Sunday, May 31, 2015

Herschel's hunt for filaments in the Milky Way

Left: The Aquila Rift. Credit: ESA/Herschel/SPIRE/PACS/Ph. André for the 'Gould Belt survey' Key Programme Consortium. Right: The star-forming cloud IC 5146. Credit: ESA/Herschel/SPIRE/PACS/D. Arzoumanian for the "Gould Belt survey" Key Programme Consortium 

The Orion A Molecular Cloud.  
Credit: ESA/Herschel/Ph. André, D. Polychroni, A. Roy, V. Könyves, N. Schneider for the Gould Belt survey Key Programme
The Polaris Flare
Credit: ESA/Herschel/SPIRE/Ph. André for the "Gould Belt survey" Key Programme Consortium and A. Abergel for the "Evolution of Interstellar Dust" Key Programme Consortium

Observations with ESA's Herschel space observatory have revealed that our Galaxy is threaded with filamentary structures on every length scale. From nearby clouds hosting tangles of filaments a few light-years long to gigantic structures stretching hundreds of light-years across the Milky Way's spiral arms, they appear to be truly ubiquitous. The Herschel data have rekindled the interest of astronomers in studying filaments, emphasising the crucial role of these structures in the process of star formation. 

Stars are born in the densest pockets of the interstellar medium, a diffuse mixture of gas and dust that pervades galaxies, including our Milky Way. One of the most intriguing questions in astrophysics concerns understanding how this material, which is typically characterised by very low density, can come together, creating denser concentrations that later evolve into compact cores and, finally, give birth to stars.

In the search for answers, astronomers observe giant molecular clouds, the cosmic incubators where gas and dust are transformed into stars. While these studies are performed using a variety of techniques, one crucial approach is the observation of infrared light, since the interstellar material shines brightly at these long wavelengths.

In this context, ESA's Herschel space observatory has been a true game changer. Probing the portion of the electromagnetic spectrum that ranges from the far-infrared to sub-millimetre wavelengths, it has collected unprecedented data during its three and a half years of observing. One of the key aspects that emerged from these observations is the presence of a filamentary network nearly everywhere in our Galaxy's interstellar medium. The picture that is emerging is that these structures are closely linked to the formation of stars.

Prior to Herschel, astronomers had already identified several filaments in interstellar clouds and recognised their potential importance for star formation. However, only with the increased sensitivity and spatial resolution granted by this observatory, combined with its large-scale surveys, could they reveal the full extent of filamentary patterns in the Milky Way.

One of the surveys performed with Herschel – the Gould Belt Survey – focussed on a giant ring of star-forming regions, all located no more than 1500 light-years away from the Sun. The vicinity of these clouds allowed astronomers to obtain exceptionally detailed images using Herschel, unearthing intricate webs of filaments in each region that they examined.

The greatest surprise was the ubiquity of filaments in these nearby clouds and their intimate connection with star formation,” explains Philippe André from CEA/IRFU, France, Principal Investigator for the Herschel Gould Belt Survey.

But there is more: these observations revealed that filaments, which may extend to several light-years in length, appear to have a universal width of about one third of a light year. This suggests that something fundamental is lurking underneath.

The astronomers are still trying to understand the details of the star formation processes taking place in these clouds, aided by the abundance and variety of data collected with Herschel.

While most filaments are dotted with compact cores, suggesting that stars are readily taking shape in these dense 'fibres' of the interstellar medium, there are also regions that exhibit complex tangles of filaments but no signs of on-going star formation. A study of the most spectacular example of this phenomenon, the Polaris Flare, indicates that filaments must somehow precede the onset of star formation.

The scenario that has emerged from the new Herschel data suggests that star formation proceeds in two steps: first, turbulent motions of the interstellar gas and dust create an intricate web of filamentary structures; then, gravity takes over, causing only the densest filaments to contract and fragment, eventually leading to the formation of stars.

Indeed, the universal width of filaments seems to correspond, at least in the nearby clouds of the Gould Belt Survey, to the scale at which interstellar material undergoes the transition from supersonic to subsonic state.

In addition, the material along filaments is not at all static: astronomers have detected what appear to be accretion flows, with the most prominent filaments drawing matter from their surroundings through a network of smaller filaments. A striking example of such processes is seen in the Taurus Molecular Cloud, where the B211/B213 filament exhibits a series of so-called 'striations' perpendicular to the main filament.

This pattern is very similar to that predicted from numerical simulations that model the process of star formation in molecular clouds. According to these simulations, interstellar material flows towards dense filaments along routes that are parallel to the direction of the local magnetic field, as was observed, so the new data indicate the importance of interstellar magnetic fields in shaping these structures.

The B211/B213 filament in the Taurus Molecular Cloud.  
Credit: ESA/Herschel/PACS, SPIRE/Gould Belt survey Key Programme/Palmeirim et al. 2013

However, star formation does not appear to take place only in filaments. While these structures seem to be the preferred sites for stellar birth, the extraordinary data from Herschel confirmed that a small fraction of stars may also form far away from dense filaments.

In particular, a detailed study of the L1641 molecular clouds in the Orion A complex suggests that star formation along filaments is the preferential channel to produce typical solar-type stars, while stars that are born away from these dense, elongated structures tend to have lower masses. This dichotomy could be a result of the greater availability of raw material to protostars that are forming on a filament compared to those that take shape in less dense environments.

Another of Herschel's key findings is that the presence and abundance of filaments are not limited to our immediate neighbourhood. In fact, these structures appear everywhere also in the Herschel infrared Galactic Plane Survey (Hi-GAL), which scanned the distribution of the interstellar medium in the huge disc – about 100 000 light-years across – where most of the Milky Way's stars form and reside.

