Thursday, July 30, 2009

Crashing comets not likely the cause of Earth's mass extinctions

A long-period comet called 2001 RX14 (Linear) turned up in images captured in 2002 by the Sloan Digital Sky Survey telescope in New Mexico. Credit: Mike Solontoi/UW

Scientists have debated how many mass extinction events in Earth's history were triggered by a space body crashing into the planet's surface. Most agree that an asteroid collision 65 million years ago brought an end to the age of dinosaurs, but there is uncertainty about how many other extinctions might have resulted from asteroid or comet collisions with Earth.
In fact, astronomers know the inner solar system has been protected at least to some degree by Saturn and Jupiter, whose gravitational fields can eject comets into interstellar space or sometimes send them crashing into the giant planets. That point was reinforced last week (July 20) when a huge scar appeared on Jupiter's surface, likely evidence of a comet impact.

New University of Washington research indicates it is highly unlikely that comets have caused any mass extinctions or have been responsible for more than one minor extinction event. The work also shows that many long-period comets that end up in Earth-crossing orbits likely originate from a region astronomers have long believed could not produce observable comets. A long-period comet takes from 200 years to tens of millions of years to make a single orbit of the sun.

"It was thought the long-period comets we see just tell us about the outer Oort Cloud, but they really give us a murky picture of the entire Oort Cloud," said Nathan Kaib, a University of Washington doctoral student in astronomy and lead author of a paper on the work being published July 30 in Science Express, the online edition of the journal Science. NASA and the National Science Foundation funded the work.

The Oort Cloud is a remnant of the nebula from which the solar system formed 4.5 billion years ago. It begins about 93 billion miles from the sun (1,000 times Earth's distance from the sun) and stretches to about three light years away (a light year is about 5.9 trillion miles). The Oort Cloud could contain billions of comets, most so small and distant as to never be observed.

There are about 3,200 known long-period comets. Among the best-remembered is Hale-Bopp, which was easily visible to the naked eye for much of 1996 and 1997 and was one of the brightest comets of the 20th century. By comparison, Halley's comet, which reappears about every 75 years, is perhaps the best-known comet, but it is a short-period comet, most of which are believed to originate in a different part of the solar system called the Kuiper Belt.

It has been believed that nearly all long-period comets that move inside Jupiter to Earth-crossing trajectories originated in the outer Oort Cloud. Their orbits can change when they are nudged by the gravity of a neighboring star as it passes close to the solar system, and it was thought such encounters only affect very distant outer Oort Cloud bodies.

It also was believed that inner Oort Cloud bodies could reach Earth-crossing orbits only during the rare close passage of a star, which would cause a comet shower. But it turns out that even without a star encounter, long-period comets from the inner Oort Cloud can slip past the protective barrier posed by the presence of Jupiter and Saturn and travel a path that crosses Earth's orbit.

In the new research, Kaib and co-author Thomas Quinn, a UW astronomy professor and Kaib's doctoral adviser, used computer models to simulate the evolution of comet clouds in the solar system for 1.2 billion years. They found that even outside the periods of comet showers, the inner Oort Cloud was a major source of long-period comets that eventually cross Earth's path.

By assuming the inner Oort Cloud as the only source of long-period comets, they were able to estimate the highest possible number of comets in the inner Oort Cloud. The actual number is not known. But by using the maximum number possible, they determined that no more than two or three comets could have struck Earth during what is believed to be the most powerful comet shower of the last 500 million years.

"For the past 25 years, the inner Oort Cloud has been considered a mysterious, unobserved region of the solar system capable of providing bursts of bodies that occasionally wipe out life on Earth," Quinn said. "We have shown that comets already discovered can actually be used to estimate an upper limit on the number of bodies in this reservoir."

With three major impacts taking place nearly simultaneously, it had been proposed that the minor extinction event about 40 million years ago resulted from a comet shower. Kaib and Quinn's research implies that if that relatively minor extinction event was caused by a comet shower, then that was probably the most-intense comet shower since the fossil record began.

"That tells you that the most powerful comet showers caused minor extinctions and other showers should have been less severe, so comet showers are probably not likely causes of mass extinction events," Kaib said.

He noted that the work assumes the area surrounding the solar system has remained relatively unchanged for the last 500 million years, but it is unclear whether that is really the case. It is clear, though, that Earth has benefitted from having Jupiter and Saturn standing guard like giant catchers mitts, deflecting or absorbing comets that might otherwise strike Earth.

"We show that Jupiter and Saturn are not perfect and some of the comets from the inner Oort Cloud are able to leak through. But most don't," Kaib said.

The work was funded by NASA and the National Science Foundation.

***

For more information, contact Kaib at 206-616-4549, 206-375-1048 or kaib@astro.washington.edu; or Quinn at 206-685-9009
or
trq@astro.washington.edu.

Source: University of Washington News and Information
uwnews@u.washington.edu
uwnews.org | uweek.org

NASA to Provide Web Updates on Objects Approaching Earth


PASADENA, Calif. -- NASA's Jet Propulsion Laboratory is introducing a new Web site that will provide a centralized resource for information on near-Earth objects - those asteroids and comets that can approach Earth. The "Asteroid Watch" site also contains links for the interested public to sign up for NASA's new asteroid widget and Twitter account.

"Most people have a fascination with near-Earth objects," said Don Yeomans, manager of NASA's Near-Earth Object Program Office at JPL. "And I have to agree with them. I have studied them for over three decades and I find them to be scientifically fascinating, and a few are potentially hazardous to Earth. The goal of our Web site is to provide the public with the most up-to-date and accurate information on these intriguing objects."

The new Asteroid Watch site is online at
http://www.jpl.nasa.gov/asteroidwatch .

It provides information on NASA's missions to study comets, asteroids and near-Earth objects, and also provides the basic facts and the very latest in science and research on these objects. News about near-Earth object discoveries and Earth flybys will be available and made accessible on the site via a downloadable widget and RSS feed. And for those who want to learn about their space rocks on the go, a Twitter feed is offered. "Asteroid Watch" also contains a link to JPL's more technical Near-Earth Objects Web site, where many scientists and researchers studying near-Earth objects go for information.

"This innovative new Web application gives the public an unprecedented look at what's going on in near-Earth space," said Lindley Johnson, program executive for the Near-Earth Objects Observation program at NASA Headquarters in Washington.

NASA supports surveys that detect and track asteroids and comets passing close to Earth. The Near-Earth Object Observation Program, commonly called "Spaceguard," also plots the orbits of these objects to determine if any could be potentially hazardous to our planet.

