A new Einstein cross is discovered

Link to paper on arXiv: https://arxiv.org/pdf/1902.10964.pdf

Abstract: https://arxiv.org/abs/1902.10964

Why does gravitational lensing produce four copies of the star and not a whole circle of copies? I would have expected the light to bend evenly around the intermediate star, giving a halo-like effect.

"While gravitationally lensed light sources are often shaped into an Einstein ring, due to the elongated shape of the lensing galaxy and the quasar being off-centre, the images form a peculiar cross-shape instead." [1]

[1] https://en.wikipedia.org/wiki/Einstein_Cross

I was also interested. It seems to be a combination of the intermediate galaxy being elliptical, and the star behind it being off-center from our point of view:

https://physics.stackexchange.com/questions/14056/how-does-g...

WMAP measurements put the age of the universe at ~13.77 billion years, so I was initially perplexed by this part of the article:

> The object acting as a lens turns out to be an elliptical galaxy located at a distance of approximately 7 billion light years (z = 0.556), while the source is at least 20 billion light years away (z = 3.03).

...but I found this explanation in the Wikipedia article on the most distant known galaxy (GN-z11), which is 32 billion light-years away [1]:

> At first glance, the distance of 32 billion light-years (9.8 billion parsecs) might seem impossibly far away in a Universe that is only 13.8 billion (short scale) years old, where a light year is the distance light travels in a year, and where nothing can travel faster than the speed of light. However, because of the expansion of the universe, the distance of 13.4 billion light years traveled by light from GN-z11 to Earth, called the light-travel distance, has expanded to a distance of 32 billion light-years during the 13.4 billion years it took the light to reach us.

[1] https://en.wikipedia.org/wiki/GN-z11#Notes

see also:

[2] https://en.wikipedia.org/wiki/Expansion_of_the_universe#Meas...