Posted on by Fraser Cain

Survey Finds Dark Accelerators

In the March 25th 2005 issue of Science Magazine, the High Energy Stereoscopic System (H.E.S.S.) team of international astrophysicists, including UK astronomers from the University of Durham, report results of a first sensitive survey of the central part of our galaxy in very high energy (VHE) gamma-rays. Included among the new objects discovered are two ‘dark accelerators’ – mysterious objects that are emitting energetic particles, yet apparently have no optical or x-ray counterpart.

This survey reveals a total of eight new sources of VHE gamma-rays in the disc of our Galaxy, essentially doubling the number known at these energies. The results have pushed astronomy into a previously unknown domain, extending our knowledge of the Milky Way in a novel wavelength regime thereby opening a new window on our galaxy.

Gamma-rays are produced in extreme cosmic particle accelerators such as supernova explosions and provide a unique view of the high energy processes at work in the Milky Way. VHE gamma-ray astronomy is still a young field and H.E.S.S. is conducting the first sensitive survey at this energy range, finding previously unknown sources.

Particularly stunning is that two of these new sources discovered by H.E.S.S. have no obvious counterparts in more conventional wavelength bands such as optical and X-ray astronomy. The discovery of VHE gamma-rays from such sources suggests that they may be `dark accelerators’, as Stefan Funk from the Max-Planck Institut in Heidelberg affirms: “These objects seem to only emit radiation in the highest energy bands. We had hoped that with a new instrument like H.E.S.S. we would detect some new sources, but the success we have now exceeds all our expectations.”

Dr Paula Chadwick of the University of Durham adds “Many of the new objects seem to be known categories of sources, such as supernova remnants and pulsar wind nebulae. Data on these objects will help us to understand particle acceleration in our galaxy in more detail; but finding these ‘dark accelerators’ was a surprise. With no counterpart at other wavelengths, they are, for the moment, a complete mystery.”

Cosmic particle accelerators are believed to accelerate charged particles, such as electrons and ions, by acting on these particles with strong shock waves. High-energy gamma rays are secondary products of the cosmic accelerators and are easier to detect because they travel in straight lines from the source, unlike charged particles which are deflected by magnetic fields. The cosmic accelerators are usually visible at other wavelengths as well as VHE gamma rays.

The H.E.S.S. array is ideal for finding these new VHE gamma ray objects, because as well as studying objects seen at other wavelengths that are expected to be sources of very high energy gamma rays, its wide field of view (ten times the diameter of the Moon) means that it can survey the sky and discover previously unknown sources.

Another important discovery is that the new sources appear with a typical size of the order of a tenth of a degree; the H.E.S.S. instrument for the first time provides sufficient resolution and sensitivity to see such structures. Since the objects cluster within a fraction of a degree from the plane of our Galaxy, they are most likely located at a significant distance – several 1000 light years from the sun – which implies that these cosmic particle accelerators extend over a size of light years.

The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in South-West Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of VHE gamma-rays, radiation a million million times more energetic than the visible light. These high energy gamma rays are quite rare – even for relatively strong sources, only about one gamma ray per month hits a square meter at the top of the earth’s atmosphere. Also, since they are absorbed in the atmosphere, a direct detection of a significant number of the rare gamma rays would require a satellite of huge size. The H.E.S.S. telescopes employ a trick – they use the atmosphere as detector medium. When gamma rays are absorbed in the air, they emit short flashes of blue light, named Cherenkov light, lasting a few billionths of a second. This light is collected by the H.E.S.S. telescopes with big mirrors and extremely sensitive cameras and can be used to create images of astronomical objects as they appear in gamma-rays.

The H.E.S.S. telescopes represent several years of construction effort by an international team of more than 100 scientists and engineers from Germany, France, the UK, Ireland, the Czech Republic, Armenia, South Africa and the host country Namibia. The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.

Original Source: PPARC News Release

Posted on by Fraser Cain

Libya’s Ubari and Murzuq Sand Seas

This Envisat image shows two huge sand dune seas in the Fezzan region of southwestern Libya, close to the border with Algeria.

Most of the face of the Sahara desert stretching across Northern Africa is bare stone and pebbles rather than sand dunes, but there are exceptions ? sprawling sea of multi-storey sand dunes known as ‘ergs’.

The Erg Ubari (also called Awbari) is the reddish sand sea towards the top of the image. A dark outcrop of Nubian sandstone separates the Erg Ubari sand from the Erg Murzuq (also called Murzuk) further south.

A persistent high-pressure zone centred over Libya keeps the centre of the Sahara completely arid for years at a time, but research has discovered evidence of ‘paleolakes’ in this region associated with a wetter and more fertile past.

Libya today has no permanent rivers or water bodies, but has various vast fossil aquifers. These natural underground basins hold enormous amounts of fresh water.

Two decades ago an ambitious project called Great Man-Made River was begun, aimed at drawing water from the aquifers beneath the Fezzan region shown in the image, via a network of underground pipes for irrigation in the coastal belt. Upon completion the huge network of pipelines will extend to about 3,380 km.

Envisat’s Medium Resolution Imaging Spectrometer (MERIS), working in Full Resolution mode to provide a spatial resolution of 300 metres, acquired this image on 24 November 2004. It has a width of 672 kilometres.

