Thursday, May 31, 2012

ALMA Turns its Eyes to Centaurus A

The radio galaxy Centaurus A, as seen by ALMA

PR Image eso1221b
The strange galaxy Centaurus A in the constellation of Centaurus

Videos

PR Video eso1222a
Zooming in on the radio galaxy Centaurus A, as seen by ALMA

Panning over the radio galaxy Centaurus A, as seen by ALMA

Image Comparison eso1222a
The radio galaxy Centaurus A, as seen by ALMA

A new image of the centre of the distinctive galaxy Centaurus A, made with the Atacama Large Millimeter/submillimeter Array (ALMA), shows how the new observatory allows astronomers to see through the opaque dust lanes that obscure the galaxy’s centre, with unprecedented quality. ALMA is currently in its Early Science phase of observations and is still under construction, but is already the most powerful telescope of its kind. The observatory has just issued the Call for Proposals for its next cycle of observations, in which the growing telescope will have increased capabilities.

Centaurus A [1] is a massive elliptical radio galaxy — a galaxy which emits strong radio waves — and is the most prominent, as well as by far the nearest, radio galaxy in the sky [2]. Centaurus A has therefore been observed with many different telescopes. Its very luminous centre hosts a supermassive black hole with a mass of about 100 million times that of the Sun.

In visible light, a characteristic feature of the galaxy is the dark band that obscures its centre (see for example eso1221). This dust lane harbours large amounts of gas, dust and young stars. These features, together with the strong radio emission, are evidence that Centaurus A is the result of a collision between a giant elliptical galaxy, and a smaller spiral galaxy whose remains form the dusty band.

To see through the obscuring dust in the central band, astronomers need to observe using longer wavelengths of light. This new image of Centaurus A combines observations at wavelengths around one millimetre, made with ALMA, and observations in near-infrared light. It thus provides a clear view through the dust towards the galaxy’s luminous centre.

The new ALMA observations, shown in a range of green, yellow and orange colours, reveal the position and motion of the clouds of gas in the galaxy. They are the sharpest and most sensitive such observations ever made. ALMA was tuned to detect signals with a wavelength around 1.3 millimetres, emitted by molecules of carbon monoxide gas. The motion of the gas in the galaxy causes slight changes to this wavelength, due to the Doppler effect [3]. The motion is shown in this image as changes in colour. Greener features trace gas coming towards us while more orange features depict gas moving away. We can see that the gas to the left of the centre is moving towards us, while the gas to the right of the centre is moving away from us, indicating that the gas is orbiting around the galaxy.

The ALMA observations are overlaid on a near-infrared image of Centaurus A obtained with the SOFI instrument attached to the ESO New Technology Telescope (NTT). The image was processed using an innovative technique that removes the screening effect of the dust (eso0944). We see a clear ring of stars and clusters glowing in a golden colour, the tattered remains of the spiral galaxy being ripped apart by the gravitational pull of the giant elliptical galaxy.

The alignment between the ring of stars seen by the NTT in infrared light and the gas seen by ALMA at millimetre wavelengths highlights different aspects of similar structures in the galaxy. This is an example of how observations with other telescopes can complement these new observations from ALMA.

Construction of ALMA, on the Chajnantor Plateau in northern Chile, will be completed in 2013, when 66 high-precision antennas will be fully operational. Half of the antennas have already been installed (see ann12035). Early scientific observations with a partial array began in 2011 (see eso1137), and are already producing outstanding results (see for example eso1216). The ALMA observations of Centaurus A shown here were taken as part of the Commissioning and Science Verification phase of the telescope.

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

Notes

[1] This galaxy is called Centaurus A because it was the first major source of radio waves discovered in the constellation of Centaurus, in the 1950s. It is also referred as NGC 5128. The galaxy was discovered by British astronomer James Dunlop on 4 August 1826.

[2] Centaurus A lies about 12 million light-years away in the southern constellation of Centaurus (The Centaur).

[3] The Doppler effect is the change in wavelength of a wave for an observer moving relative to the source of the wave. Molecules in gas clouds in space emit light at well-defined wavelengths, and so the motion of these clouds leads to slight changes in the wavelengths that are detected.

More information

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive 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 two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Contacts

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

Wednesday, May 30, 2012

Stellar Archaeology Traces Milky Way's History

Credit: NASA, ESA, and A. Feild (STScI)

Credit: NASA,ESA, and A. Feild and J. Kalirai (STScI)

Unfortunately, stars don't have birth certificates. So, astronomers have a tough time figuring out their ages. Knowing a star's age is critical for understanding how our Milky Way galaxy built itself up over billions of years from smaller galaxies.

Jason Kalirai of the Space Telescope Science Institute and The Johns Hopkins University's Center for Astrophysical Sciences, both in Baltimore, Md., has found the next best thing to a star's birth certificate. Using a new technique, Kalirai probed the burned-out relics of Sun-like stars, called white dwarfs, in the inner region of our Milky Way galaxy's halo. The halo is a spherical cloud of stars surrounding our galaxy's disk.

Those stars, his study reveals, are 11.5 billion years old, younger than the first generation of Milky Way stars. They formed more than 2 billion years after the birth of the universe 13.7 billion years ago. Previous age estimates, based on analyzing normal stars in the inner halo, ranged from 10 billion to 14 billion years.

Kalirai's study reinforces the emerging view that our galaxy's halo is composed of a layer-cake structure that formed in stages over billions of years.

"One of the biggest questions in astronomy is, when did the different parts of the Milky Way form?" Kalirai said. "Sun-like stars live for billions of years and are bright, so they are excellent tracers, offering clues to how our galaxy evolved over time. However, the biggest hindrance we have in inferring galactic formation processes in the Milky Way is our inability to measure accurate ages of Sun-like stars. In this study, I chose a different path: I studied stars at the end of their lives to determine their masses and then connected those masses to the ages of their progenitors. Given the nature of these dead stars, their masses are easier to measure than Sun-like stars."

Kalirai targeted white dwarfs in the galaxy's halo because those stars are believed to be among the galaxy's first homesteaders. Some of them are almost as old as the universe itself. These ancient stars provide a fossil record of our Milky Way's infancy, possessing information about our galaxy's birth and growth. "The Milky Way's halo represents the premier hunting ground in which to unravel the archaeology of when and how the galaxy's assembly processes occurred," Kalirai explained.

His results will appear online May 30 in a letter to the journal Nature.

White dwarfs divulge their properties so freely because they have a distinct spectral signature. Kalirai analyzed their signatures using archival spectroscopic data from the European Southern Observatory's Very Large Telescope at the Paranal Observatory in Chile. The spectroscopic data are part of the SN Ia Progenitor Survey (SPY), a census of white dwarf stars in the Milky Way. Spectroscopy divides light into its constituent colors, yielding information about a star's characteristics, including its mass and temperature. In his study, Kalirai first analyzed the spectra of several newly minted white dwarfs in the galaxy's inner halo to measure their masses. "The hottest white dwarfs are the descendants of Sun-like stars that have just extinguished their hydrogen fuel," he explained. "The masses of these white dwarfs are proportional to the masses of their progenitors, and we can use that mass to establish the age of the parent stars."

