Friday, November 30, 2012

Even Brown Dwarfs May Grow Rocky Planets

PR Image eso1248a
Artist’s impression of the disc of dust and gas around a brown dwarf

Artist’s impression of grains in the disc around a brown dwarf

The brown dwarf  ISO-Oph 102

Location of the brown dwarf ISO-Oph 102 in the constellation of Ophiuchus

Wide-field view of the Rho Ophiuchi star-forming region in visible light

 Videos

PR Video eso1248a
The growth of cosmic dust grains in the disc around the brown dwarf  ISO-Oph 102

 PR Video eso1248b
Artist’s impression of grains in the disc around a brown dwarf

 PR Video eso1248c
The Brown Dwarf ISO-Oph 102

ALMA sizes up grains of cosmic dust around failed star

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have for the first time found that the outer region of a dusty disc encircling a brown dwarf contains millimetre-sized solid grains like those found in denser discs around newborn stars. The surprising finding challenges theories of how rocky, Earth-scale planets form, and suggests that rocky planets may be even more common in the Universe than expected.

Rocky planets are thought to form through the random collision and sticking together of what are initially microscopic particles in the disc of material around a star. These tiny grains, known as cosmic dust, are similar to very fine soot or sand. However, in the outer regions around a brown dwarf — a star-like object, but one too small to shine brightly like a star — astronomers expected that grains could not grow because the discs were too sparse, and particles would be moving too fast to stick together after colliding. Also, prevailing theories say that any grains that manage to form should move quickly towards the central brown dwarf, disappearing from the outer parts of the disc where they could be detected.

“We were completely surprised to find millimetre-sized grains in this thin little disc,” said Luca Ricci of the California Institute of Technology, USA, who led a team of astronomers based in the United States, Europe and Chile. “Solid grains of that size shouldn’t be able to form in the cold outer regions of a disc around a brown dwarf, but it appears that they do. We can’t be sure if a whole rocky planet could develop there, or already has, but we’re seeing the first steps, so we’re going to have to change our assumptions about conditions required for solids to grow,” he said.

ALMA’s increased resolution compared to previous telescopes also allowed the team to pinpoint carbon monoxide gas around the brown dwarf — the first time that cold molecular gas has been detected in such a disc. This discovery, and that of the millimetre-size grains, suggest that the disc is much more similar to the ones around young stars than previously expected.

Ricci and his colleagues made their finding using the partially completed ALMA telescope in the high-altitude Chilean desert. ALMA is a growing collection of high precision, dish-shaped antennas that work together as one large telescope to observe the Universe with groundbreaking detail and sensitivity. ALMA “sees” the Universe in millimetre-wavelength light, which is invisible to human eyes. Construction of ALMA is scheduled to finish in 2013, but astronomers began observing with a partial array of ALMA dishes in 2011.

The astronomers pointed ALMA at the young brown dwarf  ISO-Oph 102, also known as Rho-Oph 102, in the Rho Ophiuchi star-forming region in the constellation of Ophiuchus (The Serpent Bearer). With about 60 times the mass of Jupiter but only 0.06 times that of the Sun, the brown dwarf has too little mass to ignite the thermonuclear reactions by which ordinary stars shine. However, it emits heat released by its slow gravitational contraction and shines with a reddish colour, albeit much less brightly than a star.

ALMA collected light with wavelengths around a millimetre, emitted by disc material warmed by the brown dwarf. The grains in the disc do not emit much radiation at wavelengths longer than their own size, so a characteristic drop-off in the brightness can be measured at longer wavelengths. ALMA is an ideal instrument for measuring this drop-off and thus for sizing up the grains. The astronomers compared the brightness of the disc at wavelengths of 0.89 mm and 3.2 mm. The drop-off in brightness from 0.89 mm to 3.2 mm was not as steep as expected, showing that at least some of the grains are a millimetre or more in size.

“ALMA is a powerful new tool for solving mysteries of planetary system formation,” commented Leonardo Testi from ESO, a member of the research team. “Trying this with previous generation telescopes would have needed almost a month of observing — impossibly long in practice. But, using just a quarter of ALMA's final complement of antennas, we were able to do it in less than one hour!” he said.

In the near future, the completed ALMA telescope will be powerful enough to make detailed images of the discs around Rho-Oph 102 and other objects. Ricci explained, “We will soon be able to not only detect the presence of small particles in discs, but to map how they are spread across the circumstellar disc and how they interact with the gas that we’ve also detected in the disc. This will help us better understand how planets come to be.”

More information

This research is presented in a paper in the Astrophysical Journal Letters.

Ricci and Testi worked with Antonella Natta of the INAF-Osservatorio Astrofisico de Arcetri, Aleks Scholz of the Dublin Institute for Advanced Studies, and Itziar de Gregorio-Monsalvo of the Joint ALMA Observatory.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), 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.

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). 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

Luca Ricci
California Institute of Technology
Tel: +1 626 395 2460
Email: lricci@astro.caltech.edu

Leonardo Testi
ESO
Garching, Germany
Tel: +49 89 3200 6541
Email: ltesti@eso.org

Douglas Pierce-Price
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6759
Email: dpiercep@eso.org

John Stoke
National Radio Astronomy Observatory (NRAO)
Charlottesville, VA, USA
Tel: +1 434 244 6816
Email: jstoke@nrao.edu

Swirling Storms on Saturn

This image from NASA's Cassini mission was taken on Nov. 27, 2012, with Cassini's narrow-angle camera. Image Credit: NASA/JPL-Caltech/Space Science Institute .  Full image and caption

This image from NASA's Cassini mission was taken on Nov. 27, 2012, with Cassini's narrow-angle imaging camera. Image Credit: NASA/JPL-Caltech/Space Science Institute .  Full image and caption -  enlarge image


This image from NASA's Cassini mission was taken on Nov. 27, 2012, with Cassini's wide-angle imaging camera. Image Credit: NASA/JPL-Caltech/Space Science Institute .  Full image and caption - enlarge image

NASA's Cassini spacecraft has been traveling the Saturnian system in a set of inclined, or tilted, orbits that give mission scientists a vertigo-inducing view of Saturn's polar regions. This perspective has yielded images of roiling storm clouds and a swirling vortex at the center of Saturn's famed north polar hexagon.

These phenomena mimic what Cassini found at Saturn's south pole a number of years ago. Cassini has also seen storms circling Saturn's north pole in the past, but only in infrared wavelengths because the north pole was in darkness. (See http://www.jpl.nasa.gov/news/news.php?release=2008-192 .) But, with the change of the Saturnian seasons, the sun has begun to creep over the planet's north pole.

This particular set of raw, unprocessed images was taken on Nov. 27, 2012, from a distance of about 250,000 miles (400,000 kilometers) from Saturn.

More raw images are available at http://saturn.jpl.nasa.gov/photos/raw/index.cfm .