JPL is a division of the California Institute of Technology in Pasadena.

DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle@jpl.nasa.gov

Wednesday, July 29, 2009

Cosmic Dance Helps Galaxies Lose Weight

D'Onghia and her colleagues simulated encounters between galaxies to determine how dwarf galaxies lose much of their stars and gas. Top Row: Interaction between a dwarf galaxy orbiting around a larger galaxy with 100 times its mass. Only the stars are plotted. The upper left panel illustrates the initial set up where the two dwarfs approach one another. The upper middle panel gives the state of the system after 2 billion years, and the upper right panel shows the appearance of the galaxies after 7 billion years. Bottom Row: Shown is the orbit of the same small galaxy (in white) around the Milky Way today (in yellow), which has 10,000 times its mass.
Credit: Elena D'Onghia (CfA)

This simulation illustrates the resonant stripping process. Stars of a dwarf galaxy (at the bottom) orbiting around a larger system (at the top) are stripped off by gravity, forming long tails of stars. Credit: Elena D'Onghia (CfA)

A study published this week in the journal Nature offers an explanation for the origin of dwarf spheroidal galaxies. The research may settle an outstanding puzzle in understanding galaxy formation.

Dwarf spheroidal galaxies are small and very faint, containing few stars relative to their total mass. They appear to be made mostly of dark matter - a mysterious substance detectable only by its gravitational influence, which outweighs normal matter by a factor of five to one in the universe as a whole.

Astronomers have found it difficult to explain the origin of dwarf spheroidal galaxies. Previous theories require that dwarf spheroidals orbit near large galaxies like the Milky Way, but this does not explain how dwarfs that have been observed in the outskirts of the "Local Group" of galaxies could have formed.

"These systems are 'elves' of the early universe, and understanding how they formed is a principal goal of modern cosmology," said lead author Elena D'Onghia of the Harvard-Smithsonian Center for Astrophysics (CfA).

D'Onghia and her colleagues used computer simulations to examine two scenarios for the formation of dwarf spheroidals: 1) an encounter between two dwarf galaxies far from giants like the Milky Way, with the dwarf spheroidal later accreted into the Milky Way, and 2) an encounter between a dwarf galaxy and the forming Milky Way in the early universe.

The team found that the galactic encounters excite a gravitational process which they term "resonant stripping," leading to the removal of stars from the smaller dwarf over the course of the interaction and transforming it into a dwarf spheroidal.

"Like in a cosmic dance, the encounter triggers a gravitational resonance that strips stars and gas from the dwarf galaxy, producing long visible tails and bridges of stars," explained D'Onghia.

"This mechanism explains the most important characteristic of dwarf spheroidals, which is that they are dark-matter dominated," added co-author Gurtina Besla.

The long streams of stars pulled off by gravitational interactions should be detectable. For example, the recently discovered bridge of stars between Leo IV and Leo V, two nearby dwarf spheroidal galaxies, may have resulted from resonant stripping.

The paper describing these results was authored by Elena D'Onghia, Gurtina Besla, Thomas J. Cox, and Lars Hernquist, all of the CfA.Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Sharpest views of Betelgeuse reveal how supergiant stars lose mass

ESO PR Photo 27d/09
ESO PR Photo 27a/09
AA plume on Betelgeuse
(artist's impression with annotations)
This artist’s impression shows the supergiant star Betelgeuse as it was revealed thanks to different state-of-the-art techniques on ESO’s Very Large Telescope, which allowed two independent teams of astronomers to obtain the sharpest ever views of the supergiant star Betelgeuse. They show that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. These discoveries provide important clues to help explain how these mammoths shed material at such a tremendous rate. The scale in units of the radius of Betelgeuse as well as a comparison with the Solar System is also provided.

ESO PR Photo 27b/09
A close look at Betelgeuse
Image of the supergiant star Betelgeuse obtained with the NACO adaptive optics instrument on ESO’s Very Large Telescope. The use of NACO combined with a so-called “lucky imaging” technique, allowed the astronomers to obtain the sharpest ever image of Betelgeuse, even with Earth’s turbulent, image-distorting atmosphere in the way. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground. The image is based on data obtained in the near-infrared, through different filters. The field of view is about half an arcsecond wide, North is up, East is left.

ESO PR Photo 27c/09
Betelgeuse in Orion
(with annotations)
This collage shows the Orion constellation in the sky (Betelgeuse is identified by the marker), a zoom towards Betelgeuse, and the sharpest ever image of this supergiant star, which was obtained with NACO on ESO’s Very Large Telescope.

video
ESO PR Video 27a/09
Zoom in on Betelgeuse

Unveiling the true face of a behemoth

Using different state-of-the-art techniques on ESO's Very Large Telescope, two independent teams of astronomers have obtained the sharpest ever views of the supergiant star Betelgeuse. They show that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. These discoveries provide important clues to help explain how these mammoths shed material at such a tremendous rate.

Betelgeuse — the second brightest star in the constellation of Orion (the Hunter) — is a red supergiant, one of the biggest stars known, and almost 1000 times larger than our Sun [1]. It is also one of the most luminous stars known, emitting more light than 100 000 Suns. Such extreme properties foretell the demise of a short-lived stellar king. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight.

Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material — about the mass of the Sun — in only 10 000 years. Two teams of astronomers have used ESO’s Very Large Telescope (VLT) and the most advanced technologies to take a closer look at the gigantic star. Their combined work suggests that an answer to the long-open mass-loss question may well be at hand.

The first team used the adaptive optics instrument, NACO, combined with a so-called “lucky imaging” technique, to obtain the sharpest ever image of Betelgeuse, even with Earth’s turbulent, image-distorting atmosphere in the way. With lucky imaging, only the very sharpest exposures are chosen and then combined to form an image much sharper than a single, longer exposure would be.

The resulting NACO images almost reach the theoretical limit of sharpness attainable for an 8-metre telescope. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground.

“Thanks to these outstanding images, we have detected a large plume of gas extending into space from the surface of Betelgeuse,” says Pierre Kervella from the Paris Observatory, who led the team. The plume extends to at least six times the diameter of the star, corresponding to the distance between the Sun and Neptune.

“This is a clear indication that the whole outer shell of the star is not shedding matter evenly in all directions,” adds Kervella. Two mechanisms could explain this asymmetry. One assumes that the mass loss occurs above the polar caps of the giant star, possibly because of its rotation. The other possibility is that such a plume is generated above large-scale gas motions inside the star, known as convection — similar to the circulation of water heated in a pot.

To arrive at a solution, astronomers needed to probe the behemoth in still finer detail. To do this Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues used interferometry. With the AMBER instrument on ESO’s Very Large Telescope Interferometer, which combines the light from three 1.8-metre Auxiliary Telescopes of the VLT, the astronomers obtained observations as sharp as those of a giant, virtual 48-metre telescope. With such superb resolution, the astronomers were able to detect indirectly details four times finer still than the amazing NACO images had already allowed (in other words, the size of a marble on the ISS, as seen from the ground).

“Our AMBER observations are the sharpest observations of any kind ever made of Betelgeuse. Moreover, we detected how the gas is moving in different areas of Betelgeuse’s surface ― the first time this has been done for a star other than the Sun”, says Ohnaka.

The AMBER observations revealed that the gas in Betelgeuse's atmosphere is moving vigorously up and down, and that these bubbles are as large as the supergiant star itself. Their unrivalled observations have led the astronomers to propose that these large-scale gas motions roiling under Betelgeuse’s red surface are behind the ejection of the massive plume into space.

Note
[1] If Betelgeuse were at the centre of our Solar System it would extend out almost to the orbit of Jupiter, engulfing Mercury, Venus, Earth, Mars and the main asteroid belt.

More Information
This research was presented in two papers to appear in Astronomy and Astrophysics:
The close circumstellar environment of Betelgeuse: Adaptive optics spectro-imaging in the near-IR with VLT/NACO, by Pierre Kervella et al., and Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER, by Keiichi Ohnaka et al.

The teams are composed of P. Kervella, G. Perrin, S. Lacour, and X. Haubois (LESIA, Observatoire de Paris, France), T. Verhoelst (K. U. Leuven, Belgium), S. T. Ridgway (National Optical Astronomy Observatories, USA), and J. Cami (University of Western Ontario, Canada), and of K. Ohnaka, K.-H. Hofmann, T. Driebe, F. Millour, D. Schertl, and G. Weigelt (Max-Planck-Institute for Radio Astronomy, Bonn, Germany), M. Benisty (INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy), A. Chelli (LAOG, Grenoble, France), R. Petrov and F. Vakili (Lab. H. Fizeau, OCA, Nice, France), and Ph. Stee (Lab. H. Fizeau, OCA, Grasse, France).

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 14 countries: Austria, Belgium, 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. 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
Contacts
Pierre Kervella
Observatoire de Paris-Meudon, France
E-mail: Pierre.Kervella@obspm.fr
Phone: +33 1 45 07 79 66

Keiichi Ohnaka
Max-Planck Institute for Radio Astronomy
Bonn, Germany
E-mail: kohnaka@mpifr-bonn.mpg.de
Phone: +49 228 525 353

Olivier Hainaut
ESO Science Liaison
Garching, Germany
E-mail: ohainaut@eso.org
Phone: +49 89 3200 6752

ESO Press Officer in Chile: Valeria Foncea - +56 2 463 3123 - vfoncea@eso.org

National contacts for the media: http://www.eso.org/public/outreach/eson/

Monday, July 27, 2009

Galaxy Zoo Hunters Help Astronomers Discover Rare ‘Green Pea’ Galaxies

The Green Peas stuck out because of their small size and green color compared to the more common galaxies – such as the one on the bottom – that Galaxy Zoo users were used to seeing. (Photo: Carolin Cardamone and Sloan Digital Sky Survey.)

A team of astronomers has discovered a group of rare galaxies called the “Green Peas” with the help of citizen scientists working through an online project called Galaxy Zoo. The finding could lend unique insights into how galaxies form stars in the early universe.

The Galaxy Zoo users, who volunteer their spare time to help classify galaxies in an online image bank, came across a number of objects that stuck out because of their small size and bright green color. They dubbed them the Green Peas.

Employing the help of the volunteers to further analyze these strange new objects, the astronomers discovered that the Green Peas are small, compact galaxies forming stars at an incredibly high rate.

“These are among the most extremely active star-forming galaxies we’ve ever found,” said Carolin Cardamone, an astronomy graduate student at Yale and lead author of the paper, to be published in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

Of the one million galaxies that make up Galaxy Zoo’s image bank, the team found only 250 Green Peas. “No one person could have done this on their own,” Cardamone said. “Even if we had managed to look through 10,000 of these images, we would have only come across a few Green Peas and wouldn’t have recognized them as a unique class of galaxies.”

The galaxies, which are between 1.5 billion and 5 billion light years away, are 10 times smaller than our own Milky Way galaxy and 100 times less massive. But surprisingly, given their small size, they are forming stars 10 times faster than the Milky Way.

“They’re growing at an incredible rate,” said Kevin Schawinski, a postdoctoral associate at Yale and one of Galaxy Zoo’s founders. “These galaxies would have been normal in the early universe, but we just don’t see such active galaxies today. Understanding the Green Peas may tell us something about how stars were formed in the early universe and how galaxies evolve.”

The Galaxy Zoo volunteers who discovered the Green Peas—and who call themselves the “Peas Corps” and the “Peas Brigade”—began discussing the strange objects in the online forum. (The original forum thread was called “Give peas a chance.”)

Cardamone asked the volunteers—many of whom had no previous astronomy background or experience—to refine the sample of objects they detected in order to determine which were bona fide Green Peas and which were not, based on their colors. By analyzing their light, Cardamone determined how much star formation is taking place within the galaxies.

“This is a genuine citizen science project, where the users were directly involved in the analysis,” Schawinski said, adding that 10 Galaxy Zoo volunteers are acknowledged in the paper as having made a particularly significant contribution. “It’s a great example of how a new way of doing science produced a result that wouldn’t have been possible otherwise.”

Podcast on iTunes: Web Users To Write 'Hitchhiker’s Guide to the Galaxies'

The Galaxy Zoo project was launched in 2007 by a team of astronomers in the U.K and U.S., including Schawinski. To date, 230,000 volunteers from all over the world have helped classify one million images of galaxies taken by the Sloan Digital Sky Survey. Galaxy Zoo 2, which launched in February 2009, lets users more fully analyze 250,000 of the brightest galaxies.

Other authors of the paper include Marc Sarzi (University of Hertfordshire); Steven Bamford (University of Nottingham); Nicola Bennert (University of California, Santa Barbara); C. M. Urry (Yale University); Chris Lintott (University of Oxford); William Keel (University of Alabama); John Parejko (Drexel University); Robert Nichol and Daniel Thomas (University of Portsmouth); Dan Andreescu (LinkLab); M. Jordan Raddick, Alex Szalay and Jan VandenBerg (Johns Hopkins University); Anze Slosar (Lawrence Berkeley National Lab).

