Astronomers Begin a Massive Survey of the Milky Way

Image credit: RAVE

Researchers from 11 countries are working together to measure the motion and composition of 50 million stars in the Milky Way. This new survey is called RAVE (Radial Velocity Experiment), and astronomers will be able to use the data gathered to construct a very detailed history of our galaxy. They will be able to determine which widely separated stars were formed at a single location, and help answer competing theories about how our galaxy formed. The pilot phase of the project will begin with the UK Schmidt telescope which can measure 600 stars a night, and then production will pick up as other observatories join the hunt.

Clues to how galaxies formed in the early Universe lie right under our nose – in our own Galaxy. The Galaxy formed by the accretion of infalling satellite galaxies, many astronomers think. Theoretical models of the formation of galaxies predict such a scenario. But not all astronomers are convinced yet and the topic is still controversial.

Now researchers from eleven countries have launched an ambitious project to reconstruct our Galaxy’s history by gathering key components of motion and chemi cal compositions for its apparently brightest 50 million stars.

RAVE (RAdial Velocity Experiment) is an all-sky stellar spectroscopy survey just started on the 1.2-m UK Schmidt telescope in eastern Australia.

Projects such as Hipparcos and Tycho have accurately measured the positions and proper motions – movement across the sky – of more than 2.5 million stars.

But to get a complete picture of stellar motions, and thus to enable astronomers to reconstruct the structure and formation history of our Galaxy, they also need radial velocities – the movement of stars towards or away from the observer. And before RAVE began only about 20,000 stellar radial velocities were in the archives.

RAVE will be able to achieve velocities accurate to within 2 km/s – about 1% of the speed at which stars typically move in the Galaxy.

“With this accuracy and this number of radial velocities we will be able to identify dozens, perhaps hundreds, of streams of stars in the solar vicinity. The streams represent debris from disrupted old satellite galaxies now engulfed by our Galaxy,” said Professor Matthias Steinmetz, Director at the Astrophysical Institute Potsdam and leader of the RAVE science team.

Even after plunging into our Galaxy, the stars of a satellite galaxy continue to move as a coherent group, and can be identified by their common velocity even after billions of years. However, only a very few of those disrupted satellites have been identified to date.

RAVE will also gather the chemical compositions of stars. These should help show which widely separated stars were formed at a common site. They should also determine whether these stars have been formed before or after the satellite galaxy of which they were a part broke up.

“RAVE will help us decide between competing models for the formation of the various structures of the Galaxy, such as the central bulge of stars and the so-called ‘thick disk’,” said Steinmetz.

“For a survey such as this, field of view is more important than aperture. The UK Schmidt telescope is a perfect tool for this work,” said Professor Brian Boyle, Director of the Anglo-Australian Observatory, which operates the telescope. The field of view of the UK Schmidt telescope covers an area more than 100 times larger than that of the Moon.

RAVE’s initial pilot phase is being carried out with the 6dF (six-degree field) instrument on the UK Schmidt. Designed and built by the Anglo-Australian Observatory, the 6dF instrument is a ‘pick and place’ robot that positions 150 fibres on the telescope’s focal plane.

Using 6dF, astronomers can collect up to 600 stellar spectra per night. And by 2005 they plan to have 100,000 – five times as many as have been measured since Hermann Carl Vogel started such work at the Astrophysical Observatory Potsdam in 1888.

In 2006 the pace of data collection will pick up even further, when 6dF instrument is replaced by a radical new instrument from the AAO – UKidna, with 2250 fibres mounted on independently movable spines.

“With UKidna we’ll be taking up to 22,000 spectra on a clear night,” said Boyle.

“Then we’ll be able to push beyond our local Galactic neighbourhood, out into the furthest corners of the Milky Way,” said Professor Rosie Wyse of Johns-Hopkins University in Baltimore.

As well as uncovering the history of our Galaxy, RAVE will establish a huge database of stellar spectra – by far the largest to date.

“This will be a vast resource for studies of the properties and evolution of stars,” said Professor Ulisse Munari of the Padova Observatory in Asagio.

With its large database of stellar spectra RAVE will also provide an ideal training set for the design of future space missions such as the European Space Agency’s cornerstone mission GAIA, which will attempt to measure positions and velocities of up to a billion stars in the Milky Way.

Original Source: AIP News Release

Closest Gamma Ray Burst Ever Discovered

Image credit: NRAO

Gamma ray bursts (GRB) are the largest known explosions in the Universe; immensely powerful, quick to fade, but usually incredibly far away. Astronomers with the National Radio Astronomy Observatory got lucky, though, when they analyzed a recent GRB and discovered it was only 2.6 billion light-years away (most are usually 4 times more distant). What causes these bursts is a mystery, but the theories usually incorporate black holes in some catastrophic way – colliding into another black hole; wrapping a magnetic field like a spring, etc. This close burst didn’t answer the mystery, but it did allow the astronomers to rule out one idea, that material from a GRB blasts out like “cannonballs”.

The closest Gamma Ray Burst (GRB) yet known is providing astronomers with a rare opportunity to gain information vital to understanding these powerful cosmic explosions. Extremely precise radio-telescope observations already have ruled out one proposed mechanism for the bursts.

“This is the closest and brightest GRB we’ve ever seen, and we can use it to decipher the physics of how these bursts work,” said Greg Taylor of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. Taylor worked with Dale Frail, also of the NRAO, along with Prof. Shri Kulkarni and graduate student Edo Berger of Caltech in studying a GRB detected on March 29, 2003. The scientists presented their findings to the American Astronomical Society’s meeting in Nashville, TN.

VLBA IMAGE of GRB 030329

(Click on Image for Larger Version)

Taylor and Frail used the National Science Foundation’s (NSF) Very Long Baseline Array (VLBA) and other radio telescopes to study the burst, known as GRB 030329. In a series of observations from April 1 to May 19, they determined the size of the expanding “fireball” from the burst and measured its position in the sky with great precision.

