Posted on by Fraser Cain

Helicopter Will Catch Samples from Genesis

In a dramatic ending that marks a beginning in scientific research, NASA’s Genesis spacecraft is set to swing by Earth and jettison a sample return capsule filled with particles of the Sun that may ultimately tell us more about the genesis of our solar system.

“The Genesis mission — to capture a piece of the Sun and return it to Earth — is truly in the NASA spirit: a bold, inspiring mission that makes a fundamental contribution to scientific knowledge,” said Steven Brody, NASA’s program executive for the Genesis mission, NASA Headquarters, Washington.

On September 8, 2004, the drama will unfold over the skies of central Utah when the spacecraft’s sample return capsule will be snagged in midair by helicopter. The rendezvous will occur at the Air Force’s Utah Test and Training Range, southwest of Salt Lake City.

“What a prize Genesis will be,” said Genesis Principal Investigator Dr. Don Burnett of the California Institute of Technology, Pasadena, Calif. “Our spacecraft has logged almost 27 months far beyond the moon’s orbit, collecting atoms from the Sun. With it, we should be able to say what the Sun is composed of, at a level of precision for planetary science purposes that has never been seen before.”

The prizes Burnett and company are waiting for are hexagonal wafers of pure silicon, gold, sapphire, diamond and other materials that have served as a celestial prison for their samples of solar wind particles. These wafers have weathered 26-plus months in deep space and are now safely stowed in the return capsule. If the capsule were to descend all the way to the ground, some might fracture or break away from their mountings; hence, the midair retrieval by helicopter, with crew members including some who have performed helicopter stunt work for Hollywood.

“These guys fly in some of Hollywood’s biggest movies,” said Don Sweetnam, Genesis project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “But this time, the Genesis capsule will be the star.”

The Genesis capsule — carrying the agency’s first sample return since the final Apollo lunar mission in 1972, and the first material collected beyond the Moon — will enter Earth’s atmosphere at 9:55 am Mountain Time. Two minutes and seven seconds after atmospheric entry, while still flying supersonically, the capsule will deploy a drogue parachute at 33 kilometers (108,000 feet) altitude. Six minutes after that, the main parachute, a parafoil, will deploy 6.1 kilometers (20,000 feet) up. Waiting below will be two helicopters and their flight crews looking for their chance to grab a piece of the Sun.

“Each helicopter will carry a crew of three,” said Roy Haggard, chief executive officer of Vertigo Inc. and director of flight operations for the lead helicopter. “The lead helicopter will deploy an eighteen-and-a-half foot long pole with what you could best describe as an oversized, Space-Age fishing hook on its end. When we make the approach we want the helicopter skids to be about eight feet above the top of the parafoil. If for some reason the capture is not successful, the second helicopter is 1,000 feet behind us and setting up for its approach. We estimate we will have five opportunities to achieve capture.”

The helicopter that does achieve capture will carry the sample canister to a clean room at the Michael Army Air Field at the U.S. Army Dugway Proving Ground, where scientists await their cosmic prize. The samples will then be moved to a special laboratory at NASA’s Johnson Space Center, Houston, where they will be preserved and studied by scientists for many years to come.

“I understand much of the interest is in how we retrieve Genesis,” added Burnett. “But to me the excitement really begins when scientists from around the world get hold of those samples for their research. That will be something.”

JPL, a division of the California Institute of Technology, manages the Genesis mission for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, developed and operates the spacecraft. Los Alamos National Laboratory and NASA’s Johnson Space Center contributed to Genesis payload development, and the Johnson Space Center will curate the sample and support analysis and sample allocation.

News and information are available at http://www.nasa.gov/genesis. More detailed background on the mission is available at http://genesismission.jpl.nasa.gov/.

Original Source: NASA News Release

Posted on by Fraser Cain

Estimating the Age of the Milky Way

Observations by an international team of astronomers with the UVES spectrometer on ESO’s Very Large Telescope at the Paranal Observatory (Chile) have thrown new light on the earliest epoch of the Milky Way galaxy.

The first-ever measurement of the Beryllium content in two stars in a globular cluster (NGC 6397) – pushing current astronomical technology towards the limit – has made it possible to study the early phase between the formation of the first generation of stars in the Milky Way and that of this stellar cluster. This time interval was found to amount to 200 – 300 million years.