The filamentary structure of the Galactic Plane.  
Credit: ESA/PACS & SPIRE Consortium, S. Molinari, Hi-GAL Project

We detected a wealth of huge filaments, with lengths ranging from a few to a hundred light-years, revealing what seems to be the 'skeleton' of our Galaxy,” explains Sergio Molinari from IAPS/INAF, Italy, Principal Investigator for the Hi-GAL Project.

While it is possible that these structures arose from different physical processes than those giving rise to the small-scale filaments observed in the Sun's vicinity, the omnipresent aspect of filamentary structures in the Milky Way is beyond doubt.

In the post-Herschel era, one thing is certain: filaments play a leading role in the build-up of galactic material, creating favourable hubs for the formation of stars. This is likely a hierarchical process, starting on very large scales and propagating onwards, to smaller and smaller scales, funnelling interstellar gas and dust into increasingly denser concentrations and thus fostering stellar birth across the Galaxy.

Filaments in outer regions of the Galactic Plane
Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project/Schisano et al. 2014

Large-scale filaments fragmenting into compact cores that later evolve into stars have been detected all across the Galactic Plane, even in its outermost, peripheral regions. As filaments grow more massive, the material within them contracts and forms smaller structures, preserving the filamentary pattern on all length scales.

Further investigation of the Hi-GAL survey has revealed new and even more prominent filaments, extending over hundreds of light-years and weaving their way through the spiral arms of the Milky Way. The study revealed nine filaments in some very dense, inner regions of the Galactic Plane, detecting these for the first time through the direct emission of dust within them, allowing an accurate determination of their mass, size and physical characteristics. Astronomers believe that almost a hundred similar, gigantic structures are still hiding in the data.

Some of the most prominent filaments detected in the Milky Way: G49 (top), G47 (bottom left) and G64 (bottom right). 
Credit: ESA/Herschel/PACS/SPIRE/Ke Wang et al. 2015

The intricate distribution of filaments in the interstellar medium revealed by Herschel has definitely revolutionised our view of how stars form in the Milky Way and, presumably, also in other similar galaxies,” comments Göran Pilbratt, ESA Herschel Project Scientist.

An increasingly coherent picture is now emerging from combining the analysis of these data with predictions from theory and numerical simulations, as astronomers continue to study the physical processes underlying the fascinating origin of stars and planets.

More information

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Herschel was launched on 14 May 2009 and completed science observations on 29 April 2013.

Related publications  

Ph. André et al. 2010, Astronomy & Astrophysics, 518, L102
S. Molinari et al. 2010, Astronomy & Astrophysics, 518, L100
D. Arzoumanian et al. 2011, Astronomy & Astrophysics, 529, L6
D. Polychroni et al. 2013, Astrophysical Journal Letters, 777, L33
P. Palmeirim et al. 2013, Astronomy & Astrophysics, 550, A38
D. Arzoumanian et al. 2013, Astronomy & Astrophysics, 553, A119
Ph. André et al. 2014, in Protostars and Planets VI, p. 27
D. Elia et al. 2013, Astrophysical Journal, 772, 45
E. Schisano et al. 2014, Astrophysical Journal, 791, 27
K. Wang et al. 2015, Monthly Notices of the Royal Astronomical Society, 450, 4043


Philippe André
CEA/DSM/IRFU Service d'Astrophysique
Centre d'Etudes de Saclay
Gif-sur-Yvette Cedex, France
Phone: +33-1-6908-9265

Sergio Molinari
Roma, Italy
Phone: +39-06-4993-4396

Göran Pilbratt
Herschel Project Scientist
Scientific Support Office
Science and Robotic Exploration Directorate
ESA, The Netherlands
Phone: +31-71-565-3621

 Source: ESA/Herschel

Saturday, May 30, 2015

Space-time Foam: NASA Telescopes Set Limits on Space-time Quantum Foam

BR 0331-1622, BR 0353-3820, BR 0418-5723
BR 0424-2209, PSS 0747+4434, PSS 1058+1245
Credit  NASA/CXC/FIT/E.Perlman et al, Illustration: NASA/CXC/M.Weiss

A new study combining data from NASA's Chandra X-ray Observatory and Fermi Gamma-ray Telescope, and the Very Energetic Radiation Imaging Telescope Array (VERITAS) in Arizona is helping scientists set limits on the quantum nature of space-time on extremely tiny scales, as explained in our latest press release.

Certain aspects of quantum mechanics predict that space-time - the three dimensions of space plus time -- would not be smooth on the scale of about ten times a billionth of a trillionth of the diameter of a hydrogen atom's nucleus. They refer to the structure that may exist at this extremely small size as "space-time foam." This artist's illustration depicts how the foamy structure of space-time may appear, showing tiny bubbles quadrillions of times smaller than the nucleus of an atom that are constantly fluctuating and last for only infinitesimal fractions of a second.

Because space-time foam is so small, it is impossible to observe it directly. However, depending on what model of space-time is used, light that has traveled over great cosmic distances may be affected by the unseen foam in ways that scientists can analyze. More specifically, some models predict that the accumulation of distance uncertainties for light traveling across billions of light years would cause the image quality to degrade so much that the objects would become undetectable. The wavelength where the image disappears should depend on the model of space-time foam used.

The researchers used observations of X-rays and gamma-rays from very distant quasars - luminous sources produced by matter falling towards supermassive black holes - to test models of the smoothness and structure of space-time. Chandra's X-ray detection of six quasars, shown in the upper part of the graphic, at distances of billions of light years, rules out one model, according to which photons diffuse randomly through space-time foam in a manner similar to light diffusing through fog. Detections of distant quasars at shorter, gamma-ray wavelengths with Fermi and even shorter wavelengths with VERITAS demonstrate that a second, so-called holographic model with less diffusion does not work.

These results appeared in the May 20th issue of The Astrophysical Journal and are available online. The authors of this study are Eric Perlman (Florida Institute of Technology), Saul Rappaport (Massachusetts Institute of Technology), Wayne Christensen (University of North Carolina), Y. Jack Ng (University of North Carolina), John DeVore (Visidyne), and David Pooley (Sam Houston State University).

