Biology
Researchers from the Centre for Ecological Research and Forestry Applications (CREAF) and the Autonomous University of Barcelona (UAB) have demonstrated, using a map of the potential distribution, the alpine marmot's capacity for adaptation in the fields of the Pyrenees. Its quick proliferation makes it a successful example of species introduct
At the end of the Pleistocene (10,000 years ago), the increase in temperatures brought an end to the alpine marmot (Marmota marmota) in the Pyrenees, but between 1950 and 1988, the French government introduced around 400 specimens into the Pyrenees. The first appearances in Spain date back to 1962-1964 in the valley of Otal (Huesca).
"As an herbivore that lives in colonies, its impact on the flora of the alpine and subalpine fields can be significant. In addition, it can be a key competitor for other herbivores that it coexists with, like the ptarmigan", Bernat Claramunt, main author and researcher in CREAF and in UAB, explains to SINC adding that the impact on the ptarmigan is "very low".
But to determine the magnitude of the direct or indirect effects of the presence of the alpine marmot on the alpine community, the team of scientists from CREAF-UAB, together with the association for environmental studies LUTRA, has ascertained the potential extent of the expansion of this species.
At the end of the Pleistocene (10,000 years ago), the increase in temperatures brought an end to the alpine marmot (Marmota marmota) in the Pyrenees, but between 1950 and 1988, the French government introduced around 400 specimens into the Pyrenees. The first appearances in Spain date back to 1962-1964 in the valley of Otal (Huesca).
"As an herbivore that lives in colonies, its impact on the flora of the alpine and subalpine fields can be significant. In addition, it can be a key competitor for other herbivores that it coexists with, like the ptarmigan", Bernat Claramunt, main author and researcher in CREAF and in UAB, explains to SINC adding that the impact on the ptarmigan is "very low".
But to determine the magnitude of the direct or indirect effects of the presence of the alpine marmot on the alpine community, the team of scientists from CREAF-UAB, together with the association for environmental studies LUTRA, has ascertained the potential extent of the expansion of this species.
The alpine marmot spreads into the Catalan Pyrenees.
Scientists have found evidence of a catastrophic event they believe was responsible for halting the birth of stars in a galaxy in the early Universe.
The researchers, led by Durham University's Department of Physics, observed the massive galaxy as it would have appeared just three billion years after the Big Bang when the Universe was a quarter of its present age.
According to their findings the galaxy exploded in a series of blasts trillions of times more powerful than any caused by an atomic bomb. The blasts happened every second for millions of years, the scientists said.
The explosions scattered the gas needed to form new stars by helping it escape the gravitational pull of the galaxy called SMM J1237+6203, effectively regulating its growth, the scientists added.
They believe the huge surge of energy was caused by either the outflow of debris from the galaxy's black hole or from powerful winds generated by dying stars called supernovae.
The research, funded by the Royal Society and the Royal Astronomical Society, is published in the Monthly Notices of the Royal Astronomical Society. Observations were carried out using the Gemini Observatory's Near-Infrared Integral Field Spectrometer (NIFS).
The researchers, led by Durham University's Department of Physics, observed the massive galaxy as it would have appeared just three billion years after the Big Bang when the Universe was a quarter of its present age.
According to their findings the galaxy exploded in a series of blasts trillions of times more powerful than any caused by an atomic bomb. The blasts happened every second for millions of years, the scientists said.
The explosions scattered the gas needed to form new stars by helping it escape the gravitational pull of the galaxy called SMM J1237+6203, effectively regulating its growth, the scientists added.
They believe the huge surge of energy was caused by either the outflow of debris from the galaxy's black hole or from powerful winds generated by dying stars called supernovae.
The research, funded by the Royal Society and the Royal Astronomical Society, is published in the Monthly Notices of the Royal Astronomical Society. Observations were carried out using the Gemini Observatory's Near-Infrared Integral Field Spectrometer (NIFS).
