Orbital chaos may destroy Earth

Image: possible orbital chaos collision between Venus and Earth

A force known as orbital chaos may cause our solar system to go haywire, leading to a possible collision between earth and Venus or Mars, according to a study released today.The good news is that the likelihood of such a smash-up is small, around one-in-2500.And even if the planets did careen into one another, it would not happen before another 3.5 billion years.

Indeed, there is a 99 per cent chance that the sun's posse of planets will continue to circle in an orderly pattern throughout the expected life span of our life-giving star, another five billion years, the study found.After that, the sun will likely expand into a red giant, engulfing earth and its other inner planets - Mercury, Venus and Mars - in the process.Astronomers have long been able to calculate the movement of planets with great accuracy hundreds, even thousands of years in advance. This is how eclipses have been predicted. But peering further into the future of celestial mechanics with exactitude is still beyond our reach, said Jacques Laskar, a researcher at the Observatoire de Paris and lead author of the study.

"The most precise long-term solutions for the orbital motion of the solar system are not valid over more than a few tens of millions of years," he said.

Using powerful computers, Mr Laskar and colleague Mickael Gastineau generated numerical simulations of orbital instability over the next five billion years.
Unlike previous models, they took into account Albert Einstein's theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in dramatically different orbital paths.The researchers looked at 2501 possible scenarios, 25 of which ended with a severely disrupted solar system.

"There is one scenario in which Mars passes very close to earth," 794 kilometres to be exact, said Mr Laskar."When you come that close, it is almost the same as a collision because the planets get torn apart."

Life on earth, if there still were any, would almost certainly cease to exist.To get a more fine-grained view of how this might unfold, Mr Laskar and Mr Gastineau ran an additional 200 computer models, slightly changing the path of Mars each time.All but five of them ended in a two-way collision involving the sun, earth, Mercury, Venus or Mars. A quarter of them saw earth smashed to pieces.The key to all the scenarios of extreme orbital chaos was the rock closest to the sun, found the study, published in the British journal Nature."Mercury is the trigger, and would be be the first planet to be destabilised because it has the smallest mass," said Mr Laskar.At some point Mercury's orbit would get into resonance with that of Jupiter, throwing the smaller orb even more out of kilter, he said.Once this happens, the so-called "angular momentum" from the much larger Jupiter would wreak havoc on the other inner planets' orbits too.

"The simulations indicate that Mercury, in spite of its diminutive size, poses the greatest risk to our present order," said University of California scientist Gregory Laughlin in a commentary, also published in Nature.

Edited By: Imran Khan
Key Terms: Observatorie de paris,Angular momentum,computer simulations and models
Year: 2009

Spitzer sees the cosmos through "warm" infrared eyes

Fig:Cygnus region. NASA/JPL-Caltech

NASA's Spitzer Space Telescope is starting a second career and taking its first shots of the cosmos since warming up. The infrared telescope ran out of coolant May 15, 2009, more than 5.5 years after launch. It has since warmed to a still-frosty -406° Fahrenheit (-208° Celsius).

New images taken with two of Spitzer's infrared detector channels — two that work at the new warmer temperature — demonstrate the observatory remains a powerful tool for probing the dusty universe. The images show a bustling star-forming region, the remains of a star similar to the Sun, and a swirling galaxy lined with stars.

"The performance of the two short-wavelength channels of Spitzer's Infrared Array Camera is essentially unchanged from what it was before the observatory's liquid helium was exhausted," said Doug Hudgins, the Spitzer program scientist at NASA headquarters in Washington. "To put that in perspective, that means Spitzer's sensitivity at those wavelengths is still roughly the same as a 30-meter ground-based telescope. This breathtaking image demonstrates Spitzer will continue to deliver world-class imagery and science during its warm mission."

The first of three images shows a cloud bursting with stars in the Cygnus region of our Milky Way galaxy. Spitzer's infrared eyes peer through and see dust, revealing young stars tucked in dusty nests. A second image shows a nearby dying star — a planetary nebula called NGC 4361 — which has outer layers that expand outward in the rare form of four jets. The last picture is of a classic spiral galaxy called NGC 4145, located approximately 68 million light-years from Earth.

"With Spitzer's remaining shorter-wavelength bands, we can continue to see through the dust in galaxies and get a better look at the overall populations of stars," said Robert Hurt, imaging specialist for Spitzer at NASA's Spitzer Science Center at the California Institute of Technology in Pasadena. "All stars are equal in the infrared."

Since its launch from Cape Canaveral, Florida, August 25, 2003, Spitzer has made many discoveries. They include planet-forming disks around stars, the composition of the material making up comets, hidden black holes, galaxies billions of light-years away, and more.

Perhaps the most revolutionary and surprising Spitzer finds involve planets around other stars, called exoplanets. In 2005, Spitzer detected the first photons of light from an exoplanet. In a clever technique, now referred to as the secondary-eclipse method, Spitzer was able to collect the light of a hot, gaseous exoplanet and learn about its temperature. Later detailed studies revealed more about the composition and structure of the atmospheres of these exotic worlds.

Warm Spitzer will address many of the same science questions as before. It also will tackle new projects, such as refining estimates of Hubble's constant, or the rate at which our universe is stretching apart; searching for galaxies at the edge of the universe; characterizing more than 700 near-Earth objects, or asteroids and comets with orbits that pass close to our planet; and studying the atmospheres of giant gas planets expected to be discovered soon by NASA's Kepler mission.

August 5, 2009

Mars orbiter shows angled view of martian crater

Oblique view of Victoria Crater. NASA/JPL-caltech/University of Arizona

August 12, 2009

The high-resolution camera on NASA's Mars Reconnaissance Orbiter has returned a dramatic oblique view of the martian crater that a rover explored for two years.

The new view of Victoria Crater shows layers on steep crater walls, difficult to see from straight overhead, plus wheel tracks left by NASA's Mars Exploration Rover Opportunity between September 2005 and August 2007. The orbiter's High Resolution Imaging Science Experiment camera shot it at an angle comparable to looking at landscape from an airplane window. Some of the camera's earlier, less angled images of Victoria Crater aided the rover team in choosing safe routes for Opportunity and contributed to joint scientific studies.



Martian dust devil with track and shadow. NASA/JPL-Caltech/University of Arizona

Another new image from the same camera catches an active dust devil leaving a trail and casting a shadow. These whirlwinds have been a subject of investigation by Opportunity's twin rover, Spirit.

The Mars Reconnaissance Orbiter has been studying Mars with an advanced set of instruments since 2006. It has returned more data about the planet than all other past and current missions to Mars combined.

Provided by JPL, Pasadena, California

Scientists discover storms in the tropics of Titan

This image of Titan is a product of observations taken with the Palomar 200-inch telescope, JPL adaptive optics system, and Cornell-built PHARO near-infrared camera. A. Bouchez

August 13, 2009

For all its similarities to Earth-clouds that pour rain — albeit liquid methane not liquid water — onto the surface producing lakes and rivers, vast dune fields in desert-like regions, plus a smoggy orange atmosphere, Saturn's largest moon, Titan, is generally "a very bland place," according to Mike Brown of the California Institute of Technology (Caltech).

"We can watch for years and see almost nothing happen," said Brown. "This is bad news for people trying to understand Titan's meteorological cycle. Not only do things happen infrequently, but we tend to miss them when they do happen because nobody wants to waste time on big telescopes."

However, just because weather occurs infrequently, it doesn't mean it never occurs, nor does it mean that astronomers can't catch it in the act.

In April 2008, that's just what Emily Schaller, now at the University of Arizona, and her colleagues accomplished when they observed a large system of storm clouds appear in the apparently dry mid-latitudes and spread in a southeastward direction across the moon. Eventually, the storm generated a number of bright but transient clouds over Titan's tropical latitudes, a region where clouds had never been seen and where it was thought they were extremely unlikely to form.

