Posted on by Fraser Cain

Heaviest Stars are Twins

Image credit: Harvard-Smithsonian CfA
About 20,000 light-years from Earth, two massive stars grapple with each other like sumo wrestlers locked in combat. Both giants, each weighing in at around 80 times the mass of our Sun, are the heaviest stars ever. They orbit each other every 3.7 days, nearly touching as they spin on the celestial stage. And they lead tempestuous lives worthy of any Hollywood couple, blasting each other with hot, violent stellar winds.

“We could not resist exploring this system because it’s so remarkable. It’s a place of true extremes,” said astronomer Alceste Bonanos (Harvard-Smithsonian Center for Astrophysics).

The binary star system Bonanos studied, known as WR 20a, was pegged as particularly interesting only weeks ago by a team of European researchers headed by Gregor Rauw. That team’s spectroscopic observations showed that both stars were very massive. However, the only way to determine the masses precisely was to establish at what angle we were viewing the system, as well as the orbital period.

Bonanos and her advisor, Krzysztof Stanek (CfA), requested photometric observations from the Optical Gravitational Lensing Experiment (OGLE) team led by Andrzej Udalski (Warsaw University Observatory). Bonanos and Stanek knew that if the system were nearly edge-on, one star would periodically pass in front of, or eclipse, the other. Fortuitously, those eclipses were detected by the OGLE group, thereby firmly establishing the characteristics of the system.

“When we realized how important it would be to obtain an accurate light curve for WR 20a, we immediately decided to contact Andrzej Udalski, who leads the Polish project known as OGLE. They are a premier facility for optical surveys, and we were very happy when they agreed to collaborate on this project,” said Stanek.

Observations were collected in May 2004 with the 1.3-meter-diameter OGLE telescope at the Las Campanas Observatory in Chile.

“The results have exceeded our expectations; after just two nights, we realized that the star significantly changed its brightness, and after a few more we were certain that the system is eclipsing,” said Udalski.

“After obtaining data each night for more than two weeks, we were able to measure very accurately the period, inclination angle, and hence the masses of the two stars,” added Stanek.

A System Of Extremes
WR 20a is part of the Westerlund 2 star cluster, which resides in a region of ionized hydrogen left over from the cluster’s formation in the constellation Carina. WR 20a contains two hot, young Wolf-Rayet stars-a type of star that is extremely rare and short-lived.

“Wolf-Rayet stars are likely progenitors of the extremely powerful explosions known as gamma-ray bursts,” said Bonanos. “These stars are already 2 or 3 million years old. In another few million years, whichever one is slightly more massive will undergo core collapse and blast off its outer layers. The companion star likely will survive despite its nearness, at least until it goes supernova sometime later.”

While other stars, such as the Pistol Star and eta Carinae, are suspected of containing enough material to make more than 100 Suns, their masses have not been determined accurately. The possibility exists that they are simply very close binaries. WR 20a is the most massive known binary system where both stars have precisely determined masses.

“It is important to study and understand these massive stars because they probe the realm of the first stars that formed in the Universe. Learning more about this system will help improve star formation models, as well as increase our understanding of the connection of these stars to supernovae and gamma-ray bursts,” said Stanek.

This research has been posted online at http://arxiv.org/abs/astro-ph/0405338 in a paper co-authored by Alceste Bonanos and Krzysztof Stanek (CfA); with Andrzej Udalski, Lukasz Wyrzykowski, Karol Zebrun, Marcin Kubiak, Michal Szymanski, Olaf Szewczyk, Grzegorz Pietrzynski, and Igor Soszynski (Warsaw University Observatory).

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

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

Asteroid Wiped Out the Dinosaurs in Hours

Image credit: NASA
According to new research led by a University of Colorado at Boulder geophysicist, a giant asteroid that hit the coast of Mexico 65 million years ago probably incinerated all the large dinosaurs that were alive at the time in only a few hours, and only those organisms already sheltered in burrows or in water were left alive.

The six-mile-in-diameter asteroid is thought to have hit Chicxulub in the Yucatan, striking with the energy of 100 million megatons of TNT, said chief author and Researcher Doug Robertson of the department of geological sciences and the Cooperative Institute for Research in Environmental Sciences. The “heat pulse” caused by re-entering ejected matter would have reached around the globe, igniting fires and burning up all terrestrial organisms not sheltered in burrows or in water, he said.

A paper on the subject was published by Robertson in the May-June issue of the Bulletin of the Geological Society of America. Co-authors include CU-Boulder Professor Owen Toon, University of Wyoming Professors Malcolm McKenna and Jason Lillegraven and California Academy of Sciences Researcher Sylvia Hope.

