Thursday, December 31, 2015

Two become one

Credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt (Geckzilla)

This image, taken with the Wide Field Planetary Camera 2 on board the NASA/ESA Hubble Space Telescope, shows the galaxy NGC 6052, located around 230 million light-years away in the constellation of Hercules.

It would be reasonable to think of this as a single abnormal galaxy, and it was originally classified as such. However, it is in fact a “new” galaxy in the process of forming. Two separate galaxies have been gradually drawn together, attracted by gravity, and have collided. We now see them merging into a single structure
As the merging process continues, individual stars are thrown out of their original orbits and placed onto entirely new paths, some very distant from the region of the collision itself. Since the stars produce the light we see, the “galaxy” now appears to have a highly chaotic shape. Eventually, this new galaxy will settle down into a stable shape, which may not resemble either of the two original galaxies.

Monday, December 28, 2015

Magnetic Fields in Powerful Radio Jets

X-ray jets from the galaxy Pictoris A. The greyscale image was taken by the Chandra X-ray Observatory and reveals the detailed X-ray structure of the jets, which extend over nearly one million light-years. The red contours show the radio emission. Astronomers analyzing these and other data have concluded that the X-ray emission is produced by rapidly moving charged particles in magnetic fields. Credit: NASA/Chandra, Hardcastle et al. 

Super-massive black holes at the centers of galaxies can spawn tremendous bipolar jets when matter in the vicinity forms a hot, accreting disk around the black hole. The rapidly moving charged particles in the jets radiate when they are deflected by magnetic fields; these jets were discovered at radio wavelengths several decades ago. In the most dramatic cases, the energetic particles move at speeds close to the speed of light and extend over hundreds of thousands of light-years, well beyond the visible boundaries of the galaxy. The physical processes that drive these jets and cause them to radiate are among the most important outstanding problems of modern astrophysics.

One of the most significant and unexpected discoveries of the Chandra X-ray Observatory was that bright X-rays are also emitted by these jets. The X-rays are also produced by the acceleration of charged particles, at least according to some models, but there are other possible mechanisms as well. Fast-moving particles can scatter background light, boosting it into the X-ray band. Alternatively, shocks can generate X-ray emission (or at least a significant portion of it), either as the jets interact with stellar winds and interstellar medium or, within the jet, as a consequence of jet variability, instability, turbulence, or other phenomena.

CfA astronomer Aneta Siemiginowska and her colleagues have studied the bright radio jet galaxy Pictoris A, located almost five hundred million light-years away, using very deep Chandra measurements - the observations used an accumulated total of over four days of time, spread over a fourteen year period. These data enabled the first detailed analysis of the spectral character of the emission all along the jets. The emission turns out to be remarkably uniform everywhere, something that is extremely unlikely if scattering were responsible, but which is a natural consequence of the magnetic field process. The scientists therefore reject the scattering model in favor of the latter. However, the jets do have within them many small clumps, internal structures, and lobes. Shocks and/or scattering are possible explanations for the emission in some of these structures. Although these new results represent some dramatic improvements in our understanding of Pic A, high-resolution radio measurements of a large sample of similar jets are now needed to refine and extend the models. Large-scale X-ray jets, for example, have been also detected in very distant quasars. The results from Pic A, together with future Chandra observations, will help astronomers determine the extent to which these distant jets also rely on the same processes, or if they invoke other ones.


"Deep Chandra Observations of Pictor A," M.J. Hardcastle, E. Lenc, M. Birkinshaw, J.H. Croston, J.L. Goodger, H.L. Marshall, E.S. Perlman, A. Siemiginowska, Ł. Stawarz, and D.M. Worrall, MNRAS 2015 (in press).

Friday, December 25, 2015

Infant Star’s Artistic Outburst

HH 34
Credit:ESA/Hubble & NASA

The artistic outburst of an extremely young star, in the earliest phase of formation, is captured in this spectacular image from the NASA/ESA Hubble Space Telescope. The colourful wisps, found in the lower left of the image, are painted onto the sky by a young star cocooned in the partially illuminated cloud of obscuring dust seen to the upper right.

Pictured punching through the enshrouding dust is an extremely hot, blue jet of gas released by the young star. As this jet speeds through space, it collides with cooler surrounding material. The result is the colourful object to the lower left, produced as the cooler material is heated by the jet (opo9524a, potw1307a).

This wispy object is known as HH34 and it is an example of a Herbig–Haro (HH) object. It resides approximately 1400 light-years away near the Orion Nebula, a large star formation region within the Milky Way. HH objects exist for a cosmically brief time — typically thousands of years — with changes seen in observations taken only a few years apart (heic1113).

Although the jet extends the entire length between the infant star and HH34, only a fraction of it appears visible. This part of the jet possesses an intricate structure of knots and ripples, thought to be caused by the different outbursts catching up and ramming into each other over time.

Thursday, December 24, 2015

Twisted Magnetic Fields Give New Insights on Star Formation

Magnetic field lines (purple) are twisted as they are dragged inward toward a swirling, dusty disk surrounding a young star in this artist's conception. 
Credit: Bill Saxton, NRAO/AUI/NSF.

Using new images that show unprecedented detail, scientists have found that material rotating around a very young protostar probably has dragged in and twisted magnetic fields from the larger area surrounding the star. The discovery, made with the National Science Foundation's Karl G. Jansky Very Large Array (VLA) radio telescope, has important implications for how dusty disks -- the raw material for planet formation -- grow around young stars.

The scientists studied a young protostar about 750 light-years from Earth in the constellation Perseus. Their observations, made in 2013 and 2014, measured the alignment, or polarization, of radio waves emitted by material, mostly dust, falling into a burgeoning disk orbiting the young star. The polarization information revealed the configuration of magnetic fields in this region near the star.

"The alignment of magnetic fields in this region near young stars is very important to the development of the disks that orbit them. Depending on its alignment, the magnetic field can either hinder the growth of the disk or help funnel material onto the disk, allowing it to grow," said Leslie Looney, of the University of Illinois at Urbana-Champaign.

As material from the envelope of dust and gas surrounding the young star falls inward toward the rotating disk, it is likely to drag magnetic field lines with it. Because of this, the structure of the magnetic field near the star will become different from the field's structure farther away.

"Our VLA observations are showing us this region, where the change in shape of the magnetic field is taking place," said Erin Cox, also of the University of Illinois Urbana-Champaign. The observations, she added, produced the first images at wavelengths of 8 and 10 millimeters to show the polarization near a protostar.

