An Arc Sculpted by Gravity

LRG-4-606

Credit: ESA/Hubble & NASA

This NASA/ESA Hubble Space Telescope image shows remarkable structures in a galaxy cluster around an object called LRG-4-606. LRG stands for Luminous Red Galaxy, and is the acronym given to a large collection of bright red galaxies found in the Sloan Digital Sky Survey (SDSS). These objects are mostly massive elliptical galaxies composed of huge numbers of old stars.

It is sobering to contemplate the sheer number of stars that this image must contain — hundreds of billions — but it also features one of the strangest phenomena known to astronomers. This particular red galaxy and its surrounding galaxies happen to be positioned so that their strong gravitational field has a dramatic effect.

Left of centre in the picture, blue galaxies in the background have been stretched and warped out of shape into narrow, pale blue arcs. This is because of an effect called gravitational lensing. The galaxy cluster has such a strong gravitational field that it is curving the fabric of space and amplifying the starlight from much more distant galaxies. Gravitational lensing normally creates elongated arcs and here, unusually, the alignment of the galaxies has made the separate arcs combine to form a half-circle.

This picture was assembled from a collection of exposures in visible and near infrared light taken with Hubble’s Wide Field Camera 3. The field of view is approximately 3 by 3 arcminutes.

NASA Space Telescope Finds Fewer Asteroids Near Earth

NEOWISE observations indicate that there are at least 40 percent fewer near-Earth asteroids in total that are larger than 330 feet, or 100 meters. Our solar system's four inner planets are shown in green, and our sun is in the center. Each red dot represents one asteroid. Object sizes are not to scale. Image credit: NASA/JPL-Caltech. Larger image | See animation

This chart illustrates how infrared is used to more accurately determine an asteroid's size.

Image credit: NASA/JPL-Caltech
Full image and caption | enlarge image

This chart illustrates how infrared is used to more accurately determine an asteroid's size.

Image credit: NASA/JPL-Caltech.
Full image and caption | Related Chart | enlarge image

WISE Finds Fewer Asteroids near Earth
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PASADENA, Calif. -- New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.

Astronomers now estimate there are roughly 19,500 -- not 35,000 -- mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought. However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 330 and 3,300-feet wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.

The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth's orbital vicinity. WISE observed infrared light from those in the middle to large-size category. The survey project, called NEOWISE, is the asteroid-hunting portion of the WISE mission. Study results appear in the Astrophysical Journal.

"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," said Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country."

WISE scanned the entire celestial sky twice in infrared light between January 2010 and February 2011, continuously snapping pictures of everything from distant galaxies to near-Earth asteroids and comets. NEOWISE observed more than 100 thousand asteroids in the main belt between Mars and Jupiter, in addition to at least 585 near Earth.

WISE captured a more accurate sample of the asteroid population than previous visible-light surveys because its infrared detectors could see both dark and light objects. It is difficult for visible-light telescopes to see the dim amounts of visible-light reflected by dark asteroids. Infrared-sensing telescopes detect an object's heat, which is dependent on size and not reflective properties.

Though the WISE data reveal only a small decline in the estimated numbers for the largest near-Earth asteroids, which are 3,300 feet (1 kilometer) and larger, they show 93 percent of the estimated population have been found. This fulfills the initial "Spaceguard" goal agreed to with Congress. These large asteroids are about the size of a small mountain and would have global consequences if they were to strike Earth. The new data revise their total numbers from about 1,000 down to 981, of which 911 already have been found. None of them represents a threat to Earth in the next few centuries. It is believed that all near-Earth asteroids approximately 6 miles (10 kilometers) across, as big as the one thought to have wiped out the dinosaurs, have been found.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.

The situation is different for the mid-size asteroids, which could destroy a metropolitan area if they were to impact in the wrong place. The NEOWISE results find a larger decline in the estimated population for these bodies than what was observed for the largest asteroids. So far, the Spaceguard effort has found and is tracking more than 5,200 near-Earth asteroids 330 feet or larger, leaving more than an estimated 15,000 still to discover. In addition, scientists estimate there are more than a million unknown smaller near-Earth asteroids that could cause damage if they were to impact Earth.

"NEOWISE was just the latest asset NASA has used to find Earth's nearest neighbors," said Lindley Johnson, program executive for the Near Earth Object Observation Program at NASA Headquarters in Washington. "The results complement ground-based observer efforts over the past 12 years. These observers continue to track these objects and find even more."

WISE is managed and operated by JPL for NASA's Science Mission Directorate in Washington. The principal investigator, Edward Wright, is at the University of California, Los Angeles. The WISE science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace and Technologies Corp. in Boulder, Colo. Science operations and data processing occur at the Infrared Processing and Analysis Center at the California Institute of Technology.

For more information about the mission, visit: http://www.nasa.gov/wise

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.clavin@jpl.nasa.gov

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov

Galaxy Caught Blowing Bubbles

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Hubble image of irregular galaxy Holmberg II

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Wide-field image of irregular galaxy Holmberg II (ground-based image)

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Zooming in on galaxy Holmberg II

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Panning across galaxy Holmberg II

Hubble’s famous images of galaxies typically show elegant spirals or soft-edged ellipses. But these neat forms are only representative of large galaxies. Smaller galaxies like the dwarf irregular galaxy Holmberg II come in many shapes and types that are harder to classify. This galaxy’s indistinct shape is punctuated by huge glowing bubbles of gas, captured in this image from the NASA/ESA Hubble Space Telescope.

The intricate glowing shells of gas in Holmberg II were created by the energetic lifecycles of many generations of stars. High-mass stars form in dense regions of gas, and later in life expel strong stellar winds that blow away the surrounding material. At the very end of their lives, they explode in as a supernova. Shock waves rip through these less dense regions blowing out and heating the gas, forming the delicate shells we see today.

Holmberg II is a patchwork of dense star-forming regions and extensive barren areas with less material, which can stretch across thousands of light-years. As a dwarf galaxy, it has neither the spiral arms typical of galaxies like the Milky Way nor the dense nucleus of an elliptical galaxy. This makes Holmberg II, gravitationally speaking, a gentle haven where fragile structures such as these bubbles can hold their shape.

While the galaxy is unremarkable in size, Holmberg II does have some intriguing features. As well as its unusual appearance — which earned it a place in Halton Arp’s Atlas of Peculiar Galaxies, a treasure trove of weird and wonderful objects — the galaxy hosts an ultraluminous X-ray source in the middle of three gas bubbles in the top right of the image. There are competing theories as to what causes this powerful radiation — one intriguing possibility is an intermediate-mass black hole which is pulling in material from its surroundings.

