Thursday, February 28, 2013

The Birth of a Giant Planet?

Artist's impression of a gas giant planet forming in the disc around the young star HD 100546 

VLT and Hubble images of the protoplanet system HD 100546
 
PR Image eso1310c
VLT image of the protoplanet around the young star HD 100546

NASA/ESA Hubble Space Telescope view of the dust disc around the young star HD 100546

The young star HD 100546 in the southern constellation of Musca 

Wide-field view of the sky around the young star HD 100546

Videos

Flying through the HD 100546 system
Flying through the HD 100546 system

Candidate protoplanet spotted inside its stellar womb

Astronomers using ESO’s Very Large Telescope have obtained what is likely the first direct observation of a forming planet still embedded in a thick disc of gas and dust. If confirmed, this discovery will greatly improve our understanding of how planets form and allow astronomers to test the current theories against an observable target.

An international team led by Sascha Quanz (ETH Zurich, Switzerland) has studied the disc of gas and dust that surrounds the young star HD 100546, a relatively nearby neighbour located 335 light-years from Earth. They were surprised to find what seems to be a planet in the process of being formed, still embedded in the disc of material around the young star. The candidate planet would be a gas giant similar to Jupiter.

So far, planet formation has mostly been a topic tackled by computer simulations,” says Sascha Quanz. “If our discovery is indeed a forming planet, then for the first time scientists will be able to study the planet formation process and the interaction of a forming planet and its natal environment empirically at a very early stage.

HD 100546 is a well-studied object, and it has already been suggested that a giant planet orbits about six times further from the star than the Earth is from the Sun. The newly found planet candidate is located in the outer regions of the system, about ten times further out [1].

The planet candidate around HD 100546 was detected as a faint blob located in the circumstellar disc revealed thanks to the NACO adaptive optics instrument on ESO’s VLT, combined with pioneering data analysis techniques. The observations were made using a special coronagraph in NACO, which operates at near-infrared wavelengths and suppresses the brilliant light coming from the star at the location of the protoplanet candidate [2].

According to current theory, giant planets grow by capturing some of the gas and dust that remains after the formation of a star [3]. The astronomers have spotted several features in the new image of the disc around HD100546 that support this protoplanet hypothesis. Structures in the dusty circumstellar disc, which could be caused by interactions between the planet and the disc, were revealed close to the detected protoplanet. Also, there are indications that the surroundings of the protoplanet are potentially heated up by the formation process.

Adam Amara, another member of the team, is enthusiastic about the finding. “Exoplanet research is one of the most exciting new frontiers in astronomy, and direct imaging of planets is still a new field, greatly benefiting from recent improvements in instruments and data analysis methods. In this research we used data analysis techniques developed for cosmological research, showing that cross-fertilisation of ideas between fields can lead to extraordinary progress.”

Although the protoplanet is the most likely explanation for the observations, the results of this study require follow-up observations to confirm the existence of the planet and discard other plausible scenarios. Among other explanations, it is possible, although unlikely, that the detected signal could have come from a background source. It is also possible that the newly detected object might not be a protoplanet, but a fully formed planet which was ejected from its original orbit closer to the star. When the new object around HD 100546 is confirmed to be a forming planet embedded in its parent disc of gas and dust, it will become an unique laboratory in which to study the formation process of a new planetary system.

Notes

[1] The protoplanet candidate orbits about 70 times further from its star than the Earth does from the Sun. This distance is comparable to the size of the orbits of outer Solar System dwarf planets such as Eris and Makemake. This location is controversial, as it does not fit well with current theories of planet formation. It is unclear at present whether the newfound planet candidate has been in its current position for the whole time since it formed or whether it could have migrated from the inner regions.

[2] The team made use of a special feature called an apodised phase plate that increases the contrast of the image close to the star.

[3] To study planet formation, astronomers cannot look at the Solar System, as all the planets in our neighborhood were formed more than four billion years ago. But for many years, theories about planet formation were strongly influenced by what astronomers could see in our local surroundings, as no other planets were known. Since 1995, when the first exoplanet around a sunlike star was discovered, several hundred planetary systems have been found, opening up new opportunities for scientists studying planetary formation. Up to now however, none have been “caught in the act” in the process of being formed, whilst still embedded in the disc of material around their young parent star.

More information

This research was presented in a paper “A Young Protoplanet Candidate Embedded in the Circumstellar disc of HD 100546”, by S. P. Quanz et al., to appear online in the 28 February 2013 issue of Astrophysical Journal Letters.

The team is composed of Sascha P. Quanz (ETH Zurich, Switzerland), Adam Amara (ETH), Michael R. Meyer (ETH), Matthew A. Kenworthy (Sterrewacht Leiden, Netherlands), Markus Kasper (ESO, Garching, Germany) and Julien H. Girard (ESO, Santiago, Chile).

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

Contacts

Sascha P. Quanz
ETH Zurich
Zurich, Switzerland
Tel: +41 (0) 44 63 32830
Email:
sascha.quanz@astro.phys.ethz.ch

Julien H. Girard
ESO
Santiago, Chile
Tel: +56 2 2463 5342
Email:
jgirard@eso.org

Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org

Source: ESO


Speedy Black Hole Holds Galaxy's History

 Rapidly rotating black hole accreting matter
ESA’s XMM-Newton and NASA’s NuSTAR have detected a rapidly rotating supermassive black hole in the heart of spiral galaxy NGC 1365. The rate at which a black hole spins encodes the history of its formation. An extremely rapid rotation could result from either a steady and uniform flow of matter spiralling in via an accretion disc (as shown in this artist impression) or as a result of the merger of two galaxies and their smaller black holes.

Also depicted in this image is an outflowing jet of energetic particles, believed to be powered by the black hole’s spin. The regions near black holes contain compact sources of high energy X-ray radiation thought, in some scenarios, to originate from the base of these jets. The nature of the X-ray emission enables astronomers to see how fast matter is swirling in the inner region of the disc, and ultimately to measure the black hole's spin rate. Download Hi-Res (955.29 kB)

A rapidly rotating supermassive black hole has been found in the heart of a spiral galaxy by ESA’s XMM-Newton and NASA’s NuSTAR space observatories, opening a new window into how galaxies grow.
Supermassive black holes are thought to lurk in the centre of almost all large galaxies, and scientists believe that the evolution of a galaxy is inextricably linked with the evolution of its black hole. 

How fast a black hole spins is thought to reflect the history of its formation. In this picture, a black hole that grows steadily, fed by a uniform flow of matter spiralling in, should end up spinning rapidly. Rapid rotation could also be the result of two smaller black holes merging.  

On the other hand, a black hole buffeted by small clumps of material hitting from all directions will end up rotating relatively slowly. 