The age of the stars in NGC 6397, as determined by means of stellar evolution models, is 13,400 ? 800 million years. Adding the two time intervals gives the age of the Milky Way, 13,600 ? 800 million years.

The currently best estimate of the age of Universe, as deduced, e.g., from measurements of the Cosmic Microwave Background, is 13,700 million years. The new observations thus indicate that the first generation of stars in the Milky Way galaxy formed soon after the end of the ~200 million-year long “Dark Ages” that succeeded the Big Bang.

The age of the Milky Way
How old is the Milky Way ? When did the first stars in our galaxy ignite ?

A proper understanding of the formation and evolution of the Milky Way system is crucial for our knowledge of the Universe. Nevertheless, the related observations are among the most difficult ones, even with the most powerful telescopes available, as they involve a detailed study of old, remote and mostly faint celestial objects.

Globular clusters and the ages of stars

Modern astro physics is capable of measuring the ages of certain stars, that is the time elapsed since they were formed by condensation in huge interstellar clouds of gas and dust. Some stars are very “young” in astronomical terms, just a few million years old like those in the nearby Orion Nebula. The Sun and its planetary system was formed about 4,560 million years ago, but many other stars formed much earlier. Some of the oldest stars in the Milky Way are found in large stellar clusters, in particular in “globular clusters” (PR Photo 23a/04), so called because of their spheroidal shape.

Stars belonging to a globular cluster were born together, from the same cloud and at the same time. Since stars of different masses evolve at different rates, it is possible to measure the age of globular clusters with a reasonably good accuracy. The oldest ones are found to be more than 13,000 million years old.

Still, those cluster stars were not the first stars to be formed in the Milky Way. We know this, because they contain small amounts of certain chemical elements which must have been synthesized in an earlier generation of massive stars that exploded as supernovae after a short and energetic life. The processed material was deposited in the clouds from which the next generations of stars were made, cf. ESO PR 03/01.

Despite intensive searches, it has until now not been possible to find less massive stars of this first generation that might still be shining today. Hence, we do not know when these first stars were formed. For the time being, we can only say that the Milky Way must be older than the oldest globular cluster stars.

But how much older?

Beryllium to the rescue
What astrophysicists would like to have is therefore a method to measure the time interval between the formation of the first stars in the Milky Way (of which many quickly became supernovae) and the moment when the stars in a globular cluster of known age were formed. The sum of this time interval and the age of those stars would then be the age of the Milky Way.

New observations with the VLT at ESO’s Paranal Observatory have now produced a break-through in this direction. The magic element is “Beryllium”!

Beryllium is one of the lightest elements [2] – the nucleus of the most common and stable isotope (Beryllium-9) consists of four protons and five neutrons. Only hydrogen, helium and lithium are lighter. But while those three were produced during the Big Bang, and while most of the heavier elements were produced later in the interior of stars, Beryllium-9 can only be produced by “cosmic spallation”. That is, by fragmentation of fast-moving heavier nuclei – originating in the mentioned supernovae explosions and referred to as energetic “galactic cosmic rays” – when they collide with light nuclei (mostly protons and alpha particles, i.e. hydrogen and helium nuclei) in the interstellar medium.

Galactic cosmic rays and the Beryllium clock
The galactic cosmic rays travelled all over the early Milky Way, guided by the cosmic magnetic field. The resulting production of Beryllium was quite uniform within the galaxy. The amount of Beryllium increased with time and this is why it might act as a “cosmic clock”.

The longer the time that passed between the formation of the first stars (or, more correctly, their quick demise in supernovae explosions) and the formation of the globular cluster stars, the higher was the Beryllium content in the interstellar medium from which they were formed. Thus, assuming that this Beryllium is preserved in the stellar atmosphere, the more Beryllium is found in such a star, the longer is the time interval between the formation of the first stars and of this star.

The Beryllium may therefore provide us with unique and crucial information about the duration of the early stages of the Milky Way.

A very difficult observation
So far, so good. The theoretical foundations for this dating method were developed during the past three decades and all what is needed is then to measure the Beryllium content in some globular cluster stars.