At a distance of about 2.6 billion light-years, GRB 030329 is hardly next door. However, compared to other GRBs at typical distances of 8-10 billion light-years, it presents an easier target for study.

“We only expect to see one burst per decade this close,” said Frail.

The precise measurement of the object’s position allowed the scientists to show that one theoretical model for GRBs can be ruled out. This model, proposed in 2000, says that the radio-wave energy emitted by the GRB comes from “cannonballs” of material shot from the explosion at extremely high speeds.

“The ‘cannonball model’ predicted that we should see the radio-emitting object move across the sky by a specific amount. We have not seen that motion,” Taylor said.

The currently standard “fireball model” of GRBs says that the radio emission comes from a rapidly-expanding shock wave. This model was first proposed by Peter Meszaros, Bohdan Paczynski and Sir Martin Rees, who won the American Astronomical Society’s Bruno Rossi Prize in 2000 for their work. In this standard model, as the shock wave expands outward, the emission becomes fainter, but the center of the observed emission does not change position.

The cannonball model, however, proposes that the emission arises from distinct concentrations of matter shot outward from the burst. As they move farther from the burst, their motion should be detected as a change in their position in the sky. On April 3, proponents of the cannonball model predicted a specific amount of motion for GRB 030329 and suggested that the VLBA’s sharp radio “vision” could detect the motion and confirm their prediction.

Instead, “our observations are consistent with no motion at all,” Taylor said. “This is at odds with the cannonball model — they made a specific prediction based on their model and the observations do not bear them out,” he added.

The scientists’ direct measurement of the size of the GRB fireball also will provide new insights into the physics behind the burst.

“By directly measuring the size and the expansion rate, we can start putting some real limits on the physics involved,” Taylor said. First, he said, “We already can confirm that the fireball is expanding at nearly the speed of light, as the standard model predicts. Next, once our May observations are fully analyzed, we can put limits on the energy of the burst and provide a test of the standard model.”

Taylor and Frail observed GRB 030329 with the VLBA on April 1 and April 6. On April 22, they used the 100-meter radio telescope in Effelsberg, Germany in addition to the VLBA. On May 19, they used the VLBA, the Very Large Array (VLA) in New Mexico, the NSF’s Robert C. Byrd Green Bank Telescope in West Virginia, and the Effelsberg telescope.

In addition to gamma-ray and X-ray observations, visible light from GRB 030329 was observed by 65 telescopes around the world. At its brightest, the visible light from this burst was detectable with moderate-sized amateur telescopes.

Gamma Ray Bursts were first detected in 1967 by a satellite monitoring compliance with the 1963 atmospheric nuclear test-ban treaty. For three decades thereafter, astronomers were unable to determine their distances from Earth, and thus were unable to begin understanding the physics underlying the explosions. In 1997, the first distance measurements were made to GRBs, and the NSF’s Very Large Array (VLA) detected the first radio emission from a GRB afterglow.

Once scientists determined that GRBs originate in distant galaxies and that they probably occur in regions of those galaxies where stars are actively forming, some 200 proposed models for what causes GRBs were reduced to a handful of viable models.

Most scientists now believe that GRBs arise from a violent explosion that ends the life of a star much more massive than the Sun. Whereas such an explosion as a typical supernova leaves a dense neutron star, a GRB explosion leaves a black hole, a concentration of mass with gravitational pull so strong that not even light can escape it.

The VLBA is a continent-wide system of ten radio- telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east, providing the greatest resolving power, or ability to see fine detail, in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO’s Array Operations Center in Socorro, New Mexico.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Sea Launch Heads for the Equator

Image credit: Sea Launch

The Odyssey Launch Platform and Sea Launch Commander set sail from their port in Los Angeles on Wednesday in preparation to launch the Thuraya-2 satellite on board a Zenit 3SL rocket. The ship and launch platform will reach the launch site, located in the Pacific Ocean at the Equator, and then begin a 72-hour countdown for launch – the 44-minute launch window begins June 10 at 1356 GMT (9:56am PDT). The Thuraya-2 satellite will provide communications in the Middle East, Europe, Africa and Asia.

The Odyssey Launch Platform and the Sea Launch Commander departed Sea Launch Home Port this week, for the launch of the Thuraya-2 satellite. Liftoff is scheduled for June 10, in a 44-minute launch window that opens at 6:56 am PDT (13:56:00 GMT).

The two Sea Launch vessels will travel from Sea Launch Home Port, in the Port of Long Beach, to the launch site on the Equator at 154o West Longitude, where a 72-hour countdown will begin upon arrival. Once the platform is ballasted to launch depth, the team will perform final tests on the rocket and spacecraft, and prepare for launch operations. The 200-foot Zenit-3SL rocket will lift the 5177 kg (11,413 lb) Thuraya-2 satellite to geosynchronous transfer orbit with a liftoff thrust of 1.6 million lbs.

Thuraya-2 was built by Boeing [NYSE:BA] for the Thuraya Satellite Telecommunications Company, of United Arab Emirates, and shipped from its satellite manufacturing facility in El Segundo, Calif. The GEO-Mobile (GEM) model satellite uses a Boeing 702 body-stabilized design and integrates a ground segment and user handsets to provide a range of cellular-like voice and data services over a vast geographic region. Sea Launch successfully inserted the first Boeing GEM model, Thuraya-1, to orbit in October 2000. It is the heaviest commercial spacecraft launched successfully to date.

