X-Ray Emissions Detected From Elusive Cosmic Objects
Posted: Wednesday, October 24, 2001
Source: University Of Colorado At Boulder (http://www.colorado.edu/)
For the first time ever, astrophysicists have observed extra energy escaping from the supermassive black hole at the center of a distant galaxy.
Undertaken with the European Space Agency’s XMM Newton satellite and an international team of researchers, the study indicates the black hole is spinning, emitting energy through a tangled web of magnetic field lines into the super-hot gases whirling slightly more slowly around it. The gas then becomes even hotter.
"The magnetic field lines are like a series of cable-like strands twisted and tightened around the black hole by intense gravity," said chief study author Joern Wilms of Tuebingen University in Germany. "Our results indicate the X-ray emissions from gas connected to the magnetic field lines are much stronger and much closer to the black hole than we expected."
A paper on the subject has been accepted for publication in the Monthly Notices of the Royal Astronomical Society in London.
"What’s really new here is evidence of additional energy coming from the spin of the black hole," said University of Colorado at Boulder Professor Mitchell Begelman of the astrophysical and planetary sciences department, a co-author on the paper. "The web of magnetic field is imposed on the black hole from the gases around it, slowing its spin."
Begelman, also a member of JILA, a joint University of Colorado-National Institute of Standards and Technology center housed on campus, likened the magnetic field to a truck clutch being let out to slow the vehicle’s speed while traveling downhill. The friction from the clutch helps brake the vehicle, just as the magnetic strands originating from the outer gaseous disk tighten around the black hole, creating friction and slowing its spin.
Christopher Reynolds, now an assistant professor at the University of Maryland at College Park and a paper co-author who worked on the study while a researcher at CU-Boulder, said the only way to explain the compact X-ray energy being observed is that the supermassive black hole is spinning.
"We would expect to see X-ray emissions distributed over a large area if they were produced by the release of gravitational energy from infalling matter into the black hole," he said. "But the big surprise is that the vast majority of these X-rays are coming from a concentrated source in the rapidly rotating disk surrounding the black hole."
Black holes are collapsed objects so tightly compacted that not even light can escape their gravitational pull. Although scientists at NASA’s Goddard Space Flight Center showed recently that small, stellar black holes believed to pepper the universe have the ability to spin, this is the first evidence that supermassive black holes also spin.
Wilms said the supermassive black hole -- known as MCG -6-30-15 and lying more than 100 million light-years from Earth -- contains material roughly equal to between one million and 10 million suns compressed into a piece of the universe much smaller than our solar system. Wilms completed a portion of his doctoral thesis at CU-Boulder under Begelman.
Begelman likened the black hole to a giant battery, storing huge amounts of energy from the constant stream of gas clouds and the occasional stars it gulps up. "It would take roughly a billion years to release all the energy stored up in MCG-6-30-15," he said.
The surprising new findings, linked to the first law of thermodynamics dealing with the conservation of energy, were predicted by scientists 25 years ago who calculated that energy stored in the spin of a black hole could be transferred to surrounding matter.
The theory goes on to predict that some of the energy flows to particle jets shooting perpendicularly from the gas disk in supermassive black hole systems called quasars. The new findings indicate that energy also can be transferred to the inner edge of the gas disk, which eventually falls into the black hole.
Understanding how fast a supermassive black hole is spinning may be an accurate and sensitive probe of how black holes are formed, said Begelman. If one is spinning relatively slowly, it probably has been growing gradually by absorbing individual clouds of gas, stars and much smaller, ordinary black holes formed by single-star collapses.
"But if it is spinning rapidly, it suggests to us that supermassive black holes were formed in a single catastrophic event, perhaps associated with the formation of a galaxy," Begelman said.
The XXM Newton Observatory launched by ESA in 1999 can collect five times as many photons as NASA’s Chandra X-Ray Observatory – which specializes in high-quality digital imagery -- allowing researchers to study the emissions of supermassive black holes in unprecedented detail, said Reynolds. But NASA has several X-ray observatories more powerful than XMM Newton in the construction or planning phase.
