I've read that gravitational lensing bends the light; I am a little confused about black holes and why lensing produces different results. Black holes absorb light whereas lensing should have also done the same but why does gravitational force help bend the light?
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1$\begingroup$ In context of Black Holes, there's a photosphere in which light orbits around the singularity. Here, you can see your back in straight direction. $\endgroup$– Earth is a SpoonCommented Apr 23, 2014 at 6:06
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3 Answers
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Black holes absorb light, but only if it gets close enough to be trapped behind the event horizon. The gravitational field of a black hole is not really different from that of any other massive object. Masses in motion are pulled towards its source, and therefore deviate from their path. Whether they actually fall into the black hole depends on primarily on their distance from the black hole. A light ray that is sufficiently far away from the black hole will only slightly deviate from its path, whereas one that is close to the event horizon may fall be trapped in an orbit and eventually fall in.
answered Apr 22, 2014 at 22:13
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$\begingroup$ thanks :), one more clarification, in this image at wiki, it show the light ray getting bent outside, how can that happen, since the object is still there and it is opaque by nature (blackhole or a large star), how can it get bent outwards than in inwards. en.wikipedia.org/wiki/File:Gravitational_lens-full.jpg $\endgroup$ Commented Apr 22, 2014 at 22:22
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$\begingroup$ Maybe I do not understand exactly what you mean, but I do not see anything bent outwards, just inwards. $\endgroup$ Commented Apr 22, 2014 at 22:26
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$\begingroup$ sorry if i am confusing, the white color beam of light, it is bent outwards. if light is traveling straight and if the object is opaque, how is the light getting bent outside (away from the object inbetween) $\endgroup$ Commented Apr 22, 2014 at 22:36
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$\begingroup$ It is not. The light rays are initially moving away from each other on the opposite sites of the lens. The lensing effect bends them inwards. $\endgroup$ Commented Apr 22, 2014 at 22:58
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1$\begingroup$ @thndrkiss I think you are confused because of the missing detail in the picture. The distant galaxy is emitting light in ALL directions, kind of like a light bulb. The illustration is only showing 2 rays of light that, when acted upon by the massive object, end-up being focused onto the nearer planet. Then, the orange arrows are supposed to be describing the 'apparent' position/size of the distant galaxy. HTH $\endgroup$ Commented Apr 22, 2014 at 23:12
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It is not the light that is bent in gravitational lensing, it is the space time around the massive object such as a galaxy or a black hole that is actually distorted. The light follows the distortion in space time, giving the lensing effect.In Einstein's General Relativity theory there is no such thing as a force of gravity, massive objects distort space time in their immediate vicinity and smaller objects fall into the "gravity well", the distortion in space-time
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I too am confused on lensing. When light is emitted onto an object outside of space, normally it is absorbed like on earth. I'm guessing since objects creates a curvature in space is what affects it? So lensing really only works outside of a planetary object? Am I just reading too much into it?
