Journal

Globular Cluster Harbors a 13-Billion-Year-Old Planet

2013-03-25T01:45:14Z

This NASA/ESA Hubble Space Telescope image above shows the center of globular cluster M4. It contains several tens of thousands stars and is noteworthy in being home to many white dwarfs—the cores of ancient, dying stars whose outer layers have drifted away into space.

In July 2003, Hubble helped make the astounding discovery of a planet called PSR B1620-26 b, 2.5 times the mass of Jupiter, which is located in this cluster. The PSR B1620-26 system lies around 5,600 light years away in globular cluster M4, boxed in green, directly west of red supergiant star Antares in Constellation ScorpiusIts age is estimated to be around 13 billion years—almost three times as old as the Solar System! It is also unusual in that it orbits a binary system of a white dwarf and a pulsar (a type of neutron star).

The existence of a 13-billion year old planet, if in fact it still exists, highlights the fact that our Solar System exits in a universe that is estimated to be between 13.5 and 14 billion years old. Some astronomers, including Sir Martin Rees of Cambridge University believe that there could be advanced civilizations out there that have existed for 1.8 gigayears (one gigayear = one billion years) and longer.

A few intrepid astronomers have concluded that the most productive to look for planets that can support life is around dim, dying stars white dwarfs so prevalent in M4.

"In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs," said Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics (CfA) and director of the Institute for Theory and Computation. Even dying stars could host planets with life - and if such life exists, we might be able to detect it within the next decade. This encouraging result comes from a new theoretical study of Earth-like planets orbiting white dwarf stars. Researchers found that we could detect oxygen in the atmosphere of a white dwarf's planet much more easily than for an Earth-like planet orbiting a Sun-like star.

When a star like the Sun dies, it puffs off its outer layers, leaving behind a hot core called a white dwarf. A typical white dwarf is about the size of Earth. It slowly cools and fades over time, but it can retain heat long enough to warm a nearby world for billions of years. Since a white dwarf is much smaller and fainter than the Sun, a planet would have to be much closer in to be habitable with liquid water on its surface. A habitable planet would circle the white dwarf once every 10 hours at a distance of about a million miles.* Before a star becomes a white dwarf it swells into a red giant, engulfing and destroying any nearby planets. Therefore, a planet would have to arrive in the habitable zone after the star evolved into a white dwarf. A planet could form from leftover dust and gas (making it a second-generation world), or migrate inward from a larger distance.

If planets exist in the habitable zones of white dwarfs, we would need to find them before we could study them. The abundance of heavy elements on the surface of white dwarfs suggests that a significant fraction of them have rocky planets. Loeb and his colleague Dan Maoz (Tel Aviv University) estimate that a survey of the 500 closest white dwarfs could spot one or more habitable Earths.

The best method for finding such planets is a transit search - looking for a star that dims as an orbiting planet crosses in front of it. Since a white dwarf is about the same size as Earth, an Earth-sized planet would block a large fraction of its light and create an obvious signal.

More importantly, we can only study the atmospheres of transiting planets. When the white dwarf's light shines through the ring of air that surrounds the planet's silhouetted disk, the atmosphere absorbs some starlight. This leaves chemical fingerprints showing whether that air contains water vapor, or even signatures of life, such as oxygen.

Astronomers are particularly interested in finding oxygen because the oxygen in the Earth's atmosphere is continuously replenished, through photosynthesis, by plant life. Were all life to cease on Earth, our atmosphere would quickly become devoid of oxygen, which would dissolve in the oceans and oxidize the surface. Thus, the presence of large quantities of oxygen in the atmosphere of a distant planet would signal the likely presence of life there.

NASA's James Webb Space Telescope (JWST), scheduled for launch by the end of this decade, promises to sniff out the gases of these alien worlds. Loeb and Maoz created a synthetic spectrum, replicating what JWST would see if it examined a habitable planet orbiting a white dwarf. They found that both oxygen and water vapor would be detectable with only a few hours of total observation time.

"JWST offers the best hope of finding an inhabited planet in the near future," said Maoz.* Recent research by CfA astronomers Courtney Dressing and David Charbonneau showed that the closest habitable planet is likely to orbit a red dwarf star (a cool, low-mass star undergoing nuclear fusion). Since a red dwarf, although smaller and fainter than the Sun, is much larger and brighter than a white dwarf, its glare would overwhelm the faint signal from an orbiting planet's atmosphere. JWST would have to observe hundreds of hours of transits to have any hope of analyzing the atmosphere's composition.

"Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf," said Loeb.

Source:

http://www.dailygalaxy.com/my_weblog/2013/03/globular-cluster-found-harboring-a-13-billion-year-old-planet-weekend-feature.html

Is Earth Undergoing a 6th Mass Extinction? --"99.9% of all Past Species Extinct"

2013-03-24T14:40:53Z

Of all species that have existed on Earth, 99.9 percent are now extinct. Many of them perished in five cataclysmic events. The classical "Big Five" mass extinctions identified by Raup and Sepkoski are widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous. According to a recent poll, seven out of ten biologists think we are currently in the throes of a sixth mass extinction. Some say it could wipe out as many as 90 percent of all species living today. Other scientists dispute such dire projections.

“If you look at the fossil record, it is just littered with dead bodies from past catastrophes,” observes University of Washington paleontologist Peter Ward. Ward says that only one extinction in Earth’s past was caused by an asteroid impact – the event 65 million years ago that ended the age of the dinosaurs. All the rest, he claims, were caused by global warming.

Ward's study, Under a Green Sky, explores extinctions in Earth’s past and predicts extinctions to come in the future. Ward demonstrates that the ancient past is not just of academic concern. Everyone has heard about how an asteroid did in the dinosaurs, and NASA and other agencies now track Near Earth objects.

Unfortunately, we may not be protecting ourselves against the likeliest cause of our species' demise. Ward explains how those extinctions happened, and then applies those chilling lessons to the modern day: expect drought, superstorms, poison–belching oceans, mass extinction of much life, and sickly green skies.

The significant points Ward stresses are geologically rapid climate change has been the underlying cause of most great "extinction" events. Those events have been, observed Harvard evolutionary biologist Stephen Gould, major drivers of evolution.

Drastic climate change has not always been gradual; there is solid empirical evidence of catastrophic warming events taking place in centuries, perhaps even decades. The impact of atmospheric warming is most potent in its modification of ocean chemistry and of circulating currents; warming inevitably leads to non-mixing anoxic dead seas.

We are already in the middle, not the beginning, of an anthropogenic global warming, caused by agriculture and deforestation, which began some 10,000 years ago but which is now accelerating exponentially; though the earliest wave of anthropogenic warming has been stabilizing and beneficial to human development, it appears to have the potential for catastrophic effects within a lifetime or two.

Looking at the ancient evidence, Ward notes that ice caps began to shrink. "Melting all the ice caps causes a 75-meter increase in sea level will remove every coastal city on our planet." It will also cover earth's most productive farmland, the author warns, adding, "It will happen if we do not somehow control CO2 rise in the atmosphere."

An analysis of the geological record of the Earth's sea level, carried out by scientists at Princeton and Harvard universities supports Ward using a novel statistical approach that reveals the planet's polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level.

According to the analysis, an additional 2 degrees of global warming could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term sea level rise. This rise would inundate low-lying coastal areas where hundreds of millions of people now reside. It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the U.S. East Coast, much of Bangladesh, and most of the Netherlands, unless unprecedented and expensive coastal protection were undertaken. And while the researchers' findings indicate that such a rise would likely take centuries to complete, if emissions of greenhouse gases are not abated, the planet could be committed during this century to a level of warming sufficient to trigger this outcome.

The last interglacial stage provides a historical analog for futures with a fairly moderate amount of warming; the high sea levels during the stage suggest that significant chunks of major ice sheets could disappear over a period of centuries in such futures.

Previous geological studies of sea level benchmarks such as coral reefs and beaches had shown that, at many localities, local sea levels during the last interglacial stage were higher than today. But local sea levels differ from those in this earlier stage; one major contributing factor is that the changing masses of the ice sheets alter the planet's gravitational field and deform the solid Earth.

As a consequence, inferring global sea level from local geological sea level markers requires a geographically broad data set, a model of the physics of sea level, and a means to integrate the two. The study's authors provide all three, integrating the data and the physics with a statistical approach that allows them to assess the probability distribution of past global sea level and its rate of change.