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

Fast Facts for BR 0331-1622:

Scale: Image is 1 arcmin across. (about 1.34 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000) RA 03h 34m 13.40s | Dec -16° 12' 04.80"
Constellation: Eridanus
Observation Dates: 17 Jun 2003
Observation Time: 1 hours 23 min
Obs. IDs: 4064
Instrument: ACIS
References: Perlman, E. et al, 2015, ApJ, 805, 10; arXiv:1411.7262
Color Code: X-ray: Blue Distance Estimate About 12.32 billion light years (z=4.36)

Fast Facts for BR 0353-3820:

Scale Image is 1 arcmin across. (about 1.31 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 03h 55m 04.90s | Dec -38° 11' 42.30"
Constellation: Eridanus
Observation Dates: 10 Sep 2003
Observation Time: 1 hours 7 min
Obs. IDs 4065
Instrument: ACIS
References: Perlman, E. et al, 2015, ApJ, 805, 10; arXiv:1411.7262
Color Code: X-ray: Blue
Distance Estimate: About 12.39 billion light years (z=4.55)

Fast Facts for BR 0418-5723:

Scale: Image is 1 arcmin across. (about 1.33 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 04h 19m 50.90s | Dec -57° 16' 13.10"
Constellation: Reticulum
Observation Dates: 17 Jun 2004
Observation Time: 1 hours 7 min
Obs. IDs: 4066
Instrument: ACIS
References: Perlman, E. et al, 2015, ApJ, 805, 10; arXiv:1411.7262
Color Code: X-ray: Blue
Distance Estimate: About 12.35 billion light years (z=4.46)

Fast Facts for BR 0424-2209:

Image is 1 arcmin across. (about 1.34 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 04h 26m 10.30s | Dec -29° 00' 28.00"
Constellation: Eridanus
Observation Dates: 14 Dec 2002
Observation Time: 24 hours 23 min (1 day 23 min)
Obs. IDs: 4067
Instrument: ACIS
References: Perlman, E. et al, 2015, ApJ, 805, 10; arXiv:1411.7262
Color Code: X-ray: Blue
Distance Estimate: About 12.3 billion light years (z=4.32)

Fast Facts for PSS 0747+4434:

Scale: Image is 1 arcmin across. (about 1.33 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 07h 47m 49.70s | Dec +44° 34' 20.10"
Constellation: Lynx
Observation Dates: 17 Dec 2002
Observation Time: 24 hours 23 min (1 day 23 min)
Obs. IDs: 4068
Instrument: ACIS
References: Perlman, E. et al, 2015, ApJ, 805, 10; arXiv:1411.7262
Color Code: X-ray: Blue
Distance Estimate: About 12.34 billion light yeras (z=4.43)


Fast Facts for PSS 1058+1245:

Scale Image is 1 arcmin across. (about 1.34 million light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 10h 58m 58.40s | Dec +12° 45' 54.80"
Constellation: Leo
Observation Dates: 02 Mar 2003
Observation Time: 24 hours 23 min (1 day 23 min)
Obs. IDs: 4069
Instrument: ACIS
References: Perlman, E. et al, 2015, ApJ, 805, 10; arXiv:1411.7262
Color Code: X-ray: Blue
Distance Estimate: About 12.3 billion light years (z=4.33)

Friday, May 29, 2015

The most crowded place in the Milky Way

Credit: NASA & ESA

This new NASA/ESA Hubble Space Telescope image presents the Arches Cluster, the densest known star cluster in the Milky Way. It is located about 25 000 light-years from Earth in the constellation of Sagittarius (The Archer), close to the heart of our galaxy, the Milky Way. It is, like its neighbour the Quintuplet Cluster, a fairly young astronomical object at between two and four million years old.

The Arches cluster is so dense that in a region with a radius equal to the distance between the Sun and its nearest star there would be over 100 000 stars!

At least 150 stars within the cluster are among the brightest ever discovered in the the Milky Way. These stars are so bright and massive, that they will burn their fuel within a short time, on a cosmological scale, just a few million years, and die in spectacular supernova explosions. Due to the short lifetime of the stars in the cluster, the gas between the stars contains an unusually high amount of heavier elements, which were produced by earlier generations of stars.

Despite its brightness the Arches Cluster cannot be seen with the naked eye. The visible light from the cluster is completely obscured by gigantic clouds of dust in this region. To make the cluster visible astronomers have to use detectors which can collect light from the X-ray, infrared, and radio bands, as these wavelengths can pass through the dust clouds. This observation shows the Arches Cluster in the infrared and demonstrates the leap in Hubble’s performance since its 1999 image of same object.

Thursday, May 28, 2015

Merging galaxies break radio silence

Artist’s illustration of galaxy with jets from a supermassive black hole 

Galaxies with relativistic jets

Radio galaxy 3C 297

Radio galaxy 3C 454.1
Radio galaxy 3C 356 

Artist’s animation of galaxy with jets from a supermassive black hole
Artist’s animation of galaxy with jets from a supermassive black hole

Fulldome clip showing animation of galaxy with jets from a supermassive black hole
Fulldome clip showing animation of galaxy with jets from a supermassive black hole 

Large Hubble survey confirms link between mergers and supermassive black holes with relativistic jets

In the most extensive survey of its kind ever conducted, a team of scientists have found an unambiguous link between the presence of supermassive black holes that power high-speed, radio-signal-emitting jets and the merger history of their host galaxies. Almost all of the galaxies hosting these jets were found to be merging with another galaxy, or to have done so recently. The results lend significant weight to the case for jets being the result of merging black holes and will be presented in the Astrophysical Journal.

A team of astronomers using the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) have conducted a large survey to investigate the relationship between galaxies that have undergone mergers and the activity of the supermassive black holes at their cores.

