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By Stephen Luntz

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X-Ray Source Explains Black Hole Behaviour

The mass of a very bright X-ray source in the Andromeda galaxy has been calculated to be only around ten solar masses, filling in our knowledge of black hole behaviour.

X-ray space telescopes have allowed us to see the universe in a part of the electro­magnetic spectrum that is largely obscured by the atmosphere, leading to the discovery of ultraluminous X-ray sources in nearby galaxies. Astronomers have debated whether these represent black holes a few times the mass of the sun feeding rapidly, or larger objects dining at a more restrained pace.

Now a Nature paper claims to have settled this question following detailed radio wave and X-ray observations. “We watched a black hole go from nibbling daintily at an appetiser to bingeing on the main course, and then gradually slowing down over dessert,” said Dr Matthew Middleton of Durham University.

Dr James Miller-Jones of the Curtin University node of the International Centre for Radio Astronomy says the dramatic variations in radio waves produced by the black hole are indicative of a smaller object. “As gas falls into a black hole, X-rays are produced and these create pressure. Eventually the pressure from the X-rays becomes so great it stops gas falling in any faster, creating a limit known as the Eddington limit.” Rapid gas collection also produces jets of charged particles shot out at close to the speed of light.

Larger black holes have higher Eddington limits because they have greater gravitational force attracting the gas. The flaring behaviour of the jets indicates that the black hole is approaching the Eddington limit, allowing the researchers to calculate its mass.

Using the Very Large Array in New Mexico, the team observed the radio emissions from the Andromeda black hole fall by half in just 30 minutes. Miller-Jones says this indicates that “the region producing radio waves is extremely small in size, no further across than the distance between Jupiter and the Sun”.

These are the first radio jets to be observed outside the Milky Way galaxy from such a small black hole.

The object would be the remnant of a star 25–35 solar masses in size that collapsed into a black hole by way of a supernova, and is now slowly feeding on the smaller companion star orbiting around it.

The team consider it likely that other ultraluminous X-ray objects are of similar size, and Miller-Jones is seeking examples in the Southern Hemisphere to examine with the Australia Telescope Compact Array.

Myosin’s Mighty Grip

The molecule myosin VI anchors secretory vesicles more than 5000 times its size, playing a crucial role in brain cells in the process.

Myosin VI is one of a class of motor proteins responsible for muscle contractions. However, unlike the other 17 known types, myosin VI travels along actin filaments towards the pointed or negative end, “travelling through cells backwards” according to A/Prof Frederic Meunier of the Queensland Brain Institute.

Myosin VI has multiple roles in the human body, and genetically induced deficiencies are associated with blindness.

Vanesa Tomatis, a PhD student of Meunier, observed that myosin VI can grab hold of vastly larger secretory vesicles and anchor them in place around the plasma membrane surrounding brain cells. Her finding was published in The Journal of Cell Biology.

Meunier described the presence of the vesicles as the “key to sustaining communication between neuronal cells,” although he says he does not know if it is the failure of this function that leads to blindness.

How myosin VI achieves the effect, which is comparable to a tugboat stopping a supertanker, remains a mystery. “The vesicle is moving quite quickly and touches the patch of myosin and is suddenly frozen,” Meunier says. “We want to know what the vesicle is binding to and how the myosin is able to hold on for such a long period of time.”

Meunier believes the arrival of a new super-resolution microscope, the first in Queensland, will allow the team to work out how these feats are achieved. However, while he says “the more you know the better it is,” Meunier does not see a direct path from this information to a treatment for myosin VI deficiencies.

Greenland Ice Core Reveals History

An ice core from Greenland has offered insights into the last time the world was warmer than it is today, providing some indications of what we can expect.

Cores taken in Antarctica can contain million-year-old ice, says Dr Mauro Rubino of CSIRO Marine and Atmospheric Research. However, since snow falls slowly there each annual layer is so thin we can get very little discrimination of what was happening during a period of time.

In contrast, Greenland lays down far more ice each year but we have struggled to find ice that dates back to before the last ice age when the world was warm.