To measure the halo's age, Kalirai compared the masses of the halo stars with those of six newly formed white dwarfs in the ancient globular star cluster M4. Fortunately, the cluster is one of Hubble's favorite targets, and astronomers have a reliable age for when it formed, 12.5 billion years ago. Kalirai found these dead cluster stars in archival visible-light images of nearly 2,000 white dwarfs taken by the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope.

He applied the same techniques that he used on the halo white dwarfs to these cluster white dwarfs. The spectroscopic observations for these stellar remnants came from the W.M. Keck Observatory in Hawaii. His measurements revealed that the halo white dwarfs are heavier than those in M4, indicating the progenitor stars that are evolving into white dwarfs today are also heavier. Therefore, these stars are younger than the M4 stars. More massive stars consume their hydrogen fuel at a faster rate and therefore end their lives more quickly than lighter-weight stars.

Although Kalirai's result is based on a small sample of stars, it does support recent work proposing that the halo is composed of two different populations of stars.

According to the research, the Milky Way's construction schedule began with the oldest globular star clusters and dwarf galaxies, which formed a few hundred million years after the big bang, settling into what is now the galaxy's halo. These populations merged over billions of years to form the structure of our Milky Way. Stars in the inner halo were born during the assembly process. Over time, the Milky Way gobbled up older dwarf galaxies that formed less than 2 billion years after the big bang. Their ancient stars settled into the outskirts of the halo, creating the outer halo.

"In the previous work, the inner population was shown to be different from the outer population in terms of the velocities and chemical abundances of the stars," Kalirai said. "There were no constraints, however, on whether there was an age difference between the two populations. Now, our work suggests an age for the inner halo stars.

"We know some of the remote globular clusters in the outer halo are much older than the inner halo stars, perhaps around 13.5 billion years old," Kalirai contined. "So, our prediction is that if you find white dwarfs in the outer halo, they would have formed from older generations of Sun-like stars. The present day masses of stars in the generation that are now forming white dwarfs would be lower, and therefore the white dwarf masses — which we can measure — will also be lower."

Kalirai hopes to apply his new technique on more halo white dwarfs in his quest to help uncover our galaxy's history.

"One of the interesting questions about the inner halo stars is, did all of them form at the same time, or did they form over a span of time?" Kalirai said. "A sample of 20 to 30 white dwarfs would allow us to see if the inferred ages from the white dwarf masses span from 11 billion to 13 billion years. That could tell us that the accretion events that helped build up the Milky Way kept happening for several billion years, as opposed to all predominantly happening at one epoch."

CONTACT

Donna Weaver
Space Telescope Science Institute, Baltimore, Md.
410-338-4493
dweaver@stsci.edu

Jason Kalirai
Space Telescope Science Institute, Baltimore, Md.
410-338-4747
jkalirai@stsci.edu

Tuesday, May 29, 2012

Ghostly Gamma-ray Beams Blast from Milky Way's Center

This artist's conception shows an edge-on view of the Milky Way galaxy. Newly discovered gamma-ray jets (pink) extend for 27,000 light-years above and below the galactic plane, and are tilted at an angle of 15 degrees. Previously known gamma-ray bubbles are shown in purple. The bubbles and jets suggest that our galactic center was much more active in the past than it is today. Credit: David A. Aguilar (CfA).

Cambridge, MA - As galaxies go, our Milky Way is pretty quiet. Active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material, and often spit twin jets in opposite directions. In contrast, the Milky Way's center shows little activity. But it wasn't always so peaceful. New evidence of ghostly gamma-ray beams suggests that the Milky Way's central black hole was much more active in the past.

"These faint jets are a ghost or after-image of what existed a million years ago," said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of a new paper in the Astrophysical Journal.

"They strengthen the case for an active galactic nucleus in the Milky Way's relatively recent past," he added.

The two beams, or jets, were revealed by NASA's Fermi space telescope. They extend from the galactic center to a distance of 27,000 light-years above and below the galactic plane. They are the first such gamma-ray jets ever found, and the only ones close enough to resolve with Fermi.

The newfound jets may be related to mysterious gamma-ray bubbles that Fermi detected in 2010. Those bubbles also stretch 27,000 light-years from the center of the Milky Way. However, where the bubbles are perpendicular to the galactic plane, the gamma-ray jets are tilted at an angle of 15 degrees. This may reflect a tilt of the accretion disk surrounding the supermassive black hole.

"The central accretion disk can warp as it spirals in toward the black hole, under the influence of the black hole's spin," explained co-author Douglas Finkbeiner of the CfA. "The magnetic field embedded in the disk therefore accelerates the jet material along the spin axis of the black hole, which may not be aligned with the Milky Way."

The two structures also formed differently. The jets were produced when plasma squirted out from the galactic center, following a corkscrew-like magnetic field that kept it tightly focused. The gamma-ray bubbles likely were created by a "wind" of hot matter blowing outward from the black hole's accretion disk. As a result, they are much broader than the narrow jets.

Both the jets and bubbles are powered by inverse Compton scattering. In that process, electrons moving near the speed of light collide with low-energy light, such as radio or infrared photons. The collision increases the energy of the photons into the gamma-ray part of the electromagnetic spectrum.

The discovery leaves open the question of when the Milky Way was last active. A minimum age can be calculated by dividing the jet's 27,000-light-year length by its approximate speed. However, it may have persisted for much longer.

"These jets probably flickered on and off as the supermassive black hole alternately gulped and sipped material," said Finkbeiner.

It would take a tremendous influx of matter for the galactic core to fire up again. Finkbeiner estimates that a molecular cloud weighing about 10,000 times as much as the Sun would be required.

"Shoving 10,000 suns into the black hole at once would do the trick. Black holes are messy eaters, so some of that material would spew out and power the jets," he said.

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

Monday, May 28, 2012

The Anatomy of a Stellar Outflow

A Hubble image of a jet of emission from a young star. A new paper reports that infrared spectra of a jet has uncovered a rich trove of diagnostic emission lines from shock-excited molecules and atoms. Credit: Reipurth, NASA, and HST.

Astronomers used to think that star formation simply involved the gradual coalescence of material under the influence of gravity. No longer. Making a new star is a complex process, among other things assembling a circumstellar disk (possibly preplanetary in nature) and at the same time ejecting material as bipolar jets perpendicular to those disks. These outflows help the young star balance its growth as new material accretes, but at the same time they disrupt the environment. Although jets from young stars have been known for over twenty years, their influences on the environment have remained uncertain, in part because the dusty natal clouds in which stars form obscure optical light.

SAO astronomers Achim Tappe, Jan Forbrich, and Charlie Lada, with two colleagues, used the spectrometer on the Spitzer Space Telescope to probe one relatively nearby, young stellar outflow. It had already been known that this fast-moving jet, as it plowed into the medium, shocked the gas; the process is much the same as when a jet plane moves faster than the speed of sound and creates a shock wave. But for young stellar outflow, the particulars were mostly mysterious. The scientists discovered in the infrared spectra a rich trove of bright emission features from at least seven different molecules excited by the shock - molecular hydrogen, water, carbon dioxide, carbon monoxide, OH, HD, and one ionized species of HCO. Numerous atomic lines were also observed.