But this is not as simple as it sounds! The main problem is that Beryllium is destroyed at temperatures above a few million degrees. When a star evolves towards the luminous giant phase, violent motion (convection) sets in, the gas in the upper stellar atmosphere gets into contact with the hot interior gas in which all Beryllium has been destroyed and the initial Beryllium content in the stellar atmosphere is thus significantly diluted. To use the Beryllium clock, it is therefore necessary to measure the content of this element in less massive, less evolved stars in the globular cluster. And these so-called “turn-off (TO) stars” are intrinsically faint.

In fact, the technical problem to overcome is three-fold: First, all globular clusters are quite far away and as the stars to be measured are intrinsically faint, they appear quite faint in the sky. Even in NGC6397, the second closest globular cluster, the TO stars have a visual magnitude of ~16, or 10000 times fainter than the faintest star visible to the unaided eye. Secondly, there are only two Beryllium signatures (spectral lines) visible in the stellar spectrum and as these old stars do contain comparatively little Beryllium, those lines are very weak, especially when compared to neighbouring spectral lines from other elements. And third, the two Beryllium lines are situated in a little explored spectral region at wavelength 313 nm, i.e., in the ultraviolet part of the spectrum that is strongly affected by absorption in the terrestrial atmosphere near the cut-off at 300 nm, below which observations from the ground are no longer possible.

It is thus no wonder that such observations had never been made before, the technical difficulties were simply unsurmountable.

VLT and UVES do the job
Using the high-performance UVES spectrometer on the 8.2-m Kuyen telescope of ESO’s Very Large Telescope at the Paranal Observatory (Chile) which is particularly sensitive to ultraviolet light, a team of ESO and Italian astronomers [1] succeeded in obtaining the first reliable measurements of the Beryllium content in two TO-stars (denoted “A0228” and “A2111”) in the globular cluster NGC 6397 (PR Photo 23b/04). Located at a distance of about 7,200 light-years in the direction of a rich stellar field in the southern constellation Ara, it is one of the two nearest stellar clusters of this type; the other is Messier 4.

The observations were done during several nights in the course of 2003. Totalling more than 10 hours of exposure on each of the 16th-magnitude stars, they pushed the VLT and UVES towards the technical limit. Reflecting on the technological progress, the leader of the team, ESO-astronomer Luca Pasquini, is elated: “Just a few years ago, any observation like this would have been impossible and just remained an astronomer’s dream!”

The resulting spectra (PR Photo 23c/04) of the faint stars show the weak signatures of Beryllium ions (Be II). Comparing the observed spectrum with a series of synthetic spectra with different Beryllium content (in astrophysics: “abundance”) allowed the astronomers to find the best fit and thus to measure the very small amount of Beryllium in these stars: for each Beryllium atom there are about 2,224,000,000,000 hydrogen atoms.

Beryllium lines are also seen in another star of the same type as these stars, HD 218052, cf. PR Photo 23c/04. However, it is not a member of a cluster and its age is by far not as well known as that of the cluster stars. Its Beryllium content is quite similar to that of the cluster stars, indicating that this field star was born at about the same time as the cluster.

From the Big Bang until now
According to the best current spallation theories, the measured amount of Beryllium must have accumulated in the course of 200 – 300 million years. Italian astronomer Daniele Galli, another member of the team, does the calculation: “So now we know that the age of the Milky Way is this much more than the age of that globular cluster – our galaxy must therefore be 13,600 ? 800 million years old. This is the first time we have obtained an independent determination of this fundamental value!”.

Within the given uncertainties, this number also fits very well with the current estimate of the age of the Universe, 13,700 million years, that is the time elapsed since the Big Bang. It thus appears that the first generation of stars in the Milky Way galaxy was formed at about the time the “Dark Ages” ended, now believed to be some 200 million years after the Big Bang.

It would seem that the system in which we live may indeed be one of the “founding” members of the galaxy population in the Universe.

More Information
The research presented in this press release is discussed in a paper entitled “Be in turn-off stars of NGC 6397: early Galaxy spallation, cosmochronology and cluster formation” by L. Pasquini and co-authors that will be published in the European research journal “Astronomy & Astrophysics” (astro-ph/0407524).

Original Source: ESO News Release

Posted on by Fraser Cain

Rosetta Can “Smell” a Comet

Image credit: ESA
One of the ingenious instruments on board Rosetta is designed to ?smell? the comet for different substances, analysing samples that have been ?cooked? in a set of miniature ovens.