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

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Steve Mullins 720-974-5859
Space Science Institute, Boulder, Colo. 
media@ciclops.org

A Peculiar Compact Blue Dwarf Galaxy

NGC 5253
Credit: ESA/Hubble & NASA
Acknowledgement: N. Sulzenauer

The NASA/ESA Hubble Space Telescope provides us this week with an impressive image of the irregular galaxy NGC 5253.

NGC 5253 is one of the nearest of the known Blue Compact Dwarf (BCD) galaxies, and is located at a distance of about 12 million light-years from Earth in the southern constellation of Centaurus. The most characteristic signature of these galaxies is that they harbour very active star-formation regions. This is in spite of their low dust content and comparative lack of elements heavier than hydrogen and helium, which are usually the basic ingredients for star formation.

These galaxies contain molecular clouds that are quite similar to the pristine clouds that formed the first stars in the early Universe, which were devoid of dust and heavier elements. Hence, astronomers consider the BCD galaxies to be an ideal testbed for better understanding the primordial star-forming process.

NGC 5253 does contain some dust and heavier elements, but significantly less than the Milky Way galaxy. Its central regions are dominated by an intense star forming region that is embedded in an elliptical main body, which appears red in Hubble’s image. The central starburst zone consists of a rich environment of hot, young stars concentrated in star clusters, which glow in blue in the image. Traces of the starburst itself can be seen as a faint and diffuse glow produced by the ionised oxygen gas.

The true nature of BCD galaxies has puzzled astronomers for a long time. Numerical simulations following the current leading cosmological theory of galaxy formation, known as the Lambda Cold Dark Matter model, predict that there should be far more satellite dwarf galaxies orbiting big galaxies like the Milky Way. Astronomers refer to this discrepancy as the Dwarf Galaxy Problem.

This galaxy is considered part of the Centaurus A/Messier 83 group of galaxies, which includes the famous radio galaxy Centaurus A and the spiral galaxy Messier 83. Astronomers have pointed out the possibility that the peculiar nature of NGC 5253 could result from a close encounter with Messier 83, its closer neighbour.

This image was taken with the Hubble’s Advanced Camera for Surveys, combining visible and infrared exposures. The field of view in this image is approximately 3.4 by 3.4 arcminutes.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Nikolaus Sulzenauer.

Source: ESA/Hubble - Space Telescope

 

Thursday, November 29, 2012

A Multi-Wavelength View of Radio Galaxy Hercules A

 
Radio Galaxy Hercules A
Credit: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA) .    


 A 3-D Perspective on Hercules A
Credit: NASA, ESA, and Z. Levay, F. Summers, G. Bacon, T. Davis, and L. Frattare (Viz 3D Team/STScI)  .  See All the Videos

This video envisions a three-dimensional look at the combined visible light and radio emission from the active galaxy Hercules A. Unusually, this giant elliptical galaxy is not found in a large cluster of galaxies, but rather within a comparatively small group of galaxies. The supermassive black hole in its core, however, spews out strong jets of energetic particles that produce enormous lobes of radio emission. The size of these radio lobes dwarfs the large galaxy and extends throughout the volume of the galaxy group. This visualization is intended only to be a scientifically reasonable illustration of the three-dimensional structures. In particular, the galaxy distances are based on a statistical model, and not measured values.

Spectacular jets powered by the gravitational energy of a supermassive black hole in the core of the elliptical galaxy Hercules A illustrate the combined imaging power of two of astronomy's cutting-edge tools, the Hubble Space Telescope's Wide Field Camera 3, and the recently upgraded Karl G. Jansky Very Large Array (VLA) radio telescope in New Mexico.

Some two billion light-years away, the yellowish elliptical galaxy in the center of the image appears quite ordinary as seen by Hubble in visible wavelengths of light. The galaxy is roughly 1,000 times more massive than the Milky Way and harbors a 2.5-billion-solar-mass central black hole that is 1,000 times more massive than the black hole in the Milky Way. But the innocuous-looking galaxy, also known as 3C 348, has long been known as the brightest radio-emitting object in the constellation Hercules. Emitting nearly a billion times more power in radio wavelengths than our Sun, the galaxy is one of the brightest extragalactic radio sources in the entire sky.

The VLA radio data reveal enormous, optically invisible jets that, at one-and-a-half million light-years wide, dwarf the visible galaxy from which they emerge. The jets are very-high-energy plasma beams, subatomic particles and magnetic fields shot at nearly the speed of light from the vicinity of the black hole. The outer portions of both jets show unusual ring-like structures suggesting a history of multiple outbursts from the supermassive black hole at the center of the galaxy.

The innermost parts of the jets are not visible because of the extreme velocity of the material, which causes relativistic effects that beam the light away from us. Far from the galaxy, the jets become unstable and break up into the rings and wisps.

The entire radio source is surrounded by a very hot, X-ray-emitting cloud of gas, not seen in this optical-radio composite.
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Hubble's view of the field also shows a companion elliptical galaxy very close to the center of the optical-radio source, which may be merging with the central galaxy. Several other elliptical and spiral galaxies that are visible in the Hubble data may be members of a cluster of galaxies. Hercules A is by far the brightest and most massive galaxy in the cluster.

For more information, contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

John Stoke
National Radio Astronomy Observatory, Charlottesville, Va.
434-244-6896
jstoke@nrao.edu

Dave Finley
National Radio Astronomy Observatory, Socorro, N.M.
575-835-7302
dfinley@nrao.edu

NASA's Cassini Sees Abrupt Turn in Titan's Atmosphere

This artist's impression of Saturn's moon Titan shows the change in observed atmospheric effects before, during and after equinox in 2009. The Titan globes also provide an impression of the detached haze layer that extends all around the moon (blue). This image was inspired by data from NASA's Cassini mission. Image Credit: ESA .  Full image and caption

This true color image captured by NASA'S Cassini spacecraft before a distant flyby of Saturn's moon Titan on June 27, 2012, shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere. Image Credit: NASA/JPL-Caltech/Space Science Institute . Full image and caption  -  enlarge image

PASADENA, Calif. -Data from NASA's Cassini spacecraft tie a shift in seasonal sunlight to a wholesale reversal, at unexpected altitudes, in the circulation of the atmosphere of Saturn's moon Titan. At the south pole, the data show definitive evidence for sinking air where it was upwelling earlier in the mission. So the key to circulation in the atmosphere of Saturn's moon Titan turned out to be a certain slant of light. The paper was published today in the journal Nature.
 
"Cassini's up-close observations are likely the only ones we'll have in our lifetime of a transition like this in action," said Nick Teanby, the study's lead author who is based at the University of Bristol, England, and is a Cassini team associate. "It's extremely exciting to see such rapid changes on a body that usually changes so slowly and has a 'year' that is the equivalent of nearly 30 Earth years."
 