The astronomers concluded that the shock has distinctive regions along its length as it plows through the natal cloud at velocities of about 40 kilometers per second. At the very tip, where the jet suddenly encounters ambient gas and slows down, there is ionized material and strong molecular hydrogen emission; closer to the star the gas temperatures and densities vary in systematic ways as previously excited gas begins to cool off. Bright knots are seen all along the jet's path, either the result of ejected hot clumps or previously existing clumps that were shocked when the jet passed. The new paper is among the first to discover and analyze the complex infrared radiation from shocks around new-born stars, and it helps open the door to new methods of probing the environment of star formation.

The Swan and the Butterfly

NGC 7026
Credit:
ESA/Hubble & NASA
Acknowledgement: Linda Morgan-O'Connor

This image from the NASA/ESA Hubble Space Telescope shows NGC 7026, a planetary nebula. Located just beyond the tip of the tail of the constellation of Cygnus (The Swan), this butterfly-shaped cloud of glowing gas and dust is the wreckage of a star similar to the Sun.

Planetary nebulae, despite their name, have nothing to do with planets. They are in fact a relatively short-lived phenomenon that occurs at the end of the life of mid-sized stars. As a star’s source of nuclear fuel runs out, its outer layers are puffed out, leaving only the hot core of the star behind. As the gaseous envelope heats up, the atoms in it are excited, and it lights up like a fluorescent sign.

Fluorescent lights on Earth get their bright colours from the gases they are filled with. Neon signs, famously, produce a bright red colour, while ultraviolet lights (black lights) typically contain mercury. The same goes for nebulae: their vivid colours are produced by the mix of gases present in them.

This image of NGC 7026 shows starlight in green, light from glowing nitrogen gas in red, and light from oxygen in blue (in reality, this appears green, but the colour in this image has been shifted to increase the contrast).

As well as visible light, NGC 7026 emits X-ray radiation, and has been studied by ESA’s XMM-Newton space telescope. X-rays are a result of the extremely high temperatures of the gas in NGC 7026.

This image was produced by the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. The image is 35 by 35 arcseconds.

A version of this image was entered into the Hubble’s Hidden Treasures Competition by contestant Linda Morgan-O'Connor. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public.

Friday, May 25, 2012

Lying in Wait for WIMPs

The Bullet Cluster of galaxies is shown in visible light, x-ray emission (pink), and the calculated distribution of invisible dark matter (blue). Dark matter can be measured on the cosmic scale by its gravitational effects, but no one knows what it is. WIMPs, weakly interacting massive particles, are the leading candidate. (Images NASA and Chandra X-Ray Observatory)

With LUX ZEPLIN Berkeley Lab researchers seek to increase the sensitivity of LUX, the most sensitive search for dark matter yet, by orders of magnitude


Although it’s invisible, dark matter accounts for at least 80 percent of the matter in the universe. No one knows what it is, but most scientists would bet on weakly interacting massive particles, or WIMPs.

LUX, the Large Underground Xenon detector at the Sanford Underground Research Facility in the Black Hills of South Dakota, is calling that bet with a titanium bottle holding 350 kilograms of liquid xenon, placed in a cavern 4,850 feet down in the former Homestake gold mine. LUX is a trap set for dark-matter WIMPs.

The LUX Collaboration is led by Rick Gaitskell of Brown University and Dan McKinsey of Yale University and brings together over 70 researchers from 14 institutions, many with extensive previous experience in detecting weakly interacting particles. Participants from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) contribute expertise from such fruitful neutrino experiments as the Sudbury Neutrino Observatory (SNO), the Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND), and the Daya Bay Reactor Neutrino Experiment.

As the lead institution within the Department of Energy for the Sanford Underground Research Facility, Berkeley Lab is making other contributions that are less specific but no less important. Kevin Lesko of the Lab’s Nuclear Science Division heads DOE’s Sanford Lab program. Since the early 2000s he’s championed the Homestake mine as the best site for this kind of research, and has spearheaded planning and development for the overall facility as well as technical preparations for specific experiments, including LUX.

“The LUX experiment and its proposed follow-on, LUX ZEPLIN, bring together a very strong collaboration, experienced in creating and operating detectors with superbly limited instrumental backgrounds,” says Lesko. “We give the collaboration extremely well-shielded facilities – 4,850 feet of rock above the detector to screen out cosmic rays, plus a surrounding rock formation that’s a factor of 10 to 20 lower in radioactivity than other underground locations – including even those that are deeper than Homestake.”

LUX is described at length in the April 2012 issue of symmetry magazine, online at http://www.symmetrymagazine.org/cms/?pid=1000939.

Lighting up the dark matter


The name “weakly interacting massive particle” is a near tautology. Dark matter has to be massive: its gravitational effects are most obvious in the shape and motion of galaxies. Yet if it interacted with atomic nuclei via the strong force, or with any matter at all via electromagnetism, it wouldn’t be dark in the first place.

A WIMP detector has to be big enough to catch at least a few interactions a year. Just as important, the detector has to pinpoint these interactions. For neutrinos – which are WIMP-like, but have miniscule mass and move at near light speed – the detector can be as simple as a large volume of water in which debris from neutrino collisions moves faster than the speed of light in water, leaving a trail of easily detected Cherenkov radiation.

By contrast, WIMPs may be tens to hundreds of times more massive than protons, dawdling along at a couple of hundred kilometers a second. Liquid xenon makes a wide target for WIMPs, because xenon atoms have a large nucleus (up to 142 nucleons), are readily ionized when struck, and are good scintillators.

LUX’s 350 kilograms of liquid xenon are held in a cylindrical titanium tank and cooled to minus 108 degrees Celsius. Above the liquid xenon is a thin space filled with xenon gas. When struck by an incoming particle, a liquid-xenon atom sheds the collision energy as a faint flash of light, which is picked up by photomultiplier tubes at the bottom and top of the detector. The electrons knocked loose in the collision are pulled straight toward the top of the tank by a strong electric field.

Xenon gas is also a good scintillator, and as the electrons are pulled into the gas they stimulate a brighter flash of light that marks the location of the collision in two side-to-side dimensions. The third dimension, depth, is supplied by the travel time between the first and second flashes, which reveals how deep in the tank the collision occurred. This method of reconstructing particle interactions in three dimensions is akin to the principle of the Time Projection Chamber, a widely used type of particle detector invented by Berkeley Lab physicist David Nygren in the 1970s.

The brightness of the two flashes reveals the energy of the collision, plus information about the kind of collision that produced it. WIMPs will have a distinctive signature. For example, unlike neutrons, the chances are nil that after hitting one nucleus a weakly interacting particle will hit another on the bounce.

The main challenge is to achieve a low enough background so that a WIMP signal isn’t swamped by flashes from cosmic-ray debris or local radioactivity. The near-mile of rock above the Davis Campus filters out most of the cosmic rays. Submersion in a 72,000-gallon tank of water, plus other shielding, protects the xenon detector from natural radioactivity in the mine’s surrounding rock. Remaining backgrounds are primarily from radioactivity in the xenon detector components themselves, which are carefully chosen to have radioactivity as low as possible.

Setting a bigger trap


Berkeley Lab researchers are among the leaders of the proposed next stage of the dark matter search at the Davis Campus. In many ways LUX ZEPLIN is a scaled-up version of LUX. The infrastructure that supports LUX, including the huge, eight-meters-in-diameter water tank that surrounds it, was deliberately built with an LZ-scale experiment in mind.

Murdock “Gil” Gilchriese and Bill Edwards, of UC Berkeley and Berkeley Lab’s Physics Division, share project-manager responsibility for LZ, a collaboration among members of LUX and the similar dark matter-search ZEPLIN (a tortuous acronym for “zoned proportional scintillation in liquid noble gases”). Successive iterations of ZEPLIN ran in England from the late 1990s to 2011, and ZEPLIN‑III achieved the best-ever background discrimination for a two-phase (liquid and gas) experiment that used a noble element as a detector.

The LUX detector (left) is filled with liquid xenon cooled to minus 108 degrees Celsius. Arrays of photomultiplier tubes (lower right) are at top and bottom and catch the faint light when a WIMP interacts with a xenon nucleus. Electrons knocked loose in the collision are pulled by a strong electric field into the xenon gas near the top of the tank and emit a brighter flash; by comparing the flashes and the time between them, the energy, position, and nature of the collision are determined. The xenon container is immersed in a tank of water to provide extra shielding (upper right). (Images McKinsey Group, Yale University, Carlos Faham, and luxdarkmatter)

The proposed LUX ZEPLIN would contain seven metric tons of liquid xenon in its innermost vessel. The xenon container would be immersed in an acrylic tank of organic liquid scintillator to help identify non-WIMP events. The outer vessel is the existing steel tank of water, which helps shield the experiment from radioactive decay in the surrounding rock. There will be many more photomultiplier tubes than indicated here.

“I have to keep telling people LZ doesn’t stand for Led Zeppelin,” Gilchriese says. “While the design we’re proposing to the National Science Foundation and the Department of Energy is based on LUX, it’s not just the size that’s different. We’re incorporating new capabilities beyond those that both LUX and ZEPLIN have already demonstrated.”

The size is certainly different. Where LUX uses 350 kilograms of liquid xenon, roughly a third of a metric ton, LZ will use seven metric tons; the inner vessel that will hold the xenon is the biggest piece of equipment that can be lowered by the mine’s lift cage, fully assembled, to the Davis Campus level.

One of the principal advances in LZ will be that its inner tank will be surrounded by a large, clear-acrylic tank filled with liquid organic scintillator. LUX, except for the overlying rock and surrounding water, is essentially self-shielding – meaning that only events in the inner part of the detector are counted, and any reactions near the walls of the tank are ignored as possible background. In LZ an outer “skin” of liquid xenon will still play a part in shielding the inner chamber’s interior from gamma rays, but the surrounding liquid organic scintillator will substantially enhance the ability to “veto” (tag as non-WIMPs) background particles.

To detect these veto events, the LZ water tank will be lined with additional photomultiplier tubes on its top, bottom, and sides. Ironically, much of the background is likely to be generated by the photomultiplier tubes themselves, and the scientists are working with the manufacturer to greatly reduce the photomultipliers’ emissions of neutrons and gamma rays.

In addition, says Gilchriese, “even this deep underground, there are still a few cosmic rays.” The background will be unambiguously identified wherever it comes from, and most of the volume of liquid xenon in the inner vessel will be a clean medium for WIMP searches.

The technology of nested vessels of different kinds of scintillator, surrounded by photomultiplier tubes, was recently put to the test at Daya Bay, which achieved spectacular success in measuring neutrino oscillations even before the experiment’s full array of antineutrino detectors had been deployed.

“Now that the Daya Bay Project is nearing completion, I’d like to apply what we’ve learned to building an experiment that’s even deeper underground and has even lower background,” says Edwards, who is U.S. Project and Operations Manager for Daya Bay, an international collaboration led by the U.S. and China. “I’m excited by the challenge of a dark matter search, trying to find that needle in a haystack – that small and so-far unobserved signal in a vast array of background.”

Because the properties of WIMPs are still theoretical, finding them depends on hypothetical characteristics such as their mass and spin. Detectors like LUX aren’t the only way to look for WIMPs. If, as many theorists propose, they are supersymmetric particles unlike anything in the Standard Model, it may be able to create them with the Large Hadron Collider, an “active” WIMP detector. LZ is a “passive” detector, yet it will be able to cover a wide range of particle masses with great sensitivity.

“People have been trying to detect dark matter directly for a quarter of a century,” says Gilchriese. “So far there have been some suggestive events but no unambiguous detections. Liquid noble-element detectors have proved themselves the most sensitive, and LUX is the biggest and most sensitive yet.”

The LZ proposal covers many other technological advances to address the challenges faced by a multi-ton, supercold detector placed deep underground. With a detector of this unprecedented sensitivity, the scientific promise is profound.

“With our South Dakota supporters we have created a state-of-the-art laboratory facility exploiting the natural advantages of Homestake,” says Lesko. “We are employing all the lessons we learned from our experimental experiences in Sudbury, Kamioka, and Gran Sasso to provide the experiments with the best possible facility in the Sanford Laboratory.”

###


Berkeley Lab and UC Berkeley members of LUX and the proposed LZ include Steve Dardin, Bill Edwards, Vic Gehman, Gil Gilchriese, Matt Hoff, Mia Ihm, Dianna Jacobs, Bob Jacobsen, and Joe Saba.

More about LUX and the LUX collaboration may be found at http://lux.sanfordlab.org/main/

More about ZEPLIN is at http://www.hep.ph.ic.ac.uk/ZEPLIN-III-Project/

For information on another major research project at the Sanford Underground Research Laboratory, the MAJORANA DEMONSTRATOR, which is the first step in a new search for evidence that neutrinos are their own antiparticles, see http://newscenter.lbl.gov/feature-stories/2012/05/16/majorana-demonstrator/

Thursday, May 24, 2012

M101: A Pinwheel in Many Colors

NGC 5467 - M101
The Pinwheel Galaxy
Credit X-ray: NASA/CXC/SAO;
IR & UV: NASA/JPL-Caltech;
Optical: NASA/STScI


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This image of the Pinwheel Galaxy, or also known as M101, combines data in the infrared, visible, ultraviolet and X-rays from four of NASA's space-based telescopes. This multi-spectral view shows that both young and old stars are evenly distributed along M101's tightly-wound spiral arms. Such composite images allow astronomers to see how features in one part of the spectrum match up with those seen in other parts. It is like seeing with a regular camera, an ultraviolet camera, night-vision goggles and X-ray vision, all at the same time.

