Tag Archives: star

A combined Hubble/ALMA image of NGC 1266. The zoom-in section shows the molecular gas being propelled by the black hole's jets (red and blue), the central ALMA data (yellow) indicate the dense molecular gas. Credit: NASA/ESA Hubble; ALMA (NRAO/ESO/NAOJ)

‘Perfect Storm’ Suffocating Star Formation around a Supermassive Black Hole

High-energy jets powered by supermassive black holes can blast away a galaxy’s star-forming fuel — resulting in so-called “red and dead” galaxies: those brimming with ancient red stars yet little or no hydrogen gas available to create new ones.

Now astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that black holes don’t have to be nearly so powerful to shut down star formation. By observing the dust and gas at the center NGC 1266, a nearby lenticular galaxy with a relatively modest central black hole, the astronomers have detected a “perfect storm” of turbulence that is squelching star formation in a region that would otherwise be an ideal star factory.
This turbulence is stirred up by jets from the galaxy’s central black hole slamming into an incredibly dense envelope of gas. This dense region, which may be the result of a recent merger with another smaller galaxy, blocks nearly 98 percent of material propelled by the jets from escaping the galactic center.

 Artist illustration of the central region of NGC 1266 near its central black hole with jet and gas motions indicated (yellow and white arrows, respectively). The large-scale gas motions induce turbulence on smaller scales, preventing star formation. Credit: B. Saxton (NRAO/AUI/NSF)
Artist illustration of the central region of NGC 1266 near its central black hole with jet and gas motions indicated (yellow and white arrows, respectively). The large-scale gas motions induce turbulence on smaller scales, preventing star formation. Credit: B. Saxton (NRAO/AUI/NSF)

“Like an unstoppable force meeting an immovable object, the molecules in these jets meet so much resistance when they hit the surrounding dense gas that they are almost completely stopped in their tracks,” said Katherine Alatalo, an astronomer with the California Institute of Technology in Pasadena and lead author on a paper published in the Astrophysical Journal. This energetic collision produces powerful turbulence in the surrounding gas, disrupting the first critical stage of star formation. “So what we see is the most intense suppression of star formation ever observed,” noted Alatalo.

Previous observations of NGC 1266 revealed a broad outflow of gas from the galactic center traveling up to 400 kilometers per second. Alatalo and her colleagues estimate that this outflow is as forceful as the simultaneous supernova explosion of 10,000 stars. The jets, though powerful enough to stir the gas, are not powerful enough to give it the velocity it needs to escape from the system.
“Another way of looking at it is that the jets are injecting turbulence into the gas, preventing it from settling down, collapsing, and forming stars,” said National Radio Astronomy Observatory astronomer and co-author Mark Lacy.

The region observed by ALMA contains about 400 million times the mass of our Sun in star-forming gas, which is 100 times more than is found in giant star-forming molecular clouds in our own Milky Way. Normally, gas this concentrated should be producing stars at a rate at least 50 times faster than the astronomers observed in this galaxy.

Previously, astronomers believed that only extremely powerful quasars and radio galaxies contained black holes that were powerful enough to serve as a star-forming “on/off” switch.

A combined Hubble/ALMA image of NGC 1266. The zoom-in section shows the molecular gas being propelled by the black hole's jets (red and blue), the central ALMA data (yellow) indicate the dense molecular gas. Credit: NASA/ESA Hubble; ALMA (NRAO/ESO/NAOJ)
A combined Hubble/ALMA image of NGC 1266. The zoom-in section shows the molecular gas being propelled by the black hole’s jets (red and blue), the central ALMA data (yellow) indicate the dense molecular gas. Credit: NASA/ESA Hubble; ALMA (NRAO/ESO/NAOJ)

“The usual assumption in the past has been that the jets needed to be powerful enough to eject the gas from the galaxy completely in order to be effective at stopping start formation,” said Lacy.

To make this discovery, the astronomers first pinpointed the location of the far-infrared light being emitted by the galaxy. Normally, this light is associated with star formation and enables astronomers to detect regions where new stars are forming. In the case of NGC 1266, however, this light was coming from an extremely confined region of the galaxy. “This very small area was almost too small for the infrared light to be coming from star formation,” noted Alatalo.

