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	Galaxy rotation problem - Wikipedia, the free encyclopedia
		The galaxy rotation problem is the discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the luminous mass.
		The presence of this discrepancy is explained by astronomers as pointing to the existence of dark matter in the halo of the galaxy.
		The explanation that requires the least adjustment to the physical laws of the universe is that there is a substantial amount of matter far from the center of the galaxy that is not emitting light in the mass-to-light ratio of the central bulge.
	en.wikipedia.org /wiki/Galaxy_rotation_problem (573 words)

	Rotation curve - Wikipedia, the free encyclopedia
		The rotation curve of a galaxy; that is, the orbital velocity as a function of distance from the centre of the galaxy.
		In astrophysics, the rotation curve of a galaxy is a graph that plots the orbital velocity of the stars or gas in the galaxy on the y-axis against the distance from the center of the galaxy on the x-axis.
		Stars rotate around the center of galaxies at a constant velocity over a large range of distances from the center of the galaxy.
	en.wikipedia.org /wiki/Rotation_curve (380 words)

	Galaxy rotation problem Info - Encyclopedia WikiWhat.com (Site not responding. Last check: 2007-11-03)
		The galaxy rotation problem is the discrepancy between the observed rotation of galaxies and the predictions of current physical theories.
		Attempts to resolve the galaxy rotation problem have included the hypothesis of dark matter and the hypothesis known as Modified Newtonian Dynamics.
		Reluctant to change Newton's law as well as Einstein's theory of relativity for galaxies only, scientists simply assumed that the rotation curve was flat because of the presence of a large amount of matter surrounding the visible part of galaxies.
	www.wikiwhat.com /encyclopedia/g/ga/galaxy_rotation_problem.html (507 words)

	Red Shift Riddles
		This time the problem is in cosmology, the study of the structure and "evolution" of the universe as revealed by its largest physical systems, galaxies and clusters of galaxies.
		Galaxies in the Fisher-Tully catalogue that showed large amounts of rotation and interval motion (the opposite extreme from the dwarf irregulars) were studied.
		Galaxies would not move away from one another; the universe would be static instead of expanding.
	www.cs.unc.edu /~plaisted/ce/redshift.html (1738 words)

	Galaxy Methods
		For galaxies in particular its presence is said to be implied because the predicted rotation speeds are so much lower than the measured, and large spherical halos of dark matter can be used in the computing to make up the difference.
		I've been working on this problem since 1994, and have yet to be allowed to give a talk in a reasonable forum and I have had two papers rejected by the Astrophysical Journal with no reasons given.
		For the forward problem they started out right, by first showing a straight-forward method of adding up the gravity effects of individual rings of arbitrary SMD on a test mass at a given radius.
	www.galaxymethods.net (841 words)

	ASTRONOMY 102- LECTURE 27 (Site not responding. Last check: 2007-11-03)
		Problem is that galaxy is in differential rotation.
		The rotation curve (a plot of distance from the center versus velocity of the stars) slants down and to the right, decreasing the further the star is from the center.
		But in fact in the majority of galaxies, the velocity of stars in the outer regions is the same as in the inner region, and the rotation curve appears flat.
	www.gettysburg.edu /academics/physics/clea/A102ol28.html (586 words)

	Consistency with Observed Rotation Curves
		Rotation curves which are truly flat and halo-dominated - such as those from isothermal halo models - are extremely difficult to reconcile with observed tidal tails unless they have a small truncation radius (i.e.
		Instead, galaxies appear to possess a variety of rotation curve shapes, and it has been suggested that rotation curve shape is correlated with luminosity and/or Hubble type of the galaxy (e.g., Persic, Salucci, and Stel 1996; McGaugh and de Blok 1998).
		Galaxies with falling rotation curves have no problem making long tails as shown by the examples in Regions I and II of Figure 5.
	www.cita.utoronto.ca /~dubinski/tt3/node14.html (1408 words)

	Galaxy rotation problem at opensource encyclopedia (Site not responding. Last check: 2007-11-03)
		In the beginning of the 1980s, the first observational evidence was reported that spiral galaxies do not spin as expected according to then current theories.
		Based on this model, matter (such as stars and gas) in the disk portion of a spiral should revolve around the center of the galaxy with orbits that are nearly Keplerian.
		As a result, based on Newton's laws, it would be expected that the average orbital speed of a an object in rotation at a given radius would decrease inversely with the square root of the radius of the orbit (the dashed line in Fig.
	www.wiki.tatet.com /Galaxy_rotation_problem.html (458 words)

	ipedia.com: Modified Newtonian dynamics Article (Site not responding. Last check: 2007-11-03)
		Reluctant to change Newton's law as well as Einstein's theory of relativity for galaxies only, scientists simply assumed that the rotation curve was flat because of the presence of a large amount of matter outside the galaxies.
		Since MOND was inspired by the desire to solve the flat rotation curve problem, it is not a surprise that using the MOND theory with observations reconciled this problem.
		C: a galaxy in the field of a neighbor galaxy, of a group or of a cluster.
	www.ipedia.com /modified_newtonian_dynamics.html (2610 words)