Note to Editors: NASA’s still images and movie files, courtesy of NASA’s Dana Berry can be accessed at: http://www.gsfc.nasa.gov/topstory/20011015blackhole.html.
Send page by E-Mail Energy from a Black Hole
Posted: Tuesday, October 23, 2001
There are plenty of black holes that gobble energy. Now astronomers have spotted one in a distant galaxy that's giving some of its energy back.
Scientists for the first time have seen energy being extracted from a black hole. Like an electric dynamo, this black hole spins and pumps energy out through cable-like magnetic field lines into the chaotic gas whipping around it, making the gas -- already infernally hot from the sheer force of crushing gravity -- even hotter.
Joern Wilms of Tuebingen University, Germany, and an international team of astronomers observed the novel "power tapping" with the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton) satellite by watching a supermassive black hole in the core of a galaxy named MCG-6-30-15. The observation also may explain the origin of particle jets in quasars.
"Never before have we seen energy extracted from a black hole," said co-author Christopher Reynolds of the University of Maryland, College Park. "We always see energy going in, not out."
"The gravity in this region appears to be so intense that the very fabric of space twists around the black hole, dragging magnetic field lines along with it," said Wilms. "The magnetic fields tighten about the black hole, slowing its spin. This 'friction' heats the region to even higher temperatures."
Scientists say most galaxies, including our Milky Way galaxy, have a supermassive black hole at their core. A supermassive black hole contains the mass of millions to billions of Suns compressed within a region smaller than our solar system. The black hole in MCG-6-30-15, over 100 million light-years from Earth, has the mass of about 100 million Suns.
The team observed the X-ray glow of iron gas traveling about half the speed of light very close to the event horizon of the black hole in MCG-6-30-15 (an "event horizon" is the theoretical border of a black hole). XMM-Newton captured the spectrum, or chemical fingerprint, of this gas. The spectrum, laid out on a graph, resembles an electrocardiogram with its spikes and dips.
The iron spectrum from MCG-6-30-15 has extremely broad "spikes," an indication of gravity tugging at the particles of light, called photons, and literally stretching the light. MCG 6-30-15's iron line was so broad, in fact, that the bulk of the light must emanate from very close to the black hole, where the force of gravity is the greatest, Reynolds said.
The total energy output, or luminosity indicated by the spectrum, however, was too bright to be powered by gravity and the free fall of matter alone. Some additional power source must exist to boost the luminosity to the observed intensity.
Co-author Mitchell Begelman of the University of Colorado said this finding may be observational evidence of a theory by Professor Roger Blandford, currently at the California Institute of Technology, and Dr. Roman Znajek, when he was at Cambridge University in England, over 25 years ago. According to the theory, rotational energy can be extracted from the black hole as it is braked by magnetic fields.
Begelman said the energy lost in MCG-6-30-15 is transferred to the inner edge of the accretion disk, a flow of gas swirling around and eventually falling into the black hole. The Blandford-Znajek theory implies that energy flows to particle jets emanating perpendicularly from the accretion disk in certain supermassive black hole systems called quasars. MCG 6-30-15 is not a quasar, but Begelman said the theory can still apply because it predicts that the magnetic field might also link to the disk.
ASCA, a Japanese X-ray satellite, found possible evidence of a spinning black hole in 1994, but the signal was too weak to observe any evidence of energy being extracted from the black hole.
XMM-Newton, launched from French Guiana by ESA in December 1999, carries three advanced X-ray telescopes with the light-collecting ability to detect millions of sources, far greater than any previous X-ray mission.
The advanced X-ray observing abilities of this satellite made this important discovery about the energy dynamics of black holes possible, and should lead to other exciting discoveries about our cosmos in the future.