With ALMA’s exquisite sensitivity and resolution, and along with observations from CARMA (the Combined Array for Research in Millimeter-wave Astronomy), the astronomers were then able to trace the location of the very dense molecular gas at the galactic center. They found that the gas is surrounding this compact source of the far-infrared light.

Under normal conditions, gas this dense would be forming stars at a very high rate. The dust embedded within this gas would then be heated by young stars and seen as a bright and extended source of infrared light. The small size and faintness of the infrared source in this galaxy suggests that NGC 1266 is instead choking on its own fuel, seemingly in defiance of the rules of star formation.

The astronomers also speculate that there is a feedback mechanism at work in this region. Eventually, the black hole will calm down and the turbulence will subside so star-formation can begin anew. With this renewed star formation, however, comes greater motion in the dense gas, which then falls in on the black hole and reestablishes the jets, shutting down star formation once again.

NGC 1266 is located approximately 100 million light-years away in the constellation Eridanus. Leticular galaxies are spiral galaxies, like our own Milky Way, but they have little interstellar gas available to form new stars.

More Information

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation 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.

 

Source: ALMA Observatory

This spectacular image of the star cluster Messier 47 was taken using the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. This young open cluster is dominated by a sprinkling of brilliant blue stars but also contains a few contrasting red giant stars.

Credit:
ESO

The Hot Blue Stars of Messier 47

This spectacular image of the star cluster Messier 47 was taken using the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. This young open cluster is dominated by a sprinkling of brilliant blue stars but also contains a few contrasting red giant stars.

Messier 47 is located approximately 1600 light-years from Earth, in the constellation of Puppis (the poop deck of the mythological ship Argo). It was first noticed some time before 1654 by Italian astronomer Giovanni Battista Hodierna and was later independently discovered by Charles Messier himself, who apparently had no knowledge of Hodierna’s earlier observation.

Although it is bright and easy to see, Messier 47 is one of the least densely populated open clusters. Only around 50 stars are visible in a region about 12 light-years across, compared to other similar objects which can contain thousands of stars.

Messier 47 has not always been so easy to identify. In fact, for years it was considered missing, as Messier had recorded the coordinates incorrectly. The cluster was later rediscovered and given another catalogue designation — NGC 2422. The nature of Messier’s mistake, and the firm conclusion that Messier 47 and NGC 2422 are indeed the same object, was only established in 1959 by Canadian astronomer T. F. Morris.

This spectacular image of the star cluster Messier 47 was taken using the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. This young open cluster is dominated by a sprinkling of brilliant blue stars but also contains a few contrasting red giant stars. Credit: ESO
This spectacular image of the star cluster Messier 47 was taken using the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. This young open cluster is dominated by a sprinkling of brilliant blue stars but also contains a few contrasting red giant stars.
Credit:
ESO



The bright blue–white colours of these stars are an indication of their temperature, with hotter stars appearing bluer and cooler stars appearing redder. This relationship between colour, brightness and temperature can be visualised by use of the Planck curve. But the more detailed study of the colours of stars using spectroscopy also tells astronomers a lot more — including how fast the stars are spinning and their chemical compositions. There are also a few bright red stars in the picture — these are red giant stars that are further through their short life cycles than the less massive and longer-lived blue stars [1].

By chance Messier 47 appears close in the sky to another contrasting star cluster — Messier 46. Messier 47 is relatively close, at around 1600 light-years, but Messier 46 is located around 5500 light-years away and contains a lot more stars, with at least 500 stars present. Despite containing more stars, it appears significantly fainter due to its greater distance.

Messier 46 could be considered to be the older sister of Messier 47, with the former being approximately 300 million years old compared to the latter’s 78 million years. Consequently, many of the most massive and brilliant of the stars in Messier 46 have already run through their short lives and are no longer visible, so most stars within this older cluster appear redder and cooler.

This image of Messier 47 was produced as part of the ESO Cosmic Gems programme [2].

Notes

[1] The lifetime of a star depends primarily on its mass. Massive stars, containing many times as much material as the Sun, have short lives measured in millions of years. On the other hand much less massive stars can continue to shine for many billions of years. In a cluster, the stars all have about the same age and same initial chemical composition. So the brilliant massive stars evolve quickest, become red giants sooner, and end their lives first, leaving the less massive and cooler ones to long outlive them.