In our solar system, only Earth, Venus, Mars and Titan have both a solid surface and a substantial atmosphere - providing natural laboratories for exploring climate processes. "Understanding Titan's atmosphere gives us clues for understanding our own complex atmosphere," said Scott Edgington, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Some of the complexity in both places arises from the interplay of atmospheric circulation and chemistry."
 
The pole on Titan that is experiencing winter is typically pointed away from Earth due to orbital geometry. Because Cassini has been in orbit around Saturn since 2004, it has been able to study the moon from angles impossible from Earth and watch changes develop over time. Models have predicted circulation changes for nearly 20 years, but Cassini has finally directly observed them happening - marking a major milestone in the mission.
 
Other Cassini instruments recently obtained images of the formation of haze and a vortex over Titan's south pole, but the data from the composite infrared spectrometer (CIRS) is sensitive to much higher altitudes, provides more quantitative information and more directly probes the circulation and chemistry. The CIRS data, which enable scientists to track changes in atmospheric temperature and the distribution of gases like benzene and hydrogen cyanide, also revealed changes in hard-to-detect vertical winds and global circulation.
 
Besides the evidence for sinking air, Cassini also detected complex chemical production in the atmosphere at up to 400 miles (600 kilometers) above the surface, revealing the atmospheric circulation extends about 60 miles (100 kilometers) higher than previously expected. Compression of this sinking air as it moved to lower altitudes produced a hot spot hovering high above the south pole, the first indication of big changes to come. The scientists were also able to see very rapid changes in the atmosphere and pinpoint the circulation reversal to about six months around the August 2009 equinox, when the sun shone directly over Titan's equator. The circulation change meant that within two years of equinox, some gases had increased in abundance 100-fold - much more extreme than anything seen so far on Titan.
 
The results also suggest that a detached layer of haze (first detected by NASA's Voyager spacecraft) may not be so detached after all, since complex chemistry and vertical atmospheric movement is occurring above this layer. This layer may instead be the region where small haze particles combine into larger, but more transparent, clumped aggregates that eventually descend deeper into the atmosphere and give Titan its characteristic orange appearance.
 
"Next, we would expect to see the vortex over the south pole build up," said Mike Flasar, the CIRS principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md. "As that happens, one question is whether the south winter pole will be the identical twin of the north winter pole, or will it have a distinct personality? The most important thing is to be able to keep watching as these changes happen."
 
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory manages the mission for NASA's Science Mission Directorate, Washington, D.C. The visual and infrared mapping spectrometer team is based at the University of Arizona, Tucson. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center in Greenbelt, Md., where the instrument was built. JPL is a division of Caltech.
 
For more information on Cassini, visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

 Elizabeth Zubritsky/Nancy Neal-Jones 301-614-5438/301-286-0039
 Goddard Space Flight, Center, Greenbelt, Md.

 elizabeth.a.zubritsky@nasa.gov / nancy.n.jones@nasa.gov

Giant black hole could upset galaxy evolution models

A group of astronomers led by Remco van den Bosch from the Max Planck Institute for Astronomy (MPIA) have discovered a black hole that could shake the foundations of current models of galaxy evolution. At 17 billion times the mass of the Sun, its mass is much greater than current models predict – in particular in relation to the mass of its host galaxy. This could be the most massive black hole found to date.


 Figure 1: Image of the disk galaxy (lenticular galaxy) NGC 1277, taken with the Hubble Space Telescope. This small, flattened galaxy contains one of the biggest central super-massive black holes ever found in its center. With the mass of 17 billion Suns, the black hole weighs in at an extraordinary 14% of the total galaxy mass.  Image credit: NASA / ESA / Andrew C. Fabian / Remco C. E. van den Bosch (MPIA)[Larger version for download]

Figure 2: NGC 1277 is embedded in the nearby Perseus galaxy cluster, at a distance of 250 million light-years from Earth. All the ellipticals and round yellow galaxies in the picture are galaxies located in this cluster. Compared to all the other galaxies around it, NGC 1277 is a relatively compact. Image credit: David W. Hogg, Michael Blanton, and the SDSS Collaboration.  [Larger version for download]

Figure 3: The Hobby-Eberly Telescope gleams in silver and gold against a deep blue night sky. This telescope, located at McDonald Observatory in Texas, was used for the survey of 700 galaxies that formed the first step of the systematic search by van den Bosch and his colleagues for the most massive galactic black holes.  Image credit: Damond Benningfield.   [Larger version for download]


Video: NGC 1277 is a compact disk galaxy with one of the biggest black holes known to date. Its black hole weighs 17 billion times the mass of the Sun, which amounts to a remarkable 14% of this galaxy's total mass. Most of the stars in the galaxy are strongly affected by the gravitational pull of this black hole. The black hole was found by van den Bosch and collaborators and published in Nature on 29 November 2012.

 The animation shows representative orbits of the galaxy's stars in this, taken from the dynamical model that was used to measure the black hole mass. The green orbit shows the orbit of the stars in the disk. The red orbit shows the strong gravitational pull near the black hole. The blue orbit is strongly influenced by the (round) dark matter halo. One second in this animation represents 22 million years of simulated time, and the horizontal size of this image amounts to 41 million lightyears (36 arcsec).

 This animation has been produced by Remco van den Bosch. It is released under creative commons and can be freely embedded.  Credit for the background Hubble Space Telescope image:  NASA / ESA / Fabian / Remco C. E. van den Bosch (MPIA).


Video 2: Remco van den Bosch (Max Planck Institute for Astronomy), lead author of the study, describes the discovery of the unusually massive black hole in the galaxy NGC 1277 in this 5 minute video.

A group of astronomers led by Remco van den Bosch from the Max Planck Institute for Astronomy (MPIA) have discovered a black hole that could shake the foundations of current models of galaxy evolution. At 17 billion times the mass of the Sun, its mass is much greater than current models predict – in particular in relation to the mass of its host galaxy. This could be the most massive black hole found to date.

To the best of our astronomical knowledge, almost every galaxy should contain in its central region what is called a supermassive black hole: a black hole with a mass between that of hundreds of thousands and billions of Suns. The best-studied super-massive black hole sits in the center of our home galaxy, the Milky Way, with a mass of about four million Suns.

For the masses of galaxies and their central black holes, an intriguing trend has emerged: a direct relationship between the mass of a galaxy's black hole and that of the galaxy's stars.

Typically, the black hole mass is a tiny fraction of the galaxy's total mass. But now a search led by Remco van den Bosch (MPIA) has discovered a massive black hole that could upset the accepted relationship between black hole mass and galaxy mass, which plays a key role in all current theories of galaxy evolution. The observations used the Hobby-Eberly Telescope and existing images from the Hubble Space Telescope.

