Fossil of Largest Known Platypus Discovered in Australia

Nov. 4, 2013 — No living mammal is more peculiar than the platypus. It has a broad, duck-like bill, thick, otter-like fur, and webbed, beaver-like feet. The platypus lays eggs rather than gives birth to live young, its snout is covered with electroreceptors that detect underwater prey, and male platypuses have a venomous spur on their hind foot. Until recently, the fossil record indicated that the platypus lineage was unique, with only one species inhabiting Earth at any one time. This picture has changed with the publication of a new study in the latest issue of theJournal of Vertebrate Paleontology that describes a new, giant species of extinct platypus that was a side-branch of the platypus family tree.

The new platypus species, namedObdurodon tharalkooschild, is based on a single tooth from the famous Riversleigh World Heritage Area of northwest Queensland. While many of Riversleigh's fossil deposits are now being radiometrically dated, the precise age of the particular deposit that produced this giant platypus is in doubt but is likely to be between 15 and 5 million years old.

"Monotremes (platypuses and echidnas) are the last remnant of an ancient radiation of mammals unique to the southern continents. A new platypus species, even one that is highly incomplete, is a very important aid in developing understanding about these fascinating mammals," said PhD candidate Rebecca Pian, lead author of the study.

Based on the size of tooth, it is estimated that this extinct species would have been nearly a meter (more than three feet) long, twice the size of the modern platypus. The bumps and ridges on the teeth also provide clues about what this species likely ate.

"Like other platypuses, it was probably a mostly aquatic mammal, and would have lived in and around the freshwater pools in the forests that covered the Riversleigh area millions of years ago," said Dr. Suzanne Hand of the University of New South Wales, a co-author of the study. "Obdurodon tharalkooschild was a very large platypus with well-developed teeth, and we think it probably fed not only on crayfish and other freshwater crustaceans, but also on small vertebrates including the lungfish, frogs, and small turtles that are preserved with it in the Two Tree Site fossil deposit."

The oldest platypus fossils come from 61 million-year-old rocks in southern South America. Younger platypus fossils are known from Australia in what is now the Simpson Desert. Before the discovery of Obdurodon tharalkooschild, these fossils suggested that platypuses became smaller and reduced the size of their teeth through time. The modern platypus completely lacks teeth as an adult and instead bears horny pads in its mouth. The name Obdurodon comes from the Greek for "lasting (obdurate) tooth" and was coined to distinguish extinct toothed platypuses from the essentially toothless modern species.

"Discovery of this new species was a shock to us because prior to this, the fossil record suggested that the evolutionary tree of platypuses was relatively linear one," said Dr. Michael Archer of the University of New South Wales, a co-author of the study. "Now we realize that there were unanticipated side branches on this tree, some of which became gigantic."

The specific epithet of the new species, tharalkooschild, honors an Indigenous Australian creation story about the origin of the platypus. In the Dreamtime, Tharalkoo was a head-strong girl duck inclined to disobey her parents. Her parents warned her not to swim downriver because Bigoon the Water-rat would have his wicked way with her. Scoffing, she disobeyed her parents and was ravished by Bigoon. By the time Tharalkoo escaped and returned to her family, the other girl ducks were laying eggs, so she did the same. But instead of a fluffy little duckling emerging from her egg, her child was an amazing chimera that had the bill, webbed hind feet, and egg-laying habit of a duck, along with the fur and front feet of a rodent -- the first Platypu
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Physicist Discovers Black Holes in Globular Star Clusters, Upsetting 40 Years of Theory: Could There Be Ripples in Spacetime?

Nov. 4, 2013 — A Texas Tech University astrophysicist was part of a team of researchers that discovered the first examples of black holes in globular star clusters in our own galaxy, upsetting 40 years of theories against their possible existence.

Tom Maccarone, an associate professor of physics, said the team detected the existence of the black holes by using an array of radio telescopes to pick up a certain type of radio frequency released by these black holes as they eat a star next to them.

The results were published in The Astrophysical Journal and featured in the National Radio Astronomy Observatory’s ENews news bulletin.