The observations also indicated that millimeter- to centimeter-sized particles are numerous in the disk surrounding the young star. Since the protostar is only about 10,000 years old -- very short in astronomical timescales -- this may mean that such grains form and grow quickly in the environment of a still-forming star.

The star, dubbed NGC1333 IRAS 4A, is one of two young stars forming within a common envelope of dust and gas. The disk around it contains material with a total mass more than twice that of our Sun.

Cox and Looney are part of an international team of astronomers studying the protostar. The scientists are reporting their results in the Astrophysical Journal Letters.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities,  Inc.

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Wednesday, December 23, 2015

Gap in Dusty Disk is Likely Embryonic Sub-Jupiter Mass Planet

Left: GPI J band (top) and K1 band (bottom) polarized intensity (Qr) images of the TW Hya disk. Right: Qr(i; j) scaled by r2(i; j), where r(i; j) is the distance (in pixels) of pixel position (i; j) from the central star, corrected for projection effects. All images are shown on a linear scale. The coronagraph is represented by the black filled circles and images are oriented with north up and east to the left.

TW Hydrae (TW Hya) is one of the best-studied young stars in the galaxy.At just 180 light years from Earth and a ripe young age of roughly 8 million years, this nearly solar-mass star and its orbiting, circumstellar disk of dust and gas are prime targets to better understand the processes involved in star and planet formation. The most sensitive telescope systems available, accessing wavelengths from radio to X-ray, have observed the TW Hya system. Astronomers have now used the Gemini Planet Imager (GPI) on Gemini South to image infrared light from TW Hya that is scattered off dust grains in its surrounding disk. The new GPI images confirm the presence of a darkened ring or gap in the disk at 23 AU (i.e., 23 times the earth-Sun distance) -- and GPI brings this gap into the sharpest focus yet. Comparison with detailed numerical simulations of planets forming in circumstellar disks indicates that the 5-AU-wide gap's observed structure could be generated by a sub-Jupiter-mass planet orbiting within the disk at a position roughly equivalent to that of Uranus in our solar system. "These GPI data reveal tell-tale disk structure in the giant-planet-forming region around TW Hya at higher resolution than any other measurements to date," says Dr. Valerie Rapson of Rochester Institute of Technology, who led the research team. “The results will help us piece together the story of how giant planets form around sun-like stars.” 

The paper is published in The Astrophysical Journal.

Paper Abstract: 

We present Gemini Planet Imager (GPI) adaptive optics near-infrared images of the giant-planet-forming regions of the protoplanetary disk orbiting the nearby (D = 54 pc), pre-main-sequence (classical T Tauri) star TW Hydrae. The GPI images, which were obtained in coronagraphic/polarimetric mode, exploit starlight scattered off small dust grains to elucidate the surface density structure of the TW Hya disk from ~80 AU to within ~10 AU of the star at ~1.5 AU resolution. The GPI polarized intensity images unambiguously confirm the presence of a gap in the radial surface brightness distribution of the inner disk. The gap is centered near ~23 AU, with a width of ~5 AU and a depth of ~50%. In the context of recent simulations of giant-planet formation in gaseous, dusty disks orbiting pre-main-sequence stars, these results indicate that at least one young planet with a mass ~0.2 MJ could be present in the TW Hya disk at an orbital semimajor axis similar to that of Uranus. If this (proto)planet is actively accreting gas from the disk, it may be readily detectable by GPI or a similarly sensitive, high-resolution infrared imaging system. 

Tuesday, December 22, 2015

Sparkling Stephan’s Quintet

Sparkling Stephan’s Quintet
Copyright: ESA/XMM-Newton (X-rays); ESA/Herschel/PACS, SPIRE (infrared); SDSS (optical)

The Stephan’s Quintet of galaxies was discovered by astronomer Édouard Stephan in 1877. At the time, however, he reported the discovery of ‘new nebulae’, as the concept of other galaxies beyond our Milky Way was only formalised in the 1920s. 

This image combines observations performed at three different wavelengths, with ESA’s Herschel and XMM-Newton space observatories as well as with ground-based telescopes, to reveal the different components of the five galaxies.

Stephan’s Quintet is one of the most spectacular galactic groups known, but only four galaxies from the originally discovered quintet are physically linked – the other was later discovered to be much closer to us. NGC 7320, the galaxy in the lower part the image, lies about 40 million light-years from us, rather than the 300 million light-years of the others.

One of them is the bright source above NGC 7320 in this view, two are the intertwined galaxies immediately to the right of image centre, and the fourth is the round patch towards the lower-right corner.

Later, it was discovered that an additional galaxy, hidden beyond the left edge of this image, sits at a similar distance to these four galaxies, reinstating the group as a quintet.

By observing these galaxies in infrared light with Herschel – shown in red and yellow – astronomers can trace the glow of cosmic dust. Dust is a minor but crucial ingredient of the interstellar matter in galaxies, which consists mainly of gas and provides the raw material for the birth of new generations of stars.

One galaxy stands out in the infrared light: the nearby NGC 7320, a spiral galaxy busy building new stars.

Shown in white, the optical light observed from ground-based telescopes reveals the shapes of the four distant galaxies, which exhibit tails and loops of stars and gas. These intricate features are an effect of their mutual gravitational attraction.

The intense dynamical activity of the distant group is also portrayed in the distribution of diffuse hot gas, which shines brightly in X-rays and was detected by XMM-Newton.

Represented in blue, the hot gas appears to sit mostly between the four colliding galaxies. It is likely a mixture of primordial gas predating the formation of the galaxies and intergalactic gas that has been stripped off the galaxies or expelled during their interactions.

A hint of a shockwave from the interaction of these four galaxies is visible as an almost vertical blue structure on the right of the image centre. This structure of hot gas also seems to trace a filament of infrared-bright dust that might have been heated by the shock.

At the top end of the shock, the infrared view reveals stars forming both within and outside the galaxies.
A faint tail of stars, gas and dust extends towards the left, leading to a dwarf galaxy glowing in infrared – the red and yellow object at the tip of the tail.

Further to the left, a dense concentration of hot gas is also visible in blue at the end of the tail, although it is unclear whether it belongs to the galactic group or is a foreground source.

Source: ESA

Monday, December 21, 2015

Zwicky 8338: Chandra Finds Remarkable Galactic Ribbon Unfurled

Zwicky 8338
Credit  X-ray: NASA/CXC/University of Bonn/G. Schellenberger et al; Optical: INT


An extraordinary ribbon of hot gas trailing behind a galaxy like a tail has been discovered using data from NASA's Chandra X-ray Observatory, as described in our latest press release. This ribbon, or X-ray tail, is likely due to gas stripped from the galaxy as it moves through a vast cloud of hot intergalactic gas. With a length of at least 250,000 light years, it is likely the largest such tail ever detected. In this new composite image, X-rays from Chandra (blue) have been combined with data in visible light from the Isaac Newton Group of Telescopes (yellow) in the Canary Islands, Spain.

