Open Yale courses ASTR 160 - Frontiers and Controversies in Astrophysics
Professor Charles Bailyn
y energía oscura
Cosmología
The first class covers the fundamental issues of cosmology and I covered at some point with the synopsis of the book "The First Three Minutes of the Universe" by Steven Weinberg ( I , II, III )
What was instead quite new for me was to understand in what way was established in recent years that the universe's expansion is accelerating rather than slowing down as it was supposed to go.
Hubble's law states that the speed at which moves away from us a galaxy is directly proportional to its distance from us.
V = H. D
V = velocity of recession due to expansion
universe D = current distance to the galaxy
Hubble constant H =
However, if we look far enough objects, the law ceases to be strictly linear, because we are looking past light. The difficulty consists in determining the distances of galaxies so far away ... (The rate is most easily measured by the Doppler effect)
In general, all the study on the exact value of the Hubble constant and its variation in the past depends on finding an effective method to measure distances across the light coming . The key is to find objects whose brightness is known by some other method. One example that was used for the nearest galaxies were the stars Cepheid variables, in which the brightness oscillation period is related to full brightness. As the brightness falls with the square of the distance, knowing the original brightness of the object, you can set the distance.
However, at distances greater than 100 megaparsecs is very difficult to find enough bright objects of this type. It was eventually discovered that a particular type of supernova, type Ia, explode, releasing the same quantity of energy, which enabled us to expand the window to the past.
The reason why this type of supernova release the same amount of energy is explained in the light of theoretical models about its origin. These are binary systems in which a white dwarf increases its mass is flowing material from a red giant neighbor. When you reach a certain amount of mass, known as the Chandrasekhar limit, there is a collapse that generates the supernova.
important thing is that the amount of nuclear fuel is always the same, so that the energy released will also constant. The future study of supernovae of this type completed to show that the Hubble constant was once higher than today, which surprised everyone. The hope was that the force of gravity gradually curbed the expansion.
Knop et al, New Constraints on ΩM , ΩΛ, and w from an Independent Set of Eleven High-Redshift Supernovae Observed with HST the moment is called "dark energy" to the case physical origin of this repulsion. It is a concept similar to the famous Einstein's cosmological constant. It is not known which can be only would cause the acceleration of the expansion.
However, as noted at the time Bailyn, although the current model fits the observations, when plotted in the graphics things that no one knows little or nothing and not directly proven existence ("material dark, dark energy) so that it is impossible to rule out a change in our understanding of physical laws is just around the corner.
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