Now, however, a 2540-metre core has been collected from Greenland that has overturned some of our ideas about what that era was like. Even this core’s interglacial-era ice lay near bedrock and has been twisted by the effects of flowing over an uneven surface. Nevertheless, Rubino extracted bubbles of air that could be matched to bubbles collected from Antarctic cores, allowing accurate dating of the layers.

During what is known as the Eemian period 115–130,000 years ago, Greenland was 4–8°C warmer and the world’s oceans were 4–8 metres higher. The warmth was a product of differences in the Earth’s orbit at the time and greater output from the sun. Greenhouse gas levels were higher than during the ice ages on either side of this period, but lower than today.

From a comparison of this and other cores, the team concluded that the Greenland ice sheet was 400 ± 250 metres thinner during the Eemian than it is today. While this is a lot of ice to lose, it is less than was previously thought.

“The findings show a modest response of the Greenland ice sheet to the significant warming in the early Eemian, and led to the deduction that Antarctica must have contributed significantly to the higher Eemian sea levels,” Rubino says.

The results are worrying as they suggest that Antarctica may be more prone to melting than previously thought. Greenland’s surface melting appears to have been high during the Eemian, and this may soon be repeated.

Radar mapping of ice density is now being used in the quest to find Greenland ice cores with even longer histories.

Forests Bring Rain and Wind

Forests drive global wind patterns and pump water to the centre of continents, according to a controversial new paper published in Atmospheric Chemistry and Physics.

The work has received so much resistance from atmospheric scientists that the paper was published with an editorial comment indicating uncertainty and a hope that the idea will raise discussion.

The idea of forests as rainmakers is not novel. Deforestation has been associated with localised loss of precipitation, but Prof Douglas Sheil of Southern Cross University’s School of Environment, Science and Engineering is proposing something much broader.

“Our study concluded that condensation and evaporation – and not temperature differences as traditionally believed – are the major drivers of atmospheric dynamics,” Sheil says.

Shiel’s co-authors, Prof Victor Gorshkov and Dr Anastassia Makarieva of the Petersburg Nuclear Physics Institute, have described the mechanism by which condensation creates low-pressure systems, drawing in wind.

“The behaviour of the world’s atmosphere is immensely complicated, and simplifications and approximations are needed,” Sheil says. “In textbook climate sciences, the pressure differences caused by condensation are stated to be small so they can be ignored. This assumption is true in some cases but, we argue, not in others.”

As a forest ecologist, Sheil contributed evidence that forests transpire to an extent that dwarfs evaporation from open water, let alone savannah.

The team proposes that deforestation has dried Australia out over the millennia, and the same may happen to Africa and South America.

“I got interested in the idea because if you plot rainfall inland from the coast, in most places it drops off exponentially but over tropical rainforest it remains more or less constant,” Sheil says. “The same thing occurs over the boreal forests of Russia, except for a few months when it is so cold the trees shut down, at which time the precipitation drops as you go inland.”

If confirmed, Sheil’s work would bolster the case for forest preservation, and suggests that desertification should be fought by replanting bands of trees inwards from the coast. He says it remains an “interesting question” whether the sort of forest matters, but believes that “it needs to be a natural forest. There are certain properties in a mature forest with closed cover, although plantations might be designed to match.”

Although physicists and forest ecologists have responded positively to the hypothesis, there has been strong resistance from many atmospheric scientists. Sheil attributes this to the baseless attacks they receive on a regular basis, and says he can understand that with so much nonsense proposed from outsiders in their field “this would get lumped in the same category”. Consequently he welcomes publication in a leading journal in the field.

If the work is confirmed Sheil agrees it will cause reconsideration of both climate and weather forecasting, a fact that has been eagerly seized on by global warming deniers even though the work strengthens the evidence for human interference in climate.

Sea Snake ID Mistake

What was once thought to be a single species of sea snake has been discovered to be three. More unusually, despite remarkable physical similarities, one species is not closely related to the others.

Beaked sea snakes are by far the most common cause of fatal marine snake bites. Australian and Asian beaked sea snakes look alike, and both are true sea snakes rather than from the distant family of sea kraits, but each is more closely related to other species than they are to each other.

