Distant galaxy and two images (a) Earth-bound observer (b) Figure 34.12 (a) Light from a distant galaxy can travel different paths to the Earth because it is bent around an intermediary galaxy by gravity. This produces several images of the more distant galaxy. (b) The images around the central galaxy are produced by gravitational lensing. Each image has
Stellar evolution
We may see thousands of stars in the dark sky. Our universe consists of billions of stars. Stars may appear tiny to us but they are huge balls of gasses. Sun is a star of average size. Some stars are even a thousand times larger than the sun. The stars do not exist forever they have a certain lifetime. The life span of the sun is about 10 billion years. The star undergoes various changes during its lifetime, this process is called stellar evolution. The structure of the sun-like star is shown below.
Red Shift
It is an astronomical phenomenon. In this phenomenon, increase in wavelength with corresponding decrease in photon energy and frequency of radiation of light. It is the displacement of spectrum of any kind of astronomical object to the longer wavelengths (red) side.
Suppose you measure the red shifts of all the images produced by gravitational lensing, .You find
that the central image has a red shift less than the outer images, and those all have the same red shift. Discuss how this not only
shows that the images are of the same object, but also implies that the red shift is not affected by taking different paths through
space. Does it imply that cosmological red shifts are not caused by traveling through space (light getting tired, perhaps)?
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