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Topic: Dark matter

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  SPACE.com -- Hubble Reveals Ghostly Ring of Dark Matter
A ghostly ring of dark matter floating in the galaxy cluster ZwCl0024+1652, one of the strongest pieces of evidence to date for the existence of dark matter.
Dark matter makes up a vast majority of gravity-exerting mass in the universe, while only about 10 percent is matter we can see and touch.
Unlike other dark matter discoveries, the ring is the first collection of dark matter that differs greatly from the distribution of ordinary matter.
www.space.com /scienceastronomy/070515_dark_ring.html   (785 words)

  Dark matter - Wikipedia   (Site not responding. Last check: )
Dark matter refers to material that can't be detected by their emitted radiation but whose presence can be inferred from gravitational effects on visible matter, like stars and galaxies.
Determining the nature of dark matter is also known as the dark matter problem or the missing mass problem, and is one of the most important problems in modern cosmology.
Dark matter is not to be confused with white matter or gray matter.
wikipedia.findthelinks.com /da/Dark_matter.html   (734 words)

 Dark matter - Wikipedia, the free encyclopedia
The dark matter hypothesis aims to explain several anomalous astronomical observations, such as anomalies in the rotational speed of galaxies (the galaxy rotation problem).
Large computer simulations of billions of dark matter particles have been used to confirm that the cold dark matter model of structure formation is consistent with the structures observed in the universe through galaxy surveys, such as the Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey, as well as observations of the Lyman-alpha forest.
An alternative to dark matter is to suppose that the inconsistencies are due to an incomplete understanding of gravitation.
en.wikipedia.org /wiki/Dark_matter   (2643 words)

 Dark Matter
In cosmology, dark matter consists of matter particles that cannot be detected by their emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies.
In addition, the existence of dark matter resolves a number of inconsistencies in the Big Bang theory, and is crucial for structure formation.
About 25% of the universe is thought to be composed of dark matter, and 70% is thought to consist of dark energy, an even stranger component distributed diffusely in space that likely cannot be thought of as ordinary particles.
www.crystalinks.com /darkmatter.html   (1582 words)

 Cosmology Primer: The Dark Universe   (Site not responding. Last check: )
Dark matter is some kind of particle that we have not yet detected in experiments here on Earth, but nevertheless comprises most of the matter in the universe.
Finally, it may be possible to detect dark matter particles indirectly, if they annihilate into photons in high-density regions of the universe; the resulting radiation would have a characteristic form that would signal the existence of a new kind of particle.
After all, matter dilutes away as the universe expands, while dark energy remains essentially constant, so their relative abundance changes dramatically; we seem to be born lucky, in an era when both matter and dark energy play an important role in the universe.
pancake.uchicago.edu /~carroll/cfcp/primer/dark.html   (1765 words)

 HubbleSite - Astrofiles about "Hubble Rules Out a Leading Explanation for Dark Matter"   (Site not responding. Last check: )
Baryonic dark matter candidates include extra-solar planets, remnants of stellar evolution such as comets, objects not massive enough to ignite hydrogen fusion called brown dwarfs, dying embers of stars such as cold white dwarfs and neutron stars, as well as interstellar and intergalactic gases.
Dark matter might have provided the "seeds," a lumpy background in which ordinary matter could congregate to form galaxies and stars.
Matter would gather in sizes comparable to current galaxies or smaller, and eventually build to become clusters and superclusters due to the gravitational attraction of the galaxies.
hubblesite.org /newscenter/newsdesk/archive/releases/1994/41/astrofile   (1160 words)

 WMAP- Content of the Universe
It is also able to determine some of the properties of the non-baryonic matter: the interactions of the non-baryonic matter with itself, its mass and its interactions with ordinary matter all affect the details of the cosmic microwave background fluctuation spectrum.
Dark matter is likely to be composed of one or more species of sub-atomic particles that interact very weakly with ordinary matter.
New forms of matter: particle physicists, scientists who work to understand the fundamental forces of nature and the composition of matter, have speculated that there are new forces and new types of particles.
map.gsfc.nasa.gov /universe/uni_matter.html   (1811 words)