This colourful image is a composite of visible and near-infrared exposures taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys.

Notes

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

Contacts

Oli Usher
Hubble/ESA
Garching, Germany
Tel: +49-89-3200-6855
Email: ousher@eso.org

Space Telescopes Reveal Secrets of Turbulent Black Hole

Image Credit: NASA, ESA, G. Kriss (STScI), and
J. de Plaa (SRON Netherlands Institute for Space Research)

Acknowledgment: B. Peterson (Ohio State University)

Science Credit: NASA, ESA, J. Kaastra (SRON Netherlands Institute for Space Research),

and G. Kriss (STScI)

An international team of astronomers using five different telescopes has uncovered striking features around a supermassive black hole in the core of the distant galaxy Markarian 509. They found a very hot corona hovering above the black hole and cold gas "bullets" in hotter diffuse gas, speeding outward with velocities over 1 million miles per hour. This corona absorbs and reprocesses the ultraviolet light from the accretion disk encircling the black hole, energizing it and converting it into X-rays. This discovery allows astronomers to make sense of some of the observations of active galaxies that have been hard to explain so far. The heart of the campaign consisted of repeated visible, X-ray, and gamma-ray observations with ESA's XMM-Newton and INTEGRAL satellites, which monitored Markarian 509 for six weeks. This was followed by long observations with NASA's Chandra X-ray Observatory and the Hubble Space Telescope. Prior to these observations short snapshots to monitor the behavior of the source at all wavelengths were taken with NASA's Swift satellite. The combined efforts of all these instruments gave astronomers an unprecedented insight into the core of an active galaxy.

The Cosmic Origins Spectrograph aboard Hubble reveals that the coolest gas in the line of sight toward Markarian 509 has 14 different velocity components at various locations in the innermost parts of this galaxy. Hubble's data, combined with X-ray observations, show that most of the visible outflowing gas is blown off from a dusty gas disk surrounding the central region more than 15 light-years away from the black hole. This outflow consists of dense, cold blobs or gas bullets embedded in hotter diffuse gas. The international consortium responsible for this campaign consists of 26 astronomers from 21 institutes on 4 continents. The first results of this campaign will be published as a series of seven papers in the journal Astronomy and Astrophysics. More results are in preparation. For more information about this study, visit:
http://www.sron.nl/index.php?option=com_content&task=view&id=3277&Itemid=754
http://www.spacetelescope.org/announcements/ann1121/

NGC 281: Living the High Life

NGC 281
Credit: X-ray: NASA/CXC/CfA/S.Wolk;
IR: NASA/JPL/CfA/S.Wolk

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High-mass stars are important because they are responsible for much of the energy pumped into our galaxy over its lifetime. Unfortunately, these stars are poorly understood because they are often found relatively far away and can be obscured by gas and dust. The star cluster NGC 281 is an exception to this rule. It is located about 9,200 light years from Earth and, remarkably, almost 1,000 light years above the plane of the Galaxy, giving astronomers a nearly unfettered view of the star formation within it.

NGC 281 in relation to the Milky Way plane.
Milky Way image by Nick Risinger, skysurvey.org

This composite image of NGC 281 contains X-ray data from Chandra (purple) with infrared observations from Spitzer (red, green, blue). The high-mass stars in NGC 281 drive many aspects of their galactic environment through powerful winds flowing from their surfaces and intense radiation that heats surrounding gas, "boiling it away" into interstellar space. This process results in the formation of large columns of gas and dust, as seen on the left side of the image. These structures likely contain newly forming stars. The eventual deaths of massive stars as supernovas will also seed the galaxy with material and energy.

NGC 281 is known informally as the "Pacman Nebula" because of its appearance in optical images. In optical images the "mouth" of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared Spitzer image the dust in this region glows brightly.

Fast Facts for NGC 281:

Scale: Image is about 18 arcmin across (about 48 light years)
Category: Normal Stars & Star Clusters
Coordinates: (J2000) RA 00h 52m 59.35s | Dec +56° 37' 18.8"
Constellation: Cassiopeia
Observation Date: 3 pointings from 11/10/05-11/12/05
Observation Time: 27 hours 30 min.
Obs. ID: 5424, 7205-7206
Color Code: X-ray (Purple); Infrared (Red, Green, Blue)
Instrument: ACIS
Distance Estimate: About 9,200 light years

Feast your Eyes on the Fried Egg Nebula

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The Fried Egg Nebula

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The Fried Egg Nebula in the constellation of Scorpius

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Wide-field image of the sky around the Fried Egg nebula

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Zooming in on The Fried Egg Nebula

Astronomers have used ESO’s Very Large Telescope to image a colossal star that belongs to one of the rarest classes of stars in the Universe, the yellow hypergiants. The new picture is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the central hypergiant. The star and its shells resemble an egg white around a yolky centre, leading the astronomers to nickname the object the Fried Egg Nebula.

The monster star, known to astronomers as IRAS 17163-3907 [1], has a diameter about a thousand times bigger than our Sun. At a distance of about 13 000 light-years from Earth, it is the closest yellow hypergiant found to date and new observations show it shines some 500 000 times more brightly than the Sun [2].

“This object was known to glow brightly in the infrared but, surprisingly, nobody had identified it as a yellow hypergiant before,” said Eric Lagadec (European Southern Observatory), who led the team that produced the new images.

The observations of the star and the discovery of its surrounding shells were made using the VISIR infrared camera on the VLT. The pictures are the first of this object to clearly show the material around it and reveal two almost perfectly spherical shells.

If the Fried Egg Nebula were placed in the centre of the Solar System the Earth would lie deep within the star itself and the planet Jupiter would be orbiting just above its surface. The much larger surrounding nebula would engulf all the planets and dwarf planets and even some of the comets that orbit far beyond the orbit of Neptune. The outer shell has a radius of 10 000 times the distance from the Earth to the Sun.

Yellow hypergiants are in an extremely active phase of their evolution, undergoing a series of explosive events — this star has ejected four times the mass of the Sun in just a few hundred years [3]. The material flung out during these bursts has formed the extensive double shell of the nebula, which is made of dust rich in silicates and mixed with gas.

This activity also shows that the star is likely to soon die an explosive death — it will be one of the next supernova explosions in our galaxy [4]. Supernovae provide much-needed chemicals to the surrounding interstellar environment and the resulting shock waves can kick start the formation of new stars.