The team studied a large selection of galaxies with extremely luminous centres — known as active galactic nuclei (AGNs) — thought to be the result of large quantities of heated matter circling around and being consumed by a supermassive black hole. Whilst most galaxies are thought to host a supermassive black hole, only a small percentage of them are this luminous and fewer still go one step further and form what are known as relativistic jets [1]. The two high-speed jets of plasma move almost with the speed of light and stream out in opposite directions at right angles to the disc of matter surrounding the black hole, extending thousands of light-years into space. The hot material within the jets is also the origin of radio waves.

It is these jets that Marco Chiaberge from the Space Telescope Science Institute, USA (also affiliated with Johns Hopkins University, USA and INAF-IRA, Italy) and his team hoped to confirm were the result of galactic mergers [2].

The team inspected five categories of galaxies for visible signs of recent or ongoing mergers — two types of galaxies with jets, two types of galaxies that had luminous cores but no jets, and a set of regular inactive galaxies [3].

“The galaxies that host these relativistic jets give out large amounts of radiation at radio wavelengths,” explains Marco. “By using Hubble’s WFC3 camera we found that almost all of the galaxies with large amounts of radio emission, implying the presence of jets, were associated with mergers. However, it was not only the galaxies containing jets that showed evidence of mergers!” [4].

“We found that most merger events in themselves do not actually result in the creation of AGNs with powerful radio emission,” added co-author Roberto Gilli from Osservatorio Astronomico di Bologna, Italy. “About 40% of the other galaxies we looked at had also experienced a merger and yet had failed to produce the spectacular radio emissions and jets of their counterparts.” 

Although it is now clear that a galactic merger is almost certainly necessary for a galaxy to host a supermassive black hole with relativistic jets, the team deduce that there must be additional conditions which need to be met. They speculate that the collision of one galaxy with another produces a supermassive black hole with jets when the central black hole is spinning faster — possibly as a result of meeting another black hole of a similar mass — as the excess energy extracted from the black hole’s rotation would power the jets.

“There are two ways in which mergers are likely to affect the central black hole. The first would be an increase in the amount of gas being driven towards the galaxy’s centre, adding mass to both the black hole and the disc of matter around it,” explains Colin Norman, co-author of the paper. “But this process should affect black holes in all merging galaxies, and yet not all merging galaxies with black holes end up with jets, so it is not enough to explain how these jets come about. The other possibility is that a merger between two massive galaxies causes two black holes of a similar mass to also merge. It could be that a particular breed of merger between two black holes produces a single spinning supermassive black hole, accounting for the production of jets.” 

Future observations using both Hubble and ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) are needed to expand the survey set even further and continue to shed light on these complex and powerful processes.


[1] Relativistic jets travel at close to the speed of light, making them one of the fastest astronomical objects known.

[2] The new observations used in this research were taken in collaboration with the 3CR-HST team. This international team of astronomers is currently led by Marco Chiaberge and has conducted a series of surveys of radio galaxies and quasars from the 3CR catalogue using the Hubble Space Telescope.

[3] The team compared their observations with the swathes of archival data from Hubble. They directly surveyed twelve very distant radio galaxies and compared the results with data from a large number of galaxies observed during other observing programmes.

[4] Other studies had shown a strong relationship between the merger history of a galaxy and the high levels of radiation at radio wavelengths that suggests the presence of relativistic jets lurking at the galaxy’s centre. However, this survey is much more extensive, and the results very clear, meaning it can now be said with almost certainty that radio-loud AGNs, that is, galaxies with relativistic jets, are the result of galactic mergers.

Note for Editors

Image credit: NASA, ESA, M. Chiaberge (STScI)


Marco Chiaberge
Space Telescope Science Institute, USA
Johns Hopkins University, USA, INAF-IRA, Italy
Tel: +1 410 338 4980

Roberto Gilli
Osservatorio Astronomico di Bologna, Italy
Tel: +39 051 2095 719
Cell: +39 347 4139847

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Cell: +49 176 62397500

Hubble Video Shows Shock Collision inside Black Hole Jet

This time-lapse movie of an extragalactic jet was assembled from 20 years of Hubble Space Telescope observations of the core of the elliptical galaxy NGC 3862. Credits: NASA, ESA, and E. Meyer STScI

In the central region of galaxy NGC 3862 an extragalactic jet of material can be seen at the 3 o'clock position (left). Hubble images (right) of knots (outlined in red, green and blue) shows them moving along the jet over 20 years. The "X" is the black hole. Credit: NASA, ESA, and E. Meyer (STScI). Hi-res Image

When you're blasting though space at more than 98 percent of the speed of light, you may need driver's insurance. Astronomers have discovered for the first time a rear-end collision between two high-speed knots of ejected matter from a super-massive black hole. This discovery was made while piecing together a time-lapse movie of a plasma jet blasted from a supermassive black hole inside a galaxy located 260 million light-years from Earth.

The finding offers new insights into the behavior of "light-saber-like" jets that are so energized that they appear to zoom out of black holes at speeds several times the speed of light. This "superluminal" motion is an optical illusion due to the very fast real speed of the plasma, which is close to the universal maximum of the speed of light.

Such extragalactic jets are not well understood. They appear to transport energetic plasma in a confined beam from the central black hole of the host galaxy. The new analysis suggests that shocks produced by collisions within the jet further accelerate particles and brighten the regions of colliding material.

The video of the jet was assembled with two decades' worth of NASA Hubble Space Telescope images of the elliptical galaxy NGC 3862, the sixth brightest galaxy and one of only a few active galaxies with jets seen in visible light. The jet was discovered in optical light by Hubble in 1992. NGC 3862 is in a rich cluster of galaxies known as Abell 1367.

The jet from NGC 3862 has a string-of-pearls structure of glowing knots of material. Taking advantage of Hubble's sharp resolution and long-term optical stability, Eileen Meyer of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, matched archival Hubble images with a new, deep image taken in 2014 to better understand jet motions. Meyer was surprised to see a fast knot with an apparent speed of seven times the speed of light catch up with the end of a slower moving, but still superluminal, knot along the string.