Citation: arxiv.org/abs/0907.4155

Press Contact: Suzanne Taylor Muzzin 203-432-8555

Friday, July 24, 2009

Hubble Captures Rare Jupiter Collision

Credit: NASA, ESA,
and H. Hammel (Space Science Institute, Boulder, Colo.),
and the Jupiter Impact Team

NASA scientists have interrupted the checkout and calibration of the Hubble Space Telescope to aim the recently refurbished observatory at a new expanding spot on the giant planet Jupiter. The spot, caused by the impact of a comet or an asteroid, is changing day to day in the planet's cloud tops.

For the past several days the world's largest telescopes have been trained on Jupiter. Not to miss the potentially new science in the unfolding drama 360 million miles away, Space Telescope Science Institute director Matt Mountain allocated discretionary time to a team of astronomers led by Heidi Hammel of the Space Science Institute in Boulder, Colo.

The Hubble picture, taken on July 23, is the sharpest visible-light picture taken of the impact feature. The observations were made with Hubble's new camera, the Wide Field Camera 3 (WFC3).

"This image of the impact on Jupiter is fantastic," said U.S. Senator Barbara A. Mikulski, D-Md., chairwoman of the Commerce, Justice and Science Appropriations Subcommittee. "It tells us that our astronauts and ground crew at the Goddard Space Flight Center successfully repaired the Hubble telescope."

"This is just one example of what Hubble's new, state-of-the-art camera can do, thanks to the STS-125 astronauts and the entire Hubble team," said Ed Weiler, associate administrator of NASA's Science Mission Directorate. "However, the best is yet to come!"

"Hubble's truly exquisite imaging capability has revealed an astonishing wealth of detail in the 2009 impact site," said Hammel. "By combining these images with our ground-based data at other wavelengths, our Hubble data will allow a comprehensive understanding of exactly what is happening to the impact debris. My sincerest congratulations and thanks to the team who created Wide Field Camera 3 and to the astronauts who installed it!"

Co-investigator Imke de Pater of the University of California at Berkeley said: "The combination of the Hubble data with mid-infrared images from the Gemini telescope will give us an insight into changes of the vertical structure of the atmosphere due to the impact."

Discovered by Australian amateur astronomer Anthony Wesley on Sunday, July 19, the spot was created when a small object plunged into Jupiter's atmosphere and disintegrated. The only other time in history such a feature has been seen on Jupiter was 15 years ago.

"This is strikingly similar to the comet Shoemaker Levy 9 that impacted Jupiter in July 1994," said team member Keith Noll of the Space Telescope Science Institute in Baltimore, Md.

"Since we believe this magnitude of impact is rare, we are very fortunate to see it with Hubble," added Amy Simon-Miller of NASA's Goddard Space Flight Center in Greenbelt, Md. She explained that the details seen in the Hubble view shows a lumpiness to the debris plume caused by turbulence in Jupiter's atmosphere. The spot is presently twice the length of the United States.

Simon-Miller estimated that the diameter of the object that slammed into Jupiter was at least the size of several football fields. The force of the explosion on Jupiter was thousands of times more powerful than the suspected comet or asteroid that exploded over the Tunguska River Valley in Siberia in June 1908.

The WFC3, installed by the STS-125 astronauts in May, is not yet fully calibrated. So while it is possible to obtain celestial images, the camera's full power cannot yet be realized for most observations. The WFC3 can still return meaningful science images that will complement the Jupiter pictures being taken with ground-based telescopes.

This is a natural color image of Jupiter as seen in visible light.

The members of the Jupiter Impact Team are:

Dr. Heidi B. Hammel (Space Science Institute, Boulder, Colo.)
Dr. Amy Simon-Miller (NASA's Goddard Space Flight Center, Greenbelt, Md.)
Dr. Keith S. Noll (Space Telescope Science Institute, Baltimore, Md.)
Dr. Michael H. Wong (Space Telescope Science Institute, Baltimore, Md.)
Prof. John T. Clarke (Boston University, Boston, Mass.)
Prof. Imke de Pater (University of California, Berkeley, Calif.)
Dr. Glenn S. Orton (Jet Propulsion Laboratory, Pasadena, Calif.)
Dr. Agustin Sanchez-Lavega (University of the Basque Country, Spain)

CONTACT
Dwayne Brown
HQ, Washington
202-358-1726
dwayne.c.brown@nasa.gov

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

The Story Behind the Discovery of “The Cygnus Bubble” PN G 75.5+1.7

A wide-field view of the Cygnus Bubble Nebula PN G75.5+1.7

The Cygnus Bubble Nebula PN G75.5+1.7 imaged in Hydrogen-Alpha (orange) and OIII (blue) wavelengths using the Kitt Peak 4-meter Mayall telescope on June 19, 2009. (north is to the left and east is down in this photo)
Photo credit: T. A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF

A close-up of the Cygnus Bubble Nebula PN G75.5+1.7

The nearly symmetrical shape of this elusive object is very similar to planetery nebula Abell 39, discovered by George Abell in 1966.
The circumference of PN G75.5+1.7 outlines a delicate edge beautifully illuminated and comparable to that of Abell 39. The interior of the nebula is unlike the partially opaque Abell 39 however, and only hints at the barest form of structure with faint wisps of OIII nebulosity
in its southern and eastern regions. Note the distinctly small blue star at the "center" of the Bubble. Could this be the central star of PN G75.5+1.7?
Photo credit: T. A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF

The first known observation of a planetary nebula was made by the famous comet hunter Charles Messier on July 12, 1764 when he discovered the Dumbbell Nebula M27 in the constellation Vulpecula. The English astronomer William Herschel quickly added to the list by ferreting out an additional 33 planetaries by the year 1794. Over the intervening years scores of additional nebula have been discovered by amateur and professional astronomers alike. Today they are still being found albeit predominately by professional search programs such as IPHAS and MASH, that data-mine the northern and southern galactic plane in wavelengths conducive to detecting these gems of the Milky Way. The use of large Earth-based telescopes these current programs employ in their research, coupled with the staggering surveys being conducted by satellites orbiting the planet, make finding a new “non-transient” deep sky object in the Milky Way galaxy or anywhere in the Universe by amateur astronomers a rare occurrence these days.