The Pinwheel Galaxy is in the constellation of Ursa Major (also known as the Big Dipper). It is about 70% larger than our own Milky Way Galaxy, with a diameter of about 170,000 light years, and sits at a distance of 21 million light years from Earth. This means that the light we're seeing in this image left the Pinwheel Galaxy about 21 million years ago - many millions of years before humans ever walked the Earth.

The hottest and most energetic areas in this composite image are shown in purple, where the Chandra X-ray Observatory observed the X-ray emission from exploded stars, million-degree gas, and material colliding around black holes.

The Electromagnetic Spectrum.
Wavelengths and energies from gamma rays to radio

The red colors in the image show infrared light, as seen by the Spitzer Space Telescope. These areas show the heat emitted by dusty lanes in the galaxy, where stars are forming.

The yellow component is visible light, observed by the Hubble Space Telescope. Most of this light comes from stars, and they trace the same spiral structure as the dust lanes seen in the infrared.

The blue areas are ultraviolet light, given out by hot, young stars that formed about 1 million years ago, captured by the Galaxy Evolution Explorer (GALEX).

Fast Facts for M101:

Scale: Image is 16.8 arcmin across
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000) RA 14h 03m 12.59s | Dec +54° 20’ 56.70''
Constellation: Ursa Major
Observation Dates: 03/26/2000 - 01/01/2005 with 26 pointings
Observation Time: 274 hours (11 days 10 hours)
Obs. IDs: 934, 2065, 4731-4737, 5296-5297, 5300, 5309, 5322-5323, 5337-5340, 6114-6115, 6118, 6152, 6169-6170, 6175
Color Code: X-ray (Purple); Infrared (Red); Optical (Yellow); Ultraviolet (Blue)
Instrument: ACIS
Also Known As: NGC 5457 - The Pinwheel Galaxy
Distance Estimate: About 21 million light years

Subaru Telescope Pioneers the Use of Adaptive Optics for Optical Observations

Figure 1: Kyoto3DII at the Nasmyth focus of the Subaru Telescope. The size of the instrument, including the frame, is 2 m high X 2 m wide X 1 m deep. The black box on the left side of the image is part of AO 188. (Credit: NAOJ)

Unlike space telescopes, ground-based telescopes must deal with observational distortions from atmospheric turbulence that degrades the spatial resolution of images. Adaptive optics systems (Note 2) correct for the distortion of light in real time and facilitate the production of high-resolution images. However, the AO systems of large, ground-based telescopes have only been used with infrared instruments. The turbulence of Earth's atmosphere distorts optical light more rapidly and significantly than infrared light. Therefore, the technical challenge of an AO system operating in optical wavelengths is to make faster and finer corrections of light distortion to obtain higher resolution images. Given the huge light-gathering capacity of the Subaru Telescope's 8.2 m primary mirror and the high performance of its AO 188 system in the infrared, the research team hypothesized that this system could also yield high-resolution images at optical wavelengths.

After using numerical simulations to confirm their hypothesis, they developed the connection between AO 188 and Kyoto3DII, an optical instrument that can operate in four modes. Because Kyoto3DII has to be positioned properly at each focus, the team designed and made a new frame mount for observations with the instrument at Nasmyth focus. The team also had to make a beam-splitter specialized for use with optical instruments. Making such a change is difficult, because the span of optical wavelengths is so short relative to infrared ones, but the team accomplished this task. On April 3, 2012 they carried out a test observation with the Kyoto3DII coupled with AO 188 and, for the first time, succeeded in performing full-scale, AO assisted scientific observations at optical wavelengths. Figure 2 shows the difference between the images obtained through this observation and those captured without AO. The team's images display the stars more clearly and at a higher spatial resolution (Note 3). The magnified images in Figure 2 show that that what looks like a very faint star when observed without AO appears as double stars when observed with AO (magnified Figure 2).

Figure 2: Images of the globular cluster M3, a region 50 arcseconds X 35 arcseconds at the observed wavelength of 660 nm and an exposure time of 10 seconds. Upper left panel: Image without using AO. Upper right panel: AO image. Lower panels are magnified images of parts of the upper panels. (Credit: NAOJ)

Kyoto3DII can operate in multiple modes, performing not only standard imaging and slit spectroscopy but also integral field spectroscopy, which has a square field of view and is a powerful tool for investigating the detailed structures of extended and multiple objects. The successful connection of Kyoto3DII with AO 188 enables the research team to carry out integral field spectroscopic observations with high resolution at optical wavelengths. Further analysis of the data will allow the astronomers to estimate the ionized state and gas motion of NGC 4151.

Figure 3: Images of NGC 4151, which has an active galactic nucleus at the center, taken by using Kyoto3DII in the integral field spectroscopy mode with an exposure time of 120 seconds. Left four panels: Images without using AO. Right four panels: Images with use of AO. Within each of the four panels, the high-resolution images of continuum emissions from stars and the active galactic nucleus (upper left), emission lines from hydrogen (upper right), sulfur (lower left), and argon (lower right) were obtained simultaneously. Continuum emissions refer thermally produced light. (Credit: NAOJ)

The team expressed their enthusiasm for the scientific promise of their newly developed basis for AO-assisted optical observations: "Using the combination of Kyoto3DII and AO 188, we hope to reveal the detailed structures of nearby galaxies and the formation processes of distant galaxies."


Note:

1. Please see details of the technical specifications and applications of Kyoto3DII at:
http://cosmos.phys.sci.ehime-u.ac.jp/~kazuya/p-3DII/index.html

2. Please see the previous press release about adaptive optics and AO 188:
http://www.naoj.org/Pressrelease/2006/11/20/index.html

3. The spatial resolution of images obtained with AO improved from 0.5 arcseconds to 0.2 arcseconds. The radius at which 50% of the energy was encompassed improved with AO from 0.60 arcseconds to 0.50 arcseconds.

Wednesday, May 23, 2012

Colliding galaxy cluster unravelled

Galaxy cluster Abell 2256 at 60 MHz made with LOFAR
An international team of astronomers has used the International LOFAR Telescope from ASTRON, the Netherlands Institute for Radio Astronomy, to study the formation of the galaxy cluster Abell 2256. Abell 2256 is a cluster containing hundreds of galaxies at a distance of 800 million lightyears. ‘The structure we see in the radio images made with LOFAR provides us with information about the origin of this cluster, explains lead author dr. Reinout van Weeren (Leiden University and ASTRON). The study will be published in the scientific journal Astronomy & Astrophysics. The research involved a large team of scientists from 26 different universities and research institutes.

LOFAR has made the first images of Abell 2256 in the frequency range of 20 to 60 MHz. What came as a surprise to scientists was that the cluster of galaxies was brighter and more complex than expected. Dr. van Weeren: ‘We think that galaxy clusters form by mergers and collisions of smaller clusters'. Abell 2256 is a prime example of a cluster that is currently undergoing a collision. The radio emission is produced by tiny elementary particles that move nearly at the speed of light. With LOFAR it is possible to study how these particles get accelerated to such speeds. ‘In particular, we will learn how this acceleration takes place in regions measuring more than 10 million light years across', says Dr. Gianfranco Brunetti from IRA-INAF in Bologna, Italy, who together with Prof. Marcus Brüggen from the Jacobs University in Bremen, coordinates the LOFAR work on galaxy clusters.