The tail is located in the galaxy cluster Zwicky 8338, which is almost 700 million light years from Earth. The length of the tail is more than twice the diameter of the entire Milky Way galaxy. The tail contains gas at temperatures of about ten million degrees, about twenty million degrees cooler than the intergalactic gas, but still hot enough to glow brightly in X-rays that Chandra can detect.

The researchers think the tail was created as a galaxy known as CGCG254-021, or perhaps a group of galaxies dominated by this large galaxy, plowed through the hot gas in Zwicky 8338. The pressure exerted by this rapid motion caused gas to be stripped away from the galaxy.

In images from Chandra and the NSF's Karl Jansky Very Large Array (not shown in composite), the galaxy CGCG254-021 appears to be moving towards the bottom of the image with the tail following behind. There is a significant gap between the X-ray tail and the galaxy, the largest ever seen. The significant separation between the galaxy and the tail might be evidence that the gas has been completely stripped off the galaxy.

Astronomers were also able to learn more about the interactions of the system by carefully examining the properties of the galaxy and its tail. The tail has a brighter spot, referred to as its "head". Behind this head is the tail of diffuse X-ray emission. The gas in the head may be cooler and richer in elements heavier than helium than the rest of the tail. In front of the head there are hints of a bow shock, similar to a shock wave formed by a supersonic plane and in front of the bow shock is the galaxy CGCG254-021.

Independent research involving observations at infrared wavelengths indicates that CGCG254-021 has the highest mass of all galaxies in Zwicky 8338. The infrared observations, together with models for how galaxies evolve, also imply that among the galaxies in the cluster, CGCG254-021 had by far the highest rate of stars forming in the recent past. However, there is no evidence for new star formation, possibly because gas has been depleted in forming the tail.

The paper describing these results was published in the November 2015 issue of Astronomy and Astrophysics and is also available online. The authors of the paper are Gerrit Schellenberger and Thomas Reiprich from the University of Bonn in Germany. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations. Swift is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Fast Facts for Zwicky 8338:

Scale: Image is 3.6 arcmin across (about 700,000 light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 18h 11m 26.75s | Dec +49° 49' 47.35"
Constellation: Hercules
Observation Date: 04 Jan 2013
Observation Time: 2 hours 13 min.
Obs. ID: 15163
Instrument: ACIS
References: Schellenberger, G. et al, 2015, A&A, 583, L2; arXiv:1510.03708
Color Code: X-ray: Blue; Optical: Yellow
Distance Estimate: About 680 million light years

Meanwhile, in a galaxy not so far, far away...

The glittering city lights of Coruscant, the Star Wars core world, might have evolved on an older, near Earth-size planet like Kepler-452b. This real-life Earth cousin exists in a system 1.5 billion years older than Earth, giving any theoretical life plenty of time to develop an advanced technological civilization. Credits: NASA/Ames/JPL-Caltech.  › Larger image

Molten exoplanet CoRoT-7b is a good analog for the Star Wars sizzling lava planet Mustafar. While you won't see any lightsaber duels on CoRoT-7b, the planet's temperature of 3,600 degrees Fahrenheit (1,982 Celsius) isn't far off from the fictional magma mining station.Credits: ESO/L. Calcada.  › Larger image

Fictional Hoth is a frozen tundra that briefly serves as a base for the hidden Rebel Alliance. It's also the nickname of real exoplanet OGLE-2005-BLG-390, a cold super-Earth whose surface temperature clocks in at minus 364 degrees Fahrenheit (minus 220 Celsius).Credits: NASA, ESA and G. Bacon (STScI).   › Larger image

Years before science discovered planets orbiting two stars, Star Wars showed Luke Skywalker facing a twin sunset on his home world Tatooine. Now NASA telescopes have found multiple planets orbiting binary star systems, including Kepler-16b.Credits: NASA/JPL-Caltech.  › Larger image

Super-Earth Kepler-22b may not hide an army of clones, but it may resemble the grey water-world of Kamino with its own super ocean. While the true composition of Kepler-22b's surface is unknown, an ocean world about the size of Earth could be comfortably habitable. Credits: Image credit: NASA/Ames/JPL-Caltech.  › Larger image

Rubble in space can signal either birth or death: the formation of a planetary system or the end of planet. For Alderaan, the Death Star's fatal strike transformed the planet into an asteroid field. In this artist's concept, the swirling disk of debris is part of the formation of a new star system, and plays a key role in the creation of new planets. Credits: NASA/JPL-Caltech.  › Larger image

The fantasy creations of the "Star Wars" universe are strikingly similar to real planets in our own Milky Way galaxy. A super Earth in deep freeze? Think ice-planet "Hoth." And that distant world with double sunsets can't help but summon thoughts of sandy "Tatooine."

No indications of life have yet been detected on any of the nearly 2,000 scientifically confirmed exoplanets, so we don't know if any of them are inhabited by Wookies or mynocks, or play host to exotic alien bar scenes (or even bacteria, for that matter).

Still, a quick spin around the real exoplanet universe offers tantalizing similarities to several Star Wars counterparts.

A more ancient Earth?

The most recently revealed exoplanet possessing Earth-like properties, Kepler-452b, might make a good stand-in for Coruscant -- the high-tech world seen in several Star Wars films whose surface is encased in a single, globe-spanning city. Kepler-452b belongs to a star system 1.5 billion years older than Earth's. That would give any technologically adept species more than a billion-year jump ahead of us. The denizens of Coruscant not only have an entirely engineered planetary surface, but an engineered climate as well. On Kepler-452b, conditions are growing markedly warmer as its star's energy output increases, a symptom of advanced age. If this planet (which is 1.6 times the size of Earth) were truly Earth-like, and if technological life forms were present, some climate engineering might be needed there as well.

City in the sky

 Mining the atmospheres of giant gas planets is a staple of science fiction. NASA, too, has examined the question, and found that gases such as helium-3 and hydrogen could be extracted from the atmospheres of Uranus and Neptune. Gas giants of all stripes populate the real exoplanet universe; in "The Empire Strikes Back," a gas giant called Bespin is home to a "Cloud City" actively involved in atmospheric mining. The toadstool-shaped city provides apparent refuge for a fleeing Princess Leia and company -- at least until Darth Vader wreaks his usual havoc.