 Universe Today - Mapping the Hidden Dark Matter
The "dark matter" that comprises a still-undetected one-quarter of the universe is not a uniform cosmic fog, says a University of California, Berkeley, astrophysicist, but instead forms dense clumps that move about like dust motes dancing in a shaft of light.
The ghost universe of dark matter is a template for the visible universe, she said.
In addition, astrophysicists modeling the motion of dark matter were puzzled to see that each clump had a density that peaked in the center and fell off toward the edges in the exact same way, independent of its size.
www.universetoday.com /am/publish/shape_dark_matter_map.html   (1129 words)

 Dark Matter Radio Broadcast
Astronomers had once assumed that the gravity of galaxies was almost entirely generated by visible matter, that is, the matter in the stars and gas which give off or interact with light.
If there were no dark matter in a galaxy, then the force of gravity would be less and the stars in the outer reaches of a galaxy would fly off into intergalactic space.
Well, if there were no dark matter, then the mass in the universe would be less than this critical value and the universe would expand forever, slowly getting colder and colder.
www.jupiterscientific.org /sciinfo/dmtrans.html   (1656 words)

 dark matter on Encyclopedia.com   (Site not responding. Last check: )
DARK MATTER [dark matter] material that is believed to make up (along with dark energy) more than 90% of the mass of the universe but is not readily visible because it neither emits nor reflects electromagnetic radiation, such as light or radio signals.
Dark matter may consist of dust, planets, intergalactic gas formed of ordinary matter, or of MACHOs [ M assive A strophysical C ompact H alo O bjects], nonluminous bodies such as burned-out stars, fl holes, and brown dwarfs ; these are the so-called hot dark matter and would be dispersed uniformly throughout the universe.
Unlike cold dark matter, which has mass but virtually no velocity or temperature, or hot dark matter, which has mass and is highly energetic, warm dark matter has mass and a low temperature corresponding to an extremely low velocity.
encyclopedia.infonautics.com /html/d1/darkmatt.asp   (636 words)

 Dark matter
The dark matter that accounts for the critical density should, at least in the case of some kinds of dark matter, participate in the density fluctuations on large scales.
The nature of the dark matter predicted by inflation is a profound and unresolved puzzle.
Baryonic dark matter does exist: it is far more uncertain whether there exists enough to solve any of the dark matter problems, that is to say, dark matter in galaxy halos, dark matter in galaxy clusters and superclusters, or dark matter in an amount suficient to close the universe.
astron.berkeley.edu /~mwhite/darkmatter/essay.html   (3290 words)

 NASA - Astronomers Find Ring of Dark Matter With Hubble Space Telescope
To find dark matter, astronomers study how faint light from more distant galaxies is distorted and smeared into arcs and streaks by the gravity of the dark matter in a foreground galaxy cluster.
In that collision, the dark matter was pulled apart from the hot cluster gas, but the dark matter still followed the distribution of cluster galaxies.
CL0024+17 is the first cluster to show a dark matter distribution that differs from the distribution of both the galaxies and the hot gas.
www.nasa.gov /home/hqnews/2007/may/HQ_07114_Hubble_Dark_Matter_Rings.html   (1085 words)

 Dark Matter
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.
The current observations and estimates of dark matter is that 20% of dark matter is probably in the form of massive neutrinos, even though that mass is uncertain.
Dark energy is implied by the fact that the Universe appears to be accelerating, rather than decelerating, as discovered by observations of distant supernovae.
zebu.uoregon.edu /~js/21st_century_science/lectures/lec23.html   (1763 words)

 Dark Matter
Dark matter is suggested as the cause of this light deflection.
Dark matter is also required on the largest scale of all, that of the entire universe.
Dark matter is also involved in the popular inflationary big bang model which predicts that the curvature of the universe must be flat (Figure 3).
www.creationresearch.org /crsq/articles/36/36_4/darkmatter.html   (3553 words)

