Discussion: Dark matter, dark energy

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workman34	41. Unraveling Mystery Of Dark Energy Jun 8 2009, 10:46 PM EDT Precision Technique Provides Vital Tool For Unraveling Mystery Of Dark Energy ScienceDaily (June 8, 2009) — Radio astronomers have directly measured the distance to a faraway galaxy, providing a valuable "yardstick" for calibrating large astronomical distances and demonstrating a vital method that could help determine the elusive nature of the mysterious Dark Energy that pervades the Universe. "We measured a direct, geometric distance to the galaxy, independent of the complications and assumptions inherent in other techniques. The measurement highlights a valuable method that can be used to determine the local expansion rate of the Universe, which is essential in our quest to find the nature of Dark Energy," said James Braatz, of the National Radio Astronomy Observatory (NRAO), who presented the work to the American Astronomical Society's meeting in Pasadena, California. [Continued...] Post reply Do you find this valuable?
workman34	42. RE: Unraveling Mystery Of Dark Energy Jun 8 2009, 10:48 PM EDT Braatz and his colleagues used the National Science Foundation's Very Long Baseline Array (VLBA) and Robert C. Byrd Green Bank Telescope (GBT), and the Effelsberg Radio Telescope of the Max Planck Institute for Radioastronomy (MPIfR) in Germany to determine that a galaxy dubbed UGC 3789 is 160 million light-years from Earth. To do this, they precisely measured both the linear and angular size of a disk of material orbiting the galaxy's central black hole. Water molecules in the disk act as masers to amplify, or strengthen, radio waves the way lasers amplify light waves. The observation is a key element of a major effort to measure the expansion rate of the Universe, known as the Hubble Constant, with greatly improved precision. That effort, cosmologists say, is the best way to narrow down possible explanations for the nature of Dark Energy. "The new measurement is important because it demonstrates a one-step, geometric technique for measuring distances to galaxies far enough to infer the expansion rate of the Universe," said Braatz. [Continued...] Post reply Do you find this valuable?
workman34	43. RE: Unraveling Mystery Of Dark Energy Jun 8 2009, 10:49 PM EDT Dark Energy was discovered in 1998 with the observation that the expansion of the Universe is accelerating. It constitutes 70 percent of the matter and energy in the Universe, but its nature remains unknown. Determining its nature is one of the most important problems in astrophysics. "Measuring precise distances is one of the oldest problems in astronomy, and applying a relatively new radio-astronomy technique to this old problem is vital to solving one of the greatest challenges of 21st Century astrophysics," said team member Mark Reid of the Harvard-Smithsonian Center for Astrophysics (CfA). The work on UGC 3789 follows a landmark measurement done with the VLBA in 1999, in which the distance to the galaxy NGC 4258 -- 23 million light-years -- was directly measured by observing water masers in a disk of material orbiting its central black hole. That measurement allowed refinement of other, indirect distance-measuring techniques using variable stars as "standard candles." [Continued...] Post reply Do you find this valuable?
workman34	44. RE: Unraveling Mystery Of Dark Energy Jun 8 2009, 10:50 PM EDT The measurement to UGC 3789 adds a new milepost seven times more distant than NGC 4258, which itself is too close to measure the Hubble Constant directly. The speed at which NGC 4258 is receding from the Milky Way can be influenced by local effects. "UGC 3789 is far enough that the speed at which it is moving away from the Milky Way is more indicative of the expansion of the Universe," said team member Elizabeth Humphreys of the CfA. Following the achievement with NGC 4258, astronomers used the highly-sensitive GBT to search for other galaxies with similar water-molecule masers in disks orbiting their central black holes. Once candidates were found, astronomers then used the VLBA and the GBT together with the Effelsberg telescope to make images of the disks and measure their detailed rotational structure, needed for the distance measurements. This effort requires multi-year observations of each galaxy. UGC 3789 is the first galaxy in the program to yield such a precise distance. [Continued...] Post reply Do you find this valuable?