LOFAR was built by a large international consortium led by the Netherlands and which includes Germany, France, the United Kingdom and Sweden. One of the main goals of LOFAR is to survey the entire northern sky at low radio frequencies, with a sensitivity and resolution about 100 times better than what has been previously done. Scientists believe that this survey will discover more than 100 million objects in the distant Universe. ‘Soon we will start our systematic surveys of the sky that will lead to great discoveries', says Prof. Huub Röttgering from Leiden University and Principal Investigator of the "LOFAR Survey Key Project".


For more information, contact:

Dr. Reinout van Weeren, astronomer,
Leiden University and ASTRON
Tel.: +31 71 527 5864
E-mail: rvweeren@strw.leidenuniv.nl
Prof. Huub Röttgering, astronomer,
Leiden University
Tel.: +31 6 41522603
E-mail: rottgering@strw.leidenuniv.nl

Femke Boekhorst,
PR & Communication, ASTRON
Tel.: +31 521 595 204
E-mail: boekhorst@astron.nl

Link to the paper:
http://home.strw.leidenuniv.nl/~rvweeren/A2256_LBA_arx.pdf

Tuesday, May 22, 2012

The Older We Get, The Less We Know (Cosmologically)

New research finds that the ideal time to study the cosmos was more than 13 billion years ago, just about 500 million years after the Big Bang - the era (shown in this artist's conception) when the first stars and galaxies began to form. Since information about the early universe is lost when the first galaxies are made, the best time to view cosmic perturbations is right when stars began to form. Modern observers can still access this nascent era from a distance by using surveys designed to detect 21-cm radio emission from hydrogen gas at those early times. High Resolution Image (jpg)

Cambridge, MA - The universe is a marvelously complex place, filled with galaxies and larger-scale structures that have evolved over its 13.7-billion-year history. Those began as small perturbations of matter that grew over time, like ripples in a pond, as the universe expanded. By observing the large-scale cosmic wrinkles now, we can learn about the initial conditions of the universe. But is now really the best time to look, or would we get better information billions of years into the future - or the past?

New calculations by Harvard theorist Avi Loeb show that the ideal time to study the cosmos was more than 13 billion years ago, just about 500 million years after the Big Bang. The farther into the future you go from that time, the more information you lose about the early universe.

"I'm glad to be a cosmologist at a cosmic time when we can still recover some of the clues about how the universe started," Loeb said.

Two competing processes define the best time to observe the cosmos. In the young universe the cosmic horizon is closer to you, so you see less. As the universe ages, you can see more of it because there's been time for light from more distant regions to travel to you. However, in the older and more evolved universe, matter has collapsed to make gravitationally bound objects. This "muddies the waters" of the cosmic pond, because you lose memory of initial conditions on small scales. The two effects counter each other - the first grows better as the second grows worse.

Loeb asked the question: When were viewing conditions optimal? He found that the best time to study cosmic perturbations was only 500 million years after the Big Bang.

This is also the era when the first stars and galaxies began to form. The timing is not coincidental. Since information about the early universe is lost when the first galaxies are made, the best time to view cosmic perturbations is right when stars began to form.

But it's not too late. Modern observers can still access this nascent era from a distance by using surveys designed to detect 21-cm radio emission from hydrogen gas at those early times. These radio waves take more than 13 billion years to reach us, so we can still see how the universe looked early on.

"21-centimeter surveys are our best hope," said Loeb. "By observing hydrogen at large distances, we can map how matter was distributed at the early times of interest."

The accelerating universe makes the picture bleak for future cosmologists. Because the expansion of the cosmos is accelerating, galaxies are being pushed beyond our horizon. Light that leaves those distant galaxies will never reach Earth in the far future. In addition, the scale of gravitationally unbound structures is growing larger and larger. Eventually they, too, will stretch beyond our horizon. Some time between 10 and 100 times the universe's current age, cosmologists will no longer be able to observe them.

"If we want to learn about the very early universe, we'd better look now before it is too late!" Loeb said.

This research was published in the Journal of Cosmology and Astroparticle Physics (JCAP) and is available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

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

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

A Spiral Within a Spiral

ESO 498-G5
Credit: ESA/Hubble & NASA

The NASA/ESA Hubble Space Telescope captured this image of the spiral galaxy known as ESO 498-G5. One interesting feature of this galaxy is that its spiral arms wind all the way into the centre, so that ESO 498-G5's core looks like a bit like a miniature spiral galaxy. This sort of structure is in contrast to the elliptical star-filled centres (or bulges) of many other spiral galaxies, which instead appear as glowing masses, as in the case of NGC 6384.

Astronomers refer to the distinctive spiral-like bulge of galaxies such as ESO 498-G5 as disc-type bulges, or pseudobulges, while bright elliptical centres are called classical bulges. Observations from the Hubble Space Telescope, which does not have to contend with the distorting effects of Earth's atmosphere, have helped to reveal that these two different types of galactic centres exist. These observations have also shown that star formation is still going on in disc-type bulges and has ceased in classical bulges. This means that galaxies can be a bit like Russian matryoshka dolls: classical bulges look much like a miniature version of an elliptical galaxy, embedded in the centre of a spiral, while disc-type bulges look like a second, smaller spiral galaxy located at the heart of the first — a spiral within a spiral.

The similarities between types of galaxy bulge and types of galaxy go beyond their appearance. Just like giant elliptical galaxies, the classical bulges consist of great swarms of stars moving about in random orbits. Conversely, the structure and movement of stars within disc-type bulges mirror the spiral arms arrayed in a galaxy's disc. These differences suggest different origins for the two types of bulges: while classical bulges are thought to develop through major events, such as mergers with other galaxies, disc-type bulges evolve gradually, developing their spiral pattern as stars and gas migrate to the galaxy’s centre.

ESO 498-G5 is located around 100 million light-years away in the constellation of Pyxis (The Compass). This image is made up of exposures in visible and infrared light taken by Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.3 by 1.6 arcminutes.

Source: ESA/Hubble - Space Telescope


Monday, May 21, 2012

Celestial Tapestry is Born of Uncertain Parentage

Gemini Legacy image of the complex planetary nebula Sh2-71 as imaged by the Gemini Multi-Object Spectrograph on Gemini North on Mauna Kea in Hawai‘i. The long-assumed central star is the brightest star near the center, but some astronomers wonder if the much dimmer and bluer star (just to the right and down a bit) might be the parent of this beautiful object. The image is composed of three narrow-band images, and each is assigned a color as follows: H-alpha (orange), HeII (blue) and [OIII] (cyan). Each image is 15 minutes in duration, the field-of-view is 5.3 x 3.6 arcminutes, and the image is rotated 110 degrees clockwise from north up, east left. Image credit: Gemini Observatory/AURA. Full Resolution TIFF (23.5MB) | JPEG (4.1MB)

A new Legacy Image from the Gemini Observatory reveals the remarkable complexity of the planetary nebula Sharpless 2-71 (Sh 2-71). Embroiled in a bit of controversy over its “birth parents” the nebula likely resulted from interactions between a pair of two old and dying stars. Legacy images like this one share the stunning beauty of the universe as revealed by the twin 8-meter Gemini telescopes in Hawai‘i and Chile.