The findings indicate that sea level during the last interglacial stage rose for centuries at least two to three times faster than the recent rate, and that both the Greenland and West Antarctic ice sheet likely shrank significantly and made important contributions to sea level rise. However, the relative timing of temperature change and sea level change during the last interglacial stage is fairly uncertain, so it is not possible to infer from the analysis how long an exposure to peak temperatures during this stage was needed to commit the planet to peak sea levels.

A similar study by a team of scientists from Bristol, Cardiff and Texas A&M universities braved the lions and hyenas of a small East African village to extract microfossils from rocks which have revealed the level of CO2 in the Earth’s atmosphere at the time of the formation of the ice-cap. New carbon dioxide data confirm that formation of the Antarctic ice-cap some 33.5 million years ago was due to declining carbon dioxide in the atmosphere.

Professor Paul Pearson from Cardiff University’s School of Earth and Ocean Sciences, who led the mission to the remote East Africa village of Stakishari said: “About 34 million years ago the Earth experienced a mysterious cooling trend. Glaciers and small ice sheets developed in Antarctica, sea levels fell and temperate forests began to displace tropical-type vegetation in many areas.

“The period culminated in the rapid development of a continental-scale ice sheet on Antarctica, which has been there ever since. We therefore set out to establish whether there was a substantial decline in atmospheric carbon dioxide levels as the Antarctic ice sheet began to grow.”

Co-author Dr Bridget Wade from Texas A&M University Department of Geology and Geophysics added: “This was the biggest climate switch since the extinction of the dinosaurs 65 million years ago. Our study is the first to provide a direct link between the establishment of an ice sheet on Antarctica and atmospheric carbon dioxide levels and therefore confirms the relationship between carbon dioxide levels in the atmosphere and global climate.”

Geologists have long speculated that the formation of the Antarctic ice-cap was caused by a gradually diminishing natural greenhouse effect. The study’s findings, published in Nature online, confirm that atmospheric CO2 started to decline about 34 million years ago, during the period known to geologists as the Eocene - Oligocene climate transition, and that the ice sheet began to form about 33.5 million years ago when CO2 in the atmosphere reached a tipping point of around 760 parts per million.

The team mapped large expanses of bush and wilderness and pieced together the underlying local rock formations using occasional outcrops of rocks and stream beds. Eventually they discovered sediments of the right age near a traditional African village called Stakishari. By assembling a drilling rig and extracting hundreds of meters of samples from under the ground they were able to obtain exactly the piece of Earth's history they had been searching for.

Ward is encouraged that we are beginning to make changes in their daily lives and demanding action from their leaders -"that we are on a planet that has violent convulsions, and that we humans are playing with nature in such a way that we could recreate what were some really awful times in earth's history, that we really tinker with the earth's atmosphere at our peril."

The image at the top of the page shows a a very well-preserved example of a Paleoniscoid fish thought related to Rhabdolepis. The paleoniscoids were the first ray-finned fish, a feature readily seen here. Some 40 or more families appeared during the Carboniferous and Permian Periods. This taxon went extinct during the Lower Permian.

Source:

www.dailygalaxy.com

Inspired by Deep Sea Sponges: Creating Flexible Minerals

2013-03-18T10:44:14Z

The nanometer size of the calcite bricks facilitates bending of the synthetic spicules. The radius of curvature upon bending is very large compared to the size of the individual particles. This prevents a fracture of the brittle mineral bricks. (Credit: Tremel work group, JGU)

Scientists at Johannes Gutenberg University Mainz (JGU) and the Max Planck Institute for Polymer Research (MPI-P) in Germany have created a new synthetic hybrid material with a mineral content of almost 90 percent, yet extremely flexible. They imitated the structural elements found in most sea sponges and recreated the sponge spicules using the natural mineral calcium carbonate and a protein of the sponge. Natural minerals are usually very hard and prickly, as fragile as porcelain.

Amazingly, the synthetic spicules are superior to their natural counterparts in terms of flexibility, exhibiting a rubber-like flexibility. The synthetic spicules can, for example, easily be U-shaped without breaking or showing any signs of fracture This highly unusual characteristic, described by the German researchers in the current issue of Science, is mainly due to the part of organic substances in the new hybrid material. It is about ten times as much as in natural spicules.

Spicules are structural elements found in most sea sponges. They provide structural support and deter predators. They are very hard, prickly, and even quite difficult to cut with a knife. The spicules of sponges thus offer a perfect example of a lightweight, tough, and impenetrable defense system, which may inspire engineers to create body armors of the future.