Many of the gas giants found so far by instruments such as NASA's Kepler Space Telescope are so-called "hot Jupiters" -- star-hugging behemoths far too thoroughly barbecued to be proper sites for floating cities. One recent discovery, however, shows that gas "exogiants" can orbit their stars at distances remarkably similar to those in our solar system. An international astronomical team discovered a twin of our own Jupiter, orbiting its star at about the same distance as Jupiter is from the sun. The star, HIP 11915, is about the same age and composition as our sun, raising the possibility that its entire planetary system might be similar to ours. This not-so-hot Jupiter, about 186 light-years away from Earth, was detected using the 11.8-foot (3.6-meter) telescope at La Silla Observatory in Chile.

Bespin's atmospheric layers include a band of breathable air, ideal for floating cities. In our galaxy, emerging technology allows us to read out the components of real exoplanet atmospheres -- including gas giants (though so far none show signs of habitable layers). And tasting the atmospheres of smaller, rocky, potentially habitable exoplanets soon could be within reach. Astronomers using K2, the second planet-finding mission of the Kepler space telescope, recently detected three such planets orbiting a nearby white dwarf star. The starlight shining through the atmospheres of these planets could reveal their composition in future observations.

Turn up the heat 

The planet Mustafar, scene of an epic duel between Obi-Wan Kenobi and Anakin Skywalker in "Revenge of the Sith," has a number of exoplanet counterparts. These molten, lava-covered worlds, such as Kepler-10b and Kepler-78b, are rocky planets in Earth's size range whose surfaces could well be perpetual infernos.

Kepler-78b, roughly 20 percent larger than Earth, weighs in at twice Earth's mass; a comparable density means it could be composed of rock and iron. That might make it, like Mustafar, suitable for mining, although its extremely tight orbit around its sun-like star, along with scorching temperatures, provides an unlikely arena for industrial operations -- or for fencing with lightsabers. Kepler-10b isn't much more pleasant. The first rocky world discovered using the Kepler telescope, it also hugs its sun, some 20 times closer than Mercury orbits ours. A balmy day on Kepler-10b means daytime highs of more than 2,500 Fahrenheit (1,371 Celsius), even hotter than lava flowing on Earth. The surface, free of any kind of atmosphere, might be boiling with iron and silicates. At 3,600 degrees Fahrenheit (1,982 Celsius), however, CoRoT-7b has Kepler-10b beat. This well-grilled planet, discovered in 2010 with France's CoRoT satellite, lies some 480 light-years away, and has a diameter 70 percent larger than Earth's, with nearly five times the mass. Possibly the boiled-down remnant of a Saturn-sized planet, its orbit is so tight that its star looms much larger in its sky than our sun appears to us, keeping its sun-facing surface molten.

Deep freeze

The planet OGLE-2005-BLG-390, nicknamed "Hoth," is a cold super-Earth that might be a failed Jupiter. Unable to grow large enough, it had to settle for a mass five times that of Earth and a surface locked in the deepest of deep freezes, with a surface temperature estimated at minus 364 degrees Fahrenheit (minus 220 Celsius). That most likely means no "Hoth"-style tauntauns to ride, or even formidably fanged abominable snowmen (aka "wampas"). Astronomers used an extraordinary planet-finding technique known as microlensing to find this world in 2005, one of the early demonstrations of this technique's ability to reveal exoplanets. In microlensing, backlight from a distant star is used to reveal planets around a star closer to us.

The planet lies toward the heart of the Milky Way, where a greater density of stars makes microlensing events more likely. The one-time event revealing the distant Hoth was captured by the Optical Gravitational Lensing Experiment, or OGLE, and confirmed by other instruments.

We won't have to travel 20,000 light years, however, to visit icy worlds. Saturn's smoggy moon, Titan, where the Cassini spacecraft's Huygens probe landed in 2005, is pocked with methane lakes and socked in permanently with thick, hydrocarbon haze. The freeze is so deep that water ice is no different from rock. Another Saturn moon, Enceladus, looks like a snowball but harbors a subsurface ocean much like Jupiter's moon Europa, another ice ball with a likely ocean underneath. That ocean would be warmed by tidal flexing as the little moon orbits Jupiter.

Sunset? Make it a double

Luke Skywalker's home planet, Tatooine, is said to possess a harsh, desert environment, swept by sandstorms as it roasts under the glare of twin suns. Real exoplanets in the thrall of two or more suns are even harsher. Kepler-16b was the Kepler telescope's first discovery of a planet in a "circumbinary" orbit -- circling both stars, as opposed to just one, in a double-star system. This planet, however, is likely cold, about the size of Saturn, and gaseous, though partly composed of rock. It lies outside its two stars' "habitable zone," where liquid water could exist. And its stars are cooler than our sun, and probably render the planet lifeless. Of course, we could look on the bright side (so to speak). When the discovery was announced in 2011, Bill Borucki, the now-retired NASA principal investigator for Kepler at Ames Research Center, Moffett Field, California, said finding the new planet might actually broaden the prospects for life in our galaxy. About half of all stars belong to binary systems, so the fact that planets form around these, as well as around single stars, can only increase the odds.

A more recently announced exoplanet, Kepler-453b, is also a circumbinary and a gas giant, though its orbit within its star's habitable zone means any moons it might have could be hospitable to life. It was the tenth circumbinary planet discovered using the Kepler telescope.

Ocean world

Kepler-22b, analog to the Star Wars planet Kamino (birthplace of the army of clone soldiers)), is a super-Earth that could be covered in a super ocean. Watery, storm-drenched Kamino makes its appearance in "Attack of the Clones."

The jury is still out on Kepler-22b's true nature; at 2.4 times Earth's radius, it might even be gaseous. But if the ocean world idea turns out to be right, we can envision a physically plausible Kamino-like planet, with the help of scientists at the Massachusetts Institute of Technology in Cambridge. An ocean world tipped on its side -- a bit like our solar system's ice giant, Uranus -- turns out to be comfortably habitable based on recent computer modeling. Researchers found that an exoplanet in Earth's size range, at a comparable distance from its sun and covered in water, could have an average surface temperature of about 60 degrees Fahrenheit (15.5 degrees Celsius). Because of its radical tilt, its north and south poles would be alternately bathed in sunlight and darkness, for half a year each, as the planet circled its star.

Scientists previously thought such a planet would seesaw between boiling and freezing, rendering it uninhabitable. But the MIT scientists' three-dimensional model showed that the planet, even with a relatively shallow ocean of about 160 feet (50 meters), would absorb heat during its odd polar summer and release it in winter. That would keep the overall climate mild and spring-like year round.

