Posted on by Fraser Cain

Recent Blast was Probably a Neutron Star Collision

Swift’s X-Ray telescope captured this image of GRB050509b embedded in the diffuse X-ray emission associated with the galaxy cluster. Image credit: NASA. Click to enlarge.
Two billion years and 25 days ago, an event destined to be a watershed in the astronomical community took place in a distant galaxy ? a blast of gamma rays lasting a mere a thirtieth of a second. The aptly-named Swift observatory ‘saw’ the gammas with its Burst Alert Telescope (BAT) instrument, worked out roughly where they were coming from, and turned its X-ray and UV telescopes. The international GCN (GRB Coordinates Network) lit up with notices from observatories all over the world (and out in space), reporting what they found when they looked there. Data came in from Namibia, the Canaries, continental US, Chile, India, the Netherlands, and above all Hawaii. The world?s leading optical telescopes, the VLT, the Kecks, Gemini, Subaru, all swung into action; the electromagnetic spectrum was covered from extremely high energy gammas to the radio.

And all for what? A few dozen gamma rays plus about a dozen X-rays? Astronomers have known for over a decade that gamma ray bursts (GRBs) come in two different kinds: ?long-soft? and ?short-hard?. GRB050509b was a short-hard one. It lasted about 30 ms, its gamma spectrum had more ?hard? gammas than ?soft? ones, and it was the first time an X-ray afterglow was ever detected.

Astronomers have been “desperately seeking afterglows” for years. These are the X-ray, UV, optical, IR, and radio waves streaming from the site of the GRB, after the gamma radiation tails off. Because we can pinpoint the source of these more accurately than the GRBs themselves, finding afterglows is the first step to working out what they are.

Before GRB050509b, astronomers were leaning towards the theory that long-soft GRBs are core-collapse supernovae (collapsars). While there have been dozens of theoretical papers published on what short-hard GRBs might be, only three scenarios seemed to fit the gamma ray data ? the merger (or collision) of a neutron star with another (or a black hole), a giant flare from a magnetar (a ?starquake? in an intensely magnetic neutron star), or some variation on the collapsar theme.

Now the first of what will likely be hundreds of papers on GRB050509b has been submitted for publication. The 28 authors conclude that “there is now observational support for the hypothesis that short-hard bursts arise during the merger of a compact binary (two neutron stars, or a neutron star and a black hole).”

The key to the researchers? conclusion is the ‘localization’ of the X-ray afterglow.

Swift?s X-ray telescope detected X-rays coming from the same region of the sky as the gammas; after some sleuthing to tie the apparent X-ray position to the astronomers? coordinate system (RA and Dec), the Swift XRT team determined that the afterglow came from a circle about 15″ (arc seconds) across, whose centre is about 10″ from the heart of an elliptical galaxy (which now has the memorable name G1), itself a member of a rich cluster of galaxies bathed in X-rays. How did they know it was an afterglow? Because it faded; the diffuse X-ray glow from clusters doesn?t do that.

And despite looking very carefully, no other electromagnetic afterglow was detected.

So now our 28 astronomers had to work out whether G1?s suburbs is where the stardeath happened, or somewhere else; what is the ?host?, in astronomer-speak.

Modern astronomy makes heavy use of statistics; to be sure they don?t have a fluke, researchers normally want lots and lots of examples. In this case, the only stats the paper?s authors could do is a calculation ? how likely is it that a short-hard GRB (assuming that such are stardeath events) would occur ?near? an elliptical galaxy, in a rich cluster, just by chance? Many different ?how likely? questions were asked; the answers in all cases are, ?not very likely?. However, no one is ruling out bad luck.

Our researchers could now turn to the various theoretical models of short-hard GRBs, and of GRB afterglows, to see how well the observational data fit the theoretical expectations, assuming the GRB went off in G1.

Good news (#1) is that the afterglow data matches well: short-hard GRBs release a lot less (gamma) energy than do long-soft ones (so afterglows from short-hard GRBs should be fainter; the gamma energy is an indicator of the energy used to power the afterglow). Better yet, since what the burst debris smashes into determines how bright the afterglow will be, the faint GRB050509b afterglow is just what you?d expect if it happened in the rarified gas of the interstellar medium of an elliptical (collapsar afterglows are bright in part because they happen in the messy remnants of the gas-dust clouds from which they were born a mere few million years earlier).

The second piece of good news is that, no trace of recent star formation could be found in G1, thus pretty much ruling out a collapsar as the progenitor. Why? Because collapsars are very young stars, and so cannot have moved far from their birthplace before their death. Further, the debris of even the wimpiest collapsar supernova would have been visible, several days afterwards.

What about a giant flare from a magnetar? This cannot be strongly ruled out for GRB050509b, but a magnetar in a galaxy like G1 is not very likely, and GRB050509b was a thousand times brighter than the strongest magnetar flare we?ve seen, to date.

That leaves the merger of a neutron star binary (or NS-BH binary). Where would we find such a binary, just ready to merge? They certainly could be found in the suburbs of spiral galaxies, or in globular clusters, but giant elliptical galaxies like G1 is mostly where.

So it?s ?case closed?? Not quite. ?Other progenitor models are still viable, and additional rapidly localized bursts from the Swift mission will undoubtedly help to further clarify the progenitor picture.?