Thuraya-2 will enable Thuraya Satellite Telecommunications to continue to grow and expand its successful business, providing communications services to the people of 100 nations in the Middle East, Europe, North and Central Africa, and South and Central Asia. Thuraya?s advanced satellite telecommunications provides blanket border-to-border coverage to nearly one third of the globe. Based in Abu Dhabi, Thuraya offers uninterrupted and seamless services that link urban and rural areas, and ensure call continuity over regions with fragmented conventional telecommunication networks.

Sea Launch Company, LLC, headquartered in Long Beach, Calif., is a world leader in providing heavy-lift commercial launch services. This multinational partnership offers the most direct and cost-effective route to geostationary orbit. With the advantage of a launch site on the Equator, the proven Zenit-3SL rocket can lift a heavier spacecraft mass or provide longer life on orbit, offering best value plus schedule assurance. Sea Launch has a current backlog of 16 firm launch contracts. For additional information, visit the Sea Launch website at:

Original Source: Boeing News Release

Astronomers Weigh a Pulsar’s Planets

Image credit: NASA

A team of astronomers have weighed a group of planets orbiting a pulsar by precisely measuring their orbits. So far, two of the system’s three planets have been weighed, and they’re 4.3 and 3.0 times the mass of the Earth. What’s unusual is that the spacing between the planets almost exactly match the spacing of Mercury, Venus and Earth – making this bizarre system the most similar to our own Solar System so far discovered. The pulsar, 1257+12, was discovered 13 years ago using the Arecibo radio telescope.

For the first time, the planets orbiting a pulsar have been “weighed” by measuring precisely variations in the time it takes them to complete an orbit, according to a team of astronomers from the California Institute of Technology and Pennsylvania State University.

Reporting at the summer meeting of the American Astronomical Society, Caltech postdoctoral researcher Maciej Konacki and Penn State astronomy professor Alex Wolszczan announced today that masses of two of the three known planets orbiting a rapidly spinning pulsar 1,500 light-years away in the constellation Virgo have been successfully measured. The planets are 4.3 and 3.0 times the mass of Earth, with an error of 5 percent.

The two measured planets are nearly in the same orbital plane. If the third planet is co-planar with the other two, it is about twice the mass of the moon. These results provide compelling evidence that the planets must have evolved from a disk of matter surrounding the pulsar, in a manner similar to that envisioned for planets around sun-like stars, the researchers say.

The three pulsar planets, with their orbits spaced in an almost exact proportion to the spacings between Mercury, Venus, and Earth, comprise a planetary system that is astonishingly similar in appearance to the inner solar system. They are clearly the precursors to any Earth-like planets that might be discovered around nearby sun-like stars by the future space interferometers such as the Space Interferometry Mission or the Terrestrial Planet Finder.

“Surprisingly, the planetary system around the pulsar 1257+12 resembles our own solar system more than any extrasolar planetary system discovered around a sun-like star,” Konacki said. “This suggests that planet formation is more universal than anticipated.”

The first planets orbiting a star other than the sun were discovered by Wolszczan and Frail around an old, rapidly spinning neutron star, PSR B1257+12, during a large search for pulsars conducted in 1990 with the giant, 305-meter Arecibo radio telescope. Neutron stars are often observable as radio pulsars, because they reveal themselves as sources of highly periodic, pulse-like bursts of radio emission. They are extremely compact and dense leftovers from supernova explosions that mark the deaths of massive, normal stars.

The exquisite precision of millisecond pulsars offers a unique opportunity to search for planets and even large asteroids orbiting the pulsar. This “pulsar timing” approach is analogous to the well-known Doppler effect so successfully used by optical astronomers to identify planets around nearby stars. Essentially, the orbiting object induces reflex motion to the pulsar which result in perturbing the arrival times of the pulses. However, just like the Doppler method, the pulsar timing method is sensitive to stellar motions along the line-of-sight, the pulsar timing can only detect pulse arrival time variations caused by a pulsar wobble along the same line. The consequence of this limitation is that one can only measure a projection of the planetary motion onto the line-of-sight and cannot determine the true size of the orbit.

Soon after the discovery of the planets around PSR 1257+12, astronomers realized that the heavier two must interact gravitationally in a measurable way, because of a near 3:2 commensurability of their 66.5- and 98.2-day orbital periods. As the magnitude and the exact pattern of perturbations resulting from this near-resonance condition depend on a mutual orientation of planetary orbits and on planet masses, one can, in principle, extract this information from precise timing observations.

Wolszczan showed the feasibility of this approach in 1994 by demonstrating the presence of the predicted perturbation effect in the timing of the planet pulsar. In fact, it was the first observation of such an effect beyond the solar system, in which resonances between planets and planetary satellites are commonly observed. In recent years, astronomers have also detected examples of gravitational interactions between giant planets around normal stars.

Konacki and Wolszczan applied the resonance-interaction technique to the microsecond-precision timing observations of PSR B1257+12 made between 1990 and 2003 with the giant Arecibo radio telescope. In a paper to appear in the Astrophysical Journal Letters, they demonstrate that the planetary perturbation signature detectable in the timing data is large enough to obtain surprisingly accurate estimates of the masses of the two planets orbiting the pulsar.

The measurements accomplished by Konacki and Wolszczan remove a possibility that the pulsar planets are much more massive, which would be the case if their orbits were oriented more “face-on” with respect to the sky. In fact, these results represent the first unambiguous identification of Earth-sized planets created from a protoplanetary disk beyond the solar system.

Wolszczan said, “This finding and the striking similarity of the appearance of the pulsar system to the inner solar system provide an important guideline for planning the future searches for Earth-like planets around nearby stars.”

Original Source: Caltech News Release

A View of the Universe Only 900 Million Years Old

Image credit: ESO

A team of astronomers based in Hawaii have discovered a distant galaxy 12.8 billion light years away which shows us what the Universe looked like when it was only 900 million years old. They found the galaxy by using a special camera installed on the Canada-France-Hawaii telescope which searches for distant objects in a very specific frequency of light. By uncovering this galaxy, located in the constellation of Cetus, right near the star Mira, the team has developed a new methodology for discovering distant objects which should help future observers look even further into the past.