Almost 244 years to the day after Messier discovered M27, a new discovery was made in the constellation Cygnus with modest amateur equipment from the historic Mount Wilson Observatory, located high in the San Gabriel Mountains overlooking the Los Angeles Basin. Beginning on the night of 26 June 2008 and running through 06 July 2008, I was engaged in an ambitious project to digitally image a swath of the Milky Way from Gamma Cygni to the Crescent Nebula NGC 6888 in the Hydrogen-Alpha wavelength (656.3 nm), attempting to capture the beautifully intricate HII regions contained therein. The project, being a multi-night affair, was designed to image eight distinct and slightly overlapping sections of sky and stitch them together into a single, large mosaic using digital imaging techniques well known to most advanced amateur imagers. Excellent weather and exquisite seeing conditions allowed me to essentially complete the project on consecutive nights, finalizing data acquisition of Pane #7 on 05 July 2008 and Pane #8 on 06 July 2008. With these final two panes "in the bag" I completed data collection on a mosaic project having a total exposure time of 32 hours.

Exhausted from multiple late-night sessions, I nevertheless decided to immediately begin preliminary processing the last panes of the mosaic (Panes 7 and 8) to determine how they would “fit” into the finished product. Stacking and combining the twelve individual 20 minute frames of Pane #7 didn’t reveal anything particularly interesting in the faint background of that scene, my eye instead being naturally drawn to the ethereal Crescent Nebula NGC 6888 itself. I decided to do a non-linear histogram stretch on the image to closely examine it for any peculiarities. To my surprise, upon close examination I noticed the faint outline of what appeared to be a nearly symmetrical “bubble” embedded within a faint HII region just a mere one-half degree from NGC 6888. Believing this apparition was but an artifact of my post-processing or an internal reflection in my imaging train, I decided to investigate further by examining an image I had taken of that exact area a year earlier using a different optical configuration and camera orientation. Again, “stretching” the histogram of this earlier image (taken 19 July 2007), I noticed this odd looking object at the very same location. At that point I knew it wasn’t an artifact but indeed a real object of unknown provenance.

Discovering a new object in some sense is both a blessing and a curse. After the initial excitement of discovery wears off, the hard work begins. Though still tired from my late-night endeavors, I began what would become an exhaustive search for information on clues to the nature of this odd object I had found. Little did I know where my investigations would lead or to the amount of work that would be required to satisfy my curiosity and ultimately lead to that Eureka moment when I knew I had found something previously undiscovered. Poring over every catalog I could find related to objects of this type and encompassing this area of the Milky Way, I could not find a single reference to this object in the professional literature. My next avenue of research led me to investigate currently running professional programs mining the Milky Way for new discoveries of this type. Again, I drew a blank and became even more convinced the time was at hand to file a report with the International Astronomical Union (IAU) through the Central Bureau for Astronomical Telegrams (CBAT), which I did on 10 July 2008. Cutting to the quick, after filing initial and supplementary reports totaling 53 pages, spending many more hours investigating additional sources provided to me by Dr. Daniel Green of the IAU, allowing review time for the opinions of professionals with expertise in the field of planetary nebulae, and engaging in a cordial series of exchanges in defense of my claim, on 16 July 2009 the IAU issued Electronic Bulletin No. 1876 announcing my discovery of this new object.

I’ve learned a few things in the nearly one year between my filing of an initial report with the IAU and the release of Bulletin No. 1876. Perhaps the most important thing gleaned from the experience was that the IAU/CBAT is really geared more towards the reporting of “transient” objects such as comets and supernovae. In its own words,

"The CBAT is the official worldwide clearinghouse for new discoveries of comets, solar-system satellites, novae, supernovae, and other transient astronomical events. It aims to serve the astronomical community in the spirit of the mandate of the Smithsonian Institution: to aid in the increase and diffusion of knowledge; as such, together with its sister projects (the Minor Planet Center and the International Comet Quarterly), the CBAT serves to lead the SAO in this mandate in terms of public visibility."

The IAU is really not equipped to handle discoveries of a “non-transient” nature such as planetary nebulae. Thanks to the patient understanding and guidance of Dr. Daniel Green of the IAU however, I was nevertheless guided through the process of reporting and defending my discovery claim. I look upon this as a personal favor by Dr. Green and am forever indebted to him for his guidance over that long year. In hindsight, I now recognize that the more direct path to pursue in staking a claim of discovery is to publish the findings in a professional journal as soon as possible. That can be a daunting task for an amateur astronomer not familiar with or connected to the professional community; however it is the preferred method.

Finally, I’d like to leave fellow amateur astronomers with some general insight gained from this experience in the hopes of assisting them in pursuit of this noble hobby. One should never assume that he or she cannot make a contribution to the field of astronomy, believing that amateurs are not equipped to compete with professionals on any level. In this golden age of technology, amateur astronomers are being recognized by the professional community for their contributions. Compared to the level of relatively simple instrumentation available to amateur astronomers just a few decades ago, the powerful and technically advanced equipment of today can and does yield meaningful results. Digital imaging has opened a vast arena of research which amateurs have exploited, running the gamut from taking ‘pretty pictures” to photometric measurements of the periodic dimming of stars resulting from exosolar planet transits. For those like myself who are content with the aesthetic endeavor of producing “pretty pictures”, I urge you to critically scrutinize your images for anything unusual in the field of view before posting them on the Internet. You may find a hidden treasure buried deep among the ubiquitous stars on your image; a gem lying there for countless eons just waiting to be discovered.

Dave Jurasevich - starimager@sbcglobal.net
Source: StarImager

***

Kitt Peak Images of PN G75.5+1.7 - Click here to see those remarkable images.

More images: http://www.lostvalleyobservatory.com/page29crescentbubblenb/

Thursday, July 23, 2009

E0102-72.3: Adding a New Dimension to an Old Explosion

Credit X-ray (NASA/CXC/MIT/D.Dewey et al.
& NASA/CXC/SAO/J.DePasquale); Optical (NASA/STScI)

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Chandra X-ray Image
and Animation of E0102

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This image of the debris of an exploded star - known as supernova remnant 1E 0102.2-7219, or "E0102" for short - features data from NASA's Chandra X-ray Observatory. E0102 is located about 190,000 light years away in the Small Magellanic Cloud, one of the nearest galaxies to the Milky Way. It was created when a star that was much more massive than the Sun exploded, an event that would have been visible from the Southern Hemisphere of the Earth over 1000 years ago.

