These new radio observations, which are the highest sensitivity of their kind ever undertaken, reveal that within a well-defined boundary around our Galaxy, dwarf galaxies are completely devoid of hydrogen gas; beyond this point, dwarf galaxies are teeming with star-forming material.
The Milky Way Galaxy is actually the largest member of a compact clutch of galaxies that are bound together by gravity. Swarming around our home Galaxy is a menagerie of smaller dwarf galaxies, the smallest of which are the relatively nearby dwarf spheroidals, which may be the leftover building blocks of galaxy formation. Further out are a number of similarly sized and slightly misshaped dwarf irregular galaxies, which are not gravitationally bound to the Milky Way and may be relative newcomers to our galactic neighborhood.
“Astronomers wondered if, after billions of years of interaction, the nearby dwarf spheroidal galaxies have all the same star-forming ‘stuff’ that we find in more distant dwarf galaxies,” said astronomer Kristine Spekkens, assistant professor at the Royal Military College of Canada and lead author on a paper published in the Astrophysical Journal Letters.
Previous studies have shown that the more distant dwarf irregular galaxies have large reservoirs of neutral hydrogen gas, the fuel for star formation. These past observations, however, were not sensitive enough to rule out the presence of this gas in the smallest dwarf spheroidal galaxies.
By bringing to bear the combined power of the GBT (the world’s largest fully steerable radio telescope) and other giant telescopes from around the world, Spekkens and her team were able to probe the dwarf galaxies that have been swarming around the Milky Way for billions of years for tiny amounts of atomic hydrogen.
“What we found is that there is a clear break, a point near our home Galaxy where dwarf galaxies are completely devoid of any traces of neutral atomic hydrogen,” noted Spekkens. Beyond this point, which extends approximately 1,000 light-years from the edge of the Milky Way’s star-filled disk to a point that is thought to coincide with the edge of its dark matter distribution, dwarf spheroidals become vanishingly rare while their gas-rich, dwarf irregular counterparts flourish.
There are many ways that larger, mature galaxies can lose their star-forming material, but this is mostly tied to furious star formation or powerful jets of material driven by supermassive black holes. The dwarf galaxies that orbit the Milky Way contain neither of these energetic processes. They are, however, susceptible to the broader influences of the Milky Way, which itself resides within an extended, diffuse halo of hot hydrogen plasma.
The researchers believe that, up to a certain distance from the galactic disk, this halo is dense enough to affect the composition of dwarf galaxies. Within this “danger zone,” the pressure created by the million-mile-per-hour orbital velocities of the dwarf spheroidals can actually strip away any detectable traces of neutral hydrogen. The Milky Way thus shuts down star formation in its smallest neighbors.
“These observations therefore reveal a great deal about size of the hot halo and about how companions orbit the Milky Way,” concludes Spekkens.
Reference: Kristine Spekkens, Natasha Urbancic, Brian S. Mason, Beth Willman, James E. Aguirre. THE DEARTH OF NEUTRAL HYDROGEN IN GALACTIC DWARF SPHEROIDAL GALAXIES. The Astrophysical Journal, 2014; 795 (1): L5 DOI: 10.1088/2041-8205/795/1/L5
Fresh research into a group of prehistoric marine crocs known as Machimosaurus reveals key details of how and where they lived.
Each species adapted features that enabled them to live and hunt in a range of habitats, just like modern-day crocodiles. They varied in body length, body skeleton, skull and lower jaw shape, and in their teeth.
The ancient croc group included a nine-metre long saltwater species, which was adapted for living in open seas, and fed on marine turtles. Its closest relatives, by contrast, lived in coastal, choppy environments.
The prehistoric crocs’ development mirrors those of today’s crocodiles, whose saltwater varieties are far bigger and suited to larger territories compared with their smaller cousins that live closer to shore or in freshwater.
A team of researchers, led by the University of Edinburgh, examined fossil specimens from museums around Europe. From detailed analysis, they were able to determine key elements of the animals’ anatomy and lifestyle, and concluded that not all were of the same species.
Until now, scientists were unsure whether more than one species of Machimosaurus existed. However, their findings show that there were at least three distinct species — one of which has been fully identified for the first time. The study is published in the journal Royal Society Open Science.