Send page by E-Mail Baboons Can Think Abstractly
Posted: Tuesday, October 16, 2001
Source: American Psychological Association (http://www.apa.org/)
Baboons Can Think Abstractly, In The First Study To Show That A Non-Human, Non-Ape Animal Shares A Central Aspect Of Human Intelligence
WASHINGTON — More non-human animals may be capable of abstract thought than previously known, with profound implications for the evolution of human intelligence and the stuff that separates homo sapiens from other animals. A trans-Atlantic team of psychologists has found evidence of abstract thought in baboons, significant because baboons are "old world monkeys," part of a different primate "super family" that -- some 30 million years ago -- split from the family that gave rise to apes and then humans. Chimpanzees, in the ape family, already have demonstrated abstract thought. Now, two trained baboons successfully determined that two differently detailed displays were fundamentally the same in their overall design. Figuring this out required analogical (this is to this as that is to that) reasoning, which many theorists view as the foundation of human reasoning and intelligence.
The study is reported in the October issue of the Journal of Experimental Psychology: Animal Behavior Processes, published by the American Psychological Association (APA).
In a series of five experiments, JoŽl Fagot, Ph.D., of the Center for Research in Cognitive Neuroscience in Marseille, France; Edward A. Wasserman, Ph.D., of both the Center for Research in Cognitive Neuroscience and the University of Iowa; and Michael E. Young, Ph.D., of the University of Iowa trained two adult baboons, one male and one female, to use a personal computer and joystick to look at and select grids that had varying collections of little pictures.
In the foundation experiment, researchers familiarized the baboons with a screen display of 16 different little pictures (four rows of four across), such as the sun, an arrow, a light bulb, a train, and a house, OR with a display of the same little picture repeated 16 times (for example, all telephones). Researchers then presented the baboons with a series of choices of two new displays. In each choice, one display was a 4x4 grid with 16 different icons (for example, a clock, a brain, a hand, a triangle…); the other was the 4x4 grid with 16 identical icons (for example, all flowers). Researchers rewarded the baboons for selecting, from two choices, the array that showed the same relationships among pictures as the sample.
Researchers wanted to see whether the baboons could learn this principle. Could the baboons perceive "sameness" even when its cues were subtle and abstract?
The baboons did indeed learn to match the "different icons" test grids to sample grids at a rate greater than chance. They also learned to match "same icons" test grids to "same icons" sample grids at a rate greater than chance. It took thousands of trials for them to learn the "relation between relations" required by the task, but they did it. Say the authors, "Although discriminating the relation between relations may not be an intellectual forte of baboons, it is nevertheless within their ken."
In the primary and subsequent four experiments, Fagot et al. also tested two humans to assess baboon versus human performance. In experiments 2-5, the researchers shrunk the numbers of items in the grid to see whether a lessening in variability (the "different" grids became closer to the "same" grids, a lessening in entropy) affected the baboons' choices. Both baboons and humans learned the basic task (although the humans learned far faster), and transferred it to novel sample displays, but humans were far more accurate at matching grids when the number of icons was reduced.
The baboons and humans seemed to have different cutoff points for discerning same vs. different, with humans being more sensitive to entropy. The authors speculate that language may play a role, because our verbal expression for "same" makes the idea of "same" more restrictive -- in other words, things really have to be identical to qualify. To baboons, the authors suggest, the concept of "same" might be fuzzier and more inclusive.
The baboons' ability to abstract opens the door to other species' cognitive potential. Fagot et al. state that additional research of non-human animals is necessary before theorists attempt to limit the capability for abstraction only to certain species. They state, "Analogical thinking and its possible precursors may very well be found in non-human animals -- if only we assiduously look for them."
Article: "Discriminating the Relation Between Relations: The Role of Entropy in Abstract Conceptualization by Baboons (Papio papio) and Humans (Homo sapiens)," JoŽl Fagot, Center for Research in Cognitive Neurosciences of the National Center for Scientific Research in Marseille, France; Edward A. Wasserman, Center for Research in Cognitive Neurosciences (as above) and the University of Iowa, Iowa City; and Michael E. Young, University of Iowa, Iowa City; Journal of Experimental Psychology – Animal Behavior Processes, Vol 27. No.4.
