred. Indeed, some results have suggested that NGC 4438 collided with the small lenticular galaxy NGC 4435, but NGC 4435 has a much higher line-of-sight velocity as seen from Earth and appears undisturbed.

Spectroscopy of selected regions along the filament between M86 and NGC 4438, obtained with the Sparsepak Integral Field Unit instrument on the WIYN 3.5-meter telescope on Kitt Peak, shows a fairly smooth velocity gradient between the galaxies, supporting the collision scenario. There are no obvious stars in the filaments.

“The image shows what you can find if you look deep and wide, and we needed to do both to see the M86-NGC4438 complex,” Kenney explains.

As in most elliptical galaxies, most of the gas within M86 is extremely hot, and therefore radiates X-rays. The X-ray distribution in M86 is irregular and sports a long plume, which had previously been interpreted as a tail of gas which is being stripped by ram pressure as M86 falls into the intracluster medium of the Virgo cluster. The new H-alpha image from Kitt Peak suggests that most of the disturbances to the interstellar medium in M86 are instead due to the collision with NGC 4438.

A current mystery in astronomy is what causes the biggest galaxies in the Universe—which are primarily ellipticals, like M86—to stop forming stars. “Something needs to heat up the gas so it doesn’t cool and form stars,” Kenney says. “A number of recent studies suggest that energy from active galactic nuclei associated with supermassive black holes may do this, but our new study shows that gravitational interactions may also do the trick.”

Low-velocity collisions, especially between small- to medium-sized galaxies, often cause an increase in the local star formation rate, as the collisions tend to cause gas to concentrate in the galaxy centers. But in high velocity collisions (which happen naturally between large galaxies, since their large gravity pulls mass inward much faster), the kinetic energy of the collision can cause the gas to heat up so much that it cannot easily cool and form stars.

While not many galaxies suffer such extreme collisions as M86, most galaxies experience minor mergers and gas accretion events, and these may play a significant role in heating the galaxy’s gas. These more common but modest events are very hard to study, since their observational signatures are weak.

“The same physical processes occur in both strong and weak encounters, and by studying the observable effects in extreme cases like M86 we can learn about the role of gravity in the heating of galaxy gas, which appears to be quite significant,” Kenney adds.

Co-authors of the study include Yale graduate student Tomer Tal, Hugh Crowl from the University of Massachusetts, WIYN Observatory Director George Jacoby, and John Feldmeier of Youngstown State University.

Kitt Peak National Observatory is part of the National Optical Astronomy Observatory (NOAO), which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. The founding members of the WIYN Observatory partnership are the University of Wisconsin, Indiana University, Yale University, and NOAO.

Saturday, October 04, 2008

NASA Spacecraft Finds the Sun is Not a Perfect Sphere

"Cantaloupe ridges" on the sun. The glowing white magnetic network is what gives the sun its extra oblateness during times of high solar activity. Amateur astronomer Gary Palmer took the picture in July 2005 using a violet calcium-K filter.
Credit: Gary Palmer

In this diagram, the sun's oblateness has been magnified 10,000 times for easy visibility. The blue curve traces the sun's shape averaged over a three month period. The black asterisked curve traces a shorter 10-day average. The "wiggles" in the 10-day curve are real, caused by strong magnetic ridges in the vicinity of sunspots.
Credit: NASA Goddard Space Flight

Scientists using NASA’s RHESSI spacecraft have measured the roundness of the sun with unprecedented precision. They find that it is not a perfect sphere. During years of high solar activity the sun develops a thin “cantaloupe skin” that significantly increases its apparent oblateness: the sun’s equatorial radius becomes slightly larger than its polar radius. Their results appear the Oct. 2nd edition of Science Express. 

“The sun is the biggest and therefore smoothest object in the solar system, perfect at the 0.001% level because of its extremely strong gravity,” says study co-author Hugh Hudson of UC Berkeley. “Measuring its exact shape is no easy task.”

The team accomplished the task by analyzing data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager, RHESSI for short, an x-ray/gamma-ray space telescope launched in 2002 on a mission to study solar flares. Although RHESSI was never intended to measure the roundness of the sun, it has turned out ideal for the purpose. RHESSI observes the solar disk through a narrow slit and spins at 15 rpm. The spacecraft’s rapid rotation and high data sampling rate (necessary to catch fast solar flares) make it possible for investigators to trace the shape of the sun with systematic errors much less than any previous study. Their technique is particularly sensitive to small differences in polar vs. equatorial radius or “oblateness.”

