On 2 July, a major contract, worth several million Euros, was signed between the CTAO’s hosting partner, ESO (European Southern Observatory), and a consortium of Chilean companies for the construction of roads and telescope foundations for the CTAO’s southern hemisphere array (CTAO-South), which is located near ESO’s Paranal Observatory in Chile. The contract, signed on behalf of the CTAO, includes more than 50 foundations for the CTAO’s Medium-Sized Telescopes (MSTs) and Small-Sized Telescopes (SSTs), as well as approximately 17 km of roads, connecting these foundations to the support facilities. The construction of this important infrastructure, which is expected to take one year, marks the beginning of telescope construction on the CTAO-South site.
“We’re excited to see telescope construction begin on site after years of planning and preparation,” says Volker Heinz, CTAO Construction Programme Manager. “We’re grateful for ESO’s support in securing this fundamental step. Soon, we’ll be ready to receive the telescopes on site, with the first expected to be built as early as the middle of next year.”
The CTAO will be the world’s largest and most powerful observatory for gamma-ray astronomy. It is composed of two arrays of telescopes: CTAO-South, and CTAO-North in La Palma, Spain. With locations in both hemispheres, the Observatory will cover the full gamma-ray sky, capturing the ever-elusive Cherenkov light. When cosmic gamma rays reach the atmosphere and interact with it, they generate a cascade of ultra-energetic particles; as they move through the air, these particles create a faint blue flash of “Cherenkov light.” By analysing this faint light, scientists can infer much about the cosmic sources, like supermassive black holes and supernova remnants, that emitted the original gamma rays.
To capture Cherenkov light, the CTAO-South site will cover an area of about three-square kilometres and consist of 51 individual telescopes of different sizes to detect both bright and faint events. The awarded contract includes the construction of foundations for the Medium-Sized Telescopes (MSTs) and Small-Sized Telescopes (SSTs). The MST and SST are two of the three telescope types that the CTAO will deploy to span its broad energy range from 20 GeV to 300 TeV. The MST, weighing approximately 89 tonnes and featuring a 12-meter mirror reflector, is designed to cover the core energy range between 150 GeV and 5 TeV. The SST, which has a dual-mirror configuration and weighs about 17.5 tonnes, will focus on detecting the most energetic cosmic sources, which emit gamma rays at the high end of the CTAO’s energy range, from 5 to 300 TeV.
As the first open ground-based observatory for gamma-ray astronomy, the CTAO will make its data and analysis software publicly available for the entire global scientific community to share, strengthening worldwide collaboration and helping to answer questions across both astronomy and particle physics, including decades-long mysteries, such as the origin and role in the galaxies of relativistic cosmic particles or the nature of dark matter.
The CTAO will be the first observatory of its kind built in Chile, able to observe the high-energy Universe with unparalleled sensitivity. Its location near Cerro Paranal, far from light pollution sources and under one of the world’s darkest and most pristine night skies, is key to detecting the extremely faint Cherenkov blue light.
In January 2025, the CTAO was established as a European Research Infrastructure Consortium (ERIC) by the European Commission. The Founding Members of the CTAO ERIC are Austria, the Czech Republic, the European Southern Observatory (ESO), France, Germany, Italy, Poland, Slovenia, and Spain. Additionally, Japan is a Strategic Partner, and the accession of Switzerland and Croatia as Founding Members is being processed.