Could GRB050509b be a stardeath in a much more distant galaxy? Maybe one of the dozen or so fuzzy blobs (a much more distant galaxy cluster? such chance alignments are very common) in or near the X-ray afterglow? Perhaps this will be discussed in future papers on GRB050509b.

Original Source: http://arxiv.org/abs/astro-ph/0505480

Posted on by Fraser Cain

New Jupiter Mission Moves Forward

Galileo’s image of Jupiter. Image credit: NASA/JPL. Click to enlarge.
NASA today announced that a mission to fly to Jupiter will proceed to a preliminary design phase. The mission is called Juno, and it is the second in NASA’s New Frontiers Program.

The mission will conduct an in-depth study of the giant planet. The mission proposes to place a spacecraft in a polar orbit around Jupiter to investigate the existence of an ice-rock core; determine the amount of global water and ammonia present in the atmosphere; study convection and deep wind profiles in the atmosphere; investigate the origin of the jovian magnetic field; and explore the polar magnetosphere.

“We are excited at the prospect of the new scientific understanding and discoveries by Juno in our continued exploration of the outer reaches of our solar system during the next decade,” said Dr. Ghassem Asrar, deputy associate administrator for NASA’s Science Mission Directorate.

At the end of the preliminary design study, the mission must pass a confirmation review that will address significant schedule, technical and cost risks before being confirmed for the development phase.

Dr. Scott Bolton of Southwest Research Institute, Boulder, Colo., is the principal investigator. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., will provide mission project management. Lockheed Martin Space Systems, Denver, will build the spacecraft.

NASA selected two proposed mission concepts for study in July 2004 from seven submitted in February 2004 in response to an agency Announcement of Opportunity. “This was a very tough decision given the exciting and innovative nature of the two missions,” Asrar added.

The selected New Frontiers science mission must be ready for launch no later than June 30, 2010, within a mission cost cap of $700 million.

The New Frontiers Program is designed to provide opportunities to conduct several of the medium-class missions identified as top priority objectives in the Decadal Solar System Exploration Survey, conducted by the Space Studies Board of the National Research Council.

The first NASA New Frontiers mission will fly by the Pluto-Charon system in 2014 and then target another Kuiper asteroid belt object.

For information about NASA’s science programs on the Web, visit: http://science.hq.nasa.gov/. For information about NASA and agency programs on the Web, visit: http://www.nasa.gov/home/index.html.

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

Original Source: NASA News Release

Posted on by Fraser Cain

A Simulation of the Whole Universe

Simulated image that shows the distribution of matter in the Universe. Image credit: MPG. Click to enlarge.
The Virgo consortium, an international group of astrophysicists from the UK, Germany, Japan, Canada and the USA has today (June 2nd) released first results from the largest and most realistic simulation ever of the growth of cosmic structure and the formation of galaxies and quasars. In a paper published in Nature, the Virgo Consortium shows how comparing such simulated data to large observational surveys can reveal the physical processes underlying the build-up of real galaxies and black holes.

The “Millennium Simulation” employed more than 10 billion particles of matter to trace the evolution of the matter distribution in a cubic region of the Universe over 2 billion light-years on a side. It kept the principal supercomputer at the Max Planck Society’s Supercomputing Centre in Garching, Germany occupied for more than a month. By applying sophisticated modelling techniques to the 25 Terabytes (25 million Megabytes) of stored output, Virgo scientists are able to recreate evolutionary histories for the approximately 20 million galaxies which populate this enormous volume and for the supermassive black holes occasionally seen as quasars at their hearts.

Telescopes sensitive to microwaves have been able to image the Universe directly when it was only 400,000 years old. The only structure at that time was weak ripples in an otherwise uniform sea of matter and radiation. Gravitationally driven evolution later turned these ripples into the enormously rich structure we see today. It is this growth which the Millennium Simulation is designed to follow, with the twin goals of checking that this new paradigm for cosmic evolution is indeed consistent with what we see, and of exploring the complex physics which gave rise to galaxies and their central black holes.

Recent advances in cosmology demonstrate that about 70 percent of our Universe currently consists of Dark Energy, a mysterious force field which is causing it to expand ever more rapidly. About one quarter apparently consists of Cold Dark Matter, a new kind of elementary particle not yet directly detected on Earth. Only about 5 percent is made out of the ordinary atomic matter with which we are familiar, most of that consisting of hydrogen and helium. All these components are treated in the Millennium Simulation.

In their Nature article, the Virgo scientists use the Millennium Simulation to study the early growth of black holes. The Sloan Digital Sky Survey (SDSS) has discovered a number of very distant and very bright quasars which appear to host black holes at least a billion times more massive than the Sun at a time when the Universe was less than a tenth its present age.

“Many astronomers thought this impossible to reconcile with the gradual growth of structure predicted by the standard picture”, says Dr Volker Springel (Max Planck Institute for Astrophysics, Garching) the leader of the Millennium project and the first author of the article, “Yet, when we tried out our galaxy and quasar formation modelling we found that a few massive black holes do form early enough to account for these very rare SDSS quasars. Their galaxy hosts first appear in the Millennium data when the Universe is only a few hundred million years old, and by the present day they have become the most massive galaxies at the centres of the biggest galaxy clusters.”

