A massive galaxy has created a rare distortion in the path of light travelling billions of years to reach us from a more distant galaxy.

It's called an Einstein cross - when the curvature of space-time around a large object in the foreground quadruples the light behind it like the points of a cross. Its confirmation and analysis adds to a slowly growing catalogue of these rare alignments that could help us better understand more distant points of the Universe.

Space-time is not nice and flat. Gravity causes it to bend and wrinkle, which can have some interesting effects on any light that passes through it. Mostly we observe these as something we call gravitational lensing.

Think of a trampoline, for example. If you put a heavy weight on the trampoline, the mat stretches and becomes curved. Then anything rolling on the mat follows the stretched and curved shape. Something similar happens in space-time: if a mass is big enough, space-time bends and curves around it.

Any light travelling through this spacetime therefore follows a curved path and looks quite different at the other end. The mass in the foreground creates a bending and magnification effect, like a large lens.

How this background light appears varies; sometimes it is diffused, sometimes reflected, sometimes it forms a ring. But if the alignment is just right, you get four copies arranged around the foreground object. This is the Einstein Cross, and they are both rare and beautiful.

An international team of scientists led by astronomer Aleksandar Cikota of the NSF NOIRLab has confirmed a particularly spectacular example in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys data.

The gravitational lens was first discovered in 2021, but Cikota and colleagues used the Very Large Telescope's MUSE instrument to make follow-up observations that confirmed its classification as an Einstein cross.

Their images show a large red foreground galaxy. It is surrounded by a string of four blue lights; these are duplicate images of a more distant lensed galaxy. Together, the system is named DESI-253.2534+26.8843.

The researchers also performed modelling using software called GIGA-Lens, a framework for modelling strong gravitational lenses. This allowed them to quickly and accurately calculate the properties of the system, and they found that the source galaxy has a total magnification of 10.47.

 

They were also able to investigate the effects of a smaller foreground galaxy, which has a weaker lensing effect.

This information is important for investigating the properties of lensed galaxies in the distant universe. Magnification allows us to see them in more detail, but you need to understand precisely the exact effect that the lensing has on the light passing through it. The team's work shows us that, using modelling, we can derive the properties of a gravitational lens faster than we could before.

"We have achieved accelerations of more than two orders of magnitude," they write in their paper.

"This tangibly demonstrates a very promising future for modelling strong lensing systems, which are expected to be discovered in the next decade."

 

Source: https://www.sciencealert.com/