Universiteit Leiden

nl en

Giant galaxies grow out of cold cosmic oceans

The largest galaxies in the Universe feed off cosmic oceans, which helps them grow. This is the presumption of an international team of scientist with two Leiden astronomers, based on observations of the ‘Spiderweb’ galaxy. The researchers published their evidence in Science on 2 December 2016.

Spiderweb galaxy

An international team of astronomers, including Leiden scientists George Miley and Huub Röttgering, turned their radio telescopes in Australia and the USA on the Spiderweb galaxy. This galaxy lies ten billion light-years away from our Milky Way. This gigantic galaxy is located in the centre of a cluster of hundreds of galaxies and still seems to grow.

Cold cosmic gas cloud

Surprisingly, the astronomers discovered that the merging galaxies revolve in a cosmic cloud of extremely cold gas. The cold gas consists mainly of hydrogen molecules, the basic material from which stars and galaxies form. This enormous gas cloud contains about a hundred billion times more mass than our Sun. This seems enough gas for the formation of many new stars.

Food for the Spiderweb

Until now, scientists thought that giant galaxies are formed by small galaxies that merge. This believe resulted in the name Spiderweb, as the small galaxies are spread out like flies in a spiderweb. The astronomers now believe that this giant galaxy feeds on this enormous gas cloud.

Bjorn Emonts

Bjorn Emonts from the Netherlands is first author of the publication and works at the Centro de Astrobiología in Spain. ‘We expected to see that super-galaxies in the distance, early universe would form in the same way as merging galaxies in the more recent universe, but this turns out to be different.’ 

Colder than expected

The cold cosmic gas in the enormous gas cloud is about minus two hundred degrees Celsius. This is much colder than calculations predicted based on the previous idea of merging galaxies. Merging galaxies are a fiery process and produce a lot of heat. Now, the new theory can explain the fact that billions of young stars are formed not only in the centre but in the entire Spiderweb galaxy.  

George Miley

Co-author George Miley discovered the Spiderweb galaxy about twenty years ago. His team studied the galaxy with the Hubble Telescope in 2006 and with the APEX-telescope in 2014. Now, researchers made observations with radio telescopes. According to Miley the Spiderweb is a fantastic laboratory for scientists to witness the birth of spectacular super-galaxies located at the hearts of galaxy clusters. ‘This beautiful galaxy keeps amazing me. We are only beginning to understand how these giant galaxies formed from the ocean of gas that surrounds them.’


Where the enormous gas cloud comes from remains a mystery. The researchers suspect that it was formed from previous stars. Besides hydrogen, this gas cloud also consists of carbon monoxide, a by-product of these previous stars. To find out more about these previous stars, the researchers aim to look deeper into the Universe’s history. For this purpose a new generation of telescopes is being built.           

Image copyright European Southern Observatory. Credit: ESO/M. Kornmesser.