Image Impossible.

A spectacular, albeit essentially impossible image caused a worldwide sensation on April 10, 2019: The first ever "photograph" of a black hole. 55 million light years away at the center of the M87 galaxy. The unbelievably strong gravitational pull means that even light cannot escape.  But, thanks to the Event Horizon Telescope - a combination of eight radio telescopes - the participating researchers outsmarted physics to a certain extent and for the first time, created an image of a black hole's shadow. This shadow is cast by the radiation from the distorted light while being irrevocably absorbed by the black hole.

ALMA - the Atacama Large Millimeter/Submillimeter Array - made a major contribution to the creation of this first image of a black hole. It is currently the largest astronomy project in the world and is located on the Chajnantor Plateau in the Chilean part of the Atacama Desert at an altitude of over 5,000 meters. This revolutionary astronomic telescope consists of 66 giant antennas. They are networked and can be arranged flexibly at a distance of up to 16 km. The individual antenna mirrors have a diameter of up to 12 meters and weigh approximately 100 tons.

Initially, the cosmic radio waves collected by the antenna's large mirror are focused onto a subreflector. The signals only reach the detector inside the antenna when this has been aligned precisely to only fractions of a millimeter. Extreme environmental conditions at an altitude of over 5,000 meters such as strong winds, high temperature differences from day to night, extreme dryness, as well as gravity and earth rotation are all factors that affect the antennas. Therefore, the subreflectors have to be realigned constantly. ALMA's developers relied on special positioning systems from PI for this purpose: Hexapods. Because of their compact design and motion in six degrees of freedom, hexapods are ideal for this task. The environmental conditions in the desert don't just affect the antennas - the hexapods have to withstand them as well. Very rigid joints, special materials, and the controller electronics had to be adapted accordingly. This obviously worked out well: ALMA was inaugurated in 2013 and has been in operation ever since. One thing is certain, we can expect ALMA to create even more spectacular images, such as that of the Black Hole in the M 87 Galaxy.

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