Often what seems obvious isn’t.

Take this new Gemini Legacy Image of the elaborate planetary nebula Sharpless 2-71. For most of its recorded history, astronomers assumed that it formed from the death throes of an obvious bright star (a known binary system) near its center. Arguments against that claim, however, have turned this case into a classic mystery of uncertain parentage.

The Gemini Legacy Image shows the long-assumed central star shining as the brightest object very close to the center of the nebula’s beautiful gas shell. But new observations have shown that the nature of a dimmer, bluer star – just to the right, and a bit lower than the obvious central star – might provide a better fit for the nebula’s “birth parent.”

The uncertainty arises from the fact that the brighter central star doesn’t appear to radiate enough high-energy (ultraviolet) light to cause the surrounding gas to glow as intensely as it does, whereas the dimmer, bluer star likely does. On the other hand, the brighter star’s binary nature would help explain the nebula’s asymmetrical structure. Astronomers do not yet known if the dimmer, bluer star also has a companion.

Another unresolved issue is whether the brighter star’s unseen companion might be hot enough to excite the gas to glow. If so, this pair might be able to hold on to its parental connection to the nebula.

A research team, led by Australian astronomers David Frew and Quentin Parker (Macquarie University, Sydney) are studying the dimmer, bluer star to understand its nature. “At the assumed distance to the nebula (roughly 1 kiloparsec or about 3,260 light-years), the faint star has about the right brightness to be the fading remnant of the nebula’s progenitor star,” says Frew.

Then again, the brighter binary star is an uncommon one that shows strong and broad hydrogen-alpha emission, which are seen in some planetary nebulae. According to Frew, this star is also unlikely to be a chance projection or alignment with the nebula, “So there could be at least three stars in this system,” he says.

Putting aside the complex issue of which star or stars formed this object, the nebula’s striking morphology also poses difficult questions. “The nebula presents a multi-polar structure and several pairs of bipolar lobes at different orientations,” says Luis Miranda of Spain’s Instituto de Astrofísica de Andalucía (CSIC) who has also studied this object extensively. “These lobes most certainly formed at different times and likely involved a binary progenitor – in particular with mass-transfer and multiple episodes of mass ejection along an axis where the orientation changes with time.”

Adding to the puzzle, Parker and Romano Corradi (Instituto de Astrofisica de Canarias, Spain) have recently discovered faint outer wisps and lobes surrounding the planetary on deep hydrogen-alpha images, taken as part of the Isaac Newton Telescope Photometric HydrogenAlpha Survey of the Northern Galactic Plane Survey. These features extend over many arcminutes (not shown in the new Gemini image), suggesting the mass loss history of this object has even more levels of complexity.

Miranda agrees, noting that the nebula’s structure is difficult to explain without a binary pair for parents. “The chaotic morphology of Sh2-71 implies that very complex processes have been involved in its formation,” says Miranda. Unfortunately, not much is known about either possible central star’s known or speculated companions. So the mystery of the nebula’s uncertain parentage remains unsolved ... for now.

Image Background Information: Gemini’s Multi-Object Spectrograph (GMOS) captured the light of Sh2-71 in its imaging mode using filters that selectively allow specific colors of visible light to reach the detector. Each color is produced by energized gas in the nebula glowing in a manner similar to a neon sign. Travis Rector of the University of Alaska Anchorage assembled the data from three filters (hydrogen alpha, helium II, and oxygen III) to form the composite color image.

Planetary nebulae are the end-state of stars like our Sun. They form when old, medium-sized stars run low on nuclear fuel, become unstable, and begin expelling their outer layers of gas into space. Often these objects appear quite symmetrical, but when multiple stars are involved, their structure looks much more complex. In such cases, astronomers believe that the transfer of gas from one star to another results in explosions and eruptions that disrupt the symmetry of the nebula - as is clearly seen in this new Gemini image.

Discovered in 1946 by Rudolph Minkowski, the nebula is located in the direction of the constellation Aquila and visible in amateur telescopes. Sh2-71 is the 71st object in a catalogue of nebulae originally assembled by the U.S. astronomer Stewart Sharpless of the US Naval Observatory in Flagstaff, Arizona. It is from his second catalogue, of 313 nebulae, published in 1959.

ABOUT THE GEMINI OBSERVATORY

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in seven partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Science and Technology Facilities Council (STFC), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq). The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

Press Contact:

Peter Michaud
Gemini Observatory
Hilo, HI 96720
Office: +1 (808) 974-2510
Cell: +1 (808) 936-6643
pmichaud@gemini.edu


Galaxies in the Young Cosmos

Now you don't see it; now you do - the image of a galaxy from a time when the universe was only a billion years old. The left image, from Hubble, sees nothing in the sky, but the longer wavelength infrared image from Spitzer (right) sees a bright source. The intense star formation activity in the galaxy, its distance, and the expansion of the universe combine to make it appear in the infrared. Credit: K. Caputi. Low Resolution Image (jpg)

Cambridge, MA - The universe was born about 13.7 billion years ago in the big bang. The Sun and its system of planets formed about five billion years ago. What happened, then, during that long, intervening stretch of nearly nine billion years? This is one of the key questions in modern science. Astronomers think that the very first stars and galaxies appeared only a few hundreds of millions of years after the big bang, and have been evolving ever since. They must have been quite different from the stars and galaxies of today, however, in part because the young universe lacked most of the chemical elements present today - those elements were made gradually in the nuclear furnaces of those stars.

Modern telescopes and infrared and submillimeter techniques have recently enabled astronomers to spot significant numbers of very distant galaxies and begin to piece together a picture of cosmic evolution. Galaxies often undergo bursts of star formation that make their dust glow in the infrared. In fact, recent results suggest that at some cosmic epochs star formation was as much as ten times more active than it is today. The power of infrared is twofold: It can measure the luminous dust, and, because cosmic expansion shifts starlight into the infrared, it can also see spectral features in that starlight that allow an estimate of the cosmic distance.

Sensitive infrared cameras staring over large fields of view are the best way to find large numbers of very distant objects for analyses SAO astronomers Jia-Sheng Huang, Giovanni Fazio, and Matt Ashby, together with a team of colleagues, used the infrared camera on the Spitzer Space Telescope to undertake a very deep and sensitive search for distant infrared galaxies in an area of the sky one twentieth the size of the full moon. They coordinated their study with infrared images from Hubble.

The scientists discovered twenty five peculiar infrared objects in their field. Follow-up analyses revealed that between eleven and nineteen of them date to cosmic epochs from 1.5 to 3 billion years after the big bang. These galaxies seem to be very massive and to contain significant amounts of warm dust. Two other sources just as massive seem to be even older, dating from a period only one billion years after the big bang. The latter present a serious challenge to current theories about galaxy evolution, which predict very few such objects should exist at such an early time. The new survey is significant not only because it has discovered such distant galaxies, but also because it points to a previously unrecognized galaxy population whose properties are significantly different from those of known galaxies at similar epochs.