ESA?s Rosetta will be the first space mission ever to land on a comet. After its lander reaches Comet 67P/Churyumov-Gerasimenko, the main spacecraft will follow the comet for many months as it heads towards the Sun.

Rosetta’s task is to study comets, which are considered the primitive building blocks of the Solar System. This will help us to understand if life on Earth began with the help of ‘comet seeding’.

The Ptolemy instrument is an ?Evolved Gas Analyser?, the first example of a new concept in space instruments, devised to tackle the challenge of analysing substances ?on location? on bodies in our Solar System.

Weighing just 4.5 kilograms and about the size of a shoe box, it was produced by a collaboration of the UK?s Rutherford Appleton Laboratory and Open University.

The analysis of these samples from the surface of the comet will establish what the cometary nucleus is made from, providing valuable information about these most primitive objects.

After the lander touches down on the comet, the Ptolemy instrument will collect comet nucleus material, believed to be a frozen mixture of ices, dust and tar, using the Sampling, Drilling and Distribution system (SD2) supplied by Tecnospazio Milano of Italy. SD2 will drill for small cores of ice and dust from depths of down to 250 millimetres.

Samples collected in this way will be delivered to one of four tiny ?ovens? dedicated to Ptolemy, which are mounted on a circular, rotatable carousel. The German-supplied carousel has 32 of these ovens, with the remainder being used by other Rosetta instruments.

Of the four Ptolemy ovens, three are for solid samples collected and delivered by SD2 while the fourth will be used to collect volatile materials from the near-surface cometary atmosphere.

By heating the solid samples to 800 ?C, the oven converts them into gases which then pass along a pipe into Ptolemy. The gas will then be separated into its constituent chemical species using a gas chromatograph.

Ptolemy can then determine which chemicals are present in the comet sample, and hence help to build up a detailed picture of what the comet is made from.

It does this using the world?s smallest ?ion-trap mass spectrometer?, a small, low-power device built with the latest miniature technology. This device will find out what gases are present in any particular sample and measure stable isotope ratios.

Original Source: ESA News Release

Posted on by Fraser Cain

Eroded Valleys on Mars

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows the Dao Valles and Niger Valles, a system of outflow channels on Mars.

The image was taken during orbit 528 in June 2004, and shows the Dao Valles and Niger Valles areas at a point where the north-eastern Hellas impact crater basin and the Hesperia Planum volcanic region meet.

The image is centred at Mars longitude 93? East and latitude 32? South. The image resolution is 40 metres per pixel.

The outflow channel system is, in some areas, 40 kilometres wide. The north-eastern ends of the two valleys are almost 200 metres deeper than the south-western regions which are also shown here. The northern Dao Valles, 2400 metres deep, is about 1000 metres deeper than the more southern Niger Valles.

The structure of the valley floor of the Niger Valles is characterised by terraced basins and chaotic fractures. The floor of the Dao Valles is much smoother, but covered with strongly eroded remnants.

These eroded valleys are in a region which is part of the southern flank of the Hadriaca Patera volcano. The surrounding surface is formed by lava streams, probably in a ‘runoff’ process.

Original Source: ESA News Release

Posted on by Fraser Cain

Cassini Discovers Two New Moons

With eyes sharper than any that have peered at Saturn before, the Cassini spacecraft has uncovered two moons, which may be the smallest bodies so far seen around the ringed planet.

The moons are approximately 3 kilometers (2 miles) and 4 kilometers (2.5 miles) across — smaller than the city of Boulder, Colorado. The moons, located 194,000 kilometers (120,000 miles) and 211,000 kilometers (131,000 miles) from the planet’s center, are between the orbits of two other saturnian moons, Mimas and Enceladus. They are provisionally named S/2004 S1 and S/2004 S2. One of them, S/2004 S1, may be an object spotted in a single image taken by NASA’s Voyager spacecraft 23 years ago, called at that time S/1981 S14.

“One of our major objectives in returning to Saturn was to survey the entire system for new bodies,” said Dr. Carolyn Porco, imaging team leader, Space Science Institute, Boulder, Colo. Porco planned the imaging sequences. “So, it’s really gratifying to know that among all the other fantastic discoveries we will make over the next four years, we can now add the confirmation of two new moons, skipping unnoticed around Saturn for billions of years until just now.”