The shallow depth, by the way, would be ideal for Kamino-style ocean platforms, allowing construction of covered cities at the ocean surface, where armies of clones could march and drill in peace.

Fly me to the exomoon

Endor, the forested realm of the Ewoks, orbits a gas giant and was introduced in "Return of the Jedi." Detection of exomoons -- that is, moons circling distant planets -- is still in its infancy for scientists here on Earth. A possible exomoon was observed in 2014 via microlensing. It will remain forever unconfirmed, however, since each microlensing event can be seen only once. If the exomoon is real, it orbits a rogue planet, unattached to a star and wandering freely through space. The planet might have hung on to its moon after somehow being ejected during the early history of a forgotten planetary system. A team of Japanese, New Zealand, and American astronomers analyzed data gathered in 2011 with telescopes in New Zealand and Tasmania, and suggested the possible exomoon. They said a small star accompanied by a large planet also could have caused the same lensing effect.

More exomoons might soon be popping out from the depths of space. The Harvard-based Hunt for Exomoons with Kepler, or HEK, has begun to scour data from Kepler for signs of them. In early 2015, the researchers examined about 60 Kepler planets and determined that existing technology is sufficient to capture evidence of exomoons.

The hunt could have powerful implications in the search for life beyond Earth. If exomoons are shown to be potentially habitable, it would open another avenue for biology; habitable moons might even outnumber habitable planets. Could they have bustling ecosystems, with life forms even more exotic than Endor's living teddy bears, swinging between trees Tarzan-style? Stay tuned.

Breaking up is hard to do

In "A New Hope," Princess Leia's home planet, Alderaan, is blown to smithereens by the Empire's Death Star as she watches in horror. Real exoplanets also can experience extreme destruction. A white dwarf star was caught in the act of devouring the last bits of a small planet in 2015, observed with the help of NASA's Chandra X-ray Observatory. White dwarfs are super-dense stellar remnants about the size of Earth, but with gravity more than 10,000 times that of our sun's surface. Tidal forces could rip a planet caught in its pull to shreds.

In "A New Hope," Princess Leia's home planet, Alderaan, is blown to smithereens by the Empire's Death Star as she watches in horror. Observers thought at first they were seeing a black hole in the act of feeding inside a star cluster on the Milky Way's rim. X-ray observations, however, matched theoretical models of a planet being torn apart by a white dwarf.

A similar observation of a closer white dwarf was made by K2 in 2014. In this case, a tiny rocky object, probably an asteroid, was being vaporized into little more than a dusty ring as it whipped around the star every 4.5 hours.

NASA's Spitzer Space Telescope also picked up signs of debris from a likely asteroid collision in 2014. But rather than a sign of planetary destruction, the colliding asteroids could be part of a construction site. This young star -- about 1,200 light years away and only 35 million years old -- is surrounded by a ring of dust where such collisions are frequent. The smashed and broken bits fuse into larger and larger agglomerations, eventually forming full-sized planets.

Our own solar system might once have looked very similar, if anyone was watching.

NASA's Ames Research Center in Moffett Field, California, manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

JPL, a division of the California Institute of Technology in Pasadena, manages the Spitzer Space Telescope for NASA.

Written by Pat Brennan

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Sunday, December 20, 2015

NuSTAR Finds Cosmic Clumpy Doughnut Around Black Hole

Galaxy NGC 1068 can be seen in close-up in this view from NASA's Hubble Space Telescope. NuSTAR's high-energy X-rays eyes were able to obtain the best view yet into the hidden lair of the galaxy's central, supermassive black hole. Image credit: NASA/JPL-Caltech. › Full image and caption

Galaxy NGC 1068 is shown in visible light and X-rays in this composite image. Image credit: NASA/JPL-Caltech/Roma Tre Univ. 
› Full image and caption

The most massive black holes in the universe are often encircled by thick, doughnut-shaped disks of gas and dust. This deep-space doughnut material ultimately feeds and nourishes the growing black holes tucked inside.

Until recently, telescopes weren't able to penetrate some of these doughnuts, also known as tori.

"Originally, we thought that some black holes were hidden behind walls or screens of material that could not be seen through," said Andrea Marinucci of the Roma Tre University in Italy, lead author of a new Monthly Notices of the Royal Astronomical Society study describing results from NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, and the European Space Agency's XMM-Newton space observatory.

With its X-ray vision, NuSTAR recently peered inside one of the densest of these doughnuts known to surround a supermassive black hole. This black hole lies at the center of a well-studied spiral galaxy called NGC 1068, located 47 million light-years away in the Cetus constellation.

The observations revealed a clumpy, cosmic doughnut.

"The rotating material is not a simple, rounded doughnut as originally thought, but clumpy," said Marinucci.v Doughnut-shaped disks of gas and dust around supermassive black holes were first proposed in the mid-1980s to explain why some black holes are hidden behind gas and dust, while others are not. The idea is that the orientation of the doughnut relative to Earth affects the way we perceive a black hole and its intense radiation. If the doughnut is viewed edge-on, the black hole is blocked. If the doughnut is viewed face-on, the black hole and its surrounding, blazing materials can be detected. This idea is referred to as the unified model because it neatly joins together the different black hole types, based solely upon orientation.v In the past decade, astronomers have been finding hints that these doughnuts aren't as smoothly shaped as once thought. They are more like defective, lumpy doughnuts that a doughnut shop might throw away.

The new discovery is the first time this clumpiness has been observed in an ultra-thick doughnut, and supports the idea that this phenomenon may be common. The research is important for understanding the growth and evolution of massive black holes and their host galaxies.

"We don't fully understand why some supermassive black holes are so heavily obscured, or why the surrounding material is clumpy," said co-author Poshak Gandhi of the University of Southampton in the United Kingdom. "This is a subject of hot research."

Both NuSTAR and XMM-Newton observed the supermassive black hole in NGC 1068 simultaneously on two occasions between 2014 to 2015. On one of those occasions, in August 2014, NuSTAR observed a spike in brightness. NuSTAR observes X-rays in a higher-energy range than XMM-Newton, and those high-energy X-rays can uniquely pierce thick clouds around the black hole. The scientists say the spike in high-energy X-rays was due to a clearing in the thickness of the material entombing the supermassive black hole.

"It's like a cloudy day, when the clouds partially move away from the sun to let more light shine through," said Marinucci.

NGC 1068 is well known to astronomers as the first black hole to give birth to the unification idea. "But it is only with NuSTAR that we now have a direct glimpse of its black hole through such clouds, albeit fleeting, allowing a better test of the unification concept," said Marinucci.