“The kinetic energy of the ejected matter would have dissipated as heat in the upper atmosphere during re-entry, enough heat to make the normally blue sky turn red-hot for hours,” said Robertson. Scientists have speculated for more than a decade that the entire surface of the Earth below would have been baked by the equivalent of a global oven set on broil.

The evidence of terrestrial ruin is compelling, said Robertson, noting that tiny spheres of melted rock are found in the Cretaceous-Tertiary, or KT, boundary around the globe. The spheres in the clay are remnants of the rocky masses that were vaporized and ejected into sub-orbital trajectories by the impact.

A nearly worldwide clay layer laced with soot and extra-terrestrial iridium also records the impact and global firestorm that followed the impact.

The spheres, the heat pulse and the soot all have been known for some time, but their implications for survival of organisms on land have not been explained well, said Robertson. Many scientists have been curious about how any animal species such as primitive birds, mammals and amphibians managed to survive the global disaster that killed off all the existing dinosaurs.

Robertson and colleagues have provided a new hypothesis for the differential pattern of survival among land vertebrates at the end of the Cretaceous. They have focused on the question of which groups of vertebrates were likely to have been sheltered underground or underwater at the time of the impact.

Their answer closely matches the observed patterns of survival. Pterosaurs and non-avian dinosaurs had no obvious adaptations for burrowing or swimming and became extinct. In contrast, the vertebrates that could burrow in holes or shelter in water — mammals, birds, crocodilians, snakes, lizards, turtles and amphibians — for the most part survived.

Terrestrial vertebrates that survived also were exposed to the secondary effects of a radically altered, inhospitable environment. “Future studies of early Paleocene events on land may be illuminated by this new view of the KT catastrophe,” said Robertson.

Original Source: CU-Boulder News Release

Posted on by Fraser Cain

Binary Black Holes Modeled on Computer

Image credit: Penn State
Scientists at Penn State have reached a new milestone in the effort to model two orbiting black holes, an event expected to spawn strong gravitational waves. “We have discovered a way to model numerically, for the first time, one orbit of two inspiraling black holes,” says Bernd Bruegmann, Associate Professor of Physics and a researcher at Penn State’s Institute for Gravitational Physics and Geometry. Bruegmann’s research is part of a world-wide endeavor to catch the first gravity wave in the act of rolling over the Earth.

A paper describing these simulations will be published in the 28 May 2004 issue of the journal Physical Review Letters. The paper is authored by Bruegmann and two postdoctoral scholars in his group at Penn State, Nina Jansen and Wolfgang Tichy.

Black holes are described by Einstein’s theory of general relativity, which gives a highly accurate description of the gravitational interaction. However, Einstein’s equations are complicated and notoriously hard to solve even numerically. Furthermore, black holes pose their very own problems. Inside each black hole lurks what is known as a space-time singularity. Any object coming too close will be pulled to the center of the black hole without any chance to escape again, and it will experience enormous gravitational forces that rip it apart.

“When we model these extreme conditions on the computer, we find that the black holes want to devour and to tear apart the numerical grid of points that we use to approximate the black holes,” Bruegmann says. “A single black hole is already difficult to model, but two black holes in the final stages of their inspiral are vastly more difficult because of the highly non-linear dynamics of Einstein’s theory.” Computer simulations of black hole binaries tend to go unstable and crash after a finite time, which used to be significantly shorter than the time required for one orbit.

“The technique we have developed is based on a grid that moves along with the black holes, minimizing their motion and distortion, and buying us enough time for them to complete one spiraling orbit around each other before the computer simulation crashes,” Bruegmann says. He offers an analogy to illustrate the “co-moving grid” strategy: “If you are standing outside a carousel and you want to watch one person, you have to keep moving your head to keep watching him as he circles. But if you are standing on the carousel, you have to look in only one direction because that person no longer moves in relation to you, although you both are going around in circles.”

The construction of a co-moving grid is an important innovation of Bruegmann’s work. While not a new idea to physicists, it is a challenge to make it work with two black holes. The researchers also added a feedback mechanism to make adjustments dynamically as the black holes evolve. The result is an elaborate scheme that actually works for two black holes for about one orbit of the spiraling motion.

“While modelling black hole interactions and gravitational waves is a very difficult project, Professor Bruegmann’s result gives a good view of how we may finally succeed in this simulation effort,” says Richard Matzner, Professor at the University of Texas at Austin and principal investigator of the National Science Foundation’s former Binary Black Hole Grand Challenge Alliance that laid much of the groundwork for numerical relativity in the 90’s.

Abhay Ashtekar, Eberly Professor of Physics and Director of the Institute for Gravitational Physics and Geometry, adds, “The recent simulation of Professor Bruegmann’s group is a landmark because it opens the door to performing numerical analysis of a variety of black hole collisions which are among the most interesting events for gravitational wave astronomy.”

