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 Re: إكتشاف مكان المادة السوداء (Re: Muna Khugali)
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الاخت منى
الاخ مامون
الاخ المعز
كل سنة وانتم بخير
أنا أطلع على ما يجري بالمنبر كثيراً واحياناص اشارك في مداخلات.
موضوع ملاحقة إكتشافات ومعلومات علماء الكونيات الجديدة من إهتماماتي والمادة المعتمة او السوداء هي من الإهتمامات القوية ايضاً للصديق الماحي على الماحي الذي لو استطعنا جذبه للكتابة في المنبر وهو من المتابعين لبعض موضوعاته لكسبنا قلماً فذا .فهل ترى يقوم صديقه وعضو المنبر الاستاذ مسعود محمد على بجذب الماحي للمنبر آمل ذلك.
ويا المعز آمل ان يمدنا مهتمون اقوى مني بالروابط ويا مامون انا على يقين بان الافكار السوداء لا تهزك والازمنة السوداء ليست عارضاً حادثاً بل ظل الإنسان على مر تاريخه على الكوكب ينظر لما يجري كانه نهاية العالم والشواهد من التاريخ وفيرة.
التامل في الكون يوسع من منظور الإنسان ورؤيته. يجب ان نتفكر في كون زمنه 15 مليار سنة ضوئية ولا نحصر انفسنا في كوكب ياتي إليه الضوء من نجم لا يبعد عنه اكثر من ثمان دقائق ضوئية يجب ان نقارن بين هاتين المسافتين ثمان دقائق ضوئية و15 مليار سنة ضوئية وتزيد.
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Re: إكتشاف مكان المادة السوداء (Re: حيدر حسن ميرغني)
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مرحباً بظهور استاذ الجيل د. بشري الفاضل،
و الله يا دكتور لمن قلت مكان المادة السوداء افتكرتو الخور بتاع سودانيز اونلاين زي ما بسموه الاخوة اعضاء المنبر.
موضوع البوست قيم و جميل اتمني ان اوفق في المشاركة الفاعلة فيه.
مودتي
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Re: إكتشاف مكان المادة السوداء (Re: Masoud)
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We believe that most of the matter in the universe is dark, i.e. cannot be detected from the light which it emits (or fails to emit). This is "stuff" which cannot be seen directly -- so what makes us think that it exists at all? Its presence is inferred indirectly from the motions of astronomical objects, specifically stellar, galactic, and galaxy cluster/supercluster observations. It is also required in order to enable gravity to amplify the small fluctuations in the Cosmic Microwave Background enough to form the large-scale structures that we see in the universe today.
Dark matter Not dark matter
For each of the stellar, galactic, and galaxy cluster/supercluster observations the basic principle is that if we measure velocities in some region, then there has to be enough mass there for gravity to stop all the objects flying apart. When such velocity measurements are done on large scales, it turns out that the amount of inferred mass is much more than can be explained by the luminous stuff. Hence we infer that there is dark matter in the Universe.
Dark matter has important consequences for the evolution of the Universe and the structure within it. According to general relativity, the Universe must conform to one of three possible types: open, flat, or closed. The total amount of mass and energy in the universe determines which of the three possibilities applies to the Universe. In the case of an open Universe, the total mass and energy density (denoted by the greek letter Omega) is less than unity. If the Universe is closed, Omega is greater than unity. For the case where Omega is exactly equal to one the Universe is "flat".
Note that the dynamics of the Universe are not determined entirely by the geometry (open, closed or flat) unless the Universe contains only matter. In our Universe, where most of Omega comes from dark energy, this relation between the mass density, spatial curvature and the future of the universe no longer holds. It is then no longer true in this case that "geometry (spatial curvature) is destiny." Instead, to find out what will happen one needs to calculate the evolution of the expansion factor of the universe for the specific case of matter density, spatial curvature and "funny energy" to find out what will happen.
Dark matter (DM) candidates are usually split into two broad categories, with the second category being further sub-divided:
Baryonic
Non-Baryonic
hot dark matter (HDM) and
cold dark matter (CDM),
depending on their respective masses and speeds. CDM candidates travel at slow speeds (hence "cold") or have little pressure, while HDM candidates move rapidly (hence "hot").
For more information
read the Essay by Joe Silk,
or the SciAm article by Vera Rubin,
learn more about the Hubble expansion
see the NCSA's Cosmos in a Computer site, which has a lot of information on dark matter and cosmology in general, including movies simulating the universe,
see astronomer G. Bothun's page, which has a lot of information on dark matter and early universe cosmology,
read this popular level article, which outlines the different dark matter candidates,
look at this dark matter tutorial, which has some experiments you can run if your browser supports Java,
or see one of the books or articles in the Bibliography.