These scenarios mirror the formation of the galaxy itself, since a fraction of all the matter drawn into the galaxy finds its way into the black hole. Because of this, astronomers are keen to measure the spin rates of black holes in the hearts of galaxies. 

One way of doing so is to observe X-rays emitted just outside the ‘event horizon’, the boundary surrounding a black hole beyond which nothing, including light, can escape. 

In particular, hot iron atoms produce a strong signature of X-rays at a specific energy, which is smeared out by the rotation of the black hole. The nature of this smearing can then be used to infer the spin rate. 

Using this technique, previous observations have suggested there are extremely rapidly spinning black holes in some galaxies. However, confirming the spin rate has been very difficult, because the X-ray spectrum can also be smeared out by absorbing clouds of gas lying close to the disc. Until now, telling the two scenarios apart has been impossible. 

For roughly 36 hours in July 2012, ESA’s XMM-Newton and NASA’s NuSTAR – the Nuclear Spectroscopic Telescope Array – simultaneously observed the spiral galaxy NGC 1365. XMM-Newton captured the lower energy X-rays, NuSTAR the higher energy data. 

The combined data proved to be key to unlocking the puzzle. A spinning black hole model makes a clear prediction for the ratio of high-energy to low-energy X-rays. The same is true for an absorbing cloud of gas. 

But importantly, the predictions are different and the new data agree only with a rapidly spinning black hole. This suggests that the galaxy has grown steadily with time, with material streaming uniformly into the central black hole. 

However, astronomers cannot yet rule out a single large event where two galaxies and their black holes subsequently merged, producing a sudden acceleration of the resulting supermassive black hole. 

“But we can completely rule out the absorption model,” says Guido Risaliti, INAF – Osservatorio Astrofisico di Arcetri, Italy, who led the investigation. 

“Now that we know how to measure black hole spin rates for certain, we can more confidently use them to infer the evolution of their host galaxies.”

Measuring black hole spins also provides a new way to test general relativity. Published in 1915, general relativity is Albert Einstein’s description of gravity. It predicts effects that are most easily seen in extremely strong gravitational fields, such as those found near black holes, and NGC 1365’s black hole is spinning almost as fast as Einstein's theory of gravity will allow. 

“Both physics and astrophysics benefit from this result,’ says Dr Risaliti, who is already applying the X-ray measurement technique to different galaxies. 

“The result is a great example of the synergy that can be achieved when complementary space missions are used together. It would have been impossible to achieve this work without the two spacecraft working in tandem,” says Norbert Schartel, ESA XMM-Newton project scientist.
 
Notes for Editors
 
“A rapidly spinning supermassive black hole at the centre of NGC 1365” by G. Risaliti et al. is published in Nature 28 February 2013; doi:10.1038/nature11938.

The European Space Agency's X-ray Multi-Mirror Mission, XMM-Newton, was launched in December 1999. It is the biggest scientific satellite to have been built in Europe and uses over 170 wafer-thin cylindrical mirrors spread over three high throughput X-ray telescopes. Its mirrors are among the most powerful ever developed. XMM-Newton's orbit takes it almost a third of the way to the Moon, allowing for long, uninterrupted views of celestial objects. The scientific community can apply for observing time on XMM-Newton on a competitive basis. 

NuSTAR is a Small Explorer mission led by the California Institute of Technology in Pasadena and managed by NASA's Jet Propulsion Laboratory, also in Pasadena, for NASA's Science Mission Directorate in Washington. 

For further information, please contact:
 
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email:
markus.bauer@esa.int

Guido Risaliti
INAF–Osservatorio Astrofisico di Arcetri
Tel: +39 055 2752286
Email
: risaliti@arcetri.astro.it

Norbert Schartel
ESA XMM-Newton Project Scientist
Tel: +34 91 8131 184
Email:
norbert.schartel@esa.int


Wednesday, February 27, 2013

Glowing, fiery shells of gas

Credit: ESA/Hubble & NASA
Acknowledgement: Jean-Christophe Lambry

It may look like something from The Lord of the Rings, but this fiery swirl is actually a planetary nebula known as ESO 456-67. Set against a backdrop of bright stars, the rust-coloured object lies in the constellation of Sagittarius (The Archer), in the southern sky.

Despite the name, these ethereal objects have nothing at all to do with planets; this misnomer came about over a century ago, when the first astronomers to observe them only had small, poor-quality telescopes. Through these, the nebulae looked small, compact, and planet-like — and so were labelled as such.

When a star like the Sun approaches the end of its life, it flings material out into space. Planetary nebulae are the intricate, glowing shells of dust and gas pushed outwards from such a star. At their centres lie the remnants of the original stars themselves — small, dense white dwarf stars.

In this image of ESO 456-67, it is possible to see the various layers of material expelled by the central star. Each appears in a different hue — red, orange, yellow, and green-tinted bands of gas are visible, with clear patches of space at the heart of the nebula. It is not fully understood how planetary nebulae form such a wide variety of shapes and structures; some appear to be spherical, some elliptical, others shoot material in waves from their polar regions, some look like hourglasses or figures of eight, and others resemble large, messy stellar explosions — to name but a few.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Jean-Christophe Lambry


Source: ESA/Hubble - Space Telescope


Tuesday, February 26, 2013

Future Evidence for Extraterrestrial Life Might Come from Dying Stars

A new study finds that we could detect oxygen in the atmosphere of a habitable planet orbiting a white dwarf (as shown in this artist's illustration) much more easily than for an Earth-like planet orbiting a Sun-like star. Here the ghostly blue ring is a planetary nebula - hydrogen gas the star ejected as it evolved from a red giant to a white dwarf.  Credit: David A. Aguilar (CfA). High Resolution Image (jpg) - Low Resolution Image (jpg)
 
Cambridge, MA - Even dying stars could host planets with life - and if such life exists, we might be able to detect it within the next decade. This encouraging result comes from a new theoretical study of Earth-like planets orbiting white dwarf stars. Researchers found that we could detect oxygen in the atmosphere of a white dwarf's planet much more easily than for an Earth-like planet orbiting a Sun-like star. 

"In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs," said Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics (CfA) and director of the Institute for Theory and Computation. 

When a star like the Sun dies, it puffs off its outer layers, leaving behind a hot core called a white dwarf. A typical white dwarf is about the size of Earth. It slowly cools and fades over time, but it can retain heat long enough to warm a nearby world for billions of years. 

Since a white dwarf is much smaller and fainter than the Sun, a planet would have to be much closer in to be habitable with liquid water on its surface. A habitable planet would circle the white dwarf once every 10 hours at a distance of about a million miles. 