"A couple of years ago, we set up a highly efficient system on a smaller telescope to figure out when to use the biggest telescopes," Brown said. The first telescope, NASA's Infrared Telescope Facility, on Mauna Kea, Hawaii, takes a spectrum of Titan almost every single night. "From that we can't tell much, but we can say 'no clouds,' 'a few clouds,' or, if we get lucky, 'monster clouds,'" he said.

"The period during which I was collecting data for my thesis corresponded entirely to an extended period of essentially no clouds, so we never really got to show the full power of the combined telescopes," Schaller said. "But then, after finishing my thesis, I walked back across campus to my office to look at the data from the previous night to find that Titan suddenly had the biggest clouds ever."

The day after the telescope's big find, Schaller, Brown, and Roe began tracking the clouds with the large Gemini telescope on Mauna Kea and watched this system evolve for a month. "And what a cool show it was," Brown said.

"The first cloud was seen near the tropics and was caused by a still-mysterious process, but it behaved almost like an explosion in the atmosphere, setting off waves that traveled around the planet, triggering their own clouds," Brown said. "Within days a huge cloud system had covered the south pole, and sporadic clouds were seen all the way up to the equator."

Schneider, an expert on atmospheric circulations, was instrumental in helping to sort out the complicated chain of events that followed the initial outburst of cloud activity.

"The month-long event has many important implications for understanding the hydrological cycle on Titan," said Brown, "but one of the reasons I am most excited about it is that it shows clouds near the equator — where the European Space Agency's Huygens probe landed — for the first time. For a while now, people have speculated that the equatorial regions are simply too dry to ever have significant clouds."

And yet, the images snapped by the Huygens probe in January 2005 revealed small-scale channels and streams that looked just like features created by fluids — by water here on Earth and probably by liquid methane on Titan.

Experts had speculated for years on how there could be streams and channels in a region with no rain. The new results suggest those speculations may prove unnecessary. "No one considered how storms in one location can trigger them in many other locations," said Brown.

Caltech, Pasadena, California

Tiny flares responsible for outsized heat of Sun's atmosphere

This false-color temperature map shows solar active region AR 10923, observed close to center of the Sun's disk. Blue regions indicate plasma near 10 million degrees K. Reale, et al.

August 17, 2009

Solar physicists at NASA have confirmed that small, sudden bursts of heat and energy — called nanoflares — cause temperatures in the thin, translucent gas of the Sun's atmosphere to reach millions of degrees.

The Sun's outer atmosphere, or corona, is made up of loops of hot gas that arch high above the surface. These loops are comprised of bundles of smaller, individual magnetic tubes or strands that can have temperatures reaching several million degrees Kelvin (K), even though the Sun's surface is only 5,700 degrees K.

Nanoflares are small, sudden bursts of energy that happen within these thin magnetic tubes in the corona. Unlike solar flares that can be viewed through satellites and ground-based telescopes, nanoflares are too small to be resolved individually. We only see the combined effect of many of them occurring at about the same time.

"Coronal loops are the fundamental building blocks of the corona," said James Klimchuk, an astrophysicist at the Goddard Space Flight Center in Greenbelt, Maryland. "Their shape is defined by the magnetic field, which guides the hot flowing gases called plasma. The magnetic field is also the source of the nanoflare energy. We believe that stresses in the field are released when thin sheets of electric current become unstable."

Klimchuk and colleagues have constructed a theoretical model to explain how nanoflares occur and how plasma within the tubes responds to the skyrocketing temperatures. "We simulate bursts of heating and predict what the loop should look like when observed with a variety of instruments," said Klimchuk.

To test their model, the team observed gas emissions in the solar corona using the NASA-funded X-Ray Telescope and Extreme Ultraviolet Imaging Spectrometer on Japan's Hinode spacecraft.

"The 10 million degree temperatures we detected in the corona can only be produced by the impulsive energy bursts," said Klimchuk. The ultra-hot plasma cools very quickly, however, which explains why it is so faint and has been so difficult to detect until now. The energy lost from the cooling conducts down to the relatively cold solar surface. The gas there is heated to about 1 million degrees K and expands upward to become the 1 million degree component of the corona that has been observed for many years.

NASA's upcoming mission to study the Sun, the Solar Dynamics Observatory, will help scientists answer the outstanding questions of coronal heating by observing the coronal plasma at different temperatures with an unprecedented combination of close-up detail and rapid sequences.

Goddard Space Center, Greenbelt, MD

Star clusters point to black holes ejected from host galaxies

This artist's conception shows a rogue black hole that has been kicked out from the center of two merging galaxies. The black hole is surrounded by a cluster of stars that were ripped from the galaxies. STScI

The tight cluster of stars surrounding a supermassive black hole after it has been violently kicked out of a galaxy represents a new kind of astronomical object and a fossil record of the kick.

A paper in The Astrophysical Journal discusses the theoretical properties of "hypercompact stellar systems" and suggests that hundreds of these faint star clusters might be detected at optical wavelengths in our immediate cosmic environment. Some of these objects may already have been picked up in astronomical surveys, reports David Merritt, from Rochester Institute of Technology (RIT), Jeremy Schnittman, from Johns Hopkins University, and Stefanie Komossa, from the Max-Planck-Institute for Extraterrestrial Physics in Germany.

Hypercompact stellar systems result when a supermassive black hole is violently ejected from a galaxy, following a merger with another supermassive black hole. The evicted black hole rips stars from the galaxy as it is thrown out. The stars closest to the black hole move in tandem with the massive object and become a permanent record of the velocity at which the kick occurred.

"You can measure how big the kick was by measuring how fast the stars are moving around the black hole," said Merritt, professor of physics at RIT. "Only stars orbiting faster than the kick velocity remain attached to the black hole after the kick."

These stars carry with them a kind of fossil record of the kick, even after the black hole has slowed down. In principle, you can reconstruct the properties of the kick, which is nice because there would be no other way to do it."

"Finding these objects would be like discovering DNA from a long-extinct species," said Komossa.

The best place to find hypercompact stellar systems, the authors said, is in cluster of galaxies like the nearby Coma and Virgo clusters. These dense regions of space contain thousands of galaxies that have been merging for a long time. Merging galaxies result in merging black holes, which is a prerequisite for the kicks.

"Even if the black hole gets kicked out of one galaxy, it's still going to be gravitationally bound to the whole cluster of galaxies," Merritt said. "The total gravity of all the galaxies is acting on that black hole. If it was ever produced, it's still going to be there somewhere in that cluster."

Merritt and his co-authors think that scientists may have already seen hypercompact stellar systems and not realized it. These objects would be easy to mistake for common star systems like globular clusters. The key signature making hypercompact stellar systems unique is a high internal velocity. This is detectable only by measuring the velocities of stars moving around the black hole, a difficult measurement that would require a long time exposure on a large telescope.

From time to time, a hypercompact stellar system will make its presence known in a much more dramatic way, when one of the stars is tidally disrupted by the supermassive black hole. In this case, gravity stretches the star and sucks it into the black hole. The star is torn apart, causing a beacon-like flare that signals a black hole.

"The only contact of these floating black holes with the rest of the universe is through their armada of stars with an occasional display of stellar fireworks to signal 'here we are,'" Merritt said.

July 10, 2009

Turbulence from large black holes halts star formation

Snapshot of gas temperatures in a three-dimensional computer simulation of a cool-core cluster. The blue ring shows the cool gas accreting onto the central black hole disk; the red and yellow jets show the hot gas ejected by this disk. Older bubbles from an earlier outburst are visible on the far left and right sides of the image. Turbulence generated by the jets mixes the hot and cool material together, which stabilizes further accretion and allows the cluster to perform its remarkable balancing act. E. Scannapieco/ M. Brueggen / ASU Fulton High Performance Computing Initiative

New simulations reveal that turbulence created by jets of material ejected from the disks of the universe's largest black holes is responsible for halting star formation. Evan Scannapieco, an assistant professor in the School of Earth and Space Exploration at Arizona State University (ASU) and Marcus Brueggen, professor of Jacobs University in Bremen, Germany, presented the new model.

