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Topic: Dark Matter Galaxy Discovered (Read 573 times) |
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DJ dAndroid
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Dark Matter Galaxy Discovered
« on: 2005-02-25 07:17:28 » |
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Astronomers have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter. The team, led by Cardiff University, UK, claims it is the first such object to be detected. A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars. It was found 50 million light-years away using radio telescopes in England and Puerto Rico.
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David Lucifer
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Re:Dark Matter Galaxy Discovered
« Reply #1 on: 2005-02-25 10:19:34 » |
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Dark matter has been postulated to make the current theory of gravitation fit with observation. From the article:
Quote:We only know of dark matter's existence because of its influence on ordinary matter.
Scientists can infer its presence by looking at the rotation of galaxies and measuring how fast their visible components are moving.
The amount of matter in a galaxy dictates the gravitational force needed to hold it together.
Astronomers have seen galaxies where the material is moving so fast that they should fly apart - as they don't, there must be a stronger gravitational force acting than can be accounted for using visible matter. |
But isn't it equally as likely that there is something wrong with our current theory of gravitation? What if it only takes the simple form on relatively small scales like Newton's equations of motion are simple at relatively low velocities? I suspect most cosmologists have thought of this already, so they must have a good reason to introduce an invisible entity like dark matter. Anyone know why?
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David Lucifer
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Re:Dark Matter Galaxy Discovered
« Reply #2 on: 2005-02-25 10:34:48 » |
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Just found this link via the extropy-chat list>>
http://www.eurekalert.org/pub_releases/2005-02/uoc-sma021405.php
Quote:
The fifth speaker, New York University physics professor Gia Dvali, will address the possibility that there is no dark energy. In the scenario proposed by Dvali and his collaborators, "the universe's acceleration is due to modification of standard laws of gravity at very large distances," he said. This modification would be caused by the existence of an extra dimension of space.
Most of the known forces of nature, such as electromagnetism, would be confined to the three dimensions perceived by humans. "Only gravity can travel in the bulk of the extra space, but even gravity does so only after traveling an enormously large distance," Dvali said.
Dvali uses the analogy of a metallic sheet submerged in water to illustrate the principle. If one hits the sheet with a hammer, shock waves will carry away the energy in all directions. "Most of the energy will travel along the two-dimensional surface. Only at a substantial distance away from the source will the energy loss to water be appreciable," he said. "According to our picture, we are in a very similar situation. We think gravity is 'normal' because we only measure it directly at relatively short distances, but cosmic acceleration indicates leakage."
If gravity is modified at large distances, it's modified everywhere. That would make it possible to verify modified gravity by measuring the orbit of the moon to within one millimeter (four hundredths of an inch), and compare that to the lunar orbital prediction as dictated by Einstein's theory of gravity. Laser-ranging experiments left on the lunar surface by the Apollo astronauts have already measured the lunar orbit with an accuracy of approximately a centimeter (four tenths of an inch). A new, more precise experiment is in the planning stages.
"In the near future we may know if modified gravity is responsible for cosmic acceleration, and all this just by looking at the moon!" Dvali said.
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I predict this will turn out to be the case and dark matter/energy will be thrown in the same bin with phlogiston and the ether.
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Walter Watts
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Re:Dark Matter Galaxy Discovered
« Reply #3 on: 2005-02-25 10:43:50 » |
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Thanks for that link Lucifer...Nice article.
I second your prediction:
"I predict this will turn out to be the case and dark matter/energy will be thrown in the same bin with phlogiston and the ether."
Walter
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Walter Watts
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Durazac15
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Re:Dark Matter Galaxy Discovered
« Reply #4 on: 2005-03-01 17:02:11 » |
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In the original article posted by WW:
Quote:| A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars. |
It seems to me that if the dark matter galaxy "rotates", or more specifically can be shown to rotate, then this eliminates the possibility of Dvalis scenario.
Without rotation, then still I would suspect that Dvali is wrong based on fact that current modeling currently and accuratly describes the Universe as it is using our current understanding of Gravity. See the following link for that.
http://news.bbc.co.uk/1/hi/sci/tech/4161323.stm
And then, even without the above story, when it comes to choosing "dark matter" or "another dimension" as the most likely possibility, I'll go with dark matter.
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