The moons were first seen by Dr. Sebastien Charnoz, a planetary dynamicist working with Dr. Andre Brahic, imaging team member at the University of Paris. “Discovering these faint satellites was an exciting experience, especially the feeling of being the first person to see a new body of our solar system,” said Charnoz. “I had looked for such objects for weeks while at my office in Paris, but it was only once on holiday, using my laptop, that my code eventually detected them. This tells me I should take more holidays.”

The smallest previously known moons around Saturn are about 20 kilometers (12 miles) across. Scientists expected that moons as small as S/2004 S1 and S/2004 S2 might be found within gaps in the rings and perhaps near the F ring, so they were surprised these small bodies are between two major moons. Small comets careening around the outer solar system would be expected to collide with small moons and break them to bits. The fact that these moons exist where they do might provide limits on the number of small comets in the outer solar system, a quantity essential for understanding the Kuiper Belt of comets beyond Neptune, and the cratering histories of the moons of the giant planets.

“A comet striking an inner moon of Saturn moves many times faster than a speeding bullet,” said Dr. Luke Dones, an imaging team member from the Southwest Research Institute in Boulder, Colo. “If small, house-sized comets are common, these moons should have been blown apart many times by cometary impacts during the history of the solar system. The disrupted moon would form a ring, and then most of the material would eventually gather back together into a moon. However, if small comets are rare, as they seem to be in the Jupiter system, the new moons might have survived since the early days of the solar system.”

Moons surrounding the giant planets generally are not found where they originally formed because tidal forces from the planet can cause them to drift from their original locations. In drifting, they may sweep through locations where other moons disturb them, making their orbits eccentric or inclined relative to the planet’s equator. One of the new moons might have undergone such an evolution.

Upcoming imaging sequences will scour the gaps in Saturn’s rings in search of moons believed to be there. Meanwhile, Cassini scientists are eager to get a closer look, if at all possible, at their new finds. Porco said, “We are at this very moment looking to see what the best times are for retargeting. Hopefully, we haven’t seen the last of them.”

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

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Chandra Sees Clouds Coming Together

A NASA Chandra X-ray Observatory image has revealed a complex of several intergalactic hot gas clouds in the process of merging. The superb Chandra spatial resolution made it possible to distinguish individual galaxies from the massive clouds of hot gas. One of the clouds, which that envelopes hundreds of galaxies, has an extraordinarily low concentration of iron atoms, indicating that it is in the very early stages of cluster evolution.

“We may be seeing hot intergalactic gas in a relatively pristine state before it has been polluted by gas from galaxies,” said Q. Daniel Wang of the University of Massachusetts in Amherst, and lead author on an upcoming Astrophysical Journal article describing the study. “This discovery should provide valuable insight into how the most massive structures in the universe are assembled.”

The complex, known as Abell 2125,is about 3 billion light years from Earth, and is seen at a time about 11 billion years after the Big Bang, when many galaxy clusters are believed to have formed. The Chandra Abell 2125 image shows several huge elongated clouds of multimillion degree gas coming together from different directions. These hot gas clouds, each of which contains hundreds of galaxies, appear to be in the process of merging to form a single massive galaxy cluster.

Chandra, Hubble Space Telescope, and Very Large Array radio telescope data show that several galaxies in the Abell 2125 core cluster are being stripped of their gas as they fall through surrounding high-pressure hot gas. This stripping process has enriched the core cluster’s gas in heavy elements such as iron.

The gas in the pristine cloud, which is still several million light years away from the core cluster, is conspicuous for its lack of iron atoms. This anemic cloud must be in a very early evolutionary stage. The iron atoms produced by supernovas in the embedded galaxies must still be contained in and around the galaxies, perhaps in grains of dust not well mixed with the observed X-ray-emitting gas. Over time, as the cluster merges with the other clusters and the hot gas pressure increases, the dust grains will be driven from the galaxies, mixed with the hot gas, and destroyed, liberating the iron atoms.

Building a massive galaxy cluster is a step-by-step enterprise that takes billions of years. Exactly how long it takes for such a cluster to form depends on many factors, such as the density of subclusters in the vicinity, the rate of the expansion of the universe, and the relative amounts of dark energy and dark matter.