Globular star clusters are large groupings of stars thought to contain some of the oldest stars in the universe. In the same distance from our sun to the nearest neighbor, Proxima Centauri, its nearest neighbor, these globular star clusters could have a million to tens of millions of stars, Maccarone said.

“The stars can collide with one another in that environment,” Maccarone said. “The old theory believed that the interaction of stars was thought to kick out any black holes that formed. They would interact with each other and slingshot black holes out of the cluster until they were all gone.”

He compared it to water vapor coming off a hot cup of coffee. As some water molecules get hot enough to turn to steam, they are let go from their environment to float off into the atmosphere even though the coffee may be below the boiling temperature of water.

The old theory stated that the stars would kick the black holes out in the same fashion – occasionally, some black holes would have enough energy to escape the cluster, and gradually, they all would leave.

While the theory may still be displaced, Maccarone said it might still be somewhat true. Black holes might still get kicked out of globular star clusters, but at a much slower rate than initially believed.

In 2007, Maccarone made the first discovery of a black hole in a globular star cluster in the neighboring NGC4472 galaxy. But rather than finding it by using radio waves, Maccarone found it by seeing an X-ray emission from the gas falling into the black hole and heating up to a few million degrees.

“Six years ago I had made the first discoveries in other galaxies,” he said. “It’s surprisingly easier to find them in other galaxies than in our own, even though they’re a thousand times as far away as these in our own galaxy are.”

This year, he and his team discovered two examples of globular star clusters in our own galaxy which host black holes by finding radio emission by using the Very Large Array of radio telescopes in New Mexico.

“As the black hole eats a star, these jets of material are coming out,” he said. “Most of the material falls into the black hole, but some is thrown outwards in a jet. To see that jet of material, we look for a radio emission. We found a few radio emissions coming from this globular star cluster that we couldn’t explain any other way.”

Maccarone said seeing black holes in globular clusters may provide a way for them to get close enough to one another to merge into bigger black holes.

“These mergers may produce the ‘ripples in spacetime’ we call gravitational waves,” he said. “Trying to detect gravitational waves is one of the biggest problems in physics right now, because it would be the strongest test of whether Einstein’s theory of relativity is correct.”

Other researchers included Laura Chomiuk and Jay Strader at Michigan State University; James Miller-Jones at Perth Curtin University in Perth, Australia; Craig Heinke at University of Alberta in Edmonton, Alberta, Canada; Eva Noyola at the University of Texas at Austin; Anil Seth at University of Utah; and Scott Ransom at the National Radio Astronomy Observatory in Charlottesville, Virginia
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Life, but Not as We Know It: Rudimentary Form of Life Sidesteps Normal Replication Process

Nov. 3, 2013 — A rudimentary form of life that is found in some of the harshest environments on earth is able to sidestep normal replication processes and reproduce by the back door, researchers at The University of Nottingham have found.

The study, published in the journal Nature, centres on Haloferax volcanii — part of a family of single-celled organisms called archaea that until recently were thought to be a type of bacteria.

The findings, led by scientists from the University’s School of Life Sciences, could offer new insights into how defective cells can multiply out of control in diseases such as cancer.

Their discovery comes in the same year as the 50^th anniversary of a landmark in the field of DNA replication — the presentation of the replicon model at the Cold Spring Harbor Symposium on DNA Replication in 1963 by François Jacob, who was later awarded the Nobel Prize in Medicine.

Dr Thorsten Allers said: “Sadly François Jacob passed away this year, but 50 years after this theory was presented it still guides the investigation of DNA replication.

“Given this anniversary, our paper in Nature is rather timely. We have shown that in some organisms, the replication origins — genetic switches that control DNA replication — are not only unnecessary but cells will actually grow faster when these origins are not present. This is totally unexpected and has forced us to re-evaluate one of the cornerstones of DNA biology.”

The paper, Accelerated Growth in the Absence of DNA Replication Origins, was co-authored by Dr Thorsten Allers, Dr Conrad Nieduszynski and Dr Michelle Hawkins in the University’s School of Life Sciences in collaboration with Dr Sunir Malla and Dr Martin Blythe in DeepSeq, the School’s state-of-the-art DNA deep sequencing laboratory.