The team says that future research will address the question of what causes the unevenness in doughnuts. The answer could come in many flavors. It's possible that a black hole generates turbulence as it chomps on nearby material. Or, the energy given off by young stars could stir up turbulence, which would then percolate outward through the doughnut. Another possibility is that the clumps may come from material falling onto the doughnut. As galaxies form, material migrates toward the center, where the density and gravity is greatest. The material tends to fall in clumps, almost like a falling stream of water condensing into droplets as it hits the ground.

"We'd like to figure out if the unevenness of the material is being generated from outside the doughnut, or within it," said Gandhi.

"These coordinated observations with NuSTAR and XMM-Newton show yet again the exciting science possible when these satellites work together," said Daniel Stern, NuSTAR project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

For more information on NuSTAR, visit: -

Source: JPL-Caltech

Saturday, December 19, 2015

VERITAS Detects Gamma Rays from Galaxy Halfway Across the Visible Universe

This artist's conception shows a blazar – the core of an active galaxy powered by a supermassive black hole. The VERITAS array has detected gamma rays from a blazar known as PKS 1441+25. Researchers found that the source of the gamma rays was within the relativistic jet but surprisingly far from the galaxy's black hole. The emitting region is at least a tenth of a light-year away, and most likely is 5 light-years away. Credit: M. Weiss/CfA.   High Resolution (jpg) - Low Resolution (jpg)

Cambridge, MA - In April 2015, after traveling for about half the age of the universe, a flood of powerful gamma rays from a distant galaxy slammed into Earth's atmosphere. That torrent generated a cascade of light - a shower that fell onto the waiting mirrors of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona. The resulting data have given astronomers a unique look into that faraway galaxy and the black hole engine at its heart.

Gamma rays are photons of light with very high energies. These gamma rays came from a galaxy known as PKS 1441+25, which is a rare type of galaxy known as a blazar. At its center it hosts a supermassive black hole surrounded by a disk of hot gas and dust.

As material from the disk swirls toward the black hole, some of it gets channeled into twin jets that blast outward like water from a fire hose only much faster - close to the speed of light. One of those jets is aimed nearly in our direction, giving us a view straight into the galaxy's core.

"We're looking down the barrel of this relativistic jet," explains Wystan Benbow of the Harvard-Smithsonian Center for Astrophysics (CfA). "That's why we're able to see the gamma rays at all."

One of the unknowns in blazar physics is the exact location of gamma-ray emission. Using data from VERITAS, as well as the Fermi Gamma-Ray Space Telescope, the researchers found that the source of the gamma rays was within the relativistic jet but surprisingly far from the galaxy's black hole. The emitting region is at least a tenth of a light-year away, and most likely is 5 light-years away. (A light-year is the distance light travels in one year, or about 6 trillion miles.)

Moreover, the region emitting gamma rays was larger than typically seen in an active galaxy, measuring about a third of a light-year across. "These jets tend to have clumps in them. It's possible that two of those clumps may have collided and that's what generated the burst of energy," says co-author Matteo Cerruti of the CfA.

Measuring high-energy gamma rays at all was a surprise. They tend to be either absorbed at the source or on their long journey to Earth. When the galaxy flared to life, it must have generated a huge flood of gamma rays.

The finding also provides insight into a phenomenon known as extragalactic background light or EBL, a faint haze of light that suffuses the universe. The EBL comes from all the stars and galaxies that have ever existed, and in a sense can track the history of the universe.

The EBL also acts like a fog to high-energy gamma rays, absorbing them as they travel through space. This new measurement sets an indirect limit on how abundant the EBL can be - too much, and it would have absorbed the gamma-ray flare. The results complement previous measurements based on direct observations.
These results have been accepted for publication in The Astrophysical Journal Letters and are available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, 


Christine Pulliam
Media Relations Manager
Harvard-Smithsonian Center for Astrophysics

The Effelsberg-Bonn HI Survey

The entire northern sky in the light of neutral atomic hydrogen (HI) as seen by the Effelsberg-Bonn HI Survey (EBHIS). Our host galaxy, the Milky Way, appears as a luminous band across the sky. The HI emission of the Andromeda galaxy (M31) is easy to spot as a bright white ellipse just below the Milky Way galaxy plane. The reddish spots at the opposite side of the plane are nearby galaxies, located a few million light years from Earth. The gas motion is color coded with different hue values, and the brightness of the color denotes the intensity of the received HI radiation. © EBHIS Project: AIfA/Jürgen Kerp & MPIfR/Benjamin Winkel.

100m Radio Telescope Maps the Complete Northern Sky in the Light of Neutral Hydrogen

Radio astronomers from Bonn University and the Max-Planck-Institut für Radioastronomie have reached a scientific milestone with their publication in the January issue of the international science journal Astronomy & Astrophysics. One of the world's largest fully steerable radio telescopes, the Effelsberg 100-m dish, surveyed the entire northern sky in the light of the neutral hydrogen (HI) 21-cm line. This effort, led by Jürgen Kerp (Argelander Institute for Astronomy) and Benjamin Winkel (Max Planck-Institut für Radioastronomie), began in 2008 and has culminated today in the initial data release of the Effelsberg-Bonn HI Survey (EBHIS). Funded by the German Research Foundation (Deutsche Forschungsgemeinschaft - DFG), the EBHIS data base is now freely accessible for all scientists around the world. In addition to the now released Milky Way data, the EBHIS project also includes unique information about HI in external galaxies out to a distance of about 750 million light years from Earth.

Hydrogen is THE ELEMENT of the universe. Consisting of a single proton and an electron it is the simplest and most abundant element in space. One could almost consider the universe as a pure hydrogen universe, albeit with some minor "pollution" by heavier elements, among these carbon, the fundamental component of all organisms on Earth. The 21-cm line is a very faint but characteristic emission line of neutral atomic hydrogen (or HI). It is not only feasible to detect the weakest signals from distant galaxies with the 100-m Effelsberg antenna, but also to determine their motion relative to Earth with high precision.

A special receiver was required in order to enable the EBHIS project. With seven receiving elements observing the sky independently from each other, it was possible to reduce the necessary observing time from decades to about five years only.

Field Programmable Gate Array (FPGA) spectrometers were developed within the course of the EBHIS project, allowing real time processing and storage of about 100 million individual HI spectra with consistently good quality. The individual HI spectra were combined using high-performance computers into a unique map of the entire northern sky and provide unsurpassed richness in detail of the Milky Way Galaxy gas.