workman34	45. RE: Unraveling Mystery Of Dark Energy Jun 8 2009, 10:52 PM EDT Team member Cheng-Yu Kuo of the University of Virginia presented an image of the maser disk in NGC 6323, a galaxy even more distant than UGC 3789. This is a step toward using this galaxy to provide another valuable cosmic milepost. "The very high sensitivity of the telescopes allows making such images of galaxies even beyond 300 million light years," said Kuo. Post reply Do you find this valuable?
workman34	46. ScienceDaily (June 10, 2009) Jun 10 2009, 10:14 PM EDT Size Of A Galaxy Can Be Determined By Its Dark Matter, Physicists And Mathematicians Show ScienceDaily (June 10, 2009) — Dark matter is an enigmatic energy that makes up most of the mass in the Universe, whose nature has not yet been identified. Researchers have succeeded in estimating the percentage of dark matter in the Universe and describing the processes related to the very existence of this matter. But, until now, no one has established the distribution and behavior of the dark matter in a galaxy. Now, astronomers in the Theoretical Physics and Cosmos Department of the University of Granada, led by Eduardo Battaner, in collaboration with researchers in the Applied Mathematics Department, have made great progress: establishing the distribution and behavior of the dark matter in a galaxy. (Continued) Post reply Do you find this valuable?
workman34	47. RE: ScienceDaily (June 10, 2009) Jun 10 2009, 10:15 PM EDT New mathematical calculations on the dark matter describe the density profiles which define how the dark matter changes in a galaxy. This had not been specified in the astronomy field yet. Until now, the behaviour of the dark matter had been estimated through simulations, but the new mathematical description approach based on equations and functions which describe each characteristic of the dark matter make this result much more reliable. Specifically this new discovery allows a better understanding of the actual size of a galaxy. The collaboration of astronomers and mathematicians has allowed the developing of the density function of dark matter in a galaxy, describing how the dark matter is arranged from the galactic centre to its outermost part. When watching a galaxy to study the dark matter, a much larger size of a galaxy can be seen compared to that identified when watching the visible radiation. At the same time, it has been concluded that the density of the dark matter in a galaxy is maximum in the centre and it gradually decreases as it gets to the outermost part, but increases considerably the total size of the galaxy. This finding introduces new criteria into the study of galactic dynamics and, of course, of the dark matter. (Continued) Post reply Do you find this valuable?
workman34	48. RE: ScienceDaily (June 10, 2009) Jun 10 2009, 10:16 PM EDT Dark matter is a main component of the Universe, which has not yet been directly observed. In fact it is the component that makes up the greatest part of the Universe mass. This concept was used for the first time by Fritz Zwicky in 1933. He deduced the existence of a considerable quantity of mass that could not be observed but had to exist as an explanation to the phenomenon of galaxy movements. Currently, the quantity of dark matter in the Universe is well known: 23% dark matter vs. just over 4% of visible matter. The rest, up to 100%, is enigmatic dark energy. Despite the fact that we know well the quantity of dark matter and its behaviour, its nature has not yet been identified. This is one of the most important challenges in cosmology. "With these results, we cannot establish what dark matter is, but we have defined its behaviour and we have information that helps to know other characteristics like its temperature," Eduardo Battaner said with regard to the results of his research. (Continued) Post reply Do you find this valuable?
workman34	49. RE: ScienceDaily (June 10, 2009) Jun 10 2009, 10:17 PM EDT Starting from the wide knowledge of the group of astronomers on the dynamics of a galaxy, and applying it through the mathematical modelling knowledge, some complex descriptive functions have been developed which represent the dynamics of the dark matter. Professor Juan Soler, of the university of Granada, has been the coordinator of the research part related to the mathematical calculus. Post reply Do you find this valuable?