	2MASS Atlas Image Gallery
		Imaging this galaxy in the near-IR allows us to look deeper through the extinction caused by the dust and also better map the light and mass distribution of the galaxy, since the light from spiral galaxies in the near-IR is dominated by lower-mass stars, which comprise most of a galaxy's visible mass.
		It is this galaxy for which water megamasers detected in the radio orbiting very near the galaxy's center indicate the presence of a supermassive fl hole and allow an accurate kinematical measurement of the fl hole's mass.
		This galaxy has been host to six historical supernovae, four of which are thought to arise from young, massive stellar progenitors, both near the nucleus and in the spiral arms, further evidence for the vigorous galactic star formation.
	www.ipac.caltech.edu /2mass/gallery/images_galaxies.html (5729 words)

	Dark Matter
		To determine the rotation curve of the Galaxy, stars are not used due to interstellar extinction.
		From comparing the mass estimates to the observed amount of light from galaxies, and from the abundance of light elements, that there is a problem with the fraction of the mass of the Universe that is in normal matter or baryons.
		Thus, it is for two reasons that the dark matter problem is important, one to determine what is the nature of dark matter, is it a new form of undiscovered matter?, the second is the determine if the amount of dark matter is sufficient to close the Universe.
	zebu.uoregon.edu /~js/ast223/lectures/lec24.html (1988 words)

	Identification of dark matter
		Zwicky (1933) was the first to infer the existence of large quantities of unseen mass, in studies of the dynamics of clusters of galaxies, but it was many years before the ``missing mass'', or dark matter, problem was widely recognised.
		It is, in fact, HI galaxy rotation curves which provide the best evidence we have for the existence of dark matter; here the dynamical interpretation, and its implication, is entirely unambiguous.
		PCM94 motivated this suggestion with arguments related to galaxy dynamics and evolution, emphasising the astrophysical appeal of dark matter in this form, and noting that if the temperature of the cold gas were close to that of the CMB then the clouds would be very difficult to detect (see also Combes and Pfenniger 1997).
	www.atnf.csiro.au /pasa/16_3/walker/paper/node2.html (797 words)

	Paradoxes Resolved, Origins Illuminated - Dark matter and black holes
		Even before the rotation problem was known, we had problems accounting for all the mass needed to bind galaxy clusters together.
		The larger the scale, the greater the discrepancy between seen and unseen matter (assuming the Newtonian law is still in effect).
		One of the big problems in ever understanding the dymamics of structure in gravity fields is the misplaced gravity center that is common to all the ideas about spheres and disks.
	www.metaresearch.org /msgboard/topic.asp?TOPIC_ID=501 (924 words)

	Evidence for Dark Matter
		Plotting contours of Galaxy density in Cancer suggested that the distribution of galaxies was not relaxed; that is secondary density maxima appeared.
		That is, do galaxies in Group A have different velcoities than galaxies in Group B or C? After a thorough analysis it was shown that these two were highly correlated and that the Cancer cluster could in fact be decomposed into individual groups.
		Observations of galaxy rotation curves and cluster velocity dispersions suggest that M/L associated with these structures is in the range 10--500; where 500 is fairly extreme.
	zebu.uoregon.edu /1997/ph410/l10.html (613 words)

	New Scientist Breaking News - Distant galaxy's subtle sidling measured (Site not responding. Last check: 2007-11-03)
		This is quite easy for objects in the solar system, such as asteroids, or even for objects in the galaxy, by "triangulating" their observed positions from two different points along Earth's orbit.
		Now, astronomers have overcome that problem by tracking bright spots of radio emission from the Triangulum Galaxy - also known as M33 - which the new study locates at 2.4 million light years from Earth.
		So the team used them as beacons to track the galaxy's rotation and sideways motion at four intervals over the course of about three years.
	www.newscientist.com /article.ns?id=dn7095 (732 words)

	Galaxies and the Universe - Dark Matter
		The basic conclusion comes from galaxy rotation curves, mass distributions inferred from hot gas around ellipticals, the velocity dispersions in clusters of galaxies, and mass tracing via gravitational lensing.
		Recall that most of these techniques are sensitive only to dark matter that is concentrated around galaxies (or more accurately, that galaxies are the marbles rolling up and down hills in dark matter, and that they have had time to fall to the bottom).
		Notice the divergence of arcs around the bright galaxy to the lower left, showing that there is a significant concentration of total mass associated with it rather than just the cluster as a whole.
	www.astr.ua.edu /keel/galaxies/darkmatter.html (3242 words)

	Dark Matter (Site not responding. Last check: 2007-11-03)
		But, when we calculate the amount of mass in a cluster using the orbital motions of its member galaxies, the result is too low for the cluster to be gravitationally bound.
		The rotation curve of a galaxy shows how the orbital velocities of the stars change with distance from the center.
		The mass of intergalactic gas is calculated to be a considerable amount, perhaps greater than the amount in galaxies and stars, but is still too little to account for the cluster stability.
	cassfos02.ucsd.edu /public/tutorial/DM.html (797 words)