Venomous species expert A/Prof Bryan Fry of the University of Queensland says: “This mix-up could have been medically catastrophic, since the CSL sea snake antivenom is made using the venom from the Asian snake based on the assumption that it was the same species. Luckily, the antivenom is not only very effective against the Australian new species but actually against all sea snakes since they all share a very streamlined fish-specific venom.”

Fry says the species’ similarity, including a hooked nose and a dagger-shaped lower jaw, comes from the common challenges of living in silty tropical estuaries. The Asian species, previously known as Enhydrina shistosa, lives in waters from Iran to Indonesia. As a result of other work by Fry it is now being renamed Hydrophis shistosa.

Somewhere around the Wallace Line, which designates a stark division for land-based plant and animal species, H. shistosa are replaced with snakes that will now be known as H. zweifeli inhabiting eastern Indonesia, New Guinea and tropical Australia.

Fry published his findings in Molecular Phylogenetics and Evolution, basing his conclusions on a genetic analysis that revealed the differences between the two species. A follow-up paper attempts to clear up the relationships between different sea snake species.

“This is the first time there has been convergent evolution observed in a lethal animal,” says Fry. “It rivals the convergence between tree pythons in Australia and South America that look identical but have different ancestries.”

Fry also determined that Sri Lankan beaked sea snakes differ from H. shistosa enough to be considered a separate species, but says this represents a much less remarkable example of genetic drift from the neighbouring species.

GBR Landslide Debris Points to Tsunami Risk

The continental slope off the Great Barrier Reef is littered with the remnants of landslides, and a huge block one cubic kilometre in diameter looks set to eventually follow them.

Residents of tropical north Queensland should not be overly alarmed, however, as while the collapse of this block would cause a monstrous tsunami it appears unlikely to fall in the near future.

“Over the past several years we have mapped hundreds of kilometres along the Great Barrier Reef margin, marvelling at the dense network of canyons and landslide scarps, but this block really stood out as a site for a potential collapse,” says Dr Jody Webster of the School of Geosciences at the University of Sydney.

The object has been named the Noggin block after the passage in which it sits. The Noggin block is located 100 km south-east of Cairns, and its fall would cause energy to ripple out “like a pebble thrown into a pond,” says Dr Robin Beaman of James Cook University.

“The Reef acts as a porous break water,” Beaman says. “Modelling shows the wave height on top of the block when it fell would be halved when it hit the shoreline.” This could still be enough to do terrific damage.

Exact estimates of the height of the tsunami are hard, but Beaman says the time taken to cross the reef can be accurately estimated at just over an hour.

Although the block shows signs of being undercut by sedimentary erosion, Beaman stresses it is stable enough that only a nearby earthquake of magnitude 7 or greater would cause it to fall, and this is very unlikely. In the longer term, multiple small quakes might eventually weaken the block to the point where it becomes a danger.

The slope below is littered with the remnants of smaller quakes, indicating long-term instability in the area, but Beaman says these are very old since corals growing on the reef nearby have been undisturbed for thousands of years.

Webster and Beaman have mapped 800–900 km of continental shelf in the area, and Beaman says: “This is the one that really jumped out at us because the canyon it is attached to is eroding. We have not found anything else as obvious as this.”

The discovery was published in Natural Hazards.

Liquid Metal Marbles Nanocoated

Nanoparticles have been used to coat liquid metal marbles, offering the potential for sensing devices and flexible electronic conductors.

Liquid metal drops are made of an alloy of gallium and tin with a melting point below 0°C. Dr Vijay Sivan of RMIT’s Platform Technologies Research Institute has announced in Advanced Functional Materials the first coating of these droplets in functional nanoparticles with specified electronic properties.

“The ‘liquid metal marbles’ our team has developed are like flexible ball bearings with extraordinary physical properties,” Sivan says. “They can endure high impacts without disintegrating, can tolerate high temperatures, can operate like semiconducting/conducting systems – the basis of transistors – and are compatible with micro- and nano-fluidic systems.”

