(Press-News.org) Astronomers using the National Science Foundation's Very Large Array (VLA) have found a long-sought "missing link" between supernova explosions that generate gamma-ray bursts (GRBs) and those that don't. The scientists found that a stellar explosion seen in 2012 has many characteristics expected of one that generates a powerful burst of gamma rays, yet no such burst occurred.
"This is a striking result that provides a key insight about the mechanism underlying these explosions," said Sayan Chakraborti, of the Harvard-Smithsonian Center for Astrophysics (CfA). "This object fills in a gap between GRBs and other supernovae of this type, showing us that a wide range of activity is possible in such blasts," he added.
The object, called Supernova 2012ap (SN 2012ap) is what astronomers term a core-collapse supernova. This type of blast occurs when the nuclear fusion reactions at the core of a very massive star no longer can provide the energy needed to hold up the core against the weight of the outer parts of the star. The core then collapses catastrophically into a superdense neutron star or a black hole. The rest of the star's material is blasted into space in a supernova explosion.
The most common type of such a supernova blasts the star's material outward in a nearly-spherical bubble that expands rapidly, but at speeds far less than that of light. These explosions produce no burst of gamma rays.
In a small percentage of cases, the infalling material is drawn into a short-lived swirling disk surrounding the new neutron star or black hole. This accretion disk generates jets of material that move outward from the disk's poles at speeds approaching that of light. This combination of a swirling disk and its jets is called an "engine," and this type of explosion produces gamma-ray bursts.
The new research shows, however, that not all "engine-driven" supernova explosions produce gamma-ray bursts.
"This supernova had jets moving at nearly the speed of light, and those jets were quickly slowed down, just like the jets we see in gamma-ray bursts," said Alicia Soderberg, also of CfA.
An earlier supernova seen in 2009 also had fast jets, but its jets expanded freely, without experiencing the slowdown characteristic of those that generate gamma-ray bursts. The free expansion of the 2009 object, the scientists said, is more like what is seen in supernova explosions with no engine, and probably indicates that its jet contained a large percentage of heavy particles, as opposed to the lighter particles in gamma-ray-burst jets. The heavy particles more easily make their way through the material surrounding the star.
"What we see is that there is a wide diversity in the engines in this type of supernova explosion," Chakraborti said. "Those with strong engines and lighter particles produce gamma-ray bursts, and those with weaker engines and heavier particles don't," he added.
"This object shows that the nature of the engine plays a central role in determining the characteristics of this type of supernova explosion," Soderberg said.
Chakraborti and Soderberg worked with an international team of scientists from five continents. In addition to the VLA, they also used data from the Giant Meterwave Radio Telescope (GMRT) in India and the InterPlanetary Network (IPN) of spacecraft equipped with GRB detectors. The team, led by Chakraborti, is reporting their work in a paper accepted to the Astrophysical Journal. Other articles, led by co-authors Raffaella Margutti and Dan Milisavljevic, also report on the X-ray and optical follow-up on SN 2012ap using a suite of space and ground-based facilities.
INFORMATION:
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
Older women with urinary tract infections who are taking the commonly prescribed antibiotic nitrofurantoin are more likely to experience treatment failure, resulting in a second antibiotic prescription or a hospital visit, than if they received another antibiotic, according to research in CMAJ (Canadian Medical Association Journal).
More than 25% of older adults have low kidney function, and bladder infections are common. Nitrofurantoin is one of the most commonly prescribed antibiotics for bladder and other urinary tract infections, with an estimated 25 million prescriptions ...
DURHAM, N.C. - Repeated alcohol exposure during adolescence results in long-lasting changes in the region of the brain that controls learning and memory, according to a research team at Duke Medicine that used a rodent model as a surrogate for humans.
The study, published April 27 in the journal Alcoholism: Clinical & Experimental Research, provides new insights at the cellular level for how alcohol exposure during adolescence, before the brain is fully developed, can result in cellular and synaptic abnormalities that have enduring, detrimental effects on behavior.