Before a star becomes a white dwarf it swells into a red giant, engulfing and destroying any nearby planets. Therefore, a planet would have to arrive in the habitable zone after the star evolved into a white dwarf. A planet could form from leftover dust and gas (making it a second-generation world), or migrate inward from a larger distance. 

If planets exist in the habitable zones of white dwarfs, we would need to find them before we could study them. The abundance of heavy elements on the surface of white dwarfs suggests that a significant fraction of them have rocky planets. Loeb and his colleague Dan Maoz (Tel Aviv University) estimate that a survey of the 500 closest white dwarfs could spot one or more habitable Earths. 

The best method for finding such planets is a transit search - looking for a star that dims as an orbiting planet crosses in front of it. Since a white dwarf is about the same size as Earth, an Earth-sized planet would block a large fraction of its light and create an obvious signal. 

More importantly, we can only study the atmospheres of transiting planets. When the white dwarf's light shines through the ring of air that surrounds the planet's silhouetted disk, the atmosphere absorbs some starlight. This leaves chemical fingerprints showing whether that air contains water vapor, or even signatures of life, such as oxygen. 

Astronomers are particularly interested in finding oxygen because the oxygen in the Earth's atmosphere is continuously replenished, through photosynthesis, by plant life. Were all life to cease on Earth, our atmosphere would quickly become devoid of oxygen, which would dissolve in the oceans and oxidize the surface. Thus, the presence of large quantities of oxygen in the atmosphere of a distant planet would signal the likely presence of life there. 

NASA's James Webb Space Telescope (JWST), scheduled for launch by the end of this decade, promises to sniff out the gases of these alien worlds. Loeb and Maoz created a synthetic spectrum, replicating what JWST would see if it examined a habitable planet orbiting a white dwarf. They found that both oxygen and water vapor would be detectable with only a few hours of total observation time. 

"JWST offers the best hope of finding an inhabited planet in the near future," said Maoz. 

Recent research by CfA astronomers Courtney Dressing and David Charbonneau showed that the closest habitable planet is likely to orbit a red dwarf star (a cool, low-mass star undergoing nuclear fusion). Since a red dwarf, although smaller and fainter than the Sun, is much larger and brighter than a white dwarf, its glare would overwhelm the faint signal from an orbiting planet's atmosphere. JWST would have to observe hundreds of hours of transits to have any hope of analyzing the atmosphere's composition. 

"Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf," said Loeb. 

Their paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is 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, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462

daguilar@cfa.harvard.edu

 
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463

cpulliam@cfa.harvard.edu

Magnetic fields in astrophysics: an electronic 'textbooklet'

 
 Fig. 1: Field lines in the head of a magnetic jet.
(Rainer Moll, MPA)

video
Fig. 2: A fluid flow stretching a bundle of field lines (mp4 movie)
(Merel van 't Hoff, MPA) 


Magnetic fields play an important role in many objects in the universe, from the Sun with its spots and the magnetically heated corona visible during a solar eclipse, to pulsars and the spectacular 'jets' from black holes and protostars. The behaviour of the magnetic field in these objects, however, is very different from experience at home or in physics class, since in astrophysical objects magnetic field lines are 'tied' to an ionized gas. The theory for such magnetic fields, called magnetohydrodynamics (MHD), is explained in a concise textbook published online. It emphasizes understanding of MHD by visualization of the flows and forces as they take place in a magnetized fluid. To this end, the text also includes a number of small video clips of basic MHD flows. 

In physical processes where magnetic fields are present, one generally also has electric fields, currents and charge densities. Mathematically speaking, one has to deal with the full set of Maxwell's equations plus the equations of motion for the particles making up the plasma - the domain of plasma physics. Luckily, for most flows seen in astronomical objects, however, this complexity is rarely necessary. The electrical conductivity of an ionized gas makes MHD an extremely accurate approximation. Compared with ordinary fluid mechanics, only the magnetic field needs to be included explicitly in the theory. The other electromagnetic quantities can be evaluated afterwards; they are neither needed for a proper description, nor of much use for physical understanding. Thanks to this simplification it has become possible to include magnetic fields realistically in numerical simulations, for example of extragalactic jets (Fig. 1). 

The price to be paid is that we have to give up some of our intuitions about the way electric and magnetic fields work. Our experience is dominated by processes taking place in the Earth's electrically insulating atmosphere (in copper wires, batteries, induction coils etc.). Most astrophysical processes on the other hand happen in an ionised gas, such as in a star, the solar wind, or the intergalactic medium. 

Because of the strong coupling between the magnetic field and the electrically conducting gas, MHD flows behave more or less like visco-elastic but otherwise ordinary fluids. This makes MHD an eminently visualizable theory (for an example see the video clip in Fig. 2), which also motivates the approach used in the textbooklet. The first chapter (only 36 pages) is a concise introduction including exercises. The exercises are important as illustrations of the points made in the text (especially the less intuitive ones). Almost all are mathematically unchallenging, though some do require a background in undergraduate physics. This is the 'essential' part. The supplement in chapter 2 contains further explanations, more specialized topics and occasional connections to topics somewhat outside the scope of MHD.

Reference

H. C. Spruit, "Essential Magnetohydrodynamics for Astrophysics",

Monday, February 25, 2013

Diagnosing the X-Ray Variability of a Galaxy's Nucleus

An optical image of the active galaxy NGC 4507. New observations of the X-ray variability of this galaxy imply that the the simple, universal unification model for active galaxies is deficient.  Credit: Carnegie Institution of Washington . Low Resolution Image (jpg)

An active galaxy is one whose nucleus contains a massive black hole that is vigorously accreting material. In the process, the nucleus typically ejects jets of particles and radiates brightly at many wavelengths, in particular at X-ray wavelengths. Nearly half of all active galactic nuclei are seen emitting X-rays that are of relatively high energy, with less energetic X-rays absent. Since typical physical processes will generate both kinds, the usual explanation is that thick gas clouds swarm near the nuclei, and they absorb the lower energy X-ray emission, leaving the higher energy radiation relatively unaffected. X-ray emitting active galaxies are important to astronomers not only because they provide insights into black holes and their surroundings, but because the X-rays are often time variable, possibly reflecting the motions of these clouds around the nucleus. These kinematics in turn provide information on how the nucleus and its galaxy formed and evolved.

Active galaxies display a range of dramatically different properties. For example, some eject long bipolar jets from their nucleus and have spectral lines with small velocities; others show no jets and have lines with large velocities. The standard "unification model" for these objects posits that all these galaxies are intrinsically similar, only for some our viewing angle is nearly edge-on to the galaxy, and for others it is close to face-on, or some angle in between. Determining the reliability and applicability of the unification model is critical to understanding these luminous objects and what powers their activity. 