Chandra first observed E0102 shortly after its launch in 1999. New X-ray data have now been used to create this spectacular image and help celebrate the ten-year anniversary of Chandra's launch on July 23, 1999. In this latest image of E0102, the lowest-energy X-rays are colored orange, the intermediate range of X-rays is cyan, and the highest-energy X-rays Chandra detected are blue. An optical image from the Hubble Space Telescope (in red, green and blue) shows additional structure in the remnant and also reveals foreground stars in the field.

The Chandra image shows the outer blast wave produced by the supernova (blue), and an inner ring of cooler (red-orange) material. This inner ring is probably expanding ejecta from the explosion that is being heated by a shock wave traveling backwards into the ejecta. A massive star (not visible in this image) is illuminating the green cloud of gas and dust to the lower right of the image. This star may have similar properties to the one that exploded to form E0102.

Analysis of the Chandra spectrum gives astronomers new information about the geometry of the remnant, with implications for the nature of the explosion. The spectrum - which precisely separates X-rays of different energies - shows some material is moving away from Earth and some is moving toward us. When the material is moving away, its light is shifted toward the red end of the spectrum due to the so-called Doppler effect. Alternatively, when material is moving toward us, the light is bluer because of the same effect.

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A clear separation was detected between the red-shifted and blue-shifted light, leading astronomers to think that the appearance of E0102 is best explained by a model in which the ejecta is shaped like a cylinder that is being viewed almost exactly end-on (see animation above). The smaller red and blue cylinders represent faster moving material closer to the cylinder axis.

This model suggests that the explosion that created the E0102 remnant may itself have been strongly asymmetric, consistent with the rapid kicks given to neutron stars after supernova explosions. Another possibility is that the star exploded into a disk of material formed when material was shed from the equator of the pre-supernova red giant star. Such asymmetries have been observed in winds from lower mass red giants that form planetary nebulas.

Fast Facts for E0102-72.3:

Scale: Image is 2.85 arcmin across
Category: Supernovas & Supernova Remnants
Coordinates: (J2000) RA 01h 04m 1.50s | Dec -72° 01' 55.7''
Constellation: Tucana
Observation Date: 25 pointings between 12/10/2000 - 02/09/2008
Observation Time: 3 days 6 hours
Obs. ID: 1308, 1311, 1530-1531, 2843-2844, 2850-2851, 3519-3520, 3544-3545, 5123-5124, 5130-5131, 6042-6043, 6074-6075, 6758-6759, 6765, 8365, 9694
Color Code: X-ray (Blue, Cyan, Orange); Optical (Blue, Green, Red)
Instrument: ACIS
Also Known As: SN010102-72
Distance Estimate: Distance to SMC is 190,000 light years

NASA's Spitzer Images Out-of-this-World Galaxy

Credit: NASA/JPL-Caltech/The SINGS Team (SSC/Caltech)

NASA's Spitzer Space Telescope has imaged a wild creature of the dark — a coiled galaxy with an eye-like object at its center.

The galaxy, called NGC 1097, is located 50 million light-years away. It is spiral-shaped like our Milky Way, with long, spindly arms of stars. The "eye" at the center of the galaxy is actually a monstrous black hole surrounded by a ring of stars. In this color-coded infrared view from Spitzer, the area around the invisible black hole is blue and the ring of stars, white.

The black hole is huge, about 100 million times the mass of our sun, and is feeding off gas and dust along with the occasional unlucky star. Our Milky Way's central black hole is tame by comparison, with a mass of a few million suns.

"The fate of this black hole and others like it is an active area of research," said George Helou, deputy director of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena. "Some theories hold that the black hole might quiet down and eventually enter a more dormant state like our Milky Way black hole."

The ring around the black hole is bursting with new star formation. An inflow of material toward the central bar of the galaxy is causing the ring to light up with new stars.

"The ring itself is a fascinating object worthy of study because it is forming stars at a very high rate," said Kartik Sheth, an astronomer at NASA's Spitzer Science Center. Sheth and Helou are part of a team that made the observations.

In the Spitzer image, infrared light with shorter wavelengths is blue, while longer-wavelength light is red. The galaxy's red spiral arms and the swirling spokes seen between the arms show dust heated by newborn stars. Older populations of stars scattered through the galaxy are blue. The fuzzy blue dot to the left, which appears to fit snuggly between the arms, is a companion galaxy.

"The companion galaxy that looks as if it's playing peek-a-boo through the larger galaxy could have plunged through, poking a hole," said Helou. "But we don't know this for sure. It could also just happen to be aligned with a gap in the arms."

Other dots in the picture are either nearby stars in our galaxy, or distant galaxies.

This image was taken during Spitzer's "cold mission," which lasted more than five-and-a-half years. The telescope ran out of coolant needed to chill its infrared instruments on May 15, 2009. Two of its infrared channels will still work perfectly during the new "warm mission," which is expected to begin in a week or so, once the observatory has been recalibrated and warms to its new temperature of around 30 Kelvin (about minus 406 degrees Fahrenheit).


About the Object

Object name: NGC 1097, Arp 77
Object type: Galaxy
Position (J2000): RA: 02h 46m 19.00s Dec: -30° 16' 29.00"
Distance: 45,000,000 Light Years
Constellation: Fornax

Instrument: IRAC

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared array camera, which made the observations, was built by NASA's Goddard Space Flight Center, Greenbelt, Md. The instrument's principal investigator is Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

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

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Wednesday, July 22, 2009

Integral Disproves Dark Matter Origin for Mystery Radiation

The left-hand panel shows the glow of 511 keV gamma rays coming from the annihilation of electrons by their antimatter counterparts, the positrons. The map shows the entire sky, with the galactic centre at the middle. The emission can be seen extending towards the right-hand side of the map. The right-hand panel shows the distribution of hard low mass X-ray binary stars. This stellar population has a distribution that matches the extent of the 511 keV map.
Credits: ESA/ Integral/ MPE (G. Weidenspointner et al.)

This is an artist’s impression of ESA’s
orbiting gamma-ray observatory, Integral.
Credits: ESA

A team of researchers working with data from ESA’s Integral gamma-ray observatory has disproved theories that some form of dark matter explains mysterious radiation in the Milky Way.

That this radiation exists has been known since the 1970s, and several theories have been proposed to explain it. Integral’s unprecedented spectral and spatial resolution showed that it strongly peaks towards the centre of the Galaxy, with an asymmetry along the Galactic disc.

Several researchers have invoked a variety of dark matter to explain Integral’s observations. Dark matter is thought to exist throughout the Universe – undetectable matter that differs from the normal material that makes up stars, planets and us. It is also believed to be present within and around the Milky Way, in the form of a halo.

