|Einstein Rings! |
Feed A Turkey! Dallasaurus!
Decaf Harmful? Real Tatooine!
Supergiant X-Ray Binaries!
|Einstein Rings! |
Light from distant galaxies is deflected
on its way to Earth by the gravitational
field of any massive object that lies in
the way... (NASA)
NASA News Release
NOVEMBER 17, 2005 - Astronomers have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA's Hubble Space Telescope, to identify 19 new "gravitationally lensed" galaxies. Among these 19, they have found eight new so-called "Einstein rings", which are perhaps the most elegant manifestation of the lensing phenomenon.
Only three such rings had previously been seen in visible light.
In gravitational lensing, light from distant galaxies is deflected on its way to Earth by the gravitational field of any massive object that lies in the way. Because of this light bending, the galaxy is distorted into an arc or multiple separate images.
Because of this light bending, the galaxy
is distorted into an arc or multiple separate
When both galaxies are exactly lined up, the light forms a bull's-eye pattern, called an Einstein ring, around the foreground galaxy.
Besides producing odd shapes, gravitational lensing gives astronomers the most direct probe of the distribution of dark matter in elliptical galaxies. Dark matter is an invisible and exotic form of matter that has not yet been directly observed.
By searching for dark matter in galaxies, astronomers hope to gain insight into galaxy formation, which must have started around lumpy concentrations of dark matter in the early universe.
When both galaxies are exactly lined up,
the light forms a bull's-eye pattern, called
an Einstein ring, around the foreground
The newly discovered lenses come from an ongoing project called the Sloan Lens Survey (SLACS). A team of astronomers, led by Adam Bolton of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and Leon Koopmans of the Kapteyn Astronomical Institute in the Netherlands, selected the candidate lenses from among several hundred thousand optical spectra of elliptical galaxies in the Sloan Digital Sky Survey.
The team was looking for clear evidence of emission from galaxies twice as far from Earth and directly behind the closer galaxies. They used Hubble's Advanced Camera for Surveys to snap images of 28 of these candidate lensing galaxies.
By studying the arcs and rings produced by 19 of these candidates, the astronomers precisely measured the mass of the foreground galaxies. These new discoveries add significantly to the approximately 100 gravitational lenses previously known.
"Being able to study these and other gravitational lenses as far back in time as several billion years allows us to see directly whether the distribution of invisible and visible mass changes with cosmic time," says Koopmans. "With this information, we can test the commonly held idea that galaxies form from collision and mergers of smaller galaxies."
The initial findings of the survey will appear in the February 2006 issue of the Astrophysical Journal.
More on Einstein Rings - http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/32
|Feed A Turkey? |
November 18, 2005 (US Newswire) - On Nov. 19, Animal Acres, LA's newly opened farm animal sanctuary, will celebrate Thanksgiving with a unique celebration called the "Feed A Turkey Ceremony" at the sanctuary in Acton, Calif.
At noon, special guests actresses Daryl Hannah and Jorja Fox (from the No. 1 hit television show CSI) will be helping feed the turkeys and speaking about the need to protect ALL animals from cruelty and neglect. Daryl and Jorja, who are vegetarians, are LA's leading celebrity advocates for animals, and their support of Animal Acres is opening hearts and minds to the plight of turkeys and other farm animals.
From noon to 4 p.m., guests will be able to enjoy tours of the sanctuary featuring three newly rescued baby pigs alongside the children's' favorite baby pig, Bagel. At 1:30 p.m. guests will gather to actually hand feed the turkeys. This will be followed by a delicious vegetarian thanksgiving meal created by LA restaurant Native Foods, one of LA's favorite vegetarian restaurants, served in the sanctuaries gorgeous courtyard.
Daryl Hannah and Jorja Fox
In addition to nine rescued turkeys, the Animal Acres sanctuary is also home to 25 chickens that were victims of Hurricane Katrina and traveled from Louisiana to find safe haven. Other adorable residents include two calves rescued from a Southern California stockyard, and over 50 sheep recently seized from a Los Angeles slaughterhouse by humane officers.