 CNN.com - Scientists: Dark matter exists - Aug 21, 2006
Dark energy is an even more mysterious phenomenon, a force of some sort that beats out gravity and is causing the universe to expand at an ever-faster pace.
And all astronomers agree that dark matter is such an exotic idea as to border on the crazy.
But the dark matter was not slowed by this effect, presumably because it does not interact with normal matter, as theory had predicted.
www.cnn.com /2006/TECH/space/08/21/dark.matter/index.html   (743 words)

 SPACE.com -- Understanding Dark Matter and Light Energy
This mysterious "dark matter" is believed by most scientists to be the most common stuff in the universe, perhaps making up 90 percent or more of the total mass.
Dark matter -- or something that we have yet to find -- exerts a gravitational pull on objects in and around distant galaxies, and even on light emitted by those objects, say scientists at NASA's Goddard Space Flight Center.
Normal matter -- you, your computer and the air you breathe -- is made of atoms, which are composed of protons, neutrons and electrons.
space.com /scienceastronomy/astronomy/dark_matter_sidebar_010105.html   (655 words)

 Dark matter at opensource encyclopedia   (Site not responding. Last check: )
Dark matter is matter that can't be detected by its emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies.
If there is the amount of dark matter hypothesized as of now the universe's expansion will slow, and could eventually stop or even reverse (leading to an eventual Big Crunch).
However, dark matter is said to form 90-95 percent of all matter in the universe.
www.wiki.tatet.com /Dark_matter.html   (1189 words)

 Dark Matter
The nature of this dark matter, and the associated "missing mass problem", is one of the fundamental cosmological issues of modern astrophysics.
The difference between cold dark matter and hot dark matter is significant in the formation of structure, because the high velocities of hot dark matter cause it to wipe out structure on small scales.
One way to accomodate this is to go to a mixed dark matter model in which you have some hot dark matter (for the large scale) and some cold dark matter to act as a seed for galaxy formation.
csep10.phys.utk.edu /astr162/lect/cosmology/darkmatter.html   (890 words)

 Open Directory - Science: Physics: Particle: Astro Particle: Dark Matter   (Site not responding. Last check: )
Dark Energy and the Microwave Background - Theory and measurements of sizes of fluctuations of cosmic microwave background agree with omega=1 giving a strong evidence for dark matter.
Dark Matter as the Fundamental Particle of the Universe - An individual interpretation on the structure of the Universe.
Dark Matter, Cosmology, and Large-Scale Structure of the Universe - A detailed discussion of the various pieces of gravitational evidence for the existence of dark matter, the different forms it might take, and their impact on cosmological theories.
dmoz.org /Science/Physics/Particle/Astro_Particle/Dark_Matter   (454 words)

 Dark matter
The dark matter that accounts for the critical density should, at least in the case of some kinds of dark matter, participate in the density fluctuations on large scales.
Preliminary indications are that an amount of dark matter about equal to the critical density must be present in order to account for the amplitude of the observed flows.
Baryonic dark matter does exist: it is far more uncertain whether there exists enough to solve any of the dark matter problems, that is to say, dark matter in galaxy halos, dark matter in galaxy clusters and superclusters, or dark matter in an amount suficient to close the universe.
astro.berkeley.edu /~mwhite/darkmatter/essay.html   (3290 words)

 Dark Matter Exposed: Animation Offers Clues to Cosmic Mystery
Scientist suspect the bulk of dark matter involves tiny particles they've yet to detect.
Dark matter particles appear not to interact with electromagnetic forces, however.
Dark matter satellite galaxies -- if they exist -- cannot be detected by conventional telescopes because they don't contain enough normal matter to fuel star birth.
www.space.com /scienceastronomy/dark_matter_animated_030415-1.html   (933 words)

 New Scientist Breaking News - Astronomers claim dark matter breakthrough   (Site not responding. Last check: )
In what seems to be the most convincing claim for dark matter so far, researchers in England and France say gamma rays coming from the centre of our galaxy show hallmarks of these ghostly particles.
The identity of the Universe's dark matter, which outweighs the visible stuff by at least a factor of seven, is the outstanding mystery of modern astronomy.
If dark matter really is made up of such light particles, every cubic centimetre of space in the vicinity of the Earth must contain a few tens of them.
www.newscientist.com /article.ns?id=dn4214   (780 words)

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