With improved telescopes and instruments, observations of extremely remote and faint galaxies have become possible that were until recently astronomers’ dreams.

One such object was found by a team of astronomers [2] with a wide-field camera installed at the Canada-France-Hawaii telescope at Mauna Kea (Hawaii, USA) during a search for extremely distant galaxies. Designated “z6VDF J022803-041618”, it was detected because of its unusual colour, being visible only on images obtained through a special optical filter isolating light in a narrow near-infrared band.

A follow-up spectrum of this object with the FORS2 multi-mode instrument at the ESO Very Large Telescope (VLT) confirmed that it is a very distant galaxy (the redshift is 6.17 [3]). It is seen as it was when the Universe was only about 900 million years old.

z6VDF J022803-041618 is one of the most distant galaxies for which spectra have been obtained so far. Interestingly, it was discovered because of the light emitted by its massive stars and not, as originally expected, from emission by hydrogen gas.

A brief history of the early Universe
Most scientists agree that the Universe emanated from a hot and extremely dense initial state in a Big Bang. The latest observations indicate that this crucial event took place about 13,700 million years ago.

During the first few minutes, enormous quantities of hydrogen and helium nuclei with protons and neutrons were produced. There were also lots of free electrons and during the following epoch, the numerous photons were scattered from these and the atomic nuclei. At this stage, the Universe was completely opaque.

After some 100,000 years, the Universe had cooled down to a few thousand degrees and the nuclei and electrons now combined to form atoms. The photons were then no longer scattered from these and the Universe suddenly became transparent. Cosmologists refer to this moment as the “recombination epoch”. The microwave background radiation we now observe from all directions depicts the state of great uniformity in the Universe at that distant epoch.

In the next phase, the primeval atoms – more than 99% of which were of hydrogen and helium – moved together and began to form huge clouds from which stars and galaxies later emerged. The first generation of stars and, somewhat later, the first galaxies and quasars [4], produced intensive ultraviolet radiation. That radiation did not travel very far, however, despite the fact that the Universe had become transparent a long time ago. This is because the ultraviolet (short-wavelength) photons would be immediately absorbed by the hydrogen atoms, “knocking” electrons off those atoms, while longer-wavelength photons could travel much farther. The intergalactic gas thus again became ionized in steadily growing spheres around the ionizing sources.

At some moment, these spheres had become so big that they overlapped completely; this is referred to as the “epoch of re-ionization”. Until then, the ultraviolet radiation was absorbed by the atoms, but the Universe now also became transparent to this radiation. Before, the ultraviolet light from those first stars and galaxies could not be seen over large distances, but now the Universe suddenly appeared to be full of bright objects. It is for this reason that the time interval between the epochs of “recombination” and “re-ionization” is referred to as the “Dark Ages”.

When was the end of the “Dark Ages”?
The exact epoch of re-ionization is a subject of active debate among astronomers, but recent results from ground and space observations indicate that the “Dark Ages” lasted a few hundred million years. Various research programmes are now underway which attempt to determine better when these early events happened. For this, it is necesary to find and study in detail the earliest and hence, most distant, objects in the Universe – and this is a very demanding observational endeavour.

Light is dimmed by the square of the distance and the further we look out in space to observe an object – and therefore the further back in time we see it – the fainter it appears. At the same time, its dim light is shifted towards the red region of the spectrum due to the expansion of the Universe – the larger the distance, the larger the observed redshift [3].

The Lyman-alpha emission line
With ground-based telescopes, the faintest detection limits are achieved by observations in the visible part of the spectrum. The detection of very distant objects therefore requires observations of ultraviolet spectral signatures which have been redshifted into the visible region. Normally, the astronomers use for this the redshifted Lyman-alpha spectral emission line with rest wavelength 121.6 nm; it corresponds to photons emitted by hydrogen atoms when they change from an excited state to their fundamental state.

One obvious way of searching for the most distant galaxies is therefore to search for Lyman-alpha emission at the reddest (longest) possible wavelengths. The longer the wavelength of the observed Lyman-alpha line, the larger is the redshift and the distance, and the earlier is the epoch at which we see the galaxy and the closer we come towards the moment that marked the end of the “Dark Ages”.

CCD-detectors used in astronomical instruments (as well as in commercial digital cameras) are sensitive to light of wavelengths up to about 1000 nm (1 ?m), i.e., in the very near-infrared spectral region, beyond the reddest light that can be perceived by the human eye at about 700-750 nm.

The bright near-infrared night sky
There is another problem, however, for this kind of work. The search for faint Lyman-alpha emission from distant galaxies is complicated by the fact that the terrestrial atmosphere – through which all ground-based telescopes must look – also emits light. This is particularly so in the red and near-infrared part of the spectrum where hundreds of discrete emission lines originate from the hydroxyl molecule (the OH radical) that is present in the upper terrestrial atmosphere at an altitude of about 80 km (see PR Photo 13a/03).

This strong emission which the astronomers refer to as the “sky background” is responsible for the faintness limit at which celestial objects can be detected with ground-based telescopes at near-infrared wavelengths. However, there are fortunately spectral intervals of “low OH-background” where these emission lines are much fainter, thus allowing a fainter detection limit from ground observations. Two such “dark-sky windows” are evident in PR Photo 13a/03 near wavelengths of 820 and 920 nm.

Considering these aspects, a promising way to search efficiently for the most distant galaxies is therefore to observe at wavelengths near 920 nm by means of a narrow-band optical filter. Adapting the spectral width of this filter to about 10 nm allows the detection of as much light from the celestial objects as possible when emitted in a spectral line matching the filter, while minimizing the adverse influence of the sky emission.

