Wednesday, March 18
Einstein - black holes and gravitional lens
The theory of general relativity has important astrophysical applications. Notably, it predicts the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars. There is evidence that, indeed, such black holes as well as more massive varieties are responsible for the intense radiation emitted by certain types of astronomical objects (such as active galactic nuclei or microquasars). The bending of light by gravity can lead to the curious phenomenon of multiple images of the same astronomical object being visible in the sky, an effect called gravitational lensing which has spawned an active new branch of astronomy. General relativity also predicts the existence of gravitational waves, which have been measured indirectly; a direct measurement is the aim of projects such as LIGO. In addition, it is the basis of current cosmological models of an expanding universe. Photo: Extragalactic astronomy: gravitational lensing. This Hubble Space Telescope image shows several blue, loop-shaped objects that actually are multiple images of the same galaxy. They have been duplicated by the gravitational lens effect of the cluster of yellow, elliptical and spiral galaxies near the photograph's center. The gravitational lens is produced by the cluster's tremendous gravitational field that bends light to magnify, brighten and distort the image of a more distant object. Text Source: Nationmaster; Knowledgehush.