Dr Mark Young, of the University of Edinburgh’s School of GeoSciences, who led the study, said: “Interesting parallels can be seen between groups of ancient crocodiles and those living today, with some able to swim out in the open sea, with others restricted to the coast. With more fossils being discovered, we look forward to learning more about this giant group of Jurassic predators.”
Reference: Mark T. Young, Stéphane Hua, Lorna Steel, Davide Foffa, Stephen L. Brusatte, Silvan Thüring, Octávio Mateus, José Ignacio Ruiz-Omeñaca, Philipe Havlik, Yves Lepage, Marco Brandalise De Andrade. Revision of the Late Jurassic teleosaurid genus Machimosaurus (Crocodylomorpha, Thalattosuchia). Royal Society Open Science, 2014; 1:140222 DOI: 10.1098/rsos.140222
It’s not as bizarre as it sounds. Earth’s magnetic field has flipped — though not overnight — many times throughout the planet’s history. Its dipole magnetic field, like that of a bar magnet, remains about the same intensity for thousands to millions of years, but for incompletely known reasons it occasionally weakens and, presumably over a few thousand years, reverses direction.
Now, a new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the last magnetic reversal 786,000 years ago actually happened very quickly, in less than 100 years — roughly a human lifetime.
“It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”
Sprain and Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in- residence of earth and planetary science, are coauthors of the study, which will be published in the November issue of Geophysical Journal International and is now available online.
Flip could affect electrical grid, cancer rates
The discovery comes as new evidence indicates that the intensity of Earth’s magnetic field is decreasing 10 times faster than normal, leading some geophysicists to predict a reversal within a few thousand years.
Though a magnetic reversal is a major planet-wide event driven by convection in Earth’s iron core, there are no documented catastrophes associated with past reversals, despite much searching in the geologic and biologic record. Today, however, such a reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down.
And since Earth’s magnetic field protects life from energetic particles from the sun and cosmic rays, both of which can cause genetic mutations, a weakening or temporary loss of the field before a permanent reversal could increase cancer rates. The danger to life would be even greater if flips were preceded by long periods of unstable magnetic behavior.
“We should be thinking more about what the biologic effects would be,” Renne said.
Dating ash deposits from windward volcanoes
The new finding is based on measurements of the magnetic field alignment in layers of ancient lake sediments now exposed in the Sulmona basin of the Apennine Mountains east of Rome, Italy. The lake sediments are interbedded with ash layers erupted from the Roman volcanic province, a large area of volcanoes upwind of the former lake that includes periodically erupting volcanoes near Sabatini, Vesuvius and the Alban Hills.
Italian researchers led by Leonardo Sagnotti of Rome’s National Institute of Geophysics and Volcanology measured the magnetic field directions frozen into the sediments as they accumulated at the bottom of the ancient lake.
Sprain and Renne used argon-argon dating, a method widely used to determine the ages of rocks, whether they’re thousands or billions of years old, to determine the age of ash layers above and below the sediment layer recording the last reversal. These dates were confirmed by their colleague and former UC Berkeley postdoctoral fellow Sebastien Nomade of the Laboratory of Environmental and Climate Sciences in Gif-Sur-Yvette, France.
Because the lake sediments were deposited at a high and steady rate over a 10,000-year period, the team was able to interpolate the date of the layer showing the magnetic reversal, called the Matuyama-Brunhes transition, at approximately 786,000 years ago. This date is far more precise than that from previous studies, which placed the reversal between 770,000 and 795,000 years ago.
“What’s incredible is that you go from reverse polarity to a field that is normal with essentially nothing in between, which means it had to have happened very quickly, probably in less than 100 years,” said Renne. “We don’t know whether the next reversal will occur as suddenly as this one did, but we also don’t know that it won’t.”
Unstable magnetic field preceded 180-degree flip
Whether or not the new finding spells trouble for modern civilization, it likely will help researchers understand how and why Earth’s magnetic field episodically reverses polarity, Renne said.
The magnetic record the Italian-led team obtained shows that the sudden 180-degree flip of the field was preceded by a period of instability that spanned more than 6,000 years. The instability included two intervals of low magnetic field strength that lasted about 2,000 years each. Rapid changes in field orientations may have occurred within the first interval of low strength. The full magnetic polarity reversal — that is, the final and very rapid flip to what the field is today — happened toward the end of the most recent interval of low field strength.
