Galaxy clusters are the largest stable structures in our Universe.

Seven billion light years away and with two million billion times the mass of our Sun, the cluster was nicknamed "El Gordo" - "the Fat One" in Spanish.

Astronomers reporting at the 219th American Astronomical Society meeting said El Gordo was currently undergoing a merger and growing even larger.

Alongside other clusters highlighted at the meeting, astronomers hope to better understand how they form, grow and collide with one another.

Galaxy clusters yield many cosmic superlatives; mergers such as the one that El Gordo appears to be undergoing are the most energetic events in the Universe, as vast amounts of matter - and the mysterious dark matter - crash into each other at breakneck speeds.

The growth of clusters and their mergers are driven by gravity; normal matter we see along with the dark matter imaged on a grand scale in Monday's announcement act to draw things together.

Meanwhile, the even more mysterious dark energy works to drive the expansion of the Universe - to draw things apart.

Mapping out the process of cluster growth will be critical to understand the interplay between these dark forces.

bbc.com