Five CfA astronomers, Andrea Marinucci, Guido Risaliti, Junfeng Wang, Martin Elvis, and Emanuele Nardini, together with three colleagues, used the Chandra and XMM-Newton satellites to study the X-ray variability of the active galaxy NGC 4507. They were trying to test whether the variation of X-rays indicated motions in absorbing clouds of gas around the black hole, and if so, whether the result was consistent with the idea that a single universal structure, viewed at different angles, could explain the basic differences between active galaxy types. 

The galaxy NGC 4507 has been known to vary in X-ray emission, but only over the rather long time scales of years. The astronomers report that when they monitored the source over shorter intervals, they found significant variations took place over timescales of months, which correspond to motions of gas clouds at distances of roughly a hundred light-years from the nucleus. This distance is much larger than what the unification model requires. The astronomers therefore conclude that a single, universal structure in active galaxies is not able to explain all the observed behaviors.
 

NASA's SDO Observes Fast-Growing Sunspot

The bottom two black spots on the sun, known as sunspots, appeared quickly over the course of Feb. 19-20, 2013. These two sunspots are part of the same system and are over six Earths across. This image combines images from two instruments on NASA's Solar Dynamics Observatory (SDO): the Helioseismic and Magnetic Imager (HMI), which takes pictures in visible light that show sunspots and the Advanced Imaging Assembly (AIA), which took an image in the 304 Angstrom wavelength showing the lower atmosphere of the sun, which is colorized in red. Credit: NASA/SDO/AIA/HMI/Goddard Space Flight Center.  › View larger

As magnetic fields on the sun rearrange and realign, dark spots known as sunspots can appear on its surface. Over the course of Feb. 19-20, 2013, scientists watched a giant sunspot form in under 48 hours. It has grown to over six Earth diameters across but its full extent is hard to judge since the spot lies on a sphere not a flat disk.

The spot quickly evolved into what's called a delta region, in which the lighter areas around the sunspot, the penumbra, exhibit magnetic fields that point in the opposite direction of those fields in the center, dark area. This is a fairly unstable configuration that scientists know can lead to eruptions of radiation on the sun called solar flares.

Karen C. Fox
NASA’s Goddard Space Flight Center


Friday, February 22, 2013

NASA Deciphering the Mysterious Math of the Solar Wind

A constant stream of particles and electromagnetic waves streams from the Sun toward Earth, which is surrounded by a protective bubble called the magnetosphere. A scientist at NASA Goddard has recently devised, for the first time, a set of equations that can help describe waves in the solar wind known as Alfven waves. Credit: European Space Agency (ESA). › View larger

Many areas of scientific research -- Earth's weather, ocean currents, the outpouring of magnetic energy from the Sun -- require mapping out the large scale features of a complex system and its intricate details simultaneously.

Describing such systems accurately, relies on numerous kinds of input, beginning with observations of the system, incorporating mathematical equations to approximate those observations, running computer simulations to attempt to replicate observations, and cycling back through all the steps to refine and improve the models until they jibe with what's seen. Ultimately, the models successfully help scientists describe, and even predict, how the system works.

Understanding the Sun and how the material and energy it sends out affects the solar system is crucial, since it creates a dynamic space weather system that can disrupt human technology in space such as communications and global positioning system (GPS) satellites.

However, the Sun and its prodigious stream of solar particles, called the solar wind, can be particularly tricky to model since as the material streams to the outer reaches of the solar system it carries along its own magnetic fields. The magnetic forces add an extra set of laws to incorporate when trying to determine what's governing the movement. Indeed, until now, equations for certain aspects of the solar wind have never been successfully devised to correlate to the observations seen by instruments in space. Now, for the first time, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., has created a set of the necessary equations, published in Physical Review Letters on Dec. 4, 2012.

"Since the 1970s, scientists have known that movement in the solar wind often has the characteristics of a kind of wave called an Alfvén wave," says Aaron Roberts, a space scientist at Goddard. "Imagine you have a jump rope and you wiggle one end so that it sends waves down the rope. Alfvén waves are similar, but the moving rope is a magnetic field line itself."

The Alfvén waves in this case tended to have great consistency in height -- or amplitude, which is the common term when talking about waves -- but they are random in direction. You might think of it like a jump rope twirling, always the same distance from center, but nonetheless able to be in many places in space. Another way scientists have envisioned the waves is as a "random walk on a sphere." Again, always the same distance from a given center, but with a variable placement.

Such metaphorical descriptions are based on what instruments in space have, in fact, observed when they see magnetic waves go by in the solar wind. But it turns out that the equations to describe this kind of movement -- equations necessary to advance scientific models of the entire system -- were not easily found.

"The puzzle has been to figure out why the amplitude is so constant," says Roberts. "But it's been very difficult to find equations that satisfy all the characteristics of the magnetic field."

Similar waves are, in fact, seen in light, known as polarized waves. But magnetic fields have additional constraints on what shapes and configurations are even possible. Roberts found a way to overlap numerous waves of different wavelengths in such a way that they ultimately made the variation in amplitude as small as possible.

To his surprise, the equations Roberts devised matched what was observed more closely than he'd expected. Not only did the equations show waves of constant amplitude, but they also showed occasional random jumps and sharp changes -- an unexplained feature seen in the observations themselves.

"Overlapping the waves in this way gives us a way of writing down equations that we didn't have before," says Roberts. "It also has this nice consequence that it is more realistic than we expected, since it shows discontinuities we actually see in the wind. This is important for simulations and models where we want to start with initial conditions that are as close to the observed solar wind as we can get."

Of course, having an equation doesn't yet tell us the reason why the waves in the solar wind are shaped in this way. Nonetheless, equations that describe how the waves move open the door to increasingly accurate simulations that may well help explain such causes. By alternately improving models and improving observations, scientists continue the cyclic nature of such research, until just what physical action on the sun causes these curiously-shaped Alfvén waves someday becomes clear.
 
Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

A glowing jet from a young star

 HH 151 
Credit: ESA/Hubble & NASA
Acknowledgement: Gilles Chapdelaine

This image shows an object known as HH 151, a bright jet of glowing material trailed by an intricate, orange-hued plume of gas and dust. It is located some 460 light-years away in the constellation of Taurus (The Bull), near to the young, tumultuous star HL Tau.

In the first few hundred thousand years of life, new stars like HL Tau pull in material that falls towards them from the surrounding space. This material forms a hot disc that swirls around the coalescing body, launching narrow streams of material from its poles. These jets are shot out at speeds of several hundred kilometres per second and collide violently with nearby clumps of dust and gas, creating wispy, billowing structures known as Herbig-Haro objects — like HH 151 seen in the image above.