This research was funded by grants from the National Science Foundation including one to the Frontier Center for Gravitational Wave Physics established by the National Science Foundation in the Penn State Institute for Gravitational Physics and Geometry.

Original Source: Penn State News Release

Posted on by Fraser Cain

Gravity Probe B’s First Month in Space

Image credit: NASA
One month into the Gravity Probe B mission ? a NASA experiment to test two predictions of Albert Einstein’s Theory of General Relativity ? all spacecraft subsystems continue to perform well, and the spacecraft orbit is stable. . Gravity Probe B is managed by the Marshall Center.

One month into the mission, all spacecraft subsystems are continuing to perform well. The spacecraft’s orbit remains stable and meets our requirements for next month’s transition into the science phase of the mission, upon completion of the spacecraft initialization and orbit checkout. The four gyroscopes are suspended, and we have indications that they are rotating slightly in their housings.

Last weekend, the team successfully performed a procedure to reduce magnetic flux that had built up around the gyroscope rotors (spheres). Magnetic flux is a measure of the number of magnetic field lines penetrating a surface. To ensure that the SQUID readouts receive clean signals from the gyroscopes and to provide the highest possible degree of accuracy during the GP-B science experiment, any magnetic flux around the gyroscope rotors must be minimized.

We reduce magnetic flux by turning on heaters and flowing helium gas, warmed to 10 Kelvin, through the probe. This process also drives off any residual helium remaining in the well of the Dewar, where the probe sits. The flux reduction procedure went smoothly, and when it was completed, the level of trapped flux remaining within the gyros was almost imperceptible. In fact, gyroscope #4, which previously had the highest amount of trapped magnetic flux of all the gyros now has the lowest level.

The flux reduction procedure added heat to the Dewar, thereby increasing the pressure inside to its maximum allowable level. The increased pressure during this stress period caused some of the spacecraft’s micro thrusters to become unstable, resulting in the spacecraft pointing in the wrong direction and triggering a “safemode.”

The 16 micro thrusters are arranged in clusters of four, and local feedback loops within each cluster enable the thrusters to communicate with each other and automatically adjust their flow rates. Ground commands were issued to isolate the unstable thrusters, which resolved the thruster cross-talk issue and enabled the spacecraft to re-orient itself. The thrusters are now functioning properly, the spacecraft’s attitude has been corrected, and it is once again pointing towards the guide star.

The flux reduction operation and subsequent thruster instability and attitude problems has delayed locking the spacecraft onto the guide star, which will be our next major activity. While we have used up some of the contingency days built into the Initialization & Orbit Checkout (IOC) schedule, this phase of the Gravity Probe B mission is still on track for completion within 60 days after launch, at which time the 13-month science data collection will begin. This will be followed by a two-month final calibration of the science instrument assembly.

NASA’s Gravity Probe B mission, also known as GP-B, will use four ultra-precise gyroscopes to test Einstein’s theory that space and time are distorted by the presence of massive objects. To accomplish this, the mission will measure two factors ? how space and time are warped by the presence of the Earth, and how the Earth’s rotation drags space-time around with it.

NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Gravity Probe B program for NASA’s Office of Space Science. Stanford University in Stanford, Calif., developed and built the science experiment hardware and operates the science mission for NASA. Lockheed Martin of Palo Alto, Calif., developed and built the GP-B spacecraft.

Original Source: NASA News Release

Posted on by Fraser Cain

ESA Releases Its Findings on Beagle 2

Image credit: ESA
The Mars Express spacecraft, carrying the Beagle 2 lander, was launched on 2 June last year, arriving in the vicinity of Mars in December. The separation of Beagle 2 from Mars Express occurred on 19 December. The satellite continued its mission with its successful insertion into a Mars orbit on 25 December, the day on which Beagle 2 was due to land.

The first radio contact with Beagle 2 was expected shortly after the scheduled landing time but no signal was received. Many radio contacts were attempted over the following days and weeks, but without result. By early February it became clear that there was no prospect of communicating with Beagle 2 and a joint ESA/UK inquiry was set up to investigate the circumstances and possible reasons that prevented completion of the Beagle 2 mission.

The report was commissioned jointly by Lord Sainsbury and ESA?s Director General, Jean-Jacques Dordain. It is not therefore a public inquiry. The Commission of Inquiry was led by ESA?s Inspector General, Ren? Bonnefoy, with David Link (former Director at Matra-Marconi Space, now EADS-Astrium(UK)) as co-Chairman.

The Commission of Inquiry, which included senior managers and experts from within Europe and also NASA and Russia, held several meetings in the UK and in ESA, interviewing the key actors, directors, managers, scientists, and engineers, who participated in the development of Beagle 2. The report has been submitted to the UK Minister for Science and Innovation and the Director General of ESA and accepted. No single technical failure or shortcoming was unambiguously identified but a few credible causes for Beagle 2?s loss were highlighted. More importantly, the Board made it clear that there were programmatic and organisational reasons that led to a significantly higher risk of Beagle 2 failure, than otherwise might have been the case.

The scope of the Inquiry covered a wide range of important issues of concern to the UK, ESA and other Member States in ESA. Some of these matters are necessarily confidential between governments and the Agency and cannot be released.

Furthermore, the development of Beagle 2 entailed close working relations between many firms in the UK. Many of those firms invested their own funds in the project and formed relations which remain commercially sensitive.

Although deciding that the Report should remain confidential, we believe it is important that the full set of Recommendations is published together with our appreciation of lessons learnt. You will, of course, have an opportunity to hear at first hand about our plans to implement those Recommendations and to ask questions.

Lessons learnt
The Inquiry Board has not singled out any act by any individual, nor any technical failure that in itself could have been the unique cause of failure of Beagle 2. In the Inquiry Board?s work, many individual decisions were analysed. However, there are institutional lessons to be learnt, many of which flow from treating the lander as an instrument, which at the time was the standard practice.

The Commission has proposed a set of 19 Recommendations on which the UK Government, ESA and the Beagle 2 project team are agreed. They can be grouped in three parts:

* those concerning best practice when selecting a complex project ? such as the Beagle 2 lander ? assessing its overall benefits and risks, planning means to manage and mitigate risks and ensuring that it is fully integrated within the overall management of the mission;
* those concerned with technical factors which may have contributed to the loss of Beagle 2, for example specification, development and testing of the airbags;
* and those concerning technical enhancements for future landers which would have aided our understanding of events during Beagle 2?s descent and subsequently improved our ability to find it or reactivate it.

In 1997, due to the failure of an earlier Russian mission, equipment was available for a mission to Mars. At the same time it was known that Mars would be at a point of closest approach to Earth during the summer of 2003. As a result ESA Member States selected the Mars Express mission, though the schedule was tight, and ESA invited proposals to consider the addition of a lander. Three European teams proposed landers and Beagle 2 was selected. It is now clear that the very high potential scientific benefits of the project may have contributed to a collective institutional underestimate by us all of the corresponding means to identify and mitigate risks that arose during development and subsequently proved difficult to resolve due to the very tight financial, mass and schedule constraints imposed by the rigid schedule set by that closest point of approach, and by overall budget constraints.

Implementation plan
1. ESA will return to Mars but next time the approach must have the capacity to handle the complexity, and scientists, engineers and industry will need to agree from the start the formal partnership arrangements and responsibilities that will apply throughout;

2. Any future complex instrument or lander must be implemented under the same management process as the mission spacecraft. BNSC has already led the way in implementing such a new policy with the European MIRI instrument for the James Webb Space Telescope. Nevertheless, scientific groups will be fully integrated into those overall arrangements;

3. A dedicated Exploration Directorate in ESA has been set up to coordinate technical requirements and approaches Europe-wide and will take responsibility for securing European capabilities for crucial elements for planetary missions;

4. Confidential Debriefing will be given to all scientific groups and industrial companies in Beagle 2 on request;

5. ESA Member States will be confidentially debriefed on the implications of this new approach in future programmes and to partnership arrangements.

The recommendations of the Commission of Inquiry:
Recommendation 1
Future lander missions should be under the responsibility of an Agency with appropriate capability and resources to manage it. The lander/orbiter mission should be managed as an integrated whole. Nationally-funded science instruments should be included in the lander on the same basis as on the orbiter.

Recommendation 2
For future science payloads which are critical to overall mission success or have a very high public profile, the ESA Executive should make a formal, comprehensive assessment of all aspects of the proposals including technical, management and finance, and advise Space Science Policy Committee (SPC) accordingly before acceptance. If the assessment is not positive, ESA should advise the SPC not to accept the proposal.

Recommendation 3
Sponsoring Agencies of nationally-funded contributions to ESA projects should ensure that the required financing is committed at the outset to meet the estimated Cost at Completion and require that a structured development programme is established.

Recommendation 4
In addition to the ESA-led reviews of interfaces, formal Project Reviews of nationally-funded contributions to ESA missions should be undertaken by the sponsoring Agency to a standard agreed with ESA and should cover the entire project.

Recommendation 5
When an independent review of a nationally-funded project, such as the Casani review of Beagle 2, is commissioned, it is essential that ESA and the Sponsoring Agency ensure that its recommendations are properly dispositioned and those which are agreed are actioned and followed up through a formal process.