We live in a hierarchical universe where small structures join larger ones. Earth is a planet in our solar system, the solar system resides in the Milky Way Galaxy, and galaxies combine into groups and clusters. Clusters are the largest structures in the universe. Researchers have long known that the gas in the centers of some galaxy clusters cools and condenses rapidly, but were puzzled why this condensed gas did not form into stars. Until recently, no model existed that successfully explained how this was possible.

Scannapieco has spent much of his career studying the evolution of galaxies and clusters. "There are two types of clusters — cool-core clusters and non-cool core clusters," he said. "Non-cool core clusters haven't been around long enough to cool, whereas cool-core clusters are rapidly cooling, although by our standards they are still very hot."

X-ray telescopes have revolutionized our understanding of the activity occurring within cool-core clusters. Although these clusters can contain hundreds or thousands of galaxies, they are mostly made up of a diffuse, but very hot gas known as the intracluster medium. This intergalactic gas is only visible to X-ray telescopes, which are able to map out its temperature and structure. These observations show that the diffuse gas is rapidly cooling into the centers of cool-core clusters.

At the core of each of these clusters is a black hole, billions of times more massive than the Sun. Some of the cooling medium makes its way down to a dense disk surrounding the black hole, some of it goes into the black hole itself, and some of it is shot outward. X-ray images clearly show jet-like bursts of ejected material, occurring in regular cycles.

But why were these outbursts so regular, and why did the cooling gas never drop to colder temperatures that lead to the formation of stars? Some unknown mechanism was creating an impressive balancing act.

"It looked like the jets coming from black holes were somehow responsible for stopping the cooling," said Scannapieco, "but until now no one was able to determine how exactly."

Scannapieco and Brueggen used the enormous supercomputers at ASU to develop their own three-dimensional simulation of the galaxy cluster surrounding one of the universe's biggest black holes. By adapting an approach developed by Guy Dimonte at Los Alamos National Laboratory and Robert Tipton at Lawrence Livermore National Laboratory, Scannapieco and Brueggen added the component of turbulence to the simulations, which was never accounted for in the past.

And that was the key ingredient.

Turbulence works in partnership with the black hole to maintain the balance. Without turbulence, jets coming from around the black hole would grow stronger and stronger, and the gas would cool catastrophically into a swarm of new stars. When turbulence is accounted for, the black hole not only balances the cooling, but also goes through regular cycles of activity.

"When you have turbulent flow, you have random motions on all scales," said Scannapieco. "Each jet of material ejected from the disk creates turbulence that mixes everything together."

Scannapieco and Brueggen's results reveal that turbulence acts to effectively mix the heated region with its surroundings so that the cool gas can't make it down to the black hole, thus preventing star formation.

Every time some cool gas reaches the black hole, it is shot out in a jet. This generates turbulence that mixes the hot gas with the cold gas. This mixture becomes so hot that it doesn't accrete onto the black hole. The jet stops and there is nothing to drive the turbulence so it fades away. At that point, the hot gas no longer mixes with the cold gas, so the center of the cluster cools, and more gas makes its way down to the black hole.

Before long, another jet forms and the gas once again is mixed together.

"We improved our simulations so that they could capture those tiny turbulent motions," said Scannapieco. "Even though we can't see them, we can estimate what they would do. The time it takes for the turbulence to decay away is exactly the same amount of time observed between the outbursts."

July 14, 2009

Study aims to maximize scientific return from Moon rovers

South Pole-Aitken Basin, the largest and deepest impact basin in the solar system, is likely to be one of the primary targets for lunar rovers. This view, which is centered on the basin, consists of color-coded topography overlaid on a shaded relief representation of the Moon. Purple and blue are low, and orange and red are high. The basin is up to 8 miles (13 kilometers) deep, with an average depth of about 6 miles (10 kilometers). Rovers may find volcanic evidence in the basin that could help unravel the Moon's thermal evolution. Clementine Science Group, Lunar and Planetary Institute

NASA and other national space agencies are again focused on lunar exploration, which raises the question of how to best use semi-autonomous rovers to explore the Moon's surface.

R. Aileen Yingst, a senior scientist at the Tucson-based Planetary Science Institute, is leading a group of Mars-rover veterans who are conducting field studies to answer that question.

The scientists are evaluating operational strategies to maximize the scientific return from rover activities. This includes determining the types of instruments the rover should carry and how they should be used to recognize surface features that speak to the Moon's volcanic history, possible ice formation at its poles, and other geologic questions.

"We've done 5 years of semi-autonomous rover operations on Mars, and we have a good day-to-day operational understanding of how that works," said Yingst, a participating scientist on the Mars Exploration Rover (MER) mission. "But there will be some significant changes in those strategies when we have rovers on the Moon, just because of the difference in time lag, among other things."

Because it takes 40 minutes to radio a martian rover and receive an answer, continuous communication is not possible. This has led scientists to upload the operational sequences for up to three days of rover activities in a single message. The rover then operates independently for that time period.

But the Moon is much closer than Mars, and the round-trip message time from Earth is only about 3 seconds, not much longer than the time lag a cable TV newsroom experiences when contacting a reporter in Baghdad. The short time lag will change how scientists direct the rover and how they will use its instruments.

Lunar geology also is different from martian geology, so the rover will be looking for different things, Yingst said. For instance, lunar rovers could search for a variety of basaltic lava types that will help explain the Moon's thermal evolution. They also may search for ice at the poles, which might occur as permafrost or coatings of ice on rocky grains, she said.

Scientists also want to date portions of the lunar surface to field check their current estimates of the age of lunar formations. This is important because the ages of many other planetary surfaces in the solar system are keyed to the age of lunar landforms and the number of craters found on them.

Yingst's team will be studying volcanic areas in New Mexico and permafrost in Alaska as Earth analogs of similar surfaces on the Moon. One field team will pretend to be an autonomous rover and will use a camera, spectrometer, and other instruments — and only the data from those instruments — to make decisions about where to go and what kind of data to collect.

A team of scientists that will use traditional field methods to study the geology will follow the rover team.

"Human geologists certainly will be able to figure out a lot more about the geology than an autonomous rover can," Yingst said. "We already know that. But then the questions are: What can they figure out that the rover can't? How do they do that? And how can we use that information to make the rover smarter and more efficient?"

She emphasized that this method is a low-cost way to explore these questions because it doesn't require building and testing costly rover prototypes. "We're mimicking the methodology, without incurring the time or expense involved in dealing with rovers and space-qualified instruments in the field," she said.

The results from this study will help scientists design more intelligent rovers and operate them more efficiently once they land on the Moon, she said.

July 27, 2009

Unveiling the true face of a mammoth star

Artist's impression showing how a vast amount of material is flung out from Betelgeuse into space. ESO/L. Calcada

An international team of astronomers, led by Keiichi Ohnaka at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, has taken the sharpest view yet of a dying mammoth star. The image shows how gas moves in different areas over the surface of a distant star. This view was made possible by combining three 1.8-meter telescopes as an interferometer, giving the astronomers the resolving power of a gigantic 48-meter telescope.

Using the European Southern Observatory's (ESO) Very Large Telescope Interferometer (VLTI) in Chile, the group discovered that the gas in the dying star's atmosphere is vigorously moving up and down, but the size of such "bubbles" is as large as the star itself. These colossal bubbles are a key for pushing material out of the star's atmosphere into space before the star explodes as a supernova.