In other words, with a maximum of light collected from the distant objects and a minimum of disturbing light from the terrestrial atmosphere, the chances for detecting those distant objects are optimal. The astronomers talk about “maximizing the contrast” of objects showing emission lines at this wavelength.

The CFHT Search Programme
Based on the above considerations, an international team of astronomers [2] installed a narrow-band optical filter centered at the near-infrared wavelength 920 nm on the CFH12K instrument at the Canada-France-Hawaii telescope on Mauna Kea (Hawaii, USA) to search for extremely distant galaxies. The CFH12K is a wide-field camera used at the prime focus of the CFHT, providing a field-of-view of approx. 30 x 40 arcmin2, somewhat larger than the full moon [5].

By comparing images of the same sky field taken through different filters, the astronomers were able to identify objects which appear comparatively “bright” in the NB920 image and “faint” (or are even not visible) in the corresponding images obtained through the other filters. A striking example is shown in PR Photo 13b/03 – the object at the center is well visible in the 920nm image, but not at all in the other images.

The most probable explanation for an object with such an unusual colour is that it is a very distant galaxy for which the observed wavelength of the strong Lyman-alpha emission line is close to 920 nm, due to the redshift. Any light emitted by the galaxy at wavelengths shorter than Lyman-alpha is strongly absorbed by intervening interstellar and intergalactic hydrogen gas; this is the reason that the object is not visible in all the other filters.

The VLT spectrum
In order to learn the true nature of this object, it is necessary to perform a spectroscopic follow-up, by observing its spectrum. This was accomplished with the FORS 2 multi-mode instrument at the 8.2-m VLT YEPUN telescope at the ESO Paranal Observatory. This facility provides a perfect combination of moderate spectral resolution and high sensitivity in the red for this kind of very demanding observation. The resulting (faint) spectrum is shown in PR Photo 13c/03.

PR Photo 13d/03 shows a tracing of the final (“cleaned”) spectrum of the object after extraction from the image shown in PR Photo 13c/03. One broad emission line is clearly detected (to the left of the center; enlarged in the insert). It is asymmetric, being depressed on its blue (left) side. This, combined with the fact that no continuum light is detected to the left of the line, is a clear spectral signature of the Lyman-alpha line: photons “bluer” than Lyman-alpha are heavily absorbed by the gas present in the galaxy itself, and in the intergalactic medium along the line-of-sight between the Earth and the object.

The spectroscopic observations therefore allowed the astronomers to identify unambiguously this line as Lyman-alpha, and therefore to confirm the great distance (high redshift) of this particular object. The measured redshift is 6.17, making this object one of the most distant galaxies ever detected. It received the designation “z6VDF J022803-041618” – the first part of this somewhat unwieldy name refers to the survey and the second indicates the position of this galaxy in the sky.

Starlight in the early Universe
However, these observations did not come without surprise! The astronomers had hoped (and expected) to detect the Lyman-alpha line from the object at the center of the 920 nm spectral window. However, while the Lyman-alpha line was found, it was positioned at a somewhat shorter wavelength.

Thus, it was not the Lyman-alpha emission that caused this galaxy to be “bright” in the narrow-band (NB920) image, but “continuum” emission at wavelengths longer than that of Lyman-alpha. This radiation is very faintly visible as a horizontal, diffuse line in PR Photo 13c/03.

One consequence is that the measured redshift of 6.17 is lower than the originally predicted redshift of about 6.5. Another is that z6VDF J022803-041618 was detected by light from its massive stars (the “continuum”) and not by emission from hydrogen gas (the Lyman-alpha line).

This interesting conclusion is of particular interest as it shows that it is in principle possible to detect galaxies at this enormous distance without having to rely on the Lyman-alpha emission line, which may not always be present in the spectra of the distant galaxies. This will provide the astronomers with a more complete picture of the galaxy population in the early Universe.

Moreover, observing more and more of these distant galaxies will help to better understand the ionization state of the Universe at this age: the ultraviolet light emitted by these galaxies should not reach us in a “neutral” Universe, i.e., before re-ionization occurred. The hunt for more such galaxies is now on to clarify how the transition from the Dark Ages happened!

Original Source: ESO News Release

Satellite Accidently Spots a Gamma-Ray Burst

Image credit: NASA

NASA’s RHESSI satellite may have uncovered new clues about the most powerful explosions in the Universe when it accidentally caught an image of a gamma-ray burst while capturing images of solar flares on the Sun. What RHESSI discovered is that the light coming from the burst is polarized, which indicates that a powerful magnetic field could be the cause. When a giant star becomes a rapidly spinning black hole, it could twist up the magnetic field so much that the whole object explodes like an uncoiled spring.

NASA’s RHESSI satellite may have uncovered one of the most important clues yet obtained on the mechanism for producing gamma-ray bursts, the most powerful explosions in the universe. This was the result of a chance observation by a satellite designed to study the Sun.

The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) satellite was snapping pictures of solar flares on December 6, 2002, when it caught an extremely bright gamma-ray burst in the background, over the edge of the Sun, revealing for the first time that the gamma rays in such a burst are polarized. The result indicates intense magnetic fields may be the driving force behind these awesome explosions.

Solar flares are tremendous explosions in the atmosphere of the Sun, powered by the sudden release of magnetic energy. Gamma-ray bursts are remote flashes of gamma-ray light that pop off about once a day randomly in the sky, briefly shining as bright as a million trillion suns. Recent observations suggest they may be produced by a special kind of exploding star (supernova), but not all supernovae generate gamma-ray bursts, so the physics of how a supernova explosion can produce a burst of gamma-rays is unclear.