For Prof Carlos Frenk (Institute for Computational Cosmology, University of Durham) the head of Virgo in the UK, the most interesting aspect of the preliminary results is the fact that the Millennium Simulation demonstrates for the first time that the characteristic patterns imprinted on the matter distribution at early epochs and visible directly in the microwave maps, should still be present and should be detectable in the observed distribution of galaxies. “If we can measure the baryon wiggles sufficiently well”, says Prof Frenk, “then they will provide us with a standard measuring rod to characterise the geometry and expansion history of the universe and so to learn about the nature of the Dark Energy.”

“These simulations produce staggering images and represent a significant milestone in our understanding of how the early Universe took shape.” said PPARC’s Chief Executive, Prof Richard Wade. “The Millennium Simulation is a brilliant example of the interaction between theory and experiment in astronomy as the latest observations of astronomical objects can be used to test the predictions of theoretical models of the Universe’s history.”

The most interesting and far-reaching applications of the Millennium Simulation are still to come according to Prof Simon White (Max Planck Institute for Astrophysics) who heads Virgo efforts in Germany. “New observational campaigns are providing us with information of unprecedented precision about the properties of galaxies, black holes and the large-scale structure of our Universe,” he notes. “Our ability to predict the consequences of our theories must reach a matching level of precision if we are to use these surveys effectively to learn about the origin and nature of our world. The Millennium Simulation is a unique tool for this. Our biggest challenge now is to make its power available to astronomers everywhere so that they can insert their own galaxy and quasar formation modelling in order to interpret their own observational surveys.”

Original Source: PPARC News Release

Posted on by Fraser Cain

Quasar Image Revises Theories About Their Jets

VLBA image of quasar 3C 273, with its long jet blasting out. Image credit: NRAO. Click to enlarge.
When a pair of researchers aimed the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope toward a famous quasar, they sought evidence to support a popular theory for why the superfast jets of particles streaming from quasars are confined to narrow streams. Instead, they got a surprise that “may send the theorists back to the drawing boards,” according to one of the astronomers.

“We did find the evidence we were looking for, but we also found an additional piece of evidence that seems to contradict it,” said Robert Zavala, an astronomer at the U.S. Naval Observatory’s Flagstaff, Arizona, station. Zavala and Greg Taylor, of the National Radio Astronomy Observatory and the Kavli Institute of Particle Astrophysics and Cosmology, presented their findings to the American Astronomical Society’s meeting in Minneapolis, Minnesota.

Quasars are generally thought to be supermassive black holes at the cores of galaxies, the black hole surrounded by a spinning disk of material being drawn inexorably into the black hole’s gravitational maw. Through processes still not well understood, powerful jets of particles are propelled outward at speeds nearly that of light. A popular theoretical model says that magnetic-field lines in the spinning disk are twisted tightly together and confine the fast-moving particles into narrow “jets” streaming from the poles of the disk.

In 1993, Stanford University and Kavli Institute astrophysicist Roger Blandford suggested that such a twisted magnetic field would produce a distinct pattern in the alignment, or polarization, of radio waves coming from the jets. Zavala and Taylor used the VLBA, capable of producing the most detailed images of any telescope in astronomy, to seek evidence of Blandford’s predicted pattern in a well-known quasar called 3C 273.

“We saw exactly what Blandford predicted, supporting the idea of a twisted magnetic field. However, we also saw another pattern that is not explained by such a field,” Zavala said.

In technical terms, the twisted magnetic field should cause a steady change, or gradient, in the amount by which the alignment (polarization) of the radio waves is rotated as one looks across the width of the jet. That gradient showed up in the VLBA observations. However, with a twisted magnetic field, the percentage of the waves that are similarly aligned, or polarized, should be at its greatest at the center of the jet and decrease steadily toward the edges. Instead, the observations showed the percentage of polarization increasing toward the edges.

That means, the astronomers say, there either is something wrong with the twisted-magnetic-field model or its effects are washed out by interactions between the jet and the interstellar medium that it is drilling through. “Either way, the theorists have to get to work to figure out how this can happen,” Zavala said.

When notified of the new results, Blandford said, “these observations are good enough to warrant further development of the theory.”

3C 273 is one of the most famous quasars in astronomy, and was the first to be recognized as a very distant object in 1963. Caltech astronomer Maarten Schmidt was working on a brief scientific article about 3C273 on the afternoon of February 5 that year when he suddenly recognized a pattern in the object’s visible-light spectrum that allowed an immediate calculation of its distance. He later wrote that “I was stunned by this development…” Just minutes later, he said, he met his colleague Jesse Greenstein, who was studying another quasar, in a hallway. In a matter of another few minutes, they found that the second one also was quite distant. 3C 273 is about two billion light-years from Earth in the constellation Virgo, and is visible in moderate-sized amateur telescopes.

The VLBA is a system of ten radio-telescope antennas, each with a dish 25 meters (82 feet) in diameter and weighing 240 tons. From Mauna Kea on the Big Island of Hawaii to St. Croix in the U.S. Virgin Islands, the VLBA spans more than 5,000 miles, providing astronomers with the sharpest vision of any telescope on Earth or in space. Dedicated in 1993, the VLBA has an ability to see fine detail equivalent to being able to stand in New York and read a newspaper in Los Angeles.