The Animal Acres "Feed A Turkey" celebration hopes to teach people that farm animals are living sentient animals who deserve protection, and kindness, too. Most states specifically exclude farm animals from anti-cruelty laws. There are no federal laws to protect farm animals from abuse. As a result, farm animals in the United States are raised, transported and slaughtered in conditions considered so cruel they have been banned in other countries.
The sanctuary is directed by Lorri Bauston who co-founded the nation's first shelter for farm animals in 1986. Considered to be the pioneer of the farm animal sanctuary movement, Bauston has helped establish dozens of sanctuaries around the country and her efforts have been featured in several documentaries. For more information call 661- 269-0986.
Animal Acres - http://www.animalacres.org
|Meet Dallasaurus! |
|Southern Methodist University News Release |
DALLAS November 16, 2005 — When amateur fossil finder Van Turner discovered a small vertebra at a construction site near Dallas 16 years ago, he knew the creature was unlike anything in the fossil record. Scientists now know the significance of Turner’s fossil as the origin of an extinct line of lizards with an evolutionary twist: a land-dwelling species that became fully aquatic.
Dallasaurus represents a missing link in the evolution
of a group of creatures called mosasaurs, prehistoric
animals that started out on land, but evolved in the seas
and dominated the oceans at the same time dinosaurs
ruled the land. (SMU)
Turner took the remains to paleontologists at the Dallas Museum of Natural History, but it took several years before scientists dubbed the find Dallasaurus turneri. Word of Dallasaurus is now reaching the scientific community with a special issue of the Netherlands Journal of Geosciences, featuring an article by Southern Methodist University paleontologist Michael Polcyn and Gordon Bell Jr. of Guadalupe National Park in Texas.
They describe Dallasaurus, a three-foot long lizard who lived 92 million years ago in the shallow seas and shores of what was then a stretch of Texas mostly under water, and also used the fossil to better understand the mosasaur family tree. Polcyn and Bell painstakingly pieced together an understanding of the anatomy and natural history of Dallasaurus from the bones Turner discovered and from some matching skeletal remains at the Texas Memorial Museum at the University of Texas in Austin.
Dallasaurus represents a missing link in the evolution of a group of creatures called mosasaurs, prehistoric animals that started out on land, but evolved in the seas and dominated the oceans at the same time dinosaurs ruled the land. One aspect of Polcyn and Bell’s research is the revelation that Dallasaurus retained complete limbs, hands and feet suitable for walking on land, whereas later mosasaurs evolved their limbs into flippers.
“This is pretty close to the beginning of the mosasaur family tree,” says Dallas Museum of Natural History Earth Sciences Curator and SMU Adjunct Professor of Paleontology Anthony R. Fiorillo, Ph.D. “It is the most complete mosasaur retaining all of its limbs found in North America.”
Mosasaurs, every bit as prolific, fascinating and nearly as big as some dinosaurs, are becoming more popular for paleontologists to study. Mosasaurs lived and became extinct alongside dinosaurs, but few paleontologists specialize in them. Later mosasaurs grew as large as their dinosaur brethren, reaching up to 45 feet in length. Until the discovery of Dallasaurus, however, only five primitive forms with land-capable limbs were known, all of them found in the Middle East and the eastern Adriatic.
“Lizards had nearly 150 million-year-long history on land; then in the Late Cretaceous, the final stage of the age of dinosaurs, one group moved into the sea and rose to the very top of the food chain,” explains Polcyn, director of SMU’s Visualization Laboratory, part of the university’s geological sciences department. “Starting out as small animals like Dallasaurus, they mastered their new marine environment and rose to become the top predator in their ecosystem, the T. Rex of the ocean.”
The Late Cretaceous period was a time of hot house temperatures and rising sea levels.
“As the earth warmed and the seas rose, small land-dwelling lizards took to the oceans and developed increasing levels of seagoing capabilities, and over 30 million years, eventually evolving into the top predator of their domain before becoming extinct some 65 million years ago” says Polcyn.
The advanced fin-bearing mosasaurs have been grouped into three major lineages. Although a small number of primitive mosasaur have been known to retain land-capable limbs, they were thought to be an ancestral group separate from the later fin-bearing forms. Dallasaurus represents a clear link to one lineage of the later forms and the first time researchers can clearly show mosasaurs evolved fins from limbs within the different lineages of mosasaurs.