Recommendation 6
For future projects, Heads of Agreement or similar formal arrangements between co-operating entities, ESA, and national sponsors, should be put in place at the outset of projects and should include formal consultations at key stages of the projects to jointly consider its status.

Recommendation 7
Fixed price contracting should be avoided solely as a mechanism for controlling costs, and used only where the sponsor and contractor are in alignment on the requirements and scope of the work and the sharing of risks between them. Both parties should be confident that the contractor has sufficient margins to manage his uncertainties and risks.

Recommendation 8
For future high-profile/high-risk projects, ESA and any Sponsoring Agency should manage the expectations of the outcome of the project in a balanced and objective way to prepare for both success and failure.

Recommendation 9
At the start of a programme, the funding authority (ies) should require that there is system-level documentation. This is necessary to provide all partners with the technical requirements for the project and sufficient design description and justification such that the margins and risks being taken in each partner?s area of responsibility are visible.

Recommendation 10
Future planetary missions should be designed with robust margins to cope with the inherent uncertainties, and they should not be initiated without adequate and timely resources to achieve that.

Recommendation 11
Future planetary entry missions should include a minimum telemetry of critical performance measurements and spacecraft health status during mission critical phases such as entry and descent.

Recommendation 12
For future planetary entry missions, a more robust communications system should be used, allowing direct commanding of the lander for essential actuations and resets without software involvement ? enabling recoveries in catastrophic situations.

Recommendation 13
Planetary probe missions involving high-level shocks from pyros and other events should undergo representative shock environmental testing at system level.

Recommendation 14
Adequate and realistic deployment tests should be performed, and sufficient time and resources must be available in the development of a new planetary mission.

Recommendation 15
Elimination of internal connectors for mass saving should be avoided if at all possible. But if unavoidable, a stringent system of check and independent crosscheck should be followed during the final wiring operation.

Recommendation 16
A back-up for the entry detection event (T0) must be included in the design of planetary entry probes.

Recommendation 17
Future planetary entry missions should include a release of the back cover and front shield, which is aerodynamically stable and analytically predictable to avoid uncontrolled contact of front shield with the lander.

Recommendation 18
Sufficient difference between ballistic coefficients of all separated items, e.g. back covers assembly and the main parachute, or other positive means, must be ensured to exclude collision after separation.

Recommendation 19
Adequate competencies in air bag and parachute technology must be available for future European planetary missions, making best use of existing expertise e.g. in USA and Russia.

Original Source: ESA News Release

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In the Shadow of Saturn’s Rings

Image credit: NASA/JPL/Space Science
Saturn?s rings cast threadlike shadows on the planet?s northern hemisphere. Note the translucent C ring and thin, outermost F ring. The image was taken with the narrow angle camera in visible light on May 10, 2004 at a distance of 27.2 million kilometers (16.9 million miles) from Saturn. Image scale is 162 kilometers (101 miles) per pixel. Contrast in the image was enhanced to aid visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

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

Posted on by Fraser Cain

New Theory Proposed for Solar System Formation

Image credit: Hubble
Like most creation stories, this one is dramatic: we began, not as a mere glimmer buried in an obscure cloud, but instead amidst the glare and turmoil of restless giants.

Or so says a new theory, supported by stunning astronomical images and hard chemical analysis. For years most astronomers have imagined that the Sun and Solar System formed in relative isolation, buried in a quiet, dark corner of a less-than-imposing interstellar cloud. The new theory challenges this conventional wisdom, arguing instead that the Sun formed in a violent nebular environment – a byproduct of the chaos wrought by intense ultraviolet radiation and powerful explosions that accompany the short but spectacular lives of massive, luminous stars.

The new theory is described in a ?Perspectives? article appearing in the May 21 issue of Science. The article was written by a group of Arizona State University astronomers and meteorite researchers who cite recently discovered isotopic evidence and accumulated astronomical observations to argue for a history of development of the Sun, the Earth and our Solar System that is significantly different from the traditionally accepted scenario.

If borne out by future work, this vision of our cosmic birth could have profound implications for understanding everything from the size and shape of our solar system to the physical makeup of the Earth and the development of the chemistry of life.

?There are two different sorts of environment where low-mass stars like the Sun form,? explained ASU astronomer Jeff Hester, the essay’s lead author. ?In one kind of star-forming environment, you have a fairly quiescent process in which an undisturbed molecular cloud slowly collapses, forming a star here? a star there. The other type of environment in which Sun-like stars form is radically different. These are more massive regions that form not only low-mass stars, but luminous high-mass stars, as well.?

