Context:
Recently, Event Horizon Telescope (ETH) confirmed that the black hole shadow was ‘real’
Gravitational Lensing:
- It occurs when a massive celestial body — such as a galaxy cluster — causes a sufficient curvature of space time for the path of light around it to be visibly bent, as if by a lens.
Gravitational lens:
- They are small objects or bodies causing the light to curve during gravitational lensing
- Individual stars act as gravitational lenses when they pass in front of more distant stars.
- Gravitational lenses can create phenomena in a wide variety of shapes and sizes
- Einstein cross – A gravitationally lensed quasar that sits directly behind the centre of the galaxy
- Einstein ring – When a galaxy or a quasar is off center from the foreground object, the lensing creates a ring or arcs instead of points.
Gravitational Microlensing:
- The phenomenon observed, when for few days or weeks light from the more distant star temporarily appears brighter because it is magnified by the gravity of the closer object for few days.
Einstein’s theory of gravity:
- Also known as General relativity and General theory of relativity
- According to Einstein’s general theory of relativity, time and space are fused together in a quantity known as spacetime.
- Within this theory, massive objects cause spacetime to curve, and gravity is simply the curvature of spacetime.
- Einstein discovered gravity is not produced by any unseen force; rather, it’s simply our experience of space-time curving and distorting in the presence of matter and energy. This curved space, in turn, sets the rules for how energy and matter move.
- Even though light travels in a straight line, light moving through a highly curved region of space-time, like the space around enormous galaxies, also travels in a curve — bending around the galaxy and splaying out into a halo.
Halo – Its look depends upon the strength of gravity and understood with perspective of the observer.
Read more about: Quasar
Source: The Hindu
Previous Year Question
Consider the following phenomena:
1. Light is affected by gravity.
2. The Universe is constantly expanding.
3. Matter warps its surrounding space-time.
Which of the above is/are the prediction/predictions of Albert Einstein’s General Theory of Relativity, often discussed in media?
[UPSC Civil Services Exam – 2018 Prelims]
(a) 1 and 2 only
(b) 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (d)