In a clear winter night sky, it is easy to spot a bright, orange star on the shoulder of the constellation Orion the Hunter, even in light-flooded big cities. That is Betelgeuse. It is a mammoth star big enough that, if it were in our solar system, it would reach the orbit of Jupiter, swallowing the inner planets Mercury, Venus, Earth, and Mars. It is also glaringly bright, emitting 100,000 times more light than the Sun. Betelgeuse is a red supergiant, and it is approaching the end of its short life of several million years. Red supergiants shed a large amount of material made of various molecules and dust, which are recycled for the next generation of stars and planets, possibly like Earth. Betelgeuse loses material equivalent to Earth's mass every year.

How these mammoth stars can lose mass, which would normally be bound to the star by the gravitational pull, is a long-standing mystery. The best way to tackle this issue is to observe the scene where the material is ejected from a star's surface. Although Betelgeuse is such a huge star, it looks like a mere reddish dot even with today's largest telescopes because the star is 640 light-years away.

Astronomers use a special technique to overcome this problem. By combining two or more telescopes as an interferometer, astronomers can achieve a much higher resolution than individual telescopes provide. The VLTI is one of the world's largest interferometers. The astronomers observed Betelgeuse with the telescope's AMBER instrument operating at near-infrared wavelengths.

"Our AMBER observations mark the sharpest view ever made on Betelgeuse," said Keiichi Ohnaka at the MPIfR. "And for the first time, we have spatially resolved the gas motion in the atmosphere of a star other than the Sun. Thus, we could observe how the gas is moving in different areas over the star's surface."

The AMBER observations have revealed that the gas in Betelgeuse's atmosphere is moving vigorously up and down. The size of these "bubbles" is also gigantic, as large as the supergiant star. While the origin of these bubbles is not yet entirely clear, the AMBER observations have shed new light on the question about how red supergiant stars lose mass. It also means that the material is not spilling out in a quiet, ordered way, but is flung out more violently in arcs or clumps.

Cosmic fireworks known as a supernova, like the famous SN1987A, will accompany the death of the mammoth star, which is expected in the next few thousand to hundred thousand years. However, as Betelgeuse is much closer to Earth than SN1987A, the supernova can be clearly seen with the unaided eye, even in daylight.

July,2009

Jupiter impact continues to impress

An infrared image of Jupiter, taken by the Keck II Telescope shows how the diameter of the impact site compares with the size of Earth. P. Kalas (UCB), M. Fitzgerald (LLNL/UCLA), F. Marchis (SETI Institute/UCB), J. Graham (UCB)

New pictures of Jupiter and its recent impact site keep pouring in, showing the rapidly growing atmospheric aftermath in increasingly greater detail. First discovered by Australian amateur astronomer Anthony Wesley on July 19, the Pacific Ocean-sized black spot is likely the result of a collision with an asteroid or comet.

The W. M. Keck Observatory, located on Hawaii's Mauna Kea volcano, confirmed the impact last week with a set of infrared images. Astronomers there plan to test theories developed 15 years ago during Comet Shoemaker-Levy 9's impact with the gas giant, the only other planetary collision ever witnessed.Later in the week, the Hubble Space Telescope's newest camera captured the sharpest visible-light picture to date of Jupiter's latest feature. Not only did the image provide greater detail on the impact itself, but also it proved astronauts successfully serviced the telescope in May.

Operators of the Keck and Hubble telescopes originally scheduled other work for the week but decided to postpone their plans to better study the unfolding events on Jupiter. They join a multitude of amateur and professional astronomers across the world now training their eyepieces on the planet's constantly changing spot.

NASA scientists estimate the colliding object was several hundreds of yards across and the force of its impact to have been thousands of times greater than the explosion in 1908 over the Siberian Tunguska River Valley.

July 27, 2009

Mars, methane and mysteries

Artist's impression of Mars Express

Mars may not be as dormant as scientists once thought. The 2004 discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. ESA plans to find out which it is. Either outcome is big news for a planet once thought to be biologically and geologically inactive.

The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, Vittorio Formisano, Istituto di Fisica dello Spazio Interplanetario CNR, Rome, and the rest of the instrument team saw a puzzling signal. As well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane. “Methane was a surprise, we were not expecting that,” says Agustin Chicarro, ESA Mars Lead Scientist. The reason is that on Earth much of the methane in our atmosphere is released by evolved life forms, such as cattle digesting food. While there are ways to produce methane without life, such as by volcanic activity, it is the possible biological route that has focused attention on the discovery.

The Mars Express detection of methane is not an isolated case. While the spacecraft was en route, two independent teams of astronomers using ground-based telescopes started to see traces of methane. After five years of intensive study, the suite of observations all confirmed the discovery and presented planetary scientists with a big puzzle.

Methane is thought to be stable in the martian atmosphere for around 300 years. So, whatever is generating the methane up there, it is a recent occurrence. In January 2009, a team led by Michael Mumma of NASA’s Goddard Space Flight Center published results that the methane they saw in 2003 was concentrated in three regions of the planet. This showed that the methane was being released at the present time and was being observed before it had time to distribute itself around the planet.

Things then took a strange turn. Instead of taking 300 years to disappear, the methane had almost entirely vanished by early 2006. Clearly something unusual is going on at Mars. “We thought we understood how methane behaved on Mars but if the measurements are correct then we must be missing something big,” says Franck Lefèvre, Université Pierre et Marie Curie, CNRS, Paris and a member of Mars Express’s SPICAM instrument team.

Together with his colleague François Forget, Mars Express Interdisciplinary Scientist in charge of atmospheric studies and also of Université Pierre et Marie Curie, CNRS, Paris, Lefèvre has investigated the disappearance using a computer model of Mars’ climate. “We have tackled the problem as atmospheric physicists, without worrying about the nature of the source of the methane,” he says.

In results published last week they found that, while their computer model can reproduce atmospheric species such as carbon monoxide and ozone, it is unable to reproduce the behaviour of the methane. “Something is removing the methane from the atmosphere 600 times faster than the models can account for,” says Lefèvre. “Consequently, the source must be 600 times more intense than originally assumed, which is considerable even by Earth’s geological standards.”


To remove methane at such a rate, suspicion falls on the surface of the planet. Either the methane is being trapped in the dust there or highly reactive chemicals such as hydrogen peroxide are destroying it, as was hinted by the Viking missions in the 1970s. If the latter, then the surface is much more hostile to organic molecules (those containing carbon) than previously thought. This will make searching for traces of past or present life much tougher and future rovers will have to drill below the martian surface to look for signs of life.

To help get to the bottom of the methane mystery, ESA and the Italian space agency (ASI) are to hold a three-day international workshop in November. The assembled scientists will discuss the results and plan strategies for the future study of methane. At the workshop, the Mars Express PFS team hopes to present a global map of martian methane. “We have made the PFS mapping a priority over the last few months,” says Olivier Witasse, ESA Project Scientist for Mars Express.

In July, ESA agreed with NASA to launch joint missions to Mars. The topic of methane is of such importance that it will be most likely addressed in these future missions. “Understanding the methane on Mars is one of our top priorities,” says Witasse.

However the methane is eventually explained, it makes Mars a more fascinating place than even planetary scientists dreamed.

10 August 2009

Astronomers Find Hyperactive Galaxies in the Early Universe

Looking almost 11 billion years into the past, astronomers have measured the motions of stars for the first time in a very distant galaxy and clocked speeds upwards of one million miles per hour, about twice the speed of our Sun through the Milky Way.

The fast-moving stars shed new light on how these distant galaxies, which are a fraction the size of our Milky Way, may have evolved into the full-grown galaxies seen around us today. The results will be published in the August 6, 2009 issue of the journal Nature, with a companion paper in the Astrophysical Journal.

"This galaxy is very small, but the stars are whizzing around as if they were in a giant galaxy that we would find closer to us and not so far back in time," says Pieter van Dokkum, professor of astronomy and physics at Yale University in New Haven, Conn., who led the study. It is still not understood how galaxies like these, with so much mass in such a small volume, can form in the early universe and then evolve into the galaxies we see in the more contemporary, nearby universe, which is about 13.7 billion years old.

The work by the international team combined data collected using NASA's Hubble Space Telescope with observations taken by the 8-meter Gemini South telescope in Chile. According to van Dokkum, "The Hubble data, taken in 2007, confirmed that this galaxy was a fraction the size of most galaxies we see today in the more evolved, older universe. The giant, 8-meter mirror of the Gemini telescope then allowed us to collect enough light to determine the overall motions of the stars using a technique not very different from the way police use laser light to catch speeding cars." The Gemini near-infrared spectroscopic observations required an extensive 29 hours on the sky to collect the extremely faint light from the distant galaxy, which goes by the designation 1255-0.

"By looking at this galaxy we are able to look back in time and see what galaxies looked like in the distant past when the universe was very young," says team member Mariska Kriek of Princeton University in Princeton, N.J. 1255-0 is so far away that the universe was only about 3 billion years old when its light was emitted.

Astronomers confess that it is a difficult riddle to explain how such compact, massive galaxies form, and why they are not seen in the current, local universe. "One possibility is that we are looking at what will eventually be the dense central region of a very large galaxy," explains team member Marijn Franx of Leiden University in the Netherlands. "The centers of big galaxies may have formed first, presumably together with the giant black holes that we know exist in today's large galaxies that we see nearby."

To witness the formation of these extreme galaxies astronomers plan to observe galaxies even farther back in time in great detail. By using the Wide Field Camera 3, which was recently installed on the Hubble Space Telescope, such objects should be detectable. "The ancestors of these extreme galaxies should have quite spectacular properties as they probably formed a huge amount of stars, in addition to a massive black hole, in a relatively short amount of time," says van Dokkum.

This research follows recent studies revealing that the oldest, most luminous galaxies in the early universe are very compact yet surprisingly have stellar masses similar to those of present-day elliptical galaxies. The most massive galaxies we see in the local universe (where we don't look back in time significantly) that have a mass similar to 1255-0 are typically five times larger than the young compact galaxy. How galaxies grew so much in the past 10 billion years is an active area of research, and understanding the dynamics in these young compact galaxies is a key piece of evidence in eventually solving this puzzle.

The Hubble Space Telescope observations were made with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

The Gemini observations were made using the Gemini Near Infrared Spectrograph (GNIRS), which is currently undergoing upgrades and will be reinstalled on the Gemini North telescope on Mauna Kea in 2010.

August 5, 2009

2009 Jupiter impact event

Hubble image of the scar taken on July 23 showing a blemish of about 5,000 miles long.

The 2009 Jupiter impact event, occasionally referred to as the Wesley impact, was a July 2009 impact on Jupiter that caused a black spot in the planet's atmosphere. The spot was similar in size to the planet's Little Red Spot and about the size of the Pacific Ocean.The impact scar is expected to last only a week or two as it becomes diluted by Jupiter's atmosphere.

Amateur astronomer Anthony Wesley discovered the impact at approximately 13:30 UTC on 19 July 2009 (almost exactly 15 years after the Jupiter impact of comet Shoemaker-Levy 9, or SL9). He was at his home observatory just outside Murrumbateman, New South Wales, Australia, using stacked images on a 14.5-inch (36.8 cm) diameter reflecting telescope equipped with a low light machine vision video camera attached to the telescope.Wesley stated that:

When first seen close to the limb (and in poor conditions) it was only a vaguely dark spot, I [thought] likely to be just a normal dark polar storm. However as it rotated further into view, and the conditions improved I suddenly realised that it wasn't just dark, it was black in all channels, meaning it was truly a black spot.

Wesley sent an e-mail to others including the NASA Jet Propulsion Laboratory in Pasadena, California reporting his observations

Paul Kalas and collaborators confirmed the sighting. They had time on the Keck II telescope in Hawaii, and had been planning to observe Fomalhaut b, but they spent some of their time looking at the Jupiter impact.Infrared observation by Keck and the NASA Infrared Telescope Facility (IRTF)at Mauna Kea showed a bright spot where the impact took place, indicating the impact warmed a 190 million square km area of the lower atmosphere at 305 W, 57 S near Jupiter's south pole.

The spot's prominence indicates that it is composed of high-altitude aerosols similar to those seen during the SL9 impact.Using near-infrared wavelengths and the IRTF, Glenn Orton and his team detected bright upwelling particles in the planet's upper atmosphere and using mid-infrared wavelengths, found possible extra emission of ammonia gas.

The force of the explosion on Jupiter was thousands of times more powerful than the suspected comet or asteroid that exploded over the Tunguska River Valley in Siberia in June 1908.(This would be over a million times more powerful than the bomb dropped on Hiroshima.)

Astronomers will further observe the impact area with a variety of instruments, including the Keck and the Hubble Space Telescope's recently installed Wide Field Camera 3.

The object that hit Jupiter was not identified before Wesley discovered the impact. A 2003 paper estimated comets with a diameter larger than 1.5 kilometers impact Jupiter about every 90 to 500 years,while a 1997 survey suggested that the astronomer Cassini may have recorded an impact in 1690.

Given the size of the SL9 impacters,it is likely that this object was less than one kilometer in diameter.Finding water at the site would indicate that the impacter was a comet,as opposed to an asteroid or a very small, icy moon.It is more likely that the object was a comet since comets generally have an unstable orbit.At the distance of Jupiter (5.2 AU) most small comets are not close enough to the Sun to be very active.

Assuming it was an inactive comet (or asteroid) about 1 km in diameter, this object would have been no brighter than about apparent magnitude 25.(Jupiter shines about 130 billion times brighter than a 25th magnitude object.)Most asteroid surveys which use a wide field of view do not see fainter than about magnitude 22 (which is 16x brighter than magnitude 25).Even detecting satellites less than 10 km in diameter orbiting Jupiter is difficult and requires some of the best telescopes in the world;it is only since 1999 with the discovery of Callirrhoe that astronomers have been able to discover many of Jupiter's smallest moons.

Huge new planet tells of game of planetary billiards

A team of scientists has found a new planet which orbits the wrong way around its host star. The planet, named WASP-17, and orbiting a star 1000 light years away, was found by the UK's WASP project in collaboration with Geneva Observatory. The discovery, which casts new light on how planetary systems form and evolve, is being announced today (12th August) in a paper submitted to Astrophysical Journal.

Since planets form out of the same swirling gas cloud that creates a star, they are expected to orbit in the same direction that the star spins. Graduate students David Anderson, of Keele University, and Amaury Triaud, of Geneva Observatory, were surprised to find that WASP-17 is orbiting the wrong way, making it the first planet known to have a ``retrograde'' orbit. The likely explanation is that WASP-17 was involved in a near collision with another planet early in its history.

WASP-17 appears to have been the victim of a game of planetary billiards, flung into its unusual orbit by a close encounter with a ``big brother'' planet. Professor Coel Hellier, of Keele University, remarks: "Shakespeare said that two planets could no more occupy the same orbit than two kings could rule England; WASP-17 shows that he was right.”

David Anderson added “Newly formed solar systems can be violent places. Our own moon is thought to have been created when a Mars-sized planet collided with the recently formed Earth and threw up a cloud of debris that turned into the moon. A near collision during the early, violent stage of this planetary system could well have caused a gravitational slingshot, flinging WASP-17 into its backwards orbit.”

The first sign that WASP-17 was unusual was its large size. Though it is only half the mass of Jupiter it is bloated to nearly twice Jupiter's size, making it the largest planet known.

