The concept of dark matter makes sense only within the current Big Bang cosmology based on, because we do not know how to explain otherwise have been able to form galaxies and galaxy clusters in such a short time like that observed. Not also explain how galaxies, in addition to form, remain intact even if the visible matter, composed of baryons, can not develop enough gravity for this purpose. Even from this perspective, the concept of dark matter makes sense only within the current Standard Model, in which the sole cosmological gravitational force, if the Standard Model is incorrect, there would be need for dark matter, since there there is no experimental evidence if not violations of a mathematical model.
Despite detailed maps of 'near Universe, covering the electromagnetic spectrum from radio waves to gamma rays, we were able to identify only 10% of its mass, as stated in 2001 at the New York Times by Bruce H. Margon, an astronomer at the University of Washington:
"The situation is somewhat embarrassing to admit that we can not find 90 percent of [the matter] of the Universe. "
The latest measurements indicate that dark matter constitutes about 23% of the universe and about 85% by mass.
was initially indicated as "missing mass", even if there is indeed matter, as they are observable gravitational effects of its mass. However, this matter does not emit any electromagnetic radiation and is therefore not detectable by means of spectroscopic analysis, from which the adjective "dark". The missing mass term can be misleading, since it is not the missing mass, but its light.
Dark matter is not to be confused with the different situation that goes by the name of dark energy.
An important observational evidence of the need for dark matter was given by the rotation curves of spiral galaxies. These galaxies contain a large population of stars placed on nearly circular orbits around the galactic center. As with planetary orbits, according to Kepler's third law with galactic orbits the stars should have larger orbital velocities smaller, but Kepler's third law applies only to nearby stars in the outskirts of a spiral galaxy, because it assumes that the mass enclosed by the orbit is constant. However, astronomers have conducted observations of orbital velocities of stars in the outlying regions of a large number of spiral galaxies, and in any case they follow Kepler's third law. Instead of decreasing at larger radii, the orbital velocities remain constant with very good approximation. The implication is that the mass enclosed by orbits of greater radius gradually increases, even for stars that are apparently close to the edge of the galaxy. Although they are at the boundaries of the bright part of the galaxy, it has a mass profile that apparently continues well beyond the regions occupied by stars.
Considering the stars at the outskirts of a spiral galaxy, with orbital velocities typically observed of 200 kilometers per second, if the galaxy were made only by the visible matter in these stars would drop in the short time since their orbital speeds are four times larger than the escape velocity from the galaxy. Given that there are no galaxies that are dispersing in this way, inside should be the mass of which are taken into account when adding up all the visible parts.
gravitational lens in a group of galaxies. On August 21, 2006, NASA issued a press release that Chandra would have found direct evidence of dark matter in the collision between two galaxy clusters. In early 2007, astronomers of the Cosmic Evolution Survey and Hubble Space Telescope, using the information obtained by the Hubble telescope and ground-based instruments, have drawn a map of dark matter noting that permeates the universe is matter where This should be visible even large amounts of dark matter, but that is also present in areas where there is visible matter.
assumptions about dark matter.
appeared in the literature several theories to explain the missing mass associated with different phenomena.
The dark mass is divided into baryonic and non baryonic:
baryonic dark matter is composed of material similar to that which constitutes stars, planets, interstellar dust, etc.., But does not emit radiation;
non-baryonic dark matter is composed of matter intrinsically different and not yet discovered. It is hypothesized that it may be supersymmetric particles such as neutralinos, or massive neutrinos or axions, or other particles ever observed, and subject only to gravitational interaction and nuclear weak. This material is called WIMPs (Weakly Interacting Massive Particles), large particles of unit mass baryonic weakly interacting with matter, and therefore difficult to detect. Three types of experiments trying to detect these particles: i) producing them in particle accelerators ii) seeing the energy that should be issued when colliding with ordinary matter, iii) annihilation of particles of dark matter present around the center of the galaxy or sun could make ordinary particles such as neutrinos, positrons, anti-protons.
currently is thought that at least 90% of non-baryonic dark matter is. In fact, the cosmic abundance of deuterium, which is a deuterium atom for every 100,000 hydrogen is extremely sensitive to the density of matter in the form of baryons. A baryonic density greater abundance of deuterium would mean much lower. Instead, the observed abundance of deuterium is compatible with the density of observable matter.
The discovery that the neutrino has mass, albeit very low, which may partly explain the excess mass of the clusters and superclusters of galaxies, but not that of individual galaxies, because it moves at a speed near that of light, escaping sooner or later the gravitational pull in and out of them.
Other possible constituents of dark matter have been identified in the MACHO (Massive Compact Halo Objects), compact objects of great mass of the halo galactic primordial blacks in the holes in the soliton stars, the stars of bosons and the quark nuggets.
To the question of the previous post brings us to the fact "if Newton was wrong or not." A physicist friend of mine has a theory on that has a certain charm.
We know from previous posts, that when a body is free to float in space time NOT affected by a severe ', but is subject only to the curvature of space, while it is prevented from freely floating (as it's spot Earth's surface) the seriousness reappears. Now it is true that if is visible matter should also be large amounts of dark matter and dark matter is probably made up largely of supersymmetric particles such as neutralinos, or massive neutrinos or axions, or other particles ever observed, and subject only to the gravitational force and weak nuclear interaction, we can imagine that:
dark matter is a kind of gas of subatomic particles floating in space-time with all the other bodies may do so.
In this case, its large mass cancel out the effects of gravity by Newton, and an astronaut in space does not suffer from the effects because free-floating along with this kind of gas that surrounds. Conversely, if a man or an object is constrained in its movements (such as the Earth's surface), would have a significant effect of dark matter and would be the dominant force of gravity.
According to this theory, Newton was not wrong, but its laws can only apply where it has a decisive influence on the dark, free-floating in space time.
Obviously the theory of my friend does not fall within the M theory of superstrings, which in any case, it is still to be proved, even if it is the most likely today.
Best wishes
Alessandra
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