“We have found that the surface of the sun has rough structure: bright ridges arranged in a network pattern, as on the surface of a cantaloupe but much more subtle,” describes Hudson. During active phases of the solar cycle, these ridges emerge around the sun’s equator, brightening and fattening the “stellar waist.” At the time of RHESSI’s measurements in 2004, ridges increased the sun’s apparent equatorial radius by an angle of 10.77 +- 0.44 milli-arcseconds, or about the same as the width of a human hair viewed one mile away. 

“That may sound like a very small angle, but it is in fact significant,” says Alexei Pevtsov, RHESSI Program Scientist at NASA Headquarters. Tiny departures from perfect roundness can, for example, affect the sun’s gravitational pull on Mercury and skew tests of Einstein’s theory of relativity that depend on careful measurements of the inner planet’s orbit. Small bulges are also telltale signs of hidden motions inside the sun. For instance, if the sun had a rapidly rotating core left over from early stages of star formation, and if that core were tilted with respect to its outer layers, the result would be surface bulging. “RHESSI’s precision measurements place severe constraints on any such models.”

The “cantaloupe ridges” are magnetic in nature. They outline giant, bubbling convection cells on the surface of the sun called “supergranules.” Supergranules are like bubbles in a pot of boiling water amplified to the scale of a star; on the sun they measure some 30,000 km across (twice as wide as Earth) and are made of seething hot magnetized plasma. Magnetic fields at the center of these bubbles are swept out to the edge where they form ridges of magnetism. The ridges are most prominent during years around Solar Max when the sun’s inner dynamo “revs up” to produce the strongest magnetic fields. Solar physicists have known about supergranules and the magnetic network they produce for many years, but only now has RHESSI revealed their unexpected connection to the sun’s oblateness.

“When we subtract the effect of the magnetic network, we get a ‘true’ measure of the sun’s shape resulting from gravitational forces and motions alone,” says Hudson. “The corrected oblateness of the non-magnetic sun is 8.01 +- 0.14 milli arcseconds, near the value expected from simple rotation.”

Further analysis of RHESSI oblateness data may help researchers detect a long-sought type of seismic wave echoing through the interior of the sun: the gravitational oscillation or “g-mode.” Detecting g-modes would open a new frontier in solar physics—the study of the sun’s internal core.

The paper reporting these results, “A large excess in apparent solar oblateness due to surface magnetism,” was authored by Martin Fivian, Hugh Hudson, Robert Lin and Jabran Zahid, and appears in the Oct. 2nd issue of Science Express.

Dr. Tony Phillips
NASA Goddard Space Flight Center

A Star That Bursts, Blinks and Disappears

This illustration shows a flare from magnetar Swift J195509+261406. A starquake is probably what triggered the object's 40 optical flares. 
Credit: NASA/Swift/Sonoma State University/A. Simonnet

"Twinkle, twinkle little star" goes the nursery rhyme. Now, astronomers are reporting on a strange case where one of the littlest of stars "twinkled" with gamma rays, X-rays, and light -- and then vanished.

The story began on June 10, 2007. That’s when a spike of gamma-rays lasting less than five seconds washed over NASA's Swift satellite. But this high-energy flash wasn't a gamma-ray burst -- the birth cry of a black hole far across the universe. It was something much closer to home.

Swift immediately reported the event’s position to astronomers all over the world. Within a minute, robotic telescopes turned to a spot in the constellation Vulpecula. Because Swift found an X-ray glow coming from this point, astronomers cataloged the object as "Swift J195509+261406," after its position in the sky and the discovering satellite. (Well, they had to call it something!)

During the next three days, the object brightened and faded in visible light. Not once, not twice -- but 40 times! Eleven days later, it flashed again, this time at infrared wavelengths. Then, it disappeared from view.

"I love it when Swift enables a discovery like this," says Neil Gehrels, the mission's lead scientist at NASA Goddard Space Flight Center in Greenbelt, Md. "The observatory is an astronomical robot built for gamma-ray burst studies, but it can also quickly point at other bizarre objects with bright flares."

Astronomers think the object was a neutron star -- the crushed innards of a massive star that long ago exploded as a supernova -- about 15,000 light-years away. Writing in the Sept. 25 issue of the science journal Nature, a team of 42 scientists concludes that Swift J195509+261406 is a special type of neutron star called a magnetar.