With a mass 17 billion times that of the Sun, the newly discovered black hole in the center of the disk galaxy NGC 1277 might even be the biggest known black hole of all: the mass of the current record holder is estimated to lie between 6 and 37 billion solar masses (McConnell et al. 2011); if the true value lies towards the lower end of that range, NGC 1277 breaks the record. At the least, NGC 1277 harbors the second-biggest known black hole.

The big surprise is that the black hole mass for NGC 1277 amounts to 14% of the total galaxy mass, instead of usual values around 0,1%. This beats the old record by more than a factor 10. Astronomers would have expected a black hole of this size inside blob-like ("elliptical") galaxies ten times larger. Instead, this black hole sits inside a fairly small disk galaxy.

Is this surprisingly massive black hole a freak accident? Preliminary analysis of additional data suggests otherwise – so far, the search has uncovered five additional galaxies that are comparatively small, yet, going by first estimates, seemed to harbor unusually large black holes too. More definite conclusions have to await detailed images of these galaxies.

If the additional candidates are confirmed, and there are indeed more black holes like this, astronomers will need to rethink fundamentally their models of galaxy evolution. In particular, they will need to look at the early universe: The galaxy hosting the new black hole appears to have formed more than 8 billion years ago, and does not appear to have changed much since then. Whatever created this giant black hole must have happened a long time ago.

Contact

Remco van den Bosch (first author)
Max Planck Institute for Astronomy 
Heidelberg, Germany
Phone: (+49|0) 6221 – 528 381
Email: bosch@mpia.de

Arjen van der Wel (co-author)
Max Planck Institute for Astronomy
Heidelberg, Germany
Phone: (+49|0) 6221 – 528 461
Email: vdwel@mpia.de

 Markus Pössel (public relations)
 Max Planck Institute for Astronomy
 Heidelberg, Germany
 Phone: (+49|0) 6221 – 528 261
 Email:
pr@mpia.de


Background information

The work described here will be published as van den Bosch et al., "An over-massive black hole in the compact lenticular galaxy NGC 1277", in the November 29 edition of the journal Nature.
The co-authors are Remco C. E. van den Bosch (Max Planck Institute for Astronomy; MPIA), Karl Gebhardt (University of Texas at Austin), Kayhan Gültekin (University of Michigan, Ann Arbor), Glenn van de Ven, Arjen van der Wel (both MPIA) and Jonelle L. Walsh (University of Texas at Austin).

Questions and Answers

What was the motivation for the present study? 
The accepted relationship between the mass of a galaxy and the mass of its central black hole is not completely understood - at least three completely different models have been put forth to explain the connection. One of the reasons we lack a complete picture of the black hole mass-galaxy mass relation is the paucity of data points: there are less than a hundred galaxies for which the central black hole mass can be measured.
A good way of testing a relationship is to look at the extremes. For the correlation of black hole and galaxy mass, little was known about the very biggest masses. That is why, in 2010, Remco van den Bosch began a systematic search for the most massive black holes in the cosmos. For black holes of this mass, it should be possible to trace stellar motion (and hence measure black hole masses) out to distances of hundreds of millions of light-years.
The initial step of the systematic search uses the Hobby-Eberly Telescope at McDonald Observatory in Texas. This telescope has a mirror of unrivaled size, with a total area of 11 by 9.8 meters, composed of 91 hexagonal mirrors. The total size makes the telescope particularly well suited for survey work of this kind, as observations for each galaxy can be completed fairly quickly. Using this telescope, van den Bosch tackled the task of taking spectra of nearly 700 nearby galaxies.
The result reported here is one of the first from this systematic search; additional results will be published as follow-up observations and black hole mass-modeling are completed for additional galaxies.
From the spectra taken with the Hobby-Eberly Telescope alone, van den Bosch and his colleagues derived a first estimate, using a well-known relation between the broadness of certain spectral lines (indicating the "velocity dispersion", roughly the amount by which stellar velocities deviate from the average) and central black hole mass. This uncovered a total of six candidates of relatively small galaxies with very large black holes. For only one of these six galaxies high spatial resolution imaging is available and it was thus the focus of the black hole mass measurement. For the five other galaxies more observations are required to measure the distribution of stars in their centers.


How was the black hole mass determined?
In order to measure the mass of the central black hole, astronomers need to track the motion of the galaxy's innermost stars – those whose orbits are strongly influenced by the black hole's gravity. The greater the black hole mass, the greater its influence and the speed of the stars in orbit around it.
Aspects of stellar motion can be measured by looking at the spectrum of light emitted in the galaxy's central region. Movement influences specific features ("Doppler shifts of spectral lines") in the galaxy's light in a systematic way, and these changes can be detected in the spectrum, allowing astronomers to reconstruct stellar motion.
The speeds and direction in which the stars move is influenced by the distribution of mass in the galaxy. The heavier the black hole, the faster the stars move in the center. The centers of galaxies are too dense and too distant to resolve the individual stars, and so we can only measure the distribution of velocities of the spectral lines.
To measure the black hole mass, van den Bosch et al. create a dynamical model of the galaxies that consists of all possible orbits along which stars can travel. Through a systematic search, they then find out which combination of orbits and black hole mass fit the observed distribution of stellar velocities best. In the case of NGC 1277, van den Bosch found the black hole mass to be 17±3 billion times that of the Sun, while the galaxy as a whole weighs in at 120 billion solar masses.

Wednesday, November 28, 2012

Biggest Black Hole Blast Discovered





 PR Image eso1247a
Artist’s impression of the huge outflow ejected from the quasar SDSS J1106+1939

New ESO observations reveal most powerful quasar outflow ever found

Astronomers using ESO’s Very Large Telescope (VLT) have discovered a quasar with the most energetic outflow ever seen, at least five times more powerful than any that have been observed to date. Quasars are extremely bright galactic centres powered by supermassive black holes. Many blast huge amounts of material out into their host galaxies, and these outflows play a key role in the evolution of galaxies. But, until now, observed quasar outflows weren’t as powerful as predicted by theorists.

Quasars are the intensely luminous centres of distant galaxies that are powered by huge black holes. This new study has looked at one of these energetic objects — known as SDSS J1106+1939 — in great detail, using the X-shooter instrument on ESO’s VLT at the Paranal Observatory in Chile [1]. Although black holes are noted for pulling material in, most quasars also accelerate some of the material around them and eject it at high speed.

“We have discovered the most energetic quasar outflow known to date. The rate that energy is carried away by this huge mass of material ejected at high speed from SDSS J1106+1939 is at least equivalent to two million million times the power output of the Sun. This is about 100 times higher than the total power output of the Milky Way galaxy — it’s a real monster of an outflow,” says team leader Nahum Arav (Virginia Tech, USA). “This is the first time that a quasar outflow has been measured to have the sort of very high energies that are predicted by theory.”

Many theoretical simulations suggest that the impact of these outflows on the galaxies around them may resolve several enigmas in modern cosmology, including how the mass of a galaxy is linked to its central black hole mass, and why there are so few large galaxies in the Universe. However, whether or not quasars were capable of producing outflows powerful enough to produce these phenomena has remained unclear until now [2].

The newly discovered outflow lies about a thousand light-years away from the supermassive black hole at the heart of the quasar SDSS J1106+1939. This outflow is at least five times more powerful than the previous record holder [3]. The team’s analysis shows that a mass of approximately 400 times that of the Sun is streaming away from this quasar per year, moving at a speed of 8000 kilometres per second.

“We couldn’t have got the high-quality data to make this discovery without the VLT’s X-shooter spectrograph,” says Benoit Borguet (Virginia Tech, USA), lead author of the new paper. “We were able to explore the region around the quasar in great detail for the first time.”

As well as SDSS J1106+1939, the team also observed one other quasar and found that both of these objects have powerful outflows. As these are typical examples of a common, but previously little studied, type of quasars [4], these results should be widely applicable to luminous quasars across the Universe. Borguet and colleagues are currently exploring a dozen more similar quasars to see if this is the case.

“I’ve been looking for something like this for a decade,” says Nahum Arav, “so it’s thrilling to finally find one of the monster outflows that have been predicted!”

Notes

[1] The team observed SDSS J1106+1939 and J1512+1119 in April 2011 and March 2012 using the X-shooter spectrograph instrument attached to ESO’s VLT. By splitting the light up into its component colours and studying in detail the resultant spectrum the astronomers could deduce the velocity and other properties of the material close to the quasar.

[2] The powerful outflow observed in SDSS J1106+1939 carries enough kinetic energy to play a major role in active galaxy feedback processes, which typically require a mechanical power input of roughly 5% of the luminosity of the quasar. The rate at which kinetic energy is being transferred by the outflow is described as its kinetic luminosity.

[3] SDSS J1106+1939 has an outflow with a kinetic luminosity of at least 1046 ergs s−1. The distances of the outflows from the central quasar (300–8000 light-years) was greater than expected suggesting that we observe the outflows far from the region in which we assume them to initially accelerated (0.03–0.4 light-years).

[4] A class known as Broad Absorption Line (BAL) quasars.

More information

This research was presented in a paper, “Major contributor to AGN feedback: VLT X-shooter observations of SIV BAL QSO outflows”, to appear in The Astrophysical Journal.

The team is composed of B. C. J. Borguet (Virginia Tech, USA), N. Arav (Virginia Tech, USA), D. Edmonds (Virginia Tech, USA), C. Chamberlain (Virginia Tech, USA), C. Benn (Isaac Newton Group of Telescopes, Spain).

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). 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

 Nahum Arav
 Virginia Tech
 Blacksburg, VA, USA
 Tel: +1 540 231 8736
 Email:
arav@vt.edu

 Benoît Borguet
 Virginia Tech
 Blacksburg, VA, USA
 Email:
b.borguet@alumni.ulg.ac.be

 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

Dust Grains Highlight the Path to Planet Formation

An international team of researchers from the National Astronomical Observatory of Japan (NAOJ) and the Japanese universities of Kobe, Hyogo, and Saitama used the Subaru Telescope to capture a clear image of the protoplanetary disk of the star UX Tauri A. The team's subsequent, detailed study of the disk's characteristics suggests that its dust particles are large in size and non-spherical in shape. This exciting result shows that these dust grains are colliding with and adhering to each other, a process that will lead to their eventual formation into planets.

A major goal of the SEEDS Project (Note 1) is to explore hundreds of nearby stars in an effort to directly image extrasolar planets and protoplanetary/debris disks. As part of this important project, the current team of researchers used the Subaru High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) mounted on the Subaru Telescope to observe UX Tau A, a young star in the constellation Taurus's molecular cloud or "star nursery", where many lower mass stars are being born. They were able to detect the disk of gas and dust around the star, its "circumstellar disk", which is then referred to as a protoplanetary disk when it is a site of planet formation.

Figure: UX Tau A's protoplanetary disk extends to a radius of 120 AU (1AU = the distance between the Earth and the Sun) with a high spatial resolution of 0.1" (arcsecond) (Credit for left and right sides of figure: NAOJ).
Left: Near-infrared intensity image of UX Tau A. White is the brightest, and then red. The background is dark blue. The disk is slightly elongated in the north-south direction (top to bottom in the figure). Its west side (on the right) is a little brighter than its east side; this indicates that the inclination of the disk is in the east-west direction and that its west side is closer to the observer (see figure on the right).  Right: Schematic diagram of the inclination of the protoplanetary disk of UX Tau A.  

The team made a detailed study of UX Tau A in the near-infrared wavelengths. They measured the polarization (Note 2) of infrared light to find out the distribution of the dust particles that scattered the infrared light. Polarized light reflected from dust particles gives important information about planetary formation in disks. Even though dust particles only make up a tiny fraction of the protoplanetary disk, they can develop into planetesimals (solid objects less than a kilometer in diameter), and eventually, planets.

The light from this disk is strongly polarized; its angle of polarization shows a concentric pattern relative to the central star. Yoichi Itoh (University of Hyogo) expressed his surprise: "The objects we have observed so far show a high degree of polarization no matter what the angle is. However, the polarization of this particular object ranges widely from 2 to 66 % as the polarization angle changes. It was a pleasant challenge to explain this characteristic."

Dust particles in the protoplanetary disk originally came from interstellar space and are only 0.1 microns in size. Small grain particles, which are much smaller than the observed wavelength, can produce a high degree of polarization regardless of their location. If the grain size is similar to the observed wavelength, the scattering performance is different. However, these principles do not account for the current observation. Itoh explained, "Only particles with a non-spherical shape and a size of 30 microns, which is much larger than the near-infrared wavelength that was used for the observation, can explain the features of our observation."

How did this happen? Dust in the disk of UX Tau A collided and stuck together to grow to 30 microns. The researchers were fortunate to witness dust particles at a critical phase in their path to becoming a fully-grown planet in the protoplanetary disk.

References: 
The research paper entitled "High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A" by Tanii et al. is scheduled to be published in the Publications of the Astronomical Observatory of Japan in December 2012.


Acknowledgements:
  • This research was supported in part by the following:
  • The Department of Science and Technology (JSPS-DST) collaboration, India
  • A Princeton University Global Collaborative Research Fund grant
  • The World Premier International Research Center Initiative (WPI Initiative)
  • Ministry of Education, Culture, Sports, and Technology (MEXT), Japan
  • National Science Foundation (NSF) grant AST-1009203, USA

Note:
  1. SEEDS. The Subaru Strategic Exploration of Exoplanets and Disks with HiCIAO/AO 188 Project began in 2009 for a five-year period using 120 observing nights at the Subaru Telescope, located at the summit of Mauna Kea on the island of Hawaii. Principal investigator Motohide Tamura (NAOJ) leads the project.
  2. Polarization. Light has characteristics of both particles and waves. A special detection method such as the polarized light measurement reveals its characteristics as a wave. When the light scatters or reflects off of the material of the target object, the outgoing light has a certain polarization angle. Therefore, the polarization measurement of the disk gives clues about the surface condition of the grain particles that reflect light from the central star.

Tuesday, November 27, 2012

Do missing Jupiters mean massive comet belts?

Artist impression of the debris disc and planets around the star known as Gliese 581, superimposed on Herschel PACS images at 70, 100 and 160 micrometre wavelengths.
 

The line drawing superimposed on the Herschel image gives a schematic representation of the location and orientation of the star, planets and disc, albeit not to scale.
 

The black oval outline sketched onto the Herschel data represents the innermost boundary of the debris disc; the approximate location of the outermost boundary is represented by the outer set of dashed lines. It is not possible to identify the central star due to smearing of the Herschel data.
 

GJ 581’s planets have masses between 2 and 15 Earth masses and are all located within 0.22 Astronomical Units (AU, where 1 AU is the distance between Earth and our Sun) of the central star. A vast debris disc extends from approximately 25 AU to 60 AU. 

Background galaxies are also visible in the Herschel field-of-view. Credits: ESA/AOES


Artist’s impression of the debris disc and planets around the star 61 Vir, superimposed on Herschel PACS images at 70, 100 and 160 micrometre wavelengths.

The line drawing superimposed on the Herschel image gives a schematic representation of the location and orientation of the star, planets and disc, albeit not to scale.


The black oval outline sketched onto the Herschel data represents the innermost boundary of the debris disc; the approximate location of the outermost boundary is represented by the outer set of dashed lines. It is not possible to identify the central star due to smearing of the Herschel data.


The two planets around 61 Vir have masses between 5 and 18 Earth masses and are both located within 0.22 Astronomical Units (AU, where 1 AU is the distance between Earth and our Sun) of the central star. A vast debris disc extends from approximately 30 AU to 100 AU.  Credits: ESA/AOES


Using ESA’s Herschel space observatory, astronomers have discovered vast comet belts surrounding two nearby planetary systems known to host only Earth-to-Neptune-mass worlds. The comet reservoirs could have delivered life-giving oceans to the innermost planets.
 
In a previous Herschel study, scientists found that the dusty belt surrounding nearby star Fomalhaut must be maintained by collisions between comets.

In the new Herschel study, two more nearby planetary systems – GJ 581 and 61 Vir – have been found to host vast amounts of cometary debris.

Herschel detected the signatures of cold dust at 200ºC below freezing, in quantities that mean these systems must have at least 10 times more comets than in our own Solar System’s Kuiper Belt.

GJ 581, or Gliese 581, is a low-mass M dwarf star, the most common type of star in the Galaxy. Earlier studies have shown that it hosts at least four planets, including one that resides in the ‘Goldilocks Zone’ – the distance from the central sun where liquid surface water could exist.

Two planets are confirmed around G-type star 61 Vir, which is just a little less massive than our Sun.

The planets in both systems are known as ‘super-Earths’, covering a range of masses between 2 and 18 times that of Earth.

Interestingly, however, there is no evidence for giant Jupiter- or Saturn-mass planets in either system.  
   
The gravitational interplay between Jupiter and Saturn in our own Solar System is thought to have been responsible for disrupting a once highly populated Kuiper Belt, sending a deluge of comets towards the inner planets in a cataclysmic event that lasted several million years.

“The new observations are giving us a clue: they’re saying that in the Solar System we have giant planets and a relatively sparse Kuiper Belt, but systems with only low-mass planets often have much denser Kuiper belts,” says Dr Mark Wyatt from the University of Cambridge, lead author of the paper focusing on the debris disc around 61 Vir.

“We think that may be because the absence of a Jupiter in the low-mass planet systems allows them to avoid a dramatic heavy bombardment event, and instead experience a gradual rain of comets over billions of years.”

“For an older star like GJ 581, which is at least two billion years old, enough time has elapsed for such a gradual rain of comets to deliver a sizable amount of water to the innermost planets, which is of particular importance for the planet residing in the star’s habitable zone,” adds Dr Jean-Francois Lestrade of the Observatoire de Paris who led the work on GJ 581.

However, in order to produce the vast amount of dust seen by Herschel, collisions between the comets are needed, which could be triggered by a Neptune-sized planet residing close to the disc.

“Simulations show us that the known close-in planets in each of these systems cannot do the job, but a similarly-sized planet located much further from the star – currently beyond the reach of current detection campaigns – would be able to stir the disc to make it dusty and observable,” says Dr Lestrade.

“Herschel is finding a correlation between the presence of massive debris discs and planetary systems with no Jupiter-class planets, which offers a clue to our understanding of how planetary systems form and evolve,” says Göran Pilbratt, ESA’s Herschel project scientist.

Notes for Editors:

“Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems,” by M. Wyatt et al., is published in the Monthly Notices of the Royal Astronomical Society 424, 2012.

“A DEBRIS disk around the planet hosting M-star GJ 581 spatially resolved with Herschel,” by J.-F. Lestrade et al., is accepted for publication in Astronomy & Astrophysics.

The observations were carried out as part of the DEBRIS (Disc Emission via a Bias-free Reconnaissance in the Infrared/Submillimetre) key project for Herschel, using both PACS and SPIRE instruments. DEBRIS is an international collaboration with researchers from Canada, the USA, the UK, Spain, Germany, France, Switzerland and Chile.
 
For more 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

 Mark Wyatt
 University of Cambridge, UK
 Email: wyatt@ast.cam.ac.uk

 Jean-Francois Lestrade
 Observatoire de Paris, France
 Email: jean-francois.lestrade@obspm.fr

 Göran Pilbratt
 ESA Herschel Project Scientist
 Tel: +31 71 565 3621
 Email: gpilbratt@rssd.esa.int

Solar Minimum; Solar Maximum

The picture on the left shows a calm sun from Oct. 2010. The right side, from Oct. 2012, shows a much more active and varied solar atmosphere as the sun moves closer to peak solar activity, a peak known as solar maximum, predicted for 2013. Both images were captured by NASA's Solar Dynamics Observatory (SDO) observing light emitted from the 1 million degree plasma, which is a good temperature for observing the quiet corona. Credit: NASA/SDO.   View larger

The sun goes through a natural solar cycle approximately every 11 years. The cycle is marked by the increase and decrease of sunspots -- visible as dark blemishes on the sun's surface, or photosphere. The greatest number of sunspots in any given solar cycle is designated as "solar maximum." The lowest number is "solar minimum."

The solar cycle provides more than just increased sunspots, however. In the sun's atmosphere, or corona, bright active regions appear, which are rooted in the lower sunspots. Scientists track the active regions since they are often the origin of eruptions on the sun such as solar flares or coronal mass ejections.

The most recent solar minimum occurred in 2008, and the sun began to ramp up in January 2010, with an M-class flare (a flare that is 10 times less powerful than the largest flares, labeled X-class). The sun has continued to get more active, with the next solar maximum predicted for 2013.

The journey toward solar maximum is evident in current images of the sun, showing a marked difference from those of 2010, with bright active regions dotted around the star.

High resolution imagery from this article is available at: http://svs.gsfc.nasa.gov/vis/a010000/a011000/a011072/index.html.


Karen C. Fox
NASA Goddard Space Flight Center, Greenbelt, MD

Monday, November 26, 2012

Cassini Finds a Video Gamers' Paradise at Saturn

 
Scientists with NASA's Cassini mission have spotted two features shaped like the 1980s video game icon "Pac-Man" on moons of Saturn. One was observed on the moon Mimas in 2010 and the latest was observed on the moon Tethys. Image credit: NASA/JPL-Caltech/GSFC/SWRI . Full image and caption

You could call this "Pac-Man, the Sequel." Scientists with NASA's Cassini mission have spotted a second feature shaped like the 1980s video game icon in the Saturn system, this time on the moon Tethys. (The first was found on Mimas in 2010). The pattern appears in thermal data obtained by Cassini's composite infrared spectrometer, with warmer areas making up the Pac-Man shape.

"Finding a second Pac-Man in the Saturn system tells us that the processes creating these Pac-Men are more widespread than previously thought," said Carly Howett, the lead author of a paper recently released online in the journal Icarus. "The Saturn system - and even the Jupiter system - could turn out to be a veritable arcade of these characters."

Scientists theorize that the Pac-Man thermal shape on the Saturnian moons occurs because of the way high-energy electrons bombard low latitudes on the side of the moon that faces forward as it orbits around Saturn. The bombardment turns that part of the fluffy surface into hard-packed ice. As a result, the altered surface does not heat as rapidly in the sunshine or cool down as quickly at night as the rest of the surface, similar to how a boardwalk at the beach feels cooler during the day but warmer at night than the nearby sand. Finding another Pac-Man on Tethys confirms that high-energy electrons can dramatically alter the surface of an icy moon. Also, because the altered region on Tethys, unlike on Mimas, is also bombarded by icy particles from Enceladus' plumes, it implies the surface alteration is occurring more quickly than its recoating by plume particles.

"Studies at infrared wavelengths give us a tremendous amount of information about the processes that shape planets and moons," said Mike Flasar, the spectrometer's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md. "A result like this underscores just how powerful these observations are."

Scientists saw the new Pac-Man on Tethys in data obtained on Sept. 14, 2011, where daytime temperatures inside the mouth of Pac-Man were seen to be cooler than their surroundings by 29 degrees Fahrenheit (15 kelvins). The warmest temperature recorded was a chilly minus 300 degrees Fahrenheit (90 kelvins), which is actually slightly cooler than the warmest temperature at Mimas (about minus 290 degrees Fahrenheit, or 95 kelvins). At Tethys, unlike Mimas, the Pac-Man pattern can also be seen subtly in visible-light images of the surface, as a dark lens-shaped region. This brightness variation was first noticed by NASA's Voyager spacecraft in 1980.

"Finding a new Pac-Man demonstrates the diversity of processes at work in the Saturn system," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Future Cassini observations may reveal other new phenomena that will surprise us and help us better understand the evolution of moons in the Saturn system and beyond."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center in Greenbelt, Md., where the instrument was built.

More information about the Cassini-Huygens mission is at: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Elizabeth Zubritsky 301-614-5438
Goddard Space Flight Center, Greenbelt, Md.
elizabeth.a.zubritsky@nasa.gov

Saturday, November 24, 2012

The Diner at the Center of the Galaxy

A new ScienceCast video explores the Milky Way's central black hole
Play it

An artist's concept of NuSTAR in Earth orbit. More

"We got lucky and captured an outburst from the black hole during our [first] observing campaign," says Fiona Harrison, the mission's principal investigator at the California Institute of Technology.

NuSTAR is an orbiting observatory designed to take pictures of violent, high-energy phenomena in the universe.  Launched on June 13, 2012, it is the only telescope capable of producing focused images of the highest-energy X-rays produced by dying stars and ravenous black holes.

"It's like putting on a new pair of glasses and seeing aspects of the world around us clearly for the first time," says Harrison.  NuSTAR's first light image of Cygnus X-1, a black hole in our galaxy that is siphoning gas off a giant-star companion, shows what she's talking about: click here

NuSTAR's sharp vision allowed it to pinpoint a burst of hard X-rays coming from the galactic center during an observing campaign in July.  Lower-energy X-ray observations by NASA's Chandra X-ray Observatory and infrared data from the Keck telescope in Hawaii confirmed the outburst.  The Milky Way's black hole had just swallowed ... something.

Black hole snacks are a violent process in which the "meal" is ripped apart by powerful tides and heated to  millions of degrees as it slides down the gullet of the gravitational singularity.   In this case, NuSTAR picked up X-rays emitted by matter being heated up to about 100 million degrees Celsius.

The observation raises hopes that astronomers will be able to solve a long-standing mystery:  Why is the Milky Way's supermassive black hole such a picky eater?

Compared to giant black holes at the centers of other galaxies, the Milky Way's is relatively quiet. More active black holes tend to gobble up matter in prodigious quantities. Ours, on the other hand, is thought only to nibble or not eat at all.

Asteroids could be a primary food source. One model holds that trillions of asteroids surround the Milky Way's core. Astronomers using the Chandra X-ray Observatory have indeed detected flares consistent with asteroids 10 km wide or larger falling into the black hole.  These space rocks would be about the same size as the asteroid that wiped out the dinosaurs on Earth 65 million years ago.  Smaller space rocks might be falling in, too, but their flares would be too weak for Chandra to detect.

NuSTAR brings something new to the problem. With its unprecedented ability to detect and make focused images of X-ray flares, the telescope will almost certainly help astronomers understand what's happening deep in the core of our galaxy.  The monster's menu might soon be revealed.

For more information about NuSTAR and its focused observations of black holes, visit the mission's home page at nustar.caltech.edu.


Author: Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit: Science@NASA

Friday, November 23, 2012

First Light for the Millennium Run Observatory

Fig. 1: False-colour images of the Hubble Ultra Deep Field as predicted by the Millennium Run Observatory (left) and as actually observed by the Hubble Space Telescope (right). The images measure about 5’ by 5’, and were constructed from virtual and real observations through the filters V (blue), i (green), and z (red). The resemblance between the virtual image constructed using the MRObs and the actual image seen by HST is striking. The MRObs images can be analysed in the same way as the real data, with the advantage that only for the MRObs images the underlying “reality” is known. Comparison of these kinds of simulated and real data will allow astronomers to test their methods, test how well the simulations reproduce the actual universe, and make predictions for future observations.

