ABSTRACT
Einstein in his General theory of relativity, estimated the deviation in the path of light in presence of a strong gravitational field like that of giant stars or black holes. This was confirmed by observation in 1919. In the following years, the phenomenon of gravitational lensing and its various aspects were also theoretically explained. Einstein had already predicted the possibility of the formation of ring-like images of the background sources and it was known as Einstein's ring. It is recently that we started making use of the benefits of gravitational lensing. The use of lensing as a gravitational telescope to observe very dark and distant objects was some among them. Today lensing has become an integral part of astrophysics. Even though it is still in its developing stage, lensing has established itself as an extremely useful Astro-physical tool with some notable successes. It has yielded significant new results in a variety of fields, including the cosmological distance scale, the mass distribution of matter in the universe, the physics of quasars, and so on. Considering these recent developments, we anticipate a much brighter future for gravity lensing. In this article, we are going to see how gravitational lensing works and how we are benefited from it. [1]
KEYWORDS
Gravitational lensing, space-time curvature, general theory of relativity, astrophysics, Hubble’s telescope, dark matter, quasars.
INTRODUCTION
Today we have various kinds of highly developed instruments to observe the distant objects. Apart from those tools, scientists also use special techniques to investigate the deep space. Gravitational lensing is one such interesting technique used by the astronomers to observe the distant celestial bodies. This method of gravitational lensing is completely based on the very strange behaviour of light to bend around the massive objects having high gravitational pull. Light tends to bend around massive objects due to bending of space time curvature around these objects. Our brains are evolved in a Euclidean world. In our environment, space is a simple 3-dimensional grid static with time where light always travels in straight lines. Thus, what we do is catch the photons with our eyes and trace their paths backward. This works perfectly only if the paths of the light are truly straight. But what if the light starts to bend their path?
GRAVITATIONAL LENSING AND ITS BENEFITS
Gravitational lensing
The whole universe is like a giant mirror or a rippling pond and many things that we see in the space are not where or what they seem to us. In real universe, both space and time can be curved which is an unimaginable phenomenon in our 3D World. According to Einstein's General theory of relativity, curvature produced by massive objects such as stars, planets, cluster of galaxies is the reason for gravity. Light follows this curvature and hence gravity bends the path of light.
The gravitational field of any massive objects converges passing light rays and that is how we come to this phenomenon of Gravitational lensing. Gravity is like a nature's magnifying glass. The space gets wrapped in the presence of massive objects and this wrapped space act like a magnifying glass. A magnifying glass collects and bend the light making the object appears to be bigger and brighter for the observer. Wrapped space also do the same for the light from distant galaxies.
Galaxy cluster are the most massive things in the universe with high gravitational force. When light from very distant galaxy passes near a cluster, its path gets distorted. Light that would have gone in different directions get bend towards the observer (telescope). This allows us to see very distant galaxy and hence detailed analysis and studies could be carried out. Here the cluster of galaxies act like an imperfect magnifying glass. This effect is known as gravitational lensing. Without this, it would be impossible for our telescopes to see far away bodies in space and to study galaxies in early universe.[2][3][4]
Applications
One of the important applications of this magnification effect is that it allows us to observe and study the objects that would otherwise be too far away and too faint to be seen. Hubble telescope make use of this strange magnification phenomenon to look into far away galaxies which are beyond the sensitivity of its 2.4 meter-diameter primary mirror, thereby allowing us to observe the most distant celestial bodies that humanity has ever seen. Hubble’s images of gravitational lensing have been used to create maps of dark matter in galaxy clusters. Almost 200 distant quasars and over 1000 galaxies have now been observed to be strongly lensed into ring-like images around foreground galaxies and clusters. These have been used as tools to study the stellar and dark matter distributions in the lenses, to observe high-redshift sources in otherwise unattainable detail, as well as to cost-effectively measure the Hubble constant and other cosmological parameters. Hubble has extremely high sensitivity and resolution which allows to see distant gravitational lenses which could not be seen through our ground-based telescopes due to hindrance by earth's atmosphere. Hence till today we are able to discover many gravitational lenses which further led to discovery of a large number of earlier galaxies.[5][6]
CONCLUSION
Gravitational lensing is considered to be one of the most evident proofs of Einstein's general relativity theory. Today, different branches of gravitational lensing are subject to intense observational research, which has already significantly enriched our understanding of astrophysics and cosmology. Gravitational lensing has a foremost importance when it comes to observation of faraway galaxies. Hence every invention made in this field is a greater achievement for the humanity.
REFERENCES
1.Gravitational lensing in astronomy, Joachim Wambsganss,
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5567250/
2. YouTube - https://youtu.be/2KMAv880v6s
3. YouTube - https://youtu.be/Dgv2WWpm7_s
4. YouTube - https://youtu.be/Meaifz6z5Js
5. Dr Cristian Eduard Rusu, Observing gravitational lenses: Present and Future.
https://www.mdpi.com/journal/universe/special_issues/observing_gravitational_lenses
6. Hubble site, Looking through a giant magnifying glass.
https://hubblesite.org/contents/articles/gravitational
lensing#:~:text=Hubble's%20images%20of%20gravitational%20lensing,dark%20matter%20in%20galaxy%2 0clusters.&text=Because%20very%20distant%20galaxies%20are,it%20can%20amplify%20its%20light.
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