Original Source: ESA News Release

Posted on by Fraser Cain

Asteroid Created a Rain of Rock

Scientists at the American Museum of Natural History and the University of Chicago have explained how a globe-encircling residue formed in the aftermath of the asteroid impact that triggered the extinction of the dinosaurs. The study, which will be published in the April issue of the journal Geology, draws the most detailed picture yet of the complicated chemistry of the fireball produced in the impact.

The residue consists of sand-sized droplets of hot liquid that condensed from the vapor cloud produced by an impacting asteroid 65 million years ago. Scientists have proposed three different origins for these droplets, which scientists call ?spherules.? Some researchers have theorized that atmospheric friction melted the droplets off the asteroid as it approached Earth?s surface. Still others suggested that the droplets splashed out of the Chicxulub impact crater off the coast of Mexico?s Yucatan Peninsula following the asteroid?s collision with Earth.

But analyses conducted by Denton Ebel, Assistant Curator of Meteorites at the American Museum of Natural History, and Lawrence Grossman, Professor in Geophysical Sciences at the University of Chicago, provide new evidence for the third proposal. According to their research, the droplets must have condensed from the cooling vapor cloud that girdled the Earth following the impact.

Ebel and Grossman base their conclusions on a study of spinel, a mineral rich in magnesium, iron and nickel contained within the droplets.

?Their paper is an important advance in understanding how these impact spherules form,? said Frank Kyte, adjunct associate professor of geochemistry at the University of California, Los Angeles. ?It shows that the spinels can form within the impact plume, which some researchers argued was not possible.?

When the asteroid struck approximately 65 million years ago, it rapidly released an enormous amount of energy, creating a fireball that rose far into the stratosphere. ?This giant impact not only crushes the rock and melts the rock, but a lot of the rock vaporizes,? Grossman said. ?That vapor is very hot and expands outward from the point of impact, cooling and expanding as it goes. As it cools the vapor condenses as little droplets and rains out over the whole Earth.?

This rain of molten droplets then settled to the ground, where water and time altered the glassy spherules into the clay layer that marks the boundary between the Cretaceous and Tertiary (now officially called the Paleogene) periods. This boundary marks the extinction of the dinosaurs and many other species.

The work that led to Ebel and Grossman?s Geology paper was triggered by a talk the latter attended at a scientific meeting approximately 10 years ago. At this talk, a scientist stated that spinels from the Cretaceous-Paleogene boundary layer could not have condensed from the impact vapor cloud because of their highly oxidized iron content. ?I thought that was a strange argument,? Grossman said. ?About half the atoms of just about any rock you can find are oxygen,? he said, providing an avenue for extensive oxidation.

Grossman?s laboratory, where Ebel worked at the time, specializes in analyzing meteorites that have accumulated minerals condensed from the gas cloud that formed the sun 4.5 billion years ago. Together they decided to apply their experience in performing computer simulations of the condensation of minerals from the gas cloud that formed the solar system to the problem of the Cretaceous-Paleogene spinels.

UCLA?s Kyte, who himself favored a fireball origin for the spinels, has measured the chemical composition of hundreds of spinel samples from around the world.

Ebel and Grossman built on on Kyte?s work and on previous calculations done by Jay Melosh at the University of Arizona and Elisabetta Pierazzo of the Planetary Science Institute in Tucson, Ariz., showing how the asteroid?s angle of impact would have affected the chemical composition of the fireball. Vertical impacts contribute more of the asteroid and deeper rocks to the vapor, while impacts at lower angles vaporize shallower rocks at the impact site.

Ebel and Grossman also drew upon the work of the University of Chicago?s Mark Ghiorso and the University of Washington?s Richard Sack, who have developed computer simulations that describe how minerals change under high temperatures.

The resulting computer simulations developed by Ebel and Grossman show how rock vaporized in the impact would condense as the fireball cooled from temperatures that reached tens of thousands of degrees. The simulations paint a picture of global skies filled with a bizarre rain of a calcium-rich, silicate liquid, reflecting the chemical content of the rocks around the Chicxulub impact crater.

Their calculations told them what the composition of the spinels should be, based on the composition of both the asteroid and the bedrock at the impact site in Mexico. The results closely matched the composition of spinels found at the Cretaceous-Paleogene boundary around the world that UCLA?s Kyte and his associates have measured.

Scientists had already known that the spinels found at the boundary layer in the Atlantic Ocean distinctly differed in composition from those found in the Pacific Ocean. ?The spinels that are found at the Cretaceous-Paleogene boundary in the Atlantic formed at a hotter, earlier stage than the ones in the Pacific, which formed at a later, cooler stage in this big cloud of material that circled the Earth,? Ebel said.

The event would have dwarfed the enormous volcanic eruptions of Krakatoa and Mount St. Helens, Ebel said. ?These kinds of things are just very difficult to imagine,? he said.

The results in this paper strengthen the link between the unique Chicxulub impact and the stratigraphic boundary marking the mass extinction 65 million years ago that ended the Age of Dinosaurs. The topic will be explored further in a new groundbreaking exhibition, ?Dinosaurs: Ancient Fossils, New Discoveries,? set to open at the American Museum of Natural History on May 14. After it closes in the New York, the exhibition will travel to the Houston Museum of Natural Science (March 3-July 30, 2006); the California Academy of Sciences, San Francisco (Sept. 15, 2006-Feb. 4, 2007); The Field Museum, Chicago (March 30-Sept. 3, 2007); and the North Carolina State Museum of Natural Sciences, Raleigh (Oct. 26, 2007-July 5, 2008).