Saturday, May 19, 2012

NASA’s Kepler Detects Potential Evaporating Planet Candidate

The artist's concept depicts a comet-like tail of a possible disintegrating super Mercury-size planet candidate as it transits its parent star named KIC 12557548. At an orbital distance of only twice the diameter of its star, the surface temperature of the potential planet is estimated to be a sweltering 3,300 degrees Fahrenheit. At such a high temperature, the surface would melt and evaporate. The energy from the resulting wind would be enough to allow dust and gas to escape into space creating a trailing dusty effluence that intermittently blocks the starlight. Image credit: NASA/JPL-Caltech. Click here for full resolution.


A Curious Signature of a Potential Tiny World

The artist's animation depicts a possible disintegrating planet candidate as it orbits its star. Dust and gas ejected from the possible planet’s sweltering surface is theorized to form a comet-like tail of trailing material. The density of the tail can change dramatically, even over a single 15-hour orbit. Kepler finds planets by searching for the slight drop in brightness seen as they pass in front of their stars. Usually that drop is constant, but in this system, the variation seen from orbit to orbit hints at a dusty tail trailing a doomed world. Credit: NASA/JPL-Caltech

Astronomers may have detected evidence of a possible planet disintegrating under the searing heat of its host star located 1,500 light-years from Earth. Similar to a debris-trailing comet, the super Mercury-size planet candidate is theorized to fashion a dusty tail. But the tail won't last for long. Scientists calculate that, at the current rate of evaporation, the dusty world could be completely vaporized within 200 million years.

A research team led by Saul Rappaport, professor emeritus of physics at MIT, Boston, Mass., has identified an unusual light pattern emanating from a star named KIC 12557548 in the Kepler space telescope's field-of-view.

NASA's Kepler space telescope detects planets and planet candidates by measuring dips in the brightness of more than 150,000 stars to search for planets crossing in front, or transiting, their stars.

"The bizarre nature of the light output from this star with its precisely periodic transit-like features and highly variable depths exemplifies how Kepler is expanding the frontiers of science in unexpected ways," said Jon Jenkins, Kepler co-investigator at the SETI Institute in Mountain View, Calif. "This discovery pulls back the curtain of how science works in the face of surprising data."

Orbiting a star smaller and cooler than our sun, the planet candidate completes its orbit in less than 16 hours-- making it one of the shortest orbits ever detected. At an orbital distance of only twice the diameter of its star, the surface temperature of the planet is estimated to be a smoldering 3,300 degrees Fahrenheit.

Scientists hypothesize that the star-facing side of the potentially rocky inferno is an ocean of seething magma. The surface melts and evaporates at such high temperatures that the energy from the resulting wind is enough to allow dust and gas to escape into space. This dusty effluence trails behind the doomed companion as it disintegrates around the star.

Additional follow-up observations are needed to confirm the candidate as a planet. The finding is published in The Astrophysical Journal and is available for download at: http://arxiv.org/abs/1201.2662

For more details on the finding visit: http://web.mit.edu/newsoffice/2012/dusty-exoplanet-0517.html

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

Michele Johnson
Phone Number: (650) 604-6982
Ames Research Center, Moffett Field, Calif.

Friday, May 18, 2012

Herschel Sees Intergalactic Bridge Aglow With Stars

The Herschel Space Observatory has discovered a giant, galaxy-packed filament ablaze with billions of new stars. The filament connects two clusters of galaxies that, along with a third cluster, will smash together in several billion years and give rise to one of the largest galaxy superclusters in the universe. Image credit: ESA/NASA/JPL-Caltech/CXC/McGill Univ. Full image and caption

The Herschel Space Observatory has discovered a giant, galaxy-packed filament ablaze with billions of new stars. The filament connects two clusters of galaxies that, along with a third cluster, will smash together and give rise to one of the largest galaxy superclusters in the universe.

Herschel is a European Space Agency mission with important NASA contributions.

The filament is the first structure of its kind spied in a critical era of cosmic buildup when colossal collections of galaxies called superclusters began to take shape. The glowing galactic bridge offers astronomers a unique opportunity to explore how galaxies evolve and merge to form superclusters.

"We are excited about this filament, because we think the intense star formation we see in its galaxies is related to the consolidation of the surrounding supercluster," says Kristen Coppin, an astrophysicist at McGill University in Canada, and lead author of a new paper in Astrophysical Journal Letters.

"This luminous bridge of star formation gives us a snapshot of how the evolution of cosmic structure on very large scales affects the evolution of the individual galaxies trapped within it," says Jim Geach, a co-author who is also based at McGill.

The intergalactic filament, containing hundreds of galaxies, spans 8 million light-years and links two of the three clusters that make up a supercluster known as RCS2319. This emerging supercluster is an exceptionally rare, distant object whose light has taken more than seven billion years to reach us.

RCS2319 is the subject of a huge observational study, led by Tracy Webb and her group at McGill. Previous observations in visible and X-ray light had found the cluster cores and hinted at the presence of a filament. It was not until astronomers trained Herschel on the region, however, that the intense star-forming activity in the filament became clear. Dust obscures much of the star-formation activity in the early universe, but telescopes like Herschel can detect the infrared glow of this dust as it is heated by nascent stars.

The amount of infrared light suggests that the galaxies in the filament are cranking out the equivalent of about 1,000 solar masses (the mass of our sun) of new stars per year. For comparison's sake, our Milky Way galaxy is producing about one solar-mass worth of new stars per year.

Researchers chalk up the blistering pace of star formation in the filament to the fact that galaxies within it are being crunched into a relatively small cosmic volume under the force of gravity. "A high rate of interactions and mergers between galaxies could be disturbing the galaxies' gas reservoirs, igniting bursts of star formation," said Geach.

By studying the filament, astronomers will be able to explore the fundamental issue of whether "nature" versus "nurture" matters more in the life progression of a galaxy. "Is the evolution of a galaxy dominated by intrinsic properties such as total mass, or do wider-scale cosmic environments largely determine how galaxies grow and change?" Geach asked. "The role of the environment in influencing galactic evolution is one of the key questions of modern astrophysics."

The galaxies in the RCS2319 filament will eventually migrate toward the center of the emerging supercluster. Over the next seven to eight billion years, astronomers think RCS2319 will come to look like gargantuan superclusters in the local universe, like the nearby Coma cluster. These advanced clusters are chock-full of "red and dead" elliptical galaxies that contain aged, reddish stars instead of young ones.

"The galaxies we are seeing as starbursts in RCS2319 are destined to become dead galaxies in the gravitational grip of one of the most massive structures in the universe," said Geach. "We're catching them at the most important stage of their evolution."

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information is online at http://www.herschel.caltech.edu , http://www.nasa.gov/herschel and http://www.esa.int/SPECIALS/Herschel .

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