Astronomy students at Bonn University had unique access to the pre-release EBHIS data. In 2013 the European Space Agency (ESA) signed a memorandum of understanding with the Bonn HI radio astronomers. ESA was granted exclusive access to EBHIS data for their Planck satellite mission and, in return, Bonn students were given unique access to Planck data for their thesis projects. Twelve Bachelor, nine Master, and five Doctoral thesis projects have been successfully completed since 2008.

The Square Kilometer Array (SKA), the world's largest future radio astronomical facility, to be constructed in Australia and South Africa, will benefit directly from the EBHIS data. Owing to the construction of SKA as a radio interferometer, it is inherently insensitive to the faint and extended HI emission of the Milky Way and nearby external galaxies. Since the HI gas is measured very well by EBHIS, only combining SKA and EBHIS data will allow one to derive a comprehensive view of the interstellar HI gas.

The Effelsberg-Bonn HI Survey will be a rich resource for science in the near and far future. Independent attempts to survey the entire northern sky with a 100-m class telescope are not scheduled. The EBHIS data will thus set the quality standard for the Milky Way Galaxy HI for the next decades.

EBHIS is based on observations with the 100-m telescope of the Max-Planck-Institut für Radioastronomie (MPIfR) at Effelsberg. The project was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) for six years.


Dr. Benjamin Winkel
Phone:+49 2257 301 167
Max-Planck-Institut für Radioastronomie, Effelsberg

Priv.-Doz. Dr. habil. Jürgen Kerp
Phone:+49 228 73-3667
Argelander-Institut für Astronomie der Universität Bonn

Dr. Norbert Junkes
Press and Public Outreach
Phone:+49 228 525-399
Max-Planck-Institut für Radioastronomie, Bonn

Original Paper

The Effelsberg–Bonn HI Survey: Milky Way gas. First Data Release 

B. Winkel, J. Kerp, L. Flöer, P. M. W. Kalberla, N. Ben Bekhti, R. Keller, and D. Lenz, 2016, Astronomy & Astrophysics, A&A 585, A41 DOI: 10.1051/0004-6361/201527007


The Effelsberg-Bonn HI Survey (EBHIS)
Web page of the EBHIS project

EBHIS Data Base at CDS
Data Archive at Centre de Données astronomiques de Strasbourg (CDS)

Effelsberg Radio Telescope

21cm 7 Beam Receiver
Receiver for HI observations at Effelsberg Radio Telescope

Digital Signal Processing
Technical Department at MPIfR

Argelander Institut for Astronomy at Bonn University

Friday, December 18, 2015

Hubble Sees the Force Awakening in a Newborn Star

Herbig-Haro Jet HH 24
Acknowledgment: NASA, ESA, the Hubble Heritage (STScI/AURA)/Hubble-Europe (ESA) Collaboration, D. Padgett (GSFC), T. Megeath (University of Toledo), and B. Reipurth (University of Hawaii).  Credit: NASA and ESA. Release Images

This is an artist's concept of the fireworks that accompany the birth of a star. The young stellar object is encircled by a pancake-shaped disk of dust and gas left over from the collapse of the nebula that formed the star. Gas falls onto the newly forming star and is heated to the point that some of it escapes along the star's spin axis. Intertwined by magnetic fields, the bipolar jets blast into space at over 100,000 miles per hour. As seen from far away, they resemble a double-bladed lightsaber from the Star Wars film series. Credit: NASA, ESA, and A. Feild (STScI)

Just about anything is possible in our remarkable universe, and it often competes with the imaginings of science fiction writers and filmmakers. Hubble's latest contribution is a striking photo of what looks like a double-bladed lightsaber straight out of the Star Wars films. In the center of the image, partially obscured by a dark, Jedi-like cloak of dust, a newborn star shoots twin jets out into space as a sort of birth announcement to the universe. Gas from a surrounding disk rains down onto the dust-obscured protostar and engorges it. The material is superheated and shoots outward from the star in opposite directions along an uncluttered escape route — the star's rotation axis. Much more energetic than a science fiction lightsaber, these narrow energetic beams are blasting across space at over 100,000 miles per hour. This celestial lightsaber does not lie in a galaxy far, far away but rather inside our home galaxy, the Milky Way.

Just in time for the release of the movie "Star Wars Episode VII: The Force Awakens," NASA's Hubble Space Telescope has photographed what looks like a cosmic, double-bladed lightsaber.

In the center of the image, partially obscured by a dark, Jedi-like cloak of dust, a newborn star shoots twin jets out into space as a sort of birth announcement to the universe.

"Science fiction has been an inspiration to generations of scientists and engineers, and the film series Star Wars is no exception," said John Grunsfeld, astronaut and associate administrator for NASA's Science Mission Directorate. “There is no stronger case for the motivational power of real science than the discoveries that come from the Hubble Space Telescope as it unravels the mysteries of the universe."

This celestial lightsaber does not lie in a galaxy far, far away, but rather inside our home galaxy, the Milky Way. It's inside a turbulent birthing ground for new stars known as the Orion B molecular cloud complex, located 1,350 light-years away.

When stars form within giant clouds of cool molecular hydrogen, some of the surrounding material collapses under gravity to form a rotating, flattened disk encircling the newborn star.

Though planets will later congeal in the disk, at this early stage the protostar is feeding on the disk with a Jabba-like appetite. Gas from the disk rains down onto the protostar and engorges it. Superheated material spills away and is shot outward from the star in opposite directions along an uncluttered escape route — the star's rotation axis.

Shock fronts develop along the jets and heat the surrounding gas to thousands of degrees Fahrenheit. The jets collide with the surrounding gas and dust and clear vast spaces, like a stream of water plowing into a hill of sand. The shock fronts form tangled, knotted clumps of nebulosity and are collectively known as Herbig-Haro (HH) objects. The prominent HH object shown in this image is HH 24.

Just to the right of the cloaked star, a couple of bright points are young stars peeking through and showing off their own faint lightsabers — including one that has bored a tunnel through the cloud towards the upper-right side of the picture.

Overall, just a handful of HH jets have been spotted in this region in visible light, and about the same number in the infrared. Hubble's observations for this image were performed in infrared light, which enabled the telescope to peer through the gas and dust cocooning the newly forming stars and capture a clear view of the HH objects.

These young stellar jets are ideal targets for NASA's upcoming James Webb Space Telescope, which will have even greater infrared wavelength vision to see deeper into the dust surrounding newly forming stars.