[2] 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 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Source: ESO 

hs-2014-48-a-web_print

The Party’s Over for These Youthful Compact Galaxies

Researchers using NASA’s Hubble Space Telescope and Chandra X-ray Observatory have uncovered young, massive, compact galaxies whose raucous star-making parties are ending early. The firestorm of star birth has blasted out most of the remaining gaseous fuel needed to make future generations of stars. Now the party’s over for these gas-starved galaxies, and they are on track to possibly becoming so-called “red and dead galaxies,” composed only of aging stars.

Astronomers have debated for decades how massive galaxies rapidly evolve from active star-forming machines to star-starved graveyards. Previous observations of these galaxies reveal geysers of gas shooting into space at up to 2 million miles an hour. Astronomers have suspected that powerful monster black holes lurking at the centers of the galaxies triggered the gaseous outflows and shut down star birth by blowing out any remaining fuel.

Now an analysis of 12 merging galaxies at the end of their star-birthing frenzy is showing that the stars themselves are turning out the lights on their own star-making party. This happened when the universe was half its current age of 13.7 billion years.

“Before our study, the common belief was that stars cannot drive high-velocity outflows in galaxies; only more powerful supermassive black holes can do that,” explained Paul Sell of Texas Tech University in Lubbock, lead author of a science paper describing the study’s results. “Through our analysis we found that if you have a compact enough starburst, which Hubble showed was the case with these galaxies, you can actually produce the velocities of the outflows we observed from the stars alone without needing to invoke the black hole.”

Team member Christy Tremonti of the University of Wisconsin-Madison first identified the galaxies from the Sloan Digital Sky Survey as post-starburst objects spouting high-speed gaseous fountains. The sharp visible-light views from Hubble’s Wide Field Camera 3 show that the outflows are arising from the most compact galaxies yet found. These galaxies contain as much mass as our Milky Way galaxy, but packed into a much smaller area. The smallest galaxies are about 650 light-years across.

In such small regions of space, these galaxies are forming a few hundred suns a year. (By comparison, the Milky Way makes only about one sun a year.) This makes for a rowdy party that wears itself out quickly, in only a few tens of millions of years. One reason for the stellar shutdown is that the gas rapidly heats up, becoming too hot to contract under gravity to form new stars. Another possibility is that the star-birthing frenzy blasts out most of the star-making gas via powerful stellar winds.

“The biggest surprise from Hubble was the realization that the newly formed stars were born so close together,” said team member Aleks Diamond-Stanic of the University of Wisconsin-Madison, who first suggested the possibility of starburst-driven outflows from these galaxies in a 2012 science paper. “The extreme physical conditions at the centers of these galaxies explain how they can expel gas at millions of miles per hour.”

To identify the mechanism triggering the high-velocity outflows, Sell and his team used the Chandra X-ray Observatory and other telescopes to determine whether the galaxies’ supermassive black holes (weighing up to a billion suns) were the powerhouses driving them. After analyzing all of the observations, the team concluded that the black holes were not the source of the outflows. Rather, it was the powerful stellar winds from the most massive and short-lived stars at the end of their lives, combined with their explosive deaths as supernovae.


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Based on their analysis of the Hubble and Chandra data, team members suggest that the “party begins” when two gas-rich galaxies collide, funneling a torrent of cold gas into the merging galaxies’ compact center. The large amount of gas compressed into the small space ignites the birth of numerous stars. The energy from the stellar firestorm then blows out the leftover gas, quenching further star formation.

“If you stop the flow of cold gas to form stars, that’s it,” explained Sell, who conducted the research while a graduate student at the University of Wisconsin-Madison. “The stars stop forming, and the galaxy rapidly evolves and may eventually become a red, dead elliptical galaxy. These extreme starbursts are quite rare, however, so they may not grow into the typical giant elliptical galaxies seen in our nearby galactic neighborhood. They may, instead, be more compact.”

The team’s results were published in the July 11 edition of the Monthly Notices of the Royal Astronomical Society.

Source: Hubble Site

This artist’s impression shows the dust and gas around the double star system GG Tauri-A. Researchers using ALMA have detected gas in the region between two discs in this binary system. This may allow planets to form in the gravitationally perturbed environment of the binary. Half of Sun-like stars are born in binary systems, meaning that these findings will have major consequences for the hunt for exoplanets.