The resulting "shock collision" caused the merging blobs to brighten significantly.

"Something like this has never been seen before in an extragalactic jet," said Meyer. As the knots continue merging they will brighten further in the coming decades. "This will allow us a very rare opportunity to see how the kinetic energy of the collision is dissipated into radiation."

It's not uncommon to see knots of material in jets ejected from gravitationally compact objects, but it is rare that motions have been observed with optical telescopes, and so far out from the black hole, thousands of light-years away. In addition to black holes, newly forming stars eject narrowly collimated streamers of gas that have a knotty structure. One theory is that material falling onto the central object is superheated and ejected along the object's spin axis. Powerful magnetic fields constrain the material into a narrow jet. If the flow of the infalling material is not smooth, blobs are ejected like a string of cannon balls rather than a steady hose-like flow.

Whatever the mechanism, the fast-moving knot will burrow its way out into intergalactic space. A knot launched later, behind the first one, may have less drag from the shoveled-out interstellar medium and catch up to the earlier knot, rear-ending it in a shock collision.

Beyond the collision, which will play out over the next few decades, this discovery marks only the second case of superluminal motion measured at hundreds to thousands of light-years from the black hole where the jet was launched. This indicates that the jets are still very, very close to the speed of light even on distances that start to rival the scale of the host galaxy. These measurements can give insights into how much energy jets carry out into their host galaxy and beyond, which is important for understanding how galaxies evolve as the universe ages.

Meyer is currently making a Hubble-image video of two more jets in the nearby universe, to look for similar fast motions. She notes that these kinds of studies are only possible because of the long operating lifetime of Hubble, which has now been looking at some of these jets for over 20 years.

Extragalactic jets have been detected at X-ray and radio wavelengths in many active galaxies powered by central black holes, but only a few have been seen in optical light. Astronomers do not yet understand why some jets are seen in visible light and others are not.

Meyer's results are being reported in the May 28 issue of the journal Nature.

For images and more information about the Hubble Space Telescope, visit: and


Felicia Chou
NASA Headquarters, Washington

Ray Villard
Space Telescope Science Institute, Baltimore

Wednesday, May 27, 2015

A Bubbly Cosmic Celebration

The star forming cloud RCW 34

The star-forming cloud RCW 34 in the constellation of Vela

Around the star-formation region Gum 19 (RCW 34)

Zooming in on the star forming cloud RCW 34
Zooming in on the star forming cloud RCW 34

Close-up pan across the star forming cloud RCW 34
Close-up pan across the star forming cloud RCW 34

In the brightest region of this glowing nebula called RCW 34, gas is heated dramatically by young stars and expands through the surrounding cooler gas. Once the heated hydrogen reaches the borders of the gas cloud, it bursts outwards into the vacuum like the contents of an uncorked champagne bottle — this process is referred to as champagne flow. But the young star-forming region RCW 34 has more to offer than a few bubbles; there seem to have been multiple episodes of star formation within the same cloud.

This new image from ESO’s Very Large Telescope (VLT) in Chile shows a spectacular red cloud of glowing hydrogen gas behind a collection of blue foreground stars. Within RCW 34 — located in the southern constellation of Vela — a group of massive young stars hide in the brightest region of the cloud [1]. These stars have a dramatic effect on the nebula. Gas exposed to strong ultraviolet radiation — as occurs in the heart of this nebula — becomes ionised, meaning that the electrons have escaped the hydrogen atoms.

Hydrogen is treasured by cosmic photographers because it glows brightly in the characteristic red colour that distinguishes many nebulae and allows them to create beautiful images with bizarre shapes. It is also the raw material of dramatic phenomena such as champagne flow. But ionised hydrogen also has an important astronomical role: it is an indicator of star-forming regions. Stars are born from collapsing gas clouds and therefore abundant in regions with copious amounts of gas, like RCW 34. This makes the nebula particularly interesting to astronomers studying stellar birth and evolution.

Vast amounts of dust within the nebula block the view of the inner workings of the stellar nursery deeply embedded in these clouds. RCW 34 is characterised by extremely high extinction, meaning that almost all of the visible light from this region is absorbed before it reaches Earth. Despite hiding away from direct view, astronomers can use infrared telescopes, to peer through the dust and study the nest of embedded stars.

Looking behind the red colour reveals that there are a lot of young stars in this region with masses only a fraction of that of the Sun. These seem to clump around older, more massive stars at the centre, while only a few are distributed in the outskirts. This distribution has led astronomers to believe that there have been different episodes of star formation within the cloud. Three gigantic stars formed in the first event that then triggered the formation of the less massive stars in their vicinity [2].

This image uses data from the FOcal Reducer and low dispersion Spectrograph (FORS) instrument attached to the VLT, which were acquired as part of the ESO Cosmic Gems programme [3].


[1] RCW 34 is also known as Gum 19 and is centred on the brilliant young star called V391 Velorum.

[2] The most massive very bright stars have short lives — measured in millions of years — but the less massive ones have lives longer than the current age of the Universe.

[3] The ESO Cosmic Gems programme is an outreach 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 telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.



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Faint Galaxies found Hiding in the Virgo Cluster

Example of a Low Surface Brightness Galaxy in the Virgo cluster. 
These galaxies are very hard to detect and the LSB mode on MegaCam enabled the possibility of such detections.  

A recent survey using the Canada-France-Hawaii Telescope has discovered hundreds of new galaxies in the Virgo Cluster, the nearest large cluster of galaxies. Most are extremely faint "dwarf" galaxies, objects hundreds of thousands of times less massive than our own galaxy, the Milky Way, and amongst the faintest galaxies known in the Universe. The Virgo cluster appears to be home to far more of such faint systems than the “Local Group” of galaxies to which the Milky Way belongs, suggesting that galaxy formation on small scales may be more complicated than previously thought, and that our Local Group may not be a typical corner of the universe.