The recent study has found that the ‘positrons’ fuelling the radiation are not produced from dark matter but from an entirely different, and much less mysterious, source: massive stars explode and leave behind radioactive elements that decay into lighter particles, including positrons, the antimatter counterparts of electrons.

The reasoning behind the original hypothesis was that positrons, being electrically charged, would be affected by magnetic fields and thus would not be able to travel far. As the radiation was observed in places that did not match the known distribution of stars, dark matter was invoked as an alternative for the origin of the positrons.

But the recent finding by a team of astronomers led by Richard Lingenfelter at the University of California at San Diego, proves otherwise. The astronomers show that the positrons formed by radioactive decay of elements left behind after explosions of massive stars are, in fact, able to travel great distances, with many leaving the thin Galactic disc.

Taking this into account, dark matter is no longer required to explain what Integral saw. A better understanding of how positrons behave has explained the mysterious radiation in our Galaxy.

Read this story in detail on the ESA Science and Technology pages .

Tuesday, July 21, 2009

Jupiter Adds a Feature

Credit: Paul Kalas (UCB), Michael Fitzgerald (LLNL/UCB),
Franck Marchis (SETI Institute/UCB), James Graham (UCB)
This infrared image taken with Keck II shows the new feature observed on
Jupiter and its relative size compared to Earth.

Credit: Paul Kalas (UCB), Michael Fitzgerald (LLNL/UCB),
Franck Marchis (SETI Institute/UCB), James Graham (UCB)
This infrared image taken with Keck II shows the new feature observed on Jupiter.

Mauna Kea, Hawai’i—Jupiter’s got a brand new mark. Something slammed into the gas giant leaving a dark bruise in the planet’s atmosphere, scientists at Keck Observatory confirmed early on the morning of July 20 Hawaiian Standard Time.

The observation, made with the Keck II telescope, marks only the second time astronomers have seen such an impact on the planet. The first collision occurred 15 years ago, when more than 20 fragments of comet Shoemaker-Levy 9 (SL9) collided with Jupiter.

The SL9 impact events were well-studied in 1994, and many theories were subsequently developed based on the observations. “Now we have a chance to test these ideas on a brand new impact event,” said Paul Kalas, one of the University of California Berkeley (UCB) astronomers who helped observe the latest impact.

Kalas, along with Michael Fitzgerald of Lawrence Livermore National Lab and UCLA, happened to have observing time on the Keck II telescope early on the morning of Monday July 20, 2009. The two were searching for the Jupiter-like planet, Fomalhaut b, which orbits the star Fomalhaut. The star is located roughly 25 light years from Earth in the direction of the constellation Piscis Austrinus.

The astronomers decided to observe Jupiter after hearing of Australian amateur astronomer Anthony Wesley’s discovery of the planet’s new feature, which they read about on the blog of UCB and SETI Institute astronomer Franck Marchis. Together, the group of UC astronomers collaborated on how best to make the observations of the new feature. Fitzgerald then performed the observations with the help of Keck Observatory astronomer Al Conrad.

“The fact that [the feature] shows up so clearly means that it’s associated with high-altitude aerosols as seen in the Shoemaker-Levy impacts,” noted James Graham of UCB, who also assisted with the new observations as well as the observations taken during the SL9 event in 1994. According to the new data, an impact must have created Jupiter’s latest feature, the team of astronomers said.

Astronomers plan to conduct further observations using the Keck II telescope and its laser-guide-star adaptive optics system later this week.

New NASA Images Indicate Object Hits Jupiter

This image shows a large impact on Jupiter's south polar region captured on July 20, 2009, by NASA's Infrared Telescope Facility in Mauna Kea, Hawaii. Image credit: NASA/JPL/Infrared Telescope Facility. Enlarge Image

Scientists have found evidence that another object has bombarded Jupiter, exactly 15 years after the first impacts by the comet Shoemaker-Levy 9.

Following up on a tip by an amateur astronomer, Anthony Wesley of Australia, that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT (6 a.m. and noon EDT) scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using NASA's Infrared Telescope Facility at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact.

New infrared images show the likely impact point was near the south polar region, with a visibly dark "scar" and bright upwelling particles in the upper atmosphere detected in near-infrared wavelengths, and a warming of the upper troposphere with possible extra emission from ammonia gas detected at mid-infrared wavelengths.

"We were extremely lucky to be seeing Jupiter at exactly the right time, the right hour, the right side of Jupiter to witness the event. We couldn't have planned it better," said Glenn Orton, a scientist at JPL.

Orton and his team of astronomers kicked into gear early in the morning and haven't stopped tracking the planet. They are downloading data now and are working to get additional observing time on this and other telescopes.

This image was taken at 1.65 microns, a wavelength sensitive to sunlight reflected from high in Jupiter's atmosphere, and it shows both the bright center of the scar (bottom left) and the debris to its northwest (upper left).

"It could be the impact of a comet, but we don't know for sure yet," said Orton. "It's been a whirlwind of a day, and this on the anniversary of the Shoemaker-Levy 9 and Apollo anniversaries is amazing."

Shoemaker-Levy 9 was a comet that had been seen to break into many pieces before the pieces hit Jupiter in 1994.

Leigh Fletcher, a NASA postdoctoral fellow at JPL who worked with Orton during these latest observations said, "Given the rarity of these events, it's extremely exciting to be involved in these observations. These are the most exciting observations I've seen in my five years of observing the outer planets!"

The observations were made possible in large measure by the extraordinary efforts of the Infrared Telescope Facility staff, including telescope operator William Golisch, who adroitly moved three instruments in and out of the field during the short time the scar was visible on the planet, providing the wide wavelength coverage.

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

Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez@jpl.nasa.gov

Testing Relativity, Black Holes and Strange Attractors in the Laboratory

Through the optical-mechanical analogy, metamaterials and other advanced optical materials can be used to study such celestial phenomena as black holes, strange attractors and gravitational lenses. Here an air-GaInAsP metamaterial mimics a photon-sphere, one of the key black hole phenomena in its interactions with light.

Xiang Zhang has been one of the pioneers in the creation of artificial optical materials and their applications to such phenomena as negative refraction, electromagnetic invisibility devices and microscopy with super-resolution. (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)


Even Albert Einstein might have been impressed. His theory of general relativity, which describes how the gravity of a massive object, such as a star, can curve space and time, has been successfully used to predict such astronomical observations as the bending of starlight by the sun, small shifts in the orbit of the planet Mercury and the phenomenon known as gravitational lensing. Now, however, it may soon be possible to study the effects of general relativity in bench-top laboratory experiments.