With the aid of computer science and SMU’s visualization laboratory, Polcyn has been able to simulate what Dallasaurus looked like, and how, based on his skeletal remains, he would swim and move from land to sea. An artist has taken Polcyn’s visualization work even one step further by creating a life-sized model of Dallasaurus, a work that is soon to be on display at the Museum along with the computer simulation.
When funds become available for reconstructing a suitable exhibit, the bones of Dallasaurus will be displayed at the Dallas Museum of Natural History. The work, however, will take several more years of additional efforts and substantial funding. A nearly 30-foot long mosasaur, some 75 million years old, already is on display at the Dallas Museum.
Major dinosaur finds are frequently the result of creatures dying in groups through flooding or drought, situations that lend themselves fairly well to more complete preservation and conservation of their bones, and much slower deterioration. Mosasaur fossils, in contrast, are rarely found in large groupings, and are only found in areas once covered by seas. Remains were quick to deteriorate under ocean currents; their bodies often fell victim to the ravages of other sea life, such as sharks, who would pick away at carcasses for food. Because of their mostly shallow sea and seaside habitats, the remains of early mosasaurs are even more rare and much harder to find.
But in the last two decades, many new discoveries and significant advances have been made in the understanding of mosasaur evolution and how they lived. Dallasaurus significantly advances that understanding by filling in a long missing piece of mosasaur evolution, specifically a time at which they transition from land to sea.
The importance of Turner’s discovery isn’t lost on the researchers putting together the pieces of the mosasaur puzzle. In fact, they predict the legacy of Turner’s discovery will live on. His contribution was honored by naming the species, “turneri,” after his last name. “Not all major discoveries are made by highly trained paleontologists,” notes Dallas Natural History Museum Curator Fiorillo. “The observant individual, even kids, can still make an important find,” he says. “Once this goes mainstream, and people begin to recognize what mosasaurs are, we’ll be finding more and more.”
SMU is a private university in Dallas with more than 10,000 students and offers degree programs through seven schools. More information about SMU is available at www.smu.edu.
The Dallas Museum of Natural History, a Smithsonian Institution affiliate, is a research and exhibition institution devoted to natural history research and public education. It is funded by public government, companies and by private foundations and individual donations, including the City of Dallas, the state of Texas, the Microsoft Foundation, the Junior League, American Airlines and the Dallas Morning News. With over 280,000 specimens, it is among the largest natural history museums in the country. Located in historic Fair Park in Dallas, the museum is open daily, 362 days annually.
Dallas Museum of Natural History - http://www.dallasdino.org
Southern Methodist University - http://www.smu.edu
|Primal Earth Was Habitable! |
Earth's crust, oceans and atmosphere were in
place very early on, and a habitable planet was
University of Colorado at Boulder News Release
November 17, 2005 - A surprising new study by an international team of researchers has concluded Earth's continents most likely were in place soon after the planet was formed, overturning a long-held theory that the early planet was either moon-like or dominated by oceans.
The team came to the conclusion following an analysis of a rare metal element known as hafnium in ancient minerals from the Jack Hills in Western Australia, thought to be among the oldest rocks on Earth. Hafnium is found in association with zircon crystals in the Jack Hills rocks, which date to almost 4.4 billion years ago.
"These results support the view that the continental crust had formed by 4.4-4.5 billion years ago and was rapidly recycled into the mantle," the researchers wrote in Science Express. Led by Professor Mark Harrison of the Australian National University, the team also included University of Colorado Assistant Professor Stephen Mojzsis and researchers from the University of California, Los Angeles and Ecole Normale Superieure University in France.
The researchers used hafnium as a "tracer" element, using isotopes to infer the existence of early continental formation on Earth dating to Hadeon Eon, which took place during the first 500 million years of Earth's history, said Mojzsis, an assistant professor of geological sciences at CU-Boulder. Mojzsis also is a member of CU-Boulder's Center for Astrobiology.
"The evidence indicates that there was substantial continental crust on Earth within its first 100 million years of existence," said Mojzsis. "It looks like the Earth started off with a bang."
A 2001 study led by Mojzsis published in the journal Nature showed evidence for the presence of water on Earth's surface roughly 4.3 billion years ago. "The view we are taking now is that Earth's crust, oceans and atmosphere were in place very early on, and that a habitable planet was established rapidly," said Mojzsis.
The study was supported in part by a grant from NASA's Exobiology Program.
University of Colorado at Boulder - http://www.colorado.edu
|Is Decaf Harmful to Your Heart? |
|American Heart Association News Release |
November 16, 2005 - Decaffeinated - not caffeinated - coffee may cause an increase in harmful LDL cholesterol by increasing a specific type of blood fat linked to the metabolic syndrome, hints a new study presented at the American Heart Association's Scientific Sessions 2005.
The Coffee and Lipoprotein Metabolism (CALM) study included 187 people, randomized to three groups: one that drank three to six cups of caffeinated coffee a day; another that drank three to six cups of decaffeinated coffee a day; and a third, the control group, that drank no coffee.
Some studies have linked coffee drinking to heart disease, but others have suggested that it is not harmful.
"The problem with the results from these previous studies is that many of them were association studies, which looked broadly at free-living populations and drew associations between lifestyle factors, volitional coffee consumption, and disease risk. Our study randomized subjects to a specific type and amount of coffee consumption, brewed in a standardized manner, just like a drug study," said H. Robert Superko, M.D., lead author of the study and chairman of molecular, genetic, and preventive cardiology at the Fuqua Heart Center and the Piedmont-Mercer Center for Health and Learning in Atlanta, Ga.
In this study researchers gave participants a nationally popular home-brewed caffeinated coffee and decaffeinated coffee brand, and coffee makers. Researchers then instructed participants on how to prepare the coffee in a standardized manner and asked them to drink only this coffee. All participants drank only black coffee.
"Whether coffee has caffeine is not the only thing that differentiates caffeinated from decaffeinated types," Superko said. "Caffeinated and decaffeinated coffees are often made from different species of beans. Caffeinated coffee, by and large, comes from a bean species called coffee Arabica, while many decaffeinated coffees are made from coffee Robusta. The decaffeination process can extract flavonoids and ingredients that give coffee flavor. So decaffeinated brands usually use a bean that has a more robust flavor."
Researchers measured the level of caffeine in the blood of the participants, as well as levels of the key heart-health indicators before and after the three-month study.
They sought to clearly demonstrate the effects of caffeinated and decaffeinated coffee consumption on key indicators of the metabolic syndrome, which is the umbrella term for a cluster of several harmful heart disease risk factors.
Researchers looked at blood pressure, heart rate, BMI, total cholesterol, triglycerides, HDL (good cholesterol) levels of insulin, glucose, non-esterified fatty acids (NEFA -- fat in the blood), apolipoprotein B (ApoB -- a protein associated with LDL or "bad" cholesterol) and high-density lipoprotein 2 (HDL2 -- a type of "really good" cholesterol).
Researchers found no significant changes among the three groups' levels of blood insulin and glucose, or other major risk factors.
But they reported for the first time that, after three months of coffee drinking, the decaffeinated group experienced a rise in fatty acids, which is the fuel in the blood that can drive the production of low-density lipoprotein LDL. ApoB went up 8 percent in the decaffeinated group but did not significantly change in the other two groups. ApoB is the only protein attached to LDL, and studies show that ApoB might be a better predictor of cardiovascular disease risk than one's LDL level.
NEFA rose an average 18 percent in the decaffeinated group, while it did not change in the other two groups.
"NEFA is the fuel that can drive the increase in ApoB and LDL," Superko said. "These results are very surprising and have never been reported before for coffee consumption. This is the first non-industry-sponsored study of its kind. Until now, researchers had not reported on a randomized prospective study looking at the mechanism of how a particular kind of coffee consumption increases ApoB and LDL-cholesterol.
"There is a real difference between caffeinated and decaffeinated coffee and, contrary to what people have thought for many years, I believe it's not caffeinated but decaffeinated coffee that might promote heart disease risk factors that are associated with the metabolic syndrome, an expanding heart-health hazard in the United States."