This is an observation showing gas in the galaxy SMM J1237+6203 seen using the Gemini Observatory’s Near-Infrared Integral Field Spectrometer (NIFS). The contours show how the blast of energy is traveling through the galaxy.Credit: Dave Alexander/Mark Swinbank, Durham University, and Gemini Observatory
Astronomers from the United States and Europe have used a gravitational lens -- a distant, light-bending clump of dark matter -- to make a new estimate of the Hubble constant, which determines the size and age of the universe.
A paper describing the work appears in the March issue of The Astrophysical Journal.
The Hubble constant has previously been calculated by using NASA's Hubble Space Telescope to look at distant supernovae, and by measurements of the cosmic microwave background -- radiation leftover from the Big Bang, said Chris Fassnacht, associate professor of physics at UC Davis. The new method provides an independent check on the other two, he said.
A gravitational lens is a distant object, such as a galaxy surrounded by dark matter, that exerts a gravitational pull on light passing through it. Other galaxies behind the lens, from our point of view, appear distorted. In the case of the object B1608+656, astronomers on Earth see four distorted images of the same background object.
Fassnacht began studying B1608+656 as a graduate student a decade ago. Because the mass distribution of the lens is now well understood as a result of recent Hubble Space Telescope observations, it is possible to use it to calculate the Hubble constant, he said.
It works something like this. Two photons of light leave the background galaxy at the same time and travel around the lens, their paths distorted in different ways by the gravitational field so that they arrive on Earth at slightly different times. Based on that time delay, it is possible to calculate the distance of the entire route, and then infer the Hubble constant.
A paper describing the work appears in the March issue of The Astrophysical Journal.
The Hubble constant has previously been calculated by using NASA's Hubble Space Telescope to look at distant supernovae, and by measurements of the cosmic microwave background -- radiation leftover from the Big Bang, said Chris Fassnacht, associate professor of physics at UC Davis. The new method provides an independent check on the other two, he said.
A gravitational lens is a distant object, such as a galaxy surrounded by dark matter, that exerts a gravitational pull on light passing through it. Other galaxies behind the lens, from our point of view, appear distorted. In the case of the object B1608+656, astronomers on Earth see four distorted images of the same background object.
Fassnacht began studying B1608+656 as a graduate student a decade ago. Because the mass distribution of the lens is now well understood as a result of recent Hubble Space Telescope observations, it is possible to use it to calculate the Hubble constant, he said.
It works something like this. Two photons of light leave the background galaxy at the same time and travel around the lens, their paths distorted in different ways by the gravitational field so that they arrive on Earth at slightly different times. Based on that time delay, it is possible to calculate the distance of the entire route, and then infer the Hubble constant.
This image taken by the Hubble Space Telescope shows gravitational lens B1608. The objects A, B, C and D are all images of the same background object, distorted by the lens. G1 and G2 are two galaxies within the lens itself.
Credit: Hubble Space Telescope
Credit: Hubble Space Telescope
Shortly after the Moon formed, an asteroid smacked into its southern hemisphere and gouged out a truly enormous crater, the South Pole-Aitken basin, almost 1,500 miles across and more than five miles deep.
"This is the biggest, deepest crater on the Moon -- an abyss that could engulf the United States from the East Coast through Texas," said Noah Petro of NASA's Goddard Space Flight Center in Greenbelt, Md. The impact punched into the layers of the lunar crust, scattering that material across the Moon and into space. The tremendous heat of the impact also melted part of the floor of the crater, turning it into a sea of molten rock.
That was just an opening shot. Asteroid bombardment over billions of years has left the lunar surface pockmarked with craters of all sizes, and covered with solidified lava, rubble, and dust. Glimpses of the original surface, or crust, are rare, and views into the deep crust are rarer still. Fortunately, a crater on the edge of the South Pole-Aitken basin may provide just such a view. Called the Apollo Basin and formed by the later impact of a smaller asteroid, it still measures a respectable 300 miles across.
"It's like going into your basement and digging a deeper hole," said Petro. "We believe the central part of the Apollo Basin may expose a portion of the Moon's lower crust. If correct, this may be one of just a few places on the Moon where we have a view into the deep lunar crust, because it's not covered by volcanic material as many other such deep areas are. Just as geologists can reconstruct Earth's history by analyzing a cross-section of rock layers exposed by a canyon or a road cut, we can begin to understand the early lunar history by studying what's being revealed in Apollo."