Astronomers have long wondered why some extra-solar planets are far bigger than expected, and WASP-17 points to the explanation. Scattered into a highly elliptical, retrograde orbit, it would have been subjected to intense tides. Tidal compression and stretching would have heated the gas-giant planet to its current, hugely bloated extent. "This planet is only as dense as expanded polystyrene, seventy times less dense than the planet we're standing on", notes Prof. Hellier.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council, which funded the research, said, “This is a fascinating new find and another triumph for the WASP team. Not only are they locating these far flung and mysterious planets but revealing more about how planetary systems, such as our own Solar System, formed and evolved. The WASP team has proved once again why this project is currently the World's most successful project searching for transiting exoplanets.”

WASP-17 is the 17th new exoplanet (planet outside our solar system) found by the Wide Area Search for Planets (WASP) consortium of UK universities. The WASP team detected the planet using an array of cameras that monitor hundreds of thousands of stars, searching for small dips in their light when a planet transits in front of them. Geneva Observatory then measured the mass of WASP-17, showing that it was the right mass to be a planet. The WASP-South camera array that led to the discovery of WASP-17 is hosted by the South African Astronomical Observatory.

Wednesday, August 12, 2009

Curiosities: How many galaxies have humans discovered?

Credit: NASA, ESA, S. Beckwith (STScI) and HUDF Team

“We don’t know,” says Ed Churchwell, professor of astronomy. “We know it’s a very large number.”

It’s in the hundreds of billions, Churchwell says. In contrast, there are but 4 billion stars in our own galaxy, the Milky Way — and the number will keep growing for some time before we run out of galaxies to count.

“To count them all, you have to be able to look far enough back in time or deep enough in space to see when galaxies were formed,” Churchwell says. “We haven’t reached that point yet. It’s not a well-determined number, but at some point we’re going to reach it.”

For the time being, those hundreds of billions in the tally are extrapolated from a picture taken by the Hubble Space Telescope in 2003 and 2004. Pointed at a single piece of space for several months — a spot covering less than one-tenth of one-millionth of the sky — Hubble returned an image of galaxies 13 billion light years away.

“You look at that and say, ‘How many galaxies can I see?’” Churchwell explains. “And that turns out to be a very large number.”

In fact, there are about 10,000 galaxies in the picture, called the Hubble Ultra Deep Field.

“Then you take that number of galaxies from that postage-stamp-sized piece of the sky and multiply it by the number of postage-stamp-sized pieces of sky,” Churchwell says. “And that turns out to be a much larger number.”

Monday, August 03, 2009

Planet Smash-Up Sends Vaporized Rock, Hot Lava Flying

This artist's concept shows a celestial body about the size of our moon slamming at great speed into a body the size of Mercury. NASA's Spitzer Space Telescope found evidence that a high-speed collision of this sort occurred a few thousand years ago around a young star, called HD 172555, still in the early stages of planet formation. The star is about 100 light-years from Earth.Spitzer detected the signatures of vaporized and melted rock, in addition to rubble, all flung out from the giant impact. Further evidence from the infrared telescope shows that these two bodies must have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour).As the bodies slammed into each other, a huge flash of light would have been emitted. Rocky surfaces were vaporized and melted, and hot matter was sprayed everywhere. Spitzer detected the vaporized rock in the form of silicon monoxide gas, and the melted rock as a glassy substance called obsidian. On Earth, obsidian can be found around volcanoes, and in black rocks called tektites often found around meteor craters.Shock waves from the collision would have traveled through the planet, throwing rocky rubble into space. Spitzer also detected the signatures of this rubble.In the end, the larger planet is left skinned, stripped of its outer layers. The core of the smaller body and most of its surface were absorbed by the larger one. This merging of rocky bodies is how planets like Earth are thought to form.Astronomers say a similar type of event stripped Mercury of its crust early on in the formation of our solar system, flinging the removed material away from Mercury, out into space and into the sun. Our moon was also formed by this type of high-speed impact: a body the size of Mars is thought to have slammed into a young Earth about 30 to 100 million years after the sun formed. The sun is now 4.5 billion years old. According to this theory, the resulting molten rock, vapor and shattered debris mixed with debris from Earth to form a ring around our planet. Over time, this debris coalesced to make the moon.

NASA's Spitzer Space Telescope has found evidence of a high-speed collision between two burgeoning planets around a young star.

Astronomers say that two rocky bodies, one as least as big as our moon and the other at least as big as Mercury, slammed into each other within the last few thousand years or so — not long ago by cosmic standards. The impact destroyed the smaller body, vaporizing huge amounts of rock and flinging massive plumes of hot lava into space.

Spitzer's infrared detectors were able to pick up the signatures of the vaporized rock, along with pieces of refrozen lava, called tektites.

"This collision had to be huge and incredibly high-speed for rock to have been vaporized and melted," said Carey M. Lisse of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., lead author of a new paper describing the findings in the Aug. 20 issue of the Astrophysical Journal. "This is a really rare and short-lived event, critical in the formation of Earth-like planets and moons. We're lucky to have witnessed one not long after it happened."

Lisse and his colleagues say the cosmic crash is similar to the one that formed our moon more than 4 billion years ago, when a body the size of Mars rammed into Earth.

"The collision that formed our moon would have been tremendous, enough to melt the surface of Earth," said co-author Geoff Bryden of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Debris from the collision most likely settled into a disk around Earth that eventually coalesced to make the moon. This is about the same scale of impact we're seeing with Spitzer — we don't know if a moon will form or not, but we know a large rocky body's surface was red hot, warped and melted."

Our solar system's early history is rich with similar tales of destruction. Giant impacts are thought to have stripped Mercury of its outer crust, tipped Uranus on its side and spun Venus backward, to name a few examples. Such violence is a routine aspect of planet building. Rocky planets form and grow in size by colliding and sticking together, merging their cores and shedding some of their surfaces. Though things have settled down in our solar system today, impacts still occur, as was observed last month after a small space object crashed into Jupiter.

Lisse and his team observed a star called HD 172555, which is about 12 million years old and located about 100 light-years away in the far southern constellation Pavo, or the Peacock (for comparison, our solar system is 4.5 billion years old). The astronomers used an instrument on Spitzer, called a spectrograph, to break apart the star's light and look for fingerprints of chemicals, in what is called a spectrum. What they found was very strange. "I had never seen anything like this before," said Lisse. "The spectrum was very unusual."

After careful analysis, the researchers identified lots of amorphous silica, or essentially melted glass. Silica can be found on Earth in obsidian rocks and tektites. Obsidian is black, shiny volcanic glass. Tektites are hardened chunks of lava that are thought to form when meteorites hit Earth.

Large quantities of orbiting silicon monoxide gas were also detected, created when much of the rock was vaporized. In addition, the astronomers found rocky rubble that was probably flung out from the planetary wreck.

The mass of the dust and gas observed suggests the combined mass of the two charging bodies was more than twice that of our moon.

Their speed must have been tremendous as well — the two bodies would have to have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour) before the collision.

Spitzer has witnessed the dusty aftermath of large asteroidal impacts before, but did not find evidence for the same type of violence — melted and vaporized rock sprayed everywhere. Instead, large amounts of dust, gravel, and boulder-sized rubble were observed, indicating the collisions might have been slower-paced. "Almost all large impacts are like stately, slow-moving Titanic-versus-the-iceberg collisions, whereas this one must have been a huge fiery blast, over in the blink of an eye and full of fury," said Lisse.

Other authors include C.H. Chen of the Space Telescope Science Institute, Baltimore, Md.; M.C. Wyatt of the University of Cambridge, England; A. Morlok of the Open University, London, England; I. Song of The University of Georgia, Athens, Ga.; and P. Sheehan of the University of Rochester, N.Y.