Cluster formation also involves complex interactions between the galaxies and the hot gas that may determine how large the galaxies in the cluster can ultimately become. These interactions determine how the galaxies maintain their gas content, the fuel for star formation. The observations of Abell 2125 provide a rare glimpse into the early steps in this process.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:

http://chandra.harvard.edu
and
http://chandra.nasa.gov

Original Source: Chandra News Release

Posted on by Fraser Cain

Evidence for Planets Around a Young Star

The sharpest image ever taken of a dust disk around another star has revealed structures in the disk which are signs of unseen planets.

Dr. Michael Liu, an astronomer at the University of Hawaii’s Institute for Astronomy, has acquired high resolution images of the nearby star AU Microscopii (AU Mic) using the Keck Telescope, the world’s largest infrared telescope. At a distance of only 33 light years, AU Mic is the nearest star possessing a visible disk of dust. Such disks are believed to be the birthplaces of planets.

“We cannot yet directly image young planets around AU Mic, but they cannot completely hide from us either. They reveal themselves through their gravitational influence, forming patterns in the sea of dust grains orbiting the star,” said Dr. Liu.

The results will be published in the August 12th online Science Express and in the September print edition of Science.

A dust disk ordinarily would appear relatively featureless and symmetric, because any disturbances would be smoothed out as the material orbits the star. However, this is not observed in the case of AU Mic. Instead, Dr. Liu has found its disk is uneven and possesses clumps. These structures arise and are maintained due to the gravitational influence of unseen planetary companions.

The clumps in AU Mic’s disk lie at separations of 25 to 40 Astronomical Units away from the central star (where one Astronomical Unit is the distance from the Earth to the Sun), or about 2 to 4 billion miles. In our own solar system, this corresponds to the regions where Neptune and Pluto reside.

AU Mic is a dim red star, with only half the mass and one-tenth the energy output as the Sun. Previous studies have shown that AU Mic is about 12 million years old, an epoch believed to be an active phase of planet formation. In comparison, our Sun is about 4.6 billion years old, or about 400 times older, and planet formation has long since ended.

“By studying very young stars like AU Mic, we gain insight into the planet formation process as it is occurring. As a result, we learn about the birth of our own solar system and its planets,” said Liu.

The images alone cannot yet tell us what kinds of planets are present, only that the planets are massive enough to gravitationally alter the distribution of the dust. However, many structures in the AU Mic disk are observed to be elliptical (non-circular), indicating that the planetary orbits are elliptical. This is different than in our own solar system, where most planets follow circular orbits.

Images of disks around nearby stars are very rare. Earlier this year, Dr. Liu and his colleagues announced the discovery of the large dusty disk around AU Mic. The light from AU Mic’s disk arises from small dust particles which reflect the light of the central star. The new images are 30 times sharper than the earlier ones, enabling discovery of the clumps in the inner disk of AU Mic.

Dr. Liu used the Keck II Telescope located on Mauna Kea, Hawaii for this research. The two Keck Telescopes are the largest infrared telescopes in the world, each with a primary mirror of 10-meter (33 feet) in diameter. The telescopes are equipped with adaptive optics, a powerful technology which corrects astronomical images for the blurring caused by the Earth’s turbulent atmosphere.

The resulting infrared images are the sharpest ever obtained of a circumstellar disk, with an angular resolution of 1/25 of an arcsecond, about 1/500,000 the diameter of the full moon. If a person’s vision were as sharp as the Keck adaptive optics system, he would be able to read a magazine that was one mile away. In the case of AU Mic, the Keck images can see features as small as 0.4 Astronomical Units, less than half the distance from the Earth to the Sun.

“It is remarkable how quickly Adaptive Optics at Keck has come from being an exotic demonstration technology to producing scientific results of unprecedented quality,” said Dr. Frederic H. Chaffee, the director of the W. M. Keck Observatory. “We are entering a new age of high resolution imaging in astronomy. Dr. Liu’s breathtaking images of possible planets in formation around AU Mic would have been unimaginable from any telescope — space-based or on Earth — a few short years ago. This is an exciting time for us all.”

A preprint of the paper may be found at the astro-ph website

http://arxiv.org/abs/astro-ph/0408164

This work was supported in part by the National Science Foundation.

