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Thursday, August 24, 2006

Dark matter : unveiled.

Spiegel Online Courtesy. Blue (dark matter), separated from visible light (red), to effect of collision (Bullet cluster).


Although the existence of dark matter (not visible, that does not emit, neither reflects electromagnetic radiation: light, X-rays, inferred by their gravitational effects), was suspected since 1930, it was since 1933, mercy to works of Fritz Zwicky of the Institute of Technology of California (Caltech), that begin to have indirect evidences of their existence. Zwicky, noted that orbital ad rotational velocities of central galaxies in cluster of galaxies, were high speed at most. He supposed then that unless a strong gravitational force (not visible, by-product of its enormous masses), maintained them centrally united, overall with clouds of gases, these must be expelled to the space. Alone the existence of a great mass of dark matter could generate these gravitational effects, unless the gravity behavior follow another physical laws in the interior of these enormous cluster of galaxies. These contributions were followed by the observations of Vera Rubin and Kent Ford (1975, Carnegie Institutuon.Washington), in the sense that the dark matter, was found located peripherally to the cluster of galaxies (galactic halo).

Also the distorsion of light (in the shape of arches: gravitational lensing), of background galaxies, mercy to interference with other bodies or, galaxies (lenses), located between the observer and background galaxies, that even permitted to calculate punctual total masses of dark matter. Also, the distribution of temperature of the gases in the cluster of galaxies, the structure and nucleosynthesis of the big bang, etc. Since then it is affirmed that the visible matter conforms barely the 5% of the universe, the dark matter the 25% and the dark energy (which generate negative pressure), a 70%. It is said, likewise that the dark matter, could be composed of not baryonic particles -somewhat different of the visible matter- : ordinary and heavy neutrinos, axions, weakly interactive massive particles -WIMPS- clouds of not luminous gas, structural components of certain planets and dwarfish stars. In the 2005, astronomers of the University of Cardiff announced the existence of a galaxy (VirgoH121), composed entirely of dark matter. Anyway, until does little it was dificcult to see dark matter.

Now it happens that what until does little was supported by hypothesis or indirect proofs, has changed to a consistent one, mercy to a series of direct observations and visible quantifications performed by American astronomers (Doug Clowe, Maxim Markevitch and others,whose paper will be soon published in the : Astrophysical Journal Letter), employing the spatial telescopes Hubble and Chandra and the optics VLT and Magellan of Chile : the collission of two clusters of galaxies (Bullet Cluster. Composite galaxy : IE0657-556), occurred does some 100 million years ago (yet even visible), generator of separation of the visible matter from the dark one. It has been verified -to consequence of the collission- the separation of hot gases, of the central galaxies (that usually remain united). The speed of gases was slowed to consequence of gravitational forces of the dark matter. If dark matter did not exist, the cluster of galaxies and the hot gases had not been separated and themselves had greater mass in the interior of gases and stars of the galactics cluster. On the contrary, the study showed the existence of huge quantities of mass (dark matter), in peripherical areas of the galaxies studied.

Materia oscura :desentrañada.

Aunque la existencia de materia oscura (no visible, que no emite, ni refleja radiación electromagnetica : luz, rayos -X-. Inferida por sus efectos gravitacionales), fué sospechada desde 1930, es recien desde 1933, merced a trabajos de Fritz Zwicky del Califonia Institute of Technology (Caltech), que se empiezan a tener evidencias indirectas de su existencia. Zwicky, observo que las velocidades orbitales y de rotacion de galaxias centrales inmersas en conglomerados de galaxias, eran elevadisimas. Supuso entonces que a menos que una fuerza gravitacional (no visible, derivada de enormes masas), las mantuviese unidas centralmente, de conjunto con nubes de gases, estas serian expulsadas centrífugamente, al espacio. Solo la existencia de una gran masa de materia oscura podria generar estos efectos gravitatorios, a menos que la gravedad se comporte de otro modo al interior de estos enormes conglomerados de galaxias. A estos aportes, se agregarian las observaciones de Vera Rubin y Kent Ford (1975, Carnegie Institute.Washington), en el sentido de que la materia oscura, se hallaba localizada periféricamente a los conglomerados de galaxias (halo galáctico).

Tambien la distorsión de la luz (en forma de arcos: gravitational lensing), proveniente de galaxias de fondo, merced a la interferencia de otros cuerpos o, galaxias (lentes), ubicadas entre el observador y las galaxias de fondo, lo que incluso permitió calcular masas totales puntuales de materia oscura. También, la distribución de temperatura de los gases presentes en conglomerados de galaxias, la estructura y nucleosintesis del big bang, etc. Desde entonces se afirma que la materia visible conforma apenas el 5% del universo, la materia oscura el 25% y la energia oscura (generadora de presion negativa), un 70%. Se dice, asimismo que la materia oscura, estaria compuesta de particulas no barionicas -algo diferentes de la materia visible- : neutrinos ordinarios y pesados, axions, weakly interactive massive particles -WIMPS- nubes de gas no luminosa, componentes estructurales de ciertos planetas y estrellas enanas. En el 2005, astronomos de la Universidad de Cardiff dieron cuenta de la existencia de una galaxia (VirgoH121), compuesta enteramente de materia oscura. Lo que fuere, hasta hace poco era dificil ver materia oscura.

Ahora resulta que lo que hasta hace poco era sustentado por hipótesis u evidencias indirectas, está deviniendo en consistente, merced a una serie de observaciones directas y cuantificaciones viabilizadas por astronomos americanos, empleando los telescopios espaciales Hubble y Chandra y los optios VLT y Magallanes de Chile : la colision de dos conglomerados de galaxias (Bullet cluster), ocurrida hace unos 150 millones de años (con efectos aun visibles), generadores de la separacion de la materia visible, de la oscura. Se ha constatado -a consecuencia de la colisión- la separacion de los gases calientes, de las galaxias centrales (usualmente unidos). La velocidad de los gases fue enlentecida a consecuencia de las fuerzas gravitacionales de la materia oscura. Si no existiese materia oscura, los conglomerados de galaxias y los gases calientes no se hubiesen separado y se tendria que haber detectado mayor masa al interior de gases y estrellas de los conglomerados galácticos. Por el contrario, el estudio demostró la existencia de ingentes cantidades de masa (materia oscura), en las areas periféricas de las galaxias estudiadas.

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