JPL manages the Spitzer mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph, which made the observations in 2004 before the telescope began its "warm" mission, was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

Monday, August 10, 2009

First Black Holes Kept to a Strict Diet, Study Shows

This frame from the simulation shows the X-rays produced by a black hole (white) and its effects on nearby gas (blue). This scene occurs 400 million years after the universe formed. The black hole, born from a star's collapse 200 million years ago, has grown by less than one percent -- about the mass of our sun -- since. Credit: KIPAC/SLAC/M. Alvarez, T. Abel and J. Wise

A new supercomputer simulation designed to track the fate of the universe's first black holes finds that, counter to expectations, they couldn't efficiently gorge themselves on nearby gas. The findings have implications for understanding the formation of galaxies and of the giant black holes that reside in their centers.

"The first stars were much more massive than most stars we see today, upwards of 100 times the mass of our sun," said John Wise, a post-doctoral fellow at NASA's Goddard Space Flight Center in Greenbelt, Md., and one of the study's authors. "For the first time, we were able to simulate in detail what happens to the gas around those stars before and after they form black holes."

The intense radiation and strong outflows from these massive stars caused nearby gas to dissipate. "These stars essentially cleared out most of the gas in their vicinity," Wise said. A fraction of these first stars didn't end their lives in grand supernovae explosions. Instead, they collapsed directly into black holes.

But the black holes were born into a gas-depleted cavity and, with little gas to feed on, they grew very slowly. "During the 200 million years of our simulation, a 100 solar-mass black hole grew by less than one percent of its mass," said Marcelo Alvarez, the study's lead author, at the Kavli Institute for Particle Astrophysics and Cosmology, located at the Department of Energy’s SLAC National Accelerator Laboratory in Menlo Park, Calif.

This simulation, which was performed on a supercomputer at SLAC, is the most detailed to date. Starting with data taken from observations of the cosmic background radiation -- a flash of light that occurred 380,000 years after the big bang that presents the earliest view of cosmic structure -- the researchers applied the basic laws that govern the interaction of matter and allowed their model of the early universe to evolve. The complex simulation included hydrodynamics, chemical reactions, the absorption and emission of radiation, and star formation.

In the simulation, cosmic gas slowly coalesced under the force of gravity and eventually formed the first stars. These massive, hot stars burned bright for a short time, emitting so much energy in the form of starlight that they pushed away nearby gas clouds.

These stars could not sustain such a fiery existence for long, and they soon exhausted their internal fuel. One of the stars in the simulation collapsed under its own weight to form a black hole. With only wisps of gas nearby, the black hole was essentially "starved" of matter on which to grow.

Yet, despite its strict diet, the black hole had a dramatic effect on its surroundings. This was revealed through a key aspect of the simulation called radiative feedback, which accounted for the way X-rays emitted by the black hole affected distant gas.

Even on a diet, a black hole produces lots of X-rays. This radiation not only kept nearby gas from falling in, but it heated gas a hundred light-years away to several thousand degrees. Hot gas cannot come together to form new stars. "Even though the black holes aren't growing significantly, their radiation is intense enough to shut off star formation nearby for tens and maybe even hundreds of millions of years," said Alvarez.

The study, which will appear in an upcoming issue of The Astrophysical Journal Letters, shows that early black holes had a surprisingly complex role in shaping the universe.

"I'm thrilled that we now can do calculations that start to capture the most relevant physics, and we can show which ideas work and which don't," said coauthor Tom Abel, also at Kavli. "In the next decade, using calculations like this one, we will settle some of the most important issues related to the role of black holes in the universe."

Monday, August 10, 2009

Variability of type 1a supernovae has implications for dark energy studies

In this image from a computer simulation, debris from a type 1a supernova explosion shows the asymmetric substructures that develop from the turbulent flame that consumes the white dwarf star. Colors represent different elements synthesized in the explosion (e.g., red=nickel-56). Image by D. Kasen et al.



This image based on a computer simulation of a type 1a supernova shows the turbulent and symmetric flame of the runaway thermonuclear burning that consumes the white dwarf star. Image by F. Ropke.

The stellar explosions known as type 1a supernovae have long been used as "standard candles", their uniform brightness giving astronomers a way to measure cosmic distances and the expansion of the universe. But a new study published this week in Nature reveals sources of variability in type 1a supernovae that will have to be taken into account if astronomers are to use them for more precise measurements in the future.

The discovery of dark energy, a mysterious force that is accelerating the expansion of the universe, was based on observations of type 1a supernovae. But in order to probe the nature of dark energy and determine if it is constant or variable over time, scientists will have to measure cosmic distances with much greater precision than they have in the past.

"As we begin the next generation of cosmology experiments, we will want to use type 1a supernovae as very sensitive measures of distance," said lead author Daniel Kasen, a Hubble postdoctoral fellow at the University of California, Santa Cruz. "We know they are not all the same brightness, and we have ways of correcting for that, but we need to know if there are systematic differences that would bias the distance measurements. So this study explored what causes those differences in brightness."

Kasen and his coauthors--Fritz Röpke of the Max Planck Institute for Astrophysics in Garching, Germany, and Stan Woosley, professor of astronomy and astrophysics at UC Santa Cruz--used supercomputers to run dozens of simulations of type 1a supernovae. The results indicate that much of the diversity observed in these supernovae is due to the chaotic nature of the processes involved and the resulting asymmetry of the explosions.

For the most part, this variability would not produce systematic errors in measurement studies as long as researchers use large numbers of observations and apply the standard corrections, Kasen said. The study did find a small but potentially worrisome effect that could result from systematic differences in the chemical compositions of stars at different times in the history of the universe. But researchers can use the computer models to further characterize this effect and develop corrections for it.

"Since we are beginning to understand how type 1a supernovae work from first principles, these models can be used to refine our distance estimates and make measurements of the expansion rate of the universe more precise," Woosley said.

A type 1a supernova occurs when a white dwarf star acquires additional mass by siphoning matter away from a companion star. When it reaches a critical mass--1.4 times the mass of the Sun, packed into an object the size of the Earth--the heat and pressure in the center of the star spark a runaway nuclear fusion reaction, and the white dwarf explodes. Since the initial conditions are about the same in all cases, these supernovae tend to have the same luminosity, and their "light curves" (how the luminosity changes over time) are predictable.

Some are intrinsically brighter than others, but these flare and fade more slowly, and this correlation between the brightness and the width of the light curve allows astronomers to apply a correction to standardize their observations. So astronomers can measure the light curve of a type 1a supernova, calculate its intrinsic brightness, and then determine how far away it is, since the apparent brightness diminishes with distance (just as a candle appears dimmer at a distance than it does up close).

The computer models used to simulate these supernovae in the new study are based on current theoretical understanding of how and where the ignition process begins inside the white dwarf and where it makes the transition from slow-burning combustion to explosive detonation.

"Since ignition does not occur in the dead center, and since detonation occurs first at some point near the surface of the exploding white dwarf, the resulting explosions are not spherically symmetric," Woosley explained. "This could only be studied properly using multi-dimensional calculations."

Most previous studies have used one-dimensional models in which the simulated explosion is spherically symmetric. Multi-dimensional simulations require much more computing power, so Kasen's group ran most of their simulations on the powerful Jaguar supercomputer at Oak Ridge National Laboratory, and also used supercomputers at the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory. The results of two-dimensional models are reported in the Nature paper, and three-dimensional studies are currently under way.

The simulations showed that the asymmetry of the explosions is a key factor determining the brightness of type 1a supernovae. "The reason these supernovae are not all the same brightness is closely tied to this breaking of spherical symmetry," Kasen said.

The dominant source of variability is the synthesis of new elements during the explosions, which is sensitive to differences in the geometry of the first sparks that ignite a thermonuclear runaway in the simmering core of the white dwarf. Nickel-56 is especially important, because the radioactive decay of this unstable isotope creates the afterglow that astronomers are able to observe for months or even years after the explosion.