“The extremely sharp radio ‘vision’ of the VLBA was absolutely necessary to do this work,” Zavala explained. “We used the highest radio frequencies at which we could detect 3C273’s jet to maximize the detail we could get, and this effort paid off with great science,” he added.

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

Original Source: NRAO News Release

Posted on by Fraser Cain

Amalthea is Just a Pile of Icy Rubble

Artist illustration of Galileo and Jupiter’s moon, Amalthea. Image credit: NASA/JPL. Click to enlarge.
Scientists studying data from NASA’s Galileo spacecraft have found that Jupiter’s moon Amalthea is a pile of icy rubble less dense than water. Scientists expected moons closer to the planet to be rocky and not icy. The finding shakes up long-held theories of how moons form around giant planets.

“I was expecting a body made up mostly of rock. An icy component in a body orbiting so close to Jupiter was a surprise,” said Dr. John D. Anderson, an astronomer at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. Anderson is lead author of a paper on the findings that appears in the current issue of the journal Science.

“This gives us important information on how Jupiter formed, and by implication, how the solar system formed,” Anderson said.

Current models imply that temperatures were high at Amalthea’s current position when Jupiter’s moons formed, but this is inconsistent with Amalthea being icy. The findings suggest that Amalthea formed in a colder environment. One possibility is that it formed later than the major moons. Another is that the moon formed farther from Jupiter, either beyond the orbit of Jupiter’s moon Europa or in the solar nebula at or beyond Jupiter’s position. It would have then been transported or captured in its current orbit around Jupiter. Either of these explanations challenges models of moon formation around giant planets.

“Amalthea is throwing us a curve ball,” said Dr. Torrence Johnson, co-author and project scientist for the Galileo mission at JPL. “Its density is well below that of water ice, and even with substantial porosity, Amalthea probably contains a lot of water ice, as well as rock.” Analysis of density, volume, shape and internal gravitational stresses lead the scientists to conclude that Amalthea is not only porous with internal empty spaces but also contains substantial water ice.

One model for the formation of Jupiter’s moons suggests that moons closer to the planet would be made of denser material than those farther out. That is based on a theory that early Jupiter, like a weaker version of the early Sun, would have emitted enough heat to prevent volatile, low-density material from condensing and being incorporated into the closer moons. Jupiter’s four largest moons fit this model, with the innermost of them, Io, also the densest, made mainly of rock and iron.

Amalthea is a small red-tinted moon that measures about 168 miles in length and half that in width. It orbits about 181,000 kilometers (112,468 miles) from Jupiter, considerably closer than the Moon orbits Earth. Galileo passed within about 99 miles of Amalthea on Nov. 5, 2002. Galileo’s flyby of Amalthea brought the spacecraft closer to Jupiter than at any other time since it began orbiting the giant planet on Dec. 7, 1995. After more than 30 close encounters with Jupiter’s four largest moons, the Amalthea flyby was the last moon flyby for Galileo.

The Galileo spacecraft’s 14-year odyssey came to an end on Sept. 21, 2003. JPL, a division of the California Institute of Technology in Pasadena, managed the Galileo mission for NASA.

Additional information about the mission is available online at: http://galileo.jpl.nasa.gov/.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Ancient Floods on Mars

Perspective view of an ancient floodplain on Mars. Image credit: ESA. Click to enlarge.
This image, taken by the High Resolution Stereo Camera (HRSC) aboard ESA?s Mars Express spacecraft, shows a large depression called Iani Chaos and the upper reaches of a large outflow channel called Ares Vallis.

Image strips were taken in October 2004, during three orbits from a 350-kilometre altitude, with a resolution of 15 metres per pixel. The strips have then been matched to a mosaic that covers an area from 17.5? western longitude to 3? North. The Iani Chaos depression ? 180 kilometres long and 200 kilometres wide ? is connected to the beginning of Ares Vallis by a 100-kilometre wide transition zone.

From here, Ares Vallis continues its course for about 1400 kilometres through the ancient Xanthe Terra highlands, bordered by valley flanks up to 2000 metres high. Eventually Ares Vallis empties into Chryse Planitia.

This image helps illuminate the complex geological history of Mars. Ares Vallis is one of several big outflow channels on Mars in this region that formed billions of years ago. Many surface features suggest that erosion of large water flows had carved Ares Vallis in the Martian landscape.

Most likely gigantic floods ran downhill, carving a deep canyon into Xanthe Terra. Rocks eroded from the valley flanks were milled into smaller fractions and transported in the running water.

Finally this sedimentary load was deposited far north at the mouth of Ares Vallis in the Chryse plains, where NASA?s Mars Pathfinder landed in 1997 to search for traces of water with its small Sojourner rover.

The scene displayed in the image shows the transition zone between Iani Chaos and Ares Vallis. A chaotic distribution of individual blocks of rock and hills forms a disrupted pattern. These ?knobs? are several hundred metres high. Scientists suggest that they are remnants of a preexisting landscape that collapsed after cavities had formed beneath the surface.

The elongated curvature of features extending from south to north along with terraces, streamlined ‘islands’ and the smooth, flat surface in the valley centre are strong hints that it was running water that carved the valley.

Ice stored in possible cavities in the Martian highland might have been melted by volcanic heat. Pouring out, the melting water would have followed the pre-existing topography to the northern lowlands.