Archaea were originally discovered in extreme environments and can survive at very high or very low temperatures, or in highly salty, acidic or alkaline water. They form one of the three distinct branches of life along with bacteria and eukaryotes, which are multi-celled organisms including humans, other animals, plants and fungi. At a genetic level, archaea have been found to be more closely related to eukaryotes, and therefore humans, than to bacteria. The salt-lovingHaloferax volcanii being studied by the Nottingham scientists originates from the Dead Sea.

Dr Allers added: “Although they look like bacteria and behave like bacteria, archaea are actually more closely related to us. Where we really see the similarities is when we look at the enzymes that are responsible for DNA replication and that’s why we thought this would be an interesting system to work on. We’ve got something that’s life but not as we know it: on the outside they look like bacteria but on the inside they look like us.”

“What we’ve discovered is that in this type of archaea, François Jacob’s replicon model, which was proposed 50 years ago and was thought by everybody to be absolutely fundamental to life, is not necessarily true.”

In order to reproduce, all life forms need to copy their DNA before the cell can divide. They do this via a series of ‘replication origins’ that are located around their chromosomes and to which proteins bind in order to start the replication process.

In eukaryotes such as humans if these replication origins are eliminated it prevents replication and eventually leads to cell death.

However, the Nottingham study, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Royal Society, found that the Haloferax volcanii is able to spontaneously begin a chain reaction of replication all around its chromosomes even when its replication origins have been eliminated.

In addition, the scientists discovered that far from being disadvantaged by having to employ this novel survival method, the archaea without chromosomal origins grew faster.

“The amazing thing that we found wasn’t just that deleting the origins still allowed the cells to grow, but that they now actually grew almost 10 per cent faster. Everybody was thinking, ‘where’s the catch?’ But we haven’t found one” Dr Conrad Nieduszynski said.

“The way cells initiates this replication process is to use a form of DNA repair that exists in all of us, but they just hijack this process for a different purpose. By using this mechanism, they kick-start replication at multiple sites around the chromosome at the same time.”

Since it appears that origins are unnecessary in Haloferax volcanii,the scientists believe that replication origins in this organism could be an example of a ‘selfish gene’ — benefitting the origins by offering the chance to be continually replicated while offering no advantage to the organism itself.

For humans it is very important that we can regulate this process of DNA replication to ensure that our chromosomes are only copied once before the cell divides, otherwise this can lead to genetic diseases including cancer.

When cancer cells develop they no longer regulate the copying of their genome — this happens because of mutations in the genes that control this process. Loss of replication control leads to cancer cells making more than just two copies of their chromosomes, which is something they have in common with what the scientists observed in Haloferax volcanii.

Dr Allers said: “Scientists think that cancer cells revert back to a more primitive state without these forms of control. This is how they resemble Haloferax volcanii. One of the other hallmarks of cancer cells is that grow faster than ordinary cells and can quickly take over the body. This is similar to what we are seeing — when you don’t regulate DNA replication and dispense with the normal checks and balances, you can have unregulated, faster growth.”

In the future if we can understand this mechanism it could give us an insight into how cancer cells can escape normal regulation and control. It could even identify new targets for killing cancer cells without harming normal cells
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Global Warming Led to Dwarfism in Mammals -- Twice

Nov. 2, 2013 — Mammal body size decreased significantly during at least two ancient global warming events. A new finding that suggests a similar outcome is possible in response to human-caused climate change, according to a University of Michigan paleontologist and his colleagues.

Researchers have known for years that mammals such as primates and the groups that include horses and deer became much smaller during a period of warming, called the Paleocene-Eocene Thermal Maximum (PETM), about 55 million years ago.

Now U-M paleontologist Philip Gingerich and his colleagues have found evidence that mammalian "dwarfing" also occurred during a separate, smaller global warming event that occurred about 2 million years after the PETM, around 53 million years ago.

"The fact that it happened twice significantly increases our confidence that we're seeing cause and effect, that one interesting response to global warming in the past was a substantial decrease in body size in mammalian species," said Gingerich, a professor of earth and environmental sciences.

The research team also includes scientists from the University of New Hampshire, Colorado College and the California Institute of Technology. The researchers are scheduled to present their findings Friday, Nov. 1, in Los Angeles at the annual meeting of the Society of Vertebrate Paleontology.