The Very Large Telescope mid-IR instrument, VISIR, captured this delicious image of the Fried Egg Nebula through three mid-infrared filters that are here coloured blue, green and red [5].

Notes

[1] The name indicates that the object was first spotted as an infrared source by the IRAS satellite in 1983 and the numbers show the star’s place in the sky, in the heart of the Milky Way in the constellation of Scorpius (The Scorpion).

[2] IRAS 17163-3907 is one of the 30 brightest stars in the infrared sky, at the wavelength of 12 microns observed by IRAS, but it had been overlooked because it is quite faint in visible light.

[3] The total mass of this star is estimated to be roughly twenty times that of the Sun.

[4] After burning all their hydrogen all stars of ten solar masses or more become red supergiants. This phase ends when the star has finished burning all of its helium. Some of these high-mass stars then spend just a few million years in the post-red supergiant phase as yellow hypergiants, a relatively short time in the life of a star, before rapidly evolving into another unusual type of star called a luminous blue variable. These hot and brilliant stars are continuously varying in brightness and are losing matter due to the strong stellar winds they expel. But this is not the end of the star’s evolutionary adventure, as it may next become a different kind of unstable star known as a Wolf-Rayet star (http://www.eso.org/public/images/wr124/), before ending its life as a violent supernova explosion.

[5] The three mid-infrared filters that were used passed light at wavelengths around 8590 nm (coloured blue), 11 850 nm (coloured green) and 12 810 nm (coloured red).
More information

This research is presented in a paper “A double detached shell around a post-Red Supergiant: IRAS 17163-3907, the Fried Egg nebula" by E. Lagadec et al., accepted for publication in the journal Astronomy & Astrophysics.

The team is composed of E. Lagadec (ESO, Garching, Germany), A.A. Zijlstra (Jodrell Bank Center For Astrophysics, Manchester, UK), R.D. Oudmaijer (University of Leeds, UK), T. Verhoelst (Instituut voor Sterrenkunde, Leuven, Belgium), N.L.J. Cox (Instituut voor Sterrenkunde), R. Szczerba (N. Copernicus Astronomical Center, Torun, Poland), D. Mékarnia (Observatoire de la Côte d’Azur, Nice, France) and H. van Winckel (Instituut voor Sterrenkunde).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links
Research paper: A&A paper

Contacts

Dr Eric Lagadec
Astronomer, ESO
Garching bei München, Germany
Tel: +49 89 3200 6932
Email: elagadec@eso.org

Richard Hook
Public Information Officer, ESO
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

Spitzer Detects a Steaming Super-Earth Eclipsing Its Star

55 Cancri e
Credit: NASA/JPL-Caltech/R. Hurt (SSC)

NASA's Spitzer Space Telescope has gathered surprising new details about a supersized and superheated version of Earth called 55 Cancri e. According to Spitzer data, the exoplanet is less dense than previously thought, a finding which profoundly changes the portrait of this exotic world. Instead of a dense rock scorched dry by its sun, 55 Cancri e likely has water vapor and other gases steaming from its molten surface.

Spitzer measured the extraordinarily small amount of light 55 Cancri e blocked when the planet crossed in front of its star. These mini-eclipses, called transits, allow astronomers to accurately determine a planet's size and calculate its density. Promisingly, the results show how astronomers can use Spitzer, operating in "warm" mode since depleting its liquid coolant in May 2009, to probe the properties of strange alien worlds.

"This work demonstrates that 'warm' Spitzer can measure an extremely faint eclipse caused by exoplanets' transits with very high precision," said Brice-Olivier Demory, a post-doctoral associate in Professor Sara Seager's group in the Earth, Atmospheric and Planetary Sciences department at the Massachusetts Institute of Technology (MIT). Demory, who is lead author of a paper accepted for publication in Astronomy & Astrophysics, said that the study "emphasizes the important role Spitzer still has to play for the detection and characterization of transiting planets."

Blazing Hot and on the Move

Astronomers first discovered 55 Cancri e in 2004, and continued investigation of the exoplanet has shown it to be a truly bizarre place. The world revolves around its sunlike star in the shortest time period of all known exoplanets - just 17 hours and 40 minutes. (In other words, a year on 55 Cancri e lasts less than 18 hours.) The exoplanet orbits about 26 times closer to its star than Mercury, the most Sun-kissed planet in our solar system. Such proximity means that 55 Cancri e's surface roasts at a minimum of 3,200 degrees Fahrenheit (1,760 degrees Celsius).

The new observations with Spitzer reveal 55 Cancri e to have a mass 7.8 times and a radius just over twice that of Earth. Those properties place 55 Cancri e in the "super-Earth" class of exoplanets, a few dozen of which have been found. Only a handful of known super-Earths, however, cross the face of their stars as viewed from our vantage point in the cosmos. At just 40 light years away, 55 Cancri e stands as the smallest transiting super-Earth in our stellar neighborhood. In fact, 55 Cancri is so bright and close that it can be seen with the naked eye on a clear, dark night.

Based on the precise Spitzer data, Demory and his colleagues came up with a revised, lower density for 55 Cancri e. Coupled with its tight orbit, 55 Cancri e possesses a unique combination of super-Earth traits. Its low density is similar to that of a cooler super-Earth called GJ1214b, discovered in 2009 orbiting a tiny, dim star. Yet 55 Cancri e's orbit is more like that of the denser, inferno worlds CoRoT-7b and Kepler-10b. "What makes 55 Cancri e so remarkable is that despite its high temperature, the planet has a low density," said Demory.

Previously, a separate international team of astronomers had made observations of 55 Cancri e in visible light with Canada's MOST telescope. Initially, their evidence implied that 55 Cancri e's diameter was smaller by 25 percent, leading to reports of 55 Cancri e as actually the densest planet known. Refinements to those observations, however, now agree with the new Spitzer findings, which rely on a transit seen in longer-wavelength infrared light.

Exoplanetary Origins and Future Demise

No longer looking like a dense planet of solid rock, 55 Cancri e instead appears to be an unprecedented world with an intriguing history. The Spitzer results suggest that about a fifth of the planet's mass must be made of light elements and compounds, including water. In the intense heat of 55 Cancri e's terribly close sun, those light materials would exist in a "supercritical" state, between that of a liquid and a gas, and might sizzle out of the planet's surface.