Although the marbles Sivan has produced are around 2 mm across, liquid metal droplets as small as 80 µm across have been manufactured. Sivan’s reference to compatibility with smaller fluidic systems is an indication of his confidence that the work can be applied at this scale.

The liquid metal cores of the marbles are good conductors, and Sivan says a current can be used to increase the responsiveness of sensing materials used as nanocoatings, or as a way to transmit detections of the marbles’ environment.

“We can use a broad range of powder coating materials, from insulating to semiconducting and highly conducting,” Sivan says.

Liquid metals can be corrosive to solid metals, but Sivan says the coating means “you can place a marble on a metallic surface and it does not come into direct contact, so it will not corrode the surface”.

Even Carnivores Rely on Plant Diversity

The diversity of animal species is closely related to the richness of plants, a huge investigation of Panamanian rainforest has found.

More than 100 researchers put in 24,000 days of work between them, seeking every inhabitant in patches of rainforest spread over an area of 5000 m2 from canopy to tree floor. In the process they collected 130,000 arthropods, a class that includes insects, spiders and crustaceans, from 6000 species.

Extrapolations based on area and genus led them to conclude that a single hectare would have included 25,000 species of animals, which is 20 times the number of plant species.

Unsurprisingly, the diversity of herbivorous arthropods was related to the diversity of the plants on which they fed. However, it turned out the same was true of the carnivores. Prof Raphael Didham of the University of Western Australia’s School of Animal Biology says this relationship had previously been “less clear”.

It was thought that the capacity of many insects to fly might lead to a different scaling relationship between their diversity and area compared with plants. However, this was found not to be the case.

Such a huge project was always going to produce more than one finding. Among the beetles detected, 70% were from new species although Didham says the ants and butterflies were much better known previously. However, as many as 90% of soil arthropods could turn out to be undescribed species.

Didham says there “are still a lot of papers on ecology to come out of this work,” including the ways the insect species stratified between the forest floor and canopy.

Didham says that the findings mean that for “broadscale conservation we can make planning decisions based on studies of plants”. However, at finer scales planning will need to take into account the microhabitat requirements of individual species.

Iron Fertilisation Isn’t a Carbon Solution

Fertilisation of the oceans with iron will not be a large-scale solution to carbon emissions although “boutique” opportunities may exist, according to a PhD student at the University of Sydney.

Much of the Southern Ocean is very poor in iron, causing low biological productivity. The addition of small concentrations of iron can produce huge plankton blooms, drawing down tens of thousands of times as much carbon as iron is released (AS, Nov/Dec 2007, p.14).

Unfortunately, while a lot of carbon can be temporarily removed from the atmosphere in this way, the blooms tend to be very temporary and most of the carbon is re-released fairly quickly.

In a paper published in the International Journal of Global Warming, Daniel Harrison examined the evidence from 14 fertilisation trials and found that in most cases the temporary nature of the blooms meant that the cost of these operations was far above the $23/tonne levied on carbon emissions in Australia at the moment. At these prices it would be far cheaper to switch from coal to cleaner fuels than to try to balance what is released during iron fertilisation programs.

Fuel is required to sail ships around the Southern Ocean to release iron, and some carbon is emitted in the mining and processing of iron. “This means that under less ideal conditions, iron fertilisation may actually create more greenhouse gas than is sequestered,” Harrison says.

However, one trial produced storage rates five times higher than the others. Harrison attributes this to a combination of factors, including the presence of a large eddy that kept the iron in the same waters so that it was reused by several generations of sea life.

“Silica is also important. Where you have silica, diatoms use the iron to build their shells, and as they are heavier they tend to sink to the bottom, carrying the carbon with them,” Harrison says.

Iron fertilisation in the right locations may offset releases at moderate costs, but Harrison believes that the potential “overall contribution to the climate problem is limited” in these places.

Nevertheless, all hope is not lost for oceanic storage. Harrison says that nitrogen fertilisation gives far better long-term storage, and despite the much higher quantities of nitrogen required, a recent study suggests it may be more economical.

Moreover, Harrison is now examining the merits of iron fertilisation to boost fish stocks, with carbon sequestration as a side bonus, potentially altering the economics.