What is Einsteins Cross?

[sail3005]

someone brought this up at my physics lecture today. what is it?

[thinktank2]

Einsteins cross is the nickname of Galaxy CGCG 378-15.

Normally light travelling over long distance will be diffused. You need a lens to focus them to a point.This galxy CGCG 378-15 acts like a lens focusing the light coming from a distant quasar.The quasar is at a distance of approximately 8 billion light-years, while the galaxy is twenty times closer (400 million light years). Gravitational lensing occurs when the light from a distant source passes through or close to a massive foreground object. Depending on the detailed alignment of foreground and background objects with the line of sight to the Earth, several images of the background object may be seen.

This effect was first predicted by Albert Einstein.

Normally when the sun is up you can't observe the stars because of the sun's brightness. During complete solar eclipse, you can see distant stars beyond the sun. This is because light from those stars which are diffused are focussed by the gravity of the sun.

[thinktank2]

[thinktank2]

http://archive.ncsa.uiuc.edu/Cyberia...steinTest.html

[sail3005]

I see. That now makes sense into relation with what we were talking about. thanks a lot.