The researchers led by Wolfgang Tremel, Professor at Johannes Gutenberg University Mainz, and Hans-Jürgen Butt, Director at the Max Planck Institute for Polymer Research in Mainz, used these natural sponge spicules as a model to cultivate them in the lab. The synthetic spicules were made from calcite (CaCO3) and silicatein-α. The latter is a protein from siliceous sponges that, in nature, catalyzes the formation of silica, which forms the natural silica spicules of sponges. Silicatein-α was used in the lab setting to control the self-organization of the calcite spicules. The synthetic material was self-assembled from an amorphous calcium carbonate intermediate and silicatein and subsequently aged to the final crystalline material. After six months, the synthetic spicules consisted of calcite nanocrystals aligned in a brick wall fashion with the protein embedded like cement in the boundaries between the calcite nanocrystals. The spicules were of 10 to 300 micrometers in length with a diameter of 5 to 10 micrometers.

As the scientists, among them chemists, polymer researchers, and the molecular biologist Professor Werner E. G. Müller from the Mainz University Medical Center, also write in their Science publication, the synthetic spicules have yet another special characteristic, i.e., they are able to transmit light waves even when they are bent.

Source:

http://www.sciencedaily.com/releases/2013/03/130315074513.htm

Distant Planetary System Is a Super-Sized Solar System

2013-03-18T05:35:16Z

Artist’s rendering of the planetary system HR 8799 at an early stage in its evolution, showing the planet HR 8799c, as well as a disk of gas and dust, and interior planets. (Credit: Dunlap Institute for Astronomy & Astrophysics; Mediafarm)

A team of astronomers, including Quinn Konopacky of the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, has made the most detailed examination yet of the atmosphere of a Jupiter-like planet beyond our Solar System.

According to Konopacky, "We have been able to observe this planet in unprecedented detail because of the advanced instrumentation we are using on the Keck II telescope, our ground-breaking observing and data-processing techniques, and because of the nature of the planetary system."

Konopacky is lead author of the paper describing the team's findings, to be published March 14th in Science Express, and March 22nd in the journal Science.

The team, using a high-resolution imaging spectrograph called OSIRIS, uncovered the chemical fingerprints of specific molecules, revealing a cloudy atmosphere containing carbon monoxide and water vapour. "With this level of detail," says Travis Barman, a Lowell Observatory astronomer and co-author of the paper, "we can compare the amount of carbon to the amount of oxygen present in the planet's atmosphere, and this chemical mix provides clues as to how the entire planetary system formed."

There has been considerable uncertainty about how systems of planets form, with two leading models, called core accretion and gravitational instability. Planetary properties, such as the composition of a planet's atmosphere, are clues as to whether a system formed according to one model or the other.

"This is the sharpest spectrum ever obtained of an extrasolar planet," according to co-author Bruce Macintosh of the Lawrence Livermore National Laboratory. "This shows the power of directly imaging a planetary system. It is the exquisite resolution afforded by these new observations that has allowed us to really begin to probe planet formation."

The spectrum reveals that the carbon to oxygen ratio is consistent with the core accretion scenario, the model thought to explain the formation of our Solar System.

The planet, designated HR 8799c, is one of four gas giants known to orbit a star 130 light-years from Earth. The authors and their collaborators previously discovered HR 8799c and its three companions back in 2008 and 2010. All the planets are larger than any in our Solar System, with masses three to seven times that of Jupiter. Their orbits are similarly large when compared to our system. HR 8799c orbits 40 times farther from its parent star than Earth orbits from the Sun; in our Solar System, that would put it well beyond the realm of Neptune.

According to the core accretion model, the star HR 8799 was originally surrounded by nothing but a huge disk of gas and dust. As the gas cooled, ice formed; this process depleted the disk of oxygen atoms. Ice and dust collected into planetary cores which, once they were large enough, attracted surrounding gas to form large atmospheres. The gas was depleted of oxygen, and this is reflected in the planet's atmosphere today as an enhanced carbon to oxygen ratio.

The core accretion model also predicts that large gas giant planets form at great distances from the central star, and smaller rocky planets closer in, as in our Solar System. It is rocky planets, not too far, nor close to the star, that are prime candidates for supporting life.

"The results suggest the HR 8799 system is like a scaled-up Solar System," says Konopacky. "And so, in addition to the gas giants far from their parent star, it would not come as a surprise to find Earth-like planets closer in."

The observations of HR 8799c were made with the Keck II 10-metre telescope in Hawaii, one of the two largest optical telescopes in the world. The telescope's adaptive optics system corrects for distortion caused by Earth's atmosphere, making the view through Keck II sharper than through the Hubble Space Telescope.

Astronomers refer to this as spatial resolution. Seeing exoplanets around stars is like trying to see a firefly next to a spotlight. Keck's adaptive optics and high spatial resolution, combined with advanced data-processing techniques, allow astronomers to more clearly see both the stellar "spotlight" and planetary "firefly."

"We can directly image the planets around HR 8799 because they are all large, young, and very far from their parent star. This makes the system an excellent laboratory for studying exoplanet atmospheres," says coauthor Christian Marois of the National Research Council of Canada. "Since its discovery, this system just keeps surprising us."

Konopacky and her team will continue to study the super-sized planets to learn more details about their nature and their atmospheres. Future observations will be made using the recently upgraded OSIRIS instrument which utilizes a new diffraction grating -- the key component of the spectrograph that separates light according to wavelength, just like a prism. The new grating was developed at the Dunlap Institute and installed in the spectrograph in December 2012.

"These future observations will tell us much more about the planets in this system," says Dunlap Fellow Konopacky. "And the more we learn about this distant planetary system, the more we learn about our own."

Source:

http://www.sciencedaily.com/releases/2013/03/130314144211.htm

Hundreds of Dinosaur Egg Fossils Found

2013-03-18T02:00:06Z

Researchers in northeastern Spain say they've uncovered hundreds of dinosaur egg fossils, including four kinds that had never been found before in the region. The eggs likely were left behind bysauropods millions of years ago.

Eggs, eggshell fragments and dozens of clutches were nestled in the stratigraphic layers of the Tremp geological formation at the site of Coll de Nargó in the Spanish province of Lleida, which was a marshy region during the Late Cretaceous Period, the researchers said.

"Eggshells, eggs and nests were found in abundance and they all belong to dinosaurs, sauropods in particular," the study's leader, Albert García Sellés from the Miquel Crusafont Catalan Palaeontology Institute, told Spanish news agency SINC this week.

"Up until now, only one type of dinosaur egg had been documented in the region: Megaloolithus siruguei," Sellés added. His team found evidence of at least four other species: Cairanoolithus roussetensis, Megaloolithus aureliensis, Megaloolithus siruguei and Megaloolithus baghensis. Megaloolithus eggs are thought to be associated with sauropods, long-necked dinosaurs that were among some of the largest to roam the planet.

The Coll de Nargó area is considered one of the most important dinosaur nesting areas in Europe, the researchers said, adding that their study shows it was used by several dinosaurs from the Late Campanian age (around 71 million years ago) to the Late Maastrichtian age (around 67 million years ago).

"We had never found so many nests in the one area before. In addition, the presence of various oospecies (eggs species) at the same level suggests that different types of dinosaurs shared the same nesting area," Sellés said, adding that the dinosaur eggs could help scientists determine the date of future findings at the site.

"It has come to light that the different types of eggs are located at very specific time intervals," Sellés explained to SINC. "This allows us to create biochronological scales with a precise dating capacity. In short, thanks to the collection of oospecies found in Coll de Nargó we have been able to determine the age of the site at between 71 and 67 million years."

The findings are published in the March issue of the journal Cretaceous Research.

Source:

http://news.yahoo.com/hundreds-dinosaur-egg-fossils-found-121945899.html

Dinosaur-Era Climate Change Study Suggests Reasons for Turtle Disappearance

2013-03-17T17:11:40Z

This shows Annie Quinney excavating ancient soils in 70 million-year-old rocks in the Drumheller badlands. (Credit: Credit: Kohei Tanaka, University of Calgary.)

The dry, barren prairie around Alberta's Drumheller area was once a lush and subtropical forest on the shores of a large inland sea, with loads of wetlands inhabited by dinosaurs, turtles, crocodiles and small mammals.

But that changed about 71-million-years ago, according to a new study by researchers Annie Quinney and Darla Zelenitsky in paleontology at the University of Calgary. The researchers' calculations show that drastic climate change occurred during a five-million-year period in Alberta's badlands. At this time, the wetlands dried up and the warm humid climate was interrupted by a sudden cool, drying spell.

The study of ancient climate change is important as it helps researchers understand the impact sudden heating and cooling may have had on plants and animals.

"This was a time of change in Alberta, the wetlands disappeared as the inland sea retreated and the climate cooled," says Quinney, a former master's student in the Department of Geoscience. She led the study recently published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, which was part of her master's degree in the Department of Geoscience.

Dramatic climate change was previously proposed to be responsible for the disappearance of turtles 71-million-years ago, because they were considered to be "climate-sensitive" animals. Results of this research, however, show that the disappearance of turtles came before the climate cooled and instead closely corresponds to habitat disturbances, which was the disappearance of wetlands.

"The big surprise is that some animals, for example turtles, appeared to be more sensitive to habitat disturbances than to climate changes. Therefore, even if climatic conditions are 'ideal,' turtles may disappear or may not recover unless habitats are just right," says Quinney.

Quinney and supervisors Zelenitsky, assistant professor in the Department of Geoscience, and François Therrien of the Royal Tyrrell Museum in Drumheller studied ancient soils preserved in the rocks in the Red Deer River valley near Drumheller that were deposited 72 to 67 million years ago and record information about the past climate and environments.

Researchers calculated precipitation and temperature levels over a five-million year interval and during that time, temperature and precipitation dropped over a few thousand years, and that cooler interval lasted for 500,000 years.

"By studying the structure and chemistry of ancient soils, we were able to estimate the ancient temperature and rainfall that prevailed when those soils formed millions of years ago," says Quinney, who is now completing a PhD at Monash University in Australia on a full scholarship.

Source:

http://www.sciencedaily.com/releases/2013/03/130314144354.htm

100-million-year-old spider attack

2013-03-17T16:28:30Z

The only fossil ever discovered of a spider attack on prey caught in its web – a 100 million-year-old snapshot of an engagement caught in amber.

The extraordinarily rare fossils are in a piece of amber that preserved this event in remarkable detail. This spider happened in the Hukawng Valley of Myanmar in the Early Cretaceous – between 97-110 million years ago – almost certainly with dinosaurs wandering nearby.

George Poinar, Jr., is a professor emeritus of zoology at Oregon State University and world expert on insects trapped in amber. He outlined the findings in a study published in the journal Historical Biology. Poinar said:

This was a male wasp that suddenly found itself trapped in a spider web. This was the wasp’s worst nightmare, and it never ended. The wasp was watching the spider just as it was about to be attacked, when tree resin flowed over and captured both of them.

The tree resin that forms amber is renowned for its ability to flow over insects, small plants and other life forms, preserving them in near perfection before it later turns into a semi-precious stone. It often gives scientists a look into the biology of the distant past. This spider, which may have been waiting patiently for hours to capture some prey, was smothered in resin just a split second before its attack.

Source:

http://earthsky.org/todays-image/100-million-year-old-spider-attack?utm_source=EarthSky+News&utm_campaign=a2fd76dce9-EarthSky_News&utm_medium=email

Magnetic fields in astrophysics: an electronic 'textbooklet'

2013-03-02T18:17:50Z

Fig. 1: Field lines in the head of a magnetic jet. (Rainer Moll, MPA)

Magnetic fields play an important role in many objects in the universe, from the Sun with its spots and the magnetically heated corona visible during a solar eclipse, to pulsars and the spectacular 'jets' from black holes and protostars. The behaviour of the magnetic field in these objects, however, is very different from experience at home or in physics class, since in astrophysical objects magnetic field lines are 'tied' to an ionized gas. The theory for such magnetic fields, called magnetohydrodynamics (MHD), is explained in a concise textbook published online. It emphasizes understanding of MHD by visualization of the flows and forces as they take place in a magnetized fluid. To this end, the text also includes a number of small video clips of basic MHD flows.