In measuring HDL cholesterol, researchers looked specifically at HDL2, a type of HDL in which high levels are particularly associated with lower risk of heart disease. They found that HDL2 didn't change significantly overall among the three groups in the study. But in the decaffeinated group, it changed significantly according to participants' body fat.
For those who had body mass indexes (BMIs) of more than 25 (considered overweight), drinking decaffeinated coffee increased HDL2 by about 50 percent. But those in the decaffeinated group, who were not considered overweight according to BMI, saw their HDL2 drop by about 30 percent.
"This illustrates to the public that this is not a simple story of one coffee is good, one coffee is bad," he added. "It illustrates a concept that is becoming very important in medicine, which is the individualization of treatment. We have to individualize therapy based on the patient's characteristics. It is important for the public to appreciate that one diet or one drug is not the optimal treatment for every patient."
Coffee drinkers in the United States consume an average of 3.1 cups each day. However, "if you only drink one cup each day, the results of our study probably have little relevance because at that level your daily coffee dose is relatively low," Superko said.
Superko said people concerned about increasing fatty acids and LDL cholesterol should think twice about drinking a lot of decaffeinated coffee. "But those who are overweight and have low levels of HDL2 but normal levels of ApoB, might consider the potential benefit of drinking decaffeinated over caffeinated coffee," he said.
According to the American Heart Association, whether high caffeine intake increases the risk of coronary heart disease is still under study, however moderate coffee drinking - 1-2 cups per day - doesn't seem to be harmful. Co-author is Peter D. Wood, Ph.D.
The National Institutes of Health (NIH) funded the study.
American Heart Association - http://www.americanheart.org
|Real Tatooine! |
Artist's conception of a triple star system (NASA)
New Scientist Magazine News Release
By Hazel Muir
November 16, 2005 - More than a thousand planets reminiscent of Tatooine – Luke Skywalker's hypnotic world with multiple suns in Star Wars – could be lurking in our galactic neighborhood.
That is the conclusion of astronomers who have come up with a simple explanation for the genesis of a recently discovered, perplexing giant planet in a nearby triple star system.
In July, Maciej Konacki, then at the California Institute of Technology in Pasadena and now at the Nicolaus Copernicus Astronomical Center in Torun, Poland, reported finding a planet inside a triple star system called HD 188753, about 150 light years from Earth.
The planet is a "hot Jupiter" – a gas giant that orbits much closer to its parent star than Jupiter does. It circles its sun-like star every 3.35 days. Farther out in the same system is a pair of smaller stars. The alien world defied all explanation because planets like this should not be able to form in a triple star system.
This is because astronomers believe a typical hot Jupiter forms in the cool outer regions of a dusty disc around its parent star and then migrates inwards due to drag from the disc. According to this model, Konacki's hot Jupiter should have formed at least three times the Earth-sun distance from the host star, or 3 astronomical units (AU).
But the gravity of the binary pair farther out should have caused the planet-forming disc to shrink so that it was contained within 1.5 AU of the main star, leaving little material to form such a large planet or drag it inwards.
Did you hear that, R2? There should be
1200 triple stars with a planet! I knew it
all long! (LucasFilm)
Now Simon Portegies Zwart of the University of Amsterdam in the Netherlands and Steve McMillan of Drexel University in Philadelphia, Pennsylvania, think they have solved the riddle. They point out that like most stars, HD 188753 probably formed inside an "open cluster" of several hundred stars. They argue that it is possible the planet first formed around the host star and then the star drew it into a tight orbit. Subsequently, a close encounter in the cluster hooked them up with the binary system.
To calculate the chances of the main star capturing the binary pair, they modeled stars zooming around within typical open clusters. Their results suggest that, on average, each cluster should contribute five or six systems like HD 188753 to our galaxy. They estimate that among the 10 million single, double and triple star systems that lie within 1600 light years of Earth, there should be 1200 triple stars with a planet – rare, but not impossible to find (Astrophysical Journal Letters, vol 633, p 141).
"Nature is always more crazy than we are; it invents things that we cannot envision at all," says Portegies Zwart. "Only after we see them and think very deeply can we come to the solution. But this is an easy solution – there's no magic involved. I'm sure we will find more of these systems in the next few years."
If many more are discovered, their orbital configurations could act as a "fossil record" of star clusters that wandered the Milky Way billions of years ago, revealing the speeds and the distribution of stars inside.
New Scientist - http://www.newscientist.com
|Doctors Ignore High-Risk Drug Warnings |
|Harvard Medical School News Release |
BOSTON November 18, 2005 – In a survey of approximately 930,000 ambulatory care patients, researchers from the Department of Ambulatory Care and Prevention (of Harvard Medical School and Harvard Pilgrim Health Care) and colleagues found that 42 percent received prescriptions for drugs with Black Box Warnings (BBW), the Food and Drug Administration's strongest label for high-risk medication.
Additionally, physicians' compliance with the recommendations of the BBWs was highly variable, which suggests that better methods are needed for ensuring the safe use of medications that carry serious risks. In the categories studied, doctors' noncompliance to BBWs ranged from 0.3 percent to 49.6 percent. These results are reported online in the Nov. 18, 2005 issue of Pharmacoepidemiology and Drug Safety.
"In ambulatory care settings, approximately 1.4 billion prescriptions are written per year," said Anita Wagner, assistant professor at DACP. "Until now, there has been no information about how frequently doctors prescribe BBW drugs, nor whether prescribing is consistent with the warnings. This study tells us that these drugs are prescribed often and that in some categories, prescribing is inconsistent with the warnings."
Wagner, Richard Platt (chairman of DACP and principal investigator of the Agency for Healthcare Research and Quality–funded Prescribing Safety Study), and colleagues in HMOs across the country conducted a retrospective study over two and a half years to find out how many ambulatory care patients were prescribed drugs with BBWs and to assess compliance to these warnings. BBWs are warnings printed in a black frame in the package insert of a drug and are intended to alert prescribers to the serious risks that may be associated with certain drugs. They describe the drug's risks, can list specific precautions for its use, and must appear on all promotional materials.
To examine prescribing compliance, Wagner and colleagues examined approximately 217,000 enrollees who had received at least one of 19 BBW drugs. The researchers considered BBWs that required laboratory monitoring when a patient began taking the medication or for the duration of the prescription; were unsafe to take with other specific medications; or were unsafe to take while pregnant.
From this group, most noncompliance with BBWs occurred when patients should have received lab tests as they began a medication; 49.6 percent of all prescriptions that should have been accompanied by a lab test at the onset of a prescription were not. Recommendations for pregnancy tests were most frequently not observed (for example, when women of childbearing age were given prescriptions for acitretin, which treats severe psoriasis).
When patients needed lab monitoring while taking a medication, there was no continued monitoring for 12.8 percent of prescription times during which the BBW recommended a test.
Nine percent of prescriptions were dispensed on the same day as a drug that is considered unsafe to take simultaneously. All involved dispensing of methotrexate with non-steroidal anti-inflammatory drugs (NSAIDS) or ketorolac with other NSAIDS (11 and 7.6 percent, respectively).
Warnings that indicated a medication was unsafe to take while pregnant had excellent compliance. Women of childbearing age received almost 79,000 prescriptions for BBW drugs that should be avoided during pregnancy. Only 95, or 0.3 percent, may have occurred during pregnancy.
"We need several things to improve the effectiveness of the warnings: to be clear about the magnitude of risk that justifies a BBW and the evidence that underlies a recommendation, to communicate warnings clearly to both clinicians and patients, and to create systems that support doctors and patients in following the recommendations," Wagner said. "We believe our data shed light on adherence to BBW recommendations and provide a preliminary basis for recommendations to improve communication about the risks of medicines."
For instance, it is possible that concise and focused wording of a warning is more effective than less direct wording. Patient-specific automated alerts to BBW drugs or recommendations at the point of prescribing and dispensing may be more effective than BBWs in package inserts. Designing such a system requires complete, consistent, and current lists of BBW medicines and clinical circumstances associated with risk of morbidity and mortality. The authors of this study recommend that the FDA establish and maintain such a list.