More massive regions are very different because once a high-mass star forms, it begins pumping out huge amounts of energy that in turn completely changes the way Sun-like stars form in the surrounding environment. ?People have long imagined that the Sun formed in the first, more quiescent type of environment,? Hester noted, ?but we believe that we have compelling evidence that this is not the case.?

Critical to the team’s argument is the recent discovery in meteorites of patterns of isotopes that can only have been caused by the radioactive decay of iron-60, an unstable isotope that has a half life of only a million and a half years. Iron-60 can only be formed in the heart of a massive star and thus the presence of live iron-60 in the young Solar System provides strong evidence that when the Sun formed (4.5 billion years ago) a massive star was nearby.

Hester’s coauthors on the Science essay include Steve Desch, Kevin Healy, and Laurie Leshin. Leshin is a cosmochemist and director of Arizona State University’s Center for Meteorite Studies. ?One of the exciting things about the research is that it is truly transdisciplinary, drawing from both astrophysics and the study of meteorites – rocks that you can pick up and hold in your hand – to arrive at a new understanding of our origins,? noted Leshin.

When a massive star is born, its intense ultraviolet radiation forms an ?HII region? – a region of hot, ionized gas that pushes outward through interstellar space. The Eagle Nebula, the Orion Nebula, and the Trifid Nebula are all well-known examples of HII regions. A shock wave is driven in advance of the expanding HII region, compressing surrounding gas and triggering the formation of new low-mass stars. ?We see triggered low-mass star formation going on in HII regions today,? said Healy, who recently completed a study of radio observations of this process at work.

The star does not have much time to get its act together, though. Within 100,000 years or so, the star and what is left of its small natal cloud will be uncovered by the advancing boundary of the HII region and exposed directly to the harsh ultraviolet radiation from the massive star. ?We see such objects emerging from the boundaries of HII regions,” Hester said. ?These are the ?evaporating gaseous globules’ or ?EGGs’ seen in the famous Hubble image of the Eagle Nebula.?

EGGs do not live forever either. Within about ten thousand years an EGG evaporates, leaving behind only the low-mass star and its now-unprotected protoplanetary disk to face the brunt of the massive star’s wrath. Like a chip of dry ice on a hot day, the disk itself now begins to evaporate, forming a characteristic tear-drop-shaped structure like the ?proplyds? seen in Hubble images of the Orion Nebula. ?Once we understood what we were looking at, we realized that we had a number of images of EGGs caught just as they were turning into proplyds,? said Hester. ?The evolutionary tie between these two classes of objects is clear.?

Within another ten thousand years or so the proplyd, too, is eroded away. All that remains is the star itself, surrounded by the inner part of the disk (comparable in size to our Solar System), which is able to withstand the continuing onslaught of radiation. It is from this disk and in this environment that planets may form.

The process leaves a Sun-like star and its surrounding disk sitting in the interior of a low density cavity with a massive star close at hand. Massive stars die young, exploding in violent events called ?supernovas.? When a supernova explodes it peppers surrounding infant planetary systems with newly synthesized chemical elements – including short-lived radioactive isotopes such as iron-60.

?This is where the meteorite data come in,? said Hester. ?When we look at HII regions we see that they are filled with young, Sun-like stars, many of which are known to be surrounded by protoplanetary disks. Once you ask the question, ?what is going to happen when those massive stars go supernova?’, the answer is pretty obvious. Those young disks are going to get enriched with a lot of freshly-made elements.?

?When you then pick up a meteorite and find a mix of materials that can only be easily explained by a nearby supernova, you realize that you are looking at the answer to a very longstanding question in astronomy and planetary science,? Desch added.

?So from this we now know that if you could go back 4.5 billion years and watch the Sun and Solar System forming, you would see the kind of environment that you see today in the Eagle or Trifid nebulas,? said Hester.

?There are many aspects of our Solar System that seem to make sense in light of the new scenario,? notes Leshin. ?For example, this might be why the outer part of the Solar System – the Kuiper Belt – seems to end abruptly. Ultraviolet radiation would also have played a role in the organic chemistry of the young solar system, and could explain other peculiar effects such as anomalies in the abundances of isotopes of oxygen in meteorites.?

One of the most intriguing speculations is that the amount of radioactive material injected into the young solar system by a supernova might have profoundly influenced the habitability of Earth itself. Heat released by the decay of this material may have been responsible for ?baking out? the planetesimals from which the earth formed, and in the process determining how much water is on Earth today.

?It is kind of exciting to think that life on Earth may owe its existence to exactly what sort of massive star triggered the formation of the Sun in the first place, and exactly how close we happened to be to that star when it went supernova,? mused Hester. ?One thing that is clear is that the traditional boundaries between fields such as astrophysics, meteoritics, planetary science, and astrobiology just got less clear-cut. This new scenario has a lot of implications, and makes a lot of new predictions that we can test.?