New developments in planetary formation and evolution theory will probably be necessary to explain 55 Cancri e's back story. According to our models of the birth of solar systems, for example, 55 Cancri e could not have formed so near its star. Maybe it started out as a more distant planet with a large gaseous atmosphere. As worlds took shape in the 55 Cancri solar system, gravitational interactions amongst the system's five known planets could have prodded a young 55 Cancri e to migrate in toward its sun. In the process, the Neptune-like exoplanet might have lost most of its atmosphere, exposing a core that sputters with the venting of heated chemicals.

It seems certain that 55 Cancri e is on a "death spiral," soon to be devoured or ripped apart by its host star. But for now, the world's serendipitous placement in our sky will allow Spitzer and other instruments to study 55 Cancri e in further detail, expanding our knowledge of how exoplanets work.

"55 Cancri e orbits a very bright star thus enabling the possibility of obtaining a wealth of observations with space-based facilities at various wavelengths," said study co-author Michael Gillon of the University of Liege in Belgium and principal investigator for the warm Spitzer program aimed at detecting transiting low-mass exoplanets. "This fact will make 55 Cancri e a landmark for our understanding of the planetary interior and atmospheric composition of super-Earths."

Other authors of the paper are Diana Valencia, Sara Seager and Bjorn Benneke of MIT; Drake Deming of the University of Maryland; Christophe Lovis, Michel Mayor, Francesco Pepe, Didier Queloz, Damien Ségransan, and Stéphane Udry of the University of Geneva; and Patricio Cubillos, Joseph Harrington, and Kevin B. Stevenson of the University of Central Florida.

Source: Spitzer Space Telescope

Galaxies in a Swarm of Star Clusters

NGC 4874
Credit: ESA/Hubble & NASA

In the centre of a rich cluster of galaxies located in the direction of the constellation of Coma Berenices, lies a galaxy surrounded by a swarm of star clusters. NGC 4874 is a giant elliptical galaxy, about ten times larger than the Milky Way, at the centre of the Coma Galaxy Cluster. With its strong gravitational pull, it is able to hold onto more than 30 000 globular clusters of stars, more than any other galaxy that we know of, and even has a few dwarf galaxies in its grasp.

In this NASA/ESA Hubble Space Telescope image, NGC 4874 is the brightest object, located to the right of the frame and seen as a bright star-like core surrounded by a hazy halo. A few of the other galaxies of the cluster are also visible, looking like flying saucers dancing around NGC 4874. But the really remarkable feature of this image is the point-like objects around NGC 4874, revealed on a closer look: almost all of them are clusters of stars that belong to the galaxy. Each of these globular star clusters contains many hundreds of thousands of stars.

Recently, astronomers discovered that a few of these point-like objects are not star clusters but ultra-compact dwarf galaxies, also under the gravitational influence of NGC 4874. Being only about 200 light-years across and mostly made up of old stars, these galaxies resemble brighter and larger versions of globular clusters. They are thought to be the cores of small elliptical galaxies that, due to the violent interactions with other galaxies in the cluster, lost their gas and surrounding stars.

This Hubble image also shows many more distant galaxies that do not belong to the cluster, seen as small smudges in the background. While the galaxies in the Coma Cluster are located about 350 million light-years away, these other objects are much further out. Their light took several hundred million to billions of years to reach us.

Most unusually, the image also shows a very faint blue satellite trail, extending across the whole image, from the upper left corner of the frame to the lower right. Because Hubble’s cameras can only see a tiny part of the sky at one time, such trails are very rare.

This picture was created from optical and near-infrared exposures taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. The field of view is 3.3 arcminutes across.

Citizen Scientists, Kepler and Keck Uncover New Planets

Artists conception of Jupiter-like exoplanets orbiting close to their stars and detected by the Kepler telescope. It takes Keck telescopes to confirm the existence of these planets and extract more information about them. Credit: NASA

Astronomers at Yale University have announced the discovery of the first two potential exoplanets found by the online citizen scientist Planet Hunters program. Users of the Planet Hunters program analyze scientific data collected by NASA’s Kepler mission to assist astronomers in finding planets orbiting nearby stars. The most likely exoplanet candidates are then studied using the 10-meter telescopes of the W.M. Keck Observatory in Hawaii to confirm the planets’ existence.

Since the online citizen science project Planet Hunters launched last December, 40,000 web users from around the world have been helping professional astronomers analyze the light from 150,000 stars in the hopes of discovering Earth-like planets orbiting around them. A new study on the discovery is slated to be published (when?) in the Monthly Notices of the Royal Astronomical Society.

“This is the first time that the public has used data from a NASA space mission to detect possible planets orbiting other stars,” said Yale astronomer and exoplanet expert Debra Fischer, who helped launch the citizen science project.

The candidate planets orbit their host stars with periods ranging from 10 to 50 days—much shorter than the 365 days it takes the Earth to orbit the Sun—and have radii that range in size from two-and-a-half to eight times Earth’s radius. Despite those differences, one of the two candidates could be a rocky, Earth-mass planet (as opposed to a giant gas planet like Jupiter), although they aren’t in the so-called “habitable zone” where liquid water, and therefore life as we know it, could exist.

Next, the professional astronomy team – a collaboration between astronomers at Yale, the University of Oxford and the Adler Planetarium in Chicago
—used the Keck Observatory in Hawaii to analyze the spectra of the host stars. The spectra reveal whether the stars are wobbling, and by how much and at what speed – all of which reveal clues to the planets orbiting them.

The Kepler team had already announced they had identified 1,200 exoplanet candidates and that they would follow up on the highest potential ones, but they had discarded the two found by Planet Hunters users for various technical reasons that led them to believe they weren’t promising candidates.

“These two candidates might have gone undetected without Planet Hunters and its citizen scientists,” said Meg Schwamb, a Yale researcher and Planet Hunters co-founder. “Obviously Planet Hunters doesn’t replace the analysis being done by the Kepler team. But it has proven itself to be a valuable tool in the search for other worlds.”

Users found the two candidates in the first month of Planet Hunters operations using data the Kepler mission made publicly available. The Planet Hunters group sent the top 10 candidates found by the citizen scientists to the Kepler team, who analyzed the data and determined that two of the 10 met their criteria for being classified as planet candidates. The two candidates were flagged as potential planets by several dozen different Planet Hunters users, as the same data are analyzed by more than one user.

“Scientists on the Kepler team obtained the data, but the public helped finance the project with their tax dollars,” Fischer said. “It’s only right that this data has been pushed back into the public domain, not just as scientifically digested results but in a form where the public can actively participate in the hunt. The space program is a national treasure—a monument to America’s curiosity about the Universe. It is such an exciting time to be alive and to see these incredible discoveries being made.”