The discovery has been announced by the “Next Generation Virgo Cluster Survey” (NGVS) team and is based on data collected, over the course of 6 years, with Megacam, a 340 Megapixel camera operating at the Canada France Hawaii Telescope and capable of observing, in a single shot, a one square degree field of view (equivalent to 4 full moons). Taking advantage of MegaCam’s wide angle coverage, the NGVS team was able to observe the Virgo cluster in its entirety, covering an area of the sky equivalent to over 400 full moons, at a depth and resolution that significantly exceed those of any existing surveys of the cluster. The resulting mosaic, comprising nearly 40 billion pixels, is the deepest, widest contiguous field ever seen is such detail.

To exploit the full power of the data, Laura Ferrarese, Lauren McArthur and Patrick Cote of the National Research Council of Canada developed a sophisticated data analysis technique that allowed them to discover many times more galaxies than were known previously, including some of the faintest and most diffuse objects ever detected.

Virgo is the nearest large cluster of galaxies, roughly 50 Million light-years away from us. Whereas the Milky Way forms part of a relatively small group of galaxies, the "Local Group", spread over the nearest few million light-years, Virgo contains dozens of bright galaxies and thousands of fainter ones. In the Local Group, the current theories of galaxy formation suggest there should be hundreds or thousands of dwarf galaxies, but fewer than 100 have been detected. Clusters such as Virgo were known to be richer hunting grounds for dwarfs, but only recently has the NGVS made it possible to set firm constraints on their numbers.

To understand the implications of these new discoveries, Jonathan Grossauer and James Taylor at the University of Waterloo ran computer simulations of clusters like Virgo, to see how many bound concentrations of dark matter they should contain at the present day. Comparing the numbers and masses of dark matter clumps to the population of galaxies discovered by the NGVS, they find a very simple pattern, where the ratio of stellar to dark matter mass changes slowly going from the smallest to the largest galaxies. It seems that in Virgo, there could be a simple relationship between dark matter mass and galaxy brightness, valid over a factor of 100,000 in stellar mass.

This is not the case in the Local Group: the low mass dark matter clumps that would be occupied by galaxies in Virgo, do not seem to have been capable of forming galaxies in the Local Group. So why are the two environments so different? A follow-up study with higher-resolution simulations by the NGVS survey team will explore how galaxies are spatially distributed throughout the cluster, to seek more clues to the mystery of dwarf galaxy formation. 

Science Contact information

James Taylor
University of Waterloo

Dr. Laura Ferrarese
NGVS Principal Investigator

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Leslie Sage
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Mary Beth Laychak
CFHT Outreach Program Manager

Tuesday, May 26, 2015

A Curious Family of Giants

An artist's impression of the newly discovered super-Jupiter exoplanet around an evolved star, only the third known example of such a system.
Credit: NASA/JPL-Caltech

There are 565 exoplanets currently known that are as massive as Jupiter or bigger, about one third of the total known, confirmed exoplanet population. About one quarter of the massive population orbits very close to its star, with periods of less than ten days (the Earth takes about 365 days to orbit the Sun). Heated by the nearby star’s radiation, these giants are often called hot Jupiters. 

Despite the large and diverse population of known giant exoplanets, only two of them orbit older, evolved stars. How and why there are so many giant planets close to their host stars is still a mystery: perhaps over time they migrate in from more distant parts of their planetary system, or instead perhaps they are born there? Evolved stars that host close-in, giant exoplanets provide a valuable wrinkle to the picture, and some clues: these stars, as they age, cool off and swell in diameter, could disrupt or even swallow any nearby planets. Finding examples allows astronomers to refine their models of planet formation and evolution.

CfA astronomers Dave Latham, David Kipping, Matthew Payne, David Sliski, Lars Buchhave, Gilbert Esquerdo, Michel Calkins, and Perry Berlind and their colleagues have discovered two new giant exoplanets around an evolved star. Kepler-432b is about 5.4 Jupiter-masses in size and orbits every 52.5 days – it is the third known example of a close-in giant around an evolved star; Kepler-434c is 2.4 Jupiter-masses and orbits much farther away, in 406 days. The host star, Kepler-432 has a mass of about 1.35 solar-masses, an age of about 3.5 billion years, and it has just finished its stable lifetime burning hydrogen and begun to swell in size, with a current diameter of 4.16 solar-diameters.

The astronomers found that the massive inner planet is strange in at least three ways. First, it is not highly irradiated or hot, unlike typical hot Jupiters. Its orbit is highly eccentric (meaning that its distance from the star varies considerably over an orbit), suggesting that it may have migrated to this orbit. Finally, its spin axis happens to be closely aligned to the star's, another curious property, especially since it is usually not found in planets that have migrated. The results highlight the remarkable range of exoplanet properties and possible formation mechanisms, and imply either that Kepler-432b is an intrinsically rare case, or that it represents a common class of exoplanets that are usually destroyed as their host star ages, but which in this case has so far managed to survive - though its days are probably numbered (perhaps only another few hundred million years).