If it is accepted, the new theory may also be of use in looking for life in the universe beyond. ?We want to know how common Earth-like planets are. The problem with answering that question is that if you don’t know how Earth-like planets are formed – if you don’t understand their connection with astrophysical environments – then all you can do is speculate,? Hester said.

?We think that we’re starting to see a very specific causal connection between astrophysical environments and the things that have to be in place to make a planet like ours.?

Original Source: ASU News Release

Posted on by Fraser Cain

NASA Loans Out Columbia Debris

Image credit: CAIB
The first pieces of Space Shuttle Columbia debris, loaned to a non-governmental agency for testing and research, are on their way from NASA’s Kennedy Space Center (KSC), Fla., to The Aerospace Corporation in El Segundo, Calif.

The Aerospace Corporation requested and will receive graphite/epoxy honeycomb skins from an Orbital Maneuvering System pod, Main Propulsion System Helium tanks, a Reaction Control System Helium tank and a Power Reactant Storage Distribution system tank. The company will use the parts to study re-entry effects on composite materials. NASA notified the Columbia crew’s families about the loan before releasing the items for study.

Earlier this year, Dr. Gary Steckel, senior scientist in the Materials Science Department in the Space Materials Laboratory at The Aerospace Corporation, viewed the items. “We believe these items are representative of the structural composite materials flown on Columbia. They will enable us to successfully meet our objective of calibrating analytical models for predicting reentry behavior of composite structures,” Steckel said.

Researchers believe the testing will show how materials are expected to respond to various heating and loads’ environments. The findings will help calibrate tools and models used to predict hazards to people and property from reentering hardware. The Aerospace Corporation will have the debris for one year to perform analyses to estimate maximum temperatures during reentry based upon the geometry and mass of the recovered composite.

“NASA’s mission includes the development of technologies that improve the safety and reliability of access to space,” said NASA’s Deputy Administrator Fred Gregory. “By allowing the scientific community to study Columbia debris, researchers will have the opportunity to gain unprecedented knowledge about the effects of reentry.”

The request from The Aerospace Corporation was one of several “Request for Information” applications NASA received to study Columbia debris. The eight pieces of hardware were inventoried inside the KSC Vehicle Assembly Building, where Columbia’s debris is stored and prepared for shipment.

“The idea of studying pieces of Columbia came to me in the debris hangar soon after the accident,” said Shuttle Launch Director Mike Leinbach. “It was clear to me we could learn a lot from it, and that we shouldn’t bury the debris as we did with Challenger’s.”

“To see the plan come together is personally rewarding,” Leinbach said. “I hope the technical community will learn as much as possible and put that knowledge to use to improve spacecraft and flight crew system designs in the future,” he said.

For information about NASA and return to flight efforts on the Internet, visit:
http://www.nasa.gov/returntoflight

For information about The Aerospace Corporation on the Internet, visit:
http://www.aero.org/home.html

Original Source: NASA News Release

Posted on by Fraser Cain

Cosmic Hurricane in Starburst Galaxy

Image credit: U WISC
Combining images from orbiting and ground-based telescopes, an international team of astronomers has located the eye of a cosmic hurricane: the source of the 1 million mile-per-hour winds that shower intergalactic space from the galaxy M82.

Situated 10 million light years from our own galaxy, the Milky Way, M82 is one of the most studied objects in the sky. Known as a starburst galaxy for the intense, bright clusters of young stars at its heart, M82 is also characterized by massive jets of hot gas — tens of thousands of light years long — that blast into intergalactic space perpendicular to the starry plane of the galaxy.

Using images combined from the Hubble Space Telescope (HST) and the WIYN Telescope on Kitt Peak, Ariz., a team of astronomers from University College London and the University of Wisconsin-Madison has traced the origin of the galaxy’s “superwind” into the starburst heart of M82. The work shows that the wind is not a single entity, but is made up of multiple gas streams that expand at different rates to form a “cosmic shower” of hot gas expelled from the starburst.

The galaxy’s mighty winds, the astronomers say, were sparked by a near-miss collision with the neighboring giant spiral galaxy M81. That close encounter, according to University College London astronomer Linda Smith, set off an explosive burst of star formation.

“M82 shows intense star formation packed into dense clusters,” says Smith. “This powers plumes of hot gas that extend for tens of thousands of light years above and below the disk of the galaxy. The jets of gas from this pulsating cosmic shower are traveling at more than a million miles an hour into intergalactic space.”

The emphasis of the new work, according to UW-Madison astronomer Jay Gallagher, was on the powerful high-temperature winds of M82 and using the Hubble and WIYN observations in combination to view the galaxy in a new way. “The Hubble and the WIYN data give us a new overall view of the M82 superwind stretching from deep within the starburst into intergalactic space.”