Such objects are very common in star-forming regions. They are short-lived, and their motion and evolution can actually be seen over very short timescales, on the order of years. They quickly race away from the newly-forming star that emitted them, colliding with new clumps of material and glowing brightly before fading away.

A version of this image was entered into the Hidden Treasures image processing competition by Gilles Chapdelaine.

Source:  ESA/Hubble

Thursday, February 21, 2013

Stellar Motions in Outer Halo Shed New Light on Milky Way Evolution

This illustration shows the disk of our Milky Way galaxy, surrounded by a faint, extended halo of old stars. Astronomers using the Hubble Space Telescope to observe the nearby Andromeda galaxy serendipitously identified a dozen foreground stars in the Milky Way halo. They measured the first sideways motions (represented by the arrows) for such distant halo stars. The motions indicate the possible presence of a shell in the halo, which may have formed from the accretion of a dwarf galaxy. This observation supports the view that the Milky Way has undergone continuing growth and evolution over its lifetime by consuming smaller galaxies.

Illustration Credit: NASA, ESA, and A. Feild (STScI)
Science Credit: NASA, ESA, A. Deason and P. Guhathakurta (University of California, Santa Cruz), and R. van der Marel, T. Sohn, and T. Brown (STScI)

Peering deep into the vast stellar halo that envelops our Milky Way galaxy, astronomers using NASA's Hubble Space Telescope have uncovered tantalizing evidence for the possible existence of a shell of stars that are a relic of cannibalism by our Milky Way.

Hubble was used to precisely measure, for the first time ever, the sideways motions of a small sample of stars located far from the galaxy's center. Their unusual lateral motion is circumstantial evidence that the stars may be the remnants of a shredded galaxy that was gravitationally ripped apart by the Milky Way billions of years ago. These stars support the idea that the Milky Way grew, in part, through the accretion of smaller galaxies.
"Hubble's unique capabilities are allowing astronomers to uncover clues to the galaxy's remote past. The more distant regions of the galaxy have evolved more slowly than the inner sections. Objects in the outer regions still bear the signatures of events that happened long ago," said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, Md.

They also offer a new opportunity for measuring the "hidden" mass of our galaxy, which is in the form of dark matter (an invisible form of matter that does not emit or reflect radiation). In a universe full of 100 billion galaxies, our Milky Way "home" offers the closest and therefore best site for detailed study of the history and architecture of a galaxy.

A team of astronomers led by Alis Deason of the University of California, Santa Cruz, and van der Marel identified 13 stars located roughly 80,000 light-years from the galaxy's center. They lie in the Milky Way's outer halo of ancient stars that date back to the formation of our galaxy.

The team was surprised to find that the stars showed more of a sideways, or tangential, amount of motion than they expected. This movement is different from what astronomers know about the halo stars near the Sun, which move predominantly in radial orbits. Stars in these orbits plunge toward the galactic center and travel back out again. The stars' tangential motion can be explained if there is an over-density of stars at 80,000 light-years, like cars backing up on an expressway. This traffic jam would form a shell-like feature, as seen around other galaxies.

Deason and her team plucked the outer halo stars out of seven years' worth of archival Hubble telescope observations of our neighboring Andromeda galaxy. In those observations, Hubble peered through the Milky Way's halo to study the Andromeda stars, which are more than 20 times farther away. The Milky Way's halo stars were in the foreground and considered as clutter for the study of Andromeda. But to Deason's study they were pure gold. The observations offered a unique opportunity to look at the motion of Milky Way halo stars.

Finding the stars was meticulous work. Each Hubble image contained more than 100,000 stars. "We had to somehow find those few stars that actually belonged to the Milky Way halo," van der Marel said. "It was like finding needles in a haystack."

The astronomers identified the stars based on their colors, brightnesses, and sideways motions. The halo stars appear to move faster than the Andromeda stars because they are so much closer. Team member Sangmo Tony Sohn of STScI identified the halo stars and measured both the amount and direction of their slight sideways motion. The stars move on the sky only about one milliarcsecond a year, which would be like watching a golf ball on the Moon moving one foot per month. Nonetheless, this was measured with 5 percent precision, made possible in visible-light observations because of Hubble's razor-sharp view and instrument consistency.

"Measurements of this accuracy are enabled by a combination of Hubble's sharp view, the many years' worth of observations, and the telescope's stability. Hubble is located in the space environment, and it's free of gravity, wind, atmosphere, and seismic perturbations," van der Marel said.

Stars in the inner halo have highly radial orbits. When the team compared the tangential motion of the outer halo stars with their radial motion, they were very surprised to find that the two were equal. Computer simulations of galaxy formation normally show an increasing tendency towards radial motion if one moves further out in the halo. These observations imply the opposite trend. The existence of a shell structure in the Milky Way halo is one plausible explanation of the researchers' findings. Such a shell can form by accretion of a satellite galaxy. This is consistent with a picture in which the Milky Way has undergone continuing evolution over its lifetime due to the accretion of satellite galaxies.

The team compared their results with data of halo stars recorded in the Sloan Digital Sky Survey. Those observations uncovered a higher density of stars at about the same distance as the 13 outer halo stars in their Hubble study. A similar excess of halo stars exists across the Triangulum and Andromeda constellations. Beyond that radius, the number of stars plummets.

Deason immediately thought the two results were more than just coincidence. "What may be happening is that the stars are moving quite slowly because they are at the apocenter, the farthest point in their orbit about the hub of our Milky Way," Deason explained. "The slowdown creates a pileup of stars as they loop around in their path and travel back towards the galaxy. So their in and out or radial motion decreases compared with their sideways or tangential motion."

Shells of stars have been seen in the halos of some galaxies, and astronomers predicted that the Milky Way may contain them, too. But until now there was limited evidence for their existence. The halo stars in our galaxy are hard to see because they are dim and spread across the sky.

Encouraged by this study, the team hopes to search for more distant halo stars in the Hubble archive. "These unexpected results fuel our interest in looking for more stars to confirm that this is really happening," Deason said. "At the moment we have quite a small sample. So we really can make it a lot more robust with getting more fields with Hubble." The Andromeda observations only cover a very small "keyhole view" of the sky.

The team's goal is to put together a clearer picture of the Milky Way's formation history. By knowing the orbits and motions of many halo stars it will also be possible to calculate an accurate mass for the galaxy. "Until now, what we have been missing is the stars' tangential motion, which is a key component. The tangential motion will allow us to better measure the total mass distribution of the galaxy, which is dominated by dark matter. By studying the mass distribution, we can see whether it follows the same distribution as predicted in theories of structure formation," Deason said.

The Hubble study will appear in an upcoming issue of the Astrophysical Journal.