Full text of the article is available from the APA Public Affairs Office and at http://www.apa.org/journals/xan/press_releases/october_2001/xan274316.html
The American Psychological Association (APA), in Washington, DC, is the largest scientific and professional organization representing psychology in the United States and is the world’s largest association of psychologists. APA’s membership includes more than 155,000 researchers, educators, clinicians, consultants and students. Through its divisions in 53 divisions of psychology and affiliations with 60 state, territorial and Canadian provincial associations, APA works to advance psychology as a science, as a profession and as a means of promoting human welfare.
Send page by E-Mail Lunar Soil Yields Evidence About Sun's Dynamic Workings
Posted: Tuesday, October 16, 2001
Source: Purdue University (http://www.purdue.edu/)
WEST LAFAYETTE, Ind. — Soil collected on the moon by Purdue University alumnus Eugene Cernan nearly 30 years ago has helped researchers at his alma mater and the University of California uncover new details about the workings of the sun.
Physicists at UC Berkeley and Purdue analyzed lunar soil samples for the presence of an element deposited on the moon's surface by the solar winds, a stream of particles constantly being ejected from the sun. The analysis revealed strong evidence that materials produced in the sun's atmosphere do not circulate farther into the interior of the sun before they are ejected, as some scientists have suggested. Instead, the materials are created in the atmosphere and then ejected directly outward, spreading throughout the solar system in the solar wind.
The findings will be reported in the journal Science on Friday (10/12), in a paper written by Kuni Nishiizumi, a researcher at UC Berkeley's Space Sciences Laboratory, and Marc Caffee, an associate professor of physics at Purdue.
The lunar soil was scooped up by Apollo 17 astronauts Cernan and Harrison Schmitt, who landed on the moon in 1972. They collected the largest lunar sample ever brought back to Earth — about 249 pounds of dirt now stored at the Johnson Space Center in Houston.
"The astronauts did a spectacular job," Caffee said, noting that robots are still no substitute for humans in space when it comes to completing complex assignments.
Cernan, who was the commander of Apollo 17, was the last man to walk on the moon. He earned a bachelor of science degree in electrical engineering from Purdue in 1956 and also holds an honorary doctorate from the university.
Nishiizumi and Caffee analyzed lunar soil for the presence of a radioactive form of the element beryllium called beryllium-10. Beryllium-10 is an isotope of beryllium; it contains four protons and six neutrons in its nucleus, unlike ordinary beryllium, which contains four protons and five neutrons. This radioactive, unstable form of beryllium decomposes in 1.6 million years, a period of time called its half-life. That means any beryllium-10 found in the lunar soil must have been deposited there long after the moon's creation, and much of it has come from the solar winds, Caffee said.
Beryllium-10 is produced in the sun's atmospheric layers — the chromosphere and corona — and eventually spewed out, along with numerous other constituents, in the solar wind.
"The sun is constantly shedding pieces of itself," Caffee said.
The Earth and other planets are shielded from the solar winds by their atmospheric envelopes and magnetic fields that surround some planetary bodies.
"The moon has no atmosphere and no magnetic field, so the solar wind is not kept in any way, shape or form from hitting the surface of the moon," he said.
The researchers extracted beryllium-10 from the lunar soil by treating the soil with nitric and hydrofluoric acids. Then, the precise quantity of beryllium-10 contained in the soil was determined by using a piece of equipment called an accelerator mass spectrometer.
The findings provided strong evidence that the beryllium, and therefore other constituents produced in the sun's atmosphere, are ejected shortly after they are produced in the atmosphere. Some researchers have suggested that materials produced in the sun's atmosphere are pulled into the sun's interior, where they circulate in convection currents for millions of years before making their way back to the sun's outer atmospheric layers.
The new findings contradict that theory, Caffee said.