"In ...
April 27, 2015--Researchers at Columbia University's Mailman School of Public Health looked at the frequency of nonmedical prescription opioid use and the risk of heroin-related behaviors and found that past-year heroin use rose among individuals taking opioids like oxycontin and these increases varied by race and ethnicity. The most significant rise in heroin use was among Hispanics and non-Hispanic whites, where the rate of heroin use for the latter group increased by 75 percent in 2008-2011 compared to earlier years. Findings are online in the journal Drug and Alcohol ...
Determining whether your snoring is merely annoying, or crosses the threshold into a life-threatening problem, isn't convenient or cheap.
The gold standard for diagnosing sleep apnea -- a disease which affects roughly 1 in 13 Americans -- requires an overnight hospital stay and costs thousands of dollars. The patient sleeps in a strange bed, gets hooked up to a tangle of wires, and undergoes an intensive polysomnography test to count how many times a night he or she struggles to breathe.
By contrast, a new app developed at the University of Washington uses a smartphone ...
EUGENE, Ore. -- (April 27, 2015) -- Two wrongs can make a right, at least in the world of visual perception and motor functioning, according to two University of Oregon brain scientists.
In a two-experiment study, published last month in the journal Frontiers in Human Neuroscience, UO neuroscientists Paul Dassonville and Scott A. Reed used eye-tracker technology in a dark laboratory to test a developing theory about how the brain determines the locations of nearby objects.
In a test of perception, 20 students were asked to report whether a line was tilted left or right ...
BOSTON - Anyone who has ever tried to lose weight knows that it's no fun to feel hungry. In fact, the drive to tame gnawing hunger pangs can sabotage even the best-intentioned dieter. But how exactly is it that fasting creates these uncomfortable feelings - and consuming food takes them away?
Working to unravel the complex wiring system that underlies this intense physiological state, investigators at Beth Israel Deaconess Medical Center (BIDMC) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health ...
Although closely related to the notorious carnivore Tyrannosaurus rex, a new lineage of dinosaur discovered in Chile is proving to be an evolutionary jigsaw puzzle, as it preferred to graze upon plants.
Palaeontologists are referring to Chilesaurus diegosuarezi as a 'platypus' dinosaur because of its extremely bizarre combination of characters that include a proportionally small skull and feet more akin to primitive long-neck dinosaurs.
Chilesaurus diegosuarezi is nested within the theropod group of dinosaurs, the dinosaurian group that gathers the famous meat eaters ...
If you're finding it difficult to stick to a weight-loss diet, scientists at the Howard Hughes Medical Institute's Janelia Research Campus say you can likely blame hunger-sensitive cells in your brain known as AGRP neurons. According to new experiments, these neurons are responsible for the unpleasant feelings of hunger that make snacking irresistible.
The negative emotions associated with hunger can make it hard to maintain a diet and lose weight, and these neurons help explain that struggle, says Scott Sternson, a group leader at Janelia. In an environment where food ...
Johns Hopkins scientists have discovered that neurons are risk takers: They use minor "DNA surgeries" to toggle their activity levels all day, every day. Since these activity levels are important in learning, memory and brain disorders, the researchers think their finding will shed light on a range of important questions. A summary of the study will be published online in the journal Nature Neuroscience on April 27.
"We used to think that once a cell reaches full maturation, its DNA is totally stable, including the molecular tags attached to it to control its genes and ...
Eating 3,000 mg per day of salt or more appears to have no adverse effect on blood pressure in adolescent girls, while those girls who consumed 2,400 mg per day or more of potassium had lower blood pressure at the end of adolescence, according to an article published online by JAMA Pediatrics.
The scientific community has historically believed most people in the United States consume too much salt in their diets. The current Dietary Guidelines for Americans recommends limiting sodium intake to less than 2,300 mg per day for healthy individuals between the ages of 2 and ...