The science team consists of A. Deason and P. Guhathakurta of UCO/Lick Observatory, University of California, Santa Cruz, Calif., and R.P. van der Marel, S.T. Sohn, and T.M. Brown of the Space Telescope Science Institute, Baltimore, Md.

CONTACT

Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
410-338-4493

dweaver@stsci.edu

Alis Deason
University of California, Santa Cruz, Calif.
831-459-3841

alis@ucolick.org

Roeland van der Marel
Space Telescope Science Institute, Baltimore, Md.
410-338-4931

marel@stsci.edu

NASA's Kepler Mission Discovers Tiny Planet System

 NASA's Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra. Credit: NASA/Ames/JPL-Caltech .  › Full image and caption

NASA's Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra.Credit: NASA/Ames/JPL-Caltech . › Full image and caption  - enlarge image

PASADENA, Calif. -- NASA's Kepler mission scientists have discovered a new planetary system that is home to the smallest planet yet found around a star similar to our sun.

The planets are located in a system called Kepler-37, about 210 light-years from Earth in the constellation Lyra. The smallest planet, Kepler-37b, is slightly larger than our moon, measuring about one-third the size of Earth. It is smaller than Mercury, which made its detection a challenge.

The moon-size planet and its two companion planets were found by scientists with NASA's Kepler mission, which is designed to find Earth-sized planets in or near the "habitable zone," the region in a planetary system where liquid water might exist on the surface of an orbiting planet. However, while the star in Kepler-37 may be similar to our sun, the system appears quite unlike the solar system in which we live.

Astronomers think Kepler-37b does not have an atmosphere and cannot support life as we know it. The tiny planet almost certainly is rocky in composition. Kepler-37c, the closer neighboring planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the farther planet, is twice the size of Earth.

The first exoplanets found to orbit a normal star were giants. As technologies have advanced, smaller and smaller planets have been found, and Kepler has shown that even Earth-size exoplanets are common.

"Even Kepler can only detect such a tiny world around the brightest stars it observes," said Jack Lissauer, a planetary scientist at NASA's Ames Research Center in Moffett Field, Calif. "The fact we've discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data."

Kepler-37's host star belongs to the same class as our sun, although it is slightly cooler and smaller. All three planets orbit the star at less than the distance Mercury is to the sun, suggesting they are very hot, inhospitable worlds. Kepler-37b orbits every 13 days at less than one-third Mercury's distance from the sun. The estimated surface temperature of this smoldering planet, at more than 800 degrees Fahrenheit (700 degrees Kelvin), would be hot enough to melt the zinc in a penny. Kepler-37c and Kepler-37d, orbit every 21 days and 40 days, respectively.

"We uncovered a planet smaller than any in our solar system orbiting one of the few stars that is both bright and quiet, where signal detection was possible," said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif., and lead author of the new study published in the journal Nature. "This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun."

The research team used data from NASA's Kepler space telescope, which simultaneously and continuously measures the brightness of more than 150,000 stars every 30 minutes. When a planet candidate transits, or passes, in front of the star from the spacecraft's vantage point, a percentage of light from the star is blocked. This causes a dip in the brightness of the starlight that reveals the transiting planet's size relative to its star.

The size of the star must be known in order to measure the planet's size accurately. To learn more about the properties of the star Kepler-37, scientists examined sound waves generated by the boiling motion beneath the surface of the star. They probed the interior structure of Kepler-37's star just as geologists use seismic waves generated by earthquakes to probe the interior structure of Earth. The science is called asteroseismology.

The sound waves travel into the star and bring information back up to the surface. The waves cause oscillations that Kepler observes as a rapid flickering of the star's brightness. Like bells in a steeple, small stars ring at high tones while larger stars boom in lower tones. The barely discernible, high-frequency oscillations in the brightness of small stars are the most difficult to measure. This is why most objects previously subjected to asteroseismic analysis are larger than the sun.

With the very high precision of the Kepler instrument, astronomers have reached a new milestone. The star Kepler-37, with a radius just three-quarters of the sun, now is the smallest bell in the asteroseismology steeple. The radius of the star is known to three percent accuracy, which translates to exceptional accuracy in the planet's size.

Ames is responsible for Kepler's ground system development, mission operations, and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development.

Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports  mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

The Space Telescope Science Institute in Baltimore archives, hosts and distributes Kepler science data. Kepler is NASA's tenth Discovery Mission and was funded by NASA's Science Mission Directorate at the agency's headquarters in Washington.

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

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington

j.d.harrington@nasa.gov
 

A cool discovery about the Sun's next-door twin

One of the great curiosities in solar science is that our Sun’s outer atmosphere – the corona – is heated to millions of degrees when its visible surface is ‘only’ about 6000 degrees. Even stranger is a curious temperature minimum of 4000 degrees lying between the two layers, in the chromosphere. Now, using ESA’s Herschel space observatory, scientists have made the first discovery of an equivalent cool layer in the atmosphere of the Sun-like star, Alpha Centauri A.  Copyright: ESA

ESA’s Herschel space observatory has detected a cool layer in the atmosphere of Alpha Centauri A, the first time this has been seen in a star beyond our own Sun. The finding is not only important for understanding the Sun’s activity, but could also help in the quest to discover proto-planetary systems around other stars. 

The Sun’s nearest neighbours are the three stars of the Alpha Centauri system. The faint red dwarf, Proxima Centauri, is nearest at just 4.24 light-years, with the tight double star, Alpha Centauri AB, slightly further away at 4.37 light-years. 

Alpha Centauri B has recently been in the news after the discovery of an Earth-mass planet in orbit around it. But Alpha Centauri A is also very important to astronomers: almost a twin to the Sun in mass, temperature, chemical composition and age, it provides an ideal natural laboratory to compare other characteristics of the two stars. 

One of the great curiosities in solar science is that the Sun’s wispy outer atmosphere – the corona – is heated to millions of degrees while the visible surface of the Sun is ‘only’ about 6000ºC. Even stranger, there is a temperature minimum of about 4000ºC between the two layers, just a few hundred kilometres above the visible surface in the part of Sun’s atmosphere called the chromosphere.

Both layers can be seen during a total solar eclipse, when the Moon briefly blocks the bright face of the Sun: the chromosphere is a pink-red ring around the Sun, while the ghostly white plasma streamers of the corona extend out millions of kilometres. 

The heating of the Sun’s atmosphere has been a conundrum for many years, but is likely to be related to the twisting and snapping of magnetic field lines sending energy rippling through the atmosphere and out into space – possibly in the direction of Earth – as solar storms. Why there is a temperature minimum has also long been of interest to solar scientists. 

Now, by observing Alpha Centauri A in far-infrared light with Herschel and comparing the results with computer models of stellar atmospheres, scientists have made the first discovery of an equivalent cool layer in the atmosphere of another star. 