"We are dealing with an object that was hibernating for decades before entering a brief activity period," explains Alberto J. Castro-Tirado, lead author of the paper. "Magnetars remain quiet for decades."

Although measuring only about 12 miles across -- about the size of a city -- neutron stars have the strongest magnetic fields in the cosmos. Sometimes, those magnetic fields are super strong -- more than 100 times the strength of typical neutron stars.

Astronomers put these magnetic monsters in their own class: magnetars. Only about a dozen magnetars are known, but scientists suspect our galaxy contains many more. We just don’t see them because they’re quiet most of the time.

So what happened last year? Why did this previously unseen star begin behaving so badly? And why did it stop?

Combine a magnetar's pumped-up magnetic field with its rapid spin, and sooner or later something has to give. Every now and then, the magnetar’s rigid crust snaps under the strain.

This "starquake" releases pent-up magnetic energy, which creates bursts of light and radiation. Once the star’s crust and magnetic field settle down, the star goes dark and disappears from our view. At least until the next quake.

Astronomers suspect that magnetars lose their punch as time passes, but Swift J195509+261406 provides the missing link between objects exhibiting regular activity and those that have settled into retirement -- and invisibility.

So twinkle, twinkle magnetar. That's how we'll learn just where you are.

Reflections of The Soul - IC 1848 by Ken Crawford

Credit:IC 1848 by Ken Crawford

If we want to be technical, Lynds Bright Nebula 667 is the designation and it's also known as Sharpless 2-199. Captured here is Collinder open clusters 34, 632 and 634 and small emission nebula 670 and 669 along with the entire cluster designation known as IC 1848. However, let's forsake science for just a few moments and take a look at what it's more commonly known as…. The "Soul Nebula".

Situated along the Perseus arm of the Milky Way galaxy, the "Soul Nebula" reflects true inner beauty as well as a generous portion of hard science. Just this year, this giant cloud of molecular gas was the target study for triggered star formation. According to the work of Thompson (et al); "We have carried out an in-depth study of three bright-rimmed clouds SFO 11, SFO 11NE and SFO 11E associated with the HII region IC 1848, using observations carried out at the James Clerk Maxwell Telescope (JCMT) and the Nordic Optical Telescope (NOT), plus archival data from IRAS, 2MASS and the NVSS. We show that the overall morphology of the clouds is reasonably consistent with that of radiative-driven implosion (RDI) models developed to predict the evolution of cometary globules. There is evidence for a photoevaporated flow from the surface of each cloud and, based upon the morphology and pressure balance of the clouds, it is possible that D-critical ionisation fronts are propagating into the molecular gas. The primary O star responsible for ionising the surfaces of the clouds is the 06V star HD 17505. Each cloud is associated with either recent or ongoing star formation: we have detected 8 sub-mm cores which possess the hallmarks of protostellar cores and identify YSO candidates from 2MASS data. We infer the past and future evolution of the clouds and demonstrate via a simple pressure-based argument that the UV illumination may have induced the collapse of the dense molecular cores found at the head of SFO 11 and SFO 11E."

With an estimated age of 1 Myr, IC 1848 is home to seventy-four sources of young stellar objects and all of them increase from outside of the rim to the center of the molecular cloud. The bright rim is an ionization front - the barrier between between the hot ionized gas of the HII region and the cold dense material of the molecular cloud where high mass stars are forming. Why is reflecting on the "Soul" so important? Probably because recent studies of meteorites have shown Fe isotopes present in the early solar nebula - suggesting our Sun was given birth in a region on high-mass star formation that experienced a supernova event. Bright-rimmed clouds like IC1848 replicate those conditions.

According to the work of J. Lett: "A bright IR source has been detected within a bright-rimmed dust cloud at the edge of the IC 1848 H II region. The source appears to be an early-type star with a circumstellar dust shell typical of protostars. This star is associated with the position of greatest CO excitation in a dense molecular cloud. The contours of CO emission correspond to those of the bright-rimmed dust cloud, showing that the star formed within the bright rim. Formaldehyde observations at 6 cm, 2 cm, and 2 mm are used to determine the density of the layer between the star and the ionized gas of the bright H..cap alpha.. rim. The location of this star, with respect to the dense molecular cloud which is subject to the external pressure of HII region, indicates the possible role of the expansion of IC 1848 in triggering star formation in dense regions at the perimeter of the H II region. The observed CO emission is used to determine the required luminosity of the embedded star. An early-type star of this luminosity should be detectable as a compact continuum source."