Original Source: IfA News Release

Posted on by Fraser Cain

Star Clusters Could Be Galaxy Remnants

Globular star clusters are like spherical cathedrals of light – collections of millions of stars lumped into a space only a few dozen light-years across. If the Earth resided within a globular cluster, our night sky would be alight with thousands of stars more brilliant than Sirius.

Our own Milky Way Galaxy currently holds about 200 globular clusters, but once possessed many more. According to the hierarchical theory of galaxy formation, galaxies have grown larger over time by consuming smaller dwarf galaxies and star clusters. And sometimes, it seems that the unfortunate prey is not swallowed whole but instead is munched like a peach, stripped of its outer layers to leave behind only the pit. New research by Paul Martini (Harvard-Smithsonian Center for Astrophysics) and Luis Ho (Observatories of the Carnegie Institution of Washington) shows that some globular clusters may be remnants of dwarf galaxies that were stripped of their outer stars, leaving only the galaxy’s nucleus behind.

Martini and Ho reported their results in the July 20, 2004, issue of The Astrophysical Journal.

Their findings hint at an important yet puzzling connection between the largest globular clusters and the smallest dwarf galaxies. “Star clusters and galaxies are quite different from a structural standpoint – star clusters are much more centrally concentrated, for example – and so the mechanisms that form them must be quite different. Identification of star clusters in the same mass range as galaxies is a very important step toward understanding how both types of objects form,” says Martini.

For their investigation, the team studied 14 globular clusters in the large elliptical galaxy Centaurus A (NGC 5128) using the 6.5-meter-diameter Magellan Clay telescope at Carnegie’s Las Campanas Observatory, Chile. The clusters were selected for their brightness, and since brighter clusters tend to contain more stars and more mass, were expected to be massive. Yet their results surprised even Martini and Ho, showing that the globular clusters of Centaurus A are much more massive than most globulars in the Local Group of galaxies (which includes the Milky Way and the Andromeda Galaxy).

“The essence of our findings is that these 14 globulars are 10 times more massive than the smaller globulars in our neighborhood, and whatever process makes them can produce some really huge objects – they begin to overlap with the smallest galaxies,” says Martini.

Martini also points out the recent discovery of a suspected intermediate-mass black hole in the Andromeda Galaxy globular cluster known as G1, which offers further evidence linking globular clusters to dwarf galaxies. The presence of a moderate-sized black hole is more understandable if it once occupied the center of a dwarf galaxy – a galaxy that lost its outer stars to the pull of Andromeda, leaving it only a shadow of its former self.

Ho, a co-discoverer of the intermediate-mass black hole in G1, adds, “One of the most surprising findings is that the black hole in G1 obeys the same tight correlation between black hole mass and host galaxy mass that has been well established for supermassive black holes in the centers of big galaxies. This puzzling result is more understandable if G1 was once the nucleus of a larger galaxy. A very interesting question is whether some of the massive clusters in Centaurus A also contain central black holes.”

Although most of our Galaxy’s globular clusters are much smaller than those of Centaurus A, the largest Milky Way globulars (such as the omega Centauri star cluster) rival those of the elliptical galaxy. The similarities between massive globulars in both galaxies may point to similar formation mechanisms. Future studies of these most massive globular clusters will explore connections between the formation processes for star clusters and galaxies.

Centaurus A is located approximately 12.5 million light-years away. It is about 65,000 light-years across and is more massive than the Milky Way and Andromeda galaxies put together. Centaurus A possesses a total of about 2000 globular clusters – more than all of the galaxies in the Local Group combined. Recent Spitzer Space Telescope observations of Centaurus A uncovered evidence that it merged with a spiral galaxy about 200 million years ago.

Original Source: Harvard-Smithsonian CfA News Release

Posted on by Fraser Cain

Genesis Heads for Home

Thirty days before its historic return to Earth with NASA’s first samples from space since the Apollo missions, the Genesis spacecraft successfully completed its twentieth trajectory maneuver.

At 12:00 Universal Time (5:00 a.m. Pacific Daylight Time), Mon., August 9, Genesis fired its 90 gram (.2 pound) thrusters for a grand total of 50 minutes, changing the solar sampler’s speed by 1.4 meters per second (about 3.1 miles per hour). The maneuver required half a kilogram (1.1 pounds) of hydrazine monopropellant to complete.

“It was a textbook maneuver,” said Ed Hirst, Genesis’s mission manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “After sifting through all the post-burn data, I expect we will find ourselves right on the money.”