Planet Hunters users are now sifting through the next 90 days of Kepler data in the hopes of adding to the count. “This is what we found after just a preliminary glance through the first round of Kepler data,” Fischer said. “There’s no doubt that, with each new round of data, there will be more discoveries to come.”

# # #

Learn more about Planet Hunters:
http://www.planethunters.org

Watch a video of Planet Hunters co-founders Debra Fischer and Kevin Schawinski explaining the project:
http://www.youtube.com/user/YaleUniversity#p/search/0/18NCx-iBHBQ

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which removes much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Adapted from a press release by Yale University

Saturn's Moon Enceladus Spreads Its Influence

Water vapor and ice erupt from Saturn's moon Enceladus, the source of a newly discovered donut-shaped cloud around Saturn. Full image and caption

Chalk up one more feat for Saturn's intriguing moon Enceladus. The small, dynamic moon spews out dramatic plumes of water vapor and ice -- first seen by NASA's Cassini spacecraft in 2005. It possesses simple organic particles and may house liquid water beneath its surface. Its geyser-like jets create a gigantic halo of ice, dust and gas around Enceladus that helps feed Saturn's E ring. Now, thanks again to those icy jets, Enceladus is the only moon in our solar system known to influence substantially the chemical composition of its parent planet.

In June, the European Space Agency announced that its Herschel Space Observatory, which has important NASA contributions, had found a huge donut-shaped cloud, or torus, of water vapor created by Enceladus encircling Saturn. The torus is more than 373,000 miles (600,000 kilometers) across and about 37,000 miles (60,000 kilometers) thick. It appears to be the source of water in Saturn's upper atmosphere.

Though it is enormous, the cloud had not been seen before because water vapor is transparent at most visible wavelengths of light. But Herschel could see the cloud with its infrared detectors. "Herschel is providing dramatic new information about everything from planets in our own solar system to galaxies billions of light-years away," said Paul Goldsmith, the NASA Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The discovery of the torus around Saturn did not come as a complete surprise. NASA's Voyager and Hubble missions had given scientists hints of the existence of water-bearing clouds around Saturn. Then in 1997, the European Space Agency's Infrared Space Observatory confirmed the presence of water in Saturn's upper atmosphere. NASA's Submillimeter Wave Astronomy Satellite also observed water emission from Saturn at far-infrared wavelengths in 1999.

While a small amount of gaseous water is locked in the warm, lower layers of Saturn's atmosphere, it can't rise to the colder, higher levels. To get to the upper atmosphere, water molecules must be entering Saturn's atmosphere from somewhere in space. But from where and how? Those were mysteries until now.

Build the model and the data will come.

The answer came by combining Herschel's observations of the giant cloud of water vapor created by Enceladus' plumes with computer models that researchers had already been developing to describe the behavior of water molecules in clouds around Saturn.

One of these researchers is Tim Cassidy, a recent post-doctoral researcher at JPL who is now at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder. "What's amazing is that the model," said Cassidy, "which is one iteration in a long line of cloud models, was built without knowledge of the observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren't expecting such detailed 'images' of the torus, and the match between model and data was a wonderful surprise."

The results show that, though most of the water in the torus is lost to space, some of the water molecules fall and freeze on Saturn's rings, while a small amount -- about 3 to 5 percent -- gets through the rings to Saturn's atmosphere. This is just enough to account for the water that has been observed there.

Herschel's measurements combined with the cloud models also provided new information about the rate at which water vapor is erupting out of the dark fractures, known as "tiger stripes," on Enceladus' southern polar region. Previous measurements by the Ultraviolet Imaging Spectrograph (UVIS) instrument aboard the Cassini spacecraft showed that every second the moon is ejecting about 440 pounds (200 kilograms) of water vapor.

"With the Herschel measurements of the torus from 2009 and 2010 and our cloud model, we were able to calculate a source rate for water vapor coming from Enceladus," said Cassidy. "It agrees very closely with the UVIS finding, which used a completely different method."

"We can see the water leaving Enceladus and we can detect the end product -- atomic oxygen -- in the Saturn system," said Cassini UVIS science team member Candy Hansen, of the Planetary Science Institute, Tucson, Ariz. "It's very nice with Herschel to track where it goes in the meantime."

While a small fraction of the water molecules inside the torus end up in Saturn's atmosphere, most are broken down into separate atoms of hydrogen and oxygen.
"When water hangs out in the torus, it is subject to the processes that dissociate water molecules," said Hansen, "first to hydrogen and hydroxide, and then the hydroxide dissociates into hydrogen and atomic oxygen." This oxygen is dispersed through the Saturn system. "Cassini discovered atomic oxygen on its approach to Saturn, before it went into orbit insertion. At the time, no one knew where it was coming from. Now we do."

"The profound effect this little moon Enceladus has on Saturn and its environment is astonishing," said Hansen.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter and several of its instruments were designed, developed and assembled at JPL.

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at JPL. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the United States astronomical community.

Rosemary Sullivant 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
Rosemary.sullivant@jpl.nasa.gov

An Angry Bird in the Sky

PR Image eso1135a
The Running Chicken Nebula

PR Image eso1135b
The Running Chicken Nebula in the constellation of Centaurus

PR Video eso1135a
Zooming in on the Running Chicken Nebula

A new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope reveals the Lambda Centauri Nebula, a cloud of glowing hydrogen and newborn stars in the constellation of Centaurus (The Centaur). The nebula, also known as IC 2944, is sometimes nicknamed the Running Chicken Nebula, from a bird-like shape some people see in its brightest region.

In the nebula, which lies around 6500 light-years from Earth, hot newborn stars that formed from clouds of hydrogen gas shine brightly with ultraviolet light. This intense radiation in turn excites the surrounding hydrogen cloud, making it glow a distinctive shade of red. This red shade is typical of star-forming regions, another famous example being the Lagoon Nebula (eso0936).

Some people see a chicken shape in pictures of this red star-forming region, giving the nebula its nickname — though there is some disagreement over exactly which part of the nebula is chicken shaped, with various bird-like features in evidence across the picture [1].

Aside from the glowing gas, another sign of star formation in IC 2944 is the series of opaque black clumps silhouetted against the red background in part of this image. These are examples of a type of object called Bok globules. They appear dark as they absorb the light from the luminous background. However, observations of these dark clouds using infrared telescopes, which are able to see through the dust that normally blocks visible light, have revealed that stars are forming within many of them.