Amadon	50. RE: ScienceDaily (June 10, 2009) Jun 14 2009, 8:49 PM EDT There is at least one piece of evidence that dark matter may not exist: this is the Pioneer anomaly; see http://en.wikipedia.org/wiki/Pioneer_anomaly This article lists a number of possible explanations for this anomaly. One of them is: "A modification of the law of gravity. The theory MOND (Modified Newtonian Dynamics) proposes that the force of gravity deviates to a very different force law at very low accelerations of order: 10−11 m/s2 from the traditional Newtonian value.[8]" In classical physics, the force of gravity varies inversely with the square of the distance. This is of interest because authors of the Urantia Book say that over large distances, this law does not hold true. See 42:12.5. It will be a revolution in physics if this is found to be true. Post reply Do you find this valuable?
workman34	51. ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:06 PM EDT Dark Energy From The Ground Up: Make Way For BigBOSS: ScienceDaily (Aug. 20, 2009) — Several ways have been proposed to examine dark energy, in hopes of finding out just what it is. One of them, “supernovae” for short, certainly works: it’s how dark energy was discovered in the first place. Other independent techniques, such as weak gravitational lensing and baryon acoustic oscillation, also promise great power but are as yet unproven. These three techniques all have a share of the proposed Joint Dark Energy Mission (JDEM), a satellite design managed by NASA with the participation of the U.S. Department of Energy. DOE’s JDEM Project Office is headquartered at Lawrence Berkeley National Laboratory and led by Michael Levi of the Physics Division. During deliberations on JDEM’s reference design in the fall and winter of 2008-2009, some members of the JDEM Science Coordination Group (SCG), which included Saul Perlmutter and David Schlegel of Berkeley Lab’s Physics Division, questioned whether a satellite was really the best platform for all three of the proposed methods. (Continued) Post reply Do you find this valuable?
workman34	52. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:08 PM EDT “Of the three main things JDEM is supposed to do, the NASA design focuses on baryon acoustic oscillation,” says Schlegel. “It’s good science, but I wondered whether it could be done just as well, or better, from the ground.” Space is the place – sometimes The goal of all experiments that seek to determine the nature of dark energy is a detailed expansion history of the universe. For supernova studies, which depend on measuring the redshift and brightness of distant Type Ia supernovae, there’s no question that space is the place. Beginning in the 1980s, methods for finding Type Ia supernovae “on demand” were developed by the international Supernova Cosmology Project (SCP), based at Berkeley Lab and headed by Perlmutter, and adopted in 1994 by a rival team, the High-Z Supernova Search Team. In the fall of 1997 the SCP concluded that the universe is expanding at an accelerating rate, propelled by a mysterious something soon to be called dark energy. The unexpected acceleration was soon confirmed by the High-Z Team. Most of the early studies were done from the ground but included a handful of supernova measurements made with the Hubble Space Telescope. To measure expansion rate with enough precision to choose among competing models of dark energy, however, exquisite spectrometry of thousands of distant Type Ia supernovae will be needed. This can only be done by flying a big telescope and an adequate spectrograph in space. That’s why the SCP inaugurated a DOE satellite proposal in 1999 called the SuperNova/Acceleration Probe, SNAP, which eventually inspired JDEM. (Continued) Post reply Do you find this valuable?
workman34	53. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:09 PM EDT Early on, SNAP included the capacity to measure weak gravitational lensing, which looks at subtle measures of the distortion of space by both ordinary and dark matter to reveal how the distribution of matter in the universe has changed over time. Weak lensing will also greatly benefit from a space-borne telescope. Baryon acoustic oscillation (BAO) is distinct from both these methods. “Baryon” is cosmology-speak for ordinary matter, and “acoustic oscillation” is a fancy name for the way galaxies tend to bunch up at roughly 500 million light-year intervals. These density oscillations have their origin in the pressure waves (like sound waves, thus acoustic) that moved through the liquid-like plasma of the early, hot universe. By the time the universe was 300,000 to 400,000 years old, it had expanded and cooled enough for atoms to form, releasing light to go on its way unimpeded – the era of decoupling. But the density oscillations left their mark as minute temperature differences in the cosmic microwave background (CMB). The denser regions, where matter was clumped more tightly, were the seeds of today’s galaxies and groups of galaxies. (Continued) Post reply Do you find this valuable?