Indeed, NGC 1848 is in the earliest stages of massive star birth, but it's hidden behind its dust. According to Murry (et al): "We have completed a multiband (ultraviolet, optical, and near-infrared) study of the interstellar extinction properties of nine massive stars in IC 1805 and IC 1848, which are both part of Cas OB6 in the Perseus spiral arm. Our analysis includes determination of absolute extinction over the wavelength range from 3 ?m to 1250 Å. We have attempted to distinguish between foreground dust and dust local to Cas OB6. This is done by quantitatively comparing extinction laws of the least reddened sightlines (sampling mostly foreground dust) versus the most reddened sightlines (sampling a larger fraction of the dust in the Cas OB6 region). We have combined previous investigations to better understand the evolution of the interstellar medium in this active star forming region. We found no variation of extinction curve behavior between moderately reddened and heavily reddened Cas OB6 stars".
Shrouded in mystery yet home to Globulettes - the seeds of brown dwarfs and free-floating planetary-mass objects. From the work of G. F. Gahm (et al): "Some H II regions surrounding young stellar clusters contain tiny dusty clouds, which on photos look like dark spots or teardrops against a background of nebular emission which we call "globulettes," since they are much smaller than normal globules and form a distinct class of objects. Many globulettes are quite isolated and located far from the molecular shells and elephant trunks associated with the regions. Others are attached to the trunks (or shells), suggesting that globulettes may form as a consequence of erosion of these larger structures. Since the globulettes are not screened from stellar light by dust clouds farther in, one would expect photoevaporation to dissolve the objects. However, surprisingly few objects show bright rims or teardrop forms. We calculate the expected lifetimes against photoevaporation. These lifetimes scatter around 4 × 106 yr, much longer than estimated in previous studies and also much longer than the free-fall time. We conclude that a large number of our globulettes have time to form central low-mass objects long before the ionization front, driven by the impinging Lyman photons, has penetrated far into the globulette. Hence, the globulettes may be one source in the formation of brown dwarfs and free-floating planetary-mass objects in the galaxy."

Apparently there's a lot to contemplate when you look into the "Soul"….

Thursday, October 02, 2008

A Celestial Landscape in Celebration of 10 Years of Stunning Hubble Heritage Images

Credit: NASA, ESA, 
and The Hubble Heritage Team (STScI/AURA)

The landmark 10th anniversary of the Hubble Space Telescope's Hubble Heritage Project is being celebrated with a 'landscape' image from the cosmos. Cutting across a nearby star-forming region are the "hills and valleys" of gas and dust displayed in intricate detail. Set amid a backdrop of soft, glowing blue light are wispy tendrils of gas as well as dark trunks of dust that are light-years in height.

The Hubble Heritage Project, which began in October 1998, has released nearly 130 images mined from the Hubble data archive as well as a number of observations taken specifically for the project. By releasing a new, previously unseen Hubble image every month, the team's intent was to showcase some of the most attractive images ever taken by the Hubble telescope, and share them with a wide audience. The Heritage team continues to create aesthetic images that present the universe from an artistic perspective.

This month's three-dimensional-looking Hubble image shows the edge of the giant gaseous cavity within the star-forming region called NGC 3324. The glowing nebula has been carved out by intense ultraviolet radiation and stellar winds from several hot, young stars. A cluster of extremely massive stars, located well outside this image in the center of the nebula, is responsible for the ionization of the nebula and excavation of the cavity.

The image also reveals dramatic dark towers of cool gas and dust that rise above the glowing wall of gas. The dense gas at the top resists the blistering ultraviolet radiation from the central stars, and creates a tower that points in the direction of the energy flow. The high-energy radiation blazing out from the hot, young stars in NGC 3324 is sculpting the wall of the nebula by slowly eroding it away.

Located in the Southern Hemisphere, NGC 3324 is at the northwest corner of the Carina Nebula (NGC 3372), home of the Keyhole Nebula and the active, outbursting star Eta Carinae. The entire Carina Nebula complex is located at a distance of roughly 7,200 light-years, and lies in the constellation Carina.