The most prominent collection of Bok globules in this image is known as Thackeray’s Globules, after the South African astronomer who discovered them in the 1950s. Visible among a group of bright stars in the upper right part of the image, these globules feature in a famous image taken by the NASA/ESA Hubble Space Telescope (link).

While Hubble offers greater detail in its image of this small area, the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory captures a much larger panorama in its images, covering an area of sky roughly the size of the full Moon [2]. Much like a zoom lens on a camera lets a photographer choose the most appropriate field of view when taking a picture, the dramatically different viewpoints offered by different telescopes can offer complementary data to scientists studying astronomical objects which cover an extended area of the sky.

If the stars cocooned in Thackeray’s Globules are still gestating, then the stars of cluster IC 2948, embedded within the nebula, are their older siblings. Still young in stellar terms, at just a few million years old, these stars shine brightly, and their ultraviolet radiation provides much of the energy that lights up the nebula. These glowing nebulae are relatively short-lived in astronomical terms (typically a few million years), meaning that the Lambda Centauri Nebula will eventually fade away as it loses both its gas and its supply of ultraviolet radiation.

Notes

[1] Ideas for where the chicken outline lies on the picture can be submitted through the Your ESO Pictures Flickr group for a chance to win some interesting prizes.

[2] This image was produced as part of the ESO Cosmic Gems programme. This is a new initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of small amounts of observing time, combined with otherwise unused time on the telescopes’ schedules so as to minimise the impact on science observations. All data collected are also made available to astronomers through ESO’s science archive.

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Hubble Space Telescope closeup of Thackeray’s Globules in the Running Chicken Nebula

ESO Cosmic Gems page

Contacts

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

Black hole, star collisions may illuminate universe's dark side

Scientists looking to capture evidence of dark matter -- the invisible substance thought to constitute much of the universe -- may find a helpful tool in the recent work of researchers from Princeton University and New York University.

The team unveiled in a report in the journal Physical Review Letters this month a ready-made method for detecting the collision of stars with an elusive type of black hole that is on the short list of objects believed to make up dark matter. Such a discovery could serve as observable proof of dark matter and provide a much deeper understanding of the universe's inner workings.

Postdoctoral researchers Shravan Hanasoge of Princeton's Department of Geosciences and Michael Kesden of NYU's Center for Cosmology and Particle Physics simulated the visible result of a primordial black hole passing through a star. Theoretical remnants of the Big Bang, primordial black holes possess the properties of dark matter and are one of various cosmic objects thought to be the source of the mysterious substance, but they have yet to be observed.

If primordial black holes are the source of dark matter, the sheer number of stars in the Milky Way galaxy -- roughly 100 billion -- makes an encounter inevitable, the authors report. Unlike larger black holes, a primordial black hole would not "swallow" the star, but cause noticeable vibrations on the star's surface as it passes through.

Thus, as the number of telescopes and satellites probing distant stars in the Milky Way increases, so do the chances to observe a primordial black hole as it slides harmlessly through one of the galaxy's billions of stars, Hanasoge said. The computer model developed by Hanasoge and Kesden can be used with these current solar-observation techniques to offer a more precise method for detecting primordial black holes than existing tools.

"If astronomers were just looking at the sun, the chances of observing a primordial black hole are not likely, but people are now looking at thousands of stars," Hanasoge said.

"There's a larger question of what constitutes dark matter, and if a primordial black hole were found it would fit all the parameters -- they have mass and force so they directly influence other objects in the universe, and they don't interact with light. Identifying one would have profound implications for our understanding of the early universe and dark matter."

Princeton and New York University researchers have simulated the effect of a primordial black hole passing through a star. Primordial black holes are among the objects hypothesized to make up dark matter -- the invisible substance thought to constitute much of the universe -- and astronomers could use the researchers' model to finally observe the elusive black holes. This image illustrates the resulting vibration waves as a primordial black hole (white dots) passes through the center of a star. The different colors correspond to the density of the primordial black hole and strength of the vibration. (Image by Tim Sandstrom)

Although dark matter has not been observed directly, galaxies are thought to reside in extended dark-matter halos based on documented gravitational effects of these halos on galaxies' visible stars and gas. Like other proposed dark-matter candidates, primordial black holes are difficult to detect because they neither emit nor absorb light, stealthily traversing the universe with only subtle gravitational effects on nearby objects.

Because primordial black holes are heavier than other dark-matter candidates, however, their interaction with stars would be detectable by existing and future stellar observatories, Kesden said. When crossing paths with a star, a primordial black hole's gravity would squeeze the star, and then, once the black hole passed through, cause the star's surface to ripple as it snaps back into place.

"If you imagine poking a water balloon and watching the water ripple inside, that's similar to how a star's surface appears," Kesden said. "By looking at how a star's surface moves, you can figure out what's going on inside. If a black hole goes through, you can see the surface vibrate."

Eyeing the sun's surface for hints of dark matter

Kesden and Hanasoge used the sun as a model to calculate the effect of a primordial black hole on a star's surface. Kesden, whose research includes black holes and dark matter, calculated the masses of a primordial black hole, as well as the likely trajectory of the object through the sun. Hanasoge, who studies seismology in the sun, Earth and stars, worked out the black hole's vibrational effect on the sun's surface.

Video simulations of the researchers' calculations were created by NASA's Tim Sandstrom using the Pleiades supercomputer at the agency's Ames Research Center in California. One clip shows the vibrations of the sun's surface as a primordial black hole -- represented by a white trail -- passes through its interior. A second movie portrays the result of a black hole grazing the Sun's surface.

Marc Kamionkowski, a professor of physics and astronomy at Johns Hopkins University, said that the work serves as a toolkit for detecting primordial black holes, as Hanasoge and Kesden have provided a thorough and accurate method that takes advantage of existing solar observations. A theoretical physicist well known for his work with large-scale structures and the universe's early history, Kamionkowski had no role in the project, but is familiar with it.

"It's been known that as a primordial black hole went by a star, it would have an effect, but this is the first time we have calculations that are numerically precise," Kamionkowski said.

"This is a clever idea that takes advantage of observations and measurements already made by solar physics. It's like someone calling you to say there might be a million dollars under your front doormat. If it turns out to not be true, it cost you nothing to look. In this case, there might be dark matter in the data sets astronomers already have, so why not look?"