	Hmm.... \| MetaFilter (Site not responding. Last check: 2007-11-03)
		The reason is that the two problems are very different: in the planetary problem, the source of gravity is the sun and the planets are treated as test particles in this field (apart from contributing minor perturbations when necessary).
		By contrast, in the galaxy problem, the source of the field is the combined rotating mass of all of the freely-gravitating elements themselves that compose the galaxy.
		The problem is that there is quite a bit of strong evidence that there is "something" there, along with a lack of corresponding evidence that "something" consists of MACHOS such as planets, dead stars, or just floating gas.
	www.metafilter.com /mefi/45765 (3643 words)

	Astro 103 - Problem Sets
		Chapter 2, Problem 4: The fl-body emission spectrum of object A peaks in the ultraviolet region of the electromagnetic spectrum, at a wavelength of 200 nm.
		Chapter 11, Problem 4: The intensity of a beam of light shinning through a dense molecular cloud is diminished by a factor of 2.5 for every 3 pc the beam travels.
		Chapter 16, Problem 1: A Seyfert galaxy is observed to have broadened emission lines indicating a speed of 1000 km/s at a distance of 1 pc from its center.
	www.astro.wisc.edu /~mab/education/astro103/problems01.html (754 words)

	Introduction (Site not responding. Last check: 2007-11-03)
		Stellar dynamics of the Galaxy to evaluate theories of density wave formation, the presence of dark matter in the disk, the rise or fall of the rotation curve at large Galactocentric distances, and the velocity dispersion of the outer halo.
		Astrometry of AGNs to discern the internal structure of the emission-line regions, to detect proper motions within clusters of galaxies, and to test the likelihood of microlensing of AGN nuclei.
		Rotational parallaxes: distances to nearby galaxies can be measured geometrically out to a few Mpc by observing the angular proper motion component of galaxy rotation and equating this to the measured circular velocity.
	www.ess.sunysb.edu /simswg/siswg/node23.html (445 words)

	[No title]
		We know from galaxy rotation curves that this behaviour is not observed.
		Galaxies have ages in excess of 10 Gyr, a figure far in excess of the typical rotation periods of stars and clouds.
		It is the passage of a density wave through the stars and clouds in a given part of the galaxy that compresses the material locally, thereby giving the appearance of an arm-like structure.
	bison.ph.bham.ac.uk /~wjc/Teaching/SIUstud7.html (444 words)

	Modified Newtonian Dynamics
		And that is exactly what's happening at the scale of galaxies, where the distances between stars are so large that the gravitational force is extremely small.
		Consequently, the velocity of stars on a circular orbit far from the center is a constant, and doesn't depend on the distance r: the rotation curve is flat.
		Milgrom thus could make the prediction that LSBs would have a rotation curve essentially flat, and with a relation between the flat velocity and the mass of the LSB identical to that of brighter galaxies.
	ca.geocities.com /mercy@rogers.com (2525 words)

	Paradoxes Resolved, Origins Illuminated - Galaxy Rotation and the MetaModel
		A recent story on space.com talks about the discovery of an X-ray halo surrounding a galaxy that is claimed to destroy the MOND theory of rotation.
		The Meta Model uses the finite range of gravity as an explanation of galactic rotation curves.
		The larger problem, of course, is that few people state their assumptions anymore.
	www.metaresearch.org /msgboard/topic.asp?TOPIC_ID=174 (392 words)

	kmarinas86's Xanga Site
		Observations of galactic rotation velocities (see Galaxy rotation problem (http://www.wikipedia.org/wiki/Galaxy_rotation_problem)) and the brightness of distant supernovas (see Dark Energy (http://www.wikipedia.org/wiki/Dark_Energy)) cause the author to suggest that the space outside our solarsystem, between the stars and between the galaxies is hyperbolic.
		It's much easier to prove the existence of smaller galaxies of a lower fractal level than of the existence of superstrings, since superstrings are over 10 orders of magnitude smaller than what I would call galaxies in a fractal universe.
		Basically, to verify the claim that there are galaxies at a smaller fractal level, you have to verify what the constitution of gluons are, the particles which mediate the strong force.
	www.xanga.com /home.aspx?user=kmarinas86 (2275 words)

	Stars Thrown Out of the Galaxy - Softpedia
		This is similar to how an ice-skater rotates: when she extends her arms she moves more slowly, when she either extends her arms above her head or keeps them close to the body she starts to rotate more rapidly.
		Taking into consideration how gravitation connects the stars in the galaxy the predicted result is that average orbital speed of a star at a specified distance away from the center would decrease inversely with the square root of the radius of the orbit (the dashed line, A, in figure below).
		the galaxy really is more like a "solid" disk made out of dark matter and stars than only like a bunch of stars flying around almost freely and influencing each other via gravity.
	news.softpedia.com /news/Stars-escaping-out-of-the-Galaxy-17222.shtml (819 words)

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