"Kepler-432: A Red Giant Interacting with One of Its Two Long-Period Giant Planets," Samuel N. Quinn, Timothy. R. White, David W. Latham, William J. Chaplin, Rasmus Handberg, Daniel Huber, David M. Kipping, Matthew J. Payne, Chen Jiang, Victor Silva Aguirre, Dennis Stello, David H. Sliski, David R. Ciardi, Lars A. Buchhave, Timothy R. Bedding, Guy R. Davies, Saskia Hekker, Hans Kjeldsen, James S. Kuszlewicz, Mark E. Everett, Steve B. Howell, Sarbani Basu, Tiago L. Campante, Jørgen Christensen-Dalsgaard, Yvonne P. Elsworth, Christoffer Karoff, Steven D. Kawaler, Mikkel N. Lund, Mia Lundkvis, Gilbert A. Esquerdo, Michael L. Calkins, and Perry Berlind, ApJ 803, 49, 2015

Monday, May 25, 2015

ALMA Reveals the Cradles of Dense Cores: the Birthplace of Massive Stars

Figure 1: An overview of a massive stellar cluster-forming molecular cloud from numerical hydrodynamical simulations (courtesy from James Dale [5]), and the context of the scale of the ALMA observations for the deeply embedded central few light-years region. Credit: ALMA(ESO/NAOJ/NRAO), H. B. Liu, J. Dale. | Download Image

Figure 2: The central part of the OB cluster-forming region G33.92+0.11, observed by ALMA. Left: Dust continuum image taken at 1.3 mm. Right: False color image showing the integrated emission of three molecules: CH3CN in yellow, 13CS in green, and DCN in magenta, respectively. The CH3CN emission mainly traces the hot molecular cores, which harbor massive stars. The 13CS emission traces warm dense gas and shocks. The DCN emission appears to follow the bulk of dense gas traced by the dust continuum emission. Credit: ALMA(ESO/NAOJ/NRAO), H. B. Liu et al. | Download Image

A Taiwanese research team used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe a large molecular gas clump [1] named G33.92+0.11, where a cluster with massive stars is forming. The excellent imaging power of ALMA allowed to reveal with unprecedented detail, the fine structure of the molecular gas at the center of the region, where two surprisingly large molecular gas arms, with sizes of ~ 3.2 light years [2], appear to be spiraling around two massive molecular cores. These results showed that the large molecular arms are indeed the cradles of dense cores, which are current or future birthplaces of massive stars. This is a crucial step forward in the understanding of how mass distributes to form both massive cores and massive stars.

How the gravitationally bound stellar clusters, for example, the young massive clusters (YMCs) and globular clusters (GCs) come to the existence, remains a fundamental problem in astrophysics. To form such complex systems, it is required that massive amounts of gas can be converted with little losses, into stars, before they start to disperse the gas by the action of their winds —the so called stellar feedback—, and such process is far from trivial. Current models propose that in order to quench the action of stellar feedback, the global collapse of the parent molecular cloud has to be very rapid.

However, this global collapse of giant [3] molecular clouds (GMC) represents an observational challenge for astronomers, because they cannot measure distances along their line of sight (data is projected in two dimensions) and because it is near impossible to measure gas velocities in the transverse directions. Nevertheless, the amplified effects of the initial rotation (angular momentum) of the clouds may translate into the formation of massive molecular clumps that are supported by centrifugal forces at the center of the collapsing GMC.

The identification of rotating structures at scales larger than the cores, may serve as evidence of such an outcome of global collapse. Also, because the massive molecular clumps are the densest regions in a collapsing GMC, they are likely the sites where the most massive stars of stellar clusters can form. To resolve the details of the morphology and kinematics of these systems will be key to understand how mass distributes in the sites of star cluster formation, such that it can form both massive and not massive stars.

A research team led by Hauyu Baobab Liu at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) observed with ALMA the luminous OB cluster-forming region G33.92+0.11, located at a distance of about 23.000 lightyears. This source is at a beginning phase of forming an OB association, which has a contained luminosity of 250 thousand times the luminosity of the Sun. Most of this light is provided by a few embedded massive stars. The research team used the archival Herschel 350 μm, which were combined with another 350 μm image from the Caltech Submillimeter Observatory (CSO) with a higher angular resolution.

"The Herschel Space Telescope archive images provided a high quality map of the 350 μm thermal emission of the external dusty gas structures around G33.92+0.11. We completed the missing small-scale pixels of this map with data from the Caltech Submillimeter Observatory. The final map revealed two molecular arms twisted in opposite directions, north and south of the cluster, converging at the central molecular clumps, indicating that perhaps the gas is being transported toward the central cluster along these spiral arms from distances as large as 20 light years," says co-author Román-Zúñiga, from the Astronomy Institute of the Universidad Nacional Autónoma de México.

The unprecedented high angular resolution and high imaging fidelity of ALMA allowed the astronomers to reveal in G33.92+0.11 A two centrally located massive molecular cores (~100-300 solar masses), connected by several spiraling dense molecular gas arms. This kind of morphology resembles the previous ALMA images of molecular gas arms surrounding the low-mass protostellar binary L1551 NE [4], however, but linearly scaled-up by a factor between 100 and 1000 (Figure 1). In addition, the observed gas arms in G33.92+0.11 A appear to be fragmenting, which results in the formation of multiple satellite cores orbiting the central two highest mass cores. Comparing the simultaneously observed molecular gas tracers including CH3CN, 13CS, and DCN shows that the gas excitation conditions in these molecular arms and cores far from being uniform across the system (Figure 2). For instance, the two highest mass cores at the center already harbor massive stars and present bright CH3CN emission. The molecular arms embedded with satellite cores in the north may be relatively cool, indicated by the good correlation between the DCN line and the 1.3 mm dust continuum emission. Finally the molecular arms connecting the central massive molecular cores from the west may contain gas that is shocked to a higher temperature or are subject to stellar heating and show stronger 13CS emission.

This team propose that the central ~1 pc scale region of G33.92+0.11 A is a flattened, massive molecular clump that is currently accreting material, which is being fed by the exterior gas filaments, and is marginally supported by centrifugal forces. At all spatial scales, the regions of higher density, that contain larger amounts of mass, form at the center of the system. Accretion may be prohibited by the angular momentum, but might be alleviated by fragmentation. The authors further propose that in the dense eccentric accretion flows, the formation of spiraling arm-like structures may be essential to the process. The subsequent fragmentation of the dense molecular arms may lead to the formation of the second generation high-mass stars.