The Genesis mission was launched in August of 2001 on a journey to capture samples from the storehouse of 99 percent of all the material in our solar system — the Sun. The samples of solar wind particles, collected on ultra-pure wafers of gold, sapphire, silicon and diamond, will be returned for analysis by Earth-bound scientists. The samples Genesis provides will supply scientists with vital information on the composition of the Sun, and will shed light on the origins of our solar system.

Helicopter flight crews, navigators and mission engineers continue to prepare for the return of the Genesis spacecraft on September 8. On that date, Genesis will dispatch a sample return capsule that will re-enter Earth’s atmosphere for a planned mid-air capture at the U.S. Air Force Utah Test and Training Range. To preserve the delicate particles of the Sun in their prisons of silicon, gold, sapphire and diamond, specially trained helicopter pilots will snag the return capsule from mid-air using the space-age equivalent of a fisherman’s rod and reel. The flight crews for the two helicopters assigned for Genesis capture and return are comprised of former military aviators and Hollywood stunt pilots.

JPL manages the Genesis mission for NASA’s Space Mission Directorate, Washington, DC. Lockheed Martin Space Systems, Denver, developed and operates the spacecraft. JPL is a division of the California Institute of Technology, the home institute of Genesis’s principal investigator Dr. Don Burnett.

More information about Genesis is available at http://genesismission.jpl.nasa.gov/. More information about the actual capture and return process is available at http://www.genesismission.org/mission/recgallery.html.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Hubble Sees a Gas Cavity in Space

In this unusual image, NASA’s Hubble Space Telescope captures a rare view of the celestial equivalent of a geode ? a gas cavity carved by the stellar wind and intense ultraviolet radiation from a hot young star.

Real geodes are baseball-sized, hollow rocks that start out as bubbles in volcanic or sedimentary rock. Only when these inconspicuous round rocks are split in half by a geologist, do we get a chance to appreciate the inside of the rock cavity that is lined with crystals. In the case of Hubble’s 35 light-year diameter “celestial geode” the transparency of its bubble-like cavity of interstellar gas and dust reveals the treasures of its interior.

The object, called N44F, is being inflated by a torrent of fast-moving particles (called a “stellar wind”) from an exceptionally hot star once buried inside a cold dense cloud. Compared with our Sun (which is losing mass through the so-called “solar wind”), the central star in N44F is ejecting more than a 100 million times more mass per second. The hurricane of particles moves much faster at about 4 million miles per hour (7 million kilometers per hour), as opposed to about 0.9 million miles per hour (1.5 million kilometers per hour) for our Sun. Because the bright central star does not exist in empty space but is surrounded by an envelope of gas, the stellar wind collides with this gas, pushing it out, like a snowplow. This forms a bubble, whose striking structure is clearly visible in the crisp Hubble image.

The nebula N44F is one of a handful of known interstellar bubbles. Bubbles like these have been seen around evolved massive stars (Wolf-Rayet stars), and also around clusters of stars (where they are called “super-bubbles”). But they have rarely been viewed around isolated stars, as is the case here.

On closer inspection N44F harbors additional surprises. The interior wall of its gaseous cavity is lined with several four- to eight-light-year-high finger-like columns of cool dust and gas. (The structure of these “columns” is similar to the Eagle Nebula’s iconic “pillars of creation” photographed by Hubble a decade ago, and is seen in a few other nebulae as well). The fingers are created by a blistering ultraviolet radiation from the central star. Like windsocks caught in a gale, they point in the direction of the energy flow. These pillars look small in this image only because they are much farther away from us than the Eagle Nebula’s pillars.

N44F is located about 160,000 light-years in our neighboring dwarf galaxy the Large Magellanic Cloud, in the direction of the southern constellation Dorado. N44F is part of the larger N44 complex, which is a large super-bubble, blown out by the combined action of stellar winds and multiple supernova explosions. N44 itself is roughly 1,000 light-years across. Several compact star-forming regions, including N44F, are found along the rim of the central super-bubble.

This image was taken with Hubble’s Wide Field Planetary Camera 2 in March 2002, using filters that isolate light emitted by sulfur (shown in blue, a 1,200-second exposure) and hydrogen gas (shown in red, a 1,000-second exposure).

Original Source: Hubble News Release