Petro presents his result Thursday, March 4 during the Lunar and Planetary Science meeting in Houston, Texas
"This is the biggest, deepest crater on the Moon -- an abyss that could engulf the United States from the East Coast through Texas," said Noah Petro of NASA's Goddard Space Flight Center in Greenbelt, Md. The impact punched into the layers of the lunar crust, scattering that material across the Moon and into space. The tremendous heat of the impact also melted part of the floor of the crater, turning it into a sea of molten rock.
That was just an opening shot. Asteroid bombardment over billions of years has left the lunar surface pockmarked with craters of all sizes, and covered with solidified lava, rubble, and dust. Glimpses of the original surface, or crust, are rare, and views into the deep crust are rarer still. Fortunately, a crater on the edge of the South Pole-Aitken basin may provide just such a view. Called the Apollo Basin and formed by the later impact of a smaller asteroid, it still measures a respectable 300 miles across.
"It's like going into your basement and digging a deeper hole," said Petro. "We believe the central part of the Apollo Basin may expose a portion of the Moon's lower crust. If correct, this may be one of just a few places on the Moon where we have a view into the deep lunar crust, because it's not covered by volcanic material as many other such deep areas are. Just as geologists can reconstruct Earth's history by analyzing a cross-section of rock layers exposed by a canyon or a road cut, we can begin to understand the early lunar history by studying what's being revealed in Apollo."
Petro presents his result Thursday, March 4 during the Lunar and Planetary Science meeting in Houston, Texas
This elevation map covering the eastern portion of South Pole-Aitken basin, including the Apollo Basin, was made using data from Japan’s Kaguya spacecraft. The false colors indicate height; red represents highlands, and blue represents the lowest areas. Dashed circles mark the location of the main and inner ring of Apollo.Credit: Japan Aerospace Exploration Agency/NASA
Digger wasps of the genus Philanthus, so-called beewolves, house beneficial bacteria on their cocoons that guarantee protection against harmful microorganisms. Scientists of the Max Planck Institute for Chemical Ecology in Jena teamed up with researchers at the University of Regensburg and the Jena Leibniz Institute for Natural Product Research – Hans-Knoell-Institute - and discovered that bacteria of the genus Streptomyces produce a cocktail of nine different antibiotics and thereby fend off invading pathogens. Using imaging techniques based on mass spectrometry, the antibiotics could be displayed in vivo on the cocoon's exterior surface. Moreover, it was shown that the use of different kinds of antibiotics provides an effective protection against infection with a multitude of different pathogenic microorganisms. Thus, for millions of years beewolves have been taking advantage of a principle that is known as combination prophylaxis in human medicine. (Nature Chemical Biology, Advance Online Publication, February 28, 2010)
Many insects spend a part of their life underground and are exposed to the risk of fungal or bacterial infections. This is also the case for many digger wasp species that construct underground nests. Unlike bees that use pollen and nectar as food to nurture their larvae, digger wasps hunt insects to feed their offspring. Because of the warm and humid conditions as well as the large amounts of organic material in their subterranean nest, both their food supply and their larvae are endangered by pathogens - mold and bacterial infection are a major threat and can cause larval death in many cases.
Symbiosis with bacteria increases survival rate of beewolf larvae
Beewolves, i.e. digger wasps that hunt for bees to feed their larvae, have evolved an elegant solution to the problem of fungal and bacterial infection. Martin Kaltenpoth and colleagues from the University of Wurzburg had already shown several years ago that beewolves form a symbiotic relationship with bacteria of the genus Streptomyces. Female beewolves cultivate these bacteria in specialized antennal gland reservoirs and apply them to the ceiling of the brood cells. Beewolf larvae later take up the bacteria and transfer the symbionts actively to their cocoons, thereby increasing their survival probability. However, it has been unclear so far how the protection is achieved.