The challenge of the new observations lay in visualizing data covering enormous distances and a huge range in brightness, says Mark Westmoquette, a graduate student at University College London.

“We solved this by overlaying the sharp images from Hubble that cover the inner galaxy, where resolving key details is critical, on top of WIYN data that show the extended wind,” Westmoquette explains. “This approach allowed us to connect inner and outer features with specific sites of star formation.”

Westmoquette likened the exercise to tracing widely dispersed plumes of industrial smoke back to the smokestack from which it originated.

“Just as in the terrestrial case, understanding the flow of chemically enriched matter from galaxies into diffuse intergalactic space requires maps extending from the source to where the plume is lost,” Westmoquette says. “It is a challenge for astronomers.”

In addition to NASA’s Hubble Space Telescope, data for the group’s observations were obtained from the 3.5-meter WIYN Telescope at the Kitt Peak National Observatory in Arizona. The observatory is supported by the National Science Foundation and a consortium of American universities, including UW-Madison.

Original Source: UW-Madison

Posted on by Fraser Cain

Closest Asteroid to the Sun Found

Image credit: NASA/JPL
The ongoing search for near-Earth asteroids at Lowell Observatory has yielded another interesting object. Designated 2004 JG6, this asteroid was found in the course of LONEOS (the Lowell Observatory Near-Earth Object Search) on the evening of May 10 by observer Brian Skiff.

“I immediately noticed the unusual motion,” said Skiff, “so it was certain that it was of more than ordinary interest.” He quickly reported it to the Minor Planet Center (MPC) in Cambridge MA, which acts as an international clearinghouse for asteroid and comet discoveries. The MPC then posted it on a Web page for verification by astronomers worldwide. It happened that all the initial follow up observations, however, were obtained by amateur and professional observers in the Southwest US. The additional sky positions measured in the ensuing few days allowed an orbit to be calculated.

The official discovery announcement and preliminary orbit were published by the MPC on May 13. This showed that the object was located between Earth and Venus (presently the very bright “evening star” in the western sky). In addition, 2004 JG6 goes around the Sun in just six months, making it the asteroid with the shortest known orbital period. Ordinary asteroids are located between the orbits of Mars and Jupiter, roughly two to four times farther from the Sun than Earth, taking several years to go around the Sun.

Instead, 2004 JG6 orbits entirely within Earth’s orbit, only the second object so far found to do so. “What makes this asteroid unique is that, on average, it is the second closest solar system object orbiting the Sun,” said Edward Bowell, LONEOS Director. Only planet Mercury orbits closer to the Sun.

As shown in the included diagram, JG6 crosses the orbits of Venus and Mercury, passing less than 30 million miles from the Sun every six months. The approximate average orbital speed of this asteroid is more than 30 km/sec, or 67,000 miles per hour. Depending on their locations, the asteroid may pass as close as 3.5 million miles from Earth and about 2 million miles from planet Mercury. In the coming weeks 2004 JG6 will pass between Earth and the Sun, just inside Earth’s orbit. It will move through the constellations Cancer and Canis Minor low in the western sky at dusk. Because of the near-exact six-month period, the asteroid should be observable again in nearly the same spot in the sky next May, having gone around the Sun twice while Earth will have made only one circuit.

From present estimates, 2004 JG6 is probably between 500 meters and 1 km in diameter. Despite its proximity, the object poses no danger of colliding with Earth.

Asteroids with orbits entirely within the Earth?s orbit have been informally called “Apoheles,” from the Hawaiian word for orbit. Apohele also has Greek roots: “apo” for outside, and “heli” for Sun. Objects orbiting entirely within Earth?s orbit are thought by dynamicist William F. Bottke of Southwest Research Institute and colleagues to comprise just two percent of the total near-Earth object population, making them rare as well as difficult to discover. This is because they stay in the daylight sky almost all of the time. There may exist about 50 Apoheles of comparable size to or larger than 2004 JG6, but many of them are certain to be unobservable from the ground.

The first asteroid found entirely inside Earth?s orbit was 2003 CP20, found just over a year ago by the NASA-funded Lincoln Laboratory Near-Earth Asteroid Research project, which observes near Socorro, New Mexico. Although larger than 2004 JG6, 2003 CP20 is a little more distant from the Sun.

LONEOS is one of five programs funded by NASA to search for asteroids and comets that may approach our planet closely. The NASA program?s current goal is to discover 90 percent of near-Earth asteroids larger than 1 km in diameter by 2008. There are thought to be about 1,100 such asteroids.

Original Source: Lowell Observatory News Release