Astronomy, in general, but radio astronomy, in particular, could be a very powerful force to attract and hold public attention and promote education, Italian astrophysicist Dr Tiziana Venturi argued in a recent lecture cohosted by the Academy of Science in South Africa and the South African National Space Agency in Pretoria.

The only forms of direct astronomy that could be carried out from the surface of the planet earth were optical astronomy and radio astronomy, she pointed out, “because the atmosphere surrounding earth is actually blocking a lot of radiation”. Astronomy at other wavelengths had to be carried out using space telescopes.

“Radio astronomy was born serendipitously, in the1930s,” she noted. It was a spin-off from research into the sources radio interference (‘static’) with transatlantic wireless signals, undertaken in the US by Karl Jansky, of Bell Telephone Laboratories (now Nokia Bell Labs). During his research, Jansky determined that some of the interference was not only extraterrestrial in origin, but came from beyond the solar system.

Every body, she explained, because it has temperature, emits radiation. This is the “so-called black body radiation”. In astronomy, the most famous black body radiation is the Cosmic Microwave Background, which is the radiation left over from the Big Bang – the birth of our universe.

However, at first, radio astronomy suffered from a significant limitation – its lack of ‘angular resolution’, or the fineness of detail it could discern. To match the fineness of detail that a human eye can see, using a single radio telescope, would require a dish with a diameter of 500 m! The largest practical size for a fully steerable radio telescope dish is 100 m (and there are only two such instruments in the world – in Germany and the US). Larger dishes are fixed.

This changed with the development of Very Long Baseline Interferometry (VLBI). This involves a number of widely spaced radio telescopes observing the same object at the same time. The effect is the same as having a single radio telescope dish with the same diameter as the diameter of the network of dishes undertaking VLBI. And radio telescopes in a VLBI network cannot only be hundreds of kilometres apart, they can be thousands of kilometres apart. For example, South Africa’s radio telescope at Hartebeesthoek (west of Pretoria) is part of the European VLBI network. The development of optical fibre has been a huge boost to VLBI, linking the radio telescopes in the various VLBI networks.

The most recent example she cited of radio astronomy having a major impact on public consciousness worldwide was last year’s revelation of the first-ever image of a Black Hole, released by a VLBI consortium known as the Event Horizon Telescope. This grouping involves eight radio telescopes, scattered across half the planet, at locations in the US (Hawaii and Arizona), Mexico, Spain, Chile and in Antarctica (quite literally at the South Pole).

Their target was the supermassive Black Hole believed to be situated at the heart of the Messier 97 (M87) galaxy, which is the dominant member of the galaxy cluster known as Virgo. M87 has a jet of material streaking out from its centre at incredibly high speeds, of nonthermal origin, providing indirect evidence of the existence of a Black Hole. (The supermassive Black Hole in the centre of our own galaxy, the Milky Way, is closer but much more difficult to observe.)

Imaging the M87 Black Hole required extremely high resolution, highlighted Venturi – hence, the need for such a widely spaced network of radio telescopes. But the resulting image (technically of the shadow of the Black Hole, surrounded by a ring of light, bent by the fierce gravity of the phenomenon, as a Black Hole is by definition invisible) dominated the front pages of newspapers around the world.

It is “one thing to postulate the existence of Black Holes, as inferred from other phenomena, another thing is actually seeing it,” she stressed. Black Holes have gone from theory to fact. We now know they really exist. The impact of this achievement demonstrates that “astronomy is an incredibly strong tool . . . it’s really powerful – never stop dreaming”. It catches the attention of the general public very effectively and so stimulates education

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