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Aside on flatness
Current indications from the cosmic microwave background are that the universe is spatially flat. That implies that the sum of all of the energy (density) in the universe equals the critical density, i.e. the total Omega is 1. This is quite interesting because as the Universe expands the value of Omega changes. In fact the value 1 is unstable, and the Universe would prefer to evolve towards one of the two natural values: 0, if the expands forever further apart until the Universe is almost totally empty ; and infinity, if the matter recollapses to a state of higher and higher density. Then the observation that Omega is fairly close to 1 today, means that it must have been even closer to 1 in the past. It is unsatisfying to believe that we just happen to live at the time when Omega is just starting to depart from 1 by a small factor. It is much more appealing to consider that we do not live at a special epoch, so that Omega is still close to 1 today. But then we need to explain why Omega started out very close to 1 in the early universe. The theory of inflation provides just such a justification - most versions of inflation predict that the early Universe was driven extremely close to flat, and that it is still very close to flat today. If this is so, then at least 90% the energy of the Universe is dark! Note that although the universe may be flat, that does not mean that matter makes up the critical density. In addition to dark matter there is dark energy, e.g. a cosmological constant, that needs to be included in the accounting.
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Re: إكتشاف مكان المادة السوداء (Re: Bushra Elfadil)
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قبل ما نطمع في تعليق من الماحي يفتح شهيتنا للونسة حول الموضوع.. ده تقريبا خلاصة ما حدث للمادة إستنادا على نظرية إنشتين:
"نظرية النسبية العامّة هي نظرية وضعها العالم الالماني المولد الأمريكي الجنسية ألبرت إنشتين ونشرها عام 1915، والنظرية النسبية العامة هي تعميم للنظرية النسبية الخاصة والتي غيرت مفهوم النسبية في قياس الكميات الفيزيائية ليصبح نظاما من أربعة أبعاد يكون الزمن البعد الرابع فيها ، وبالتالي لم يعد من الدقة بمكان الحديث عن الكميات الفيزيائية بإهمال البعد الزمني النسبي والذي تمثله السرعة.
وأضافت النظرية النسبية العامة فكرة تقعر الفراغ بوجود المادة ، وهو الأمر الذي يعني أن الخطوط المستقيمة تتشوه بوجود الكتلة ، وأثبتت النظرية النسبية العامة عندما تحقق تنبؤ أينشتاين بالتباعد الظاهري لنجمين في فترة وذلك يعود إلى تشوه مسار الضوء القادم من النجمين بسبب مرورهما قرب الشمس ذات الكتلة العالية نسبيا وبالتالي تقوس خط سير الضوء القادم من النجمين".
تصوير ثنائي الأبعاد للفضاء-الزمن. وجود المادة يؤدي الى ثني سطح الفضاء-الزمني. يفسر هذا الثني على أنه ظاهرة الجاذبية.
Gravitational Lensing Explanation
This illustration explains how gravitational lensing, a prediction of Einstein's theory of general relativity, can be used to determine the location of mass in a galaxy cluster. Gravity from mass in the galaxy cluster distorts light from background galaxies. In the idealized case shown here, two distorted images of one background galaxy are seen above and below the real location of the galaxy. By looking at the shapes of many different background galaxies, it is possible to make a map showing where the gravity and therefore the mass in the cluster is located. This is an excellent technique for studying dark matter.
Scale: Image is 13.5 x 10.6 arcmin
(Illustration: NASA/CXC/M.Weiss)
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These images show the galaxy cluster 1E 0657-56, also known as the bullet cluster. The optical image from Magellan and HST shows galaxies in orange and white. Hot gas in the cluster, which contains the bulk of the normal matter in the cluster, is shown by the Chandra X-ray Observatory image in pink. Most of the mass in the cluster is shown in blue, as measured by gravitational lensing, the distortion of background images by mass in the cluster. This mass is dominated by dark matter. The clear separation between normal matter and dark matter has not been seen before and gives the strongest evidence yet that most of the matter in the Universe is dark.
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Chandra X-ray Image of 1E 0657-56
Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. Never previously seen, this discovery, made with NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.
Scale: Full-field image is 13.5 x 10.6 arcmin
(Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.;
Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.)
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collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.
"This is the most energetic cosmic event, besides the Big Bang, which we know about," said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
These observations provide the strongest evidence yet that most of the matter in the universe is dark. Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories cannot explain the observed effects of this collision.
كثر التعديل لزوم ترتيب المواد و ضبط حجوم الصور!..
(عدل بواسطة Elmuez on 01-09-2007, 05:11 PM)
(عدل بواسطة Elmuez on 01-09-2007, 05:18 PM)
(عدل بواسطة Elmuez on 01-09-2007, 06:12 PM)
(عدل بواسطة Elmuez on 01-09-2007, 06:15 PM)
(عدل بواسطة Elmuez on 01-09-2007, 06:37 PM)
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Re: إكتشاف مكان المادة السوداء (Re: Bushra Elfadil)
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أضعف الايمان هو قوقل.