Renne is continuing his collaboration with the Italian-French team to correlate the lake record with past climate change.
Reference: L. Sagnotti, G. Scardia, B. Giaccio, J. C. Liddicoat, S. Nomade, P. R. Renne, C. J. Sprain. Extremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal. Geophysical Journal International, 2014; 199 (2): 1110 DOI: 10.1093/gji/ggu287
They’re the oldest identified fossils displaying the creature in stages of pre-metamorphosis and metamorphosis.
“Among animals with backbones, everything, including us, evolved from jawless fishes,” said Desui Miao, University of Kansas Biodiversity Institute collection manager, who co-authored today’s PNAS paper. “To understand the whole arc of vertebrate evolution, we need to know these animals. The biology of the lamprey holds a molecular clock to date when many evolutionary events occurred.”
Miao said features of the human body come from the jawless fishes, such as the lamprey, a slowly evolving organism — often parasitic — which has inhabited Earth at least since the Devonian, about 400 million years ago.
“For example, a jawless fish such as a lamprey has seven pairs of gill arches, and the anterior pair of these gill arches evolved into our upper and lower jaws,” he said. “Our middle ear bones? They come from the same pair of gill arches.”
Indeed, lamprey evolution sheds light on the development of all animals with a backbone. Because of this, scientists have yearned to discover more history about the stages of the aquatic creature’s three-phased life cycle.
However, lamprey larvae are small and soft, thus seldom fossilized.
“They just don’t have hard parts,” Miao said. “Even fully developed fossil lampreys are rare because they lack skeletons. Most fossil fishes are bony fishes — fish we eat and leave bones on the plate. But lampreys don’t have bones or teeth that can be preserved as fossils.”
Fortunately, during the lush Lower Cretaceous era, freshwater lakes covered Inner Mongolia. These waters were chock-full with the ancestors of today’s lampreys, and many fossils became beautifully preserved in a layer of late-Cretaceous shale, including larvae.
“This type of rock preserves very fine details of fossils,” Miao said. “The same rock preserved evidence of dinosaur feathers from this era. The lamprey larvae were found by local people and some by our Chinese colleagues who specialize in early fishes.”
According to the KU researcher and fellow authors Meemann Chang, Feixiang Wu and Jiangyong Zhang of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing, the larval fossils show the life cycle of the lamprey “emerged essentially in its present mode no later than the Early Cretaceous.”
This cycle consists of a long-lasting larval stage, a metamorphosis and a comparatively brief adulthood with a markedly different anatomy, according to the PNAS paper. The larvae come from the fossil lamprey species Mesomyzon mangae.
“Our larvae look modern,” Miao said. “The developmental stage is almost identical to today’s lamprey. Before this, we didn’t know how long lampreys have developed via metamorphosis. Now, we know it goes back 125 million years at least. In other words, lampreys haven’t changed much — and that’s very interesting.”
Then, like today, lampreys lived in both freshwater and saltwater. At the larval stage, they’d have dwelled in the sand or mud and drawn nutrients from micro-organisms in the water. Then, as mature lampreys, some of them would have subsisted by fastening themselves to host organisms and swigging their blood — often killing their host in the end.
“They attach to larger fish or whales,” Miao said. “They hold on forever.”
Reference: M.-m. Chang, F. Wu, D. Miao, J. Zhang. Discovery of fossil lamprey larva from the Lower Cretaceous reveals its three-phased life cycle. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1415716111
The researchers used the radiation leak measurement method to help find the ideal star-forming galaxy that contained holes in its cold gas cover. Studying the radiation that seeps through these holes has been a conundrum for scientists for years.
Consisting of thick, dense cold gas, the cover stretches across a galaxy like a blanket. While an effective tool for helping make stars, this cover presents a challenge for astrophysicists hoping to learn how the radiation that stars produce could be used in the ionization process. Scientists have been on a quest for decades to find just the right galaxy with this character trait.
“It’s like the ozone layer, but in reverse,” Borthakur said. “The ozone layer protects us from the sun’s radiation but we want the gas cover the other way around. The star forming regions in galaxies are covered with cold gases so the radiation cannot come out. If we can find out how the radiation gets out of the galaxy, we can learn what mechanisms ionized the universe.”