workman34	54. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:10 PM EDT The cosmic microwave background provides the starting point for a natural ruler to measure how much, and how smoothly, the universe has expanded since the era of decoupling. The ruler is extended forward in time by measuring variations in the density of galaxies – especially old, bright, red galaxies and quasars – across billions of light-years. The expansion history of the universe emerges when the markings of the ruler, as seen in more recent cosmic structures, are calibrated against the scale frozen in when the universe was less than 400,000 years old. Grounded cosmology But does one need a telescope in space to measure baryon acoustic oscillations? David Schlegel didn’t think so. In 2006 he and his colleague Nikhil Padmanabhan, both members of the Sloan Digital Sky Survey (SDSS), completed the largest three-dimensional map of the universe ever made until then, in which they first detected the 500-million-light-year scale of baryon oscillations. Now Schlegel leads the SDSS’s Baryon Oscillation Spectroscopic Survey, BOSS, whose goal is to map one and a half million galaxies and quasars and measure the varying densities of hydrogen gas in the universe. It will be the first survey with a chance at using BAO to measure the universe’s expansion history. (Continued) Post reply Do you find this valuable?
workman34	55. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:11 PM EDT As a member of JDEM’s Science Coordination Group, however, Schlegel was taken aback by NASA’s emphasis on baryon acoustic oscillation. “I was surprised that JDEM, a $600-million mission, was going down what seemed a risky scientific pathway,” he says. “Last winter, I was scheduled to give a talk at an SCG meeting the next day in Washington with no idea what I was going to say,” Schlegel recalls. “On my way down from New Haven on the train I just decided to work out the numbers to see if what JDEM wanted to do with BAO could be done from the ground. Remarkably, no one had done that. Instead of asking what kind of instrument we needed to do the science, the approach had been, ‘here’s the instrument we’re giving you, what can you do with it?’” Schlegel’s back-of-the-envelope BAO calculations looked “encouraging,” as he put it, and his presentation to the SCG raised a few eyebrows. But he realized existing programs were no threat to JDEM’s “figure of merit” for BAO – a more or less abstract number based on the 2006 DOE-NASA-National Science Foundation Dark Energy Task Force’s calculation of how useful a given experimental result would be for measuring dark energy. JDEM’s figure of merit is 313. The figure of merit for BOSS, the biggest ground-based BAO search underway so far, is 107. (Continued) Post reply Do you find this valuable?
workman34	56. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:12 PM EDT Nevertheless, Schlegel couldn’t shake the idea, and in February of 2009, once NASA had finalized their design ideas, he started thinking about it more seriously. “To match what JDEM proposes to do, we would need a bigger telescope than the SDSS telescope in New Mexico we’re using for BOSS. Optimum would be a 4-meter telescope that could accommodate a spectrograph with a wide field of view, covering three degrees of the sky,” Schlegel says. (For comparison, the full moon is half a degree in diameter.) “There are only 14 4-meter telescopes in the world, seven of them U.S.-operated. And whether any of them had three-degree field-of-view imaging capability, I wasn’t sure.” Two of the candidate telescopes are operated by the National Science Foundation’s National Optical Astronomical Observatory (NOAO), which oversees the Kitt Peak National Observatory in Arizona with its 4-meter Mayall Telescope, and the Cerro Tololo Inter-American Observatory in Chile, which also has a 4-meter telescope. Schlegel’s inquiries indicated that the NOAO astronomers would indeed be interested in exploring the possibility of BAO studies. (Continued) Post reply Do you find this valuable?