"The decay of nickel-56 is what powers the light curve. The explosion is over in a matter of seconds, so what we see is the result of how the nickel heats the debris and how the debris radiates light," Kasen said.

Kasen developed the computer code to simulate this radiative transfer process, using output from the simulated explosions to produce visualizations that can be compared directly to astronomical observations of supernovae.

The good news is that the variability seen in the computer models agrees with observations of type 1a supernovae. "Most importantly, the width and peak luminosity of the light curve are correlated in a way that agrees with what observers have found. So the models are consistent with the observations on which the discovery of dark energy was based," Woosley said.

Another source of variability is that these asymmetric explosions look different when viewed at different angles. This can account for differences in brightness of as much as 20 percent, Kasen said, but the effect is random and creates scatter in the measurements that can be statistically reduced by observing large numbers of supernovae.

The potential for systematic bias comes primarily from variation in the initial chemical composition of the white dwarf star. Heavier elements are synthesized during supernova explosions, and debris from those explosions is incorporated into new stars. As a result, stars formed recently are likely to contain more heavy elements (higher "metallicity," in astronomers' terminology) than stars formed in the distant past.

"That's the kind of thing we expect to evolve over time, so if you look at distant stars corresponding to much earlier times in the history of the universe, they would tend to have lower metallicity," Kasen said. "When we calculated the effect of this in our models, we found that the resulting errors in distance measurements would be on the order of 2 percent or less."

Further studies using computer simulations will enable researchers to characterize the effects of such variations in more detail and limit their impact on future dark-energy experiments, which might require a level of precision that would make errors of 2 percent unacceptable.

This study was supported by the Department of Energy's Scientific Discovery through Advanced Computing (SciDAC) program. Computer time was provided by NERSC and ORNL through an award from DOE's Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program.

Wednesday, August 12, 2009

Super Planetary Nebulae

Image Composed by E. Crawford & S. Griffith

A team of scientists in Australia and the United States, led by Associate Professor Miroslav Filipović from the University of Western Sydney, have discovered a new class of object which they call “Super Planetary Nebulae.” They report their work in the journal Monthly Notices of the Royal Astronomical Society.

Planetary nebulae are shells of gas and dust expelled by stars near the end of their lives and are typically seen around stars comparable or smaller in size than the Sun.

The team surveyed the Magellanic Clouds, the two companion galaxies to the Milky Way, with radio telescopes of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia Telescope National Facility. They noticed that 15 radio objects in the Clouds match with well known planetary nebulae observed by optical telescopes.

The new class of objects are unusually strong radio sources. Whereas the existing population of planetary nebulae is found around small stars comparable in size to our Sun, the new population may be the long predicted class of similar shells around heavier stars.

Filipović’s team argues that the detections of these new objects may help to solve the so called “missing mass problem” – the absence of planetary nebulae around central stars that were originally 1 to 8 times the mass of the Sun. Up to now most known planetary nebulae have central stars and surrounding nebulae with respectively only about 0.6 and 0.3 times the mass of the Sun but none have been detected around more massive stars.

The new Super Planetary Nebulae are associated with larger original stars (progenitors), up to 8 times the mass of the Sun. And the nebular material around each star may have as much as 2.6 times the mass of the Sun.

“This came as a shock to us”, says Filipović, “as no one expected to detect these object at radio wavelengths and with the present generation of radio telescopes. We have been holding up our findings for some 3 years until we were 100% sure that they are indeed Planetary Nebulae”.

Some of the 15 newly discovered planetary nebulae in the Magellanic Clouds are 3 times more luminous then any of their Milky Way cousins. But to see them in greater detail astronomers will need the power of a coming radio telescope – the Square Kilometre Array planned for the deserts of Western Australia.

Friday, August 14, 2009

CSU Experiment Takes Flight With NASA

Fig: Single crystal nanorode

For the first time in more than eight years, NASA is able to conduct scientific testing and studies in Outer space. On August 25, 2009, NASA will take six experiments, two from the US and four from Europe, into the science laboratory aboard Space Shuttle Discovery.

The two US experiments are aimed at studying the way in which single-crystal castings solidify on earth vs. in space. Single-crystal castings are critical components in high-temperature gas-turbine engines that are used in high-speed aircraft and land-based power turbines.

On earth, convection, which is the transfer of heat by movement, is always present. Due to this natural convection, single-crystal castings often become deformed. Therefore, when they are incorporated into the construction of an object, such as an airplane blade, the object is rendered useless by the assembling engineer.

In space, there is less convection. Therefore, the researchers want to see if, and how, single-crystal castings solidify differently in space. They are hoping that once in space, the single-crystal castings will solidify without the deformities they're prone to on earth.

If this is the case, then it would help eliminate error and defects in the formations of the castings, reduce the number of blades that are rejected from high-speed aircrafts and land-based power turbines, and ultimately chance the processing behavior in the industry.

Professor Surrendra Tewari from Cleveland State University is responsible for the US-based experiments, while Professor David R. Poirier and Professor Robert Erdmann, both from the University of Arizona are in charge of the modeling. Dr. Frank R. Szofran, from NASA Marshall Space Flight Center is the Project Manager.

Professor Tewari and Professor Poirier have worked together on several NASA-sponsored research programs since the early nineties.

As part of a collaborative research program with the European Space Agency (ESA), NASA is launching its first Materials Science Research Rack (MSRR-1) to be integrated into the US Laboratory Module Destiny, which will carry the ESA-Materials Science Laboratory Low Gradient Furnace (MSL-LGF) for future low gravity materials science experiments by the astronauts.

Each alloy sample to be processed in the MSL-LGF is contained in a Specimen Cartridge Assembly (SCA), which makes it safe and convenient for the astronauts to carry out the space experiments.

Dark Energy Star

A dark-energy star is a hypothetical compact astrophysical object, which a minority of physicists feel might constitute an alternative explanation for observations of astronomical black hole candidates. Dark energy is invisible to the human eye; however, it can be tracked with difficulty by gamma astronomy.

The concept was proposed by physicist George Chapline. The theory states that infalling matter is converted into vacuum energy or dark energy, as the matter falls through the event horizon. The space within the event horizon would end up with a large value for the cosmological constant and have negative pressure to exert against gravity. There would be no information-destroying singularity.

In March 2005, physicist George Chapline claimed that quantum mechanics makes it a "near certainty", that black holes do not exist and are instead dark energy stars. The dark energy star is a different concept than that of a gravastar.

Dark-energy stars were first proposed, because in quantum physics, absolute time is required; however, in general relativity, an object falling towards a black hole would to an outside observer seem to have time pass infinitely slowly at the event horizon. The object itself would feel as if time flowed normally.

In order to reconcile quantum mechanics with black holes, Chapline theorized that a phase transition in the phase of space occurs at the event horizon. He based his ideas on the physics of superfluids. As a column of superfluid grows taller, at some point, density increases, slowing down the speed of sound, so that it approaches zero. However, at that point, quantum physics makes sound waves dissipate their energy into the superfluid, so that the zero sound speed condition is never encountered.

In the dark-energy star hypothesis, infalling matter approaching the event horizon decay into successively lighter particles. Nearing the event horizon, environmental effects accelerate proton decay. This may account for high energy cosmic ray sources and positron sources in the sky. When the matter falls through the event horizon, the energy equivalent of some or all of that matter is converted into dark energy. This negative pressure counteracts the mass the star gains, avoiding a singularity. The negative pressure also gives a very high number for the cosmological constant.

Furthermore, 'primordial' dark-energy stars could form by fluctuations of space-time itself, which is analogous to "blobs of liquid condensing spontaneously out of a cooling gas." This not only alters the understanding of black holes, but has the potential to explain the dark energy and dark matter, that are indirectly observed.