They concluded that decreased body size "seems to be a common evolutionary response" by mammals to extreme global warming events, known as hyperthermals, "and thus may be a predictable natural response for some lineages to future global warming."

The PETM lasted about 160,000 years, and global temperatures rose an estimated 9 to 14 degrees Fahrenheit at its peak. The smaller, later event analyzed in the latest study, known as ETM2 (Eocene Thermal Maximum 2), lasted 80,000 to 100,000 years and resulted in a peak temperature increase of about 5 degrees Fahrenheit.

Teeth and jaw fossils of early hoofed mammals and primates that spanned this later climatic event were collected in Wyoming's Bighorn Basin, and the size of molar teeth was used as a proxy for body size. The researchers found that body size decreased during ETM2, but not as much as the dwarfism seen in PETM fossils.

For example, the study revealed that a lineage of early horses the size of a small dog, called Hyracotherium, experienced a body-size decrease of about 19 percent during ETM2. The same horse lineage showed a body-size decrease of about 30 percent during the PETM. After both events, the animals rebounded to their pre-warming size.

"Interestingly, the extent of mammalian dwarfism may be related to the magnitude of the hyperthermal event," said team member Abigail D'Ambrosia of the University of New Hampshire.

An ancient ungulate called Diacodexis decreased about 20 percent in size during ETM2, and the primate Cantius decreased 8 percent.

The burning of fossil fuels and the resulting release of heat-trapping greenhouse gases -- mainly carbon dioxide -- is blamed for present-day climate warming. The ancient warming events may have been caused by the release of seabed methane clathrates, a kind of methane ice found in ocean sediments, though this topic remains an area of active research, Gingerich said. Methane is a more potent greenhouse gas than carbon dioxide, and atmospheric methane is eventually transformed into carbon dioxide and water.

The parallels between ancient hyperthermals and modern-day warming make studies of the fossil record particularly valuable, said team member Will Clyde of the University of New Hampshire.

"Developing a better understanding of the relationship between mammalian body size change and greenhouse gas-induced global warming during the geological past may help us predict ecological changes that may occur in response to current changes in Earth's climate," Clyde said.

In 2006, Gingerich proposed that mammalian dwarfing could be a response to the lower nutritional value of plants grown under elevated carbon dioxide levels. Under such conditions, plants grow quickly but are less nutritious than they would normally be.

Animals eating such plants might adapt by becoming smaller over time. Evidence from the ETM2 fossils is consistent with that hypothesis, and research on the topic is ongoing, Gingerich said.

The research was funded by the National Science Foundation (EAR0958821), Geological Society of America, Paleontological Society and Sigma Xi
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Synaptic Transistor Learns While It Computes

Nov. 2, 2013 — It doesn't take a Watson to realize that even the world's best supercomputers are staggeringly inefficient and energy-intensive machines.

Our brains have upwards of 86 billion neurons, connected by synapses that not only complete myriad logic circuits; they continuously adapt to stimuli, strengthening some connections while weakening others. We call that process learning, and it enables the kind of rapid, highly efficient computational processes that put Siri and Blue Gene to shame.

Materials scientists at the Harvard School of Engineering and Applied Sciences (SEAS) have now created a new type of transistor that mimics the behavior of a synapse. The novel device simultaneously modulates the flow of information in a circuit and physically adapts to changing signals.

Exploiting unusual properties in modern materials, the synaptic transistor could mark the beginning of a new kind of artificial intelligence: one embedded not in smart algorithms but in the very architecture of a computer. The findings appear in Nature Communications.

"There's extraordinary interest in building energy-efficient electronics these days," says principal investigator Shriram Ramanathan, associate professor of materials science at Harvard SEAS. "Historically, people have been focused on speed, but with speed comes the penalty of power dissipation. With electronics becoming more and more powerful and ubiquitous, you could have a huge impact by cutting down the amount of energy they consume."

The human mind, for all its phenomenal computing power, runs on roughly 20 Watts of energy (less than a household light bulb), so it offers a natural model for engineers.

