HESS LogoHigh Energy Stereoscopic System

Reflector plane of one of the H.E.S.S. telescopes.

H.E.S.S. is a system of Imaging Atmospheric Cherenkov Telescopes that investigates cosmic gamma rays in the energy range from 10s of GeV to 10s of TeV. The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay homage to Victor Hess , who received the Nobel Prize in Physics in 1936 for his discovery of cosmic radiation. The instrument allows scientists to explore gamma-ray sources with intensities at a level of a few thousandths of the flux of the Crab nebula (the brightest steady source of gamma rays in the sky). H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality. The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003, and were officially inaugurated on September 28, 2004. A much larger fifth telescope - H.E.S.S. II - is operational since July 2012, extending the energy coverage towards lower energies and further improving sensitivity.

The H.E.S.S. observatory is operated by a collaboration of more than 260 scientists from about 40 scientific institutions and 13 different countries: Namibia and South Africa, Germany, France, the UK, Ireland, Austria, the Netherlands, Poland, Sweden, Armenia, Japan, and Australia. To date, the H.E.S.S. Collaboration has published over 100 articles in high-impact scientific journals, including the top-ranked ‘Nature’ and ‘Science’ journals.

In 2006, H.E.S.S. was awarded the Descartes Prize of the European Commission - the highest recognition for collaborative research - and in 2010 the prestigious Rossi Prize of the American Astronomical Society. In a survey in 2006, H.E.S.S. was ranked the 10th most influential observatory worldwide, joining the ranks with the Hubble Space Telescope or the telescopes of the European Southern Observatory ESO in Chile.

September 2012 marked the 10th anniversary of the inaugration of the first H.E.S.S. telescope. See See the highlights in H.E.S.S. history, the H.E.S.S. Hall of Fame for the most highly-cited H.E.S.S. publications, and the H.E.S.S. Sky featured in the September 2012 Source of the Month column.

Celebrated on Sept. 28, 2012 was also the inauguration of the H.E.S.S. II telescope. Following a workshop on Heja Lodge near Windhoek, the H.E.S.S. II telescope was inaugurated on Sept. 28, 2012; keynote speaker was the Hon. Minister of Education, Dr. Abraham Iyambo. Many hundred visitors came to the Open Day on Sept. 30, 2012 to see the giant new H.E.S.S. II telescope. See web galeries with pictures from the inauguration, from the open day and more telescope images are now online. See also the telescopes 'dancing' (80 MB version, 8 MB version) . Images by Christian Föhr, MPIK.

In 2015-2016, the camera of the four H.E.S.S. I telescopes were fully refurbished using state of the art electronics and in particular the NECTAr readout chip designed for the next big experiment in the field, the Cherenkov telescope array (CTA). The new camera were inaugurated on Sept. 27th, 2016.

In 2017, the installation of new cameras allowed the H.E.S.S. team to capture detailed images of the blazar Markarian 421, marking the beginning of significant technological upgrades that would enhance their observational capabilities over the following years.

By 2018, the team had detected new sources in the H.E.S.S. Galactic Plane Survey, contributing to the growing catalog of gamma-ray sources within our galaxy. This year also saw detailed studies of pulsar wind nebulae and the gamma-ray emission from regions such as HESS J1809-193.

In 2019, significant upgrades were completed, including the installation of a new camera on the largest telescope, CT5. This upgrade enabled the creation of the first gamma-ray sky map with the updated system, leading to new discoveries and improved data quality.

Despite the challenges posed by the COVID-19 pandemic in 2020, H.E.S.S. maintained its operations, achieving a record amount of observational data. The team adapted to the restrictions and continued their work, making notable discoveries such as the detection of very-high-energy gamma-ray emission from the colliding wind binary Eta Carinae.

In 2021, the collaboration made groundbreaking observations of the recurrent nova RS Ophiuchi, providing new insights into particle acceleration mechanisms. This year also marked the first observation of a nova outburst in very-high-energy gamma rays, further showcasing the array's capabilities.

The following year, 2022, saw the publication of several important studies, including a comprehensive analysis of dark matter annihilation signals in the inner galaxy. Additionally, H.E.S.S. observed a significant outburst from a previously quiet zone near a black hole, shedding light on the complex behaviors of these cosmic giants.

As of 2023, H.E.S.S. continued to push the boundaries of gamma-ray astronomy, reporting detailed studies of various gamma-ray sources, including the Virgo Cluster and the blazar PKS 1510-089. These efforts have significantly advanced the understanding of high-energy cosmic events and the environments that produce them.

Read more about: