Monday, January 31, 2011

The Star City that Never Sleeps

IC 391
Credit: ESA/Hubble & NASA

Hubble's Advanced Camera for Surveys has captured this moment in the ever-changing life of a spiral galaxy called IC 391. Although these massive star cities appear static and unchanging, their stellar inhabitants are constantly moving and evolving, with new stars being born and old stars reaching the ends of their lives —often in spectacular fashion, with an immense supernova explosion that can be viewed from Earth.

On 3 January 2001, members of the Beijing Astronomical Observatory discovered such an explosion within IC 391 and it was named SN 2001B. This was a Type Ib supernova, which occurs when a massive star runs out of fuel for nuclear fusion and collapses, emitting vast amounts of radiation and creating a powerful shock wave. Hubble has contributed much to our understanding of supernovae in recent years, and it has made an extensive study of supernova 1987A (heic0704), the brightest such stellar explosion to be seen from Earth in over 400 years.

IC 391 lies about 80 million light-years away in the constellation of Camelopardalis (the Giraffe) in the far northern part of the sky. The British amateur observer William Denning discovered it in the late nineteenth century, and described it as faint, small and round.

This picture was assembled from images taken with Hubble’s Wide Field Channel on the Advanced Camera for Surveys. Images through a blue filter (F435W) were coloured blue, those through a green filter (F555W) are shown as green and those through a near-infrared filter (F814W) are shown in red. The exposure times were 800 s, 700 s and 700 s respectively and the field of view is 2.1 by 1.4 arcminutes.

Friday, January 28, 2011

The Secret of Stellar Youth

The globular cluster Palomar 1
Credit: ESA/Hubble & NASA

The NASA/ESA Hubble Space Telescope has captured a clear view of the unusual globular cluster Palomar 1, whose youthful beauty is a puzzle for astronomers. This faint and sparse object is very different from the more familiar brilliant and very rich globular clusters and had to wait until 1954 for its discovery by George Abell on photographs from the Palomar Schmidt telescope.

Globular clusters are tightly bound conglomerations of stars, which are found in the outer reaches of the Milky Way, in its so-called halo. They are amongst the oldest objects in a galaxy, containing very old stars and no gas, which means there is no possibility of newborn stars introducing some fresh blood into the cluster.

However, at 6.3 to 8 billion years old, Palomar 1 is a youngster in globular cluster terms — little more than half the age of most the other globulars in our Milky Way, which formed during our galaxy’s violent early history. However, astronomers suspect that globular youngsters, such as Palomar 1, formed in a more sedate manner. Possibly a gas cloud meandered around in the Milky Way’s halo until a trigger kick-started star formation. Another possibility is that the Milky Way captured the stellar group; perhaps it was adrift in the Universe before it was gravitationally attracted to our galaxy, or maybe it had a violent beginning after all and is the remnant of a dwarf galaxy that was devoured by the Milky Way.

Behind the sparsely populated Palomar 1 several background galaxies are seen and a few nearby bright foreground Milky Way stars are also visible. Together with Palomar 1 these objects make up an attractive “family portrait”.

This picture was created from images taken with the Wide Field Channel of the Advanced Camera for Surveys. Images through orange (F606W, coloured blue) and near-infrared (F814W, coloured red) filters were combined. The exposure times were 1965 s per filter and the field of view is 3.0 arcminutes across.

Wednesday, January 26, 2011

NASA's Hubble Finds Most Distant Galaxy Candidate Ever Seen in Universe

UDFj-39546284
Credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), R. Bouwens (University of California, Santa Cruz, and Leiden University), and the HUDF09 Team. View this image

Astronomers have pushed NASA's Hubble Space Telescope to its limits by finding what they believe is the most distant object ever seen in the universe. Its light traveled 13.2 billion years to reach Hubble, roughly 150 million years longer than the previous record holder. The age of the universe is 13.7 billion years.

The dim object, called UDFj-39546284, is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe's current age. It is tiny. Over one hundred such mini-galaxies would be needed to make up our Milky Way.

Astronomers were surprised to find evidence that the rate at which the universe was forming stars grew precipitously in about a 200-million-year time span.

"We're seeing huge changes in the rate of star birth that tell us that if we go a little further back in time we're going to see even more dramatic changes," says Garth Illingworth of the University of California at Santa Cruz. The rate of star birth increased by about a factor of ten going from 480 million years to 650 million years after the Big Bang.

"These observations provide us with our best insights yet into the earlier primeval objects that have yet to be found," adds Rychard Bouwens of the Leiden University in the Netherlands.

Astronomers don't know exactly when the first stars appeared in the universe, but every step farther from Earth takes them deeper into the early universe's "formative years" when stars and galaxies were just beginning to emerge in the aftermath of the Big Bang. "We're moving into a regime where there are big changes afoot. Another couple of hundred million years toward the Big Bang, that will be the time where the first galaxies really are starting to get built up," says Illingworth.

Bouwens and Illingworth are reporting the discovery in the January 27 issue of the British science journal Nature.

The even more distant proto-galaxies that Illingworth expects are out there will require the infrared vision of NASA's James Webb Space Telescope, which is the successor to Hubble. Planned for launch later this decade, Webb will provide confirming spectroscopic measurements of the object's tremendous distance being reported today.

After over a year of detailed analysis, the object was positively identified in the Hubble Ultra Deep Field – Infrared (HUDF-IR) data taken in the late summer of both 2009 and 2010. This observation was made with the Wide Field Camera 3 (WFC3) starting just a few months after it was installed into the Hubble Space Telescope in May of 2009, during the last NASA space shuttle servicing mission to Hubble.

The object appears as a faint dot of starlight in the Hubble exposures. It is too young and too small to have the familiar spiral shape that is characteristic of galaxies in the local universe. Though its individual stars can't be resolved by Hubble, the evidence suggests that this is a compact galaxy of hot stars that first started to form over 100-200 million years earlier, from gas trapped in a pocket of dark matter.

The proto-galaxy is only visible at the farthest infrared wavelengths observable by Hubble. This means that the expansion of the universe has stretched and thereby reddened its light more than that of any other galaxy previously identified in the HUDF-IR, to the very limit of what Hubble can detect. Webb will go deeper into infrared wavelengths and will be at least an order of magnitude more sensitive than Hubble, allowing it to more efficiently hunt for primeval galaxies at even greater distances, at earlier times, closer to the Big Bang.

Astronomers plumb the depths of the universe, and probe its history, by measuring how much the light from an object has been stretched by the expansion of space. This is called the redshift value or "z." In general, the greater the observed "z" value for a galaxy, the more distant it is in time and space as observed from our own Milky Way. Before Hubble was launched, astronomers could only see galaxies out to a z of approximately 1, corresponding to halfway across the universe.

The original Hubble Deep Field taken in 1995 leapfrogged to z=4, or roughly 90 percent of the way back to the beginning of time. The Advanced Camera for Surveys (ACS) produced the Hubble Ultra Deep Field of 2004, pushing back the limit to z~6. ACS was installed on Hubble during Servicing Mission 3B in 2002. Hubble's first infrared camera, the Near Infrared Camera and Multi-Object Spectrometer, reached out to z=7. The WFC3 first took us back to z~8, and has now plausibly penetrated for the first time to z=10. The Webb Space Telescope is expected to leapfrog to z of approximately 15, 275 million years after the Big Bang, and possibly beyond. The very first stars may have formed between z of 30 and 15.

The hypothesized hierarchical growth of galaxies — from stellar clumps to majestic spirals and ellipticals — didn't become evident until the Hubble Space Telescope deep-field exposures. The first 500 million years of the universe's existence, from z of 1000 to 10, is now the missing chapter in the hierarchical growth of galaxies. It's not clear how the universe assembled structure out of a darkening, cooling fireball of the Big Bang. As with a developing embryo, astronomers know there must have been an early period of rapid changes that would set the initial conditions to make the universe of galaxies what it is today.

CONTACT

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

Garth Illingworth
University of California, Santa Cruz
831-459-2843
gdi@ucolick.org

Rychard Bouwens
University of California, Santa Cruz, and Leiden University, Netherlands
831-459-5276
bouwens@ucolick.org

Asteroids Ahoy! Jupiter Scar Likely from Rocky Body

These infrared images obtained from NASA's Infrared Telescope Facility in Mauna Kea, Hawaii, show particle debris in Jupiter's atmosphere after an object hurtled into the atmosphere on July 19, 2009. Image credit: NASA/IRTF/JPL-Caltech/University of Oxford. Full image and caption

This infrared image, showing thermal radiation at a wavelength of 9.7 microns, was obtained by the Gemini North Telescope in Hawaii. Image credit: Gemini Observatory/AURA/UC Berkeley/SSI/ JPL-Caltech. Full image and caption - enlarge image

These images show eight different looks at the aftermath of a body - probably an asteroid - hitting Jupiter on July 19, 2009. Image credit: NASA/JPL-Caltech/IRTF/STScI/ESO/Gemini Observatory/AURA/A. Wesley. Full image and caption - enlarge image

A hurtling asteroid about the size of the Titanic caused the scar that appeared in Jupiter's atmosphere on July 19, 2009, according to two papers published recently in the journal Icarus.

Data from three infrared telescopes enabled scientists to observe the warm atmospheric temperatures and unique chemical conditions associated with the impact debris. By piecing together signatures of the gases and dark debris produced by the impact shockwaves, an international team of scientists was able to deduce that the object was more likely a rocky asteroid than an icy comet. Among the teams were those led by Glenn Orton, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Leigh Fletcher, researcher at Oxford University, U.K., who started the work while he was a postdoctoral fellow at JPL.

"Both the fact that the impact itself happened at all and the implication that it may well have been an asteroid rather than a comet shows us that the outer solar system is a complex, violent and dynamic place, and that many surprises may be out there waiting for us," said Orton. "There is still a lot to sort out in the outer solar system."

The new conclusion is also consistent with evidence from results from NASA's Hubble Space Telescope indicating the impact debris in 2009 was heavier or denser than debris from comet Shoemaker-Levy 9, the last known object to hurl itself into Jupiter's atmosphere in 1994.

Before this collision, scientists had thought that the only objects that hit Jupiter were icy comets whose unstable orbits took them close enough to Jupiter to be sucked in by the giant planet's gravitational attraction. Those comets are known as Jupiter-family comets. Scientists thought Jupiter had already cleared most other objects, such as asteroids, from its sphere of influence. Besides Shoemaker-Levy, scientists know of only two other impacts in the summer of 2010, which lit up Jupiter's atmosphere.

The July 19, 2009 object likely hit Jupiter between 9 a.m. and 11 a.m. UTC. Amateur astronomer Anthony Wesley from Australia was the first to notice the scar on Jupiter, which appeared as a dark spot in visible wavelengths. The scar appeared at mid-southern latitudes. Wesley tipped off Orton and colleagues, who immediately used existing observing time at NASA's Infrared Telescope Facility in Mauna Kea, Hawaii, the following night and proposed observing time on a host of other ground-based observatories, including the Gemini North Observatory in Hawaii, the Gemini South Telescope in Chile, and the European Southern Observatory's Very Large Telescope in Chile. Data were acquired at regular intervals during the week following the 2009 collision.

The data showed that the impact had warmed Jupiter's lower stratosphere by as much as 3 to 4 Kelvin at about 42 kilometers above its cloudtops. Although 3 to 4 Kelvin does not sound like a lot, it is a significant deposition of energy because it is spread over such an enormous area.

Plunging through Jupiter's atmosphere, the object created a channel of super-heated atmospheric gases and debris. An explosion deep below the clouds – probably releasing at least around 200 trillion trillion ergs of energy, or more than 5 gigatons of TNT -- then launched debris material back along the channel, above the cloud tops, to splash back down into the atmosphere, creating the aerosol particulates and warm temperatures observed in the infrared. The blowback dredged up ammonia gas and other gases from a lower part of the atmosphere known as the troposphere into a higher part of the atmosphere known as the stratosphere.

"Comparisons between the 2009 images and the Shoemaker-Levy 9 results are beginning to show intriguing differences between the kinds of objects that hit Jupiter," Fletcher said. "The dark debris, the heated atmosphere and upwelling of ammonia were similar for this impact and Shoemaker-Levy, but the debris plume in this case didn't reach such high altitudes, didn't heat the high stratosphere, and contained signatures for hydrocarbons, silicates and silicas that weren't seen before. The presence of hydrocarbons, and the absence of carbon monoxide, provide strong evidence for a water-depleted impactor in 2009."

The detection of silica in this mixture of Jovian atmospheric gases, processed bits from the impactor and byproducts of high-energy chemical reactions was significant because abundant silica could only be produced in the impact itself, by a strong rocky body capable of penetrating very deeply into the Jovian atmosphere before exploding, but not by a much weaker comet nucleus. Assuming that the impactor had a rock-like density of around 2.5 grams per cubic centimeter (160 pounds per cubic foot), scientists calculated a likely diameter of 200 to 500 meters (700 to 1,600 feet).

Scientists computed the set of possible orbits that would bring an object into Jupiter in the right range of times and at the right locations. Then they searched the catalog of known asteroids and comets to find the kinds of objects in these orbits. An object named 2005 TS100 – which is probably an asteroid but could be an extinct comet – was one of the closest matches. Although this object was not the actual impactor, it has a very chaotic orbit and made several very close approaches to Jupiter in computer models, demonstrating that an asteroid could have hurtled into Jupiter.

"We weren't expecting to find that an asteroid was the likely culprit in this impact, but we've now learned Jupiter is getting hit by a diversity of objects," said Paul Chodas, a scientist at NASA's Near-Earth Object Program Office at JPL. " Asteroid impacts on Jupiter were thought to be quite rare compared to impacts from the so-called 'Jupiter-family comets,' but now it seems there may be a significant population of asteroids in this category."

Scientists are still working to figure out what that frequency at Jupiter is, but asteroids of this size hit Earth about once every 100,000 years. The next steps in this investigation will be to use detailed simulations of the impact to refine the size and properties of the impactor, and to continue to use imaging at infrared, as well as visible wavelengths, to search for debris from future impacts of this size or smaller.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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

Supergiant star gains thick dusty waist

New 3D imaging technique reveals velocity field of
baby-like feature in old star close to death

How is it possible that HD 62623, a hot supergiant star at the verge of death, is surrounded by a disc, generally only associated to baby stars? Using long-baseline stellar interferometry at ESO's VLT interferometer, a team led by Florentin Millour from Observatoire de la Côte d'Azur and Anthony Meilland from Max Planck Institute for Radio Astronomy could generate for the first time a three-dimensional high angular and high spectral resolution image of this star and its closest environment. They conclude that a solar-mass companion star is the key for this mystery. To attain their goal, the researchers adapted an imaging technique from radioastronomy that uses interferometric datasets.

Figure 1: 3D images of HD 62623, obtained with the VLTI (left), compared to the model of a rotating disk (right). In the boxes, the gas kinematics is shown (3rd dimension): blue-coloured gas approaches the observer, while red-coloured gas recedes from the observer. The size of the inner gas disk of approx. 2 milli-arcseconds corresponds to 1.3 astronomical units (distance Earth-Sun), while the outer dust ring seen in the images has a radius corresponding to 4 astronomical units, assuming 2100 light years as distance to HD 62623. Images: F. Millour et al.

HD 62623 is an exotic hot supergiant star. Contrary to its well-known twin, the bright star Deneb in the summer triangle, and almost all stars with the same spectral class, this star is surrounded by a dense and complex environment composed of plasma and dust. Hot supergiant stars are very bright stars, so bright, that they push their strong wind with their own photons. Such a wind would normally prevent matter from condensing as dust next to the star. To better understand dust formation processes in the harsh environment of such stars, it is highly desirable to disentangle the geometry of the gas and dust in the surroundings of the central source, but also to access the kinematics of this close environment.

"Thanks to our interferometric observations with Amber we could synthetize a 3D image of HD 62623 as seen through a virtual 130 m-diameter telescope", says Florentin Millour, leading author of the study. "The resolution is an order of magnitude higher compared with the world's largest optical telescopes of 8-10 m diameter." The Amber instrument is located at the Very Large Telescope Interferometer (VLTI) in Chile. The scientists significantly improved the image quality by adapting the so-called "self-calibration" method, which is well-known from radio interferometry. The obtained image combines spatial and velocity information, showing not only the shape of the close environment of HD 62623, but also its kinematics or motion. Up to now, the necessary kinematics information was missing in such images.

"Our new 3D image locates the dust-forming region around HD 62623 very precisely, and it provides evidence for the rotation of the gas around the central star" explains Anthony Meilland. "This rotation is found to be Keplerian, the same way the Solar system planets rotate around the Sun." A nearby companion star, with approximately the mass of our Sun, could be the reason of such a disc around HD 62623. This companion, though not directly detected due to its brightness thousands of times lower than the primary star, is betrayed by a central cavity between the gas disk and the central star. The presence of the companion could explain the exotic characteristics of HD 62623, exactly like the monster among the old stars wthin our Galaxy, Eta Carinae.

The new 3D imaging technique presented in this work is equivalent to integral-field spectroscopy, but gives access to a 15 times larger angular resolution or capacity to detect fine details in the images. "With these new capacities, the VLTI will be able to provide a better comprehension of many sky targets, too small to be resolved by the largest telescopes", concludes Florentin Millour. "We could aim at young stellar disks or jets, or even the central regions of active galaxies."

Figure 2: Four domes of the 1.8 m Auxiliary Telescopes (AT), utilized for the Very Large Telescope Interferometer (VLTI). ESO, Cerro Paranal, Chile. Image: F. Millour, OCA, Nice, France.

The Very Large Telescope Interferometer (VLTI) utilizes telescopes at ESO's Paranal site, either the 8.2 m UTs or the 1.8m ATs (Auxiliary Telescopes). Amber (Astronomical Multi-BEam Recombiner) is one of the science instruments of the VLTI. It is an interferometric beam combiner, sensitive in the near-infrared wavelength range (from 1 to 2.5 microns), built in collaboration with institutes from Grenoble (Laboratoire d'Astrophysique de Grenoble), Nice (Laboratoire d'Astrophysique Universitaire de Nice und Observatoire de la Côte d'Azur), Florence (Observatorio Astrofisico di Arcetri) and Bonn (Max Planck Institute for Radio Astronomy).

Original Paper:

Imaging the spinning gas and dust in the disc around the supergiant A[e] star HD62623 , Florentin Millour, Anthony Meilland, Olivier Chesneau, Philippe Stee, Samer Kanaan, Romain Petrov, Denis Mourard, Stefan Kraus, 2011, Astronomy & Astrophysics, Vol. 526, A107. DOI: 10.1051/0004-6361/201016193 (see also Imaging the spinning gas and dust in the disc around the supergiant A[e] star HD62623 , arXiv:1012.2957v1 [astro-ph.SR]).

Parallel and Earlier Press Releases:

First 3D View from the VLT Interferometer, ESO Announcement, January 26, 2011. Motions in the disc around a supergiant star revealed.

Première image 3D de l'environnement proche d'une étoile supergéante chaude, CNRS, Communiqué de presse national, Paris , 26 Janvier 2011.

Seeing a Stellar Explosion in 3D, ESO1032 - Science Release, August 04, 2010. VLT image of supernova 1987A.

All Stars are Born the Same Way, PRI (MPIfR) 07/2010 (1), July 15, 2010. VLTI and APEX observations reveal the mystery of massive star birth.

The Little Man and the Cosmic Cauldron, ESO0817 - Photo Release, May 27, 2008. VLT images two nebulae in Carina.


Further Information:

Max Planck Institute for Radio Astronomy (MPIfR)

Infrared Interferometry Group at MPIfR

Observatoire de la Cote d'Azur

European Southern Observatory (ESO)

Astronomical Multi-BEam combineR (AMBER)


Contact:

Dr. Anthony Meilland, Max-Planck-Institut für Radioastronomie, Bonn. Fon: +49-228-525-188 E-mail: meilland@mpifr-bonn.mpg.de

Dr. Florentin Millour
, Observatoire de la Cote d'Azur, Nice, France. Fon: +33 4 92 00 30 68 E-mail: fmillour@oca.eu

Dr. Norbert Junkes, Public Outreach, Max-Planck-Institut für Radioastronomie, Bonn. Fon: +49-228-525-399 E-mail: njunkes@mpifr-bonn.mpg.de

First Light for VIRUS-W spectrograph

Fig. 1: "First Light" for VIRUS-W: This image (from the Sloan Digital Sky Survey) shows the galaxy NGC2903 and the field of view of the spectrograph. Credit: SDSS

Fig. 2: These are the first observational data taken by VIRUS-W at the beginning of November. The false colour image in the bottom row, left, shows an enlarged area of the galaxy NGC2903 shown in Fig.1. The bottom right image shows the reconstructed image by VIRUS-W, combining the total light received in each fibre. The top images show the velocities of the stars inside the galaxy. The left image gives the mean velocity, where blue indicates that the stars are moving towards us and red indicates that they are moving away. As all stars in lower half move away and all stars in the upper half move towards us, this means that the galaxy is rotating. The top right image shows the velocity dispersion, which increases towards the centre. This indicates that the motion of the stars becomes more chaotic the closer they are to the core of the galaxy.
Credit: M. Fabricius, MPE

The new observing instrument VIRUS-W, built by the Max Planck Institute for Extraterrestrial Physics and the University Observatory Munich, saw "first light" on 10th November at the Harlan J. Smith Telescope of the McDonald observatory in Texas. Its first images of a spiral galaxy about 30 million light-years away where an impressive confirmation of the capabilities of the instrument, which can determine the motion of stars in near-by galaxies to a precision of a few kilometres per second.

As imaging field spectrograph, VIRUS-W can simultaneously produce 267 individual spectra - one for each of its glass fibres. By dispersing the light into its constituent colours, astronomers thus are able to study properties such as the velocity distribution of the stars in a galaxy. For this they use the so called Doppler shift, which means that the light from stars moving towards or away from us is shifted to blue or red wavelengths, respectively. This effect can also be observed on Earth, when a fast vehicle, such as a racing car, is driving past: the sound of the approaching car is higher, while for the departing car it is lower.

VIRUS-W´s unique feature is the combination of a large field of view (about 1x2 arcminutes) with a relatively high spectral resolution. With the large field of view astronomers can study near-by galaxies in just one or few pointings, while the high spectral resolution permits a very accurate determination of the velocity dispersion in these objects. In this way the astronomers obtain the large-scale kinematic structure of near-by spiral galaxies, which gives important insight into their formation history.

Most galaxies are too distant and the separation between the billions upon billions of stars is too small to resolve it with even the best, cutting-edge instruments. The astronomers therefore cannot study individual stars but only the average motion along a specific line of sight.

The measured velocity distributions are characterised by two parameters: The mean velocity reveals the large-scale motion of the stars along the line of sight. The velocity dispersion measures how much the velocities of the individual stars differ from this mean velocity. If the stars have more or less the same velocity, the dispersion is small, if they have very different velocities, the dispersion is broad. For spiral galaxies, where the stars travel in fairly regular circular orbits, the velocity dispersion is mostly small. In elliptical galaxies, however, the stars have rather disordered orbits and so the dispersion is broad.

With the high spectral resolution of VIRUS-W, the astronomers can investigate relatively small velocity dispersions, down to about 20 km/s. This was impressively confirmed by the first images taken by VIRUS-W of the near-by spiral galaxy NGC2903 (see Figure). "When we attached VIRUS-W around midnight on the 10th of November to the 2.7m telescope, we were very happy to see that the data delivered by VIRUS-W was of science quality virtually from the first moment on," says Maximilian Fabricius from the Max-Planck-Institute for Extraterrestrial Physics. "As the first galaxy to observe we had selected the strongly barred galaxy NGC2903 at a distance of about 30 million lightyears - right in front of our doorstep. The data we collected reveal a centrally increasing velocity dispersion from about 80 km/s to 120 km/s within the field of view of the instrument. This was a very exciting moment and only possible because of the remarkable teamwork during the commissioning with a lot of support by the observatory staff!" The observing time at the telescope was made available by the VENGA project, to which VIRUS-W will be contributing from the beginning of 2011 onwards. It will then provide detailed kinematic data to this study.

The main instrument for VENGA is VIRUS-P, a spectrograph operating at the 2,7m Harlan J. Smith-Teleskope of the McDonald observatory since 2007. This instrument is a prototype of the VIRUS spectrographs being developed for the HETDEX project led by the University of Texas in Austin. For a study of the large scale distribution of galaxies, HETDEX will combine about 100 spectrographs at the 9.2m Hobby-Eberly Telescope of the McDonald observatory to form one large instrument. VIRUS-W (where the W stands for a later mission at the Wendelstein telescope of the Munich Observatory) is based on the same basic VIRUS design. Because of its broader spectral coverage and despite its much lower resolution, the prototype VIRUS-P already gives interesting insight into the age and chemical composition of stars and the interstellar medium as well as information about the star formation rate.

Links :

Press Release of the McDonald Observatory
VENGA Projekt
MPE Press Release June 2010

Dr. Hannelore Hämmerle
Press Officer
Max-Planck-Institut für extraterrestrische Physik
phone: +49 89 30000-3980
email: hanneh@mpe.mpg.de

Maximilian Fabricius
Max-Planck-Institut für extraterrestrische Physik, Garching
phone: +49 89 30000-3694
email: mxhf@mpe.mpg.de

Prof. Dr. Ralf Bender , Dr. Frank Grupp
Max-Planck-Institut für extraterrestrische Physik, Garching
Universitätssternwarte München
email: bender@mpe.mpg.de , fug@usm.lmu.de

Dr. Roberto Saglia
Max-Planck-Institut für extraterrestrische Physik, Garching
email: saglia@mpe.mpg.de

Dr. Niv Drory
Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM)
phone: (+52 55) 5622 4014
fax: (+52 55) 5616 0653

Contact: MPE public outreach department

Tuesday, January 25, 2011

Runaway Star Plows Through Space

The blue star near the center of this image is Zeta Ophiuchi. When seen in visible light it appears as a relatively dim red star surrounded by other dim stars and no dust. Image credit: NASA/JPL-Caltech/UCLA. Full image and caption

A massive star flung away from its former companion is plowing through space dust. The result is a brilliant bow shock, seen here as a yellow arc in a new image from NASA's Wide-field Infrared Survey Explorer, or WISE.

The star, named Zeta Ophiuchi, is huge, with a mass of about 20 times that of our sun. In this image, in which infrared light has been translated into visible colors we see with our eyes, the star appears as the blue dot inside the bow shock.

Zeta Ophiuchi once orbited around an even heftier star. But when that star exploded in a supernova, Zeta Ophiuchi shot away like a bullet. It's traveling at a whopping 54,000 miles per hour (or 24 kilometers per second), and heading toward the upper left area of the picture.

As the star tears through space, its powerful winds push gas and dust out of its way and into what is called a bow shock. The material in the bow shock is so compressed that it glows with infrared light that WISE can see. The effect is similar to what happens when a boat speeds through water, pushing a wave in front of it.

This bow shock is completely hidden in visible light. Infrared images like this one from WISE are therefore important for shedding new light on the region.

JPL manages and operates WISE for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by NASA's Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information is online at http://www.nasa.gov/wise, http://wise.astro.ucla.edu and http://www.jpl.nasa.gov/wise .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Monday, January 24, 2011

The Cat's Eye Nebula

This image of the Cat's Eye Nebula or NGC 6543 was obtained using the Wide Field Camera on the Isaac Newton Telescope. It is a three-colour composite made from data collected using filters to isolate the light emitted by hydrogen alpha (H-alpha), doubly ionised oxygen (OIII) and ionised sulfur (SII) atoms, and coded in the image as red, green and blue respectively. Credit: D. López and R. Barrena (IAC) [ JPEG | TIFF | PDF (with text) ]

NGC 6543, nicknamed the Cat's Eye Nebula, is one of the most complex of the planetary class nebula, stars that throw of spheres of gas at the end of their lives. It is located in the constellation Draco and is thought to have been created 1000 years ago by two stars orbiting each other.

This image was obtained and processed by members of the IAC astrophotography group (A. Oscoz, D. López, P. Rodríguez-Gil and L. Chinarro).

More information:

NGC 6543 - Monthly IAC Astrophoto
IAC Astronomical Picture of the Month

Javier Méndez
Public Relations Officer

Thursday, January 20, 2011

No direct link between black holes and Dark Matter

Messier 101 (NGC 5457, a galaxy with a massive dark halo but no bulge and no detected black hole. Observations show that this giant galaxy cannot contain a black hole that is even as small as the relatively small black hole in our Milky Way galaxy. Image Credit: wikisky.org

NGC 6503, another example of a bulge-less galaxy with a massive halo and a small black hole. Image Credit: wikisky.org

Messier 31 (NGC 224), the neighbour of our Milky Way with a large classical bulge. As was shown by Bender, Kormendy and collaborators in 2005, this galaxy contains a black hole of 140 million solar masses, about 40 times bigger than the black hole in our own Galaxy (Astrophysical Journal 631, 280). Image Credit: wikisky.org

The Sombrero galaxy (M104, NGC 4594) is another example of a bulge dominated galaxy. The Sombrero contains a black hole of 1000 million solar masses as measured by Kormendy, Bender and collaborators in 1996 (Astrophysical Journal 473, L91). Image Credit: HST, STScI

Massive black holes have been found at the centres of almost all galaxies, where the largest galaxies - who are also the ones embedded in the largest halos of Dark Matter - harbour the most massive black holes. This led to the speculation that there is a direct link between Dark Matter and black holes, i.e. that exotic physics controls the growth of a black hole. Scientists at the Max Planck Institute of Extraterrestrial Physics, the University Observatory Munich and the University of Texas in Austin have now conducted an extensive study of galaxies to prove that black hole mass is not directly related to the mass of the Dark Matter halo but rather seems to be determined by the formation of the galaxy bulge. Their findings are published in a Letter to the journal Nature on 20th January.

Galaxies, such as our own Milky Way, consist of billions of stars, as well as great amounts of gas and dust. Most of this can be observed at different wavelengths, from radio and infrared for cooler objects up to optical and X-rays for parts that have been heated to high temperatures. However, there are also two important components that do not emit any light and can only be inferred from their gravitational pull.

All galaxies are embedded in halos of so-called Dark Matter, which extends beyond the visible edge of the galaxy and dominates its total mass. This component cannot be observed directly, but can be measured through its effect on the motion of stars, gas and dust. The nature of this Dark Matter is still unknown, but scientists believe that it is made up of exotic particles unlike the normal (baryonic) matter, which we, the Earth, Sun and stars are made of.

The other invisible component in a galaxy is the supermassive black hole at its centre. Our own Milky Way harbours a black hole, which is some four million times heavier than our Sun. Such gravity monsters, or even larger ones, have been found in all luminous galaxies with central bulges where a direct search is feasible; most and possibly all bulgy galaxies are believed to contain a central black hole. However, also this component cannot be observed directly, the mass of the black hole can only be inferred from the motion of stars around it.

In 2002, it was speculated that there may exist a tight correlation between the mass of the Black Hole and the outer rotation velocities of galaxy disks, which is dominated by the Dark Matter halo, suggesting that the unknown physics of exotic Dark Matter somehow controls the growth of black holes. On the other hand, it had already been shown a few years earlier that black hole mass is well correlated with bulge mass or luminosity. Since larger galaxies in general also contain larger bulges, it remained unclear which of the correlations is the primary one driving the growth of black holes.

By studying galaxies embedded in massive dark halos with high rotation velocities but small or no bulges, John Kormendy and Ralf Bender tried to answer this question. They indeed found that galaxies without a bulge - even if they are embedded in massive dark matter halos - can at best contain very low mass black holes. Thus, they could show that black hole growth is mostly connected to bulge formation and not to dark matter.

"It is hard to conceive how the low-density, widely distributed non-baryonic Dark Matter could influence the growth of a black hole in a very tiny volume deep inside a galaxy," says Ralf Bender from the Max Planck Institute for Extraterrestrial Physics and the University Observatory Munich. John Kormendy, from the University of Texas, adds: "It seems much more plausible that black holes grow from the gas in their vicinity, primarily when the galaxies were forming." In the accepted scenario of structure formation, galaxy mergers occur frequently, which scramble disks, allow gas to fall into the centre and thus trigger starbursts and feed black holes. The observations carried out by Kormendy and Bender indicate that this must indeed be the dominant process of black hole formation and growth.

Original paper :

Supermassive black holes do not correlate with dark matter halos of galaxies"
John Kormendy & Ralf Bender
Nature, Vol. 469, pp. 374-376, 20 January 2011

Contact :

Dr. Ralf Bender
Max-Planck-Institut für extraterrestrische Physik
phone: +49 89 30000-3702
email: bender@mpe.mpg.de

John Kormendy
Mount Stromlo Observatory
The Australian National University, Canberra, Australia
office phone: +61 2 6125 6374 (no messages here, please)
cell phone: +61 4 0579 7710 (messages OK)
email: kormendy@astro.as.utexas.edu

Dr.Hannelore Hämmerle
Press Officer
Max-Planck-Institut für extraterrestrische Physik
phone: +49 89 30000-3980
email: hanneh@mpe.mpg.de

print version in pdf format

Swift Survey Finds 'Missing' Active Galaxies

A newfound population of heavily absorbed active galaxies (orange curve) is thought to make the greatest contribution to the cosmic X-ray background (light blue). Both have similar spectral shapes and peak at similar energies. Adding in the known contributions from less-absorbed active galaxies (yellow and purple) appears to fully account for the background. Credit: NASA/Goddard Space Flight Center. Larger image




What we see from an active galaxy's black hole depends on our viewing angle. Seen edge-on, the dense clouds of dust and gas around the central black hole prevent all but the most penetrating radiation to reach us. Credit: NASA/Goddard Space Flight Center. View/download transcript and other formats

Seen in X-rays, the entire sky is aglow. Even far away from bright sources, X-rays originating from beyond our galaxy provide a steady glow in every direction. Astronomers have long suspected that the chief contributors to this cosmic X-ray background were dust-swaddled black holes at the centers of active galaxies. The trouble was, too few of them were detected to do the job.

An international team of scientists using data from NASA's Swift satellite confirms the existence of a largely unseen population of black-hole-powered galaxies. Their X-ray emissions are so heavily absorbed that little more than a dozen are known. Yet astronomers say that despite the deeply dimmed X-rays, the sources may represent the tip of the iceberg, accounting for at least one-fifth of all active galaxies.

"These heavily shrouded black holes are all around us," said Neil Gehrels, the Swift principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md., and a co-author of the new study. "But before Swift, they were just too faint and too obscured for us to see."

The findings appear in the Feb. 10 issue of The Astrophysical Journal.

Most large galaxies contain a giant central black hole, and those observed in the Swift study weigh in at about 100 million times the sun's mass. In an active galaxy, matter falling toward the supermassive black hole powers high-energy emissions so intense that two classes of active galaxies, quasars and blazars, rank as the most luminous objects in the universe.

The X-ray background led astronomers to suspect that active galaxies were undercounted. Astronomers could never be certain that they had detected most of even the closest active galaxies. Thick clouds of dust and gas surround the central black hole and screen out ultraviolet, optical and low-energy (or soft) X-ray light. While infrared radiation can make it through the material, it can be confused with warm dust in the galaxy's star-forming regions.

However, some of the black hole's more energetic X-rays do penetrate the shroud, and that's where Swift comes in.

Since 2004, Swift's Burst Alert Telescope (BAT), developed and operated at NASA Goddard, has been mapping the entire sky in hard X-rays with energies between 15,000 and 200,000 electron volts -- thousands of times the energy of visible light. Gradually building up its exposure year after year, the survey is now the largest, most sensitive and most complete census at these energies. It includes hundreds of active galaxies out to a distance of 650 million light-years.

From this sample, the researchers eliminated sources less than 15 degrees away from the dusty, crowded plane of our own galaxy. All active galaxies sporting an energetic particle jet were also not considered, leaving 199 galaxies.

Although there are many different types of active galaxy, astronomers explain the different observed properties based on how the galaxy angles into our line of sight. We view the brightest ones nearly face on, but as the angle increases, the surrounding ring of gas and dust absorbs increasing amounts of the black hole's emissions.

Astronomers assumed that there were many active galaxies oriented edgewise to us, but they just couldn't be detected because the disk of gas attenuates emissions too strongly.

"These extremely obscured active galaxies are very faint and difficult to find. Out of a sample of 199 sources, we detected only nine of them," said Davide Burlon, the lead author of the study and a graduate student at the Max Planck Institute for Extraterrestrial Physics in Munich.

"But even Swift's BAT has trouble finding these highly absorbed sources, and we know that the survey undercounts them," Burlon explained. "When we factored this in, we found that these shrouded active galaxies are very numerous, making up about 20 to 30 percent of the total."

"With Swift we have now quantified exactly how many active galaxies there are around us -- really, in our back yard," said Marco Ajello at the SLAC National Accelerator Laboratory, Menlo Park, Calif. "The number is large, and it agrees with models that say they are responsible for most of the X-ray background." If the numbers remain consistent at greater distances, when the universe was substantially younger, then there are enough supermassive black holes to account for the cosmic X-ray background.

The team then merged Swift BAT data with archived observations from its X-Ray Telescope in an effort to study how the intensity of the galaxies' emissions changed at different X-ray energies.

"This is the first time we could investigate the average spectrum of heavily absorbed active galaxies," said Ajello. "These galaxies are responsible for the shape of the cosmic X-ray background -- they create the peak of its energy."

All of this is consistent with the idea that the cosmic X-ray background is the result of emission from obscured supermassive black holes active when the universe was 7 billion years old, or about half its current age.

Swift, launched in November 2004, is managed by Goddard. It was built and is being operated in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and General Dynamics in Falls Church, Va.; the University of Leicester and Mullard Space Sciences Laboratory in the United Kingdom; Brera Observatory and the Italian Space Agency in Italy; plus additional partners in Germany and Japan.


Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Wednesday, January 19, 2011

The Orion Nebula: Still Full of Surprises

PR Image eso1103a
The Orion Nebula

The jewel in Orion’s sword

PR Video eso1103a
Zooming in on the Orion Nebula

PR Video eso1103b
Panning across the Orion Nebula

This ethereal-looking image of the Orion Nebula was captured using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory, Chile. This nebula is much more than just a pretty face, offering astronomers a close-up view of a massive star-forming region to help advance our understanding of stellar birth and evolution. The data used for this image were selected by Igor Chekalin (Russia), who participated in ESO’s Hidden Treasures 2010 astrophotography competition. Igor’s composition of the Orion Nebula was the seventh highest ranked entry in the competition, although another of Igor’s images was the eventual overall winner.

The Orion Nebula, also known as Messier 42, is one of the most easily recognisable and best-studied celestial objects. It is a huge complex of gas and dust where massive stars are forming and is the closest such region to the Earth. The glowing gas is so bright that it can be seen with the unaided eye and is a fascinating sight through a telescope. Despite its familiarity and closeness there is still much to learn about this stellar nursery. It was only in 2007, for instance, that the nebula was shown to be closer to us than previously thought: 1350 light-years, rather than about 1500 light-years.

Astronomers have used the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile to observe the stars within Messier 42. They found that the faint red dwarfs in the star cluster associated with the glowing gas radiate much more light than had previously been thought, giving us further insights into this famous object and the stars that it hosts. The data collected for this science project, with no original intention to make a colour image, have now been reused to create the richly detailed picture of Messier 42 shown here.

The image is a composite of several exposures taken through a total of five different filters. Light that passed through a red filter as well as light from a filter that shows the glowing hydrogen gas, were coloured red. Light in the yellow–green part of the spectrum is coloured green, blue light is coloured blue and light that passed through an ultraviolet filter has been coloured purple. The exposure times were about 52 minutes through each filter.

This image was processed by ESO using the observational data found by Igor Chekalin (Russia) [1], who participated in ESO’s Hidden Treasures 2010 astrophotography competition [2], organised by ESO in October–November 2010, for everyone who enjoys making beautiful images of the night sky using real astronomical data.

Notes

[1] Igor searched through ESO’s archive and identified datasets that he used to compose his image of Messier 42, which was the seventh highest ranked entry in the competition, out of almost 100 entries. His original work can be seen here. Igor Chekalin was awarded the first prize of the competition for his composition of Messier 78, and he also submitted an image of NGC3169, NGC3166 and SN 2003cg, which was ranked second highest.

[2] ESO’s Hidden Treasures 2010 competition gave amateur astronomers the opportunity to search through ESO’s vast archives of astronomical data, hoping to find a well-hidden gem that needed polishing by the entrants. Participants submitted nearly 100 entries and ten skilled people were awarded some extremely attractive prizes, including an all expenses paid trip for the overall winner to ESO's Very Large Telescope (VLT) on Cerro Paranal, in Chile, the world’s most advanced optical telescope. The ten winners submitted a total of 20 images that were ranked as the highest entries in the competition out of the near 100 images.

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. 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 VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links
ESO’s Hidden Treasures 2010 competition

Research papers:
http://adsabs.harvard.edu/abs/2009ApJS..183..261D
http://iopscience.iop.org/0004-637X/722/2/1092
Photos of La Silla Observatory

Contacts

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

Tuesday, January 18, 2011

Inclined Orbits Prevail in Exoplanetary Systems

Figure 1:Schematic Diagram of the Rossiter-McLaughlin (RM) Effect. Because of stellar rotation called “spin”, the stellar surface or “disk” has two parts: the approaching side (blue) and the receding side (red). During a planetary passage or “transit”, the observed radial velocity (RV) or speed of the star exhibits an apparent irregularity because of the stellar spin. When the transiting planet blocks the approaching side of the disk (blue), the star appears to be receding, and the RV shows an apparent red-shift. When the transiting planet conceals the receding side of the stellar disk, the star appears to be approaching, and the RV exhibits an apparent blue-shift. These anomalous RV shifts occur along the trajectory of the planet relative to the stellar disk.

The diagram shows two different trajectories. The left panels indicate alignment between the stellar spin axis and the planetary orbital axis while the right panels show misalignment of the two axes by 50 degrees. Therefore, precise measurements of RVs during a planetary transit enable an estimation of the angle between the two axes.


Figure 2:The RM Effect in the HAT-P-11 System Based on May 2010 Observations at the Subaru Telescope. The red line shows the RVs taken by the Subaru Telescope’s High Dispersion Spectrograph (HDS) while the blue one shows the published RVs taken with the Keck Telescope’s High Resolution Echelle Spectrometer (HIRES).

The solid black line represents the best-fit curve. Each RV error exhibited in this figure includes stellar jitter. The bottom panel shows the RV residuals from the best-fit curve. Residuals are measurements from the observations minus those for best-fit.


Figure 3:The RM Effect in the XO-4 System Based on January 2010 Observations at the Subaru Telescope.

Measurements of the RVs taken by the Subaru Telescope are shown in relation to two lines: 1) a solid line that shows the best-fit curve and 2) a dotted line that shows a model curve, assuming a perfect spin-orbit alignment. The bottom shows the residuals of the RV data from the best-fit curve.


Figure 4:Illustration of the HAT-P-11 System Based on Observations from Subaru Telescope. The planet orbits the star in a highly inclined orbit.

A research team led by astronomers from the University of Tokyo and the National Astronomical Observatory of Japan (NAOJ) has discovered that inclined orbits may be typical rather than rare for exoplanetary systems -- those outside of our solar system. Their measurements of the angles between the axes of the star's rotation (stellar rotational axis) and the planet's orbit (planetary orbital axis) of exoplanets HAT-P-11b and XO-4b demonstrate that these exoplanets' orbits are highly tilted. This is the first time that scientists have measured the angle for a small planet like HAT-P-11 b. The new findings provide important observational indicators for testing different theoretical models of how the orbits of planetary systems have evolved.

Since the discovery of the first exoplanet in 1995, scientists have identified more than 500 exoplanets, planets outside of our solar system, nearly all of which are giant planets. Most of these giant exoplanets closely orbit their host stars, unlike our solar system's giant planets, like Jupiter, that orbit the Sun from a distance. Accepted theories propose that these giant planets originally formed from abundant planet-forming materials far from their host stars and then migrated to their current close locations. Different migration processes have been suggested to explain close-in giant exoplanets.

Disk-planet interaction models of migration focus on interactions between the planet and its protoplanetary disk, the disk from which it originally formed. Sometimes these interactions between the protoplanetary disk and the forming planet result in forces that make the planet fall toward the central star. This model predicts that the spin axis of the star and the orbital axis of the planet will be in alignment with each other.

Planet-planet interaction models of migration have focused on mutual scatterings among giant planets. Migration can occur from planet scattering, when multiple planets scatter during the creation of two or more giant planets within the protoplanetary disk. While some of the planets scatter from the system, the innermost one may establish a final orbit very close to the central star. Another planet-planet interaction scenario, Kozai migration, postulates that the long-term gravitational interaction between an inner giant planet and another celestial object such as a companion star or an outer giant planet over time may alter the planet's orbit, moving an inner planet closer to the central star. Planet-planet migration interactions, including planet-planet scattering and Kozai migration, could produce an inclined orbit between the planet and the stellar axis.

Overall, the inclination of the orbital axes of close-in planets relative to the host stars' spin axes emerges as a very important observational basis for supporting or refuting migration models upon which theories of orbital evolution center. A research group led by astronomers from the University of Tokyo and NAOJ concentrated their observations with the Subaru Telescope on investigating these inclinations for two systems known to have planets: HAT-P-11 and XO-4. The group measured the Rossiter-McLaughlin (hereafter, RM) effect of the systems and found evidence that their orbital axes incline relative to the spin axes of their host stars.

The RM effect refers to apparent irregularities in the radial velocity or speed of a celestial object in the observer's line of sight during planetary transits. Unlike the spectral lines that are generally symmetrical in measures of radial velocity, those with the RM effect deviate into an asymmetrical pattern (see Figure 1). Such apparent variation in radial velocity during a transit reveals the sky-projected angle between the stellar spin axis and planetary orbital axis. Subaru Telescope has participated in previous discoveries of the RM effect, which scientists have investigated for approximately thirty-five exoplanetary systems thus far.

In January 2010, a research team led by the current team's astronomers from the University of Tokyo and the National Astronomical Observatory of Japan used the Subaru Telescope to observe the planetary system XO-4, which lies 960 light years away from Earth in the Lynx region. The system's planet is about 1.3 times as massive as Jupiter and has a circular orbit of 4.13 days. Their detection of the RM effect showed that the orbital axis of the planet XO-4 b tilts to the spin axis of the host star. Only the Subaru Telescope has measured the RM effect for this system so far.

In May and July 2010, the current research team conducted targeted observations of the HAT-P-11 exoplanetary system, which lies 130 light years away from the Earth toward the constellation Cygnus. The Neptune-sized planet HAT-P-11 b orbits its host star in a non-circular (eccentric) orbit of 4.89 days and is among the smallest exoplanets ever discovered. Until this research, scientists had only detected the RM effect for giant planets. The detection of the RM effect for smaller-sized planets is challenging because the signal of the RM effect is proportional to the size of the planet; the smaller the transiting planet, the fainter the signal.

;The team took advantage of the enormous light-collecting power of the Subaru Telescope's 8.2m mirror as well as the precision of its High Dispersion Spectrograph. Their observations not only resulted it the first detection of the RM effect for a smaller Neptune-sized exoplanet but also provided evidence that the orbital axis of the planet inclines to the stellar spin axis by approximately 103 degrees in the sky. A research group in the U.S. used the Keck Telescope and made independent observations of the RM effect of the same system in May and August 2010; their results were similar to those from the University of Tokyo/NAOJ team's May and July 2010 observations.

The current team's observations of the RM effect for the planetary systems HAT-P-11 and XO-4 have shown that they have planetary orbits highly tilted to the spin axes of their host stars. The latest observational results about these systems, including those obtained independently of the findings reported here, suggest that such highly inclined planetary orbits may commonly exist in the universe. The planet-planet scenario of migration, whether caused by planet-planet scattering or Kozai migration, rather than the planet-disk scenario could account for their migration to the present locations.

However, measurements of the RM effect for individual systems cannot decisively discriminate between the migration scenarios. Statistical analysis can help scientists determine which, if any, process of migration is responsible for the highly inclined orbits of giant planets. Since different migration models predict different distributions of the angle between the stellar axis and planetary orbit, developing a large sample of the RM effect enables scientists to support the most plausible migration process. Inclusion of the measurements of the RM effect for such a small-sized planet as HAT-P-11 b in the sample will play an important role in discussions of planetary migration scenarios.

Many research groups are planning to make observations of the RM effect with telescopes around the world. The current team and the Subaru Telescope will play an integral role in investigations to come. Continuous observations of transiting exoplanetary systems will contribute to an understanding of the formation and migration history of planetary systems in the near future.

NOTE 1:
This migration model is based on the Kozai cycle introduced in 1962 by Yoshihide Kozai, the founding Director General of the National Astronomical Observatory of Japan.

Monday, January 17, 2011

Islands of Stars in the River

NGC 1345
Credit: ESA/Hubble & NASA


The spiral galaxy NGC 1345 and its loose and ragged arms dominate this rich image from the NASA/ESA Hubble Space Telescope. It is a member of the Eridanus Galaxy Cluster — a group of about 70 galaxies that lies 85 million light-years away in the constellation of Eridanus (the River). This region of the night sky is well populated with bright galaxies, with the Fornax Cluster of galaxies also nearby on the celestial sphere, although the two clusters are actually separated by about 20 million light-years. Collectively, they are known as the Fornax Supercluster or the Southern Supercluster.

John Herschel discovered NGC 1345 in 1835 from South Africa. He described it as small and very faint and it is still far from easy to see it even with quite a large amateur telescope, where it appears as a small, circular fuzz.

Apart from the main galaxy that dominates the picture, lots more distant galaxies of many shapes and sizes can be seen in this image, some shining right through the foreground galaxy. NGC 1345 itself features an elongated bar extending from the nucleus and spiral arms that emanate outwards, making it a barred spiral type. Classifying galaxy shapes is an important part of astronomical research as it tells us much about how the Universe has evolved. But computers aren’t really ideal for the task; people are much better at recognising shapes, which is why a citizen-science project called Galaxy Zoo: Hubble is asking members of the public to help sift through the vast archive of images and classify galaxies by type. If you would like to join the cause, there’s a link to the project below.

This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images taken through a blue filter (F435W) were coloured blue and images through a near-infrared filter (F814W) were coloured red. The exposure times were 17.5 minutes per filter in total and the field of view is 3.2 by 1.6 arcminutes.

Links
http://www.galaxyzoo.org/

Saturday, January 15, 2011

M82: Chandra Images Torrent of Star Formation

M82
Credit NASA/CXC/Wesleyan/R.Kilgard et al.


A new Chandra X-ray Observatory image of Messier 82, or M82, shows the result of star formation on overdrive. M82 is located about 12 million light years from Earth and is the nearest place to us where the conditions are similar to those when the Universe was much younger with lots of stars forming.

M82 is a so-called starburst galaxy, where stars are forming at rates that are tens or even hundreds of times higher than in a normal galaxy. The burst of star birth may be caused by a close encounter or collision with another galaxy, which sends shock waves rushing through the galaxy. In the case of M82, astronomers think that a brush with its neighbor galaxy M81 millions of years ago set off this torrent of star formation.

M82 is seen nearly edge-on with its disk crossing from about 10 o'clock to about 4 o'clock in this image from Chandra (where low, medium, and high-energy X-rays are colored red, green, and blue respectively.) Among the 104 point-like X-ray sources in the image, eight so far have been observed to be very bright in X-rays and undergo clear changes in brightness over periods of weeks and years. This means they are excellent candidates to be black holes pulling material from companion stars that are much more massive than the Sun. Only a handful of such binary systems are known in the Local Group of galaxies containing the Milky Way and M31.

Chandra observations are also important in understanding the rapid rate at which supernovas explode in starburst galaxies like M82. When the shock waves travel through the galaxy, they push on giant clouds of gas and dust, which causes them to collapse and form massive stars. These stars, in turn, use up their fuel quickly and explode as supernovas. These supernovas produce expanding bubbles of multimillion-degree gas that extend for millions light years away from the galaxy's disk. These bubbles are seen as the large red areas to the upper right and lower left of the image.

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

Fast Facts for M82:

Scale: Image is 12.75 arcmin across (44,500 light years)
Category: Normal Galaxies & Starburst Galaxies, Black Holes
Coordinates (J2000) RA 09h 55m 50.70s | Dec +69° 40' 37.00
Constellation: Ursa Major
Observation Date: 7 pointings from Sep 20, 1999 to Jul 28, 2010
Observation Time: 142 hours 47 min (5 days, 22 hours, 47 min)
Obs. ID: 361, 10542-10545, 10925, 11800
Color Code: Red (0.3-1.1 keV); Green (0.7-2.2 keV); Blue (2.2-6 kev)
Instrument: ACIS
Also Known As: Cigar Galaxy
Distance Estimate: About 12 million light years

GRS 1915+105: Taking the Pulse of a Black Hole System

GRS 1915+105
Credit X-ray (NASA/CXC/Harvard/J.Neilsen et al); Optical (Palomar DSS2)


This optical and infrared image from the Digitized Sky Survey shows the crowded field around the binary system GRS 1915+105 (GRS 1915 for short) located near the plane of our Galaxy. The top-left inset shows a close-up of the Chandra image of GRS 1915 , and the bottom-right inset shows the remarkable "heartbeats" seen in the X-ray light from this system. Using Chandra and the Rossi X-ray Timing Explorer (RXTE), astronomers have discovered what drives these heartbeats and given new insight into the ways that black holes can regulate their intake and severely curtail their growth.

GRS 1915 contains a black hole about 14 times the mass of the Sun that is feeding off material from a nearby companion star. As the material swirls toward the black hole, a disk forms. The black hole in GRS 1915 has been estimated to rotate at the maximum possible rate, allowing material in the inner disk to orbit very close to the black hole -- at a radius only 20% larger than the event horizon -- where the material travels at 50% the speed of light.

Researchers monitored this black hole system with Chandra and RXTE over a period of eight hours. As they watched, GRS 1915 gave off a short, bright pulse of X-ray light approximately every 50 seconds. This type of rhythmic cycle closely resembles an electrocardiogram of a human heart -- though at a slower pace. It was previously known that GRS 1915 can develop such heartbeats, but researchers gained new understanding into what drives the beats, and used the pulses to figure out what controls how much material the black hole consumes from the RXTE data.

video

The astronomers also used Chandra's high-resolution spectrograph to study the effects of this heartbeat variation on regions of the disk very far from the black hole, at distances of about 100,000 to a million times the radius of the event horizon. By analyzing the Chandra spectrum, they found a very strong wind being driven away from the outer parts of the disk. The rate of mass expelled in this wind is remarkably high, as much as 25 times the maximum rate at which matter falls onto the black hole. This massive wind drains material from the outer disk and eventually causes the heartbeat variation to shut down.

Fast Facts for GRS 1915+105:

Scale: 5 degrees across (58 light years)
Category: Black Holes, Neutron Stars/X-ray Binaries
Coordinates: (J2000) RA 19h 15m 11.60s | Dec +10° 56' 44.00''
Constellation: Aquila
Observation Date: May 23rd, 2001
Observation Time: 8 hours 20 min
Obs. ID: 1945
Color Code: X-ray (Violet); Optical (Red, Green, Blue)
Instrument: ACIS/HETG
Distance Estimate: 40,000 light years