Borthakur said scientists know that these leaky galaxies exist, but finding one has been a problem. This, in turn, makes it difficult for researchers to have a clearer understanding of how the reionization process works.
For star-gazers, reionization is core to the history of the cosmos as it marks the birth of the very first stars and galaxies.
Moments after the start of the Big Bang, the hot, newly born universe began to expand and quickly cool. Several hundred thousand years later, free proton and electron particles in the universe began to connect to each other and form neutral hydrogen atoms. The neutral gas began to collapse into the first stars and galaxies, which then began to radiate brightly.
Using observations made with the Cosmic Origin Spectrograph onboard the Hubble Space Telescope, the research team found the right galaxy to study. In the study, the researchers credit a combination of unusually strong winds, intense radiation and a massive, highly star-forming galaxy for proving the validity of the indicator.
This method, first created by Heckman in 2001, can sort out what gas is present and also accurately measure the percentage of holes in the gas cover, said Borthakur.
“The confirmation of the indicator is key,” she said. “The implications are now people can use this indicator to study distant galaxies at longer wavelengths.”
Reference: S. Borthakur, T. M. Heckman, C. Leitherer, R. A. Overzier. A local clue to the reionization of the universe. Science, 2014; 346 (6206): 216 DOI: 10.1126/science.1254214
“Going beyond the lab to allow the patient to face real-world challenges is the main contribution of this work,” says Max Ortiz Catalan, research scientist at Chalmers University of Technology and leading author of the publication.
“We have used osseointegration to create a long-term stable fusion between man and machine, where we have integrated them at different levels. The artificial arm is directly attached to the skeleton, thus providing mechanical stability. Then the human’s biological control system, that is nerves and muscles, is also interfaced to the machine’s control system via neuromuscular electrodes. This creates an intimate union between the body and the machine; between biology and mechatronics.”
The direct skeletal attachment is created by what is known as osseointegration, a technology in limb prostheses pioneered by associate professor Rickard Brånemark and his colleagues at Sahlgrenska University Hospital. Rickard Brånemark led the surgical implantation and collaborated closely with Max Ortiz Catalan and Professor Bo Håkansson at Chalmers University of Technology on this project.
The patient’s arm was amputated over ten years ago. Before the surgery, his prosthesis was controlled via electrodes placed over the skin. Robotic prostheses can be very advanced, but such a control system makes them unreliable and limits their functionality, and patients commonly reject them as a result.
Now, the patient has been given a control system that is directly connected to his own. He has a physically challenging job as a truck driver in northern Sweden, and since the surgery he has experienced that he can cope with all the situations he faces; everything from clamping his trailer load and operating machinery, to unpacking eggs and tying his children’s skates, regardless of the environmental conditions (read more about the benefits of the new technology below).
The patient is also one of the first in the world to take part in an effort to achieve long-term sensation via the prosthesis. Because the implant is a bidirectional interface, it can also be used to send signals in the opposite direction — from the prosthetic arm to the brain. This is the researchers’ next step, to clinically implement their findings on sensory feedback.
“Reliable communication between the prosthesis and the body has been the missing link for the clinical implementation of neural control and sensory feedback, and this is now in place,” says Max Ortiz Catalan. “So far we have shown that the patient has a long-term stable ability to perceive touch in different locations in the missing hand. Intuitive sensory feedback and control are crucial for interacting with the environment, for example to reliably hold an object despite disturbances or uncertainty. Today, no patient walks around with a prosthesis that provides such information, but we are working towards changing that in the very short term.”
The researchers plan to treat more patients with the novel technology later this year.
“We see this technology as an important step towards more natural control of artificial limbs,” says Max Ortiz Catalan. “It is the missing link for allowing sophisticated neural interfaces to control sophisticated prostheses. So far, this has only been possible in short experiments within controlled environments.”