Such findings will not only reveal details about the sun's workings, but they also will provide new insights into how the sun and the solar system were formed 4.5 billion years ago.
"Surprisingly, there are a lot of things we still don't know about the sun," Caffee said.
He and Nishiizumi are working on a new NASA mission called Genesis, a spacecraft launched this summer that will collect particles from the solar wind.
The spacecraft is expected to complete its mission within two years and return to Earth.
Send page by E-Mail Study Suggests Mechanical Forces Drive Early Heart Development
Posted: Tuesday, October 9, 2001
Source: Washington University In St. Louis (http://www.wustl.edu/)
The poet in us might see the heart as "a lonely hunter"; the adolescent as a toy that’s easily broken. But the biomedical engineer sees the heart as a pump, plain and simple, a machine shaped by genetics and complex biomechanical forces.
Larry A. Taber, Ph.D., professor of biomedical engineering at Washington University in St. Louis, has been probing the forces, stresses and deformations of the heart since the mid-1980s. A major focus of his work is to show that biomechanical forces may be as important as genetics in shaping the heart. Recently, he has developed a theory on tissue growth and morphogenesis (shape change) and applied it to understanding the developing heart in chicken embryos, which is remarkably similar to its counterpart in humans.
Taber is studying a phenomenon known as looping, one of the most critical stages of embryo heart development, where the heart at just two days of age in chickens (three weeks in humans) bends outward and rotates to the right. This is an almost ballet-like move that must happen perfectly to avoid misconnections of arteries in the heart walls and holes in the heart, among other serious developmental problems.
Taber’s theory factors cellular contraction into looping, and he has found that the split-second looping process of bending and rotation is actually driven by at least two different mechanical forces. His research could help scientists better understand the roles physics and mechanics play in the developing heart and in heart defects.
Because geneticists currently do most of the research in this field, Taber and other biomedical engineers studying heart development provide clues into the cause-and- effect of the gene’s masterplan, as well as a different perspective.
"You can knock out a gene and the heart might do something, but you don’t really know the underlying mechanism," Taber says. "You only know you take this gene out and you see this effect. My collaborators and I are between the gene and the effect that people see. We’re tyring to understand exactly what’s driving the heart to respond the way it does.
"Genetics researchers will say ‘The heart either loops or it doesn’t, and if it loops it either goes left or right,’ and those often are the only distinctions made. "They don’t say, ‘It’s possible that it bends and doesn’t rotate.’ In our experiments, however,we see that that might happen. The point we’re trying to get across now is that to understand heart development, we have to look at bending and rotation as distinct components."
Taber discussed his theory, experiments and future direction of cardiac biomechanics in "Biomechancis of Cardiovascular Development," in the 2001 edition of Annual Revue of Biomedical Engineering. His work is supported by the National Institutes of Health (NIH). The chicken embryo heart is very close to the human heart in its development processes. It takes 21 days to hatch a chicken; at day 1, tubes form on two sides of the embryo and come together to form one tube. At this juncture (two-and-a-half weeks in the human embryo) the heart is just starting to beat. During the second day, blood flow starts and by the third day the tube is beginning to look like a heart, with septums later forming in two different regions to create left and right ventricles on one side, and right and left atria on the other.
Taber and his colleagues are stumped so far on the bending component of looping, though his graduate student, Evan Zamir, has developed techniques that will help them measure the stiffness in different regions of the heart tube. It appears that regional stiffness plays a role in bending. Another student, Mathieu Remond, is looking into whether cells in one region might contract more than cells on other sides, forcing the bending.
As for rotation, another Taber collaborator, Dimitri Voronov, Ph.D., a visiting scientist at Washington University , has discovered that a membrane that covers the tube may play a major role in causing the rotation to go to the right. "We believe that when the heart is formed it’s slightly biased to the right normally , and that the membrane pushes it the rest of the way," Taber explained. Taber says engineers are just now looking at growth in the mature heart. His theory will be valuable in looking at these situations. Growth occurring in the mature heart is extremely important and plays a role in adaptation to high blood pressure (thicker heart walls) and heart attack.