Original Source: University of Chicago News Release

Posted on by Fraser Cain

First Centennial Prizes Announced

Image credit: Spaceward
NASA and its partner, the Spaceward Foundation, today announced prizes totaling $400,000 for four prize competitions, the first under the agency’s Centennial Challenges program.

NASA’s Centennial Challenges promotes technical innovation through a novel program of prize competitions. It is designed to tap the nation’s ingenuity to make revolutionary advances to support the Vision for Space Exploration and NASA goals. The first two competitions will focus on the development of lightweight yet strong tether materials (Tether Challenge) and wireless power transmission technologies (Beam Power Challenge).

“For more than 200 years, prizes have played a key role in spurring new achievements in science, technology, engineering and exploration,” said NASA’s Associate Administrator for Exploration Systems Mission Directorate, Craig Steidle. “Centennial Challenges will use prizes to help make the Vision for Space Exploration a reality,” he added.

“This is an exciting start for the Centennial Challenges program,” said Brant Sponberg, program manager for Centennial Challenges. “The innovations from these competitions will help support advances in aerospace materials and structures, new approaches to robotic and human planetary surface operations, and even futuristic concepts like space elevators and solar power satellites,” he said.

The Tether Challenge centers on the creation of a material that combines light weight and incredible strength. Under this challenge, teams will develop high strength materials that will be stretched in a head-to-head competition to see which tether is strongest.

The Beam Power challenge focuses on the development of wireless power technologies for a wide range of exploration purposes, such as human lunar exploration and long-duration Mars reconnaissance. In this challenge, teams will develop wireless power transmission systems, including transmitters and receivers, to power robotic climbers to lift the greatest weight possible to the top of a 50-meter cable in under three minutes.

The winners of each initial 2005 challenge will receive $50,000. A second set of Tether and Beam Power challenges in 2006 are more technically challenging. Each challenge will award purses of $100,000, $40,000, and $10,000 for first, second, and third place.

“We are thrilled with our partnership with NASA and we’re excited to take the Tether and Beam Power challenges to the next level,” said Meekk Shelef, president of the Spaceward Foundation.

The Centennial Challenges program is managed by NASA’s Exploration Systems Mission Directorate. The Spaceward Foundation is a public-funds non-profit organization dedicated to furthering the cause of space access in educational curriculums and the public.

For more information about the Challenges on the Internet, visit:

http://centennialchallenges.nasa.gov

Original Source: NASA News Release

Posted on by Fraser Cain

Greece Joins the ESA

Image credit: ESA
Following its ratification of the ESA Convention, Greece has now become ESA?s 16th Member State. The official announcement was made to the ESA Council on 16 March by Per Tegn?r, Chairman of the ESA Council.

Cooperation between ESA and the Hellenic National Space Committee began in the early 1990s and in 1994 Greece signed its first cooperation agreement with ESA. This led to regular exchange of information, the award of fellowships, joint symposia, mutual access to databases and laboratories, and studies on joint projects in fields of mutual interest.

In September 2003 Greece formally applied to join ESA. Subsequent negotiations were followed in the summer of 2004 by the signing of an agreement on accession to the ESA Convention by Jean-Jacques Dordain, ESA Director General on behalf of ESA, and by Dimitris Sioufas, the Minister for Development, on behalf of the Greek Government.

Greece already participates in ESA?s telecommunication and technology activities, and the Global Monitoring for Environment and Security Initiative. Now, with the deposition of its instrument of ratification of the Convention for the establishment of ESA with the French Government on 9 March 2005,

Original Source: ESA News Release

Posted on by Fraser Cain

Dark Energy Survey Will Study 300 Million Galaxies

Image credit: Hubble
University scientists have co-founded an international collaboration that seeks to measure with new precision the mysterious force causing the universe to fly apart. Plans call for the project, named the Dark Energy Survey, to collect data on approximately 300 million galaxies spanning two-thirds of the history of the universe.

The survey could begin making observations as early as the fall of 2009. Although the DES remains more than four years away, more ambitious surveys will take at least a decade to produce results. ?I don?t want to wait that long,? said Joshua Frieman, Professor in Astronomy & Astrophysics and the College.

According to physics accounting methods, dark energy makes up 70 percent of the universe. Dark energy might be a manifestation of Albert Einstein?s cosmological constant, a force that acts at all times and in all places throughout the universe. It might also be a breakdown of Einstein?s theory of gravity on vast scales.

?It essentially requires gravity to be repulsive,? said Wayne Hu, Associate Professor in Astronomy & Astrophysics. ?That?s possible under our standard theories of gravity, but it?s not expected.? Whatever dark energy is, Frieman said, ?it?s likely to have profound implications for fundamental physics.?

The DES collaboration consists of researchers at Chicago, Fermi National Accelerator Laboratory, the University of Illinois at Urbana-Champaign, the Lawrence Berkeley National Laboratory and the Cerro Tololo Inter-American Observatory, as well as groups from the United Kingdom and Barcelona, Spain. Funding for the $20 million project is likely to come primarily from the U.S. Department of Energy, European funding agencies, the member institutions, and other agencies and sources.