Credit:

ESO/L. Calçada

Planet-forming Lifeline Discovered in a Binary Star System

ALMA Examines Ezekiel-like “Wheel in a Wheel” of Dust and Gas


For the first time, researchers using ALMA have detected a streamer of gas flowing from a massive outer disc toward the inner reaches of a binary star system. This never-before-seen feature may be responsible for sustaining a second, smaller disc of planet-forming material that otherwise would have disappeared long ago. Half of Sun-like stars are born in binary systems, meaning that these findings will have major consequences for the hunt for exoplanets. The results are published in the journal Nature on 30 October 2014.

A research group led by Anne Dutrey from the Laboratory of Astrophysics of Bordeaux, France and CNRS used theAtacama Large Millimeter/submillimeter Array (ALMA) to observe the distribution of dust and gas in a multiple-star system called GG Tau-A [1]. This object is only a few million years old and lies about 450 light-years from Earth in the constellation of Taurus (The Bull).

This artist’s impression shows the dust and gas around the double star system GG Tauri-A. Researchers using ALMA have detected gas in the region between two discs in this binary system. This may allow planets to form in the gravitationally perturbed environment of the binary. Half of Sun-like stars are born in binary systems, meaning that these findings will have major consequences for the hunt for exoplanets. Credit: ESO/L. Calçada
This artist’s impression shows the dust and gas around the double star system GG Tauri-A. Researchers using ALMA have detected gas in the region between two discs in this binary system. This may allow planets to form in the gravitationally perturbed environment of the binary. Half of Sun-like stars are born in binary systems, meaning that these findings will have major consequences for the hunt for exoplanets.
Credit:
ESO/L. Calçada

Like a wheel in a wheel, GG Tau-A contains a large, outer disc encircling the entire system as well as an inner disc around the main central star. This second inner disc has a mass roughly equivalent to that of Jupiter. Its presence has been an intriguing mystery for astronomers since it is losing material to its central star at a rate that should have depleted it long ago.

While observing these structures with ALMA, the team made the exciting discovery of gas clumps in the region between the two discs. The new observations suggest that material is being transferred from the outer to the inner disc, creating a sustaining lifeline between the two [2].

Material flowing through the cavity was predicted by computer simulations but has not been imaged before. Detecting these clumps indicates that material is moving between the discs, allowing one to feed off the other,” explains Dutrey. “These observations demonstrate that material from the outer disc can sustain the inner disc for a long time. This has major consequences for potential planet formation.”

Planets are born from the material left over from star birth. This is a slow process, meaning that an enduring disc is a prerequisite for planet formation. If the feeding process into the inner disc now seen with ALMA occurs in other multiple-star systems the findings introduce a vast number of new potential locations to find exoplanets in the future.

The first phase of exoplanet searches was directed at single-host stars like the Sun [3]. More recently it has been shown that a large fraction of giant planets orbit binary-star systems. Now, researchers have begun to take an even closer look and investigate the possibility of planets orbiting the individual stars of multiple-star systems. The new discovery supports the possible existence of such planets, giving exoplanet discoverers new happy hunting grounds.

Emmanuel Di Folco, co-author of the paper, concludes: “Almost half the Sun-like stars were born in binary systems. This means that we have found a mechanism to sustain planet formation that applies to a significant number of stars in the Milky Way. Our observations are a big step forward in truly understanding planet formation.

Notes

[1] GG Tau-A is part of a more complex multiple-star system called GG Tauri. Recent observations of GG Tau-A using the VLTI have revealed that one of the stars — GG Tau Ab, the one not surrounded by a disc — is itself a close binary, consisting of GG Tau-Ab1 and GG Tau-Ab2. This introduced a fifth component to the GG Tau system.

[2] An earlier result with ALMA showed an example of a single star with material flowing inwards from the outer part of its disc.

[3] Because orbits in binary stars are more complex and less stable, it was believed that forming planets in these systems would be more challenging than around single stars.

Source: ESO

Artist’s impression of exocomets around Beta Pictoris. Credit: ESO

Two Families of Comets Found Around Nearby Star

Two Families of Comets Found Around Nearby Star


The HARPS instrument at ESO’s La Silla Observatory in Chile has been used to make the most complete census of comets around another star ever created. A French team of astronomers has studied nearly 500 individual comets orbiting the star Beta Pictoris and has discovered that they belong to two distinct families of exocomets: old exocomets that have made multiple passages near the star, and younger exocomets that probably came from the recent breakup of one or more larger objects. The new results will appear in the journal Nature on 23 October 2014.

