I write articles and posts on a lot of different topics, both for my own blog and at Ars Technica. Many of those subjects drift pretty far from my putative area of expertise, but occasionally I get to write about something I know pretty well. To wit: last week, a group of researchers using the 4-meter Blanco telescope at Cerro Tololo (best known for its use in discovering dark energy in 1998) have measured distances to galaxy clusters very precisely. (Here’s my galaxy cluster primer, written as a podcast for 365 Days of Astronomy.) Their study, as with a major chunk of my thesis work, was intended to pin down the effect of dark energy—cosmic acceleration—on galaxy cluster formation and evolution. In particular, if dark energy’s effects change over time, that would have a profound influence on the number and size of galaxy clusters that form in a given era. To get a handle on this, we need a detailed census of clusters, dating back to the earliest times.

A new survey of galaxy clusters marks the beginning of a promising effort to map the birth and growth of galaxy clusters back to relatively early times. Jeeseon Song and colleagues used optical and infrared telescopes to measure the distances of 158 bright clusters in a large patch of the southern sky, looking back in time to when the Universe was less than one-third its current age. These observations provide the beginnings of a history of galaxy cluster evolution, which should help constrain models of dark energy. [Read more…]