Many insects spend a part of their life underground and are exposed to the risk of fungal or bacterial infections. This is also the case for many digger wasp species that construct underground nests. Unlike bees that use pollen and nectar as food to nurture their larvae, digger wasps hunt insects to feed their offspring. Because of the warm and humid conditions as well as the large amounts of organic material in their subterranean nest, both their food supply and their larvae are endangered by pathogens - mold and bacterial infection are a major threat and can cause larval death in many cases.
Symbiosis with bacteria increases survival rate of beewolf larvae
Beewolves, i.e. digger wasps that hunt for bees to feed their larvae, have evolved an elegant solution to the problem of fungal and bacterial infection. Martin Kaltenpoth and colleagues from the University of Wurzburg had already shown several years ago that beewolves form a symbiotic relationship with bacteria of the genus Streptomyces. Female beewolves cultivate these bacteria in specialized antennal gland reservoirs and apply them to the ceiling of the brood cells. Beewolf larvae later take up the bacteria and transfer the symbionts actively to their cocoons, thereby increasing their survival probability. However, it has been unclear so far how the protection is achieved.
The beewolf larva hibernates for several months in its cocoon before the adult insect hatches. Antibiotics on the surface of the cocoon, produced by symbionts, guarantee protection against microbial pests during such long developmental stage. The amount of antibiotics was visualized by means of imaging techniques based on mass spectrometry (LDI imaging) and merged as pseudocolors onto the cocoon.Credit: Johannes Kroiss and Martin Kaltenpoth, MPI for Chemical Ecology, Jena
A Solid Case of Entanglement
For the first time, physicists have convincingly demonstrated that physically separated particles in solid-state devices can be quantum-mechanically entangled. The achievement is analogous to the quantum entanglement of light, except that it involves particles in circuitry instead of photons in optical systems. Both optical and solid-state entanglement offer potential routes to quantum computing and secure communications, but solid-state versions may ultimately be easier to incorporate into electronic devices. The experiment is reported in an upcoming issue of Physical Review Letters and highlighted with a Viewpoint in the January 11 issue of Physics (http://physics.aps.org.)
In optical entanglement experiments, a pair of entangled photons may be separated via a beam splitter. Despite their physical separation, the entangled photons continue to act as a single quantum object. A team of physicists from France, Germany and Spain has now performed a solid-state entanglement experiment that uses electrons in a superconductor in place of photons in an optical system.
As conventional superconducting materials are cooled, the electrons they conduct entangle to form what are known as Cooper pairs. In the new experiment, Cooper pairs flow through a superconducting bridge until they reach a carbon nanotube that acts as the electronic equivalent of a beam splitter. Occasionally, the electrons part ways and are directed to separate quantum dots -- but remain entangled. Although the quantum dots are only a micron or so apart, the distance is large enough to demonstrate entanglement comparable to that seen in optical systems.
In optical entanglement experiments, a pair of entangled photons may be separated via a beam splitter. Despite their physical separation, the entangled photons continue to act as a single quantum object. A team of physicists from France, Germany and Spain has now performed a solid-state entanglement experiment that uses electrons in a superconductor in place of photons in an optical system.
As conventional superconducting materials are cooled, the electrons they conduct entangle to form what are known as Cooper pairs. In the new experiment, Cooper pairs flow through a superconducting bridge until they reach a carbon nanotube that acts as the electronic equivalent of a beam splitter. Occasionally, the electrons part ways and are directed to separate quantum dots -- but remain entangled. Although the quantum dots are only a micron or so apart, the distance is large enough to demonstrate entanglement comparable to that seen in optical systems.
This is an SEM image of a typical Cooper pair splitter. The bar is 1 micrometer. A central superconducting electrode (blue) is connected to two quantum dots engineered in the same single wall carbon nanotube (in purple). Entangled electrons inside the superconductor can be coaxed to move in opposite directions in the nanotube, ending up at separate quantum dots, while remaining entangled.
Nervous culprit found for Tassie devil facial tumor disease
Cells that protect nerves are the likely origin of the Devil Facial Tumour Disease (DFTD) that has been devastating Australia's Tasmanian devil population, an international team of scientists has discovered.
Devil Facial Tumour Disease (DFTD) is a transmissible cancer that affects only Tasmanian devils and was first reported in 1996. It is spread by biting and quickly kills the animals. The disease is characterised by large tumours, mostly on the face and mouth, which often spread to internal organs.
The research collaboration, led by Australian scientists, has found that DFTD originates from cells called Schwann cells, which protect peripheral nerve fibres.
The results have been published today in the international journalScience.
Through the discovery, the team has now identified a genetic marker that could be used to accurately diagnose the perplexing cancer, which has seen the devil listed as endangered and facing extinction.
Lead author Dr Elizabeth Murchison from the Australian National University said the Schwann cell discovery was significant as there are currently no specific diagnostic tests, treatments or vaccines available for the disease.
"We took biopsies from devil tumours and extracted genetic data from them," Dr Murchison said.
Dr Tony Papenfuss from Melbourne's Walter and Eliza Hall Institute then led the team that determined which genes were switched on in the tumours and identified their genetic signature.
"When we compared the signature of the tumours to other normal tissues we found the tumours were most like Schwann cells," Dr Papenfuss said.
Associate Professor Greg Woods from the University of Tasmania's Menzies Research Institute said the Schwann cell find was an important step in the process to further understand the disease.
"Devils develop tumours of all different types and the genetic markers we have identified are useful for telling apart the tumours that occur in DFTD from other kinds of tumours," Associate Professor Woods said.
The Schwann cell research was conducted as part of the Save the Tasmanian Devil Program's efforts to further explore DFTD. It was supported by the National Health and Medical Research Council and the University of Tasmania's Dr Eric Guiler Tasmanian Devil Research Grant
Devil Facial Tumour Disease (DFTD) is a transmissible cancer that affects only Tasmanian devils and was first reported in 1996. It is spread by biting and quickly kills the animals. The disease is characterised by large tumours, mostly on the face and mouth, which often spread to internal organs.
The research collaboration, led by Australian scientists, has found that DFTD originates from cells called Schwann cells, which protect peripheral nerve fibres.
The results have been published today in the international journalScience.
Through the discovery, the team has now identified a genetic marker that could be used to accurately diagnose the perplexing cancer, which has seen the devil listed as endangered and facing extinction.
Lead author Dr Elizabeth Murchison from the Australian National University said the Schwann cell discovery was significant as there are currently no specific diagnostic tests, treatments or vaccines available for the disease.
"We took biopsies from devil tumours and extracted genetic data from them," Dr Murchison said.
Dr Tony Papenfuss from Melbourne's Walter and Eliza Hall Institute then led the team that determined which genes were switched on in the tumours and identified their genetic signature.
"When we compared the signature of the tumours to other normal tissues we found the tumours were most like Schwann cells," Dr Papenfuss said.
Associate Professor Greg Woods from the University of Tasmania's Menzies Research Institute said the Schwann cell find was an important step in the process to further understand the disease.
"Devils develop tumours of all different types and the genetic markers we have identified are useful for telling apart the tumours that occur in DFTD from other kinds of tumours," Associate Professor Woods said.
The Schwann cell research was conducted as part of the Save the Tasmanian Devil Program's efforts to further explore DFTD. It was supported by the National Health and Medical Research Council and the University of Tasmania's Dr Eric Guiler Tasmanian Devil Research Grant
Dr. Tony Papenfuss from the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, has identified Schwann cells as the likely origin of the devil facial tumor disease that has been devastating Australia's Tasmanian devil population.
First known binary star is discovered to be a triplet, quadruplet, quintuplet, sextuplet system
In ancient times, people with exceptional vision discovered that one of the brightest stars in the Big Dipper was, in fact, two stars so close together that most people cannot distinguish them. The two stars, Alcor and Mizar, were the first binary stars—a pair of stars that orbit each other—ever known.
Modern telescopes have since found that Mizar is itself a pair of binaries, revealing what was once thought of as a single star to be four stars orbiting each other. Alcor has been sometimes considered a fifth member of the system, orbiting far away from the Mizar quadruplet.
Now, an astronomer at the University of Rochester and his colleagues have made the surprise discovery that Alcor is also actually two stars, and is apparently gravitationally bound to the Mizar system, making the whole group a sextuplet. This would make the Mizar-Alcor sextuplet the second-nearest such system known. The discovery is especially surprising because Alcor is one of the most studied stars in the sky.