“The study of these structures has been limited to the Sun until now, but we clearly see the signature of a similar temperature inversion layer at Alpha Centauri A,” says René Liseau of the Onsala Space Observatory, Sweden, and lead author of the paper presenting the results. 

“Detailed observations of this kind for a variety of stars might help us decipher the origin of such layers and the overall atmospheric heating puzzle.” 

Understanding the temperature structure of stellar atmospheres may also help to determine the presence of dusty planet-forming discs around other stars like the Sun.

“Although it is likely only a small effect, a temperature minimum region in other stars could result in us underestimating the amount of dust present in a cold debris disc surrounding it,” says Dr Liseau.

“But armed with a more detailed picture of how Alpha Centauri A shines, we can hope to make more accurate detections of the dust in potential planet-bearing systems around other Sun-like stars.”

“These observations are an exciting example of how Herschel can be used to learn more about processes in our own Sun, as well as in other Sun-like stars and the dusty discs that may exist around them,” says Göran Pilbratt, ESA’s Herschel Project Scientist.

“α Centauri A in the far infrared. First measurement of the temperature minimum of a star other than the Sun,” by R. Liseau et al. is published in Astronomy & Astrophysics 549, L7 (2013). 

The survey was conducted as part of the DUNES (Dust around Nearby Stars) Herschel Key Programme. Data were collected by the PACS instrument at 100 μm and 160 μm for the DUNES survey, and PACS 70 μm and 160μm and SPIRE 250 μm, 350 μm and 500 μm data obtained as part of the Hi-GAL programme were also analysed. Additional space- and ground-based infrared data were also included. 

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

For further information, please contact:
 
Markus Bauer


ESA Science and Robotic Exploration Communication Officer


Tel: +31 71 565 6799


Mob: +31 61 594 3 954


Email:
markus.bauer@esa.int

René Liseau
Chalmers University of Technology, Onsala Space Observatory, Sweden
Tel: +46 31 772 55 05
Email:
rene.liseau@chalmers.se

Göran Pilbratt

ESA Herschel Project Scientist


Tel: +31 71 565 3621


Email:
gpilbratt@rssd.esa.int

Wednesday, February 20, 2013

Sweeping the Dust from a Cosmic Lobster

The Lobster Nebula seen with ESO’s VISTA telescope

 PR Image eso1309b
The stellar nursery NGC 6357 in the constellation of Scorpius

Wide-field view of the area of NGC 6357

Comparison of VISTA image of NGC 6357 with a visible light image

Videos

Zooming in on a VISTA infrared image of NGC 6357
Zooming in on a VISTA infrared image of NGC 6357

Comparison of VISTA image of NGC 6357 with a visible light image
Comparison of VISTA image of NGC 6357 with a visible light image

New infrared VISTA image of NGC 6357

A new image from ESO’s VISTA telescope captures a celestial landscape of glowing clouds of gas and tendrils of dust surrounding hot young stars. This infrared view reveals the stellar nursery known as NGC 6357 in a surprising new light. It was taken as part of a VISTA survey that is currently scanning the Milky Way in a bid to map our galaxy’s structure and explain how it formed.

Located around 8000 light-years away in the constellation of Scorpius (The Scorpion), NGC 6357 — sometimes nicknamed the Lobster Nebula [1] due to its appearance in visible-light images — is a region filled with vast clouds of gas and tendrils of dark dust. These clouds are forming stars, including massive hot stars which glow a brilliant blue-white in visible light.

This image uses infrared data from ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) at the Paranal Observatory in Chile. It is just a small part of a huge survey called VISTA Variables in the Vía Láctea (VVV) that is imaging the central parts of the Galaxy (eso1242). The new picture presents a drastically different view to that seen in visible-light images — such as the image taken with the 1.5-metre Danish telescope at La Silla — as infrared radiation can penetrate much of the covering of dust that shrouds the object [2].

One of the bright young stars in NGC 6357, known as Pismis 24-1, was thought to be the most massive star known — until it was found to actually be made up of at least three huge bright stars, each with a mass of under 100 times that of our Sun. Even so, these stars are still heavyweights — some of the most massive in our Milky Way. Pismis 24-1 is the brightest object in the Pismis 24 star cluster, a bunch of stars that are all thought to have formed at the same time within NGC 6357.

VISTA is the largest and most powerful survey telescope ever built, and is dedicated to surveying the sky in infrared light. The VVV survey is scanning the central bulge and some of the plane of our galaxy to create a huge dataset that will help astronomers to discover more about the origin, early life, and structure of the Milky Way.

Parts of NGC 6357 have also been observed by the NASA/ESA Hubble Space Telescope (heic0619a) and ESO’s Very Large Telescope (eso1226a). Both telescopes have produced visible-light images of various parts of this region — comparing these images with this new infrared image above shows some striking differences. In the infrared the large plumes of red-hued material are much reduced, with tendrils of pale, purple gas stretching out from the nebula in different areas.

Notes

[1] The informal name of Lobster Nebula is also sometimes given to the spectacular star-forming region Messier 17 (eso0925), although that object is more often called the Omega Nebula.

[2] Infrared observations can reveal features that cannot be seen in visible-light pictures, for example because an object is too cold, obscured by thick dust, or is very distant, meaning that its light has been stretched towards the red end of the spectrum by the expansion of the Universe.

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”.

Links

Contacts

Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org

3-D Observations of the Outflow from an Active Galactic Nucleus

A Japanese team of astronomers, led by Toru Misawa (Shinshu University), has used the Subaru Telescope to observe a distant gravitationally-lensed quasar (Note 1) and probed an active galactic nucleus in its central region. Looking through multiple sight lines, the astronomers obtained a 3-D view of the quasar and discovered complex small structures inside outflows from the galactic nucleus. These outflows will spread widely and eventually affect the evolution of the host galaxy.

Figure 1: An artist's rendition of the central region of the quasar. A gaseous disk surrounds a central black hole. The outflow is gas streaming from the disk outward along the curved mesh, which indicates the distortion of space/time, and is distinguished from a jet that is blowing vertically. The arrows A, B, and C indicate the light paths observed, which probably pass near the surface of an outflow. (Credit: Shinshu University and the National Astronomical Observatory of Japan)

Quasars are bright central regions of some distant galaxies. Their luminosities are often hundreds of times greater than those of their host galaxies (Note 2). Scientists believe that their light source is a very bright gaseous disk surrounding a supermassive black hole at the center of the galaxy. Gas streams called "outflows" move outward from the disk (Figure 1) and have a substantial influence on surrounding interstellar/intergalactic regions. However, because quasars at large distances look like mere stars, their internal structures are not easy to investigate.