The findings are being presented in a press conference at the American Astronomical Society meeting in Nashville, Tenn., by two University of California, Berkeley, researchers: Dr. Wayne Coburn, a postdoctoral fellow at UC Berkeley’s Space Sciences Laboratory, and Dr. Steven Boggs, assistant professor of physics. They are authors of a paper about this discovery published in the May 22 issue of Nature.

“RHESSI was sent into space to uncover the secrets of solar flares, the largest explosions in our Solar System, so I am delighted that it has been able to serendipitously provide new information about gamma-ray bursts, the largest explosions in the whole universe,” said Dr. Brian Dennis, RHESSI Mission Scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md.

“Curiously, magnetic fields seem to be driving both the local solar flares and the distant gamma-ray bursts, two immensely powerful events,” added Dennis.

The strong polarization measured by RHESSI provides a unique window on how these bursts are powered, according to Boggs. He interprets the measurements to mean that the burst originates from a region of highly structured magnetic fields, stronger than the fields at the surface of a neutron star – until now, the strongest magnetic fields observed in the universe. “The polarization is telling us that the magnetic fields themselves are acting as the dynamite, driving the explosive fireball we see as a gamma-ray burst,” he said.

The gamma rays measured by RHESSI were about 80 percent polarized, consistent with the maximum possible polarization from electrons spiraling around magnetic field lines. The spiraling causes electrons to produce light by “synchrotron radiation”. Polarized light, familiar to most of us as the reflected light blocked by Polaroid sunglasses, is light with its magnetic and electric fields vibrating primarily in one direction, not randomly. Such coherence implies an underlying physical symmetry, in this case, aligned magnetic fields.

Though the electrons are probably accelerated to nearly the speed of light in shock waves, the fact that the gamma rays are maximally polarized implies that the shock waves themselves are driven by an underlying strong magnetic field.

“The amount of polarization they found is so intense, that it looks like it’s pure synchrotron radiation and nothing else, and all the other theories are going to have to bite the dust now,” said Dr. Kevin Hurley, a UC Berkeley gamma-ray burst physicist who since 1990 has operated the Third Interplanetary Network (IPN3) of six satellites linked together to pinpoint gamma-ray bursts and immediately alert astronomers. However, for such a novel measurement, further independent confirmation is crucial, Boggs added.

The discovery of polarization reveals how a gamma-ray burst is powered – through the generation of a strong, large-scale magnetic field. The next question is: Why do some supernovae lead to a strong, organized magnetic field? This might be a question we can only address through theory, but the pieces of evidence are in place for theorists to unravel, Boggs said.

Though he leaves it to theorists to work out how such strong magnetic fields could be generated, Boggs said that the burst is probably preceded by the core collapse of a massive star directly to a black hole. A black hole itself has no magnetic field, but the local magnetic field can thread through the black hole. If rapidly spinning, the black hole will wind up the local field like a string on a top. The energy density in the tightly wound, compressed field would eventually get so high that the field would rebound outward in a massive fireball, dragging matter with it.

Original Source: NASA News Release

Astronomers Find a Supernova Factory

Image credit: NRAO

Using the National Science Foundation’s Very Long Baseline Array (VLBA), astronomers have discovered a recently exploded supernova 140 million light years from Earth. The supernova is in a region where two galaxies are colliding together, and furiously forming new stars. The astronomers consider this super star cluster region a “supernova factory” because a star goes off there once every two years – they’re hoping to catch more massive stars going supernova.

Using the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope, astronomers have discovered a newly-exploded star, or supernova, hidden deep in a dust-enshrouded “supernova factory” in a galaxy some 140 million light-years from Earth.

“This supernova is likely to be part of a group of super star clusters that produce one such stellar explosion every two years,” said James Ulvestad, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. “We’re extremely excited by the tremendous insights into star formation and the early Universe that we may gain by observing this ‘supernova factory,'” he added.

Ulvestad worked with Susan Neff of NASA’s Goddard Space Flight Center in Greenbelt, MD, and Stacy Teng, a graduate student at the University of Maryland, on the project. The scientists presented their findings to the American Astronomical Society’s meeting in Nashville, TN.

“These super star clusters likely are forming in much the same way that globular clusters formed in the early Universe, and thus provide us with a unique opportunity to learn about how some of the first stars formed billions of years ago,” Neff said.

The cluster is in an object called Arp 299, a pair of colliding galaxies, where regions of vigorous star formation have been found in past observations. Since 1990, four other supernova explosions have been seen optically in Arp 299.

Observations with the NSF’s Very Large Array (VLA) earlier showed a region near the nucleus of one of the colliding galaxies which had all the earmarks of prolific star formation. The astronomers focused on this region, prosaically dubbed “Source A,” with the VLBA and the NSF’s Robert C. Byrd Green Bank Telescope in 2002, and found four objects in this dusty cloud that are likely young supernova remnants. When they observed the region again in February 2003, there was a new, fifth, object located only 7 light-years from one of the previously detected objects.

More observations on April 30-May 1, 2003, showed that this new object has typical characteristics of a supernova explosion by a young, massive star.

“This supernova is exploding in a very dense environment, quite different from the environments of supernova explosions that can be seen in visible light,” Teng said. “This is the kind of dense environment in which stars likely formed in the early Universe,” she added.

The astronomers believe the super star cluster in Arp 299 saw its most recent peak of star formation some 6-8 million years ago, and now its massive stars, 10-20 times (or more) as massive as the Sun, are ending their lives in supernova explosions. Super star clusters typically contain up to a million stars, which is why the scientists think Source A will see frequent supernova explosions.

“We plan to keep watching this region, and hope that we can study numerous supernovae, and gain important new information about the processes of star formation, both in the early Universe and at the present time,” Neff said.

“Because of the dust and the distance, only a radio telescope with the VLBA’s ability to see fine detail can find the supernovae in this region,” Ulvestad said.