Beta Pictoris is a young star located about 63 light-years from the Sun. It is only about 20 million years old and is surrounded by a huge disc of material — a very active young planetary system where gas and dust are produced by the evaporation of comets and the collisions of asteroids.

Artist’s impression of exocomets around Beta Pictoris. Credit: ESO
Artist’s impression of exocomets around Beta Pictoris. Credit: ESO

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study sets the scene: “Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system.”

For almost 30 years astronomers have seen subtle changes in the light from Beta Pictoris that were thought to be caused by the passage of comets in front of the star itself. Comets are small bodies of a few kilometres in size, but they are rich in ices, which evaporate when they approach their star, producing gigantic tails of gas and dust that can absorb some of the light passing through them. The dim light from the exocomets is swamped by the light of the brilliant star so they cannot be imaged directly from Earth.

To study the Beta Pictoris exocomets, the team analysed more than 1000 observations obtained between 2003 and 2011 with the HARPS instrument on the ESO 3.6-metre telescope at the La Silla Observatory in Chile.

The researchers selected a sample of 493 different exocomets. Some exocomets were observed several times and for a few hours. Careful analysis provided measurements of the speed and the size of the gas clouds. Some of the orbital properties of each of these exocomets, such as the shape and the orientation of the orbit and the distance to the star, could also be deduced.

This analysis of several hundreds of exocomets in a single exo-planetary system is unique. It revealed the presence of two distinct families of exocomets: one family of old exocomets whose orbits are controlled by a massive planet [1], and another family, probably arising from the recent breakdown of one or a few bigger objects. Different families of comets also exist in the Solar System.

The exocomets of the first family have a variety of orbits and show a rather weak activity with low production rates of gas and dust. This suggests that these comets have exhausted their supplies of ices during their multiple passages close to Beta Pictoris [2].

The exocomets of the second family are much more active and are also on nearly identical orbits [3]. This suggests that the members of the second family all arise from the same origin: probably the breakdown of a larger object whose fragments are on an orbit grazing the star Beta Pictoris.

Flavien Kiefer concludes: “For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago.”

Notes

[1] A giant planet, Beta Pictoris b, has also been discovered in orbit at about a billion kilometres from the star and studied using high resolution images obtained with adaptive optics.

[2] Moreover, the orbits of these comets (eccentricity and orientation) are exactly as predicted for comets trapped inorbital resonance with a massive planet. The properties of the comets of the first family show that this planet in resonance must be at about 700 million kilometres from the star  — close to where the planet Beta Pictoris b was discovered.

[3] This makes them similar to the comets of the Kreutz family in the Solar System, or the fragments of Comet Shoemaker-Levy 9, which impacted Jupiter in July 1994.

Source: ESO

This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters.

Credit:

ESO/M. Kornmesser

Construction Secrets of a Galactic Metropolis

Astronomers have used the APEX telescope to probe a huge galaxy cluster that is forming in the early Universe and revealed that much of the star formation taking place is not only hidden by dust, but also occurring in unexpected places. This is the first time that a full census of the star formation in such an object has been possible.


This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters. Credit: ESO/M. Kornmesser
This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters.
Credit:
ESO/M. Kornmesser

Galaxy clusters are the largest objects in the Universe held together by gravity but their formation is not well understood. TheSpiderweb Galaxy (formally known as MRC 1138-262 [1]) and its surroundings have been studied for twenty years, using ESO and other telescopes [2], and is thought to be one of the best examples of a protocluster in the process of assembly, more than ten billion years ago.

But Helmut Dannerbauer (University of Vienna, Austria) and his team strongly suspected that the story was far from complete. They wanted to probe the dark side of star formation and find out how much of the star formation taking place in the Spiderweb Galaxy cluster was hidden from view behind dust.

The team used the LABOCA camera on the APEX telescope in Chile to make 40 hours of observations of the Spiderweb Cluster at millimetre wavelengths — wavelengths of light that are long enough to peer right through most of the thick dust clouds. LABOCA has a wide field and is the perfect instrument for this survey.

Carlos De Breuck (APEX project scientist at ESO, and a co-author of the new study) emphasises: “This is one of the deepest observations ever made with APEX and pushes the technology to its limits — as well as the endurance of the staff working at the high-altitude APEX site, 5050 metres above sea level.