Figure 2: Left: Schematic drawing of the gravitational lensing, showing SDSS J1029+2623 (at ~10 billion light years), a cluster of galaxies (at ~5 billion light years), and Earth. An outflow is a very small domain surrounded by a large ring of dust.  

Right: An Earthly analogy of gravitational lensing. The diagram shows how scenery looks from different directions (without considering the image distortion by the lensing) and serves as a comparison to the lensed images of the quasar. (Credit: Shinshu University and the National Astronomical Observatory of Japan)
 
The current team used the large light-gathering power of the 8.2 m Subaru Telescope mounted with its high-resolution spectrograph HDS (High Dispersion Spectrograph) to observe the quasar SDSS J1029+2623 (from now on referred to as "J 1029") and examine its structure. This quasar is ~10 billion light years distant from Earth (Note 1) toward the constellation Leo, and a massive cluster of galaxies, ~5 billion light years away, lies between the quasar and Earth (Figure 2). Because astronomical objects are usually very distant, they are difficult to study from different angles. Nevertheless, gravitational lensing opens up this possibility. If a cluster of galaxies lies along the line of sight to a distant quasar, then part of the light from the distant quasar (the "lensed quasar") bends around the intervening cluster (the "lensing cluster"), and observers will see more highly resolved and brighter images of the now magnified background quasar. Due to the gravitational lensing by the cluster intervening between J 1029 and Earth, there is significant distortion in the light path from the quasar, and it splits into three images: A, B, and C (Figure 3, Note 3). The maximum separation angle, ~22".5 (Note 4), between images A and B is a current record; it is larger than the typical separation of quasar images lensed by a single galaxy. The team hypothesized that each lensed image could contain information on the outflow from the quasar when viewed from different angles (Figures 1 and 2).

Figure 3: Color image of the region around SDSS J1029+2623, taken with Hubble Space Telescope. Quasar images (marked with A, B, and C) are gravitationally lensed by a foreground cluster of galaxies. Three galaxies of the lensing cluster (marked as G1a, b and G2) are visible. (Credit: Shinshu University, the National Astronomical Observatory of Japan, and Kavli Institute for the Physics and Mathematics of the Universe)

The team used Subaru Telescope's HDS to perform spectroscopic observations of the brightest two images A and B (Note 5), and their results supported their hypothesis. Any absorber between the quasar and Earth provides absorption features in the spectra of the quasar images. While most absorption features originate from foreground objects that are physically unrelated to the quasar, some show clear evidence of origins from the outflow, such as partial coverage by clouds (Note 6). Those features show a clear difference between the images A and B, although they are generally similar (Figure 4). This result supports the idea that the sight lines are going through different areas of the outflow from different directions. When viewed through one eye alone, an object appears to be two-dimensional, but viewing with both eyes yields a 3-D image that provides multi-directional information. This process is analogous to what occurred in the observations (Figure 2, Note 7).

Figure 4: Comparison of absorption features of three elements, carbon, nitrogen, and hydrogen (from top to bottom), seen in spectra of the lensed images A (red line) and B (blue line). All of them arise at the outflow. A horizontal axis is an outflow velocity from the light source, defined as negative if it heads to Earth. The shaded area shows a clear difference between the images A and B. (Credit: Shinshu University and the National Astronomical Observatory of Japan)

It is surprising that the absorption profiles arising in the outflow show clear differences between them, despite the small separation angle of ~22".5. Misawa commented on this discovery saying, "The outflow may not necessarily be homogeneous, but could instead have a complex internal structure with a number of clumpy gas clouds like cirrocumulus clouds in Earth's atmosphere. The team plans to observe the area in image C in more detail." Direct observation of a clumpy structure in tandem with theoretical analysis will contribute to revealing the mysterious formation history of these outflows.

The team has also explored other explanations for the outflows. Because the light paths of the images A and B are different, they have a substantial time difference between them when they reach Earth (Note 8). If the internal structure of the outflow varies with time, the two images deliver information about different epochs even if they pass through the same region of the outflow. The astronomers intend to conduct observations with the Subaru Telescope in March, 2013 to test the "time-variation" scenario.

References:
The research paper on which this release is based was published on-line in the January 15, 2013 edition of The Astronomical Journal: T. Misawa et al., "Spectroscopy along Multiple, Lensed Sight Lines through Outflowing Winds in the Quasar SDSS J1029+2623", vol. 145, issue 2, article id. 48 (2013). The authors of the paper are:
  • T. Misawa, Shinshu University, Japan
  • N. Inada, Nara National College of Technology, Japan
  • K. Ohsuga, National Astronomical Observatory of Japan, Japan
  • P. Gandhi, Institute of Space and Astronautical Science, Japan
  • R. Takahashi, Tomakomai National College of Technology, Japan
  • M. Oguri, Kavli Institute for the Physics and Mathematics of the Universe, Japan
Acknowledgements:
This research was supported by the following:
  • Special Postdoctoral Research Program of RIKEN, the Japan Society for the Promotion of Science (23740148, 23740161)
  • Shinshu University Research Grant for Exploratory Research by Young Scientists
  • The FIRST program "Subaru Measurements of Images and Redshifts (SuMIRe)"
  • World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan
Notes:
  1. It corresponds to a redshift of z~2.197. A "z" or redshift value measures how much the expansion of space has stretched the light from an object. Generally, the greater the observed z value for a galaxy, the more distant it is in time and space from Earth.
  2. Because their appearance is star-like, they are called "quasi-stellar objects" and abbreviated as quasars.
  3. An international team led by Naohisa Inada and Masamune Oguri (both are members of the current research team) discovered the first quasar (SDSS J1004+4112) that is lensed by a cluster of galaxies (http://www.sdss.org/news/releases/20031217.lensing.html). Only three quasars that are lensed by a cluster of galaxies have been discovered so far (SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745). Among them, SDSS J1029+2623 has the largest separation angle.
  4. 1 arcsec (1") is a unit of angle, defined as 1/3600 of 1 degree. Human eyes cannot distinguish such a small angle.
  5. The observed flux ratio of the three lensed images is A:B:C ~ 0.95:1.00:0.24.
  6. This means that an absorber only partially covers the background light source toward the sight line. Because foreground interstellar or intergalactic media are larger than the light source of the quasar by more than several orders, only small gas clouds in the vicinity of the quasar can reproduce a partial coverage.
  7. Similar observation has been also performed for the other lensed quasar DSS J1004+4112 (Green, P. 2006, the Astrophysical Journal, vol. 644, pp.733-741).
  8. The image A leads the image B by 744 days (Fohlmeister, J. et al., 2013, The Astrophysical Journal, vol. 764, 186).