"On the horizon, people are going to be looking at how the mechanical properties of the heart change as it develops," Taber says. "The active properties of heart tissue cause shape changes, as well as cause the heart to beat and pump blood. Until we have a handle on these properties, we cannot trust the predictions of our theoretical models."
Send page by E-Mail Scientists Make Key Finding Underlying Genetic Stability
Posted: Friday, October 5, 2001
Source: Los Alamos National Laboratory (http://www.lanl.gov/)
LOS ALAMOS, N.M., Oct. 4 2001 - Biologists at the U.S. Department of Energy's Los Alamos National Laboratory have discovered new insights into how two common proteins found in mammalian cells can cause chromosomes to fuse together -mutations that can destroy cells or give rise to cancer.
The research, by Susan Bailey and Edwin Goodwin of Los Alamos' Biosciences Division, was published recently in the journal Science.
Bailey, Goodwin and their colleagues looked at the role of telomeres in protecting chromosome ends. Chromosomes are made of deoxyribonucleic acid - DNA - and are the carriers of genetic information. Human cells contain 22 pairs of chromosomes plus two gender chromosomes. Telomeres are specialized protective structures at the end of each arm of the X-shaped chromosomes.
Without telomeres, natural chromosome ends appear to the cell like broken DNA ends in need of repair. Mutations in certain genes impair the protective function of telomeres leading to inappropriate "repair," in effect causing chromosomes to fuse together end to end. Chromosome end fusions destabilize the orderly transmission of genetic information to the next generation of cells. The Los Alamos researchers studied telomere dysfunction in order to learn more about how a normal telomere works.
Each chromosome has four telomeres. Mammalian telomeres contain a unique DNA sequence, discovered earlier by Los Alamos' Human Genome Project, as well as specialized proteins that together create a protective cap at the ends of chromosome arms.
Bailey and Goodwin looked at the role of two proteins in telomere function. One protein was known to play a role in telomere function and chromosome end capping. The other protein originally was shown to help repair damaged DNA, but later was shown by Bailey and Goodwin to also help protect natural chromosome ends.
The researchers used human cells provided by Titia DeLange of Rockefeller University that contained artificially induced changes to the first protein and mouse cells with mutations in the second protein. Under normal circumstances, when cells divide they produce exact duplicates, including exact duplicates of the chromosomes they contain. Bailey, Goodwin and their colleagues found that the progeny of cells containing the altered proteins often contained chromosomes that had fused with other chromosomes at one arm. The fused chromosomes had a sausage-like appearance and were easy to distinguish from normal chromosomes. Due to their genetic abnormalities, the damaged daughter cells often were unable to thrive.
The fusing chromosome arms in the dying daughter cells indicated that the malfunction might be associated with telomere replication and indicative that the protein changes induced in the original cells played a role. But Bailey and Goodwin noticed something else - something extraordinary and unexpected.
Using a Los Alamos-developed technique called chromosome-orientation fluorescence in situ hybridization - CO-FISH -that highlights which half strand of the DNA double helix underwent replication during the cell-division process, the researchers determined that the fusion only occurred on specific arms of the chromosomes. What's more, Bailey and Goodwin noticed that fusion never occurred in a chromosome on two arms on the same-side of the "X"; if more than one fusion occurred in a single chromosome, the fusion always occurred on opposite arms on opposite sides. This indicated to the researchers that not all telomeres in a chromosome are the same, because if they were, the researchers would have expected to see same-side fusion in at least some cases simply based on the laws of chance.
"A lot of research has been done on telomeres in the biological community, and the conventional thought was that all telomeres are created alike," said Goodwin. "Our research shows that this is not the case. There are two different processes for protecting telomeres and they have distinct genetic requirements."