Frieman heads the University?s component of the collaboration. Joining him and Hu in the collaboration are John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics and the College; Scott Dodelson, Professor in Astronomy & Astrophysics and the Physical Sciences Collegiate Division; Stephen Kent, Associate Professor in Astronomy & Astrophysics; Erin Sheldon, Fellow in the Kavli Institute for Cosmological Physics; and Risa Wechsler, Hubble Fellow in the Kavli Institute for Cosmological Physics. Frieman and Dodelson also are members of Fermilab?s Theoretical Astrophysics Group, which Dodelson heads, while Kent heads Fermilab?s Experimental Astrophysics Group.

The DES will entail installing a 520-megapixel camera on the existing four-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile. ?This would be larger than any existing optical camera in the world,? Frieman said.

A few hundred megapixels may not sound like much, Frieman said, ?but they?re not the same pixels that go into your hand-held. They have much higher sensitivity. They?re high-precision, high-efficiency detectors.? Furthermore, the camera will allow the scientists to survey the sky 10 times faster than they could at any existing U.S. observatory.

?The camera that?s now on the telescope just has too small a field of view. It would take us many decades to do the survey,? Frieman said.

The new camera will enable the DES to employ four techniques in attempting to discriminate between the two broad explanations for dark energy?the cosmological constant or a breakdown of gravity.

?The first method and the one that really drives the survey design is to count clusters of galaxies,? Frieman said. In this effort it will work in tandem with Carlstrom?s South Pole Telescope, which is scheduled to begin making observations in March 2007.

The SPT will help reveal if dark energy has suppressed the formation of galaxy clusters over the history of the universe. A radio telescope, the SPT will detect galaxy clusters by the way they distort the microwave radiation left over from the big bang. If theorists know how distant and how massive the galaxy clusters are, they can predict how many there should be in the presence of dark energy. The DES will make optical measurements to estimate their distance through the colors of the galaxies and their mass by gravitational lensing, the distortion of light by an intervening galaxy cluster. ?That?s a really elegant test,? Hu said.

The third technique employs gravitational lensing on a cosmic scale. Theorists can predict the effect of the dark energy on the large-scale distribution of the dark matter. With its large survey area, the DES can measure the tiny distortion of the images of galaxies induced by fluctuations in the dark matter density.

The fourth method involves the same technique that led to the 1998 discovery of dark energy: measuring the distance to a certain type of exploding star to reconstruct the expansion history of the universe. Astronomers studied these exploding stars expecting to find that the expansion of the universe had slowed as time went on. They discovered instead an accelerated expansion.

?These techniques complement each other very well,? Frieman said. ?They suffer from different sources of error, so if they agree, that gives you confidence in your result.?

For his part, Hu hopes the tests will reveal some discrepancy between predictions and reality. ?To me that would be the most exciting thing.?

Original Source: University of Chicago News Release

Posted on by Fraser Cain

First Light Seen from an Extrasolar Planet

NASA’s Spitzer Space Telescope has for the first time captured the light from two known planets orbiting stars other than our Sun. The findings mark the beginning of a new age of planetary science, in which “extrasolar” planets can be directly measured and compared.

“Spitzer has provided us with a powerful new tool for learning about the temperatures, atmospheres and orbits of planets hundreds of light-years from Earth,” said Dr. Drake Deming of NASA’s Goddard Space Flight Center, Greenbelt, Md., lead author of a new study on one of the planets.

“It’s fantastic,” said Dr. David Charbonneau of the Harvard- Smithsonian Center for Astrophysics, Cambridge, Mass., lead author of a separate study on a different planet. “We’ve been hunting for this light for almost 10 years, ever since extrasolar planets were first discovered.” The Deming paper appears today in Nature’s online publication; the Charbonneau paper will be published in an upcoming issue of the Astrophysical Journal.

So far, all confirmed extrasolar planets, including the two recently observed by Spitzer, have been discovered indirectly, mainly by the “wobble” technique and more recently, the “transit” technique. In the first method, a planet is detected by the gravitational tug it exerts on its parent star, which makes the star wobble. In the second, a planet’s presence is inferred when it passes in front of its star, causing the star to dim, or blink. Both strategies use visible-light telescopes and indirectly reveal the mass and size of planets, respectively.

In the new studies, Spitzer has directly observed the warm infrared glows of two previously detected “hot Jupiter” planets, designated HD 209458b and TrES-1. Hot Jupiters are extrasolar gas giants that zip closely around their parent stars. From their toasty orbits, they soak up ample starlight and shine brightly in infrared wavelengths.

To distinguish this planet glow from that of the fiery hot stars, the astronomers used a simple trick. First, they used Spitzer to collect the total infrared light from both the stars and planets. Then, when the planets dipped behind the stars as part of their regular orbit, the astronomers measured the infrared light coming from just the stars. This pinpointed exactly how much infrared light belonged to the planets. “In visible light, the glare of the star completely overwhelms the glimmer of light reflected by the planet,” said Charbonneau. “In infrared, the star-planet contrast is more favorable because the planet emits its own light.”

The Spitzer data told the astronomers that both planets are at least a steaming 1,000 Kelvin (727 degrees Celsius, 1340 Fahrenheit). These measurements confirm that hot Jupiters are indeed hot. Upcoming Spitzer observations using a range of infrared wavelengths are expected to provide more information about the planets’ winds and atmospheric compositions.

