Gravitational Lens Effect

Did you know that very strong gravity can actually bend light?  Gravitational lenses are formed when light from a  very distant source is bent around an object with a very large mass.  Albert Einstein’s general theory of relativity predicted this phenomenon.

Albert Einstein published an article describing this effect in 1937, but it wasn’t until 1979 that the effect was confirmed by direct observation of the “Twin QSO”  SBS 0957+561.   The gravity from a massive object – like a galaxy cluster or a black hole warps space and time and bends everything, including light, around it.  You can see this effect in the picture above.  Notice the faint arcs of light.  That is light from a very distant galaxy that has been bent around a closer galaxy cluster.  Interestingly enough, gravitational lensing acts equally on all types of electromagnetic radiation, not just visible light.

How Gravitational Lensing Works

There are three classes of gravitational lensing.

STRONG LENSING:  Where there are easily visible distortions of light such as Einstein Rings, arcs and multiple images.  The picture at the top of the post is an example of this.

WEAK LENSING:  Where the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources to find coherent distortions of only a few percent.

MICROLENSING:  Where no distortion in shape can be seen, but the amount of light recieved from a background object changes over time.   

Most of the gravitational lenses in the past have been discovered accidentally.   However, a systematic search for them done in radio frequencies using the Very Large Array (VLA) in New Mexico led to the discovery of 22 new lensing systems an now there are several ongoing surveys of the night sky to identify and catalog them.

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