The difference in telomeres apparently lies in the way chromosomes are replicated, Bailey and Goodwin found. When chromosomes duplicate themselves, their DNA double helices separate into two strands and then rebuild their DNA structure on each half strand. Because DNA polymerases - the protein catalysts that make the new DNA strands - proceed in only one direction, the two new telomeres replicated from the original parent telomere are produced by two different mechanisms.
In one case, the telomere's double helix terminates in a blunt end. In the other case, the telomere ends with a minute chemical overhang. This overhang is important because it allows the telomere to loop back on itself - forming a so-called "t-loop" - to complete its end cap. The first process is known as leading-strand DNA synthesis; the second is known as lagging-strand DNA synthesis.
Bailey, Goodwin and their colleagues found that chromosome fusion occurred only at sites on the chromosomes where telomeres had been formed by the leading-strand process.
The research indicates that both altered proteins induced in the cells used for study play a role in capping the ends of telomeres formed by leading-strand DNA synthesis, but are not required to cap telomeres replicated by lagging-strand synthesis.
Bailey and Goodwin's research is significant because it has shown the existence of two types of telomeres and also gives insight into the roles of two proteins in normal cell function.
All of Bailey's and Goodwin's co-authors of the paper are former Los Alamos researchers, and include: Michael Cornforth, Department of Radiation Oncology, University of Texas Medical Branch; and Akihiro Kurimasa and David Chen, Cell and Molecular Biology Division, Lawrence Berkeley National Laboratory.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.
Send page by E-Mail Strange Trail Suggests Presence Of Galactic Interloper
Posted: Monday, October 1, 2001
Source: University Of Illinois At Urbana-Champaign (http://www.uiuc.edu/)
CHAMPAIGN, Ill. — Scientists have discovered what looks like a jet contrail, possibly left behind by a dwarf star traveling through interstellar space.
As reported in the September issue of The Astronomical Journal, astronomer Peter R. McCullough at the University of Illinois at Urbana-Champaign and research scientist Robert Benjamin at the University of Wisconsin at Madison found a straight and narrow filament of ionized gas stretching 2.5 degrees across the sky near the Big Dipper in the constellation Ursa Major.
"We believe the gas trail was produced by the radiation from a white dwarf or some other
low-luminosity source zipping through the local interstellar medium and leaving behind an ionized wake," McCullough said. "The problem is that we have not yet identified the source."
While other possible explanations were considered – such as a jet of low-density stellar radiation or a linear wisp of gas associated with some nearby nebula – they are not favored because the filament’s properties are so different from other examples of those types of objects, McCullough said.
The filament is roughly Y-shaped. The vertical segment of the Y is about 1.2 degrees long and about 20 arcseconds wide. The full width of the two diagonal segments is about 5 arcminutes. The distance to the gas trail is not known, but it is suspected to be approximately 300 light-years from Earth.
"We know that white dwarfs – hot, dense stars not much bigger than a large planet – can leave these kinds of trails, but they will be very faint," Benjamin said. Such trails had been predicted to exist by two Harvard astronomers in the early 1980s, but had never been seen. "This could be the brightest trail visible from Earth and therefore the first one found."
If that turns out to be the case, astronomers might locate other such trails by photographing candidate white dwarfs whose distance and direction of motion are accurately known.
The object was first photographed in January 1997 with a small camera equipped with a hydrogen-alpha filter. Additional observations were made in April and May 1999 with a different filter mounted on the UI’s 40-inch reflecting telescope at Mount Laguna Observatory in southern California. The researchers also detected the object with the Wisconsin Hydrogen-Alpha Mapper (WHAM), confirming that the source was not from beyond our galaxy. The research was funded in part by the National Science Foundation.
"The filament’s large angular size also suggests it is nearby, and therefore we should be able to identify what created it," McCullough said. If the source can be identified and studied, astronomers could use its properties to probe interesting parameters of the local interstellar medium – such as the density of the ambient gas and the level of turbulence in interstellar space.
"The culprit could be sitting right under our noses and we don’t recognize it," McCullough said. Additional observations with other telescopes may solve this cosmic whodunit.
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