"Finding that Alcor had a stellar companion was a bit of serendipity," says Eric Mamajek, assistant professor of physics and astronomy at the University of Rochester, and leader of the team that found the star. "We were trying a new method of planet hunting and instead of finding a planet orbiting Alcor, we found a star."
Mamajek says that a separate group of scientists, led by Ben Oppenheimer of the American Natural History Museum, has also just found that the Alcor companion is physically associated with the star.
That group has also recorded a rough spectrum of the star, which Mamajek says confirms his prediction that the companion is a cool and dim M-class dwarf star.
Mamajek and colleagues at the University of Arizona used the Multiple Mirror Telescope in Arizona, which has a secondary mirror capable of flexing slightly to compensate for the twinkling the Earth's atmosphere normally imparts to starlight. With the clearest images he could obtain of nearby stars, Mamajek's team used computer algorithms to remove as much glare as possible from the image of a star in the hopes of spotting a planet near the star. Planets are so much dimmer than their parent stars that spotting one is like trying to discern a firefly next to a spotlight from several miles away, says Mamajek.
Modern telescopes have since found that Mizar is itself a pair of binaries, revealing what was once thought of as a single star to be four stars orbiting each other. Alcor has been sometimes considered a fifth member of the system, orbiting far away from the Mizar quadruplet.
Now, an astronomer at the University of Rochester and his colleagues have made the surprise discovery that Alcor is also actually two stars, and is apparently gravitationally bound to the Mizar system, making the whole group a sextuplet. This would make the Mizar-Alcor sextuplet the second-nearest such system known. The discovery is especially surprising because Alcor is one of the most studied stars in the sky.
"Finding that Alcor had a stellar companion was a bit of serendipity," says Eric Mamajek, assistant professor of physics and astronomy at the University of Rochester, and leader of the team that found the star. "We were trying a new method of planet hunting and instead of finding a planet orbiting Alcor, we found a star."
Mamajek says that a separate group of scientists, led by Ben Oppenheimer of the American Natural History Museum, has also just found that the Alcor companion is physically associated with the star.
That group has also recorded a rough spectrum of the star, which Mamajek says confirms his prediction that the companion is a cool and dim M-class dwarf star.
Mamajek and colleagues at the University of Arizona used the Multiple Mirror Telescope in Arizona, which has a secondary mirror capable of flexing slightly to compensate for the twinkling the Earth's atmosphere normally imparts to starlight. With the clearest images he could obtain of nearby stars, Mamajek's team used computer algorithms to remove as much glare as possible from the image of a star in the hopes of spotting a planet near the star. Planets are so much dimmer than their parent stars that spotting one is like trying to discern a firefly next to a spotlight from several miles away, says Mamajek.
This image shows Alcor and the newly discovered Alcor B, as imaged by scientists at the University of Rochester.
Vampires and collisions rejuvenate stars
Using the NASA/ESA Hubble Space Telescope, astronomers have uncovered two distinct kinds of "rejuvenated" stars in the globular cluster Messier 30. A new study shows that both stellar collisions and a process sometimes called vampirism are behind this cosmic "face lift". The scientists also uncover evidence that both sorts of blue stragglers were produced during a critical dynamical event (known as "core collapse") that occurred in Messier 30 a few billion years ago.
Stars in globular clusters are generally extremely old, with ages of 12-13 billion years. However, a small fraction of them appear to be significantly younger than the average population and, because they seem to have been left behind by the stars that followed the normal path of stellar evolution and became red giants, have been dubbed blue stragglers. Blue stragglers appear to regress from "old age" back to a hotter and brighter "youth", gaining a new lease on life in the process. A team of astronomers used Hubble to study the blue straggler star content in Messier 30, which formed 13 billion years ago and was discovered in 1764 by Charles Messier. Located about 28 000 light-years away from Earth, this globular cluster — a swarm of several hundred thousand stars — is about 90 light-years across.