"Gas structures similar to spiral arms should be common in many systems at many different scales, as long as they are unstable to gravity and have non-negligible rotation. The superb images made with ALMA are starting to show this,"says co-author Galván-Madrid.


[1] In our nomenclature, massive molecular clumps refer to dense molecular gas structures with sizes of ∼0.5-1 pc, massive molecular cores refer to the ⟨ 0.1 pc size overdensities embedded within a clump, and condensations refer to the distinct molecular substructures within a core. Fragmentation refers to the dynamical process that produces or enhances the formation of multiple objects.

[2] 1 parsec (pc) ~ 3.2 light years ~ 3.086×1016 meters.

[3] The typical spatial scales of stellar cluster-forming molecular clouds are 101-2 pc.

[4] More in the press release Dec 04, 2014: Astronomers Identify Gas Spirals as a Nursery of Twin Stars through ALMA Observation 

[5] For details, please see Dale, J. E., Ngoumou, J., Ercolano, B., Bonnell, I. A., 2014, MNRAS, 442, 694

More information

These observational results were published in the Astrophysical Journal (ApJ, 804, 37) by Liu et al. as "ALMA resolves the spiraling accretion flow in the luminous OB cluster forming region G33.92+0.11".
This research was conducted by Hauyu Baobab Liu (Academia Sinica Institute of Astronomy and Astrophysics); Roberto Galván-Madrid (Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México); Izaskun Jiménez-Serra (Department of Physics and Astronomy, University College London and European Southern Observatory, Garching Germany); Carlos Román-Zúñiga (Instituto de Astronomía, Universidad Nacional Autónoma de México); Qizhou Zhang (Harvard-Smithsonian Center for Astrophysics); Zhiyun Li (Department of Astronomy, University of Virginia); Huei-Ru Chen (Institute of Astronomy and Department of Physics, National Tsing Hua University).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organization for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia.

The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.


Valeria Foncea
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Richard Hook 

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Sunday, May 24, 2015

NASA's WISE Spacecraft Discovers Most Luminous Galaxy in Universe

This artist's concept depicts the current record holder for the most luminous galaxy in the universe
Image credit: NASA/JPL-Caltech.   › Full image and caption

A remote galaxy shining with the light of more than 300 trillion suns has been discovered using data from NASA's Wide-field Infrared Survey Explorer (WISE). The galaxy is the most luminous galaxy found to date and belongs to a new class of objects recently discovered by WISE -- extremely luminous infrared galaxies, or ELIRGs.

"We are looking at a very intense phase of galaxy evolution," said Chao-Wei Tsai of NASA's Jet Propulsion Laboratory in Pasadena, California, lead author of a new report appearing in the May 22 issue of The Astrophysical Journal. "This dazzling light may be from the main growth spurt of the galaxy's black hole."

The brilliant galaxy, known as WISE J224607.57-052635.0, may have a behemoth black hole at its belly, gorging itself on gas. Supermassive black holes draw gas and matter into a disk around them, heating the disk to roaring temperatures of millions of degrees and blasting out high-energy, visible, ultraviolet and X-ray light. The light is blocked by surrounding cocoons of dust. As the dust heats up, it radiates infrared light.

Immense black holes are common at the cores of galaxies, but finding one this big so "far back" in the cosmos is rare. Because light from the galaxy hosting the black hole has traveled 12.5 billion years to reach us, astronomers are seeing the object as it was in the distant past. The black hole was already billions of times the mass of our sun when our universe was only a tenth of its present age of 13.8 billion years. 

The new study outlines three reasons why the black holes in the ELIRGs could have grown so massive. First, they may have been born big. In other words, the "seeds," or embryonic black holes, might be bigger than thought possible.

"How do you get an elephant?" asked Peter Eisenhardt, project scientist for WISE at JPL and a co-author on the paper. "One way is start with a baby elephant." 

The other two explanations involve either breaking or bending the theoretical limit of black hole feeding, called the Eddington limit. When a black hole feeds, gas falls in and heats up, blasting out light. The pressure of the light actually pushes the gas away, creating a limit to how fast the black hole can continuously scarf down matter. If a black hole broke this limit, it could theoretically balloon in size at a breakneck pace. Black holes have previously been observed breaking this limit; however, the black hole in the study would have had to repeatedly break the limit to grow this large.
Alternatively, the black holes might just be bending this limit.

"Another way for a black hole to grow this big is for it to have gone on a sustained binge, consuming food faster than typically thought possible," said Tsai. "This can happen if the black hole isn't spinning that fast."

If a black hole spins slowly enough, it won't repel its meal as much. In the end, a slow-spinning black hole can gobble up more matter than a fast spinner. 

"The massive black holes in ELIRGs could be gorging themselves on more matter for a longer period of time," said Andrew Blain of University of Leicester in the United Kingdom, a co-author of this report. "It's like winning a hot-dog-eating contest lasting hundreds of millions of years."

More research is needed to solve this puzzle of these dazzlingly luminous galaxies. The team has plans to better determine the masses of the central black holes. Knowing these objects' true hefts will help reveal their history, as well as that of other galaxies, in this very crucial and frenzied chapter of our cosmos.

WISE has been finding more of these oddball galaxies in infrared images of the entire sky captured in 2010. By viewing the whole sky with more sensitivity than ever before, WISE has been able to catch rare cosmic specimens that might have been missed otherwise. 

The new study reports a total of 20 new ELIRGs, including the most luminous galaxy found to date. These galaxies were not found earlier because of their distance, and because dust converts their powerful visible light into an incredible outpouring of infrared light.

"We found in a related study with WISE that as many as half of the most luminous galaxies only show up well in infrared light," said Tsai.

JPL manages and operates WISE for NASA's Science Mission Directorate in Washington. The spacecraft was put into hibernation mode in 2011, after it scanned the entire sky twice, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects.

For more information on WISE, visit:

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Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California

Felicia Chou
NASA Headquarters, Washington

Source:  JPL-Caltech