The findings also reawaken a mystery that some astronomers had laid to rest. Planet HD 209458b is unusually puffy, or large for its mass, which some scientists thought was the result of an unseen planet’s gravitational pull. If this theory had been correct, HD 209458b would have a non-circular orbit. Spitzer discovered that the planet does in fact follow a circular path. “We’re back to square one,” said Dr. Sara Seager, Carnegie Institution of Washington, Washington, co-author of the Deming paper. “For us theorists, that’s fun.”

Spitzer is ideally suited for studying extrasolar planets known to transit, or cross, stars the size of our Sun out to distances of 500 light-years. Of the seven known transiting planets, only the two mentioned here meet those criteria. As more are discovered, Spitzer will be able to collect their light – a bonus for the observatory, considering it was not originally designed to see extrasolar planets. NASA’s future Terrestrial Planet Finder coronagraph, set to launch in 2016, will be able to directly image extrasolar planets as small as Earth.

Shortly after its discovery in 1999, HD 209458b became the first planet detected via the transit method. That result came from two teams, one led by Charbonneau. TrES-1 was found via the transit method in 2004 as part of the NASA-funded Trans-Atlantic Exoplanet Survey, a ground-based telescope program established in part by Charbonneau.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Super Star Cluster Discovered in Our Own Milky Way

Super star clusters are groups of hundreds of thousands of very young stars packed into an unbelievably small volume. They represent the most extreme environments in which stars and planets can form.

Until now, super star clusters were only known to exist very far away, mostly in pairs or groups of interacting galaxies. Now, however, a team of European astronomers [1] have used ESO’s telescopes to uncover such a monster object within our own Galaxy, the Milky Way, almost, but not quite, in our own backyard!

The newly found massive structure is hidden behind a large cloud of dust and gas and this is why it took so long to unveil its true nature. It is known as “Westerlund 1” and is a thousand times closer than any other super star cluster known so far. It is close enough that astronomers may now probe its structure in some detail.

Westerlund 1 contains hundreds of very massive stars, some shining with a brilliance of almost one million suns and some two-thousand times larger than the Sun (as large as the orbit of Saturn)! Indeed, if the Sun were located at the heart of this remarkable cluster, our sky would be full of hundreds of stars as bright as the full Moon. Westerlund 1 is a most unique natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in our Galaxy live and die.

From their observations, the astronomers conclude that this extreme cluster most probably contains no less than 100,000 times the mass of the Sun, and all of its stars are located within a region less than 6 light-years across. Westerlund 1 thus appears to be the most massive compact young cluster yet identified in the Milky Way Galaxy.

Super Star Clusters
Stars are generally born in small groups, mostly in so-called “open clusters” that typically contain a few hundred stars. From a wide range of observations, astronomers infer that the Sun itself was born in one such cluster, some 4,500 million years ago.

In some active (“starburst”) galaxies, scientists have observed violent episodes of star formation (see, for example, ESO Press Photo 31/04), leading to the development of super star clusters, each containing several million stars.

Such events were obviously common during the Milky Way’s childhood, more than 12,000 million years ago: the many galactic globular clusters – which are nearly as old as our Galaxy (e.g. ESO PR 20/04) – are indeed thought to be the remnants of early super star clusters.

All super star clusters so far observed in starburst galaxies are very distant. It is not possible to distinguish their individual stars, even with the most advanced technology. This dramatically complicates their study and astronomers have therefore long been eager to find such clusters in our neighbourhood in order to probe their structure in much more detail.

Now, a team of European astronomers [1] has finally succeeded in doing so, using several of ESO’s telescopes at the La Silla observatory (Chile).

Westerlund 1
The open cluster Westerlund 1 is located in the Southern constellation Ara (the Altar constellation). It was discovered in 1961 from Australia by Swedish astronomer Bengt Westerlund, who later moved from there to become ESO Director in Chile (1970 – 74). This cluster is behind a huge interstellar cloud of gas and dust, which blocks most of its visible light. The dimming factor is more than 100,000 – and this is why it has taken so long to uncover the true nature of this particular cluster.

In 2001, the team of astronomers identified more than a dozen extremely hot and peculiar massive stars in the cluster, so-called “Wolf-Rayet” stars. They have since studied Westerlund 1 extensively with various ESO telescopes.

They used images from the Wide Field Imager (WFI) attached to the 2.2-m ESO/MPG as well as from the SUperb Seeing Imager 2 (SuSI2) camera on the ESO 3.5-m New Technology Telescope (NTT). From these observations, they were able to identify about 200 cluster member stars.

To establish the true nature of these stars, the astronomers then performed spectroscopic observations of about one quarter of them. For this, they used the Boller & Chivens spectrograph on the ESO 1.52-m telescope and the ESO Multi-Mode Instrument (EMMI) on the NTT.

An Exotic Zoo
These observations have revealed a large population of very bright and massive, quite extreme stars. Some would fill the solar system space within the orbit of Saturn (about 2,000 times larger than the Sun!), others are as bright as a million Suns.

Westerlund 1 is obviously a fantastic stellar zoo, with a most exotic population and a true astronomical bonanza. All stars identified are evolved and very massive, spanning the full range of stellar oddities from Wolf-Rayet stars, OB supergiants, Yellow Hypergiants (nearly as bright as a million Suns) and Luminous Blue Variables (similar to the exceptional Eta Carinae object – see ESO PR 31/03).