More about: How the technology works
The new technology is based on the OPRA treatment (osseointegrated prosthesis for the rehabilitation of amputees), where a titanium implant is surgically inserted into the bone and becomes fixated to it by a process known as osseointegration (Osseo = bone). A percutaneous component (abutment) is then attached to the titanium implant to serve as a metallic bone extension, where the prosthesis is then fixated. Electrodes are implanted in nerves and muscles as the interfaces to the biological control system. These electrodes record signals which are transmitted via the osseointegrated implant to the prostheses, where the signals are finally decoded and translated into motions.
More about: Benefits of the new technology, compared to socket prostheses
Direct skeletal attachment by osseointegration means:
- Increased range of motion since there are no physical limitations by the socket — the patient can move the remaining joints freely
- Elimination of sores and pain caused by the constant pressure from the socket
- Stable and easy attachment/detachment
- Increased sensory feedback due to the direct transmission of forces and vibrations to the bone (osseoperception)
- The prosthesis can be worn all day, every day
- No socket adjustments required (there is no socket)
Implanting electrodes in nerves and muscles means that:
- Due to the intimate connection, the patients can control the prosthesis with less effort and more precisely, and can thus handle smaller and more delicate items.
- The close proximity between source and electrode also prevents activity from other muscles from interfering (cross-talk), so that the patient can move the arm to any position and still maintain control of the prosthesis.
- More motor signals can be obtained from muscles and nerves, so that more movements can be intuitively controlled in the prosthesis.
- After the first fitting of the controller, little or no recalibration is required because there is no need to reposition the electrodes on every occasion the prosthesis is worn (as opposed to superficial electrodes).
- Since the electrodes are implanted rather than placed over the skin, control is not affected by environmental conditions (cold and heat) that change the skin state, or by limb motions that displace the skin over the muscles. The control is also resilient to electromagnetic interference (noise from other electric devices or power lines) as the electrodes are shielded by the body itself.
- Electrodes in the nerves can be used to send signals to the brain as sensations coming from the prostheses.
Reference: M. Ortiz-Catalan, B. Hakansson, R. Branemark. An osseointegrated human-machine gateway for long-term sensory feedback and motor control of artificial limbs. Science Translational Medicine, 2014; 6 (257): 257re6 DOI: 10.1126/scitranslmed.3008933
Australian astronomers used a method developed almost 100 years ago to discover that the weight of dark matter in our own galaxy is 800,000,000,000 (or 8 x 1011) times the mass of the Sun.
They probed the edge of the Milky Way, looking closely, for the first time, at the fringes of the galaxy about 5 million billion kilometres from Earth.
Astrophysicist Dr Prajwal Kafle, from The University of Western Australia node of the International Centre for Radio Astronomy Research, said we have known for a while that most of the Universe is hidden.
“Stars, dust, you and me, all the things that we see, only make up about 4 per cent of the entire Universe,” he said.
“About 25 per cent is dark matter and the rest is dark energy.”
Dr Kafle, who is originally from Nepal, was able to measure the mass of the dark matter in the Milky Way by studying the speed of stars throughout the galaxy, including the edges, which had never been studied to this detail before.
He used a robust technique developed by British astronomer James Jeans in 1915 — decades before the discovery of dark matter.
Dr Kafle’s measurement helps to solve a mystery that has been haunting theorists for almost two decades.
“The current idea of galaxy formation and evolution, called the Lambda Cold Dark Matter theory, predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don’t see that,” Dr Kafle said.
“When you use our measurement of the mass of the dark matter the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see; the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy.”
University of Sydney astrophysicist Professor Geraint Lewis, who was also involved in the research, said the missing satellite problem had been “a thorn in the cosmological side for almost 15 years.”
“Dr Kafle’s work has shown that it might not be as bad as everyone thought, although there are still problems to overcome,” he said.
The study also presented a holistic model of the Milky Way, which allowed the scientists to measure several interesting things such as the speed required to leave the galaxy.
“Be prepared to hit 550 kilometres per second if you want to escape the gravitational clutches of our galaxy,” Dr Kafle said.
“A rocket launched from Earth needs just 11 kilometres per second to leave its surface, which is already about 300 times faster than the maximum Australian speed limit in a car!”
Reference: Prajwal Raj Kafle, Sanjib Sharma, Geraint F. Lewis, Joss Bland-Hawthorn. On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution. The Astrophysical Journal, 2014; 794 (1): 59 DOI: 10.1088/0004-637X/794/1/59