For additional information, contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Mathias Jäger
ESA/Hubble, Garching, Germany

Deborah Padgett
NASA Goddard Space Flight Center, Greenbelt, Maryland

Bo Reipurth (available only after Jan. 8, 2016)
University of Hawaii, Hilo, Hawaii

Tom Megeath
University of Toledo, Toledo, Ohio

Source: HubbleSite

A home for old stars

Credit: NASA & ESA, Acknowledgement: Judy Schmidt (Geckzilla)

This image, taken with the Wide Field Planetary Camera 2 on board the NASA/ESA Hubble Space Telescope, shows the globular cluster Terzan 1. Lying around 20 000 light-years from us in the constellation of Scorpius (The Scorpion), it is one of about 150 globular clusters belonging to our galaxy, the Milky Way

Typical globular clusters are collections of around a hundred thousand stars, held together by their mutual gravitational attraction in a spherical shape a few hundred light-years across. It is thought that every galaxy has a population of globular clusters. Some, like the Milky Way, have a few hundred, while giant elliptical galaxies can have several thousand. They contain some of the oldest stars in a galaxy, hence the reddish colours of the stars in this image — the bright blue ones are foreground stars, not part of the cluster. 

The ages of the stars in the globular cluster tell us that they were formed during the early stages of galaxy formation! Studying them can also help us to understand how galaxies formed. 

Terzan 1, like many globular clusters, is a source of  X-rays. It is likely that these X-rays come from binary star systems that contain a dense neutron star and a normal star. The neutron star drags material from the companion star, causing a burst of X-ray emission. The system then enters a quiescent phase in which the neutron star cools, giving off X-ray emission with different characteristics, before enough material from the companion builds up to trigger another outburst. 

Thursday, December 17, 2015

ALMA Reveals Planetary Construction Sites

Artist’s impression of a transitional disc around a young star

PR Image eso1549b
Schematic view of a transitional disc around a young star
ALMA imaging of the transitional disc HD 135344B

ALMA imaging of the transitional disc DoAr 44

Artist’s impression of a transitional disc around a young star

Artist’s impression of a transitional disc around a young star
Artist’s impression of a transitional disc around a young star

New evidence for young planets in discs around young stars

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have found the clearest indications yet that planets with masses several times that of Jupiter have recently formed in the discs of gas and dust around four young stars. Measurements of the gas around the stars also provide additional clues about the properties of those planets.

Planets are found around nearly every star, but astronomers still do not fully understand how — and under what conditions — they form. To answer such questions, they study the rotating discs of gas and dust present around young stars from which planets are built. But these discs are small and far from Earth, and the power of ALMA was needed for them to reveal their secrets.

A special class of discs, called transitional discs, have a surprising absence of dust in their centres, in the region around the star. Two main ideas have been put forward to explain these mysterious gaps. Firstly, the strong stellar winds and intense radiation could have blown away or destroyed the encircling material [1]. Alternatively, massive young planets in the process of formation could have cleared the material as they orbit the star [2].

The unparalleled sensitivity and image sharpness of ALMA have now allowed the team of astronomers, led by Nienke van der Marel from the Leiden Observatory in the Netherlands to map the distribution of gas and dust in four of these transitional discs better than ever before [3]. This in turn has allowed them to choose between the two options as the cause of the gaps for the first time.

The new images show that there are significant amounts of gas within the dust gaps [4]. But to the team’s surprise, the gas also possessed a gap, up to three times smaller than that of the dust.

This could only be explained by the scenario in which newly formed massive planets have cleared the gas as they travelled around their orbits, but trapped the dust particles further out [5].

“Previous observations already hinted at the presence of gas inside the dust gaps,” explains Nienke van der Marel. “But as ALMA can image the material in the entire disc in much greater detail than other facilities, we could rule out the alternative scenario. The deep gap points clearly to the presence of planets with several times the mass of Jupiter, creating these caverns as they sweep through the disc.”

Remarkably, these observations were conducted utilising just one tenth of the current resolving power of ALMA, as they were performed whilst half of the array was still under construction on the Chajnantor Plateau in northern Chile.

Further studies are now needed to determine whether more transitional discs also point towards this planet-clearing scenario, although ALMA’s observations have, in the meantime, provided astronomers with a valuable new insight into the complex process of planetary formation.

“All the transitional discs studied so far that have large dust cavities also have gas cavities. So, with ALMA, we can now find out where and when giant planets are being born in these discs, and compare these results with planet formation models,” says Ewine van Dishoeck, also of Leiden University and the Max Planck Institute for Extraterrestrial Physics in Garching [6]. “Direct planetary detection is just within reach of current instruments, and the next generation telescopes currently under construction, such as the European Extremely Large Telescope, will be able to go much further. ALMA is pointing out where they will need to look.”


[1] This process, which clears the dust and gas from the inside out, is known as photoevaporation. 

[2] Such planets are difficult to observe directly (eso1310) and previous studies at millimetre wavelengths (eso1325) have failed to achieve a sharp view of their inner, planet-forming zones where these different explanations could be put to the test. Other studies (eso0827) could not measure the bulk of the gas in these discs. 

[3] The four targets of these investigations were SR 21, HD 135344B (also known as SAO 206462), DoAr 44 and Oph IRS 48. 

[4] The gas present in transitional discs consists primarily of hydrogen, and is traced through observations of the carbon monoxide — or CO — molecule. 

[5] The process of dust trapping is explained in an earlier release (eso1325). 

[6] Other examples include the HD 142527 (eso1301 and here) and J1604-2130 transitional discs.

More Information

This research was presented in a paper entitled “Resolved gas cavities in transitional disks inferred from CO isotopologs with ALMA”, by N. van der Marel, et al., to appear in Astronomy & Astrophysics in December 2015.

The team is composed of N. van der Marel (Leiden University, Leiden, the Netherlands; Institute for Astronomy, University of Hawaii, Honolulu, USA), E. F. van Dishoeck (Leiden University, Leiden, the Netherlands; Max Planck Institute for Extraterrestrial Physics, Garching, Germany), S. Bruderer (Max-Planck Institute for Extraterrestrial Physics, Garching, Germany), S. M. Andrews (Harvard-Smithsonian Center for Astrophysics, Massachusetts, USA), K. M. Pontoppidan (Space Telescope Science Institute, Baltimore, Maryland, USA), G. J. Herczeg (Peking University, Beijing, China), T. van Kempen (Leiden University, Leiden, the Netherlands) and A. Miotello (Leiden University, Leiden, the Netherlands).

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”.



Nienke van der Marel
Institute for Astronomy, University of Hawaii
Honolulu, USA

Ewine van Dishoeck
Leiden Observatory
Leiden, The Netherlands
Tel: +31 71 527 5814

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591

Source: ESO