23 Jun 2023
Namibia is to help 'film' a black hole for the first time. Heino Falcke, professor of astroparticle physics and radio astronomy at Radboud University in Nijmegen, said this at the Namibia Scientific Society in Windhoek earlier this week. He and his colleagues in the field had made global headlines in 2019 with the first photo of a black hole. In his talk, Falcke explained why Gamsberg, about 120 km west of Windhoek, is an ideal further location in his international network of observatories.
Black Holes are spaces in space with extreme mass density. Falcke also vividly calls them 'monsters of destruction'. This is because they attract matter with their enormous gravitational forces and swallow it up as if in a powerful whirlpool (for more on Black Holes see article on Wikipedia).
This also applies to light. Which poses a problem: How can a black hole be seen at all and, in order to prove its existence, photographed? Answer: By means of plasma streams that are visible around the hole. They are emitted due to the tremendous energy released by the fall of matter into the hole. The radiation from these plasma streams can be picked up with radio telescopes in the millimetre frequency range.
The next problem: The largest black hole in our galaxy, Sagittarius A* (SgrA*), is (fortunately!) 26,000 light years away. Which means that light, with its speed of just under 300,000 km per second, takes 26,000 years to cover the distance. Even the largest telescope dishes are too tiny to provide an image of such distant objects.
That is why Falcke and his colleagues have set up several telescopes at widely separated locations on Earth. They provide data from their different viewing angles, which can be combined to produce clearer images by computer. Locations so far include France, Spain, Greenland, the US states of Arizona and Hawaii, Mexico, Chile and the South Pole.
With this global network of the Event Horizon Telescope (EHT), it was possible to measure the size of SgrA* in the centre of the Milky Way and thus confirm previous calculations. Incredibly, its diameter is larger than that of our solar system.
The first photo of a black hole in the centre of the galaxy Messier 87 caused a worldwide sensation in 2019. It was compiled from data collected by EHT over several days in 2017.
Africa has so far been a 'blind' spot in the EHT collaboration. The research team around Falcke wants to close this gap with the Africa Millimeter Telescope (AMT) project. The launch is planned for Namibia.
A radio telescope (Swedish-ESO Submillimetre Telescope, SEST) with a diameter of 15 metres, which was in operation in Chile until 2003, is to be installed on or near the Gamsberg (see also an article on this on Wikipedia). In the area, the High Energy Stereoscopic System (H.E.S.S.) telescope has been in operation since 2002 (see article on Wikipedia), which receives gamma rays from space.
Why Namibia? Why at the Gamsberg? Because the climate is dry and moderately warm. Humid air distorts the rays. Therefore, the higher the altitude, the better the reception. Another big plus: The centre of our Milky Way and thus the black hole SgrA* can be 'seen' from the area around the Gamsberg for up to 14 hours a day. Only Chile comes close to this value.
With the location in Namibia, however, the researchers are also extending the total observation time and expanding the number of viewing angles. The goal of Heino Falcke's research team is to create a 'film' from 'snapshots' taken at 15-minute intervals that shows the plasma flows around the black hole in motion.
Namibia has yet to determine the exact location of the observation station. The surface of Table Mountain is only accessible via a narrow, partly very steep and narrowly winding concrete access road. Transporting the parts for the telescope would be costly and risky. The ring on which the telescope can be rotated weighs five tonnes.
The necessary funds for the project are available. According to Falcke, Radboud University Nijmegen (Nijmegen) is providing 12 million euros. This includes operation over 12 years. 14 million euros have been pledged by the European Research Council (ERC), and almost 3.5 million euros are coming from the Dutch Research Council (Nederlandse Wetenschappelijk Onderzoek Instituten, NWO). Namibia will also get a big boost from the project beyond the construction and operation of the radio telescope. 500,000 euros, Falcke said, are earmarked for doctoral scholarships and other support programmes for Namibian researchers.
Before and after his talk, Falcke signed his book, which will be published in 2020: Heino Falcke, Jörg Römer (2020): "Light in the Darkness. Black Holes, the Universe and Us." It tells the story of astronomy up to the first picture of a black hole in an easy-to-understand and entertaining way.
Sven-Eric Stender
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