All stars so far analysed in Westerlund 1 weigh at least 30-40 times more than the Sun. Because such stars have a rather short life – astronomically speaking – Westerlund 1 must be very young. The astronomers determine an age somewhere between 3.5 and 5 million years. So, Westerlund 1 is clearly a “newborn” cluster in our Galaxy!

The Most Massive Cluster
Westerlund 1 is incredibly rich in monster stars – just as one example, it contains as many Yellow Hypergiants as were hitherto known in the entire Milky Way!

“If the Sun were located at the heart of Westerlund 1, the sky would be full of stars, many of them brighter than the full Moon”, comments Ignacio Negueruela of the Universidad de Alicante in Spain and member of the team.

The large quantity of very massive stars implies that Westerlund 1 must contain a huge number of stars. “In our Galaxy, explains Simon Clark of the University College London (UK) and one of the authors of this study, “there are more than 100 solar-like stars for every star weighing 10 times as much as the Sun. The fact that we see hundreds of massive stars in Westerlund 1 means that it probably contains close to half a million stars, but most of these are not bright enough to peer through the obscuring cloud of gas and dust”. This is ten times more than any other known young clusterin the Milky Way.

Westerlund 1 is presumably much more massive than the dense clusters of heavy stars present in the central region of our Galaxy, like the Arches and Quintuplet clusters. Further deep infrared observations will be required to confirm this.

This super star cluster now provides astronomers with a unique perspective towards one of the most extreme environments in the Universe. Westerlund 1 will certainly provide new opportunities in the long-standing quest for more and finer details about how stars, and especially massive ones, do form.

… and the Most Dense
The large number of stars in Westerlund 1 was not the only surprise awaiting Clark and his colleagues. From their observations, the team members also found that all these stars are packed into an amazingly small volume of space, indeed less than 6 light-years across. In fact, this is more or less comparable to the 4 light-year distance to the star nearest to the Sun, Proxima Centauri!

It is incredible: the concentration in Westerlund 1 is so high that the mean separation between stars is quite similar to the extent of the Solar System.

“With so many stars in such a small volume, some of them may collide”, envisages Simon Clark. “This could lead to the formation of an intermediate-mass black hole more massive than 100 solar masses. It may well be that such a monster has already formed at the core of Westerlund 1.”

The huge population of massive stars in Westerlund 1 suggests that it will have a very significant impact on its surroundings. The cluster contains so many massive stars that in a time span of less than 40 million years, it will be the site of more than 1,500 supernovae. A gigantic firework that may drive a fountain of galactic material!

Because Westerlund 1 is at a distance of only about 10,000 light-years, high-resolution cameras such as NAOS/CONICA on ESO’s Very Large Telescope can resolve its individual stars. Such observations are now starting to reveal smaller stars in Westerlund 1, including some that are less massive than the Sun. Astronomers will thus soon be able to study this exotic galactic zoo in great depth.

More information
The research presented in this ESO Press Release will soon appear in the leading research journal Astronomy and Astrophysics (“On the massive stellar population of the Super Star Cluster Westerlund 1” by J.S. Clark and colleagues). The PDF file is available at the A&A web site. A second paper (“Further Wolf-Rayet stars in the starburst cluster Westerlund 1”, by Ignacio Negueruela and Simon Clark) will also soon be published in Astronomy and Astrophysics. It is available as astro-ph/0503303.
A Spanish press release issued by Universidad de Alicante is available on the web site of Ignacio Negueruela.

Note
[1]: The team is composed of Simon Clark (University College London, UK), Ignacio Negueruela (Universidad de Alicante, Spain), Paul Crowther (University of Sheffield, UK), Simon Goodwin (University of Wales, Cardiff, UK), Rens Waters (University of Amsterdam) and Sean Dougherty (Dominion Radio Astrophysical Observatory).

Original Source: ESO News Release

Posted on by Fraser Cain

What’s Up This Week – Mar 21 – 27, 2005

Image credit: Alwyn Botha
Monday, March 21 – For readers looking for an exceptional morning challenge with either binoculars or small scopes, try 8th magnitude comet C/2003 T4 LINEAR. On this date it will be in the same binocular field west of the M2 and continue southeast toward Beta Aquarii over the next four mornings.

Tonight the most outstanding feature on the lunar surface will be the “Bay of Rainbows” – Sinus Iridum. Take the time to power up on the area and enjoy its many wonderful features such as bright Promontoriums LaPlace to the northeast and Heraclides to the southwest. It is ringed by the Juras Mountains where you will spot crater Bianchini in the center with Sharp to its west. Look for the punctures Helicon and Le Verrier in the smooth sands of Mare Ibrium and the long, smooth “dune” of Dorsae Heim interrupted by C. Herschel.

Tuesday, March 22 – Tonight there will be two meteor showers – the Camelopardalids and the March Geminids. While the Camelopardalids have no definite peak, they have a screaming fall rate of about one per hour and are the slowest recorded meteors at 7 kps. The March Geminids were discovered in 1973 and confirmed in 1975. The fall rate is usually about 40 per hour and they are considered “slow”. With the bright skies tonight, it will be difficult to distinguish them, but trace back to the point of origin to identify which stream.