The APEX observations revealed that there were about four times as many sources detected in the area of the Spiderweb compared to the surrounding sky. And by carefully comparing the new data with complementary observations made at different wavelengths they were able to confirm that many of these sources were at the same distance as the galaxy cluster itself and must be parts of the forming cluster.

Helmut Dannerbauer explains: “The new APEX observations add the final piece needed to create a complete census of all inhabitants of this mega star city. These galaxies are in the process of formation so, rather like a construction site on Earth, they are very dusty.”

But a surprise awaited the team when they looked at where the newly detected star formation was taking place. They were expecting to find this star formation region on the large filaments connecting galaxies. Instead, they found it concentrated mostly in a single region, and that region is not even centred on the central Spiderweb Galaxy in the protocluster [3].

Helmut Dannerbauer concludes: “We aimed to find the hidden star formation in the Spiderweb cluster — and succeeded — but we unearthed a new mystery in the process; it was not where we expected! The mega city is developing asymmetrically.

To continue the story further observations are needed — and ALMA will be the perfect instrument to take the next steps and study these dusty regions in far greater detail.

Notes

[1] The Spiderweb Galaxy contains a supermassive black hole and is a powerful source of radio waves — which is what led astronomers to notice it in the first place.

[2] This region had been intensively observed by a variety of ESO telescopes since the mid-1990s. The redshift (and hence the distance) of the radio galaxy MRC1138-262 (the Spiderweb Galaxy) was first measured at La Silla. The first visitor modeFORS observations on the VLT discovered the protocluster and afterwards further observations were made with ISAAC,SINFONIVIMOS and HAWK-I. The APEX LABOCA data complement optical and near-infrared datasets from ESO telescopes. The team also used a 12-hour VLA image to cross-identify the LABOCA sources in the optical images.

[3] These dusty starbursts are thought to evolve into elliptical galaxies like those seen around us today in nearby galaxy clusters.

More information

This research was presented in a paper, “An excess of dusty starbursts related to the Spiderweb galaxy”, by Dannerbauer, Kurk, De Breuck et al., to appear online in the journal Astronomy & Astrophysics on 15 October 2014.

APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. Operation of APEX at Chajnantor is entrusted to ESO.

The team is composed of H. Dannerbauer (University of Vienna, Austria), J. D. Kurk (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), C. De Breuck (ESO, Garching, Germany), D. Wylezalek (ESO, Garching, Germany), J. S. Santos (INAF–Osservatorio Astrofisico di Arcetri, Florence, Italy), Y. Koyama (National Astronomical Observatory of Japan, Tokyo, Japan [NAOJ]; Institute of Space Astronomical Science, Kanagawa, Japan), N. Seymour (International Centre for Radio Astronomy Research, Curtin University, Perth, Australia), M. Tanaka (NAOJ; Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Japan), N. Hatch (University of Nottingham, United Kingdom), B. Altieri (Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Cañada, Spain [HSC]), D. Coia (HSC), A. Galametz (INAF–Osservatorio di Roma, Italy), T. Kodama (NAOJ), G. Miley (Leiden Observatory, the Netherlands), H. Röttgering (Leiden Observatory), M. Sanchez-Portal (HSC), I. Valtchanov (HSC), B. Venemans (Max-Planck Institut für Astronomie, Heidelberg, Germany) and B. Ziegler (University of Vienna).

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 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Source: ESO

 

A plot of the transmission spectrum for exoplanet HAT-P-11b, with data from NASA's Kepler, Hubble and Spitzer observatories combined. The results show a robust detection of water absorption in the Hubble data. Transmission spectra of selected atmospheric models are plotted for comparison.
Image Credit: NASA/ESA/STScI

NASA Telescopes Find Clear Skies and Water Vapor on Exoplanet

Astronomers using data from three of NASA’s space telescopes — Hubble, Spitzer and Kepler — have discovered clear skies and steamy water vapor on a gaseous planet outside our solar system. The planet is about the size of Neptune, making it the smallest planet from which molecules of any kind have been detected.