This image is a composite of data taken with two of Hubble's science instruments. Data taken with the Advanced Camera for Surveys (ACS) in 2006 isolated light emitted by hydrogen. More recent data, taken in 2008 with the Wide Field Planetary Camera 2 (WFPC2), isolated light emitted by sulfur and oxygen gas. To create a color composite, the data from the sulfur filter are represented by red, from the oxygen filter by blue, and from the hydrogen filter by green.

The Heritage project has released images using several of Hubble's optical cameras: the Wide Field Planetary Camera (WF/PC), which was installed when the telescope was first deployed in 1990; WFPC2, which replaced WFPC in 1993 and is still in service today; and ACS, which was added in 2002. After the Hubble Servicing Mission in early 2009, the Hubble Heritage team hopes to continue using ACS as well as the newest of the optical cameras, Wide Field Camera 3.

For additional information, contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Md.

Keith Noll
Space Telescope Science Institute, Baltimore, Md.

Nathan Smith
University of California, Berkeley, Calif.

Wednesday, October 01, 2008

Infrared Echoes give NASA's Spitzer a Supernova Flashback

The Cassiopeia A supernova's first flash of radiation 
makes six clumps of dust (circled) unusually hot.
Credit:NASA/JPL-Caltech/E. Dwek and R. Arendt

Hot spots near the shattered remains of an exploded star are echoing the blast's first moments, say scientists using data from NASA's Spitzer Space Telescope.

Eli Dwek of NASA's Goddard Space Flight Center in Greenbelt, Md. and Richard Arendt of the University of Maryland, Baltimore County, say these echoes are powered by radiation from Cassiopeia A supernova shock wave that blew the star apart some 11,000 years ago.

"We're seeing the supernova's first flash," Dwek said.

Previously, other Spitzer researchers discovered hot spots near the Cassiopeia A supernova remnant and recognized the spots' importance as light echoes of the original blast. Dwek and Arendt used Spitzer data to probe this hot dust and pin down the cause of the echoes more precisely.

Six knots of silicate dust near the remnant show temperatures between -173 and -123 degrees Celsius (-280 and -190 degrees Fahrenheit). Although this might seem frigid by earthly standards, such temperatures are downright hot compared to typical interstellar dust.

Writing in the October 1 issue of The Astrophysical Journal, the scientists show that the only event that could make the grains this hot is the powerful and short-lived pulse of ultraviolet radiation and X-rays that heralded the death of the star. The flash was a hundred billion times brighter than the sun, but lasted only a day or so.

"They've identified the precise event during the demolition of the star that produces the echo we see," said Michael Werner, the project scientist for Spitzer at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Light from the explosion reached Earth in the 17th century, but no one noticed. The Spitzer find gives astronomers a second chance to study the supernova as it unfolds.

Although the explosion originally escaped detection, its aftermath -- a hot, expanding gas cloud known as Cassiopeia A (Cas A, for short) -- is one of the best-studied supernova remnants. The blast zone lies 11,000 light-years away in the constellation Cassiopeia.

When a massive star runs out of nuclear fuel, its core collapses into a superdense, city-sized object called a neutron star. As the neutron star forms, it stiffens and rebounds. This triggers a mammoth shock wave that blows the star's outer layers to smithereens. The exiting shock creates a high-energy flash that precedes the supernova's rise in visible light.

Evidence for a flash associated with this "shock breakout" existed only in computer simulations until January 9, 2008. That's when NASA's Swift satellite detected a 5-minute-long X-ray pulse from galaxy NGC 2770. A few days later, a new supernova -- designated SN 2008D -- appeared in the galaxy.

The infrared echoes from Cas A arise from dust clouds about 160 light-years farther away than the remnant. The supernova's initial radiation pulse expands through space at the speed of light, then encounters the clouds and heats their dust grains. The dust, in turn, re-radiates the energy at infrared wavelengths.

The breakout radiation took 160 years to reach the clouds and, once heated, the dust's infrared energy had to make up the same distance. This extra travel time results in a 320-year offset between the supernova's initial outward-moving flash and arrival of the dust's infrared echo at Earth. The researchers plan to use the echoes to paint an intimate portrait of the explosion, the star and the immediate environment.

When light from the Cas A supernova first reached Earth in the late 1600s, no one reported seeing a new star. On August 16, 1680, the English astronomer John Flamsteed might have seen the supernova without recognizing it. He recorded a faint naked-eye star near the position of Cas A, but none exists there now.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer 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.

Francis Reddy / Rob Gutro
Goddard Space Flight Center
301-286-4453 / 301-286-4044 /