"The transistor we've demonstrated is really an analog to the synapse in our brains," says co-lead author Jian Shi, a postdoctoral fellow at SEAS. "Each time a neuron initiates an action and another neuron reacts, the synapse between them increases the strength of its connection. And the faster the neurons spike each time, the stronger the synaptic connection. Essentially, it memorizes the action between the neurons."

In principle, a system integrating millions of tiny synaptic transistors and neuron terminals could take parallel computing into a new era of ultra-efficient high performance.

While calcium ions and receptors effect a change in a biological synapse, the artificial version achieves the same plasticity with oxygen ions. When a voltage is applied, these ions slip in and out of the crystal lattice of a very thin (80-nanometer) film of samarium nickelate, which acts as the synapse channel between two platinum "axon" and "dendrite" terminals. The varying concentration of ions in the nickelate raises or lowers its conductance -- that is, its ability to carry information on an electrical current -- and, just as in a natural synapse, the strength of the connection depends on the time delay in the electrical signal.

Structurally, the device consists of the nickelate semiconductor sandwiched between two platinum electrodes and adjacent to a small pocket of ionic liquid. An external circuit multiplexer converts the time delay into a magnitude of voltage which it applies to the ionic liquid, creating an electric field that either drives ions into the nickelate or removes them. The entire device, just a few hundred microns long, is embedded in a silicon chip.

The synaptic transistor offers several immediate advantages over traditional silicon transistors. For a start, it is not restricted to the binary system of ones and zeros.

"This system changes its conductance in an analog way, continuously, as the composition of the material changes," explains Shi. "It would be rather challenging to use CMOS, the traditional circuit technology, to imitate a synapse, because real biological synapses have a practically unlimited number of possible states -- not just 'on' or 'off.'"

The synaptic transistor offers another advantage: non-volatile memory, which means even when power is interrupted, the device remembers its state.

Additionally, the new transistor is inherently energy efficient. The nickelate belongs to an unusual class of materials, called correlated electron systems, that can undergo an insulator-metal transition. At a certain temperature -- or, in this case, when exposed to an external field -- the conductance of the material suddenly changes.

"We exploit the extreme sensitivity of this material," says Ramanathan. "A very small excitation allows you to get a large signal, so the input energy required to drive this switching is potentially very small. That could translate into a large boost for energy efficiency."

The nickelate system is also well positioned for seamless integration into existing silicon-based systems.

"In this paper, we demonstrate high-temperature operation, but the beauty of this type of a device is that the 'learning' behavior is more or less temperature insensitive, and that's a big advantage," says Ramanathan. "We can operate this anywhere from about room temperature up to at least 160 degrees Celsius."

For now, the limitations relate to the challenges of synthesizing a relatively unexplored material system, and to the size of the device, which affects its speed.

"In our proof-of-concept device, the time constant is really set by our experimental geometry," says Ramanathan. "In other words, to really make a super-fast device, all you'd have to do is confine the liquid and position the gate electrode closer to it."

In fact, Ramanathan and his research team are already planning, with microfluidics experts at SEAS, to investigate the possibilities and limits for this "ultimate fluidic transistor."

He also has a seed grant from the National Academy of Sciences to explore the integration of synaptic transistors into bioinspired circuits, with L. Mahadevan, Lola England de Valpine Professor of Applied Mathematics, professor of organismic and evolutionary biology, and professor of physics.

"In the SEAS setting it's very exciting; we're able to collaborate easily with people from very diverse interests," Ramanathan says.

For the materials scientist, as much curiosity derives from exploring the capabilities of correlated oxides (like the nickelate used in this study) as from the possible applications.

"You have to build new instrumentation to be able to synthesize these new materials, but once you're able to do that, you really have a completely new material system whose properties are virtually unexplored," Ramanathan says. "It's very exciting to have such materials to work with, where very little is known about them and you have an opportunity to build knowledge from scratch."

"This kind of proof-of-concept demonstration carries that work into the 'applied' world," he adds, "where you can really translate these exotic electronic properties into compelling, state-of-the-art devices."

This research was supported by the National Science Foundation (NSF), the Army Research Office's Multidisciplinary University Research Initiative, and the Air Force Office of Scientific Research. The team also benefited from the facilities at the Harvard Center for Nanoscale Systems, a member of the NSF-supported National Nanotechnology Infrastructure Network. Sieu D. Ha, a postdoctoral fellow at SEAS, was the co-lead author; additional coauthors included graduate student You Zhou and Frank Schoofs, a former postdoctoral fellow.