One significant aspect of Kesden and Hanasoge's technique, Kamionkowski said, is that it narrows a significant gap in the mass that can be detected by existing methods of trolling for primordial black holes .

The search for primordial black holes has thus far been limited to masses too small to include a black hole, or so large that "those black holes would have disrupted galaxies in heinous ways we would have noticed," Kamionkowski said. "Primordial black holes have been somewhat neglected and I think that's because there has not been a single, well-motivated idea of how to find them within the range in which they could likely exist."

The current mass range in which primordial black holes could be observed was set based on previous direct observations of Hawking radiation -- the emissions from black holes as they evaporate into gamma rays -- as well as of the bending of light around large stellar objects, Kesden said. The difference in mass between those phenomena, however, is enormous, even in astronomical terms. Hawking radiation can only be observed if the evaporating black hole's mass is less than 100 quadrillion grams. On the other end, an object must be larger than 100 septillion (24 zeroes) grams for light to visibly bend around it. The search for primordial black holes covered a swath of mass that spans a factor of 1 billion, Kesden explained -- similar to searching for an unknown object with a weight somewhere between that of a penny and a mining dump truck.

He and Hanasoge suggest a technique to give that range a much-needed trim and established more specific parameters for spotting a primordial black hole. The pair found through their simulations that a primordial black hole larger than 1 sextillion (21 zeroes) grams -- roughly the mass of an asteroid -- would produce a noticeable effect on a star's surface.

"Now that we know primordial black holes can produce detectable vibrations in stars, we could try to look at a larger sample of stars than just our own sun," Kesden said.

"The Milky Way has 100 billion stars, so about 10,000 detectable events should be happening every year in our galaxy if we just knew where to look."

This research was funded by grants from NASA and by the James Arthur Postdoctoral Fellowship at New York University.

by Morgan Kelly

Source: Princeton University

NASA's WISE Mission Captures Black Hole's Wildly Flaring Jet

This artist's concept illustrates what the flaring black hole called GX 339-4 might look like. Infrared observations from NASA's Wide-field Infrared Survey Explorer (WISE) reveal the best information yet on the chaotic and extreme environments of this black hole's jets. Image credit: NASA. Full image and caption

PASADENA, Calif. -- Astronomers using NASA's Wide-field Infrared Survey Explorer (WISE) have captured rare data of a flaring black hole, revealing new details about these powerful objects and their blazing jets.

Scientists study jets to learn more about the extreme environments around black holes. Much has been learned about the material feeding black holes, called accretion disks, and the jets themselves, through studies using X-rays, gamma rays and radio waves. But key measurements of the brightest part of the jets, located at their bases, have been difficult despite decades of work. WISE is offering a new window into this missing link through its infrared observations.

"Imagine what it would be like if our sun were to undergo sudden, random bursts, becoming three times brighter in a matter of hours and then fading back again. That's the kind of fury we observed in this jet," said Poshak Gandhi, a scientist with the Japan Aerospace Exploration Agency (JAXA). He is the lead author of a new study on the results appearing in the Astrophysical Journal Letters. "With WISE's infrared vision, we were able to zoom in on the inner regions near the base of the stellar-mass black hole's jet for the first time and the physics of jets in action."

The black hole, called GX 339-4, had been observed previously. It lies more than 20,000 light-years away from Earth near the center of our galaxy. It has a mass at least six times greater than the sun. Like other black holes, it is an ultra-dense collection of matter, with gravity that is so great even light cannot escape. In this case, the black hole is orbited by a companion star that feeds it. Most of the material from the companion star is pulled into the black hole, but some of it is blasted away as a jet flowing at nearly the speed of light.

"To see bright flaring activity from a black hole, you need to be looking at the right place at the right time," said Peter Eisenhardt, the project scientist for WISE at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "WISE snapped sensitive infrared pictures every 11 seconds for a year, covering the whole sky, allowing it to catch this rare event."

Observing the jet's variability was possible because of images taken of the same patch of sky over time, a feature of NEOWISE, the asteroid-hunting portion of the WISE mission. WISE data enabled the team to zoom in on the very compact region around the base of the jet streaming from the black hole. The size of the region is equivalent to the width of a dime seen at the distance of our sun.

The results surprised the team, showing huge and erratic fluctuations in the jet activity on timescales ranging from 11 seconds to a few hours. The observations are like a dance of infrared colors and show that the size of the jet's base varies. Its radius is approximately 15,000 miles (24,140 kilometers), with dramatic changes by as large as a factor of 10 or more.

"If you think of the black hole's jet as a firehose, then it's as if we've discovered the flow is intermittent and the hose itself is varying wildly in size," Poshak said.

The new data also allowed astronomers to make the best measurements yet of the black hole's magnetic field, which is 30,000 times more powerful than the one generated by Earth at its surface. Such a strong field is required for accelerating and channeling the flow of matter into a narrow jet. The WISE data are bringing astronomers closer than ever to understanding how this exotic phenomenon works.

A video showing variations of the black hole jet, as seen via WISE observations, is online at http://www.astro.isas.jaxa.jp/~pgandhi/wise_gx339/wise_blackhole_anim.html .

Poshak Gandhi is supported by the JAXA International Top Young Fellowship program. Other authors of the paper include: A.W. Blain of the University of Leicester, United Kingdom; D.M. Russell and S. Markoff of the University of Amsterdam; P. Casella of the University of Southampton, United Kingdom; J. Malzac of Centre National de la Recherche Scientifique and Université de Toulouse, France; S. Corbel of Université Paris Diderot and Commissariat à l'énergie atomique Saclay, France; P. D'Avanzo of Istituto Nazionale di Astrofisica, Italy; F.W. Lewis of Faulkes Telescope Project, Wales; M. Cadolle Bel of the European Space Astronomy Centre, Spain; P. Goldoni of Laboratoire Astroparticule et Cosmologie, France and Commissariat à l'énergie atomique Saclay, France; S. Wachter of the California Institute of Technology, Pasadena, Calif.; D. Khangulyan of the Japan Aerospace Exploration Agency; and A. Mainzer of JPL.

JPL manages and operated WISE for NASA's Science Mission Directorate in Washington. The spacecraft was put into hibernation mode after it scanned the sky twice, completing its main objectives. The mission was selected under NASA's Explorers Program, which is managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah; and the spacecraft was built by Ball Aerospace and Technologies Corp., in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise .

Whitney Clavin 818-354-4673 Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Trent Perrotto 202-358-0321 NASA Headquarters, Washington
Trent.j.perrotto@nasa.gov

Herschel probes the dusty history of a giant star

About 5 billion years from now, our Sun will expand into a red giant, swelling to such a size that it may swallow the Earth. It will then begin to shed huge amounts of dust, surrounding itself with an expanding circumstellar envelope (CSE) that ultimately will become a planetary nebula. New insights into this process have been revealed by ESA's Herschel Space Observatory, which is providing unprecedented images of the complex, outer structure of a nearby CSE.

A study of IRC+10216 has revealed a series of dust shells that have never been seen before. Credit: ESA/PACS/MESS Consortia. Hi-Res [jpg] 684.24 kb

As part of a long term programme to study aging stars, known as the Mass loss of Evolved StarS (MESS) survey, Herschel's Photodetector Array Camera and Spectrometer (PACS) instrument has been used to observe a nearby, carbon-rich star known as IRC+10216, or CW Leonis.

Classified as an Asymptotic Giant Branch (AGB) star, IRC+10216 has evolved into a red giant, several thousand times bigger than the Sun, and is now nearing the final stages of its life.

Nuclear reactions in its core have transformed most of its hydrogen into helium, and the star is now characterised by an inert carbon-oxygen core, surrounded by two separate layers where nuclear fusion is taking place - an inner layer of helium and an outer layer of hydrogen. These layers are surrounded by a strongly convective outer envelope of hydrogen.

As the star evolves through the AGB phase, burning its nuclear fuel faster and faster, it is cooling and expanding, allowing dust to condense in its outer envelope. At the same time, IRC+10216 has begun to pulsate, causing a stellar wind of dust and gas to be expelled from its surface into the surrounding space. Measurements show that the dust is expanding outwards at a velocity of 14.5 km/s.

The presence of this dusty cocoon has been known for many years, but, until now, no instruments have been able to observe the structure of its cold outer regions, where the temperature plummets to –248 °C. Now, PACS infrared images taken at wavelengths of 70, 100 and 160 microns have revealed multiple dust shells in the circumstellar envelope of IRC+10216. The results are published this week in the journal Astronomy & Astrophysics.

Some new features in the circumstellar envelope of IRC+10216 (CW Leonis) are indicated in this annotated image. (A) The arc indicates the location of a bow shock, situated about 1 light year from the star; dust shells, corresponding to the ejection of material from the star at (B) 16 000 years, (C) 12 750 years, (D) 2500 years and (E) 1175 years ago are also indicated. Credit: ESA/PACS/MESS Consortia. Hi-Res [jpg] 1,267.26 kb

The extremely sensitive PACS instrument has unveiled at least a dozen dust shells (or arcs) that have never been seen before. While arcs which had been ejected within the last 4000 years were previously observed up to 80 arc seconds from the star, the new images show material which was ejected some 16 000 years ago and is now visible at a distance of 320 arc seconds.

Arcs which were shed much earlier than this are no longer visible. Although the mass-loss process started some 220 000 years ago, the earliest arcs have been destroyed by the violent interaction of the stellar wind with the interstellar medium at the bow shock interface, about one light year (almost 9.5 million million kilometers) from IRC+10216.

Surprisingly, the almost spherical shells are non-concentric, of variable thickness, and unevenly spaced. The arcs contain some 50 per cent more dust mass than the smooth envelope and local density variations are also visible within one of the arcs.

The complex internal structure of the nebula is a record of how the star has been losing mass during the recent past. A number of possible explanations for the asymmetric structure of the dust shells have been examined by the authors of the new paper.

"The shell separation distances indicate that they were ejected some 500 to 1700 years apart," said Leen Decin from the Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Belgium, lead author of the paper.

"The irregular spacing between the arcs suggests that the structure is not caused by the regular gravitational perturbations associated with an unseen binary companion in orbit around the star.

"A second hypothesis favours enhanced dust formation from magnetic cool spots on the star, rather like the coronal mass ejections which are associated with sunspots. However, the large size of the arcs suggests that there would have to be several sizeable starspots existing in close proximity at the same time. Furthermore, the spacing of the shells shows no evidence of the periodicity that would be expected if the star was experiencing a cycle of rising and falling magnetic activity, like our Sun.

"It seems more likely that the arcs are caused by slight variations in ejection velocity or in the time the ejection took place as the star pulsates and loses mass. Variations in the clumpiness of the dust, associated with temperature variations in the nebula, may also play a part."

Located some 500 light years from Earth, IRC+10216 is one of the best-known examples of the 150 or so evolved stars which are being studied in the MESS survey, one of the guaranteed time, key observational programmes being undertaken with the PACS and SPIRE instruments on board Herschel.

"The angular resolution of these instruments provides accurate maps of the far infrared emission of different types of evolved stars," said Groenewegen from the Observatory of Belgium in Brussels, Investigator of the MESS programme. "This helps us to infer detailed information on the mass, size and structure of the dust shells, and possible grain size/temperature gradients, significantly improving our knowledge of the mass-loss history of these giant stars."

Herschel image of IRC+20216 (CW Leonis). The bow shock is clearly visible to the left of the star. Credit: ESA/PACS/SPIRE/MESS Consortia. Hi-Res [jpg] 714.34 kb

IRC+10216 was also the subject of a recent paper, published in the journal Nature, in which Leen Decin described the detection of warm water vapour in the sooty envelope of the carbon star. One way to create water in this carbon-rich environment is by means of photochemistry, induced by the penetration of highly energetic interstellar photons of ultraviolet light into a non-homogeneous envelope.

The new PACS detection of arcs in the outer envelope confirms that the nebula surrounding IRC+10216 is variable in structure, and that photochemistry is an important process in creating warm water vapour.

"By virtue of its large telescope enabling us to see these structures in such fine detail, Herschel is adding to our understanding of this iconic star," commented Göran Pilbratt, ESA's Herschel Project Scientist.

Reference publication

L. Decin, et al., "Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS". Published online in Astronomy & Astrophysics on 20 September 2011.

Contacts

Leen Decin
Katholieke Universiteit Leuven
Department Natuurkunde en Sterrenkunde
Belgium
Email: Leen.Decin@ster.kuleuven.be
Phone: +32 16 327041

Martin Groenewegen
Royal Observatory of Belgium
Ringlaan 3
B-1180 Brussels
Belgium
Email: marting@oma.be
Phone: +32 2 3730203

Göran Pilbratt
Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate
ESA, The Netherlands
Email: gpilbratt@rssd.esa.int
Phone: +31 71 565 3621