The VLBA is a continent-wide system of ten radio- telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east, providing the greatest resolving power, or ability to see fine detail, in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO’s Array Operations Center in Socorro, New Mexico.

The VLBA has made landmark contributions to astronomy, including making the most accurate distance measurement ever made of an object beyond the Milky Way Galaxy; the first mapping of the magnetic field of a star other than the Sun; “movies” of motions in powerful cosmic jets and of distant supernova explosions; the first measurement of the propagation speed of gravity; and long-term measurements that have improved the reference frame used to map the Universe and detect tectonic motions of Earth’s continents.

Original Source: NRAO News Release

Galaxy Orbiting Milky Way in the Wrong Direction

Image credit: NRAO

Before this week, “Complex H” was thought to be a strange cloud of stars with an unusual trajectory near the Milky Way. But as it turns out, this object is actually a companion galaxy crashing into the outer reaches of our own galaxy in exactly the opposite direction of the Milky Way’s rotation. New observations from the National Science Foundation’s Robert C. Byrd Green Bank Telescope (the world’s largest steerable radio telescope) have placed the object at 108,000 light years from the Milky Way’s centre.

New observations with National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) suggest that what was once believed to be an intergalactic cloud of unknown distance and significance, is actually a previously unrecognized satellite galaxy of the Milky Way orbiting backward around the Galactic center.

Jay Lockman of the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, discovered that this object, known as “Complex H,” is crashing through the outermost parts of the Milky Way from an inclined, retrograde orbit. Lockman’s findings will be published in the July 1 issue of the Astrophysical Journal, Letters.

“Many astronomers assumed that Complex H was probably a distant neighbor of the Milky Way with some unusual velocity that defied explanation,” said Lockman. “Since its motion appeared completely unrelated to Galactic rotation, astronomers simply lumped it in with other high velocity clouds that had strange and unpredictable trajectories.”

High velocity clouds are essentially what their name implies, fast-moving clouds of predominately neutral atomic hydrogen. They are often found at great distances from the disk of the Milky Way, and may be left over material from the formation of our Galaxy and other galaxies in our Local Group. Over time, these objects can become incorporated into larger galaxies, just as small asteroids left over from the formation of the solar system sometimes collide with the Earth.

Earlier studies of Complex H were hindered because the cloud currently is passing almost exactly behind the outer disk of the Galaxy. The intervening dust and gas that reside within the sweeping spiral arms of the Milky Way block any visible light from this object from reaching the Earth. Radio waves, however, which have a much longer wavelength than visible light, are able to pass through the intervening dust and gas.

The extreme sensitivity of the recently commissioned GBT allowed Lockman to clearly map the structure of Complex H, revealing a dense core moving on an orbit at a 45-degree angle to the plane of the Milky Way. Additionally, the scientist detected a more diffuse region surrounding the central core. This comparatively rarefied region looks like a tail that is trailing behind the central mass, and is being decelerated by its interaction with the Milky Way.

“The GBT was able to show that this object had a diffuse ‘tail’ trailing behind, with properties quite different from its main body,” said Lockman. “The new data are consistent with a model in which this object is a satellite of the Milky Way in an inclined, retrograde orbit, whose outermost layers are currently being stripped away in its encounter with the Galaxy.”

These results place Complex H in a small club of Galactic satellites whose orbits do not follow the rotation of the rest of the Milky Way. Among the most prominent of these objects are the Magellanic Clouds, which also are being affected by their interaction with the Milky Way, and are shedding their gas in a long stream.

Since large galaxies, like the Milky Way, form by devouring smaller galaxies, clusters of stars, and massive clouds of hydrogen, it is not unusual for objects to be pulled into orbit around the Galaxy from directions other than that of Galactic rotation.

“Astronomers have seen evidence that this accreting material can come in from wild orbits,” said Butler Burton, an astronomer with the NRAO in Charlottesville, Virginia. “The Magellanic clouds are being torn apart from their interaction with the Milky Way, and there are globular clusters rotating the wrong way. There is evidence that stuff was going every-which-way at the beginning of the Galaxy, and Complex H is probably left over from that chaotic period.”

The new observations place Complex H at approximately 108,000 light-years from the Galactic center, and indicate that it is nearly 33,000 light-years across, containing approximately 6 million solar masses of hydrogen.

Radio telescopes, like the GBT, are able to observe these cold, dark clouds of hydrogen because of the natural electromagnetic radiation emitted by neutral atomic hydrogen at radio wavelengths (21 centimeters).

Globular clusters, and certain other objects in the extended Galactic halo, can be studied with optical telescopes because the material in them has collapsed to form hot, bright stars.

The GBT is the world’s largest fully steerable radio telescope. It was commissioned in August of 2000, and continues to be outfitted with the sensitive receivers and components that will allow it to make observations at much higher frequencies.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Uncovering More Details About the Solar Wind

Image credit: SOHO

The ESA’s SOHO spacecraft has uncovered new details about the Sun’s solar wind which might overturn previously held theories about exactly how the wind is generated. Astronomers believed that the fast wind emanates from gaps between giant plumes found near the Sun’s polar regions. But the new theory, supported by data from SOHO is that it’s the plumes themselves which are hurling the particles of the fast wind into space. If this controversial theory turns out to be correct, it will clear up a big misunderstanding about the Sun.

We have known for 40 years that space weather affects the Earth, which is buffeted by a ‘wind’ from the Sun, but only now are we learning more about its precise origins. Solving the mystery of the solar wind has been a prime task for ESA’s SOHO spacecraft. Its latest findings, announced on 20 May 2003, may overturn previous ideas about the origin of the ‘fast’ solar wind, which occurs in most of the space around the Sun.