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Surprising Variation Among Genomes of Individual Neurons from Same Brain

Nov. 1, 2013 — It was once thought that each cell in a person's body possesses the same DNA code and that the particular way the genome is read imparts cell function and defines the individual. For many cell types in our bodies, however, that is an oversimplification. Studies of neuronal genomes published in the past decade have turned up extra or missing chromosomes, or pieces of DNA that can copy and paste themselves throughout the genomes.

The only way to know for sure that neurons from the same person harbor unique DNA is by profiling the genomes of single cells instead of bulk cell populations, the latter of which produce an average. Now, using single-cell sequencing, Salk Institute researchers and their collaborators have shown that the genomic structures of individual neurons differ from each other even more than expected. The findings were published November 1 in Science.

"Contrary to what we once thought, the genetic makeup of neurons in the brain aren't identical, but are made up of a patchwork of DNA," says corresponding author Fred Gage, Salk's Vi and John Adler Chair for Research on Age-Related Neurodegenerative Disease.

In the study, led by Mike McConnell, a former junior fellow in the Crick-Jacobs Center for Theoretical and Computational Biology at the Salk, researchers isolated about 100 neurons from three people posthumously. The scientists took a high-level view of the entire genome -- -- looking for large deletions and duplications of DNA called copy number variations or CNVs -- -- and found that as many as 41 percent of neurons had at least one unique, massive CNV that arose spontaneously, meaning it wasn't passed down from a parent. The CNVs are spread throughout the genome, the team found.

The miniscule amount of DNA in a single cell has to be chemically amplified many times before it can be sequenced. This process is technically challenging, so the team spent a year ruling out potential sources of error in the process.

"A good bit of our study was doing control experiments to show that this is not an artifact," says Gage. "We had to do that because this was such a surprise -- -- finding out that individual neurons in your brain have different DNA content."

The group found a similar amount of variability in CNVs within individual neurons derived from the skin cells of three healthy people. Scientists routinely use such induced pluripotent stem cells (iPSCs) to study living neurons in a culture dish. Because iPSCs are derived from single skin cells, one might expect their genomes to be the same.

"The surprising thing is that they're not," says Gage. "There are quite a few unique deletions and amplifications in the genomes of neurons derived from one iPSC line."

Interestingly, the skin cells themselves are genetically different, though not nearly as much as the neurons. This finding, along with the fact that the neurons had unique CNVs, suggests that the genetic changes occur later in development and are not inherited from parents or passed to offspring.

It makes sense that neurons have more diverse genomes than skin cells do, says McConnell, who is now an assistant professor of biochemistry and molecular genetics at the University of Virginia School of Medicine in Charlottesville. "The thing about neurons is that, unlike skin cells, they don't turn over, and they interact with each other," he says. "They form these big complex circuits, where one cell that has CNVs that make it different can potentially have network-wide influence in a brain."

Spontaneously occurring CNVs have also been linked to risk for brain disorders such as schizophrenia and autism, but those studies usually pool many blood cells. As a result, the CNVs uncovered in those studies affect many if not all cells, which suggests that they arise early in development.

The purpose of CNVs in the healthy brain is still unclear, but researchers have some ideas. The modifications might help people adapt to new surroundings encountered over a lifetime, or they might help us survive a massive viral infection. The scientists are working out ways to alter genomic variability in iPSC-derived neurons and challenge them in specific ways in the culture dish.

Cells with different genomes probably produce unique RNA and then proteins. However, for now, only one sequencing technology can be applied to a single cell.

"If and when more than one method can be applied to a cell, we will be able to see whether cells with different genomes have different transcriptomes (the collection of all the RNA in a cell) in predictable ways," says McConnell.

In addition, it will be necessary to sequence many more cells, and in particular, more cell types, notes corresponding author Ira Hall, an associate professor of biochemistry and molecular genetics at the University of Virginia. "There's a lot more work to do to really understand to what level we think the things we've found are neuron-specific or associated with different parameters like age or genotype," he says.