Although blue stragglers have been known since the early 1950s, their formation process is still an unsolved puzzle in astrophysics. "It’s like seeing a few kids in the group picture of a rest-home for retired people. It is natural to wonder why they are there," says Francesco Ferraro from the University of Bologna in Italy, lead author of the study that will be published this week in Nature. Researchers have been studying these stars for many years and knew that blue stragglers are indeed old. They were thought to have arisen in a tight binary system. In such a pair, the less massive star acts as a "vampire", siphoning fresh hydrogen from its more massive companion star. The new fuel supply allows the smaller star to heat up, growing bluer and hotter — behaving like a star at an earlier stage in its evolution.
Stars in globular clusters are generally extremely old, with ages of 12-13 billion years. However, a small fraction of them appear to be significantly younger than the average population and, because they seem to have been left behind by the stars that followed the normal path of stellar evolution and became red giants, have been dubbed blue stragglers. Blue stragglers appear to regress from "old age" back to a hotter and brighter "youth", gaining a new lease on life in the process. A team of astronomers used Hubble to study the blue straggler star content in Messier 30, which formed 13 billion years ago and was discovered in 1764 by Charles Messier. Located about 28 000 light-years away from Earth, this globular cluster — a swarm of several hundred thousand stars — is about 90 light-years across.
Although blue stragglers have been known since the early 1950s, their formation process is still an unsolved puzzle in astrophysics. "It’s like seeing a few kids in the group picture of a rest-home for retired people. It is natural to wonder why they are there," says Francesco Ferraro from the University of Bologna in Italy, lead author of the study that will be published this week in Nature. Researchers have been studying these stars for many years and knew that blue stragglers are indeed old. They were thought to have arisen in a tight binary system. In such a pair, the less massive star acts as a "vampire", siphoning fresh hydrogen from its more massive companion star. The new fuel supply allows the smaller star to heat up, growing bluer and hotter — behaving like a star at an earlier stage in its evolution.
This illustration demonstrates the two ways that blue stragglers — or "rejuvenated" stars — in globular clusters form. The upper illustration shows the collision model where two low-mass stars in an overcrowded environment experience a head-on collision, combining their fuel and mass and to form a single hot star. The lower illustration depicts the "vampire" model consisting of a pair of stars that undergo a transformation, with the lower-mass star draining its larger-mass companion of hydrogen that fuels its rebirth.
Absence of evidence for a meteorite impact event 13,000 years ago
An international team of scientists led by researchers at the University of Hawaii at Manoa have found no evidence supporting an extraterrestrial impact event at the onset of the Younger Dryas ~13000 years ago.
The Younger Dryas is an abrupt cooling event in Earth's history. It coincided with the extinction of many large mammals including the woolly mammoth, the saber toothed jaguar and many sloths. This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America. This paradigm was challenged two years ago by a group of researchers that reported finding high iridium concentrations in terrestrial sediments dated during this time period, which led them to theorise that an impact event was instead the instigator of this climate shift. A team led by François Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM) decided to also investigate this theory, to add more evidence to what they considered a conceptually appealing theory. However, not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas. Their results will be published in the December 7th early online edition of the prestigious journal the Proceedings of the National Academy of Sciences.
The idea that an impact event may have been the instigator for this cooling period was appealing because of several alleged impact markers, especially the high iridium concentrations that the previous team reported. However, it is difficult for proponents of this theory to explain why no impact crater of this age is known. "There is a black mat layer across North America which is correlated to the Younger Dryas climatic shift seen in Greenland ice cores dated at 13 thousand years ago by radio carbon," explains Paquay. "Initially I thought this type of layer could be associated with an impact event because concentration in the proxies of widespread wildfires are sky high. That plus very high levels of iridium (which is one indicator used to indicate extraterrestrial impact events). So the theory was conceptually appealing, but because of the missing impact site, the idea of one or multiple airburst arose."
The Younger Dryas is an abrupt cooling event in Earth's history. It coincided with the extinction of many large mammals including the woolly mammoth, the saber toothed jaguar and many sloths. This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America. This paradigm was challenged two years ago by a group of researchers that reported finding high iridium concentrations in terrestrial sediments dated during this time period, which led them to theorise that an impact event was instead the instigator of this climate shift. A team led by François Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM) decided to also investigate this theory, to add more evidence to what they considered a conceptually appealing theory. However, not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas. Their results will be published in the December 7th early online edition of the prestigious journal the Proceedings of the National Academy of Sciences.
