The first to suggest the existence of dark matter using stellar velocities was Dutch astronomer Jacobus Kapteyn in 1922. In 1906, Henri Poincaré in "The Milky Way and Theory of Gases" used the French term matière obscure ("dark matter") in discussing Kelvin's work. Lord Kelvin thus concluded "Many of our supposed thousand million stars, perhaps a great majority of them, may be dark bodies". By using these measurements, he estimated the mass of the galaxy, which he determined is different from the mass of visible stars. In a talk given in 1884, Lord Kelvin estimated the number of dark bodies in the Milky Way from the observed velocity dispersion of the stars orbiting around the center of the galaxy. The hypothesis of dark matter has an elaborate history. 4.1.3 Dark matter aggregation and dense dark matter objects.3.9 Sky surveys and baryon acoustic oscillations.3.8 Type Ia supernova distance measurements.These models attempt to account for all observations without invoking supplemental non-baryonic matter. These include modified Newtonian dynamics, tensor–vector–scalar gravity, or entropic gravity. Current models favor a cold dark matter scenario, in which structures emerge by the gradual accumulation of particles.Īlthough the scientific community generally accepts dark matter's existence, some astrophysicists, intrigued by specific observations that are not well-explained by ordinary dark matter, argue for various modifications of the standard laws of general relativity. Dark matter is classified as "cold," "warm," or "hot" according to its velocity (more precisely, its free streaming length). Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded. The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, particularly weakly interacting massive particles (WIMPs), though axions have drawn renewed attention due to the non-detection of WIMPs in experiments. Dark matter is thought to be non-baryonic it may be composed of some as-yet-undiscovered subatomic particles. īecause no one has directly observed dark matter yet – assuming it exists – it must barely interact with ordinary baryonic matter and radiation except through gravity. Thus, dark matter constitutes 85% of the total mass, while dark energy and dark matter constitute 95% of the total mass-energy content. In the standard Lambda-CDM model of cosmology, the total mass-energy content of the universe contains 5% ordinary matter and energy, 27% dark matter, and 68% of a form of energy known as dark energy. Other lines of evidence include observations in gravitational lensing and the cosmic microwave background, along with astronomical observations of the observable universe's current structure, the formation and evolution of galaxies, mass location during galactic collisions, and the motion of galaxies within galaxy clusters. Some galaxies would not have formed at all and others would not move as they currently do. The primary evidence for dark matter comes from calculations showing that many galaxies would behave quite differently if they did not contain a large amount of unseen matter. For this reason, most experts think that dark matter is abundant in the universe and has had a strong influence on its structure and evolution. Various astrophysical observations – including gravitational effects which cannot be explained by currently accepted theories of gravity unless more matter is present than can be seen – imply dark matter's presence. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect, or emit electromagnetic radiation and is, therefore, difficult to detect. Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |