Hubble finds source of Magellanic Stream

Astronomers explore origin of gas ribbon wrapped around our galaxy

Astronomers using the NASA/ESA Hubble Space Telescope have solved the 40-year-old mystery of the origin of the Magellanic Stream, a long ribbon of gas stretching nearly halfway around the Milky Way. New Hubble observations reveal that most of this stream was stripped from the Small Magellanic Cloud some two billion years ago, with a smaller portion originating more recently from its larger neighbour.

The Magellanic Clouds, two dwarf galaxies orbiting our galaxy, are at the head of a huge gaseous filament known as the Magellanic Stream. Since the Stream's discovery in the early 1970s, astronomers have wondered whether this gas comes from one or both of the satellite galaxies. Now, new Hubble observations show that most of the gas was stripped from the Small Magellanic Cloud about two billion years ago — but surprisingly, a second region of the stream was formed more recently from the Large Magellanic Cloud.

A team of astronomers determined the source of the gas filament by using Hubble's Cosmic Origins Spectrograph (COS), along with observations from ESO's Very Large Telescope, to measure the abundances  of heavy elements, such as oxygen and sulphur, at six locations along the Magellanic Stream. COS detected these elements from the way they absorb the ultraviolet light released by faraway quasars as it passes through the foreground Stream. Quasars are the brilliant cores of active galaxies.

The team found low abundances of oxygen and sulphur along most of the stream, matching the levels in the Small Magellanic Cloud about two billion years ago, when the gaseous ribbon was thought to have been formed.

Overview of the Large Magellanic Cloud
(ground-based image)

In a surprising twist, the team discovered a much higher level of sulphur in a region closer to the Magellanic Clouds. "We're finding a consistent amount of heavy elements in the stream until we get very close to the Magellanic Clouds, and then the heavy element levels go up," says Andrew Fox, a staff member supported by ESA at the Space Telescope Science Institute, USA, and lead author of one of two new papers reporting these results. "This inner region is very similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy more recently."

This discovery was unexpected; computer models of the Stream predicted that the gas came entirely out of the Small Magellanic Cloud, which has a weaker gravitational pull than its more massive cousin.

"As Earth's atmosphere absorbs ultraviolet light, it's hard to measure the amounts of these elements accurately, as you need to look in the ultraviolet part of the spectrum to see them," says Philipp Richter of the University of Potsdam, Germany, and lead author on the second of the two papers. "So you have to go to space. Only Hubble is capable of taking measurements like these."

All of the Milky Way's nearby satellite galaxies have lost most of their gas content — except the Magellanic Clouds. As they are more massive than these other satellites they can cling on to this gas, using it to form new stars. However, these Clouds are approaching the Milky Way and its halo of hot gas. As they drift closer to us, the pressure of this hot halo pushes their gas out into space. This process, together with the gravitational tug-of-war between the two Magellanic Clouds, is thought to have formed the Magellanic Stream .

"Exploring the origin of such a large stream of gas so close to the Milky Way is important," adds Fox. "We now know which of our famous neighbours, the Magellanic Clouds, created this gas ribbon, which may eventually fall onto our own galaxy and spark new star formation. It's an important step forward in figuring out how galaxies obtain gas and form new stars."

Source : Space Telescope Science Institute (STScI).
By Science and universe ( Nandan)

'Soft' approach leads to revolutionary energy storage

Monash University researchers have brought next generation energy storage closer with an engineering first - a graphene-based device that is compact, yet lasts as long as a conventional battery. 

Published today in Science, a research team led by ProfessorDan Li of the Department of Materials Engineering has developed a completely new strategy to engineer graphene-based supercapacitors (SC), making them viable for widespread use in renewable energy storage, portable electronics and electric vehicles.

Graphene sheet model. (Credit: © nobeastsofierce / Fotolia) 

SCs are generally made of highly porous carbon impregnated with a liquid electrolyte to transport the electrical charge. Known for their almost indefinite lifespan and the ability to re-charge in seconds, the drawback of existing SCs is their low energy-storage-to-volume ratio - known as energy density. Low energy density of five to eight Watt-hours per litre, means SCs are unfeasibly large or must be re-charged frequently.

Professor Li's team has created an SC with energy density of 60 Watt-hours per litre - comparable to lead-acid batteries and around 12 times higher than commercially available SCs.

"It has long been a challenge to make SCs smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses," Professor Li said.

Graphene, which is formed when graphite is broken down into layers one atom thick, is very strong, chemically stable and an excellent conductor of electricity.

To make their uniquely compact electrode, Professor Li's team exploited an adaptive graphene gel film they had developed previously. They used liquid electrolytes - generally the conductor in traditional SCs - to control the spacing between graphene sheets on the sub-nanometre scale. In this way the liquid electrolyte played a dual role: maintaining the minute space between the graphene sheets and conducting electricity. 

Unlike in traditional 'hard' porous carbon, where space is wasted with unnecessarily large 'pores', density is maximised without compromising porosity in Professor Li's electrode. 

To create their material, the research team used a method similar to that used in traditional paper making, meaning the process could be easily and cost-effectively scaled up for industrial use. 

"We have created a macroscopic graphene material that is a step beyond what has been achieved previously. It is almost at the stage of moving from the lab to commercial development," Professor Li said. 

The work was supported by the Australian Research Council.

Source : Monash University.

By Science and Universe

Elliptical Crater on Mercury

This color image, taken on May 1, 2013 by the Wide Angle Camera (WAC) instrument aboard NASA's MESSENGER spacecraft orbiting Mercury, features Hovnatanian crater, named for Armenian painter Hakop Hovnatanian. The crater's elliptical shape and the bright rays' butterfly pattern indicate that a very oblique impact produced the crater. The brightness of the rays indicate that they are relatively young features on Mercury's surface.

This image was acquired as a targeted high-resolution 11-color image set. Acquiring 11-color targets is a new campaign that began in March, 2013 and that utilizes all of the camera's 11 narrow-band color filters. Because of the large data volume involved, only features of special scientific interest are targeted for imaging in all 11 colors.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the solar system's innermost planet. MESSENGER has acquired over 150,000 images and extensive other data sets, and is capable of continuing orbital operations until early 2015.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

By Science and Universe

New Water Splitting Technique Efficiently Produces Hydrogen Fuel

An artist's conception of a commercial hydrogen production plant that uses sunlight to split water in order to produce clean hydrogen fuel. (Image courtesy University of Colorado Boulder)

A University of Colorado Boulder team has developed a radically new technique that uses the power of sunlight to efficiently split water into its components of hydrogen and oxygen, paving the way for the broad use of hydrogen as a clean, green fuel.

The CU-Boulder team has devised a solar-thermal system in which sunlight could be concentrated by a vast array of mirrors onto a single point atop a central tower up to several hundred feet tall. The tower would gather heat generated by the mirror system to roughly 2,500 degrees Fahrenheit (1,350 Celsius), then deliver it into a reactor containing chemical compounds known as metal oxides, said CU-Boulder Professor Alan Weimer, research group leader.

As a metal oxide compound heats up, it releases oxygen atoms, changing its material composition and causing the newly formed compound to seek out new oxygen atoms, said Weimer.  The team showed that the addition of steam to the system -- which could be produced by boiling water in the reactor with the concentrated sunlight beamed to the tower -- would cause oxygen from the water molecules to adhere to the surface of the metal oxide, freeing up hydrogen molecules for collection as hydrogen gas.

“We have designed something here that is very different from other methods and frankly something that nobody thought was possible before,” said Weimer of the chemical and biological engineering department. “Splitting water with sunlight is the Holy Grail of a sustainable hydrogen economy.”

Image : A laboratory model of a multi-tube solar reactor at the University of Colorado Boulder that can be used to split water in order to produce clean hydrogen fuel. (Photo courtesy University of Colorado Boulder) - 

A paper on the subject was published in the Aug. 2 issue of Science. The team included co-lead authors Weimer and Associate Professor Charles Musgrave, first author and doctoral student Christopher Muhich, postdoctoral researcher Janna Martinek, undergraduate Kayla Weston, former CU graduate student Paul Lichty, former CU postdoctoral researcher Xinhua Liang and former CU researcher Brian Evanko.

One of the key differences between the CU method and other methods developed to split water is the ability to conduct two chemical reactions at the same temperature, said Musgrave, also of the chemical and biological engineering department. While there are no working models, conventional theory holds that producing hydrogen through the metal oxide process requires heating the reactor to a high temperature to remove oxygen, then cooling it to a low temperature before injecting steam to re-oxidize the compound in order to release hydrogen gas for collection.

“The more conventional approaches require the control of both the switching of the temperature in the reactor from a hot to a cool state and the introduction of steam into the system,” said Musgrave. “One of the big innovations in our system is that there is no swing in the temperature. The whole process is driven by either turning a steam valve on or off.”

“Just like you would use a magnifying glass to start a fire, we can concentrate sunlight until it is really hot and use it to drive these chemical reactions,” said Muhich. “While we can easily heat it up to more than 1,350 degrees Celsius, we want to heat it to the lowest temperature possible for these chemical reactions to still occur. Hotter temperatures can cause rapid thermal expansion and contraction, potentially causing damage to both the chemical materials and to the reactors themselves.”

In addition, the two-step conventional idea for water splitting also wastes both time and heat, said Weimer, also a faculty member at CU-Boulder’s BioFrontiers Institute. “There are only so many hours of sunlight in a day,” he said.

The research was supported by the National Science Foundation and by the U.S. Department of Energy.

With the new CU-Boulder method, the amount of hydrogen produced for fuel cells or for storage is entirely dependent on the amount of metal oxide -- which is made up of a combination of iron, cobalt, aluminum and oxygen -- and how much steam is introduced into the system. One of the designs proposed by the team is to build reactor tubes roughly a foot in diameter and several feet long, fill them with the metal oxide material and stack them on top of each other. A working system to produce a significant amount of hydrogen gas would require a number of the tall towers to gather concentrated sunlight from several acres of mirrors surrounding each tower.

Weimer said the new design began percolating within the team about two years ago. “When we saw that we could use this simpler, more effective method, it required a change in our thinking,” said Weimer.  “We had to develop a theory to explain it and make it believable and understandable to other scientists and engineers.”

Despite the discovery, the commercialization of such a solar-thermal reactor is likely years away. “With the price of natural gas so low, there is no incentive to burn clean energy,” said Weimer, also the executive director of the Colorado Center for Biorefining and Biofuels, or C2B2. “There would have to be a substantial monetary penalty for putting carbon into the atmosphere, or the price of fossil fuels would have to go way up.”

C2B2 is an arm of the Colorado Energy Research Collaboratory involving CU-Boulder, the Colorado School of Mines, Colorado State University and the National Renewable Energy Laboratory in Golden. The collaboratory works with industry partners, public agencies and other institutions to commercialize renewable energy technologies, support economic growth in the state and nation and educate the future workforce.

Article source :  University of Colorado at Boulder. 

By Science and Universe

A cometary graveyard

<<Image : These illustration show the asteroid belt in the present day and in the early Solar System, located between the Sun (at centre) and four terrestrial planets (near the Sun) and Jupiter (at bottom left). The top image shows the conventional model for the asteroid belt; largely composed of rocky material. The middle image shows the proposed model, with a small number of active comets and a dormant cometary population. The lower diagram shows how the asteroid belt might have looked in the early Solar System, with vigorous cometary activity. Credit: Ignacio Ferrin / University of Antioquia

A team of astronomers from the University of Anitoquia, Medellin, Colombia, have discovered a graveyard of comets. The researchers, led by Antioquia astronomer Prof. Ignacio Ferrin, describe how some of these objects, inactive for millions of years, have returned to life leading them to name the group the 'Lazarus comets'. The team publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Comets are amongst the smallest objects in the Solar System, typically a few km across and composed of a mixture of rock and ices. If they come close to the Sun, then some of the ices turn to gas, before being swept back by the light of the Sun and the solar wind to form a characteristic tail of gas and dust.

Most observed comets have highly elliptical orbits, meaning that they only rarely approach the Sun. Some of these so-called long period comets take thousands of years to complete each orbit around our nearest star. There is also a population of about 500 short period comets, created when long period comets pass near Jupiter and are deflected in orbits that last anything between 3 and 200 years. Although uncommon events, comets also collide with the Earth from time to time and may have helped bring water to our planet.

The new work looked at a third and distinct region of the Solar System, the main belt of asteroids between the orbits of Mars and Jupiter. This volume of space contains more than 1 million objects ranging in size from 1 m to 800 km. The traditional explanation for asteroids is that they are the building blocks of a planet that never formed, as the movement of the pieces was disrupted by the strong gravitational field of Jupiter.

In the last decade 12 active comets have been discovered in the asteroid main belt region. This was something of a surprise and the Medellin team set out to investigate their origin. The team, made up of Prof. Ferrin and his colleagues Profs. Jorge Zuluaga and Pablo Cuartas, now think they have an explanation.

"We found a graveyard of comets", exclaims Professor Ferrín. He adds: "Imagine all these asteroids going around the Sun for aeons, with no hint of activity. We have found that some of these are not dead rocks after all, but are dormant comets that may yet come back to life if the energy that they receive from the Sun increases by a few per cent."

Surprisingly, this can happy fairly easily, as the orbits of many objects in the asteroid belt are nudged by the gravity of Jupiter. The shape of their orbits can then change, leading to a decrease in the minimum distance between the object and the Sun (perihelion) and a slight increase in average temperature.

According to this interpretation, millions of years ago the main belt was populated by thousands of active comets. This population aged and the activity subsided. What we see today is the residual activity of that glorious past. Twelve of those rocks are true comets that were rejuvenated after their minimum distance from the Sun was reduced a little. The little extra energy they received from the Sun was then sufficient to revive them from the graveyard.

Prof. Ferrin describes the 12 active comets. "These objects are the 'Lazarus comets', returning to life after being dormant for thousands or even millions of years. Potentially any one of the many thousands of their quiet neighbours could do the same thing."

Article Source : Royal Astronomical Society (RAS).

By Science & Universe

The when and where of the Y: Research on Y chromosomes uncovers new clues about human ancestry

Abstract image of X and Y chromosomes. (Credit: iStockphoto)

First full-chromosome sequencing effort shows most recent male & female common ancestors lived around the same time

More than 7 billion people live on this planet – members of a  single species that originated in one place and migrated all over the Earth over tens of thousands of years.

But even though we all trace our family lineage to a few common ancestors, scientists still don’t know exactly when and how those few ancestors started to give rise to the incredible diversity of today’s population.

A brand-new finding, made using advanced analysis of DNA from all over the world, sheds new light on this mystery. By studying the DNA sequence of Y chromosomes of men from many different populations, scientists have determined that their male most recent common ancestor (MRCA) lived sometime between 120,000 and 156,000 years ago.

It’s the first time the human ancestry has been traced back through the male line by sequencing the DNA of many entire Y chromosomes.

And, it agrees reasonably well with previous findings about our female most recent common ancestor, made by studying DNA carried down through the human race’s female line. Such studies used DNA from mitochrondria -- structures inside cells – and placed that time of the most recent common ancestor between 99,000 and 148,000 years ago. That agreement makes the new finding especially significant:

The research was done by a team of scientists from Stanford University, the University of Michigan Medical School, Stony Brook University, and their colleagues, and is published in the journalScience.

The team hopes their work will lead to further research on Y chromosomes as vehicles for studying human history – and tracing male lineages back to the common “Adam” ancestors.

The new paper details how the team was able to make reliable measurements of the sequence variation along the Y chromosome – which is handed down only from father to son without exchanging, or recombining, genetic material with other chromosomes. Jeffrey Kidd, Ph.D., an assistant professor in U-M's departments ofHuman Genetics andComputational Medicine & Bioinformatics who worked on the new study, notes that only recently has it become possible to sequence Y chromosomes, because of technical limitations of previous approaches.

Kidd notes that this initial paper on Y chromosome sequence diversity provides important first evidence that the male most recent common ancestor did not live more recently than the female most recent common ancestor.

“We’re interested in understanding the historical relationships between many different human populations, and the migration patterns that have led to the peopling of the world,” he says. “We hope that others will make use of this approach and sequence additional chromosomes of interest that are related to the peopling of specific places.”

The study involved Y chromosomes obtained through the Human Genome Diversity Project, and from other sources. It included chromosomes from 69 men in several populations in sub-Saharan Africa, and from Siberia, Cambodia, Pakistan, Algeria and Mexico.

The great migrations of our ancestors out of Africa, across Asia and Europe and into the Americas all helped shape today’s populations – as did more recent forces related to colonialism and ever-growing global mobility.

Genetic studies such as this one may help anthropologists understand those migrations – and their timing – even better by giving them a genetic “clock” to use when studying today’s humans, or potentially DNA extracted from ancient bones. It may also help scientists understand the great genetic diversity seen across Africa, and the evolution process that led to modern humans.

The reconciliation of the timing of ancestors some might call “Adam” and “Eve”, however, may be this study’s most important immediate implication. 

“This has been a conundrum in human genetics for a long time,” said Carlos D. Bustamante, Ph.D., a professor of genetics at Stanford and senior author of the study. “Previous research has indicated that the male MRCA lived much more recently than the female MRCA. But now our research shows that there’s no discrepancy. In fact, if anything, the Y chromosome may be a bit older.”

Article source : University of Michigan Health System.

By Science and Universe