"This will require new information about risks, about the way drugs are used in everyday practice, about effective methods of influencing clinicians' prescribing, and about ensuring that patients understand how to use their drug as safely as possible," Wagner said.
Harvard Medical School - http://www.hms.harvard.edu
|Supergiant X-Ray Binaries! |
This artist's impression shows a high-mass binary system, composed
of a supergiant luminous star (in blue) and a compact stellar object,
such as a neutron star. As discovered by ESA's Integral observatory,
many of these supergiant systems produce strong and exceptionally
fast-rising X-ray outbursts lasting a few hours only, hence their name
'supergiant fast X-ray transients'. The outbursts may depend on the
way stellar material is exchanged between the supergiant star and
the compact object. (ESA)
European Space Agency News Release
November 16, 2005 - ESA’s Integral gamma-ray observatory has discovered a new, highly populated class of X-ray fast ‘transient’ binary stars, undetected in previous observations.
With this discovery, Integral confirms how much it is contributing to revealing a whole hidden Universe.
The new class of double star systems is characterized by a very compact object that produces highly energetic, recurrent and fast-growing X-ray outbursts, and a very luminous ‘supergiant’ companion.
The compact object can be an accreting body such as a black hole, a neutron star or a pulsar. Scientists have called such class of objects ‘supergiant fast X-ray transients’. ‘Transients’ are systems which display periods of enhanced X-ray emission.
Before the launch of Integral, only a dozen X-ray binary stars containing supergiants had been detected. Actually, scientists thought that such high-mass X-ray systems were very rare, assuming that only a few of them would exist at once since stars in supergiant phase have a very short lifetime.
However, Integral’s data combined with other X-ray satellite observations indicate that transient supergiant X-ray binary systems are probably much more abundant in our Galaxy than previously thought.
In particular, Integral is showing that such ‘supergiant fast X-ray transients’, characterized by fast outbursts and supergiant companions, form a wide class that lies hidden throughout the Galaxy.
Due to the transitory nature, in most cases these systems were not detected by other observatories because they lacked the combination of sensitivity, continuous coverage and wide field of view of Integral.
They show short outbursts with very fast rising times – reaching the peak of the flare in only a few tens of minutes – and typically lasting a few hours only. This makes the main difference with most other observed transient X-ray binary systems, which display longer outbursts, lasting typically a few weeks up to months.
In the latter case, the long duration of the outburst is consistent with a ‘viscous’ mass exchange between the star and an accreting compact object.
In ‘supergiant fast X-ray transients’, associated with highly luminous supergiant stars, the short duration of the outburst seems to point to a different and peculiar mass exchange mechanism between the two bodies.
This may have something to do with the way the strong radiative winds, typical of highly massive stars, feed the compact object with stellar material.
This simulated sequence shows the interaction between the stellar material carried by the wind
of a supergiant star and its 'receiving' companion - a compact stellar object such as a neutron star.
In the vicinity of the compact object it is possible to see the development of a turbulent shocked flow.
(Credits: JM Blondin, North Carolina State University)
Scientists are now thinking about the reasons for such short outbursts. It could be due to the supergiant donor ejecting material in a non-continuous way. For example, a clumpy and intrinsically variable nature of a supergiant’s radiative winds may give rise to sudden episodes of increased accretion rate, leading to the fast X-ray flares.
Alternatively, the flow of material transported by the wind may become, for reasons not very well understood, very turbulent and irregular when falling into the enormous gravitational potential of the compact object.
“In any case, we are pretty confident that the fast outbursts are associated to the mass transfer mode from the supergiant star to the compact object,” says Ignacio Negueruela, lead author of the results, from the University of Alicante, Spain.
“We believe that the short outbursts cannot be related to the nature of the compact companion, as we observed fast outbursts in cases where the compact objects were very different - black holes, slow X-ray pulsars or fast X-ray pulsars.”
Studying sources such as ‘supergiant fast X-ray transients’, and understanding the reasons for their behavior, is very important to increase our knowledge of accretion processes of compact stellar objects. Furthermore, it is providing valuable insight into the evolution paths that lead to the formation of high-mass X-ray binary systems.
European Space Agency - http://www.esa.int