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Dark Matter Map Gives Clues To Galaxies
Jan. 8, 2007
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(Christian Science Monitor) This article was written by Peter N. Spotts.
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The map of the universe, which astronomers have been plotting for some 20 years, reveals that the vast numbers of visible galaxies are not randomly arrayed, but rather display a breathtaking structure. Now scientists are detecting structure in the universe's unseen "dark matter" — whose gravity herds stars into galaxies and galaxies into enormous clusters tens of millions of light-years across.
Sunday, a team of astronomers unfolded the first large-scale map of dark matter, one of the cosmos's most enigmatic ingredients. Such maps are vital to understanding how galaxies evolved and gathered themselves into larger structures, researchers say.
To the untrained eye, the map looks a bit like a hiker's topographic map. But to astrophysicists, the 3-D map — which represents a time span dating back to roughly half the age of the universe — is independent evidence confirming their thesis of how the cosmos evolved after the big bang some 13.6 billion years ago.
Filaments of dark matter grow as time passes, the map indicates. Galaxies form within the filaments. Where filaments cross and join, larger amounts of dark matter accumulate — corresponding to galaxy clusters astronomers can see.
A bigger span of sky
The results represent "an exciting new view of the dark universe," according to Eric Linder, an astrophysicist at the Lawrence Berkeley National Laboratory, in Berkeley, Calif. "Most attempts at detecting dark matter have involved a single galaxy or cluster of galaxies," he says. The new map "scans a much wider area of the universe" — a patch roughly equivalent to an area that would be covered by eight full moons corralled into a single part of the sky, as seen from Earth.
Dark matter has puzzled astronomers ever since its existence was first posited nearly 75 years ago. Nobody can see it directly, so astronomers infer its presence by the influence its gravity exerts on other celestial objects. Without it, for example, galaxies would fly apart as they spin, because the mass of a galaxy's visible matter is not sufficient to generate enough gravity to hold the galaxy together.
Moreover, nobody knows what it's made of, although scientists are testing several ideas. But on the list of ingredients that make up the cosmos, dark matter is a big deal: Cosmologists estimate that it accounts for 23 percent of the universe's matter and energy budget. Matter that astronomers can see makes up only 4 percent of the total. Dark energy accounts for the balance.
The astronomical 'how to'
To locate dark matter on such large scales, the mapping team of astronomers took a page from Albert Einstein's theory of general relativity and used gravity as a lens. One of the theory's successful predictions: Gravity can bend light, similar to the detour a glass lens imposes as light passes through it.
The team, led by Richard Massey at the California Institute of Technology in Pasadena, gathered detailed images of roughly 500,000 galaxies. Gravity from dark matter distorted the shapes of the galaxies, and the team used those distortions to calculate the mass of dark matter between each object and Earth. Using the Hubble Space Telescope, they spent 1,000 hours imaging 575 overlapping patches of sky. Astronomers gathered follow-up information on the individual galaxies and on normal matter using ground-based telescopes and the European Space Agency's XMM-Newton orbiting X-ray telescope.
The team presented its results Sunday in an early online edition of the journal Nature and at a press briefing at the winter meeting of the American Astronomical Society in Seattle.
The data covered three onionlike "layers" of distance, so the map gives scientists a glimpse at how changes in dark-matter distribution altered the distribution of visible matter over time.
For example, notes team member Nick Scoville, several of the early dark-matter structures hold galaxies that are in the process of forming clusters. And the ages of many of these galaxies appear to show that galaxies formed from smaller collections of stars.
This would favor one recipe for dark matter: so-called cold dark matter, made of fundamental particles that have far larger masses than a proton and that interact only weakly with ordinary matter. Physicists are hunting for some of these directly at particle accelerators around the world.
The new map reinforces what astronomers call the "concordance" view of the universe's matter-energy proportions — drawn from maps of the visible universe, as well as from new maps of the microwave radiation left over from the big bang.
New puzzles posed
But the new data present puzzles of their own. The map shows some areas where luminous matter and dark matter don't track each other, notes Dr. Linder. This suggests that the idea of dark matter as skeleton for the large-scale structure and distribution of bright matter may break down under certain situations.
"We may need to fine-tune our ideas of how galaxies form," he says.
What is clear is that cosmic cartography is entering yet another new era.
© 2007 The Christian Science Monitor. All rights reserved.
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Bushra Elfadil
Muna Khugali
حيدر حسن ميرغني
Salah Musa
Elbagir Osman
فيس بوك
تويتر
انستقرام
يوتيوب
بنتيريست