workman34	57. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:13 PM EDT Says Schlegel, “So I asked Michael Sholl, the optical designer in the JDEM project office here, whether the 4-meter Mayall could be adapted for a spectrograph with a three-degree field of view. He said, ‘I’ll look into it and get back to you.’” A string of luck Schlegel fully expected Sholl to tell him it couldn’t be done. And when Sholl knocked on his office door and said, “I’m really sorry, I can’t get to three degrees.” Schlegel thought that was the end of it – until Sholl added, “The best I can do is 2.94.” Says Schlegel, “I dropped everything. We were in business.” It turned out that the telescope design which would allow a three-degree (oh all right, a 2.94-degree) spectrograph was common to only three of the world’s 4-meter telescopes. NOAO’s Kitt Peak and Cerro Tololo had two of them. (Continued) Post reply Do you find this valuable?
workman34	58. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:14 PM EDT The spectroscopic instrument that would fit these telescopes had already been developed at Berkeley Lab using Laboratory Directed Research and Development funds, but wasn’t completed in time to be installed on BOSS. BOSS’s spectrograph uses optical fibers fitted into holes in metal “plug plate” masks, drilled in the precise position of galaxies mapped from previous photos. To obtain redshift and other spectral information, each fiber conducts the light of a single galaxy to a sensitive CCD. Each plate is limited to 1,000 fibers. BOSS will use some 1,500 virtually hand-made plates to gather the light of 1.5 million quasars and galaxies. The new spectrograph does away with plug plates altogether. Target galaxy positions are stored in a computer, which directs the positioning of an array of thousands of optical fibers for each exposure. A single aluminum block machined to the curvature of the modified telescope’s 1 meter focal plane is divided into 5,000 cells, each perforated by a cylindrical hole. “In each hole live a couple of robots,” says Schlegel, “actuators that can position the fibers to an accuracy of 15 microns” – 15 millionths of a meter. The robots put the tip of the fiber right where the light from the distant galaxy falls – even, if necessary, outside the hole – and positions the fibers in the focal plane with no dead space, gathering the light of some 4,000 galaxies at a time. (Continued) Post reply Do you find this valuable?
workman34	59. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:15 PM EDT To accommodate the spectrograph, the existing telescopes would need to be modified with a 2-meter secondary mirror. It so happened that a glass blank for just such a mirror, intended for the SNAP satellite, had already been bought and paid for by DOE. DOE offered it to NASA for JDEM, but NASA wasn’t interested. It was available. Schlegel realized that he and his colleagues were looking at the possibility of mounting a three-degree spectrograph on existing telescopes that could gather millions of galaxies with extraordinary spectral resolution – precision that would allow the study not just of density variations of galaxies but in the hydrogen gas that fills the universe, something JDEM could not do, covering a much wider range of redshifts than JDEM, and looking much farther back in time. Because the new approach had evolved from the existing BOSS, it was tagged BigBOSS. (Continued) Post reply Do you find this valuable?
workman34	60. RE: ScienceDaily (Aug. 20, 2009) Aug 22 2009, 7:16 PM EDT Into the fray “In a March 3 phone call to Kitt Peak we decided to go for broke,” Schlegel says. “Every 10 years the National Academy of Science’s Decadal Survey lays out a roadmap for future astronomy and astrophysics research. White papers describing proposals were due April 1. Most people work for years on these proposals; we did it in four weeks.” The joint DOE-NSF BigBOSS white paper was submitted to the Decadal Survey on time and has since gathered a string of approvals from government committees; the Decadal Survey report is due at year’s end. “We made a Hail Mary pass and hit every committee,” says Schlegel. “Our case is strong.” BigBOSS proposes to advance in two stages, the first at Kitt Peak covering the northern sky, the second at Cerro Tololo. BigBOSS North would look at the distribution of 30 million galaxies and a million quasars. After this survey is complete the project would move to Chile, where BigBOSS South would add another 20 million galaxies and quasars. Both surveys would measure distortions in hydrogen gas. (Continued) Post reply Do you find this valuable?

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