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Grade: 12

                        

why light can not attracted by gravity ?

6 years ago

Answers : (1)

Rinkoo Gupta
askIITians Faculty
80 Points
							Gravity affects light in much the same way it affects matter. Gravity can bend a beam of light, and if powerful enough, it can keep light from escaping something that is emitting light.

But the effect is very weak, and we don't see it in everyday life.

It was predicted by Einstein's theory of general relativity, but only confirmed by observation relatively recently.

Generally speaking, you can see the bending effect only with things that are very heavy, and very far away. There is a phenomenon called "'gravitational lensing," in which something very large, like a galaxy, takes the light from something even farther away, like another galaxy, and bends the light emanating from it and focuses it at us. It is a little like holding a magnifying lens near a candle. Not all of the light gets caught by the lens, but some does, and for somebody in exactly the right spot, the light is intensified.
Here is a diagram of how that happens.
Light from the distant galaxy on the right is being focused on us by the galaxy in the middle.

For us, that happens only with very specific galaxies that happen to be in the right spots. And what we see isn't a nicely focused image, it is more like distorted smears of light. But believe it or not, that distorted image is still enough to tell us a great deal about that distant galaxy.

Here is a picture of gravitational lensing creating what is called Einstein rings.




The ring is created by light from the more distant object being bent around the sides, top and bottom of the closer object. Einstein rings are created only when the two objects are in perfect alignment. More often the bent light creates partial arcs.

Another visible example of light being affected by gravity is in the neighborhood of a black hole. Black holes have such strong gravity that they can bend light visibly even when they are very close to you (because the intense gravitational field can bend light at a sharper angle.) Here is an animation of a black hole bending the light that surrounds it.







The "black hole" in the center is not a physical object. It is the boundary beyond which light is bent so far that it does not escape. It is called the "event horizon" and events and objects occuring inside it are effectively isolated from the rest of the universe.

But close to the event horizon, you are seeing light rays that are being bent completely around the black hole. In fact, it is your own image, distorted and compressed.

But just like the image above, you can see how the images of distant stars are compressed and curved into arcs.

Thanks & Regards
Rinkoo Gupta
AskIITians Faculty
6 years ago
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