Earlier results from SOHO established that the gas of the fast wind leaks through magnetic barriers near the Sun’s visible surface. Straight, spoke-like features called plumes have also been seen rising from the solar atmosphere at the polar regions, where much of the fast wind comes from. According to previous ideas, the gas of the fast wind streams out in the gaps between the plumes.

“Not so,” says Alan Gabriel of the Institut d’Astrophysique Spatiale near Paris, France. Careful observations with SOHO now suggest that most of the fast wind leaves the Sun via the plumes themselves, which are denser than their surroundings. Gabriel and his team tracked gas rising at about 60 kilometres per second to a height of 250 000 kilometres above the Sun’s visible surface.

“If this controversial result is right, it will clear up a big misunderstanding,” says Bernhard Fleck, ESA’s Project Scientist for SOHO. “We need to know how the fast wind is subsequently accelerated to 750 kilometres per second. To find out, we’d better be looking in the right places.”

SOHO has also investigated the origin of a slower wind, half the speed of the fast wind, which comes from the Sun’s equatorial regions. The gas of the ‘slow’ wind leaks from triangular features called ‘helmets’, which are plainly protruding into the Sun’s atmosphere during a solar eclipse. Blasts of gas called ‘coronal mass ejections’ also contribute to the solar wind in the equatorial zone of the Sun.

The ESA/NASA Ulysses spacecraft has twice passed over the poles of the Sun and signalled the relative importance of these fast and slow winds. Its measurements show that the fast wind predominates in the heliosphere, which is a huge bubble blown into interstellar space by the Sun’s outpourings, and extending far beyond the outermost planets. In interplanetary space, the fast wind often collides with the slow wind. Like the mass ejections, the collisions create shock waves that agitate the Earth’s space environment.

The four satellites of ESA’s Cluster mission are now studying the interaction between the solar wind and our planet’s defences. The Earth’s magnetic field creates a bubble within the heliosphere, but it does not give us perfect protection from Sun’s storms. Ulysses, SOHO, and Cluster together provide an extraordinary overview of solar behaviour and its effects, both near and far in the Solar System.

Original Source: ESA News Release

Researchers Stop Light in Its Tracks

Image credit: NASA

Researchers at Harvard University demonstrated that they can slow light and even completely stop it for several thousandths of a second. They built a chamber containing a cloud of sodium atoms cooled to almost absolute zero and then fired a light pulse into this cloud. The pulse slowed to a stop and even turned off ? the researchers were able to revive it again by firing a laser into the cloud. Although this breakthrough happened a couple of years ago, and an upcoming special edition of Scientific American called ?The Edge of Physics? will provide an update to the research.

NASA-funded research at Harvard University, Cambridge, Mass., that literally stops light in its tracks, may someday lead to breakneck-speed computers that shelter enormous amounts of data from hackers.

The research, conducted by a team led by Dr. Lene Hau, a Harvard physics professor, is one of 12 research projects featured in a special edition of Scientific American entitled “The Edge of Physics,” available through May 31.

In their laboratory, Hau and her colleagues have been able to slow a pulse of light, and even stop it, for several-thousandths of a second. They’ve also created a roadblock for light, where they can shorten a light pulse by factors of a billion.

“This could open up a whole new way to use light, doing things we could only imagine before,” Hau said. “Until now, many technologies have been limited by the speed at which light travels.”

The speed of light is approximately 300,000 kilometers per second (about 186,000 miles per second or 670 million miles per hour). Some substances, like water and diamonds, can slow light to a limited extent. More drastic techniques are needed to dramatically reduce the speed of light. Hau’s team accomplished “light magic” by laser-cooling a cigar-shaped cloud of sodium atoms to one-billionth of a degree above absolute zero, the point where scientists believe no further cooling can occur. Using a powerful electromagnet, the researchers suspended the cloud in an ultra-high vacuum chamber, until it formed a frigid, swamp-like goop of atoms.

When they shot a light pulse into the cloud, it bogged down, slowed dramatically, eventually stopped, and turned off. The scientists later revived the light pulse and restored its normal speed by shooting an additional laser beam into the cloud.

Hau’s cold-atom research began in the mid-1990s, when she put ultra-cold atoms in such cramped quarters they formed a type of matter called a Bose-Einstein condensate. In this state, atoms behave oddly, and traditional laws of physics do not apply. Instead of bouncing off each other like bumper cars, the atoms join together and function as one entity.

The first slow-light breakthrough for Hau and her colleagues came in March 1998. Later that summer, they successfully slowed a light beam to 38 miles per hour, the speed of suburban traffic. That’s 2 million times slower than the speed of light in free space. By tinkering with the system, Hau and her team made light stop completely in the summer of 2000.

These breakthroughs may eventually be used in advanced optical-communication applications. “Light can carry enormous amounts of information through changes in its frequency, phase, intensity or other properties,” Hau said. When the light pulse stops its information is suspended and stored, just as information is stored in the memory of a computer. Light-carrying quantum bits could carry significantly more information than current computer bits. Quantum computers could also be more secure by encrypting information in elaborate codes that could be broken only by using a laser and complex decoding formulas.

Hau’s team is also using slow light as a completely new probe of the very odd properties of Bose-Einstein condensates. For example, with the light roadblock the team created, they can study waves and dramatic rotating-vortex patterns in the condensates.

The Harvard research team includes Hau; Drs. Zachary Dutton, Chien Liu, Brian Busch and Michael Budde; and graduate students Christopher Slowe, Naomi Ginsberg and Cyrus Behroozi. More information about Hau’s research is available on the Internet, at

For information about NASA’s Fundamental Physics Program on the Internet, visit or

Hau conducts research under NASA’s Fundamental Physics in Physical Sciences Research Program, part of the agency’s Office of Biological and Physical Research, Washington. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology, Pasadena, manages the Fundamental Physics program.

Original Source: NASA News Release