A hundred kilometres further, a ten-kilometre-wide valley arm merges into Ares Vallis from the west. Large amounts of water originating from Aram Chaos (outside the image) joined the stream of Ares Vallis. Fan-shaped deposits on the valley floor are the remnants of landslides at the northern flanks.

At the freshly eroded cliffs possible lava layers are visible: such layers are found almost everywhere in Xanthe Terra. Further downstream, another valley branch enters Ares Vallis from the east after passing through an eroded impact crater in Xanthe Terra. West of Ares Vallis, a subtler riverbed is running parallel to the main valley.

The High Resolution Stereo Camera (HRSC) experiment on the ESA Mars Express Mission is led by Principal Investigator (PI) Prof. Dr. Gerhard Neukum who is also responsible for the technical design of the camera. The science team of the experiment consists of 45 Co-Investigators from 32 institutions and ten nations.

The camera was developed at the German Aerospace Centre (DLR) under the leadership of the PI and constructed in cooperation with industrial partners (EADS-Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH).

Original Source: ESA News Release

Posted on by Fraser Cain

Measuring the Shape of Stars

Galaxy Cluster Abell 2218 distorting the light from several more distant galaxies. Image credit: ESO. Click to enlarge.
Fifty years after his death, Albert Einstein’s work still provides new tools for understanding our universe. An international team of astronomers has now used a phenomenon first predicted by Einstein in 1936, called gravitational lensing, to determine the shape of stars. This phenomenon, due to the effect of gravity on light rays, led to the development of gravitational optics techniques, among them gravitational microlensing. It is the first time that this well-known technique has been used to determine the shape of a star.

Most of the stars in the sky are point-like, making it very difficult to evaluate their shape. Recent progress in optical interferometry has made it possible to measure the shape of a few stars. In June 2003, for instance, the star Achernar (Alpha Eridani) was found to be the flattest star ever seen, using observations from the Very Large Telescope Interferometer (see ESO Press Release for details about this discovery). Until now, only a few measurements of stellar shape have been reported, partly due to the difficulty of carrying such measurements. It is important, however, to obtain further accurate determinations of stellar shape, as such measurements help to test theoretical stellar models.

For the first time, an international team of astronomers [1], led by N.J. Rattenbury (from Jodrell Bank Observatory, UK), applied gravitational lensing techniques to determine the shape of a star. These techniques rely on the gravitational bending of light rays. If light coming from a bright source passes close to a foreground massive object, the light rays will be bent, and the image of the bright source will be altered. If the foreground massive object (the ‘lens’) is point-like and perfectly aligned with the Earth and the bright source, the altered image as seen from the Earth will be a ring shape, the so-called ‘Einstein ring’. However, most real cases differ from this ideal situation, and the observed image is altered in a more complicated way. The image below shows an example of gravitational lensing by a massive galaxy cluster.

Gravitational microlensing, as used by Rattenbury and his colleagues, also relies on the deflection of light rays by gravity. Gravitational microlensing is the term used to describe gravitational lensing events where the lens is not massive enough to produce resolvable images of the background source. The effect can still be detected as the distorted images of the source are brighter than the unlensed source. The observable effect of gravitational microlensing is therefore a temporary apparent magnification of the background source. In some cases, the microlensing effect may increase the brightness of the background source by a factor of up to 1000. As already pointed out by Einstein, the alignments required for the microlensing effect to be observed are rare. Moreover, as all stars are in motion, the effect is transitory and non-repeating. Microlensing events occur over timescales from weeks to months, and require long-term surveys to be detected. Such survey programs have existed since the 1990s. Today, two survey teams are operating: a Japan/New Zealand collaboration known as MOA (Microlensing Observations in Astrophysics) and a Polish/Princeton collaboration known as OGLE (Optical Gravitational Lens Experiment). The MOA team observes from New Zealand and the OGLE team from Chile. They are supported by two follow-up networks, MicroFUN and PLANET/RoboNET, that operate about a dozen telescopes around the globe.

The microlensing technique has been applied to search for dark matter around our Milky Way and other galaxies. This technique has also been used to detect planets orbiting around other stars. For the first time, Rattenbury and his colleagues were able to determine the shape of a star using this technique. The microlensing event that was used was detected in July 2002 by the MOA group. The event is named MOA 2002-BLG-33 (hereafter MOA-33). Combining the observations of this event by five ground-based telescopes together with HST images, Rattenbury and his colleagues performed a new analysis of this event.

The lens of event MOA-33 was a binary star, and such binary lens systems produce microlensing lightcurves that can provide much information about both the source and lens systems. The particular geometry of the observer, lens and source systems during the MOA-33 microlensing event meant that the observed time-dependent magnification of the source star was very sensitive to the actual shape of the source itself. The shape of the source star in microlensing events is usually assumed to be spherical. Introducing parameters describing the shape of the source star into the analysis allowed the shape of the source star to be determined.