While bright Aristarchus and the graceful old Gassendi will try to steal tonight’s lunar show, continue on towards the Southern Highlands to look for the long ellipse of crater Schiller near the limb. Small crater Bayer borders its northeastern edge.

Born on this day in 1799 was Friedrich Argelander, creator of the first international astronomical organization. Argelander also compiled star catalogues and studied variable stars. With deep sky studies improbable for the next few days, why don’t we try taking a look at a variable ourselves? RT (star 48) Aurigae is a bright cephid that is located roughly halfway between Epsilon Geminorum and Theta Aurigae. This perfect example of a pulsating star follows a precise timetable of 3.728 days and fluxes by close to one magnitude.

Wednesday, March 23 – Tonight let’s travel to the far southern edge of the lunar surface to visit three craters. Past study, the lava-filled Wargentin, is bordered by shallow Nasmyth to the east and Phoclydes to the southeast. This pair makes a wonderful “impression” on the Moon, for together they look like a giant shoe print!

The first photo of the Moon was taken tonight in 1840 by J.W. Draper. (Yes, it was done in 1839 by L.J.M. Daguerre – but contained no detail.) Why don’t you try as well? Camcorders, webcams and digital cameras are inexpensive ways of experimenting and even a common disposable camera can yield surprising results when held to the eyepiece of a telescope. Circle your thumb and index finger around the pair to aid in alignment and block stray light. Just click and say “green cheese”…

Thursday, March 24 – With the lunar terminator highlighting crater Grimaldi on the western limb, let’s try our hand at a more difficult feature. To Grimaldi’s east you will see the complex structure of crater Damoiseau. Extending from a break on its western rim edge is a long surface “crack” that runs north to south between the pair. This challenging feature is known as Rima Grimaldi.

On this night in 1893, Walter Baade – the developer of the concept of stellar population – became the first human to resolve the Andromeda Galaxy’s companions into individual stars. Tonight we’ll stay within our own galaxy as we travel 85 light years away to learn about “The Little King” – Regulus.

Ranking as the twenty-first brightest star in the night sky, Alpha Leonis is a helium type star about 5 times larger and 160 times brighter than our own Sun. Speeding away from us at 3.7 kilometers per second, Regulus is also a multiple system whose 8th magnitude companion is easily seen in small telescopes. The companion is itself a double at around magnitude 13 and is a dwarf of an uncertain type. There is also a 13th magnitude fourth star in this grouping, but it is believed that it is not associated with Regulus since the “Little King” is moving toward it and will be about 14″ away in 785 years.

Friday, March 25 – Tonight is Full Moon and time to explore the bright ray systems that criss-cross its surface. One of the strongest will eminate from crater Tycho and head toward the southwest limb. If libration is favourable in your area, you might catch a glimpse of the Doerful Mountains on the Moon’s edge. This incredible mountain range comes within a kilometer of being as tall as the Himalayas. If the Earth and the Moon were the same size, we would find the Doerfuls are three times higher than Everest!

On this date in 1655, Christian Huygens was still celebrating his earlier discovery of Saturn’s rings when he made an even more important contribution – Titan. 350 years later, the probe named for Huygens is now exploring Saturn’s largest satellite and you can as well. Even small telescopes can easily see the first moon discovered in our solar system to have an atmosphere. Before you observe, try checking the current positions of Saturn’s moons so you know precisely where to look.

Saturday, March 26 – Heads up southwestern Australia! The Moon will occult Jupiter for you on this this universal date. Please check this IOTA page to see a path map and compute times for your location. For the majority of northern hemisphere viewers, you will get to see a very pleasing conjunction of the two around 1 degree apart.

With the strong influence of the Moon to the east, let’s journey this evening towards another lovely multiple system as we explore Beta Monocerotis. Located about a fist width northwest of Sirius, Beta is one of the finest true triple systems for the small telescope. At low power, the 450 light year distant white primary will show the blue B and C stars to the southeast. If skies are stable, up the magnification to split the E/W oriented pair. All three stars are within a magnitude of each other and make Beta one of the finest sights for late winter skies.

Sunday, March 27 – Tonight as the Moon rises, check the eastern limb where you will see the terminator has advanced toward the eastern edge of Mare Crisium. With the shadows throwing its mountained walls into relief, we can see where this Washington state-sized area could possibly have been impact formed. Crisium is unique simply because it does not connect to any other mare. While the walls don’t seem that high at around 450 meters, that’s comparable to taking on the Vasques Cirque vertical drop at Winter Park, Colorado… without the skis!

Until next week? Keep smiling and looking up! May all your journeys be at light speed… ~Tammy Plotner

Posted on by Fraser Cain

Seeing the Planks in Einstein’s Cross

Image credit: Hubble
Spiral galaxy PGC 69457 is located near the boundary of fall constellations Pegasus and Aquarius some 3 degrees south of third magnitude Theta Pegasi – but don’t dig out that 60mm refractor to look for it. The galaxy is actually some 400 million light years away and has an apparent brightness of magnitude 14.5. So next fall may be a good time to hook up with that “astro-nut” friend of yours who is always heading off into the sunset to get well away from city lights sporting a larger, much larger, amateur instrument…

But there are plenty of 14th magnitude galaxies in the sky – what makes PGC 69457 so special?

