Chemical evolution

Basically everything we touch in daily life is built up from tiny particles called atoms. The lightest elements, hydrogen and helium, were created shortly after the universe came into being approximately 13 billion years ago. But what about the carbon, oxygen, and iron in our bodies? When and where were they produced?

We already know that these elements are produced in the cores of stars through a process called nuclear fusion. Elements like oxygen and iron are created when these stars explode. It is, however, still unclear when most of the stars exploded and how. The formation of these stars is of course connected to the formation of galaxies and the evolution of the universe.

Clusters of galaxies are the largest bound objects in the universe and they consist of hundreds or even thousands of galaxies. Because of their large mass, the produced elements cannot escape from the cluster. And, because of the large distances toward these clusters, we can look back in time and measure the composition of clusters in the past. These are two of many reasons why clusters are very interesting objects to study the history of heavier elements.

The galaxies in clusters are actually embedded in an enormous dilute cloud of hot gas. Because of the high temperature of 10 million degrees, the gas is only visible in X-rays. Using space-based X-ray observatories, like XMM-Newton, Chandra, and Suzaku, we can measure the amounts of the most important elements with great precision. We believe that these observations provide the means to solve a part of the large puzzle of cosmic chemical evolution.


Jelle de Plaa studied Astrophysics at Utrecht University from 1998-2002 and did his PhD at SRON from 2002-2007 (see Thesis). In the years between 2007 and 2009 he worked as a post-doc at Delft Technical University. Since 2009, he is back at SRON and currently employed as Senior Software Design Engineer in the Astrophysics programme.

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