The idea that an impact event may have been the instigator for this cooling period was appealing because of several alleged impact markers, especially the high iridium concentrations that the previous team reported. However, it is difficult for proponents of this theory to explain why no impact crater of this age is known. "There is a black mat layer across North America which is correlated to the Younger Dryas climatic shift seen in Greenland ice cores dated at 13 thousand years ago by radio carbon," explains Paquay. "Initially I thought this type of layer could be associated with an impact event because concentration in the proxies of widespread wildfires are sky high. That plus very high levels of iridium (which is one indicator used to indicate extraterrestrial impact events). So the theory was conceptually appealing, but because of the missing impact site, the idea of one or multiple airburst arose."
The woolly mammoth was one of the large mammals that became extinct in North America at the onset of the Younger Dryas approx. 13,000 years ago.
LROC's first look at the Apollo landing sites
The imaging system on board NASA's Lunar Reconnaissance Orbiter (LRO) recently had its first of many opportunities to photograph the Apollo landing sites. The Lunar Reconnaissance Orbiter Camera (LROC) imaged five of the six Apollo sites with the narrow angle cameras (NACs) between July 11 and 15, within days of the 40th anniversary of the Apollo 11 mission.
The early images obtained by LROC, operated by Arizona State University Professor Mark Robinson, show the lunar module descent stages left behind by the departing astronauts. Their locations are made evident by their long shadows, which result from a low sun angle at the time of collection.
"In a three-day period we were able to image five of the six Apollo sites – the LROC team anxiously awaited each image," says LROC Principal Investigator Mark Robinson, professor in the School of Earth and Space Exploration in ASU's College of Liberal Arts and Sciences. "Of course we were very interested to get our first peek at the lunar module descent stages just for the thrill – and to see how well the cameras had come into focus."
For additional information about the LROC instrument and to view the first Apollo landing site images, visit: http://lroc.sese.asu.edu.
The orbiter's current elliptical orbit resulted in image resolutions from the NACs that were slightly different for each site but were all about four feet per pixel. Since the deck of the descent stage is about 14 feet in diameter, the Apollo relics themselves fill about four pixels. However, because the Sun was low to the horizon when the images were acquired, even subtle variations in topography create long shadows. Standing just over ten feet above the surface, each Apollo descent stage creates a distinct shadow that fills roughly 20 pixels.
The early images obtained by LROC, operated by Arizona State University Professor Mark Robinson, show the lunar module descent stages left behind by the departing astronauts. Their locations are made evident by their long shadows, which result from a low sun angle at the time of collection.
"In a three-day period we were able to image five of the six Apollo sites – the LROC team anxiously awaited each image," says LROC Principal Investigator Mark Robinson, professor in the School of Earth and Space Exploration in ASU's College of Liberal Arts and Sciences. "Of course we were very interested to get our first peek at the lunar module descent stages just for the thrill – and to see how well the cameras had come into focus."
For additional information about the LROC instrument and to view the first Apollo landing site images, visit: http://lroc.sese.asu.edu.
The orbiter's current elliptical orbit resulted in image resolutions from the NACs that were slightly different for each site but were all about four feet per pixel. Since the deck of the descent stage is about 14 feet in diameter, the Apollo relics themselves fill about four pixels. However, because the Sun was low to the horizon when the images were acquired, even subtle variations in topography create long shadows. Standing just over ten feet above the surface, each Apollo descent stage creates a distinct shadow that fills roughly 20 pixels.
The Apollo 14 lunar module (LM Antares) and the Apollo Lunar Surface Experiment Package are visible in this image (note the astronaut tracks between the two artifacts). At the current altitude and lighting the descent stage is clearly visible with its angular shadow (right) and shadow cast by leg (near arrow tip). The LROC NAC image data has not been calibrated, the faint vertical stripes are a natural part of the image and will be removed later after the full suite of calibration data is collected during the commissioning phase.