Eye in the sky on black holes in Namibia

The Africa Millimetre Telescope (AMT) project, led by international and Namibian partners, aims to advance global black hole research from Namibia’s Gamsberg plateau.

The project sets out to establish the first state-of-the-art millimetre-wavelength astronomical observatory in Africa. Namibia’s Khomas Hochland area offers one of the best sites in the world for this, says Radboud Radio Lab director and AMT Africa project director Marc Klein Wolt.

In April the project inched closer to realising its main purpose: providing an essential link to the network of telescopes around the globe known as the Event Horizon Telescope (EHT), which produced the first picture of a black hole.

“The EHT network functions as a virtual telescope the size of Earth, and its imaging quality is comparable to photographing an apple on the moon from Earth. For the future of black hole research, more telescopes are needed in the EHT network,” says Klein Wolt.

The AMT initiative is led by Radboud University in the Netherlands, in collaboration with other institutions including the University of Namibia (Unam), Oxford University, the University of Amsterdam and the University of Groningen. 

On April 10 2019, the EHT revealed its first image of a black hole at the centre of the M87 galaxy, about 55-million light years away. Namibia’s AMT project spokesperson, Zandré Duvenhage, says this black hole is 6.5-billion times bigger than the sun.

“With this ground-breaking accomplishment, the EHT presented direct evidence for the existence of black holes, showing that Einstein’s theory of general relativity was right,” he says. Duvenhage says Africa needs a millimetre-wavelength telescope to improve the quality of images for future black hole research.

The optical air quality of Namibia’s Khomas Hochland area makes it ideal for setting up such a telescope. The flat Gamsberg mountain, 120km southwest of Windhoek, is comparable to Cape Town’s Table Mountain. Gamsberg, standing at 2,347m, dominates the horizon for up to 100km.

In 1970, the Max Planck Institute for Astronomy (MPG) established an observatory there and it operates the site, which was also a candidate for the Very Large Telescope, later built in Chile. MPG spokesperson Markus Nielbock says the Gamsberg surface area belongs to the institute. The International Amateur Observatory also operates its own telescopes there, according to an agreement with the MPG. 

Klein Wolt says: “We’ve been working on building a telescope, either on or near the Gamsberg mountain, since 2016, but in 2023 the Radboud University and Unam signed a formal agreement on this.”

For brainy astronomers, Gamsberg’s allure lies in looking up at the very dark skies at “event horizons” — not down the breathtaking drop of about 1,100m to the Namib plains.

But getting up the mountain is no mean feat. Klein Wolt refers to the track up Gamsberg as “an indication of direction”, rather than a road. And moving equipment up the mountain is an even bigger challenge. “The mount of the telescope alone weighs 1.5t,” he says.

During Klein Wolt’s visit to Namibia in April, final site selections were made. He says the Gamsberg plateau was chosen for its optimal observing conditions, and it remains the primary site for the project’s second phase. 

“This mountaintop project will be the first to open up opportunities for many other international projects to come to Namibia, placing this location at the forefront of black hole research. This mountaintop has been identified as one of the best locations for astronomy worldwide for more than 50 years,” he says.

During the first phase of the AMT project, the telescope will be installed close to Namibia’s High Energy Stereoscopic System (Hess) gamma-ray observatory site. Ground-breaking research is done observing the sky above the Namibian highlands at this site, but the aim is different in that it studies very high-energy gamma-ray sources.

During the second phase, the telescope will be moved from Hess to Gamsberg once road access has been completed. “This transition depends on securing additional funding for the road construction,” Klein Wolt says. About N$200m is still needed for this.

[Gamsberg mountain] has been identified as one of the best locations for astronomy worldwide for more than 50 years

—  Marc Klein Wolt

Another challenge is completing the construction of the AMT within a certain time frame, Duvenhage says. Klein Wolt adds: “We must use our European and Dutch research funding promptly to avoid repayment. This project is like a space launch — we have one chance to make it successful.”

Construction will start in the middle of next year. “The building will take about a year, followed by another year to become operational.” But the construction of a road remains a stumbling block, he says. 

Radboud University will provide €12m for manpower and investment in the telescope itself over more than a decade. In addition, €14m has been guaranteed by the European Research Council, and almost €3.5m will come from the Dutch Research Council. 

Meanwhile, a programme initiated by Unam and Radboud has earmarked €500,000 for doctoral scholarships and scientific outreach programmes in Namibia.

Apart from the AMT Gamsberg project, Duvenhage says he is especially proud of AMT’s mobile planetarium, which aims to inspire the next generation of bright minds with the help of the AMT fellowship programme.

The high-end technology of the mobile planetarium projects the night sky onto an inflatable dome. Astonishingly, the planetarium, used in school outreaches across Namibia, contains almost every single data point yet recorded by a telescope in the world. “This effectively means learners are taken on an interactive tour of the universe,” Duvenhage says.

One of the most frequent questions the team of scientists has to answer is: can we really photograph a black hole? Are they not entirely dark, since light cannot escape from them?

The reply goes along these lines: “The first image of a black hole is not a classical photograph. It is a radiolight image, the result of complex observational and computational interpretation (deconvolution). Further, it is not of the black hole itself, but of the ‘shadow’ — the closest we can come to imaging a completely dark object that consumes all light and matter. The black hole boundary — the event horizon for which the EHT is named — casts this shadow.”

Now you know.