What is Dark Matter?
What is the universe created of? star absorption spectra showed that the Sun contains acquainted components, and spectra of stars in distant galaxies conjointly disclosed their presence. Even exotic objects like as white dwarfs, supernovas, and nucleon stars contain the acquainted building blocks of matter. As for galaxies, up till concerning thirty years agone, they gave the impression to be composed of protons, neutrons and electrons–called baryonic matter–but currently it seems most of the mass in galaxies, and clusters of galaxies, is created of one thing else, a as yet unobserved reasonably matter. This conclusion is supported by a confluence of findings starting from galactic rotation to cosmology to attractive force lensing.
Galactic Clusters Dynamics
In 1938, One Scientist found the first proof of matter that interacts through gravitation but not through the electromagnetism, thus it emits no light–hence the name “dark matter.”
Scientist studied the statistics of the motion and site of galaxies within the Coma cluster, a big system spanning quite twenty,000,000 light-years (more than two hundred times the dimensions of a typical spiral galaxy).
Scientist assumed the cluster was spherically symmetrical, that the mutual gravity of all the galaxies attracts each toward the cluster’s center, and on the typical the outer galaxies need
to move per Newtonian mechanics underneath the influence of a mass up to the full mass of the cluster (see sidebar). By mensuration the physicist shifts of the spectral lines from these galaxies, Scientist determined their average rate. severally, he measured the radius of the cluster. He calculated the full cluster mass necessary to supply the galactic motions that he had discovered, and then, for comparison, he calculated the full mass supported the brightness of the galaxies. These 2 results were in violent disagreement–the mass supported the brightness of the galaxies was solely a few tenth of the mass necessary to supply the discovered motions.
Nothing came of scientist’s exceptional result for pretty much forty years. Then, Vera Rubin and W.K. Ford shocked the natural philosophy community by reportage new chemical analysis measurements showing that stars in spiral galaxies rotate concerning galactic centers at concerning constant speed, freelance of radial distance. supported the brightness of the central “bulge,” astronomers had assumed that most of the mass was targeted there, wherever it’d have made a star system-like distribution of velocities, decreasing with distance from the middle. within the face of disbelief and criticism, Rubin and Ford stood their ground, and their results were if truth be told borne out by ensuing add each spiral and ellipticals.