Rattenbury and his colleagues estimated the MOA-33 background star to be slightly elongated, with a ratio between the polar and equatorial radius of 1.02 -0.02/+0.04. However, given the uncertainties of the measurement, a circular shape of the star cannot be completely excluded. The figure below compares the shape of the MOA-33 background star with those recently measured for Altair and Achernar. While both Altair and Achernar are only a few parsecs from the Earth, the MOA-33 background star is a more distant star (about 5000 parsecs from the Earth). Indeed, interferometric techniques can only be applied to bright (thus nearby) stars. On the contrary, the microlensing technique makes it possible to determine the shape of much more distant stars. Indeed, there is currently no alternative technique to measure the shape of distant stars.

This technique, however, requires very specific (and rare) geometrical configurations. From statistical considerations, the team estimated that about 0.1% of all detected microlensing events will have the required configurations. About 1000 microlensing events are observed every year. They should become even more numerous in the near future. The MOA group is presently commissioning a new Japan-supplied 1.8m wide-field telescope that will detect events at an increased rate. Also, a US led group is considering plans for a space-based mission called Microlensing Planet Finder. This is being designed to provide a census of all types of planets within the Galaxy. As a by-product, it would also detect events like MOA-33 and provide information on the shapes of stars.

Original Source: Jodrell Bank Observatory

Posted on by Fraser Cain

Soyuz Launches Foton-M Spacecraft

Russian Soyuz rocket launches carrying Foton-M. Image credit: ESA. Click to enlarge.
An unmanned Foton-M spacecraft carrying a mainly European payload was put into orbit by a Russian Soyuz-U launcher today at 14:00 Central European Time (18:00 local time) from the Baikonur Cosmodrome in Kazakhstan.

Following the launch and nine minutes of propelled flight, the Foton-M2 spacecraft is now in low-earth orbit where it will remain for 16 days before its reentry module lands close to the Russian/Kazakh border.

During the mission European experiments and equipment will be monitored by ESA’s Operations Team at the Payload Operations Centre based at Esrange near Kiruna, Sweden. They will be responsible for receiving, evaluating and disseminating scientific data generated by European payloads on Foton such as the Fluidpac and Agat experiment facilities. During 6 of the 16 daily orbits, the Foton spacecraft will be in a suitable orbital position for Kiruna to receive signals from it. Should any experiment parameters need adjustment, the commands will be sent direct from Kiruna to the specific experiment facility.

The European payload carried by Foton-M2 covers a scientific programme consisting of 39 experiments in fluid physics, biology, material science, meteoritics, radiation dosimetry and exobiology. The European Space Agency has been cooperating with the Russian Space Agency on this type of scientific mission for 18 years. With 385 kg of European experiments and equipment out of the overall payload of 600 kg, this mission constitutes the largest European contribution that has been put into orbit on such missions. The Foton-M2 mission provides reflight opportunities for almost the entire Foton-M1 experiment programme lost due to launcher failure on 15 October 2002.

Applied research plays a prominent role with heat transfer experiments in the European FluidPac facility, chemical diffusion experiments in the SCCO (Soret Coefficients in Crude Oil), and material science investigations in the Agat and Polizon furnaces. These experiments are expected to contribute, respectively, to new heat-exchanger designs, to more efficient oil exploration processes, and to better semiconductor alloys.

As on previous missions, biological research receives a great deal of attention, this time with the emphasis on fundamental questions about the origin and spread of life forms in the universe. Biopan, which is hosting most of these experiments, is making its fifth scientific flight on a Foton mission. Education is also playing a part in the mission with a germination experiment, which has come from ESA’s student programme.

“Foton is one of the very important platforms that ESA uses for experimentation in weightlessness,” said Daniel Sacotte, ESA’s Director of Human Spaceflight, Microgravity and Exploration Programmes, “and with more than half the total available payload being taken up by European experiments and hardware, this shows the efforts that Europe is making to expand the boundaries of research in space to help improve life on Earth.”

The mission is being carried out under an agreement signed between ESA and the Russian Space Agency Roskosmos on 21 October 2003 covering two Foton flights (Foton-M2 and Foton-M3, scheduled for 2007), which will have a combined total of 660 kg of ESA-supplied scientific payloads on board. The agreement also ties in two Russian partner companies: TsSKB-Progress in Samara and the Barmin Design Bureau for General Engineering (????) in Moscow.

“This was the first Foton launch from the Baikonur Cosmodrome in Kazakhstan as all previous launches have been from the Plesetsk Cosmodrome in Russia” explains Antonio Verga, ESA’s Project Manager for Foton missions. “The Foton-M2 reentry module is expected to reenter earth’s atmosphere on 16 June and land in an uninhabitated area near the town of Orenburg, Russia, close to the Russian/Kazakh border. The capsule and the experiments will be recovered within a few hours of the landing. Time-sensitive ESA experiments will be flown back immediately to Rotterdam via Samara and turned over to researchers for analysis at ESA/ESTEC in Noordwijk, the Netherlands.”

Original Source: ESA News Release

Posted on by Fraser Cain

What’s Up This Week – May 30 – June 5, 2005

NGC 4038/39. Image credit: Astro Physics. Click to enlarge.
Monday, May 30 – Legend tells us the constellation of Crater is the cup of the gods – cup befitting the god of the skies, Apollo. Who holds this cup, dressed in black? It’s the Raven, Corvus. The tale is a sad one – a story of a creature sent to fetch water for his master, only to tarry too long waiting on a fig to ripen. When he realized his mistake, the sorry Raven returned to Apollo with his cup and brought along the serpent Hydra in his claws as well. Angry, Apollo tossed them into the sky for all eternity and it is in the south they stay until this day.