 Fig. 2: The MRObs observations allow us to visualize the colours, shapes and sizes of galaxies as predicted by the simulations in ways that were previously impossible. In the left panel, galaxies at z~2 are indicated according to their stellar masses and star formation rates (SFR) as predicted by the simulations. In the panel on the right, the same galaxies are plotted, but now they are shown as they would appear in a simulated HST colour-composite image (with the same quality as recent data from the GOODS/ERS programme). The diagram on the right contains a wealth of extra information compared to the standard diagram shown left: The simulated galaxy population at z~2 consists of a blue star-forming sequence as well as a population of massive, red and compact galaxies in which star formation has already shut down, qualitatively similar to observational findings. The MRObs approach has the advantage of allowing astronomers to also quantitatively investigate how the properties of real and simulated galaxies compare.

Fig. 3: A screenshot of the MRObs browser, the new online tool provided by MPA that allows users to explore the virtual observations and interact with the underlying MR database. Top panel: basic view of the browser showing a small region of a synthetic HST/GOODS observation (in V, i, z filters). Users can pan around and zoom the synthetic observation and query the MR database by clicking on a galaxy. Information about the selected object (marked by a white square) is retrieved from the MR database and displayed in the information panel on the right-hand side of the screen. Bottom panel: the user can highlight all galaxies belonging to the same “friends-of-friends” group as the selected galaxy. In this case, the selected galaxy turns out to be the central galaxy of a group at z~0.5.

The famous Millennium Run (MR) simulations now appear in a completely new light - literally. The project, led by Gerard Lemson of the MPA and Roderik Overzier of the University of Texas, combines detailed predictions from cosmological simulations with a virtual observatory in order to produce synthetic astronomical observations. In analogy to the moment when newly constructed astronomical observatories receive their “first light”, the Millennium Run Observatory (MRObs) has produced its first images of the simulated universe. These virtual observations allow theorists and observers to analyse the purely theoretical data in exactly the same way as they would purely observational data. Building on the success of the Millennium Run Database, the simulated observations are now being made available to the wider astronomical community for further study. The MRObs browser - a new online tool - allows users to explore the simulated images and interact with the underlying physical universe as stored in the database. The team expects that the advantages offered by this approach will lead to a richer collaboration between theoretical and observational astronomers.

Cosmological simulations aim to capture our current understanding of galaxy evolution, aid in the interpretation of complex astronomical observations, and make detailed predictions for future experiments. Simulations and observations, however, are often compared in a somewhat indirect way: physical quantities are estimated from the observational data and compared to the models. An important complication with this approach is that observations typically give a highly distorted view of the universe, making the process of extracting physical information a challenge.

 Many problems in astrophysics could therefore benefit from doing it the other way round: the entire observing process is applied to the simulations, so that the models can be viewed fully from an observer’s perspective. A small team composed of current and former members of the Max Planck Institute for Astrophysics has now developed the Millennium Run Observatory (MRObs), a theoretical, virtual observatory that uses virtual telescopes to ‘observe’ semi-analytic galaxy distributions based on the MR dark matter simulations developed at MPA. The MRObs produces data that can be processed and analysed using standard observational software packages developed for real observations.

 How does it work? The MRObs produces fully physically-motivated, synthetic images of the night sky by stringing together a great number of products from cosmological simulations, various existing astronomical software packages, and software newly created for the MRObs. Halo merger trees based on the MR simulation (using only dark matter) form the backbone for the semi-analytic modelling of galaxies inside haloes. This modelling is based on simple recipes for, e.g., gas cooling, star formation, supernova and AGN heating, gas stripping and merging between galaxies. At each time step of the simulation, the physical properties of each galaxy are used to select stellar population templates from a library of theoretical spectra to predict the intrinsic spectra. ‘Light cones’ are constructed that arrange the simulated galaxies in a way that is similar to how galaxies appear to an observer on the sky. Next, multi-band apparent magnitudes are calculated, including the effects of absorption by the inter-galactic medium. The light cone is then projected onto a virtual sky, and the positions, shapes, sizes and observed-frame apparent magnitudes of the galaxies are used to build a ‘perfect’ or ‘pre-observation’ image. The perfect image is fed into the MRObs telescope simulator that applies a detector model (pixel scale, readout noise, dark current, sensitivity and gain), sky background, point spread function, and noise. The result is a realistic, synthetic telescope image. Source extraction algorithms are applied to the simulated image resulting in a catalogue of the apparent properties of all objects detected in the image. This catalogue of objects can be cross-matched with the higher level data available in the MR database in order to compare the real physical properties of the galaxies with those extracted from the images.

 The MRObs extends the MR simulations by producing data products that most directly correspond to observations, namely synthetic images and extracted source catalogues. The data simulated with the MRObs so far includes portions of the Sloan Digital Sky Survey (SDSS), the Canada France Hawaii Telescope Legacy Survey (CFHT-LS), the Great Observatories Origins Deep Survey (GOODS), the GOODS WFC3 Early Release Science (ERS), the Hubble Ultra Deep Field (HUDF, see Figure 1), as well as the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The information provided covers light cone catalogues linked to structural properties of galaxies, pre-observation model images, mock telescope images and source catalogues that can all be traced back to the dark matter, semi-analytic galaxy and light cone catalogues already available in the MR database. This will aid theorists in testing analytical models against observations, aid observers in making detailed predictions for observations as well as better analyses of observational data, and allow the community to subject the models to new tests. For example, the MRObs can be used to visualize the appearance of galaxy clusters, to predict the structural properties of galaxies across the stellar mass versus star formation rate plane (see Figure 2), or to answer the question of how many galaxies could be detected at a redshift of about 10. The data can be explored interactively in the MRObs browser (Figure 3).

 The development of the MRObs coincides with the celebration of the first 500 papers based on the MR simulations, proving that the MPA-led Millennium Run project is still as successful today as it was 7 years ago. Future expansions of the MRObs project are already underway, such as incorporating the more recent Millennium-Run II and Millennium XXL simulations to extend the dynamic range, implementing improved cosmological parameters and galaxy modelling techniques, and creating a wider range of virtual telescopes and simulated surveys that will aid theorists and observers alike.


 Roderik Overzier and Gerard Lemson


Further reading
Overzier, R., Lemson, G., Angulo, R., Bertin, E., Blaizot, J., Henriques, B., Marleau, G., White, S., "The Millennium Run Observatory: first light", 2012, MNRAS, in press (arXiv:1206.6923)

Further references

 Millennium Run Observatory Web Portal and access to the MRObs browser