A plot of the transmission spectrum for exoplanet HAT-P-11b, with data from NASA's Kepler, Hubble and Spitzer observatories combined. The results show a robust detection of water absorption in the Hubble data. Transmission spectra of selected atmospheric models are plotted for comparison. Image Credit: NASA/ESA/STScI
A plot of the transmission spectrum for exoplanet HAT-P-11b, with data from NASA’s Kepler, Hubble and Spitzer observatories combined. The results show a robust detection of water absorption in the Hubble data. Transmission spectra of selected atmospheric models are plotted for comparison.
Image Credit: NASA/ESA/STScI

“This discovery is a significant milepost on the road to eventually analyzing the atmospheric composition of smaller, rocky planets more like Earth,” said John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate in Washington. “Such achievements are only possible today with the combined capabilities of these unique and powerful observatories.”
Clouds in a planet’s atmosphere can block the view to underlying molecules that reveal information about the planet’s composition and history. Finding clear skies on a Neptune-size planet is a good sign that smaller planets might have similarly good visibility.
“When astronomers go observing at night with telescopes, they say ‘clear skies’ to mean good luck,” said Jonathan Fraine of the University of Maryland, College Park, lead author of a new study appearing in Nature. “In this case, we found clear skies on a distant planet. That’s lucky for us because it means clouds didn’t block our view of water molecules.”
The planet, HAT-P-11b, is categorized as an exo-Neptune — a Neptune-sized planet that orbits the star HAT-P-11. It is located 120 light-years away in the constellation Cygnus. This planet orbits closer to its star than does our Neptune, making one lap roughly every five days. It is a warm world thought to have a rocky core and gaseous atmosphere. Not much else was known about the composition of the planet, or other exo-Neptunes like it, until now.
Part of the challenge in analyzing the atmospheres of planets like this is their size. Larger Jupiter-like planets are easier to see because of their impressive girth and relatively inflated atmospheres. In fact, researchers already have detected water vapor in the atmospheres of those planets. The handful of smaller planets observed previously had proved more difficult to probe partially because they all appeared to be cloudy.
In the new study, astronomers set out to look at the atmosphere of HAT-P-11b, not knowing if its weather would call for clouds. They used Hubble’s Wide Field Camera 3, and a technique called transmission spectroscopy, in which a planet is observed as it crosses in front of its parent star. Starlight filters through the rim of the planet’s atmosphere; if molecules like water vapor are present, they absorb some of the starlight, leaving distinct signatures in the light that reaches our telescopes.
Using this strategy, Hubble was able to detect water vapor in HAT-P-11b. But before the team could celebrate clear skies on the exo-Neptune, they had to show that starspots — cooler “freckles” on the face of stars — were not the real sources of water vapor. Cool starspots on the parent star can contain water vapor that might erroneously appear to be from the planet.
The team turned to Kepler and Spitzer. Kepler had been observing one patch of sky for years, and HAT-P-11b happens to lie in the field. Those visible-light data were combined with targeted Spitzer observations taken at infrared wavelengths. By comparing these observations, the astronomers figured out that the starspots were too hot to have any steam. It was at that point the team could celebrate detecting water vapor on a world unlike any in our solar system. This discovery indicates the planet did not have clouds blocking the view, a hopeful sign that more cloudless planets can be located and analyzed in the future.
“We think that exo-Neptunes may have diverse compositions, which reflect their formation histories,” said study co-author Heather Knutson of the California Institute of Technology in Pasadena. “Now with data like these, we can begin to piece together a narrative for the origin of these distant worlds.”
The results from all three telescopes demonstrate that HAT-P-11b is blanketed in water vapor, hydrogen gas and likely other yet-to-be-identified molecules. Theorists will be drawing up new models to explain the planet’s makeup and origins.
“We are working our way down the line, from hot Jupiters to exo-Neptunes,” said Drake Deming, a co-author of the study also from University of Maryland. “We want to expand our knowledge to a diverse range of exoplanets.”
The astronomers plan to examine more exo-Neptunes in the future, and hope to apply the same method to super-Earths — massive, rocky cousins to our home world with up to 10 times the mass. Although our solar system doesn’t have a super-Earth, NASA’s Kepler mission is finding them in droves around other stars. NASA’s James Webb Space Telescope, scheduled to launch in 2018, will search super-Earths for signs of water vapor and other molecules; however, finding signs of oceans and potentially habitable worlds is likely a ways off.
“The work we are doing now is important for future studies of super-Earths and even smaller planets, because we want to be able to pick out in advance the planets with clear atmospheres that will let us detect molecules,” said Knutson.
Once again, astronomers will be crossing their fingers for clear skies.

Source: NASA

ALMA Finds Double Star with Weird and Wild Planet-forming Discs

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have found wildly misaligned planet-forming gas discs around the two young stars in the binary system HK Tauri. These new ALMA observations provide the clearest picture ever of protoplanetary discs in a double star. The new result also helps to explain why so many exoplanets — unlike the planets in the Solar System — came to have strange, eccentric or inclined orbits. The results will appear in the journal Nature on 31 July 2014.

Unlike our solitary Sun, most stars form in binary pairs — two stars that are in orbit around each other. Binary stars are very common, but they pose a number of questions, including how and where planets form in such complex environments.

ALMA has now given us the best view yet of a binary star system sporting protoplanetary discs  — and we find that the discs are mutually misaligned!” said Eric Jensen, an astronomer at Swarthmore College in Pennsylvania, USA.

The two stars in the HK Tauri system, which is located about 450 light-years from Earth in the constellation of Taurus (The Bull), are less than five million years old and separated by about 58 billion kilometres — this is 13 times the distance of Neptune from the Sun.

The fainter star, HK Tauri B, is surrounded by an edge-on protoplanetary disc that blocks the starlight. Because the glare of the star is suppressed, astronomers can easily get a good view of the disc by observing in visible light, or at near-infrared wavelengths.

Artist’s impression of the discs around the young stars HK Tauri A and B. Credit ESO
Artist’s impression of the discs around the young stars HK Tauri A and B. Credit ESO

The companion star, HK Tauri A, also has a disc, but in this case it does not block out the starlight. As a result the disc cannot be seen in visible light because its faint glow is swamped by the dazzling brightness of the star. But it does shine brightly in millimetre-wavelength light, which ALMA can readily detect.

Using ALMA, the team were not only able to see the disc around HK Tauri A, but they could also measure its rotation for the first time. This clearer picture enabled the astronomers to calculate that the two discs are out of alignment with each other by at least 60 degrees. So rather than being in the same plane as the orbits of the two stars at least one of the discs must be significantly misaligned.

This clear misalignment has given us a remarkable look at a young binary star system,” said Rachel Akeson of the NASA Exoplanet Science Institute at the California Institute of Technology in the USA. “Although there have been earlier observations indicating that this type of misaligned system existed, the new ALMA observations of HK Tauri show much more clearly what is really going on in one of these systems.

Stars and planets form out of vast clouds of dust and gas. As material in these clouds contracts under gravity, it begins to rotate until most of the dust and gas falls into a flattened protoplanetary disc swirling around a growing central protostar.

But in a binary system like HK Tauri things are much more complex. When the orbits of the stars and the protoplanetary discs are not roughly in the same plane any planets that may be forming can end up in highly eccentric and tilted orbits [1].

Our results show that the necessary conditions exist to modify planetary orbits and that these conditions are present at the time of planet formation, apparently due to the formation process of a binary star system,” noted Jensen. “We can’t rule other theories out, but we can certainly rule in that a second star will do the job.

Since ALMA can see the otherwise invisible dust and gas of protoplanetary discs, it allowed for never-before-seen views of this young binary system. “Because we’re seeing this in the early stages of formation with the protoplanetary discs still in place, we can see better how things are oriented,” explained Akeson.

Looking forward, the researchers want to determine if this type of system is typical or not. They note that this is a remarkable individual case, but additional surveys are needed to determine if this sort of arrangement is common throughout our home galaxy, the Milky Way.

Jensen concludes: “Although understanding this mechanism is a big step forward, it can’t explain all of the weird orbits of extrasolar planets — there just aren’t enough binary companions for this to be the whole answer. So that’s an interesting puzzle still to solve, too!

Notes

[1] If the two stars and their discs are not all in the same plane, the gravitational pull of one star will perturb the other disc, making it wobble or precess, and vice versa. A planet forming in one of these discs will also be perturbed by the other star, which will tilt and deform its orbit.

More information

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

This research was presented in a paper entitled “Misaligned Protoplanetary Disks in a Young Binary Star System”, by Eric Jensen and Rachel Akeson, to appear in the 31 July 2014 issue of the journal Nature.

The team is composed of Eric L. N. Jensen (Dept. of Physics & Astronomy, Swarthmore College, USA) and Rachel Akeson (NASA Exoplanet Science Institute, IPAC/Caltech, Pasadena, USA).

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 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Source: ESO