This week it will be our pleasure to study the Cup and the Raven. The galaxies I have chosen are done particularly for those of us who still star hop. I will start with a “marker” star that should be easily visible unaided on a night capable of supporting this kind of study. The field stars are quite recognizable in the finder and this is an area that takes some work. Because these galaxies approach magnitude 13, they are best suited to the larger telescope.

Now, let’s go between map and sky and identify both Zeta and Eta Crater and form a triangle. Our mark is directly south of Eta the same distance as between the two stars. At low power, the 12.7 magnitude NGC 3981 sits inside a stretched triangle of stars. Upon magnification, an elongated, near edge-on spiral structure with a bright nucleus appears. Patience and aversion makes this “stand up” galaxy appear to have a vague fading at the frontiers with faint extensions. A moment of clarity is all it takes to see tiny star caught at the edge.

Tuesday, May 31 – For early morning observers in the Middle East, you can enjoy an event as the Moon occults Psi 1 Aquarii. Please check this IOTA webpage for details in your area. For all observers, have a look this morning before dawn to see a very pleasing pairing of the waning Moon and Mars, but if you live in southern Africa or South America, you see this as an occultation! Please check this IOTA webpage so you don’t miss it.

Tonight’s study object, 12.7 magnitude NGC 3956 is about a degree due south of NGC 3981. When first viewed, it appears as edge-on structure at low power. Upon study. it takes on the form of a highly inclined spiral. A beautiful multiple star, and a difficult double star also reside with the NGC 3956 – appearing almost to triangulate with it. Aversion brings up a very bright core region which over the course of time and study appears to extend away from the center, giving this very sweet galaxy more structure than can be called from it with one observation.

Wednesday, June 1 – Our galaxy for tonight is a little more than two degrees further south of our last study. The 12.8 magnitude NGC 3955 is a very even, elongated spiral structure requiring a minimum of aversion once the mind and eye “see” its position. Not particularly an impressive galaxy, the NGC 3955 does, however, have a star caught at the edge as well. After several viewings, the best structure I can pull from this one is a slight concentration toward the core.

Thursday, June 2 – Tonight we’ll study an interacting pair and all that is required is that you find 31 Corvii, an unaided eye star west of Gamma and Epsilon Corvii. Now we’re ready to nudge the scope about one degree north. The 11th magnitude NGC 4038/39 is a tight, but superior pair of interacting galaxies. Often referred to as either the “Ringtail” or the “Antenna”, this pair deeply captured the public’s imagination when photographed by the Hubble. (Unfortunately, we don’t have the Hubble, but what we have is set of optics and the patience to find them.) At low power the pair presents two very stellar core regions surrounded by a curiously shaped nebulosity. Now, drop the power on it and practice patience – because it’s worth it! When that perfect moment of clarity arrives, we have crackling structure. Unusual, clumpy, odd arms appear at strong aversion. Behind all this is a galactic “sheen” that hints at all the beauty seen in the Hubble photographs. It’s a tight little fellow, but worth every moment it takes to find it.

Friday, June 3 – Tonight return to 31 Corvii and head one half degree northwest to discover 11.6 magnitude NGC 4027. Relatively large, and faint at low power, this one also deserves both magnification and attention. Why? Because it rocks! It has a wonderful coma shape with a single, unmistakable bold arm. The bright nucleus seems to almost curl along with this arm shape and during aversion a single stellar point appears at its tip. This one is a real treat!

While out tonight, stay on watch for the peak of the Tau Herculids meteor shower. The radiant is near Corona Borealis. We will be in this stream for about a month and you can catch about 15 per hour maximum. Most are quite faint, but sharp-eyed observers will enjoy it.

Saturday, June 4 – Tonight let’s look to the sky again and fixate on Eta Crater – our study lay one half degree southeast. The 12.8 magnitude NGC 4033 is a tough call even for a large scope. Appearing elliptical at low power, it does take on some stretch at magnification. It is smallish, even and quite unremarkable. It requires good aversion and a bit of patience to find. Good luck!

Sunday, June 5 – The last of our studies resides by a star, one degree west of Beta Corvii. In order to “see” anything even remotely called structure in NGC 4462, this one is a high power only galaxy that is best when the accompanying star is kept out of the field as much as possible. It holds a definite stellar nucleus and a concentration that pulls away from it making it almost appear barred. On an exceptional night with a large scope, wide aversion and moments of clarity show what may be three to four glints inside the structure. Ultra tiny pinholes in another universe? Or perhaps an unimaginably huge, bright globular clusters? While attention is focused on trying to draw out these points, you’ll notice this galaxy’s structure much more clearly. Another true beauty and fitting way to end this particular study field.

If you’re just in the mood to skywatch, the stay up a little later to catch the Scorpiid meteor shower peak. The radiant will be near Ophiuchus and the fall rate is about 20 per hour with some fireballs.