In physical processes where magnetic fields are present, one generally also has electric fields, currents and charge densities. Mathematically speaking, one has to deal with the full set of Maxwell's equations plus the equations of motion for the particles making up the plasma - the domain of plasma physics. Luckily, for most flows seen in astronomical objects, however, this complexity is rarely necessary. The electrical conductivity of an ionized gas makes MHD an extremely accurate approximation. Compared with ordinary fluid mechanics, only the magnetic field needs to be included explicitly in the theory. The other electromagnetic quantities can be evaluated afterwards; they are neither needed for a proper description, nor of much use for physical understanding. Thanks to this simplification it has become possible to include magnetic fields realistically in numerical simulations, for example of extragalactic jets (Fig. 1).

The price to be paid is that we have to give up some of our intuitions about the way electric and magnetic fields work. Our experience is dominated by processes taking place in the Earth's electrically insulating atmosphere (in copper wires, batteries, induction coils etc.). Most astrophysical processes on the other hand happen in an ionised gas, such as in a star, the solar wind, or the intergalactic medium.

Because of the strong coupling between the magnetic field and the electrically conducting gas, MHD flows behave more or less like visco-elastic but otherwise ordinary fluids. This makes MHD an eminently visualizable theory (for an example see the video clip inFig. 2), which also motivates the approach used in the textbooklet. The first chapter (only 36 pages) is a concise introduction including exercises. The exercises are important as illustrations of the points made in the text (especially the less intuitive ones). Almost all are mathematically unchallenging, though some do require a background in undergraduate physics. This is the 'essential' part. The supplement in chapter 2 contains further explanations, more specialized topics and occasional connections to topics somewhat outside the scope of MHD.

Fig. 2: A fluid flow stretching a bundle of field lines (mp4 movie) (Merel van 't Hoff, MPA)

Essential magnetohydrodynamics for_astrophysics from Sergio Sancevero

Source:

http://www.mpa-garching.mpg.de/mpa/institute/news_archives/news1302_aaa/news1302_aaa-en.html

Researchers Discovered the Mysterious Structure of a Black Hole Seen Edge On

2013-03-02T11:34:32Z

Edge-on view of the accretion disc, as seen from the Earth. A raised structure (like a donut), seen in the interior, causes the light from the inner parts of the disc (those closest to the black hole) to be eclipsed. This 'donut' gyrates around the black hole in a few minutes and produces eclipses over more or less regular intervals. Copyright: Gabriel Pérez Díaz, Servicio MultiMedia (IAC)

Swift J1357.2-0933 is a black hole obscured by a disc of gas with a vertical structure (rather like a donut) that continues to expand

This is the first time a black hole has been seen with this inclination and it's the first time that eclipses in brightness have been detected in this kind of system

The structure described in the study could be present in many other systems, which would make Swift J1357.2-0933 the prototype of a hitherto veiled population with a high inclination"

Like an immense donut (or toroid) that expands daily. That's how Jesús Corral-Santana, a researcher at the Instituto de Astrofísica de Canarias (IAC), describes the odd - hitherto unknown - structure of the binary system Swift J1357.2-0933, consisting of a 'normal' star and a stellar-mass black hole (which feeds off its companion star). The investigation, just published in Science journal with Corral as first author, follows the stages of the outburst of the system, an event that occurs only once in decades or centuries.

The team observed strange eclipses in the system that lasted and were repeated every few minutes. This finding led them to two conclusions: they had to be viewing the black hole edge on (it had an inclination of at least 75 degrees) and it presented an odd vertical structure within the accretion disc of the system. In other words, the matter being drawn from the companion star formed an outflow in the shape of a whirlpool, rather like water flowing down a plughole.

As Jorge Casares, also an IAC researcher, coauthor of the paper and Principal investigator (PI), explains, 'this kind of structure is possibly present in many - or all - X-ray binaries, the class of systems to which Swift J1357.2-0933 belongs. So the object we've observed could be the prototype of a hitherto hidden population of highly inclined systems in which the black hole is obscured.' Statistically, around 20% of systems could be of this type.

Black holes are formed following the death of very massive stars, and their detection is complicated. 'Since they don't emit any light, they're nearly impossible to find if they are alone,' says Casares. 'In cases where they have a companion star, their probability of detection is much higher, since their presence is betrayed by the "cannibalization" of the companion star by the black hole.' This explains why, since the first detection of such a system in 1964, only 18 other black holes have been found in our Galaxy. Swift J1357.2-0933, discovered by the Swift X-ray satellite and studied by the IAC team, is the latest one in the list. There are a further 32 black-hole candidates, but these haven't yet been confirmed.