To begin with most galaxies don’t “block” the view of an even more distant quasar (QSO2237+0305). And should others exist, few have just the right distribution of high-density bodies needed to cause light to “bend” in a way that an otherwise invisible object is visible. With PGC 69457 you get not one – but four – separate 17th magnitude views of the same quasar for the trouble of setting up one 20 inch truss tube dobsonian. Is it worth it? (Can you say “quadruple your observing pleasure”?)

But the phenomenon behind such a view is even more interesting to professional astronomers. What can we learn from such a unique effect?

The theory is already well established – Albert Einstein predicted it in his “General Theory of Relativity” of 1915. Einstein’s core idea was that an observer undergoing acceleration and one stationary in a gravitational field could not tell the difference between the two on their “weight”. By exploring this idea to its fullest, it became clear that not only matter but light (despite being massless) undergoes the same sort of confusion. Because of this, light approaching a gravitational field at an angle is “accelerated toward” the source of the gravity – but because the velocity of light is constant such acceleration only effects light’s path and wavelength – not its actual speed.

Gravitational lensing itself was first detected during the total solar eclipse of 1919. This was seen as a slight shift in the positions of stars near the Sun’s corona as captured on photographic plates. Because of this observation, we now know that you don’t need a lens to bend light – or even water to refract the image of those Koi swimming in the pond. Light like matter takes the path of least resistance and that means following the gravitational curve of space as well as the optical curve of a lens. The light from QSO2237+0305 is only doing what comes naturally by surfing the contours of “space-time” arcing around dense stars lying along the line of sight from a distant source through a more neighboring galaxy. The really interesting thing about Einstein’s Cross comes down to what it tells us about all the masses involved – those in the galaxy that refracts the light, and the Big One in the heart of the quasar that sources it.

In their paper “Reconstruction of the microlensing light curves of the Einstein Cross” Korean astrophysicist Dong-Wook Lee (et al) of Sejong University in association with Belgian astrophysicist J. Surdez (et al) of the University of Liege, found evidence of an accretion disk surrounding the black hole in Quasar QSO2237+0305. How is such a thing possible at the distances involved?

Lenses in general “collect and focus light” and those “gravitational lenses” (Lee at al posit a minimum of five low-mass but highly condensed bodies) within PGC 69457, do the same. In this way, light from a quasar that would normally travel well away from our instruments “wraps around” the galaxy to come toward us. Because of this we “see” 100,000 times more detail than otherwise possible. But there is a catch: Despite getting 100,000 times more resolution, we still only see light, not detail. And because there are several masses refracting light in the galaxy, we see more than one view of the quasar.

To get useful information from the quasar, you have to collect light over long periods of time (months to years) and use special analytical algorithms to pull the resulting data together. The method used by Lee and associates is called LOHCAM (LOcal Hae CAustic Modeling). (HAE itself is an acronym for High Amplification Events). Using LOHCAM and data available from OGLE (Optical Gravitational Lensing Experiment) and GLIPT (Gravitational Lens International Time Project), the team determined not only that LOHCAM works as hoped but that QSO2237+0305 may include a detectable accretion disk (from which it draws matter to power its light engine). The team has also determined the approximate mass of the quasars black hole, the size of the ultraviolet region radiating from it, and estimated the transverse motion of the black hole as it moves relative to the spiral galaxy.

The central black hole in Quasar QSO2237+0305 is thought to have a combined mass of 1.5 billion Suns – a value rivaling those of the largest central black holes ever discovered. Such a mass number represents 1 percent of the total number of stars in our own Milky Way galaxy. Meanwhile and by comparison, QSO2237+0305’s black hole is roughly 50 times more massive than that in the center of our own galaxy.

Based on “double-peaks” in luminosity from the quasar, Lee et al used LOHCAM to also determine the size of QSO2237+0305’s accretion disk, its orientation, and detected a central obscuration region around the black hole itself. The disk itself is roughly 1/3rd of a light year in diameter and is turned face on towards us.

Impressed? Well let’s also add that the team has determined the minimum number of microlenses and related masses found in the lensing galaxy. Depending on transverse velocity assumed (in LOHCAM modeling), the smallest range from that of a gas giant – such as the planet Jupiter – through that of our own Sun.

So how does this “hole” thing work?

The OGLE and GLIPT projects monitored changes in the intensity of visual light streaming to us from each of the four 17th magnitude views of the quasar. Since most quasars are unresolvable,due to their great distances in space, by telescope. Fluctuations in luminosity are seen only as a single point of data based on the brightness of the entire quasar. However, QSO2237+0305 presents four images of the quasar and each image highlights luminosity originating from a different perspective of the quasar. By telescopically monitoring all four images simultaneously, slight variations in image intensity can be detected and recorded in terms of magnitude, date, and time. Over several months to years, a considerable number of such “high amplification events” can occur. Patterns emerging out of their occurrence (from one 17th magnitude view to the next) can then be analyzed to show motion and intensity. Out of this a super high resolution view of normally unseen structure within the quasar is possible.

Could you and your friend with that 20 inch dob-newtonian do this?

Sure – but not without some very expensive equipment and a good handle on some complex mathematical imaging algorithms. A nice place to start however might simply be to ogle the galaxy and hang with the cross for awhile…

Written by Jeff Barbour