The constellations of both Crater and Corvus hold many, many more such fine galaxy studies. Perhaps another year we shall hunt them all down, eh? But for now, our eyes are on Virgo for next week’s new Moon study. I look forward to the galaxy fields again, but not half as much as I look forward to taking you there. Until next week? May all your journeys be at Light Speed… ~Tammy Plotner

Posted on by Mark Mortimer

Book Review: Four Astronomy Books for Kids

The Planets by Gail Gibbons is a primary level reader. Go outdoors with a youngster and point out the bright red dot of Mars. Then, return indoors and peruse the friendly and accurate portrayal of this planet in the book. For instance, with Mars, there is a diagram that shows its relative orbital position about the sun and a realistic drawing of the Martian globe. There is one diagram per page and underneath each diagram there is some text with relevant facts. Again with Mars, we read how it is the fourth planet from the Sun, about 142 million miles away and two robotic vehicles are exploring its surface. Each of the planets has a two page spread and appropriate factual data.

This book would easily satisfy the bedtime story for the young space buff. A touch of history, a sprinkling of physics and some clever visual representations might instil some knowledge and even awaken that nascent curiosity. For those who are just learning to read, this book will acquaint them with words more challenging than ‘See Spot run’. Further, because of the faithful rendering of the planets, they will knowingly begin to associate traits with names, e.g. the rings belong to Saturn.

Whether you are doing the reading or helping a younger one with theirs, The Planets will start opening up the concept of space and where we are within it.

Admittedly, children grow up way too fast. Primary readers quickly become outdated and children will seek new challenges. The book Stargazer by Ben Morgan is just the solution. Within it are many outdoor and indoor activities to keep a child’s mind turning and their fingers busy.

Within it are more than thirty ways of exploring the skies. Following these will enable youngsters and their elders to happily spend time learning in harmony. Together you can make a planisphere, set up an experiment to check for life and prepare a lunar calendar. These and the other activities will push children into the more abstract thinking associated with the sciences, and at the same time their significance can easily be grasped by an adult so as to relay their deeper meaning.

In keeping with the shorter attention span of the young, the activities are fairly simple and for the most part quick to complete. A two page description is all most have and need. Each has background information, a list of ‘ingredients’ and step by step instructions. For instance, the atmosphere of Jupiter is discussed. Then using simple kitchen items the reader is guided into making patterns of liquids similar to Jupiter’s great red spot. Side comments note the Galileo probe and the Voyager probes that each visited Jupiter.

Stargazer encompasses a broad range of experiments to help a child learn get acquainted with the scientific method and further appreciate the enormity of our universe. In its small format, it is easy to carry and use at club or group meetings while fold-out field guides to the constellations would assist in outdoor discoveries.

In a similar way, Joe Rhatigan and Rain Newcomb in their book Out of This World Astronomy set their own stage for discovery and learning by doing. Within this book are fifty science projects to help grasp the nuances of our solar system, galaxies and even the big bang. With photographs, drawings and sketches, their projects can be accomplished with ease while intertwined related material lets a young reader explore further.

The projects are clearly laid out. A preliminary rationale demonstrates the activity and its relation to the real-life scenario. Again there is a list of required elements and then a step by step guide takes you through the project toward any conclusions. For instance, to grasp the relative distance of the orbits, the reader can head to their nearest football field, place a marker for the sun at one end zone and then use the yard lines to place markers at the appropriate location for each of the planets. Like most of the others, this activity is clear, simple, yet, succinct.

Between the projects, Rhatigan and Newcomb have included many of the mainstays of star watching. The proper use of red lights, how to estimate angles using finger widths, and the construction of the telescope types are all presented. Helpful hints guide the user in finding the planets. Quizzes reinforce the understanding of significant attributes while historical tidbits show the influence the stars have held on generations gone by.

Given the larger format and hardcover, the book Out of This World Astronomy seems better as a static reference. The experiments probably need a bit of planning and the information pages between the experiments are best for a single person sitting down and contemplating. However, the activities are of course more fun with another person or in a group.

The fourth book in this review is a junior level reference work, the Scholastic Atlas of Space. Perhaps the ubiquitous science project is raising its head or your child is asking questions that are beyond your ken. The simple explanations and inviting pictures included within this book will have the two of you happily learning more and getting homework done in no time.

As in keeping with a reference, the book is divided into particular subject matters. Each has background information, relevancy and association. For example under “looking into space” the text discusses the history of observation, broadens the knowledge by discussing the electromagnetic spectrum and then highlights the current top-of-the-heap ability, the Keck telescope on Mount Mauna Kea and the Hubble space telescope.

The subjects extend through the typical space arena. The beginning of the universe, galaxies and formation of stars lead into solar systems. Then, of course, each of our solar system’s planet gets portrayed with their own two page spread of pictures and drawings. The book concludes with a list of facts, star charts for the northern and southern hemisphere, and a helpful glossary.

Though the Scholastic Atlas of Space is a great reference, it really isn’t an atlas. However, one point where it and the Stargazer are well thought out is that they provide units in both metric (i.e. kilometres) and imperial (i.e. miles) values. Out of This World Astronomy give values only in imperial units though it does have a conversion chart in the very back. Nevertheless, all four excel at emphasizing visual imagery rather than text information, a fact alone that sets them apart as being well suited for the young audience.

The stars are free to anyone who wants to view their beauty. Sharing in their twinkling makes their value even greater. So don’t spend too many late nights alone watching the stars spin and rotate about. Use any of the four books described above to easily introduce the wonders of the night skies to young children and together you can expand your horizons.

Review by Mark Mortimer.