Xiang Zhang, a faculty scientist with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and professor at the University of California Berkeley, lead a study in which it was determined that the interactions of light and matter with spacetime, as predicted by general relativity, can be studied using the new breed of artificial optical materials that feature extraordinary abilities to bend light and other forms of electromagnetic radiation.

“We propose a link between the newly emerged field of artificial optical materials to that of celestial mechanics, thus opening a new possibility to investigate astronomical phenomena in a table-top laboratory setting,” says Zhang. “We have introduced a new class of specially designed optical media that can mimic the periodic, quasi-periodic and chaotic motions observed in celestial objects that have been subjected to complex gravitational fields.”

A paper describing this work is now available on-line in the journal Nature Physics. The paper is titled: “Mimicking Celestial Mechanics in Metamaterials.” Co-authoring it with Zhang were his post-doctoral students Dentcho Genov and Shuang Zhang.

Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center, has been one of the pioneers in the creation of artificial optical materials. Last year, he and his research group made headlines when they fashioned unique metamaterials - composites of metals and dielectrics - that were able to bend light backwards, a property known as a negative refraction that is unprecedented in nature. More recently, he and his group fashioned a “carpet cloak” from nanostructured silicon that concealed the presence of objects placed under it from optical detection. These efforts not only suggested that true invisibility materials are within reach, Zhang said, but also represented a major step towards transformation optics that would “open the door to manipulating light at will.”

Now he and his research group have demonstrated that a new class of metamaterials called “continuous-index photon traps” or CIPTs can serve as broadband and radiation-free “perfect” optical cavities. As such, CIPTs can control, slow and trap light in a manner similar to such celestial phenomena as black holes, strange attractors and gravitational lenses. This equivalence between the motion of the stars in curved spacetime and propagation of the light in optical metamaterials engineered in a laboratory is referred to as the “optical-mechanical analogy.”

Zhang says that such specially designed metamaterials can be valuable tools for studying the motion of massive celestial bodies in gravitational potentials under a controlled laboratory environment. Observations of such celestial phenomena by astronomers can sometimes take a century of waiting.

“If we twist our optical metamaterial space into new coordinates, the light that travels in straight lines in real space will be curved in the twisted space of our transformational optics,” says Zhang. “This is very similar to what happens to starlight when it moves through a gravitational potential and experiences curved spacetime. This analogue between classic electromagnetism and general relativity, may enable us to use optical metamaterials to study relativity phenomena such as gravitational lens.”

In their demonstration studies, the team showed a composite of air and the dielectric Gallium Indium Arsenide Phosphide (GaInAsP). This material provided operation at the infrared spectral range and featured a high refractive index with low absorptions.

In their paper, Zhang and his coauthors cite as a particularly intriguing prospect for applying artificial optical materials to the optical-mechanical analogy the study of the phenomenon known as chaos. The onset of chaos in dynamic systems is one of the most fascinating problems in science and is observed in areas as diverse as molecular motion, population dynamics and optics. In particular, a planet around a star can undergo chaotic motion if a perturbation, such as another large planet, is present. However, owing to the large spatial distances between the celestial bodies, and the long periods involved in the study of their dynamics, the direct observation of chaotic planetary motion has been a challenge. The use of the optical-mechanical analogy may enable such studies to be accomplished in a bench-top laboratory setting on demand.

“Unlike astronomers, we will not have to wait 100 years to get experimental results,” Zhang says.

This research was supported by the U.S. Army Research Office and by the National Science Foundation which funds the UC Berkeley Nano-scale Science and Engineering Center.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE’s Office of Science and is managed by the University of California. Visit our Website at www.lbl.gov/

Contact: Lynn Yarris (510) 486-5375, lcyarris@lbl.gov

Scientist: Xiang Zhang, 510-643-4978, xiang@berkeley.edu

Thursday, July 16, 2009

First Light for ACAM - the WHT's New Imager / Spectrograph

A versatile new high-throughput imager and spectrograph, ACAM, was successfully commissioned on the William Herschel Telescope in June 2009, and is now available for use by the astronomical community.
ACAM was designed entirely by engineers and astronomers at ING, and was built in collaboration with Kevin Dee of Engineering & Project Solutions Ltd.

ACAM first-light image of spiral galaxy Messier 51. This is a composite of images through several different filters, with red colour highlighting regions where new stars are forming. The circular field of view is 8 arcmin across (about one quarter the angular diameter of the moon).
Credit: Pablo Rodríguez-Gil, Chris Benn, Andrew Cardwell. [ JPEG ].

ACAM can be used either for imaging (as above) through broad-band or narrow-band filters, or for taking spectra. In spectroscopy mode, the light from the object under study is dispersed by a VPH (volume-phase holographic) grating. For a 0.5-arcsec slit, the on-axis spectroscopic resolution is approximately 900 at a wavelength of 6000Å.

ACAM is mounted permanently at a folded-Cassegrain focus of the telescope, and can be deployed at a few minutes notice. This allows astronomers to switch quickly from the main camera in use for the night, to ACAM, for rapid follow-up of unusual events.

ACAM's exceptional versatility will allow astronomers to carry out a broad range of high-impact science projects which otherwise would not be possible with the WHT, in particular those requiring one or more of: rapid response; narrow-band imaging; wide field of view; low-resolution spectroscopy; or high camera throughput (very litte light is lost in the optics);
Example projects include:
  • Rapid follow-up of distant supernova explosions and gamma-ray bursts, to investigate the physics of these violent events.
  • Studies of large planets outside our solar system, e.g. time-series imaging of the host stars to search for changes in orbital periods hinting at the presence of earth-sized planets.
  • Narrow-band imaging of low-redshift galaxies, to discover where in galaxies the formation of new stars takes place.
  • Initial spectroscopic investigation of very faint objects discovered serendipitously with other WHT instruments.
ACAM being craned up to the WHT.
Credit: Javier Méndez (ING).

ACAM, now mounted permanently at one of the folded
Cassegrain foci of the WHT.
Credit: Javier Méndez (ING).

Some of the ACAM team at the telescope: Domingo Alvarez, Carlos Martin, Renee Pit, Kevin Dee, Diego Cano, Tibor Agocs, Juerg Rey, Sevando Rodriguez, Alan Chopping, Roberto Martinez.
Credit: Kevin Dee.

The ACAM first-light team: Carlos Martín, Craige Bevil, Tibor Agocs, Kevin Dee, Chris Benn, Andrew Cardwell, Pablo Rodríguez and Don Abrams. Credit: Pablo Rodríguez (ING).