Other authors on the study are Michael Lindberg and Svetlana Shumilina of the Department of Biochemistry and Molecular Genetics at the University of Virginia School of Medicine; Kristen Brennand, now at the Icahn School of Medicine at Mount Sinai in New York; Julia Piper, now at Harvard University in Cambridge, Massachusetts; Thierry Voet and Joris Vermeesch of the Center for Human Genetics, KU Leuven, Leuven, Belgium; Chris Cowing-Zitron of Salk's Laboratory of Genetics; and Roger Lasken of the J. Craig Venter Institute in San Diego.

This work was supported by the Crick-Jacobs Center for Theoretical and Computational Biology, the G. Harold & Leila Y. Mathers Foundation, the National Institutes of Health, the Leona M. and Harry B. Helmsley Charitable Trust, the JPB Foundation, and the Burroughs Wellcome Fund
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Magnetic 'Force Field' Shields Giant Gas Cloud During Collision With Milky Way

Oct. 31, 2013 — Doom may be averted for the Smith Cloud, a gigantic streamer of hydrogen gas that is on a collision course with the Milky Way Galaxy. Astronomers using the National Science Foundation's Karl G. Jansky Very Large Array (VLA) and Robert C. Byrd Green Bank Telescope (GBT) have discovered a magnetic field deep in the cloud's interior, which may protect it during its meteoric plunge into the disk of our Galaxy.

This discovery could help explain how so-called high velocity clouds (HVCs) remain mostly intact during their mergers with the disks of galaxies, where they would provide fresh fuel for a new generation of stars.

Currently, the Smith Cloud is hurtling toward the Milky Way at more than 150 miles per second and is predicted to impact in approximately 30 million years. When it does, astronomers believe, it will set off a spectacular burst of star formation. But first, it has to survive careening through the halo, or atmosphere, of hot ionized gas surrounding the Milky Way.

"The million-degree upper atmosphere of the Galaxy ought to destroy these hydrogen clouds before they ever reach the disk, where most stars are formed," said Alex Hill, an astronomer at Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) and lead author of a paper published in theAstrophysical Journal. "New observations reveal one of these clouds in the process of being shredded, but a protective magnetic field shields the cloud and may help it survive its plunge."

Many hundreds of HVCs zip around our Galaxy, but their obits seldom correspond to the rotation of the Milky Way. This leads astronomers to believe that HVCs are the left-over building blocks of galaxy formation or the splattered remains of a close galactic encounter billions of years ago.

Though massive, the gas that makes up HVCs is very tenuous, and computer simulations predict that they lack the necessary heft to survive plunging through the halo and into the disk of the Milky Way.

"We have long had trouble understanding how HVCs reach the Galactic disk," said Hill. "There's good reason to believe that magnetic fields can prevent their 'burning up' in the halo like a meteorite burning up in Earth's atmosphere."

Despite being the best evidence yet for a magnetic field inside an HVC, the origin of the Smith Cloud's field remains a mystery. "The field we observe now is too large to have existed in its current state when the cloud was formed," said Hill. "The field was probably magnified by the cloud's motion through the halo."

Earlier research indicates the Smith Cloud has already survived punching through the disk of our Galaxy once and -- at about 8,000 light-years from the disk -- is just beginning its re-entry now.

"The Smith Cloud is unique among high-velocity clouds because it is so clearly interacting with and merging with the Milky Way," said Felix J. Lockman, an astronomer at the National Radio Astronomy Observatory (NRAO) in Green Bank, W.Va. "Its comet-like appearance indicates it's already feeling the Milky Way's influence."

Since the Smith Cloud appears to be devoid of stars, the only way to observe it is with exquisitely sensitive radio telescopes, like the GBT, which can detect the faint emission of neutral hydrogen. If it were visible with the naked eye, the Smith Cloud would cover almost as much sky as the constellation Orion.

When the Smith Cloud eventually merges with the Milky Way, it could produce a bright ring of stars similar to the one relatively close to our Sun known as Gould's Belt.

"Our Galaxy is in an incredibly dynamic environment," concludes Hill, "and how it interacts with that environment determines whether stars like the Sun will continue to form."

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc
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