Many X-ray binaries are characterized by decades-long - even centuries-long - periods of quiescence, and it is easy to confuse them with normal stars when in this state. But, with no prior warning, these system can erupt, brightening dramatically (by as much as a million times their normal brilliance), in any part of the Galaxy. This enables them to be detected by satellites scanning the sky in X-rays. The system fades back to quiescence after a few months.

It's then, adds Corral-Santana, that the scientific community can analyse its structure: a 'normal' star and a compact object (either a black hole, as in this case, or a neutron star). The star transfers material to its companion, forming an accretion disc.

In the case of Swift J1357.2-0933, the IAC researcher continues, more data have been gathered owing to its relative proximity, estimated at 5000 light years and its great distance above the plane of the Milky Way, where most of the matter of the Galaxy is concentrated, meaning that light from the binary system is not dimmed by interstellar dust or glare from nearby stars.

The scientists found that the system has a very short period, a mere 2.8 hours. In that time the companion star completes an orbit around the black hole. They also measured the mass of the black hole to be three times that of the Sun. 'That's a lower limit. In fact, the mass could be very much greater than that. Further observations during the period of quiescence would enable us to get a more accurate value,' Corral-Santana explains.

However, the most unusual find concerns the eclipses of the system. From images taken with various telescopes at the Teide and Roque de los Muchachos Observatories (the IAC-80, Liverpool, Mercator and INT), it was found that eclipses occurred in which the brightness of the system dropped by 30% in only seven seconds, and that they were repeated at longer intervals after a few days. 'It's the first time a phenomenon with these characteristics has been observed. None of the 50 known transitory X-ray binaries (18 with confirmed black holes and 32 candidates)
produces eclipses by the companion star,' the IAC astrophysicist points out.

What could be causing the eclipses? The researchers are clear that they aren't produced by the companion star since these have orbital periods of 2.8 hours and the eclipses are produced every few minutes and are of extremely short duration. Corral-Santana further adds, 'The period in which the eclipses are repeated gets progressively longer each day. This fact suggests that the eclipses are produced by a vertical structure that is initially located close to the black hole and gradually moves outwards like a wave from the inner part of the accretion disc.

This discovery is closely linked with another: 'The simple fact of detecting the eclipses indicates that the system is viewed at a high inclination, even greater than 75 degrees. In effect, we're looking at it edge on,' says the scientist, who further describes the structure as, 'probably like a donut, with the black hole permanently hidden in the middle.'

Source:

http://www.iac.es/divulgacion.php?op1=16&id=790&lang=en

Elliptical Galaxy Reveals a Spectacular "Ruins" of Black Holes and Neutron Stars

2013-03-02T01:37:02Z

The Chandra X-Ray Observatory image of the elliptical galaxy NGC 4261 revealed dozens of black holes and neutron stars strung out across tens of thousands of light years like beads on a necklace. The spectacular structure, which is not apparent from the optical image of the galaxy, is thought to be the remains of a collision between galaxies a few billion years ago, when a smaller galaxy was captured and pulled apart by the gravitational tidal forces of NGC 4261. As the doomed galaxy fell into the larger galaxy, large streams of gas were pulled out into long tidal tails. Shock waves in these tidal tails triggered the formation of many massive stars.

Over the course of a few million years, these stars evolved into neutron stars or black holes. A few of these collapsed stars had companion stars, and became bright X-ray sources as gas from the companions was captured by their intense gravitational fields.

The currently favored view is that elliptical galaxies are produced by collisions between spiral galaxies. Computer simulations of galaxy collisions support this idea, and optical evidence of tails, shells, ripples, arcs and other structures have been interpreted as evidence for this theory.

However as the image above shows, the optical evidence rather quickly fades into the starry background of the galaxy, whereas the X-ray signature lingers for hundreds of millions of years. Chandra's image of NGC 4261 shows that X-ray observations may be the best way to identify the ancient remains of mergers between galaxies.

The Hubble Space Telescope picture below of the center of NGC 4261 tells a dramatic tale. The gas and dust in this disk are swirling into what is almost certainly a super, perhaps super-super massive black hole. The disk is probably what remains of the smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars. Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.

Source:

http://www.dailygalaxy.com/my_weblog/2013/03/elliptical-galaxy-reveals-spectacular-ruins-of-black-holes-and-neutron-stars.html